i 
TABLE OF CONTENTS 
 
DECLARATION viii 
ACKNOWLEDGEMENTS ix 
LIST OF TABLES x 
LIST OF FIGURES xi 
ABSTRACT xvii 
 
CHAPTER 1              INTRODUCTION  
1.1 Background 1 
1.2 Motivation 2 
1.3 Objectives 6 
 
CHAPTER 2             LITERATURE REVIEW  
2.1 Introduction 8 
2.2 The concept of soil quality  9 
 2.2.1 Development of the concept 9 
 2.2.2 Soil quality and soil health 11 
 2.2.3 Opposition to the concept 11 
 2.2.4 Soil quality definition 12 
 2.2.5 Soil quality indicators 13 
2.3 Sugar cane production and soil quality 14 
 2.3.1 General 14 
 2.3.2 Biological parameters 16 
  2.3.2.1 Organic matter 16 
  2.3.2.2 Microbial biomass 22 
 2.3.3 Chemical parameters 25 
  2.3.3.1 pH 25 
  2.3.3.2 Cation exchange capacity 29 
  2.3.3.3 Plant available nutrients 30 
  2.3.3.4 Salinity and/or sodicity 31 
 2.3.4 Physical parameters 31 
  2.3.4.1 Bulk density 31 
 ii 
  2.3.4.2 Infiltration rate 33 
  2.3.4.3 Plant available water 35 
  2.3.4.4 Aggregate stability 35 
  2.3.4.5 Particle size distribution 36 
2.4 Conclusion 37 
 
CHAPTER 3           CHARACTERIZATION OF THE STUDY AREA  
3.1 Introduction 38 
3.2 Location 38 
3.3 Physiography 38 
3.4 Climate 40 
 3.4.1 Temperature 40 
 3.4.2 Rainfall 40 
3.5 Geology 42 
3.6 Soils 45 
 3.6.1 Soil map of 1962 45 
  3.6.1.1 Zonal soils 46 
  3.6.1.2 Intrazonal soils 48 
  3.6.1.3 Azonal soils 51 
 3.6.2 Soil map of 1984 52 
3.7 Sugar industry 53 
 3.7.1 General 53 
 3.7.2 Present status 54 
  3.7.2.1 Gross domestic product 54 
  3.7.2.2 Employment 55 
  3.7.2.3 Organizations 55 
  3.7.2.4 Sugar markets 56 
 3.7.3 The future 58 
 3.7.4 Research and development 59 
3.8 Conclusion 60 
 
 
 
 iii 
CHAPTER 4              MATERIAL AND METHODS  
4.1 Comparative studies 61 
4.2 Choice of sites 62 
4.3 Sampling procedure 63 
4.4 Soil quality parameters 65 
4.5 Methodology for determination 65 
 4.5.1 Organic matter 65 
 4.5.2 Microbial biomass 66 
 4.5.3 pH 67 
 4.5.4 Cation exchange capacity 67 
 4.5.5 Exchangeable bases 68 
 4.5.6 Particle size distribution 68 
 4.5.7 Aggregate size distribution 69 
 4.5.8 Water stability of aggregates 69 
 4.5.9 Bulk density 71 
 4.5.10 Plant available water 71 
 4.5.11 Stabilized infiltration rate 72 
 
CHAPTER 5          INFLUENCE OF SUGAR CANE PRODUCTION ON   
                                 SOME SOIL BIOLOGICAL PARAMETERS  
5.1 Introduction 74 
5.2 Procedure 76 
 5.2.1 General 76 
 5.2.2 Data processing and analysis 77 
 5.2.3 Data presentation 78 
5.3 Results and discussion 79 
 5.3.1 Organic matter 79 
  5.3.1.1 Effects of manual and mechanized sugar cane  
cropping practices on organic matter 79 
  5.3.1.2 Organic matter and length of time during which  
sugar cane has been cropped manually 86 
  5.3.1.3 Organic matter and length of time during which  
mechanized practices have been adopted 88 
 iv 
 5.3.2 Microbial biomass 88 
  5.3.2.1 Effects of sugar cane cropping and mechanized  
practices on microbial biomass 88 
  5.3.2.2 Microbial biomass and length of time during which  
sugar cane has been cropped 95 
  5.3.2.3 Microbial biomass and length of time during which  
mechanized practices have been adopted 97 
5.4 Conclusion 97 
 
CHAPTER 6            INFLUENCE OF SUGAR CANE PRODUCTION ON   
                                   SOME SOIL CHEMICAL PROPERTIES  
6.1 Introduction 100 
6.2 Procedure 103 
 6.2.1 General 103 
 6.2.2 Data processing and analysis 104 
 6.2.3 Data presentation 104 
6.3 Results and discussion 104 
 6.3.1 Soil pH 104 
  6.3.1.1 Effects of manual and mechanized sugar cane  
cropping practices on soil pH 104 
  6.3.1.2 Soil pH and length of time during which sugar cane  
has been cropped manually 108 
  6.3.1.3 Soil pH and length of time during which  
mechanized practices have been adopted 109 
 6.3.2 Cation exchange capacity 110 
  6.3.2.1 Effects of manual and mechanized sugar cane  
cropping practices on cation exchange capacity 110 
  6.3.2.2 Cation exchange capacity and length of time during  
which sugar cane has been cropped manually 112 
  6.3.2.3 Cation exchange capacity and length of time during  
which mechanized practices have been adopted 113 
 
 
 v 
 6.3.3 Exchangeable bases 114 
  6.3.3.1 Effects of manual and mechanized sugar cane  
cropping practices on exchangeable bases 114 
  6.3.3.2 Exchangeable bases and length of time during  
which sugar cane has been cropped manually 121 
  6.3.3.3 Exchangeable bases and length of time during  
which mechanized practices have been adopted 121 
 6.3.4 Base saturation 124 
  6.3.4.1 Effects of manual and mechanized sugar cane  
cropping practices on base saturation 124 
  6.3.4.2 Base saturation and length of time during which  
sugar cane has been cropped manually 126 
  6.3.4.3 Base saturation and length of time during which  
mechanized practices have been adopted 127 
6.4 Conclusion 128 
 
 
CHAPTER 7            INFLUENCE OF SUGAR CANE PRODUCTION ON   
                                   SOME SOIL PHYSICAL PARAMETERS  
7.1 Introduction 129 
7.2 Procedure 131 
 7.2.1 General 131 
 7.2.2 Data processing and analysis 132 
 7.2.3 Data presentation 132 
7.3 Results and discussion 133 
 7.3.1 Particle size distribution 133 
  7.3.1.1 Effects of manual and mechanized sugar cane  
cropping practices on particle size distribution 133 
  7.3.1.2 Particle size distribution and length of time during  
which sugar cane has been cropped manually 137 
  7.3.1.3 Particle size distribution and length of time during  
which mechanized practices have been adopted 139 
 7.3.2 Aggregate size distribution 140 
 vi 
 
  7.3.2.1 Effects of manual and mechanized sugar cane  
cropping practices on aggregate size distribution 140 
  7.3.2.2 Aggregate size distribution and length of time  
during which sugar cane has been cropped manually 144 
  7.3.2.3 Aggregate size distribution and length of time  
during which mechanized practices have been  
adopted 144 
 7.3.3 Water stability of aggregates 145 
  7.3.3.1 Effects of manual and mechanized sugar cane  
cropping practices on the water stability of  
aggregates 145 
  7.3.3.2 Water stability of aggregates and length of time  
during which sugar cane has been cropped manually 148 
  7.3.3.3 Water stability of aggregates and length of time  
during which mechanized practices have been  
adopted 149 
 7.3.4 Bulk density 150 
  7.3.4.1 Effects of manual and mechanized sugar cane  
cropping practices on bulk density 150 
  7.3.4.2 Bulk density and length of time during which sugar  
cane has been cropped manually 153 
  7.3.4.3 Bulk density and length of time during which  
mechanized practices have been adopted 154 
 7.3.5 Plant available water 155 
  7.3.5.1 Effects of manual and mechanized sugar cane  
cropping practices on plant available water 155 
  7.3.5.2 Plant available water and length of time during  
which sugar cane has been cropped manually 157 
  7.3.5.3 Plant available water and length of time during  
which mechanized practices have been adopted 158 
 
 
 vii 
 7.3.6 Stabilized infiltration rate 159 
  7.3.6.1 Effects of manual and mechanized sugar cane  
cropping practices on stabilized infiltration rate 159 
  7.3.6.2 Stabilized infiltration rate and length of time during  
which sugar cane has been cropped manually 161 
  7.3.6.3 Stabilized infiltration rate and length of time during  
which mechanized practices have been adopted 162 
7.4 Conclusion 163 
 
CHAPTER 8             SUMMARY AND RECOMMENDATIONS  
8.1 Summary 165 
 8.1.1 Purpose of the study 165 
 8.1.2 Results evolved from study 166 
8.2 Implications and recommendations for the sugar industry of Mauritius  169 
 8.2.1 Application of research results 169 
 8.2.2 Suggestions for future research 173 
 
REFERENCES 177 
 
APPENDIX 1 194 
 
 viii 
DECLARATION 
 
 
I declare that the thesis hereby submitted by me for the Philosophiae Doctor degree at the 
University of the Free State is my own independent work and has not previously been 
submitted by me at another University. I furthermore cede copyright of the thesis in 
favour of the University of the Free State. 
 
 
 
 
 
 
 
 
Signature      May 14, 2007 
 
 ix 
ACKNOWLEDGEMENTS 
 
I wish to put on record my deep sense of gratitude to my promoter Prof. C. C. Du Preez, 
Head of the Department of Soil, Crop and Climate Sciences at the University of the Free 
State, for his constant availability, highly pertinent suggestions and critical evaluation for 
the whole duration of this thesis. 
 
I am extremely grateful to my co-promoter, Dr. K. F. Ng Kee Kwong, who has been a 
constant guide for me for the whole course of this study, showing great patience in 
reading through all the manuscripts and putting forward extremely precise and valuable 
remarks and suggestions. 
 
I hereby acknowledge with great pleasure the contribution of my colleagues at the 
Mauritius Sugar Industry Research Institute. The Director, Dr. J. C. Autrey, has supported 
me in undertaking this study and has made the necessary resources available. My Head of 
Department, Mr. D. Ah-Koon, has been highly supportive and has ensured that this study 
could proceed under ideal conditions. A special word of thanks to my two collaborators, 
Messrs. K. Muthy and L. Volcy, who have greatly contributed to this study by helping 
with the field work and laboratory analyses, and to all my other colleagues, particularly 
Mr. S. Soyfoo, who have, in one way or another, helped in this study. 
 
I am indebted to the managers and the personnel of the sugar estates who have been 
extremely helpful in providing information and support in the field. I wish to personally 
acknowledge the contribution of the following persons: for Médine - Messrs. B. d’Arifat 
and S. Leprédour; for Richeterre - Mr. G. Fleurant; for Mon Désert Alma - Mr. S. 
Préfumo; for Deep River Beau Champ - Mr. P. Lagesse; and for Savannah - Mr. B. Piat. 
 
This work would not have been possible without the unflinching support of my family. I 
wish to thank my parents for having shown to me the value of knowledge and, most of all, 
I thank my wife Bernadette, my son Shaun and my daughter Tanya, for all their love and 
encouragement. 
 
 x 
LIST OF TABLES 
 
2.1 Selected indicators of soil quality and some processes they impact 14 
2.2 Changes in particle size fractions to 45 cm depth in Mauritius soils  
associated with sugar cane cropping 36 
3.1 Soil Groups of Mauritius 45 
3.2 Some chemical properties of the zonal soils 47 
3.3 Some chemical properties of the intrazonal soils 49 
4.1 Study sites representing the five major soil groups of Mauritius 62 
4.2 Treatments studied for five soil groups 63 
6.1 Weight in gram of one cmol  c kg
-1 of exchangeable chemical  
elements 103 
 
 xi 
LIST OF FIGURES 
 
1.1 Evolution of area in Mauritius cultivated from 1971 until 2003  
with sugar cane 2 
1.2 Evolution of sugar productivity in Mauritius from 1984 until 2003,  
excluding the drought year 1999 and cyclone years 1994 and 2002 3 
2.1 Decrease of soil organic matter content observed seven years after  
native grassland was converted to sugar cane land 17 
2.2 Decline of soil organic matter content through time on account of  
sugar cane production in South Africa 19 
2.3 Effect of sugar cane trash management on soil organic carbon  
content in South Africa 22 
2.4 Change in soil microbial biomass carbon as a result of sugar cane  
production in South Africa 23 
2.5 Microbial biomass carbon recorded in South African soil profiles  
with sugar cane and grassland 24 
2.6 Microbial biomass carbon recorded in soil profiles with sugar cane  
subjected to different harvesting procedures 25 
2.7 Decline of topsoil pH through time on account of sugar cane  
production in Papua New Guinea 27 
2.8 Change in subsoil pH after ten years of continuous sugar cane  
production in Papua New Guinea 28 
2.9 Change in the CEC of a soil profile after ten years of continuous  
cane production in Papua New Guinea 29 
2.10 Bulk densities recorded beneath sugar cane interrows and rows  
and in grassland 32 
2.11 Infiltration rates recorded in sugar cane interrows and rows and in  
grassland 34 
3.1 Location of Mauritius in the South West Indian Ocean 39 
3.2 Mean annual rainfall distribution over Mauritius 41 
3.3 Simplified geological map of Mauritius 43 
3.4 Soil map of Mauritius 46 
3.5 Markets for sugar produced in Mauritius 57 
 xii 
4.1 Pairing of trenches for bulking of samples (plan view) 64 
4.2 Soil sampling procedure from trench wall (plan view) 65 
4.3 Desorption curves obtained using Haines apparatus 70 
4.4 Differential curves derived from desorption curves 70 
4.5 Infiltration curve derived from CSIRO disk permeameter test 73 
5.1  Effects of manual and mechanized sugar cane cropping practices  
on organic carbon concentration of the five major soil groups of  
Mauritius 81 
5.2 Effects of manual and mechanized sugar cane cropping practices  
on total nitrogen concentration of the five major soil groups of  
Mauritius 82 
5.3 Effects of manual and mechanized sugar cane cropping practices  
on carbon:nitrogen ratio of the five major soil groups of Mauritius 83 
5.4 Effects of length of time under manual sugar cane cropping on  
organic C concentration, total N concentration and carbon:nitrogen  
ratio of the two major soil groups in the sub-humid zone of  
Mauritius 87 
5.5 Effects of length of time for which mechanized practices have  
been implemented on organic C concentration, total N  
concentration and carbon:nitrogen ratio of P soil of Mauritius  
cropped with sugar cane 89 
5.6 Effects of manual and mechanized sugar cane cropping practices  
on biomass carbon content (kg/ha over 15 cm soil depth) of the  
five major soil groups of Mauritius 90 
5.7 Effects of manual and mechanized sugar cane cropping practices  
on biomass nitrogen content (kg/ha over 15 cm soil depth) of the  
five major soil groups of Mauritius 91 
5.8 Effects of manual and mechanized sugar cane cropping practices  
on biomass carbon:nitrogen ratio of top 15 cm of the five major  
soil groups of Mauritius 92 
 
 
 
 xiii 
5.9 Effects of length of time under manual sugar cane cropping on  
biomass C and N contents (kg/ha over 15 cm soil depth), and  
biomass carbon:nitrogen ratio of the two major soil groups in the  
sub-humid zone of Mauritius 96 
5.10 Effects of length of time for which mechanized practices have  
been implemented on biomass C and N contents (kg/ha over 15 cm  
soil depth) and biomass carbon:nitrogen ratio of P soil of  
Mauritius cropped with sugar cane 98 
6.1 Effects of manual and mechanized sugar cane cropping practices  
on pH of the five major soil groups of Mauritius 105 
6.2 Effects of length of time under manual sugar cane cropping on pH  
of the two major soil groups in the sub-humid zone of Mauritius 109 
6.3 Effects of length of time for which mechanized practices have  
been implemented on pH of P soil of Mauritius cropped with sugar  
cane 109 
6.4 Effects of manual and mechanized sugar cane cropping practices  
on cation exchange capacity of the five major soil groups of  
Mauritius 111 
6.5 Effects of length of time under manual sugar cane cropping on  
cation exchange capacity of the two major soil groups in the sub-  
humid zone of Mauritius 113 
6.6 Effects of length of time for which mechanized practices have  
been implemented on cation exchange capacity of P soil of  
Mauritius cropped with sugar cane 114 
6.7 Effects of manual and mechanized sugar cane cropping practices  
on potassium concentration of the five major soil groups of  
Mauritius 115 
6.8 Effects of manual and mechanized sugar cane cropping practices  
on calcium concentration of the five major soil groups of  
Mauritius 116 
6.9 Effects of manual and mechanized sugar cane cropping practices  
on magnesium concentration of the five major soil groups of  
Mauritius 117 
 xiv 
6.10 Effects of length of time under manual sugar cane cropping on  
potassium, calcium and magnesium concentrations of the two  
major soil groups in the sub-humid zone of Mauritius 122 
6.11 Effects of length of time for which mechanized practices have  
been implemented on potassium, calcium and magnesium  
concentrations of P soil of Mauritius cropped with sugar cane 123 
6.12 Effects of manual and mechanized sugar cane cropping practices  
on base saturation (%) of the five major soil groups of Mauritius 125 
6.13 Effects of length of time under manual sugar cane cropping on  
base saturation (%) of the two major soil groups in the sub-humid  
zone of Mauritius 126 
6.14 Effects of length of time for which mechanized practices have  
been implemented on base saturation (%) of P soil of Mauritius  
cropped with sugar cane 127 
7.1 Effects of manual and mechanized sugar cane cropping practices  
on particle size distribution of the five major soil groups of  
Mauritius 134 
7.2 Effects of manual and mechanized sugar cane cropping practices  
on particle size distribution of soil layers of the five major soil  
groups of Mauritius 135 
7.3 Effects of length of time under manual sugar cane cropping on  
particle size distribution of the two major soil groups in the sub-  
humid zone of Mauritius 138 
7.4 Effects of length of time under manual sugar cane cropping on  
particle size distribution of soil layers of the two major soil groups  
in the sub-humid zone of Mauritius 138 
7.5 Effects of length of time for which mechanized practices have  
been implemented on particle size distribution of P soil of  
Mauritius cropped with sugar cane 139 
7.6 Effects of length of time for which mechanized practices have  
been implemented on particle size distribution of soil layers of P  
soil of Mauritius cropped with sugar cane 140 
 
 xv 
7.7 Effects of manual and mechanized sugar cane cropping practices  
on aggregate size distribution (geometric mean diameter in mm) of  
the five major soil groups of Mauritius 141 
7.8 Effects of length of time under manual sugar cane cropping on  
aggregate size distribution (geometric mean diameter in mm) of  
the two major soil groups in the sub-humid zone of Mauritius 144 
7.9 Effects of length of time for which mechanized practices have  
been implemented on aggregate size distribution (geometric mean  
diameter in mm) of P soil of Mauritius cropped with sugar cane 145 
7.10 Effects of manual and mechanized sugar cane cropping practices  
on aggregate stability index of the five major soil groups of  
Mauritius 146 
7.11 Effects of length of time under manual sugar cane cropping on  
aggregate stability index of the two major soil groups in the sub-  
humid zone of Mauritius 148 
7.12 Effects of length of time for which mechanized practices have  
been implemented on aggregate stability index of P soil of  
Mauritius cropped with sugar cane 149 
7.13 Effects of manual and mechanized sugar cane cropping practices  
on bulk density of the five major soil groups of Mauritius 151 
7.14 Effects of length of time under manual sugar cane cropping on  
bulk density of the two major soil groups in the sub-humid zone of  
Mauritius 153 
7.15 Effects of length of time for which mechanized practices have  
been implemented on bulk density of P soil of Mauritius cropped  
with sugar cane 154 
7.16 Effects of manual and mechanized sugar cane cropping practices  
on plant available water (mm of water in 50 cm soil) of the five  
major soil groups of Mauritius 156 
7.17 Effects of length of time under manual sugar cane cropping on  
plant available water (mm of water in 50 cm soil) of the two major  
soil groups in the sub-humid zone of Mauritius 157 
 
 xvi 
7.18 Effects of length of time for which mechanized practices have  
been implemented on plant available water (mm of water in 50 cm  
soil) of P soil of Mauritius cropped with sugar cane 158 
7.19 Effects of manual and mechanized sugar cane cropping practices  
on stabilized infiltration rate of the five major soil groups of  
Mauritius 160 
7.20 Effects of length of time under manual sugar cane cropping on  
stabilized infiltration rate of the two major soil groups in the sub-  
humid zone of Mauritius 162 
7.21 Effects of length of time for which mechanized practices have  
been implemented on stabilized infiltration rate of P soil of  
Mauritius cropped with sugar cane 163 
 
 xvii 
ABSTRACT 
 
Sugar cane is the most important crop on the Indian Ocean island of Mauritius, covering 
some 85% of its cultivated area. In spite of the progress in agronomic practices and 
development of better sugar cane varieties, no apparent gain has been observed in sugar 
cane productivity over the last twenty years. This situation has raised the question as to 
whether the soils of Mauritius were not subject to a decline in quality, a phenomenon 
observed elsewhere on account of sugar cane monocropping. In this context, a study was 
done to establish whether or not sugar cane production, and the adoption of mechanized 
practices, were impacting negatively on soil quality, with special attention being devoted 
to any temporal effect. 
 
This study was conducted between 2002 and 2006 on five sugar estates representing the 
five major soil groups of Mauritius, namely the P, L, H, B and F groups. To assess the 
effects of sugar cane cropping on soil quality, pristine soils were compared with sugar 
cane soils not subjected to derocking and/or land grading. The latter were then compared 
to sugar cane soils where such land preparation practices had been implemented to assess 
the effects of adopting mechanized practices. For temporal effects, older cane soils (> 50 
years) were compared to younger cane soils (< 25 years) in the P and L groups, and early 
mechanized soils (> 10 years) were compared to recently mechanized soils (< 3 years) in 
the P group only. The soil quality parameters that were determined were biological - 
organic matter and microbial biomass; chemical - pH, cation exchange capacity and 
exchangeable bases; and physical - particle size distribution, aggregate size distribution 
and stability to water, bulk density, plant available water, and stabilized water infiltration 
rate. 
 
Sugar cane cropping had both positive and negative effects on soil quality. These effects 
were associated with cultural practices, mainly tillage, organic amendments, fertilization, 
and trash management. Some of these differed according to climate, and therefore led to 
contrasting results. Topsoil organic matter generally decreased with cropping, probably 
because of exposure to accelerated decomposition following tillage. Subsoil organic 
matter increased since tillage also produced mixing of topsoil with subsoil. Topsoil 
microbial biomass decreased with sugar cane cropping for less material was available for 
decomposition. The higher subsoil organic matter content had a positive effect on 
 xviii 
aggregate stability. Addition of organic amendments to the soil generally improved pH, 
exchangeable bases and base saturation. Acidification also occurred in one instance, 
probably because of nitrogenous fertilizers. Fertilization increased yields and this led to a 
higher return of organic matter to the soil. Trash management at harvest played an 
important role in soil quality. Pre-harvest trash burning lowered the return of 
carbonaceous material to the soil, whereas trash conservation under green cane harvesting 
had an enhancing effect. 
 
The adoption of mechanized practices did not affect soil chemical quality. Soil organic 
matter content decreased following mechanization in the dry zones as a result of increased 
soil disturbance. The most important effects of the adoption of mechanized practices were 
on soil physical quality with compaction occurring in the topsoil as a result of 
mechanized harvesting. Water infiltration rate declined because of reduced topsoil macro-
porosity, while plant available water increased. 
 
Soil quality was not systematically aggraded or degraded under long-term cropping in the 
sub-humid soils of Mauritius, and changes were mainly small and variable. However, soil 
quality declined with time after the adoption of mechanized practices as large amounts of 
amendments were initially added to the soil and subsequently allowed to be depleted. The 
impact of adopting mechanized practices on soil physical quality was observed right from 
the onset and did not evolve with time. 
 
Soil quality can be enhanced by rebuilding topsoil organic matter levels through trash 
retention, addition of large amounts of organic wastes and green manuring. The best 
strategy to combat compaction is prevention, via the use of low-pressure tyres, combined 
field operations and controlled traffic paths. 
 
 
 
 
Key words: compaction, mechanized practices, organic matter, trash management 
 
 
 
 xix 
UITTREKSEL 
 
Suikerriet is die belangrikste gewas op die Indiese Oseaan eiland Mauritius en dit beslaan 
ongeveer 85% van die bewerkte oppervlakte.  Ten spyte van die vooruitgang in 
agronomiese praktyke en ontwikkeling van beter suikerriet variëteite is daar blykbaar 
geen waarneembare toename in suikerriet produktiwiteit oor die afgelope 20 jaar.  Hierdie 
situasie het die vraag laat ontstaan of die gronde van Mauritius se kwaliteit nie 
onderworpe is aan ‘n daling, ‘n verskynsel wat ook elders voorkom weens die 
monoverbouing van suikerriet.  Dit is in hierdie konteks dat die studie gedoen is om vas te 
stel of suikerriet produksie, en die implementering van gemeganiseerde praktyke ‘n 
negatiewe inpak op grondkwaliteit gehad het oor tyd. 
 
Hierdie studie is tussen 2002 en 2006 op vyf suikerlandgoede, wat verteenwoordigend 
van die vyf hoof grondgroepe in Mauritius is, gedoen te wete die P, L, H, B en F groepe.  
Om die effek van suikerrietverbouing op grondkwaliteit vas te stel, is onversteurde 
gronde vergelyk met suikerrietgronde waaruit geen klippe verwyder en/of gelyk gemaak 
is nie.  Laasgenoemde is dan vergelyk met suikerrietgronde waar sulke 
grondvoorbereidingspraktyke geïmplementeer is om die effekte van gemeganiseerde 
praktyke vas te stel.  Om tydseffekte vas te stel, is ou suikerrietgronde (> 50 jaar) met 
nuwe suikerrietgronde (< 25 jaar) vergelyk in die P en L groepe, en vroeër 
gemeganiseerde gronde (> 10 jaar) met onlangse gemeganiseerde gronde (< 3 jaar) 
vergelyk in die P groep slegs.  Die grondkwaliteitsparameters wat bepaal is, is biologies - 
organiese materiaal en mikrobiese biomassa; chemies - pH, katioonuitruilkapasiteit en 
uitruilbare katione; en fisies - deeltjiegrootteverspreiding, aggregaatgrootteverspreiding 
en stabiliteit teen water, brutodigtheid, waterhouvermoë, en gestabiliseerde 
waterinfiltrasietempo. 
 
Suikerrietverbouing het positiewe en negatiewe effekte op grondkwaliteit gehad.  Hierdie 
effekte is geassosieer met verbouingspraktyke, hoofsaaklik bewerking, organiese 
verbeteraars, bemesting en restebestuur.  Sommige van die verskil met klimaat en gee 
daarom aanleiding tot kontrasterende resultate.  Bogrond organiese materiaal het oor die 
algemeen afgeneem met gewasverbouing, waarskynlik as gevolg van blootstelling aan 
versnelde ontbinding na bewerking.  Ondergrond organiese materiaal het toegeneem 
omdat bewerking lei tot die vermenging van bogrond met ondergrond.  Bogrond 
 xx 
mikrobiese biomassa het afgeneem met suikerrietverbouing omdat minder materiaal vir 
ontbinding beskikbaar was.  Die hoër ondergrond organiese materiaalinhoud het ‘n 
positiewe effek op aggregaatstabiliteit gehad.  Toevoeging van organiese verbeteraars tot 
die grond het oor die algemeen ‘n verbetering in pH, uitruilbare basisse en 
basisversadiging tot gevolg gehad.  Versuring het ook in een geval voorgekom, 
waarskynlik as gevolg van stikstofbevattende bemestingstowwe.  Bemesting het 
opbrengste verhoog en die het gelei tot ‘n hoër toevoeging van organiese materiaal tot die 
grond.  Restebestuur tydens oes het ‘n belangrike rol gespeel in grondkwaliteit.  Vooroes 
brand van reste het die toevoeging van koolstofbevattende materiaal tot die grond verlaag, 
terwyl die bewaring van reste wanneer groen suikerriet geoes word dit verhoog het. 
 
Die implementering van gemeganiseerde praktyke het nie die chemiese grondkwaliteit 
geaffekteer nie.  Grondorganiese materiaalinhoud het afgeneem met meganisasie in die 
droë sones as gevolg van verhoogde grondversteuring.  Die belangrikste effekte van 
gemeganiseerde praktyke op die fisiese grondkwaliteit was verdigting in die bogrond 
weens gemeganiseerde oes.  Tempo van waterinfiltrasie het afgeneem weens verlaagde 
bogrond makroporositeit terwyl waterhouvermoë toegeneem het. 
 
Grondkwaliteit het nie sistematies verbeter of verswak met langtermyn gewasverbouing 
in die subhumiede gronde van Mauritius nie, en veranderinge was hoofsaaklik klein en 
varieerbaar.  Nietemin, grondkwaliteit het met tyd afgeneem na die implementering van 
gemeganiseerde praktyke want groot hoeveelhede verbeteraars is aanvanklik toegevoeg 
tot die grond waarna uitputting daarvan toegelaat is.  Die impak van gemeganiseerde 
praktyke op fisiese grondkwaliteit is waargeneem vanaf implementering en het nie met 
tyd na vore gekom nie. 
 
Grondkwaliteit kan verbeter word deur die bogrond se organiese materiaalvlakke deur 
retensie van reste, toevoeging van groot hoeveelhede organiese afval en grondbemesting.  
Voorkoming is die beste strategie om verdigting teen te werk deur gebruik te maak van 
laedruk bande, gekombineerde bewerkingsoperasies en beheerde spoorverkeer. 
 
Sleutelwoorde: gemeganiseerde praktyke, organiese materiaal, restebestuur, verdigting. 
 
 1 
CHAPTER 1 
 
INTRODUCTION 
 
1.1 Background 
 
Mauritius was discovered in September 1598 when a Dutch fleet under admiral Wybrandt 
van Warwijk sighted the uninhabited island in the course of a journey to India. The Dutch 
first settled the island in May 1638 and introduced sugar cane on 8 November 1639 when the 
“Cappel” brought the first plants from Batavia (North Coombes, 1993). The extracted juice 
was initially used for the production of a spirituous liquor called “arrack”, and the first sugar 
proper was made in 1696.  
 
The Dutch abandoned the island in 1710 and the French occupation started in 1721. By 1755, 
the French were producing enough sugar to meet the needs of the inhabitants of the colony, 
Réunion island and sailing ships that called at the harbour. In 1801, annual sugar production 
had reached 3000 t and “arrack” production 1400 kl. Cane was being cultivated over an area 
of 4220 ha and 60 mills were in operation. 
 
The British captured the island in 1810 and a new impetus was given to cane cultivation. In 
1825, sugar production had increased to 10 800 t and there were 10 975 ha under cane. By 
1860, the island was producing 130 000 t of sugar annually. Significant technical progress 
was achieved subsequently with the coming into being of new institutions devoted to research 
and development in sugar cane. The Station Agronomique was set up in 1893, followed by 
the Department of Agriculture in 1913 and the Sugar Cane Research Station as from 1930. In 
1953, all research pertaining to sugar cane was placed under the responsibility of the newly 
created Mauritius Sugar Industry Research Institute (MSIRI). The advent of these institutions 
has led to an island-wide increase in sugar production over the last century to reach a 
maximum of 718 000 t in 1973 from a cultivated area of 87 000 ha (PROSI, 1997). 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 2 
1.2. Motivation 
 
After reaching a peak of 87 000 ha in the mid-seventies, the area under cane has continually 
declined, at a rate of some 400 ha per year (Figure 1.1). The main reasons for this decrease 
were the land demand for urban development from an expanding population, the setting up of 
scattered factories in export processing zones and the need for additional infrastructure to 
accompany the development of the country in terms of roads, hospitals, sports facilities, 
traffic centres, etc. (Tyack, 1990). 
 
90
85
80
75
70
1960 1970 1980 1990 2000 2010
Year
Figure 1.1 Evolution of area in Mauritius cultivated from 1971 until 2003 with sugar cane 
(Compiled from data in MSIRI Annual Reports, 1972 – 2004) 
 
In the year 2002, sugar cane was grown on over some 75 000 ha (MSIRI, 2003), which 
represented about 90% of the total cultivated area in the country. Some 520 000 t of sugar 
were produced, with a productivity of 7.19 t ha-1. This was much lower than the 8.89 t ha-1 of 
1973 and the peak productivity of 9.10 t ha-1 recorded in 1986 (PROSI, 1997). Indeed, over 
the last twenty years there has been no apparent gain in productivity, the average value 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Area (x 1000 ha)
 3 
stagnating at around 8.0 t ha-1 with a slight declining trend, in spite of the introduction of new 
cane varieties and a constant input of inorganic fertilizers (Figure 1.2). 
 
10.0
9.0
8.0
7.0
6.0
5.0
1980 1985 1990 1995 2000 2005
Year
 
Figure 1.2 Evolution of sugar productivity in Mauritius from 1984 until 2003, excluding the 
drought year 1999 and cyclone years 1994 and 2002 (Compiled from data in MSIRI Annual 
Reports, 1985 – 2004) 
 
Cane cultivation in Mauritius is similar to other countries in that it is grown with little or no 
break crop in between replantings. There is very little crop rotation in the cane lands and in 
most cases, the cane is grown continuously for long periods of time. It is ratooned, i.e. 
allowed to regrow repeatedly after the harvest of the plant cane until the yield has decreased 
to such an extent that replanting is necessary, seven ratoons being generally the optimal crop 
cycle. Regular replanting is needed as the yield gradually decreases following repeated 
harvest of the shoots produced by regrowth from the existing cane stools, a natural 
phenomenon called ratoon decline (Shrivastava et al., 1992). This practice of allowing canes 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Productivity (t/ha)
 4 
to ratoon is a very old one, which existed even as early as 1838 (North Coombes, 1993) when 
replanting was done every five years. 
 
Sugar cane cultivation in Mauritius is done under monocropping, with the soil being tilled 
once every eight years when replanting. As such, in addition to the yield losses caused by 
ratoon decline, the crop also suffers from yield decline, a loss of productive capacity of sugar 
cane growing soils under long-term monoculture (Garside et al., 2001). Coleman (1974) 
reviewed research conducted over a ten-year period in the USA on the “variety decline of 
sugar cane” phenomenon, which was studied from agronomic, pathological and physiological 
viewpoints. In agronomic terms, it had been demonstrated that it was difficult to find a 
specific cause for long-term yield reduction. Very often, differences might be caused by 
climatic or environmental conditions, which would override a specific cause. In pathological 
terms, it was shown that soil micro-organisms did reduce yield under certain conditions, with 
environmental conditions playing a role in the evolution of the microbial population. 
However, the evidence was not over a long enough period to implicate any specific organism, 
and additional studies were needed to confirm this finding. As far as physiological studies 
were concerned, there was no obvious basis to blame yield decline on photosynthetic 
differences. In the end, Coleman (1974) considered that inconclusive results were obtained 
from these attempts at documenting yield decline resulting from monoculture. 
 
The yield decline issue was given new impetus in Australia as from 1993 through the 
establishment of a joint venture to research the subject (Garside, 1997). Emphasis in this new 
approach was on the ability of the soil to sustain sugar cane production. Several studies have 
been implemented within this initiative to study different soil-related aspects of the problem. 
These have demonstrated that the productive capacity of the soils was reduced by sugar cane 
monoculture (Garside, 1997; Garside et al., 2001). 
 
Holt and Mayer (1998) found that reduced levels of soil microbial biomass with long-term 
sugar cane monoculture could also contribute to yield decline. Garside et al. (2002) obtained 
better cane yields with fumigation using fungicide alone and together with nematicide when 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 5 
compared to untreated controls. For their part, Pankhurst et al. (2003) have identified several 
soil organisms that contribute to yield decline, including a fungal root pathogen and the 
lesion nematode. They also demonstrated that different rotation breaks (sown pasture, 
alternate crops, bare fallow) would reduce populations of known soil biota and significantly 
increase the yield of the succeeding cane crop. 
 
Results from physico-chemical studies on soils were less conclusive. Bramley et al. (1996) 
did not find any consistent effect of time under sugar cane monoculture on soil chemical 
properties, but some marked effects consistent with soil acidification were noted. For their 
part, McGarry and Bristow (2001) found some degree of physical degradation with old sugar 
cane land, mainly in terms of increased bulk density and lower available water. 
 
Apart from Australia, yield decline under sugar cane monoculture has also been studied in 
other countries. For instance, in South Africa, Meyer and Van Antwerpen (2001) have 
reviewed the yield productivity plateau of the local sugar industry with reference to soil 
quality. They concluded that continuous cropping with sugar cane had adversely affected soil 
productivity, this degradation being attributable to increased soil acidification, loss of soil 
organic matter and an imbalance in soil biota. A similar situation has occurred in Papua New 
Guinea where Hartemink (1998a) found a marked decline in soil fertility under sugar cane 
monocropping, even though nutrient levels remained favourable for sugar cane cultivation. In 
this case, there was a drop in pH accompanied by a decrease in cation exchange capacity 
(CEC), exchangeable potassium, organic carbon and total nitrogen. 
 
Such results from different sugar-producing countries raise the question as to whether sugar 
cane production can be maintained at its current level in Mauritius with the existing cultural 
practices. Wong You Cheong and Chan (1977) had already undertaken preliminary studies on 
changes in physical and chemical properties of the main soils of Mauritius following long 
term cultivation of sugar cane. They have found a decrease in soil pH, organic matter content, 
exchangeable calcium and percentage base saturation. On the physical side, they measured a 
decrease in aggregate stability, but did not find any definite trend in terms of bulk density, 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 6 
plant available water or clay contents. There was thus a certain degree of soil degradation 
even in those days when, apart from soil tillage, most cultural operations were manually 
executed. 
 
Soil degradation is likely to be exacerbated by the increasing use of machinery. Mechanized 
harvesting is gaining importance in Mauritius, rising from 1139 ha (1.5% of total area 
harvested) in 1990 to 5028 ha (7.2% of total area harvested) in 1995 and reaching 13 742 ha 
(19.0% of total area harvested) in 2002 (MSIRI, 2003). However, further increases in the 
mechanically harvested area are hampered in several regions by the presence of rocks and 
stones that damage harvester blades, and by inappropriate field shapes and topography. These 
problems are being addressed by large scale derocking, which is defined as rock removal 
using mechanical means, and by land preparation. Fields need to be re-sized, leveled and 
derocked to achieve these objectives. Eventually, only fields that are relatively flat and rock-
free, with long sugar cane rows, will be economically viable for sugar cane production. 
 
So far, more than 50% of rocky land has undergone some form of derocking and it is 
estimated that some 58 to 101 million t of rocks can still be raked out of those rocky soils that 
are yet to be derocked (Jhoty and Ramsamy, 2003). While the adoption of such measures is 
undoubtedly essential to achieve the goal of complete mechanization of cultural operations, 
and hence lowering of production costs, their effects on soil remain unknown. For the 
industry to maintain its production in the long-term, it is essential that the effects of all these 
new practices on soil properties be established, with particular attention to soil quality, i.e. to 
the ability of the soil to meet its various functions, such as supplying a medium for plant 
growth, controlling water flow in the environment and acting as an environmental filter. 
 
1.3 Objectives 
 
In view of the observations on the issue of yield decline with sugar cane monoculture 
reported in the literature, and its possible links with degradation of soil properties, a study 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 7 
was initiated at the MSIRI to determine the effects of sugar cane cropping and the adoption of 
mechanized practices on soil quality in Mauritius. This project has the following objectives: 
 
1. To establish the effects of manual sugar cane production practices on some biological, 
chemical and physical soil quality parameters of the island’s five major soil groups using 
pristine soils as a reference. 
 
2. To establish the effects of mechanized sugar cane production practices on some 
biological, chemical and physical soil quality parameters of the island’s five major soil 
groups using sugar cane soils that have not been subjected to these practices as a 
reference. 
 
3. To establish the effects of time under manual sugar cane production practices on some 
biological, chemical and physical soil quality parameters of two major soil groups on the 
island. 
 
4. To establish the effects of time under mechanized sugar cane production practices on 
some biological, chemical and physical soil quality parameters of one major soil group on 
the island. 
 
5. To formulate recommendations to maintain and restore soil quality, and to identify 
avenues for future research in this field. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 8 
CHAPTER 2 
 
LITERATURE REVIEW 
 
2.1 Introduction 
 
Modern-day agriculture relies heavily on external inputs, particularly non-renewable fossil 
fuels, for the synthesis of fertilizers and pesticides, and for the energy needs of tillage, harvest 
and other cultural operations. Such a heavy reliance on non-renewable resources raises 
questions about the long-term sustainability of agriculture (Doran et al., 1996). There is an 
increasing concern about the sustainability of the energy- and chemically- intensive industrial 
agricultural model, as soil degradation has often accompanied agricultural expansion (Lal, 
2001). This has led to renewed interest in evaluating the soil resource, this interest being 
further stimulated by an increasing awareness that soil is a critically important component of 
the Earth’s biosphere, functioning not only in the production of food and fibre, but also in the 
maintenance of local, regional and global environmental quality. In this respect, a new 
concept was needed to evaluate the quality of the soil resource. Soil quality can be 
conceptualized as a three-legged stool, the function and balance of which requires an 
integration of three major components – sustainable biological productivity; environmental 
quality; and plant and animal health (Karlen et al., 1997). As far as sugar industries are 
concerned, the relevance of soil quality indicators to sugar producing soils needs to be 
considered, and the use of such indicators has been advocated to further investigate soil 
degradation and sustainability under continuous sugar cane producing conditions (Haynes, 
1997). 
 
In this review, the development of the soil quality concept will be explored through time and 
the contributions of different workers to its refinement will be presented. The current ideas on 
soil quality will be examined and the term will be differentiated from the term “soil health”. 
The concept also has its detractors and some of their arguments will be assessed. After 
defining the concept, the various physical, chemical and biological soil quality indicators will 
be detailed and the minimum data set (MDS) concept examined. The major part of this 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 9 
literature review will then focus on the research work that studied the effects of sugar cane 
production practices on the quality of soils in different cane-growing countries. Finally, some 
conclusions will be drawn from the current state of knowledge on the subject. 
 
2.2 The concept of soil quality 
 
2.2.1 Development of the concept 
 
The foundation for the development of the concept of soil quality is, according to the Soil 
Quality Institute (1996), found in the views put forward by Leopold (1933). He was among 
the first scientists to envision land conservation, discussing the fundamental concepts of 
conservation and laying down the theoretical foundation for the concept of soil quality. In 
more recent times, Warkentin and Fletcher (1977) further developed these ideas, putting 
forward a holistic approach to soil, whereby they postulated that due consideration should be 
given to its possible multiple uses, even in intensive agriculture. They concluded that the 
optimum had to be found between the two most important uses of soil, namely food 
production and recycling of organic materials. 
 
The broader concept of soil quality was effectively introduced into the literature in the mid to 
late 1980's, when several reports and books brought attention to the increasing degradation of 
agricultural soil resources and its implications for sustainable agriculture and environmental 
health (Karlen et al., 2001). It was in the 1990’s that the concept gradually evolved and 
became formalized in its present form. Soil quality was viewed and described from different 
perspectives, and the current theory and concepts were established. The increased emphasis 
on sustainable land use during that period has been crucial in this evolution. In this context, 
Larson and Pierce (1991) expressed the view that the soil is in a continually changing, 
dynamic situation, where its quality would be either degrading, sustaining or aggrading, in 
processes that are driven by both natural and managed environments. Consequently, they 
argued that the quality of a soil is largely defined by soil function and that it represents a 
composite of the physical, chemical, and biological properties that allow it to carry out such 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 10 
diverse functions as providing a medium for plant growth, regulating and partitioning water 
flow through the environment, and serving as an environmental filter. Parr et al. (1992), for 
their part, thought that there are various properties that interact in complex ways to determine 
a soil's potential fitness for sustained crop production. In their view, the soil quality concept 
had to be broadened from its initial soil productivity viewpoint to include attributes of food 
safety and quality, human and animal health, and environmental quality. Warkentin (1995) 
described soil quality from an ecological perspective, asserting that it should be seen in terms 
of the optimum functioning of the soil in an ecosystem. In his opinion, the roles of soil in 
ecosystem processes, and the characteristics that make it particularly suitable to carry out 
these roles, should form the basis for evaluating soil quality. For their part, Kennedy and 
Papendick (1995) considered that the microbial status of a soil would be a better and more 
sensitive indicator of its quality than other soil properties since the microbial community is 
continually adapting to the environment, and changing faster than other soil characteristics. 
Karlen et al. (1997) tried to integrate these various perceptions of the concept in terms of its 
three major components, namely sustained biological productivity, environmental quality, 
and plant and animal health, and stressed that multiple soil uses had to be balanced against 
goals for environmental quality. They refocused the issue on the primary purpose for 
assessing soil quality, which is to use it as a tool for evaluating the sustainability of various 
soil management practices. 
 
In recent years, the emphasis has shifted towards measuring soil quality using methodologies 
that would be comparable, and acceptable to the farming community. Thus, Nortcliff (2002) 
stressed that any index of soil quality had to consider soil function, and these are varied and 
often complex. Chosen indicators of soil function must be measured in a standardized way to 
be replicable and comparable, which would be possible only through co-operation among 
interested parties. Two areas of emphasis, namely education and assessment, have been 
recognized as integral parts of the concept (Karlen et al., 2003). For Doran (2002), the 
challenge lies in taking the right approach to translate science into practice. This requires the 
involvement of growers in the development of a soil quality index that would be acceptable 
to its target audience, as attempted by Andrews et al. (2003). 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 11 
 
2.2.2 Soil quality and soil health 
 
There has been a certain degree of confusion between the terms soil quality and soil health. 
For Harris et al. (1996), the two terms could be interchangeably and functionally defined as 
“the fitness of soil to carry out biological production and environmental protection functions 
within specified land use, landscape and climate boundaries”. Doran (2002) used the two 
terms in combination as he considered them to have a similar meaning, even though scientists 
generally prefer to use “soil quality” while producers prefer “soil health” (Doran et al., 1996). 
Scientists prefer soil quality since it implies quantifiable parameters of its physical, chemical 
and biological properties. On the other hand, producers prefer soil health since it portrays soil 
as a living, dynamic organism that functions holistically rather than as an inanimate mixture 
of sand, silt and clay. 
 
Even though the two terms have similar meanings, there are enough differences to justify that 
they ought to be differentiated (Karlen et al., 1997). Farmers prefer the more integrative soil 
health term as they could characterize it using indicators of both soil and non-soil target 
systems (Romig et al., 1996). Thus, the farmers’ diagnosis of a soil’s condition primarily uses 
qualitative or sensory means in addition to quantitative data. Soil health is therefore more of a 
qualitative term, characterized at the farmers’ level by descriptive and qualitative properties 
using direct value judgments, viz. unhealthy versus healthy. In contrast, the term soil quality 
has greater appeal to the scientific community since it implies that parameters defining it are 
measurable and quantifiable and as a result, scientific literature refers essentially to soil 
quality rather than soil health. 
 
2.2.3 Opposition to the concept 
 
Criticisms and reservations have been expressed about the concept of soil quality. Sojka and 
Upchurch (1999) challenged the applicability of the concept in integrating the simultaneity of 
diverse and often conflicting functions of the soil. They stated their concern that a single soil 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 12 
quality index was unattainable and that having individual indices for all soils and 
circumstances would be unachievable, complex and completely confusing. They further 
argued that, while air and water quality could be defined, soil quality could not be defined 
since, as opposed to air and water, there is no such thing as pure soil. Sojka et al. (2003) 
further developed these views as they considered the definition of soil quality to be elusive 
and value-laden. They believed that the concept carried policy overtones, led to regional and 
taxonomic biases, failed to reconcile conceptual contradictions, and that its ambiguous 
definitions were confounded by countless circumstance-specific, function-dependent 
scenarios. They also argued that it did not offer practical means to manage conflicting soil 
management requirements for the multiple functions of soil that it acknowledges to occur 
simultaneously. Sojka et al. (2003) expressed their reluctance to endorse the holistic approach 
advocated by the soil quality concept in replacing the traditional approach of specific problem 
solving used in soil science. They concluded by suggesting that emphasis should be laid on 
quality soil management rather than management of soil quality as a professional and 
scientific goal for all scientists. For their part, Letey et al. (2003) also opposed the soil quality 
concept, but suggested that, if the concept were to be retained, soil use should be the criteria 
for attribute evaluation, rather than soil function or capacity. 
 
2.2.4 Soil quality definition 
 
As reviewed by Doran and Parkin (1994), several workers have tried to find a correct 
definition for the concept of soil quality, and the common factor in all these definitions was 
the “capacity of the soil to function effectively at present and in the future”. Based on these 
previous definitions, they concluded that soil quality should be defined as “The capacity of a 
soil to function within ecosystem boundaries to sustain biological productivity, maintain 
environmental quality, and promote plant and animal health”. In view of the various 
definitions put forward in the literature, the ad hoc committee S-581 set up by the Soil 
Science Society of America has come up with the following definition for soil quality (Karlen 
et al., 1997): "The capacity of a specific kind of soil to function, within natural or managed 
ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 13 
and air quality, and support animal health and habitation". 
 
2.2.5 Soil quality indicators 
 
While putting forward its theory and concepts, Larson and Pierce (1991) were already 
addressing issues of ways and means of evaluating soil quality and its change due to 
management practices. They believed that indicators of soil quality and its changes should 
reflect the soil’s ability to perform the three critical functions of providing a medium for plant 
growth, controlling water movement through the environment and acting as an environmental 
filter. This ability to perform these three functions could be measured by means of a 
minimum data set (MDS) incorporating different selected soil parameters, such as nutrient 
availability, total and labile organic carbon, texture, plant available water capacity, structure, 
strength, maximum rooting depth, pH, and electrolytic conductivity. 
 
Doran and Parkin (1996) proposed an upgraded MDS for screening the condition, quality and 
health of soil, incorporating chosen physical, chemical and biological indicators. This new 
MDS included additional soil biological data such as microbial biomass carbon and nitrogen, 
potentially mineralizable nitrogen (anaerobic incubation), and soil respiration, water content 
and temperature. Karlen et al. (1997) expanded on this list of selected soil quality indicators 
and included soil aggregation as a new indicator (Table 2.1). Most of these parameters have 
stood the test of time and are still relevant. They constitute the core of the work that has been 
done on the changes in soil quality that take place as a result of sugar cane cultivation. 
 
 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 14 
Table 2.1. Selected indicators of soil quality and some processes they impact (Karlen et al., 
1997) 
 
Measurement Process affected 
Organic matter Nutrient cycling, pesticide and water retention, soil structure 
Infiltration Runoff and leaching potential, plant water use efficiency, erosion potential 
Aggregation Soil structure, erosion resistance, crop emergence, infiltration 
pH Nutrient availability, pesticide absorption and mobility 
Microbial Biological activity, nutrient cycling, capacity to degrade pesticides 
biomass 
Forms of N Availability to crops, leaching potential, mineralization and immobilization 
rates 
Bulk density Plant root penetration, water- and air-filled pore space, biological activity 
Topsoil depth Rooting volume for crop production, water and nutrient availability 
Conductivity or Water infiltration, crop growth, soil structure 
salinity 
Available Capacity to support crop growth, environmental hazard 
nutrients 
 
 
2.3 Sugar cane production and soil quality 
 
2.3.1 General 
 
Determining the long-term effects of sugar cane cultivation on soil quality is difficult as it is 
not possible to have a direct basis for comparison, mainly because the initial properties of the 
soil prior to cane cultivation are not known. Had it been otherwise, comparison could have 
been made between the initial “before cane” status and the subsequent “after cane” status. 
Only a few studies have been made in this sort of situation, but these were for relatively short 
periods. For instance, changes in the properties of three Oxisols were monitored annually in 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 15 
Fiji for six years, all three sites having initially been under native vegetation prior to the 
development of the sugar cane project (Masilaca et al., 1986). Most of the time, however, the 
effects of sugar cane cultivation on soil quality have been determined in a less direct manner, 
with the properties of soils under sugar cane being compared to those of adjacent native 
(uncultivated) zones, as in e.g. Van Antwerpen and Meyer (1996) and Garside et al. (1997). 
 
These studies have shown that sugar cane cultivation had variable effects on soil quality. 
Most of the time, the effects were perceived to be negative. Thus, throughout the sugar cane 
producing areas of the world, it was common to find a diminution in soil quality attributable 
to sugar cane production (Haynes and Hamilton, 1999). Soil quality research work from 
various sugar cane producing regions, such as Fiji, Swaziland, Papua New Guinea, Australia 
and South Africa has shown that the conversion of virgin land to sugar cane production 
resulted in a progressive loss in soil quality. The main symptoms of this soil degradation were 
loss of soil organic matter, soil acidification and/or salinisation, and compaction of the inter-
row. This general soil degradation has been confirmed by the research work dedicated to 
yield decline in Australia by the Sugar Yield Decline Joint Venture, and in South Africa by 
SASEX. Both research groups have shown that land cultivated to sugar cane was degraded 
relative to virgin land since soil chemical, physical and biological properties had significantly 
changed for the worse under continuous sugar cane production (Meyer and Van Antwerpen, 
2001). 
 
However, there were instances where the effects of sugar cane cultivation were found not to 
be detrimental to the soil. In their study over three climatically different zones in North 
Queensland, Bramley et al. (1996) found no evidence of a consistent effect of time under 
sugar cane monoculture on soil chemical properties, even if the results did suggest a general 
decline in soil fertility over time. In the Goondi mill area of Queensland, McLean (1975) 
found only small changes in physical and chemical properties associated with the long-term 
(almost one century) cultivation and growth of sugar cane under the monocultural system. In 
Bundaberg, Queensland, McGarry et al. (1996) concluded that sugar cane cultivation had 
resulted in favourable changes in several soil physical and chemical properties, such as 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 16 
improvements in bulk density and increase in organic matter content, even though these had 
not led to improved aggregate stability or increased microbial biomass. 
 
The various studies aimed at determining the effects of sugar cane cultivation on soil quality 
have concentrated mostly on certain specific parameters. Two biological indicators have 
received specific attention, namely soil organic matter and microbial biomass. However, most 
of the work has been done on soil chemical properties, specifically soil acidification, cation 
exchange capacity, available nutrients such as calcium, magnesium, potassium and 
phosphorus, and salinity. A soil physical quality indicator that has received specific attention 
turned out to be soil compaction in the inter-rows. The stabilized infiltration rate of the soil, 
its plant available water and texture, and the stability of aggregates to water were the other 
physical indicators that have been studied. 
 
 
2.3.2 Biological parameters 
 
2.3.2.1 Organic matter 
 
An initial decrease in soil organic matter (SOM) has been commonly observed when virgin 
land was put under sugar cane (Haynes and Hamilton, 1999). This decrease was most marked 
in the topsoil, i.e. in the top 10 to 15 cm, as expressed by changes in organic carbon and total 
nitrogen in the soil profile (Figure 2.1). The extent of this reduction varied according to sites 
and soil types. However, changes in SOM content did not follow the same trend in the 
subsoil. At greater depths, SOM content tended to decrease but not to a significant degree. 
Under certain circumstances, there were even cases where SOM content increased in the 
subsoil. 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 17 
 
 Organic C (g kg -1) Total N (g kg -1)
 5 15 25 35 45 0.0 0.5 1.0 1.5 2.0 2.50
 
 20
 
40
 
 
60
 
 80
 
 
 Sugar cane land
Native grassland
 
Figure 2.1 Decrease of soil organic matter content observed seven years after native grassland 
was converted to sugar cane land (redrawn from Haynes and Hamilton, 1999). 
 
There are other examples to illustrate that there is a decrease in SOM content in the topsoil 
following cane cultivation. For instance, Van Antwerpen and Meyer (1996) studied 29 sites 
in the KwaZulu–Natal province of South Africa under three soil types and observed that, at 
all sites, there was a significant decline in the SOM content of the upper layer following the 
introduction of sugar cane. In the North East Swaziland lowveld, Henry and Ellis (1996) 
studied two soil types under sugar cane and found that cropping resulted in a decrease of 
about 8% in organic carbon and 26% in total nitrogen in the top 15 cm layer of the two soils. 
In Queensland, Australia, McGarry et al. (1996) found an organic carbon content of about 
1.5% in the top 5 cm of an uncultivated soil as opposed to about 1.0% in the soil from a cane 
row. However, not all studies have concluded that SOM content would decrease when virgin 
land is put under sugar cane. Thus, in North Queensland, Bramley et al. (1996) found that the 
organic carbon content of a soil from “old” cane land was in the order of 2.8% compared to 
some 1.6% for a “new” cane land soil. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
SSooiill  ddeepptthh  ((ccmm))
 18 
 
Even though SOM content generally decreased with the introduction of sugar cane, this 
decline did not occur at a constant rate. This decrease occurred rapidly just after sugar cane 
introduction, slowed down after a few years, before levelling out to a new equilibrium when 
the SOM content remained constant. This trend is best illustrated by Dominy et al. (2001), 
who found that soil organic carbon content declined rapidly in the first ten years after putting 
a virgin soil under sugar cane and then stabilized to a new equilibrium level after thirty years 
in the low clay soil and fifty years in the high clay soil (Figure 2.2). 
 
The rate of decline in SOM content was measured by Hartemink (1998b) in Papua New 
Guinea between 1979 and 1996 for two soil types that were under rainfed sugar cane 
production. In that relatively short interval, the organic carbon level declined by about 40% 
from 5.5% to 3.1%, giving an average decline rate of 0.14% per year. A similar exercise was 
undertaken for a long-term situation in two climatically different KwaZulu-Natal dryland 
regions (Qongqo and Van Antwerpen, 2000). It was found that SOM content decreased from 
4.7% to 2.9% in 50 years (average loss rate of 0.04% per year) at the South Coast, and from 
6.1% to 5.8% in 30 years (loss rate of 0.01% per year) in the Midlands. The data from 
Dominy et al. (2001) also indicated that the initial SOM decline rate was less marked for 
soils with higher clay contents, since SOM decreased at 0.13% per year in the soil with high 
clay compared to 0.30% per year for the soil with low clay, over the first ten years after sugar 
cane introduction. However, in the long-term, the protective effect of clay was no longer 
obvious and SOM decline rate stabilized to a much lower rate of 0.02% per year for both 
soils. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 19 
60
50
High clay content soil 
40
30
20
Low clay content soil 
10
0
Period of cropping (years)
 
 
Figure 2.2 Decline of soil organic carbon content through time on account of sugar cane 
production in South Africa (redrawn from Dominy et al., 2001). 
 
In addition to the determination of decline rate in SOM content, another aspect that has been 
studied is the fate of its various components. Skjemstad et al. (1999) conducted a study on 
three soil types in Queensland, comparing “old” to “new” cane lands. They showed that cane 
production resulted in very little change in the overall chemistry of soil organic carbon. In the 
whole soil profile, total organic carbon did not decline with increasing time under cane 
production, even though there was probably some movement of carbon down the profile. The 
proportion of light fraction organic carbon, defined as having a density lower than 1.6 g cm-3, 
remained relatively constant irrespective of cultivation history. Generally, this fraction 
decreased with increasing depth but there were no obvious and consistent differences 
between virgin/new sites and old sites. On the other hand, inert organic matter, viz. charcoal 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Organic C (g kg-1)
0
1 - 10
10 - 20
20 - 30
30 - 40
40 - 50
>50
 20 
had accumulated in the profile as a result of annual cane burning. This increase had possibly 
masked the losses in the more labile forms of carbon that were important for maintaining 
adequate soil structure and fertility. Thus, while the total organic C content might be constant 
or even increase, the relative contribution of different C pools might change. This could 
explain why the soil structure might decline even though total organic carbon content 
remained unchanged. 
 
The possibility that organic carbon originating from surface horizons could move down the 
profile, and thus increase the SOM content of deeper layers, is supported by data from 
Masilaca et al. (1986), who found an increase in organic C in the 30-40 cm layer. In this case, 
the downward movement of organic C could be ascribed to the secondary effects of ripping 
and rotovating during the initial land preparation. For their part, McGarry et al. (1996) found 
that a sugar cane cultivated site had almost twice the amount of organic carbon between 5 and 
45 cm depth, compared to an uncultivated one. Below the 45 cm depth, there was no 
noteworthy difference. In this case, the difference was explained by a two-year break in the 
cultivated site, during which the site was planted with peanuts, followed by tomatoes and 
zucchinis. After these two years, the site had been ploughed to a depth of 40 cm prior to 
replanting sugar cane, and the residues of the break crops could have helped to increase the 
OM content in the subsoil. 
 
However, the evolution of OM content in the subsoil of sugar cane fields is not as clear-cut as 
for the topsoil. It has also been found in other studies that OM content either remained 
unchanged or decreased in the subsoil. Van Antwerpen and Meyer (1996), for example, 
found that OM content was lower in the subsoil of a cane planted field compared to one 
under native vegetation. However, the difference in organic carbon between the two 
situations diminished with increasing depth. For their part, Henry and Ellis (1996) found that 
there was no difference between virgin and cane soils deeper down in the soil profile of an 
Oxisol, but found marked reductions over the entire sampling depth in a duplex soil, 
measured at 22% for the 15-30 cm layer and 50% for the 45-60 cm layer. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 21 
The changes in SOM content throughout the profile have been attributed to various causes by 
Dominy et al. (2001) who put forward three main reasons: (i) a lower return of carbonaceous 
residues to the soil; (ii) enhanced aggregate disruption and exposure of physically-protected 
organic material to microbial action following cultivation; and (iii) enhanced rates of 
decomposition due to more favourable conditions. Another possible reason was put forward 
by Masilaca et al. (1986), who noted that the soil organic carbon content declined in the early 
months following planting and suggested that it was an artifact caused by mixing of topsoil 
and subsoil during land preparation. 
 
A few practices play an important role in arresting the degradation in SOM content. The 
change from cane burning to green harvesting and trash retention has been identified as an 
essential evolution in this respect. Wood (1985) conducted a study at 19 sites in the Herbert 
Valley of North Queensland and found a substantial decline in SOM content of the top 10 
cm, where the organic carbon content was reduced by more than 50%. A further 20% 
reduction was noted in the next 10 cm layer. Wood (1985) concluded that this substantial 
decline was due to the removal of crop residues associated with the pre- and post-harvest 
burning of trash. On the other hand, Bramley et al. (1996) compared “old” to “new” sugar 
cane land in North Queensland but found no marked difference in soil organic carbon 
content, except at one site where the organic carbon content in the “old” land was higher in 
the top 5-cm layer, but lower throughout the rest of the profile. As opposed to the situation 
investigated by Wood (1985), the higher SOM content in the study of Bramley et al. (1996) 
could be ascribed to the beneficial effect of green cane harvesting and trash blanketing 
system. The work by Graham et al. (1999) confirmed that trash blanketing has beneficial 
effects on organic carbon content in the topsoil (Figure 2.3). Soil under trash blanketing had a 
higher organic carbon level than cane soil harvested under burnt condition, and even higher 
than virgin soil. Thus, it appears that long-term sugar cane production with trash retention has 
actually led to an increased SOM content, while burning reduced SOM content. 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 22 
 
 SoSiol iol rOgragnaic
-1
ni cc acrabrboonn ( (mgg  kg -1))
 
30 35 40 45 50
 0
 
5
 
10
 
 15
 20
 25
 
30
 Grass
 Burnt and tops removed
Trashed
 
Figure 2.3 Effect of sugar cane trash management on soil organic carbon content in South 
Africa (compiled from Graham et al., 1999). 
 
Further confirmation of the beneficial effects of green harvesting came from Skjemstad et al. 
(1999) who noted that even in situations where total organic carbon did decline, the practice 
of cane trashing had maintained the light carbon fraction in proportion to total organic carbon 
in soil. 
 
2.3.2.2 Microbial biomass 
 
A marked decline in soil microbial biomass has been observed under sugar cane cultivation 
when compared to virgin sites. Thus, declines in microbial biomass carbon of 32 and 83% 
have been measured in the 0 to 5 cm and 15 to 20 cm layers respectively when a site 
cultivated with sugar cane was compared to an uncultivated one (McGarry et al., 1996). In 
fact, the decrease in soil microbial biomass associated with cane production has been found 
to follow the same trend as for organic carbon, except that this decrease was more 
Effects of sugar cane production practices on soil qual ity in Mauritius 
DDeepptthh  ((ccmm))
 23 
pronounced (Dominy et al., 2001). As with SOM content, microbial biomass carbon 
decreased rapidly for the first ten years after the introduction of sugar cane, and stabilized 
thereafter at a new equilibrium level within twenty years (Figure 2.4). The microbial quotient 
(microbial biomass carbon as a percentage of total soil organic carbon) stood initially at 
2.60%, but decreased to 1.37% for a Ferrasol and 1.46% for a Cambisol under the effect of 
sugar cane production. However, the microbial biomass carbon content was more affected 
than SOM content depth-wise, since it was lower in the top 25 cm of the soil profile (Figure 
2.5). 
 
1100
900
700
High clay content soil 
500
Low clay content soil 
300
100
Period of cropping (years)
 
Figure 2.4 Change in soil microbial biomass carbon as a result of sugar cane production in 
South Africa (redrawn from Dominy et al., 2001). 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Microbial biomass C (mg kg-1)
0
1 - 10
10 - 20
20 - 30
30 - 40
40 - 50
>50
 24 
 
 MMicicrorobbiaiall  bBiioomass C(margb oCn  k(mg-g1) C kg -1)
 0 200 400 600 800 1000
 0
 5
 10
 15
 20
 25
 30
 35
 40
 Grassland Sugar cane
 
Figure 2.5 Microbial biomass carbon recorded in South African soil profiles with sugar cane 
and grassland (adapted from Dominy et al., 2001). 
 
 
The depressing effect of sugar cane cultivation on soil microbial biomass contents can be 
reversed under specific circumstances. In a study comparing native soil with sugar cane soil 
under contrasting harvesting conditions, Graham et al. (1999) have demonstrated that even 
though the virgin site had a higher microbial biomass carbon content throughout the profile 
than a sugar cane plot that was burnt prior to harvest, it had a lower content than another plot 
where no burning took place and where trash was conserved at harvest (Figure 2.6). This 
observation was explained by the fact that, with annual fertilizer applications, there was an 
increased return of organic residues to the soil in the form of decaying roots, litter trash and 
tops. This increased return had led to an increase in soil microbial population in response to 
the higher amount of residues available for decomposition. In contrast, there was no such 
effect in cases where the residues were burnt prior to harvest. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
DDeepptthh  ((ccmm))
 25 
 -1
Microbial Biomass (mg C k-1g )
 ial biomas  (mg C kg )
 0 100 200 300 400 500
0
 
 5
 
10
 
 15
 Grass20
 Burnt and tops removed
25
 
Trashed
 30
Figure 2.6 Microbial biomass carbon recorded in soil profiles with sugar cane subjected to 
different harvesting procedures (adapted from Graham et al., 1999). 
 
 
2.3.3 Chemical properties 
 
2.3.3.1 pH 
 
Soils under sugar cane generally have a lower pH than those under native vegetation (Haynes 
and Hamilton, 1999). This decrease in soil pH can be accompanied by a concurrent increase 
in exchangeable aluminium levels (Wong You Cheong and Chan, 1977). However, new 
sugar cane cultivation does not automatically mean soil acidification. For instance, Van 
Antwerpen and Meyer (1996) observed that there was no significant difference in pH 
between virgin and cane soils, even though cultivation led to a decrease of the order of 0.26 
pH units under dryland conditions, and an increase of 0.14 pH units under irrigated 
conditions. For their part, Masilaca et al. (1986) did not find any clear trend in the evolution 
of topsoil pH, which fell immediately after planting, but seemed to rise again in the longer 
term. There could also be an effect in relation to soil depth, as in the case where cropping 
Effects of sugar cane production practices on soil qual ity in Mauritius 
DDeepptthh  ((ccmm))
 26 
under sugar cane led to a slight acidification of the topsoil, whereas the converse was true of 
the subsoil (Henry and Ellis, 1996). This observation was explained by the fact that bases 
could have been leached from the topsoil into the subsoil as a result of irrigation. 
 
Three main causes have been identified for the accelerated acidification of soils under sugar 
cane cultivation (Meyer et al., 1998): (i) oxidation of ammoniacal fertilizers to nitric acid; (ii) 
mineralization of organic matter; and (iii) leaching of basic cations from soil. However, the 
detrimental effect of ammoniacal fertilizers, particularly ammonium sulphate, is regarded as 
the most important (Wood, 1965; McLean, 1975; Wood, 1985). In contrast, the acidifying 
effect of urea, which is more commonly used than ammonium sulphate, is 50% less than the 
latter since its net potential acidity is 0.072 compared to 0.143 kmol H+ kg-1 N for ammonium 
sulphate (Noble et al., 1997). The fertilizer-induced acidification process for both urea and 
ammonium sulphate is caused by the release of two hydrogen ions per unit of ammonium 
through the soil microbial process of nitrification and can be summarized in Equation 2.1 
(Haynes and Hamilton, 1999): 
 
NH +4  + 2O2 → NO
-
3  + H2O + 2H
+       (2.1) 
 
The process of soil acidification associated with fertilization was confirmed by Graham et al. 
(1999) who measured mean pH values of 5.8 and 5.1 in unfertilized and fertilized treatments 
respectively, the difference being attributed to continual use of acidifying nitrogenous 
fertilizers for 49 consecutive years without concomitant liming. 
 
The acidification rate was actually quite fast for South African soils since average pH values 
have been found to decline from 6.17 in 1980-82 to 5.61 in 1996-97, a 5.6-fold increase in 
acidification in terms of hydrogen ion activity over that period (Meyer et al., 1998). This 
rapid decline was confirmed by Qongqo and Van Antwerpen (2000) who estimated the rate 
of decline to be some 0.025 pH unit year-1. Similarly, in Papua New Guinea, Hartemink 
(1998c) found that the pH value of topsoil declined from 6.5 in 1979 to around 5.7 in 1996, 
an average decline of about 0.047 pH unit year-1 (Figure 2.7). The initial decrease from 1979 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 27 
to 1982 was probably caused by the increased mineralization of organic matter associated 
with initial cultivation, while the decrease in the 1990’s coincided with the application of 
ammonium sulphate instead of the previously used urea. 
 
 6.6
 6.5
 
6.4
 
 6.3
 
6.2
 pH
 6.1
 
6
 
5.9
 
 5.8
 
5.7
 
1975 1980 1985 1990 1995 2000
 
Figure 2.7 Decline of topsoil pH through time on account of sugar cane production in Papua 
New Guinea (adapted from Hartemink, 1998c). 
 
In addition to topsoil acidification, a significant decrease of 0.2 to 0.4 pH units after 10 years 
of continuous sugar cane cultivation was also recorded in the subsoil (Figure 2.8). Hartemink 
(1998c) estimated that the soil under study had a buffering capacity of 125 kmol H+ ha-1 pH-1 
and warned that if the current fertilizer practices were maintained, it would take only ten 
more years for the mean soil pH to fall below the critical threshold of 5.0. 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
ppHHww
 28 
 
pHw
 
5.5 6.0 6.5 7.0
 
0
 
 
20
 
 40
 
 60
 80
 
100
 
Natural grassland
 
Continuous sugar cane
 
Figure 2.8 Change in subsoil pH after ten years of continuous sugar cane production in Papua 
New Guinea (compiled from Hartemink, 1998c). 
 
There is little doubt that soil acidification occurs following the introduction of sugar cane on 
virgin soil, with long-term negative impact on soil quality. For instance, Noble et al. (1997) 
reviewed the linkage between sugar cane production and soil acidity and concluded that the 
continual decline in soil pH and associated infertility could have a significant impact on the 
long-term sustainability of sugar cane production systems. For their part, Schroeder et al. 
(1994) were concerned that acidification was becoming a major problem in South Africa, 
describing it as the most important yield-limiting factor in KwaZulu-Natal. Increased acidity 
with continuous cropping was identified as part of the chemical and physical degradation of 
soils in the South African sugar industry. This was confirmed by Meyer et al. (1998), who 
found a marked increase in soil acidification across the South African sugar industry. This 
decrease in soil pH associated with sugar cane cultivation can be considered to be a menace 
to the long-term fertility of the soil, and by extension, to the sustainability of the sugar 
industry if no corrective measures such as liming are taken. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
DDeepptthh  ((ccmm))
 29 
 
2.3.3.2 Cation exchange capacity 
 
The cation exchange capacity (CEC) was generally lower for soils under sugar cane 
compared to those under native vegetation (Wood, 1985; Henry and Ellis, 1996). Such an 
observation is not surprising since CEC is directly related to SOM content, and the latter has 
been demonstrated to generally decrease following sugar cane cultivation. Masilaca et al. 
(1986) differentiated between topsoil and subsoil CEC. While topsoil CEC tended to decline 
on account of lower OM content, the subsoil CEC increased. This was probably caused by the 
downward movement of OM when the soil was ripped and rotovated during the initial land 
preparation. On the other hand, Hartemink (1998b) found that the CEC decreased 
significantly with time throughout the soil profile (Figure 2.9). McLean (1975) was the 
exception in that he did not note any change in topsoil CEC. 
 
 
CEmCm (mol m kgol-1 -1c c kg )
 
 200 300 400 500 600
 0
 10
 20
 
30
 
40
 
 50
 60
 
1980s 1990s
 
 
Figure 2.9 Change in the CEC of a soil profile after ten years of continuous sugar cane 
production in Papua New Guinea (compiled from Hartemink, 1998b). 
Effects of sugar cane production practices on soil qual ity in Mauritius 
DDeepptthh  ((ccmm))
 30 
 
2.3.3.3 Plant available nutrients 
 
The levels of plant available nutrients in sugar cane soils might be higher or lower than in 
virgin ones, depending on whether fertilizer inputs were higher or lower than the amounts of 
nutrients removed in the harvested crop, plus any other losses such as leaching (Haynes and 
Hamilton, 1999). Two important exchangeable bases, namely calcium and magnesium, have 
been found to decrease in several studies (Wood, 1985; Masilaca et al., 1986; Van 
Antwerpen and Meyer, 1996; Meyer et al., 1998; Qongqo and Van Antwerpen, 2000). Wood 
(1965) has quantified the decrease in calcium, which fell from 922 mg kg-1 in virgin soil to 
656 mg kg-1 in sugar cane soil. It appears that, in most cases, insufficient amounts of bases 
are being added to compensate for crop removal and leaching (Masilaca et al., 1986). 
 
Similarly, exchangeable potassium levels tend to decrease, through both removal by cane and 
leaching losses. In Papua New Guinea, Hartemink (1998b) noted a decrease in potassium in 
newly planted soil from 14.2 to 8.5 mmol  kg-1c . Henry and Ellis (1996) also noted that levels 
of potassium have declined over the soil profile in Swaziland and that this deterioration was 
further aggravated by increasing imbalances between basic cations as shown by the increases 
in (Ca+Mg)/K ratios. By contrast, the opposite was noted in South Africa, with a build-up of 
potassium in soils under sugar cane, which could be directly attributed to an overuse of 
potassium fertilizers by growers (Meyer et al., 1998). 
 
The levels of extractable phosphorus in sugar cane soils depend on fertilizer use and have 
been found to both increase (Wood, 1985; Henry and Ellis, 1996) and decrease (Van 
Antwerpen and Meyer, 1996; Meyer et al., 1998). McLean (1975) measured an increase in 
phosphorus from 14.2 mg kg-1 in a virgin soil to 30.5 mg kg-1 in sugar cane soil, while 
Hartemink (1998a) observed the opposite, having measured a decrease from 40 mg kg-1 to 28 
mg kg-1 in a space of fifteen years. These changes were mostly confined to the topsoil and 
very little phosphorus was found to be removed from the soil horizons deeper than 30 cm. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 31 
 
2.3.3.4 Salinity and/or sodicity 
 
Salinity and/or sodicity of soils are expressed in terms of changes in their electrical 
conductivity (EC) and sodium adsorption ratio (SAR). Changes in these parameters occurred 
in sugar cane soils essentially under irrigated conditions and were dependent on the quality of 
irrigation water. In Swaziland, it was found that sugar cane production had no negative effect 
on salinity or sodicity of a duplex soil (Henry and Ellis, 1996). However, the EC and SAR of 
this soil decreased dramatically, reflecting the effects of good surface and subsurface 
drainage, the use of irrigation water with low electrolyte concentration and the application of 
gypsum. The opposite situation was found in South Africa, where a higher EC and SAR were 
measured in irrigated sugar cane soils compared to virgin ones, with a build-up of salinity and 
sodicity in such areas (Van Antwerpen and Meyer, 1996). 
 
2.3.4 Physical parameters 
 
2.3.4.1 Bulk density 
 
Bulk density was the main soil physical quality indicator to be affected when soils under 
sugar cane were compared to those under native vegetation. Thus, soils had an increased bulk 
density following the introduction of sugar cane into hitherto virgin area, clearly 
demonstrating that sugar cane production had a compacting effect on soil. This compaction 
was related to mechanized operations and therefore occurred mainly within the zones of 
machinery traffic. In the absence of traffic, the soil would probably not be compacted. For 
instance, Wong You Cheong and Chan (1977) did not observe any change in bulk density in 
their study on long-term cultivation, probably because of the limited use of heavy machinery 
in sugar cane production in Mauritius at that time. 
 
However, heavy machinery has been increasingly utilized over the years for sugar cane 
production in many countries. As a result, it is not surprising to find a significant increase in 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 32 
bulk density of the topsoil under sugar cane compared to the virgin situation (e.g. McLean, 
1975; Wood, 1985; Van Antwerpen and Meyer, 1996). Compaction was most marked in the 
inter-row, where most of the traffic occurs. This is confirmed by Hartemink (1998b), who 
found that the bulk density was significantly higher under the cane inter-row than under 
grassland, but there was little compaction under the cane row (Figure 2.10). The topsoil bulk 
density of the inter-row was higher by 0.20 g cm-3, an average increase of 19% when 
compared to natural grassland. McGarry et al. (1996) also noted a similar increase in the 
topsoil bulk density, which was higher by 10 to 17%. 
 
Bulk density (g cm -3)
1.0 1.1 1.2 1.3 1.4
0
10
20
30
40
50
Grass Row Interrow
 
 
Figure 2.10 Bulk densities recorded beneath sugar cane inter-rows and rows and in grassland 
(adapted from Hartemink, 1998b). 
 
Qongqo and Van Antwerpen (2000) were able to determine the average rate of compaction 
for two sites in South Africa. They found an increase in bulk density from 1.56 to 1.77 g cm-3 
in 50 years at one site, giving a compaction rate of 0.004 g cm-3 per year. At the other site, the 
bulk density increased from 1.18 g cm-3 to 1.33 g cm-3 in 30 years, equivalent to a 
compaction rate of 0.005 g cm-3 per year. For their part, McGarry and Bristow (2001) found 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Depth (cm)
 33 
bulk density increases of 18% and 22% in sugar cane inter-rows and rows respectively 
compared to rainforest at one site, and further increases ranging between 3% and 13% at 
other sites. 
 
Traffic on account of mechanization is associated with several cultural operations. Relative 
contributions to compaction from each source are probably of different magnitudes. McLean 
(1975) differentiated between two main sources of compaction, namely short-term 
compaction associated with mechanical harvester and bin traffic, and long-term compaction 
associated with cultivation during crop growth. Wood (1985) suggested that compaction and 
breakdown in soil structure were due to soil damage caused by harvester and haulout traffic, 
excessive cultivation, and situations where farmers had been forced to harvest under 
excessively wet conditions. Ng Cheong et al. (1999) found that soil compaction did occur 
with harvester traffic, even under relatively dry conditions, but without significantly affecting 
cane yield. For their part, Henry and Ellis (1996) ruled out trafficking as the sole responsible 
factor for increased bulk density because compaction was also observed at depth, but failed to 
identify other potential sources of compaction. 
 
2.3.4.2 Infiltration rate 
 
Compaction, surface crusting and other forms of physical deterioration will affect the 
infiltration rate of water into the soil. A reduction in stabilized infiltration rate is thus a clear 
sign of deterioration in soil physical properties. In most cases, soils under sugar cane had a 
lower stabilized infiltration rate than those under native vegetation. For instance, Garside et 
al. (1997) found that infiltration rates were lower in cropped fields compared to virgin ones, 
the lower rates being generally associated with increases in soil strength. Their conclusion 
was that compaction was directly affecting infiltration rate and that effective rooting depths 
could also be potentially affected. Hartemink (1998b) found, as illustrated in Figure 2.11, that 
the average infiltration rate (after more than 4 hours) in the sugar cane inter-rows was very 
low (average 16 mm h-1) compared to grassland (average 259 mm h-1) or sugar cane rows 
(average 290 mm h-1). 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 34 
 
 900
 
 800
 
700
 
 600
 
500
 
 
400
 
 300
 
200
 
 
100
 
 0
0 50 100 150 200 250 300
 
Time (mins)
 
Cane row Interrow Grassland
 
Figure 2.11 Infiltration rates recorded in sugar cane inter-rows and rows and in grassland 
(compiled from Hartemink, 1998b). 
 
There was no significant difference between the infiltration rates of the grassland or sugar 
cane rows, suggesting that it was not the presence of sugar cane per se that affected 
infiltration rate, but more likely the traffic associated with the crop. This is partly confirmed 
by Henry and Ellis (1996), who found that cropping had little effect on the final infiltration 
rate of a duplex soil while that of an Oxisol deteriorated under cropping from 16.2 to 8.7 mm 
h-1. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
--11--11
IInnffIInniillffttiirrllaattrrttaaiittooii  ooRRnn  aarraatteettee    ((((mmmmmmmm    hhhh))))
 35 
 
2.3.4.3 Plant available water 
 
There is little consistency in the way in which plant available water (PAW) of a soil has been 
affected by the introduction of a sugar cane crop. In Mauritius, Wong You Cheong and Chan 
(1977) found that the effect of sugar cane cultivation on the PAW varied with soils and 
cropping conditions. Soils under sugar cane had lower PAW than soils under native 
vegetation in dry areas, but higher PAW in the wet zones. For their part, Masilaca et al. 
(1986) found no significant change in PAW at two sites and an increased PAW at a third site, 
but had no explanation to offer for these differences. Henry and Ellis (1996) also found little 
effect of cropping on PAW, with a lower capacity of 2.8% for soils under sugar cane. In 
South Africa, Van Antwerpen and Meyer (1996) noted a significant increase in PAW with 
cultivation in a dryland situation. Conversely, Garside et al. (1997) found lower PAW in cane 
soils in Australia, which were also generally associated with increases in soil strength. In the 
same country, McGarry and Bristow (2001) measured a reduction in PAW at four sites, 
which ranged from 8% to 20%. 
 
 
2.3.4.4 Aggregate stability 
 
In general, soils under sugar cane had much lower aggregate stability than those under native 
vegetation (Wong You Cheong and Chan, 1977; McGarry et al., 1996). The effect tended to 
be more marked in aggregates at the soil surface. McGarry et al. (1996) noted that aggregates 
from the top 10 cm of a cultivated site slaked after 2 hours, while aggregates from an 
uncultivated site did not slake at all. Qongqo and Van Antwerpen (2000) found that soil 
aggregate stability decreased as the period under sugar cane increased, with a rate of 0.87% 
per year for a sandy loam and 0.64% per year for a clayey soil. Dominy et al. (2001) 
explained this decreased aggregate stability by the fact that, with increasing years under sugar 
cane, SOM level declined and soil aggregates became less strongly bound, thereby reducing 
the aggregate stability. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 36 
 
2.3.4.5 Particle size distribution 
 
The evidence suggests that there is very little difference in textural properties between sugar 
cane-planted soils and those under native vegetation (McLean, 1975; Van Antwerpen and 
Meyer, 1996). McGarry and Bristow (2001) studied the soil’s textural properties at seven 
sites and found that only one displayed differing textures. Wong You Cheong and Chan 
(1977) found some changes in clay content, but these varied with soil and no reason could be 
assigned to the measured differences (Table 2.2). However, it is interesting to note that under 
sub-humid conditions, sugar cane cropping appeared to have led to an increase in clay content 
at the expense of the silt content, possibly as a result of topsoil mixing with the more clayey 
subsoil. On the other hand, there was a decrease in clay content in one soil from the super-
humid region, and this could be due to soil erosion, with the clay fraction being more 
susceptible to detachment and entrainment by rainfall. 
 
Table 2.2. Changes in particle size fractions to 45 cm depth in Mauritius soils associated with 
sugar cane cropping (Wong You Cheong and Chan, 1977). 
 
Soil* Climate Soil under native vegetation Soil under sugar cane 
  Sand (%) Silt (%) Clay (%) Sand (%) Silt (%) Clay (%) 
P Sub-humid 31.8 34.6 33.6 31.2 21.4 47.4 
L Sub-humid 11.8 25.8 62.5 6.5 19.6 73.8 
B Super-humid 36.1 27.6 36.3 50.7 22.0 27.3 
F Super-humid 47.9 25.8 26.3 46.3 27.9 25.8 
* P: Latosolic Reddish Prairie  L: Low Humic Latosol 
 B: Latosolic Brown Forest  F: Humic Ferruginous Latosol 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 37 
 
2.4 Conclusion 
 
The quality of a soil determines its capacity to perform several functions, namely sustaining 
plant and animal productivity, maintaining or enhancing water and air quality, and supporting 
animal health and habitation. Since it is not possible to measure how the soil is performing 
these various functions, soil quality is determined through indicators that are used in the 
screening of soil condition. Research work on soil quality in South Africa, Australia and 
elsewhere has led to the identification of possible indicators of soil quality for soils under 
sugar cane. These indicators are biological – soil organic matter and soil microbial biomass; 
chemical – pH, cation exchange capacity and exchangeable bases; and physical - soil texture 
(particle size distribution), soil structure (aggregate distribution and stability), bulk density, 
plant available water and stabilized infiltration rate. 
 
These quality indicators have been determined for soils under sugar cane and compared to 
those of soils under native vegetation in countries such as South Africa, Australia, or Papua 
New Guinea. Such comparisons have clearly indicated that sugar cane soils are degraded in 
these countries and that, under current conditions, the long-term sustainability of sugar cane 
production is not guaranteed. Several cultural practices have been held responsible for this 
degradation, particularly tillage, fertilization, mechanization and irrigation. There is no reason 
why Mauritius should be an exception to the rule, since the cultural practices associated with 
sugar cane cultivation in Mauritius are similar to those of the aforementioned countries. It is 
therefore essential to determine the extent to which the quality of soils in Mauritius is 
affected by sugar cane cultivation, before any remedial action can be taken to ensure the long-
term sustainability of the industry. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 38 
CHAPTER 3 
 
CHARACTERIZATION OF THE STUDY AREA 
 
3.1 Introduction 
 
In this chapter, a general description of the island of Mauritius will be presented, with 
particular reference to its physical environment and its sugar industry. Its geography and 
physiography will be briefly described. Details will be given about the climate of the island, 
with emphasis on variations in temperature and rainfall, which give rise to different agro-
climatic zones. This will be followed by an account of the geology of the island, which plays 
an essential role in the nature of its soils. The latter will be described using the soil maps of 
1962 and 1984. Finally, the current status of the sugar industry of Mauritius will be reviewed 
with emphasis on its contribution to the economy of the island. 
 
3.2 Location 
 
Mauritius is an island of volcanic origin situated between the parallels of 19o58’ and 20o32’ 
south latitude and the meridians of 57o17’ and 57o46’ east longitude in the South West Indian 
Ocean (Figure 3.1). It is approximately 800 km east of Madagascar and 2000 km off the coast 
of continental Africa. The island has an elliptical shape, with a major axis running North 
North East – South South West over a distance of 61 km and perpendicular to this is a minor 
axis of 46 km. The total land area is in the order of 1860 km2. 
 
3.3 Physiography 
 
Mauritius consists essentially of a ring of peaks about 600 to 900 m high, enclosing a central 
plateau rising from about 300 m in the north to 600 m in the south west. To the north of the 
mountains, the northern plain with the prominent volcanic cones of Mont Piton, The Mount, 
Butte Aux Papayes and Forbach falls gently to the sea with an average slope of less than 1%. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 39 
To the west, a coastal plain about 5 km wide in the north tapers down to the Morne Babant 
peak in the south coast of the island. In the west and south, the lavas of the volcanic cones 
which built up the central plateau have spilled around the mountain ranges and flowed to the 
sea forming coastal plains with a general slope of about 2%. In the south west corner of 
Mauritius, the area of Chamarel, derived from ash produced at the time of the Early Lavas of 
the Younger Volcanic Series, has been strongly dissected and eroded, as have the southern 
slopes of Savanne and Grand Port mountain ranges. The island is drained by several river 
systems distributed mainly in the Intermediate Lavas; the rivers themselves though not large, 
are very deeply incised (Parish and Feillafé, 1965). 
 
 
 
Figure 3.1 Location of Mauritius in the South West Indian Ocean (adapted from Université 
Michel de Montaigne – Bordeaux 3, 1997) 
 
Thus, there are three distinct topographic patterns connected with the age of the parent lava. 
There are the comparatively small but often scenically dramatic mountain ranges of the oldest 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 40 
lavas. Then, there are the gently rolling topography of the Intermediate Lavas of the Younger 
Volcanic Series with deeply incised rivers and some terraces and now stabilized gullies. 
Finally, there are the Late Lavas, with many extremely rocky areas of distinctly hummocky 
appearance and an almost complete absence of surface drainage, dominated by the vents that 
gave rise to them (Parish and Feillafé, 1965). 
 
3.4 Climate 
 
3.4.1 Temperature 
 
Mauritius is a small isolated land mass situated near the southern edge of the tropical belt. It 
is practically free from continental influences and thus enjoys a maritime climate, viz. 
tropical-maritime during summer (November to April) and sub-tropical in winter (May to 
October). However, the weather does not remain the same for more than a few days 
consecutively as it is affected by disturbances of both temperate and tropical types (Padya, 
1984). The South-East trade winds are dominant in the winter months, giving way to periods 
of calm and light winds in summer which are frequently interrupted by tropical depressions 
or cyclones. Very high winds and intense rainfall characterize these tropical depressions. 
 
The highest mean temperature occurs in February and the lowest in August while the range of 
the mean temperature is about 5.5 oC at most places. However, the mean daily range of 
temperature is about 6 oC in the centre, and about 7 to 8 oC on the coast. The weather is also 
highly dependent on the island’s topography. Thus, midsummer temperatures at the centre are 
similar to midwinter temperatures on the coast (Padya, 1984). 
 
3.4.2 Rainfall 
 
The mean annual rainfall over the island as a whole is in the order of 2100 mm (Padya, 
1984). Orography and prevailing winds have a distinct effect on rainfall distribution. Annual 
rainfall on the windward Eastern coast is around 1600 mm, rises to almost 4000 mm near the 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 41 
centre and then decreases gradually to less than 1000 mm on the leeward Western coast 
(Figure 3.2). 
 
 
 
Figure 3.2 Mean annual rainfall distribution over Mauritius (Parish and Feillafé, 1965) 
 
About 70% of the total rainfall occurs in the summer months of November to April. October 
is the driest month, with only 3.5% of the total, while March is the wettest with 15% of the 
total. The monthly average increases from November through March, decreases sharply in 
April and May, and then decreases more gradually until October. 
 
Thermal and moisture efficiency indices have been derived from rainfall and air temperature 
data. Mauritius has been divided into distinct agro-climatic zones according to 
Thornthwaite’s classification using these indices (Halais and Davy, 1969). These agro-
Effects of sugar cane production practices on soil qual ity in Mauritius 
 42 
climatic zones range from super-humid mesothermal in the centre to semi-arid megathermal 
on the western coast. The semi-arid zone covers only a very small area (0.3% of the island), 
and is therefore of no significance. Hence the island is divided into three main agro-climatic 
zones, namely sub-humid, humid and super-humid. The sub-humid zone covers the low 
rainfall (< 1600 mm annually), high temperature region confined to the coastal belt which is 
more important on the leeward side; it covers 19.4% of the island. The humid zone is an 
intermediate rainfall region (1600 – 2600 mm annually) between the coastal belt and the 
centre of the island, representing 34.7% of the island. Finally, the super-humid zone is a high 
rainfall (> 2600 mm annually) and relatively low temperature region, in the higher parts of 
the island’s centre and covers 45.6% of the island. 
 
3.5 Geology 
 
The rocks of Mauritius, apart from some consolidated coral and shell debris and the reefs and 
dunes around most of the coast, are entirely volcanic in origin and are of two distinct 
geological ages. The older volcanic series, as defined by Simpson (1951), gave rise to the 
highly eroded mountainous features of the landscape. The foothills and bases of these 
mountains were then flooded by younger lavas which formed the central plateau and the plain 
of the north. An intermediate stage of volcanic activity which was confined to the south-west 
corner of the island gave rise to a series of lava flows and a considerable area of ash 
deposition quite distinct from both the older and recent lavas. 
 
The Older Lavas have thus given rise to the Older Volcanic Series in or before the Early 
Tertiary (Simpson, 1951). This was followed by a major erosion interval before the advent of 
the Younger Volcanic series which gave rise to the Early Lavas in the Late Tertiary. There 
followed a minor erosion interval sequence before the same Younger Volcanic Series gave 
rise to the Late Lavas in the Pleistocene. 
 
The Older Volcanic Series consist mainly of compact and unvesiculated olivine basalt and 
coarse agglomerate, cut by numerous dykes and a few intrusive trachyte domes. The Early 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 43 
Lavas of the Younger Series, which are mildly vesiculated olivine basalts, built up the south-
western plateau of Plaine Champagne and Pétrin, whilst the highly dissected Chamarel area 
was formed by the pyroclastic activity preceding the pouring out of the very liquid lavas. The 
Late Lavas of the Younger Series followed after a short erosion interval, without a preceding 
phase of pyroclastic activity. Flow after flow of lava poured out from a series of shield 
volcanoes flooding almost the whole island, and building up to a height of 660 m near the 
central town of Curepipe (Figure 3.3). 
 
Twenty-five vents on well-preserved shield volcanoes exist, all lying on a line trending NNE 
- SSW from end to end of the island; some of the northern vents are surrounded by a carpet of 
pyroclasts ejected during the last stage of their activity. 
 
 
 
Figure 3.3. Simplified geological map of Mauritius (after Simpson, 1951) 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 44 
 
For the purpose of soil classification, Parish and Feillafé (1965) have further sub-divided the 
Late Lavas of the Younger Volcanic Series, as the soils of the island fall into two distinct age 
categories, namely deep mature soils and shallow rocky soils. In many areas, relatively 
shallow layers of lava on which soils with varying degrees of maturity have developed overlie 
the deep mature soils. Parish and Feillafé (1965) have thus further divided the geology of 
Mauritius into Older Volcanic Series followed by Younger Volcanic Series comprising of 
Early, Intermediate and Late Lavas in chronological order. The Older Volcanic Series consist 
of mountain peaks and ranges, while the Early Lavas are associated with the south-western 
plateau of Pétrin and Plaine Champagne, and the highly dissected area of Chamarel. The 
Intermediate Lavas have given rise to deep soils with well developed drainage systems while 
the Late Lavas gave rise to rocky soils without surface drainage systems. 
 
The country covered by the mature soils varies from a flat to a rolling topography, with 
deeply incised river gorges and some minor terraces, whilst the topography of the areas 
covered by the rocky soils tends to be hummocky and is almost completely free of any 
surface drainage system. The rocks and boulders of the mature soils are usually coarse 
grained doleritic basalts with some vesiculation, whilst the rocky soils contain doleritic 
basalts that are highly vesiculated. Apart from the Plaine des Roches up to the flanks of 
L’Escalier, which is of the pahoehoe lava type, the most recent lava flows of Mauritius give 
the appearance of having been of the aa type (Parish and Feillafé, 1965). 
 
There are alternate layers of lava and soil in the sides of the deeply incised river gorges and at 
the exposed faces of the mountain ranges. In fact, the whole geology of Mauritius is made up 
of layers from different lava flows and weathered material on which have been superimposed 
the effects of erosion due to the torrential rains which occur during the cyclone season. 
Around the coast, raised coral reefs and consolidated shell and coral debris can be found 
overlying a deep tuff at heights of more than 20 m above sea-level. These observed features 
may be assigned to the fluctuations of the sea level during the Pleistocene glacial and inter-
glacial periods and/or vertical movements of the land mass due to volcanic instability. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 45 
 
3.6 Soils 
 
3.6.1 Soil Map of 1962 
 
The first soil map of Mauritius with a scale of 1:100 000 (Figure 3.4) was published in 1962 
(Parish and Feillafé, 1965) and this system is still the most commonly used within the cane-
planting community. Owing to the close similarity between parts of the Hawaiian Islands and 
Mauritius with respect to geology, climate, soils and cropping, the classification system used 
by Cline in 1955 for the soil survey of the territory of Hawaii was applied to Mauritius. 
However, there are some noteworthy differences between the two islands, the main one being 
that, contrary to Hawaii, a large proportion of Mauritius is covered by rocky soils formed on 
the recent lava flows. The system was thus adapted to take into account such differences. 
 
In this classification system, the soils are divided into zonal, intrazonal and azonal orders 
(Table 3.1). As with the Hawaiian system, the Great Soil Groups have been sub-divided into 
families, each of which represents an area of fairly uniform climate and topography, and 
therefore of similar soils. 
 
Table 3.1. Soil Groups of Mauritius (Parish and Feillafé, 1965) 
 
Zonal Intrazonal Azonal 
Low Humic Latosol Latosolic Reddish Prairie Alluvial Soil 
Humic Latosol Latosolic Brown Forest Regosol 
Humic Ferruginous Latosol Grey Hydromorphic Lithosol 
 Dark Magnesium Clay  
 Low Humic Gley  
 Ground Water Laterite  
 Mountain Slope Complex  
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 46 
 
Figure 3.4 Soil map of Mauritius (after Parish and Feillafé, 1965) 
 
 
3.6.1.1 Zonal soils 
 
The zonal soils of Mauritius fall into the Latosol sub-order and are represented by three Great 
Soil Groups, the Low Humic Latosols, the Humic Latosols and the Humic Ferruginous 
Latosols. They have developed mainly on the Intermediate Lavas under a mean annual 
rainfall ranging from < 1000 mm to > 5000 mm. Surface and internal drainage are adequate 
and they have thus permitted the fullest expression of climate and vegetation as soil forming 
factors. Some chemical properties of the zonal soils are summarized in Table 3.2. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 47 
Table 3.2. Some chemical properties of the zonal soils (adapted from Parish and Feillafé, 
1965) 
 
Property  Soil group  
 L H F 
pH ~6 - 7 5.4 - 6.2 5.5 
CEC (meq%) 25 15 - 25 20 
Organic matter (%) 4.8 5 - 7 6.9 - 10.4 
Nitrogen (%) 0.27 0.26 0.3 
C/N ratio 10.7 9.5 - 13.5 18 
 
The Low Humic Latosols (L) have developed on the Intermediate Lavas within the sub-
humid and low rainfall humid zones. They are deep to moderately deep soils with good 
internal drainage and a fairly high base status, with a low organic matter content. They have a 
red to brown A horizon that displays a strong medium to fine sub-angular blocky structure. 
Their B horizon is red to reddish brown, with a massive to weakly prismatic structure. The 
texture of the Low Humic Latosols is silty clay to silty clay loam. Kaolinite is the dominant 
mineral with goethite and sometimes gibbsite in lesser amounts. This soil group covers 
16.4% of the total area of Mauritius and is divided into four families, namely Richelieu (L1), 
Réduit (L2), Ebène (L3) and Bonne Mère (L4). 
 
The Humic Latosols (H) have developed on the Intermediate Lavas in the humid to super-
humid zones, i.e. from a mean annual rainfall of 1500 to 3750 mm. They have a well-
developed dark brown A horizon overlying a reddish brown B horizon which grades into 
parent material. Their texture is clay by mechanical analysis but they behave like silty clays. 
They contain equal quantities of kaolinite, goethite and gibbsite. This soil group covers 5.2% 
of the total area of Mauritius and is divided into two families, Rosalie (H1) and Riche Bois 
(H2). 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 48 
The Humic Ferruginous Latosols (F) have developed on the Early and Intermediate Lavas of 
the Younger Volcanic Series and on the lavas of the Older Volcanic Series. They are strongly 
weathered soils occurring in the high rainfall region of the island with mean annual rainfalls 
ranging from 2500 to more than 5000 mm. They have a thin A1 horizon rich in organic 
matter, a crumb-structured A2 horizon with iron and aluminium oxide concretions overlying 
a compact B horizon which grades into parent material. The clay fraction is mainly gibbsite 
and goethite, with very little kaolinite. This soil group covers 11.4% of the total area of 
Mauritius and is divided into four families, namely Belle Rive (F1), Sans Souci (F2), 
Midlands (F3) and Chamarel (F4). 
 
3.6.1.2 Intrazonal soils 
 
The soils classified under this order are those that have developed under conditions where the 
effects of climate and vegetation are masked by local factors of environment such as relief, 
drainage and composition of the parent material. Soils developed on Late Lavas in the dry 
areas have been classified as Latosolic Reddish Prairie (P) soils and in the wet areas as 
Latosolic Brown Forest (B) soils. Soils in the dry valleys of the Older Volcanic series are the 
Dark Magnesium Clays (M). The Grey Hydromorphic (D) soils occur when drainage is poor 
on the Intermediate Lavas in dry areas, whilst the Low Humic Gley (G) occurs in the humid 
and super-humid zones. The Ground Water Laterites occur only in the super-humid zone. The 
Mountain Slope Complexes (S) are characterized by strong erosion. Some chemical 
properties of the intrazonal soils are summarized in Table 3.3. 
 
The Latosolic Reddish Prairie soils have developed on the Late Lavas, with annual rainfall 
lower than 2500 mm. They have a dark coloured A horizon, high in organic matter, which 
grades into a lighter, reddish or reddish-brown B horizon. The profile contains varying 
amounts of cobbles and gravel of unweathered or slightly weathered basalt and bed-rock 
exposures are common. They vary in texture from clay loams to silty clays. The clay fraction 
is dominantly kaolinite, with less than 5% iron and aluminium oxides and no 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 49 
montmorillonite. This soil group covers 19.9% of the total area of Mauritius and is divided 
into three families, namely Médine (P1), Labourdonnais (P2) and Mont Choisy (P3). 
 
 
Table 3.3. Some chemical properties of the intrazonal soils (adapted from Parish and Feillafé, 
1965) 
 
Property   Soil type    
 P B M D G S 
pH 6.0 - 7.1 5.0 - 6.3 6.9 7 4.3 – 5.5 5.2 – 6.7 
CEC (meq%) 30 - 50 30 >50 35 10 29 - 37 
Organic matter (%) 6.8 12 >7 4.9 10 5.3 – 6.2 
Nitrogen (%) 0.3 0.6 0.30 0.28 N/A N/A 
C/N ratio 11 14 15 10 N/A N/A 
N/A: Not Available 
 
The Latosolic Brown Forest soils have developed on the Late Lavas in the super-humid area. 
In time, they should develop into Humic Ferruginous Latosols and in fact, there are some 
areas where there has been so much iron oxide deposition that they are very close to being 
zonal soils. They are characterized by a dark coloured A horizon, very high in organic matter, 
that grades into a lighter, coloured B horizon over parent rock at shallow depth. The profile 
contains varying amounts of weathered cobbles and gravels. They vary in texture from clay 
loams to silty clays or clay. The clay fraction has moderate to very small amounts of 
kaolinite, and rather more gibbsite than goethite. Many small waterlogged spots are 
encountered within this soil group, which covers 16.5% of the total area of Mauritius and is 
divided into two families, namely Rose Belle (B1) and Bois Chéri (B2). 
 
The Dark Magnesium Clays have physical properties showing the dominant influence of 
montmorillonite with a high degree of saturation by magnesium. These soils have developed 
under low rainfall conditions, 1000 to 1500 mm annually, on the lower slopes of the 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 50 
mountains and in valleys where the parent rock is of the Older Volcanic Series. They are self-
mulching black or dark grey clays with accumulations of calcium carbonate in the lower 
horizons. As they are formed from colluvium and alluvium, there are often gravels and 
cobbles in the profile and they tend to be transitional to Lithosols on the steeper slopes of 
mountains. Dark Magnesium Clays are heavy clay soils, with montmorillonite completely 
dominant and very little kaolinite. There are two families in this soil group, Plaine Lauzun 
(M1) and Magenta (M2), covering 3.8% of the total area of Mauritius. 
 
The Grey Hydromorphic soils are plastic clays formed as a result of periodical water logging. 
They occur mainly in the sub-humid zone (1250 mm per annum) on Intermediate Lavas. They 
are characterized by an A horizon with a greyish cast over a B horizon with grey, yellow and 
brown mottlings. There are two families in this soil group, Balaclava (D1) and Saint André 
(D2) covering 1.1% of the total area of Mauritius. 
 
The Low Humic Gley is characterized by an almost permanently high water-table which has 
created a zone of strongly reducing conditions. The group is divided into two families, Pétrin 
(G1) and Valetta (G2). In the Pétrin family, a shallow A horizon tinted with some organic 
matter overlies an ash grey horizon. The Valetta family displays a more or less humic A 
horizon, over a horizon with prevalent mottlings and small iron concretions, over the gley 
horizon proper. 
 
The Ground Water Laterites occur only in the super-humid zone on the Early Lavas of the 
Younger Volcanic Series. They are completely senile soils with a permanently high water-
table. 
 
The Mountain Slope Complexes are mapped between the boundary of the Intermediate and 
Late Lavas of the Younger Volcanic Series and the Older Volcanic Series and the 30% slope 
contour. They occur between 1500 and 5000 mm rainfall and the parent material are the lavas 
of the Older Volcanic Series and the Early Lavas of the Younger Volcanic Series. Two 
families have been defined, which cover 5.3% of the total area of Mauritius, the Nicolière 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 51 
family (S1) for the sub-humid to humid region and the Ferney family (S2) for the super-
humid region. The Nicolière family is a shallow greyish brown clay soil with unweathered 
rock in the profile. 
 
3.6.1.3 Azonal soils 
 
Soils classified as azonal have little or no profile development, apart from some organic 
matter accumulation in the surface horizon. They are thus likely to show some of the 
characteristics of the zonal soils occurring in the same area. Three main soil groups have been 
classified, the Alluvial soils, the Regosols and Lithosols. 
 
The Alluvial soils are young soils developed from recent alluvium. They may differ on the 
basis of texture according to the nature of the alluvium. Thus, some are silts or silty clays, 
with or without pebbles, whilst others are clays washed from the neighbouring 
mountainsides. 
 
The Regosols consist of soils with little or no profile development on deep unconsolidated 
deposits other than alluvium. The parent material is wind-blown coral sand. The A horizon is 
a dark brown sand or loamy sand formed by a mixture of coral sand and organic matter over a 
light grey or very pale brown coral sand. Their pH averages 8.5. 
 
The Lithosols are situated on the rough broken land of mountains and gorges, and rock-land 
comprising areas of almost unweathered rock. Four land types have been separated, two of 
which are rough broken land (T1 and T2) and the other two are rock-land (T3 and T4). The 
T1 occurs on mountains or very steep slopes where soil development is offset by erosion. On 
the other hand, the T2 occurs in the mountain gorges. The T1 and T2 land types occur on 
slopes exceeding 30% and vary considerably in their properties depending on rainfall, slope 
stability and ground cover. The T3 is a skeletal soil high in organic matter on hummocky bed-
rock while T4 has a thin cover of soil high in organic matter on smooth bed-rock lava. The 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 52 
T3 and T4 land types are rich in organic matter and are slightly to moderately acid with a 
CEC of around 65 meq 100 g-1. This soil group covers 16.6% of the total area of Mauritius. 
 
The Great Soil Groups of Mauritius can be correlated with the US and FAO soil classification 
systems, namely Soil Taxonomy (Soil Survey Staff, 1999) and World Reference Base for Soil 
Resources (FAO, 1998). In general, the Latosol is equivalent to the Oxisol (Soil Survey Staff, 
1999) and to either the Nitosol or Acrisol (FAO, 1998). On the other hand, the Latosolic soil 
is equivalent to the Inceptisol (Soil Survey Staff, 1999) and to the Cambisol (FAO, 1998). 
 
 
3.6.2 Soil map of 1984 
 
Willaime (1984) has produced a more recent soil map with a scale of 1:50 000, the Carte 
Pédologique de l’Ile Maurice. This map is based on the French CPCS system. Willaime 
states that the interaction of essential pedogenetic factors like parent rock, topography and 
climate has given rise to soils under the influence of two major processes: 
 In areas that are sufficiently humid and well-drained, the process of “ferrallitisation”, 
characterized by the eluviation of bases and silica, the release of iron and aluminium 
oxides and hydroxydes, and the formation of clays of the kaolinite family 
 In relatively dry, poorly-drained areas, the process of “bisiallitisation”, characterized by 
the removal of bases and silica, and the genesis of expanding clays of the montmorillonite 
family. 
 
Two secondary processes can further superimpose their effects on the two major processes 
above: 
 Erosion, giving rise to eroded soils through sediment loss or to soils formed under the re-
deposition of eroded material 
 Hydromorphism, which influences soils in areas with poor external drainage. 
 
Four broad soil categories have been defined in this system: 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 53 
1. Poorly evolved soils, such as those found on mountains, in gorges, etc. 
2. Soils mainly affected by the “bisiallitisation” process, namely vertisols and other dark 
soils 
3. Soils mainly affected by the “ferrallitisation” process, namely “ferrallithic” soils 
4. Soils mainly affected by water-logging phenomena, namely hydromorphic soils. 
 
This system is further refined for the most important soil category, the “ferrallithic” soils, 
which cover more than 75% of the island. In this case, the intensity of base saturation is taken 
into account. The “ferrallithic” soils are thus further classified as being little, moderately, 
highly or very highly unsaturated. 
 
3.7 Sugar industry 
 
3.7.1 General 
 
The Mauritius Chamber of Agriculture (2003) has reviewed the history and evolution of 
sugar cane cultivation in Mauritius. Fields with sugar cane have been a predominant feature 
of the landscape of Mauritius for more than two centuries. Sugar cane was one of several 
plant species of economic interest to be introduced in Mauritius under the Dutch 
administration. However, it was only in the following century that its cultivation was 
developed to a significant scale, together with other crops such as cotton, indigo, coffee and 
spices as the island started its economic development under French rule. Sugar cane proved 
to be the crop best suited to the local climatic, soil and topographic conditions and was 
therefore grown on a commercial basis. It is now the single most important crop in Mauritius 
and presently occupies some 72 000 ha, which represents about 40 percent of the country’s 
total area (186 000 ha), and 85 percent of the cultivated area (87 000 ha, excluding forests). 
However, the success of sugar in Mauritius is attributable not only to the high adaptability of 
the sugar cane plant to local conditions but also, to a large extent, to the fact that the country 
has benefited from preferential trade agreements with the United Kingdom (UK) and later 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 54 
with the European Union (EU), thanks to its membership of the Commonwealth and then the 
African-Caribbean-Pacific (ACP) group of nations. 
 
In fact, Mauritius has made the most of the advantages derived from these trade preferences, 
particularly the Sugar Protocol and, to a lesser extent, the Special Preferential Sugar (SPS) 
Agreement. The Sugar Protocol, which was initially attached to the Lomé Convention and 
later on the ACP/EU Cotonou Agreement in 2001, has allowed duty free access for fixed 
quantities of ACP sugar at a guaranteed price into the EU market. By providing Mauritius 
with a predictable and stable source of earnings over the years, the Sugar Protocol has played 
an essential role in developing the local sugar industry and fostering the country’s economic 
diversification. The revenues derived from these sugar exports have been re-invested into the 
sugar sector and into other economic activities, such as manufacturing, tourism and finance, 
which have today developed into major pillars of the economy of Mauritius. Nevertheless, 
sugar is still a major foreign currency earner and will remain an important sector of the 
economy for quite some time, and will continue to play a vital role in the socio-economic 
fabric of Mauritius. 
 
3.7.2 Present status 
 
3.7.2.1 Gross domestic product 
 
Over the years, the share of sugar production in the economy of Mauritius has, in relative 
terms, dwindled and is expected to reach 3.5% of the gross domestic product in 2004 (from 
25% in the 1970’s) as compared to 22% for manufacturing industries, 18% for tourism and 
19% for financing and business services. The reduced importance of the sector in the 
country’s economy can be explained by the diversification of the economy of Mauritius with 
the rapid growth, during the 1980’s and 1990’s, of the manufacturing industry geared towards 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 55 
export, as well as the expansion of the tourism industry and the emergence of financial 
services, with consequential effects on employment and contribution to value added. The 
sugar sector has, in real terms, continued to bring additional revenue to the country and to the 
farming community at large. It is still an important contributor to the economy with sugar 
exports representing 19% of foreign exchange earnings. 
 
3.7.2.2 Employment 
 
In 2003, there were 11 sugar-milling factories and 23 sugar estates, with about 52% of the 
total sugar cane lands belonging to large sugar companies, which produce 55% of the total 
sugar. The remaining 48% of the sugar cane area belongs to some 28 000 individual planters. 
Direct employment in the sector stands at roughly 4% of total employment (around 20 000 
persons) as compared to 29% in 1980. It is worth noting that employment in the sugar sector 
has decreased substantially with the introduction of a Voluntary Retirement Scheme (VRS) in 
2001, which was taken up by some 7800 workers who opted for early retirement. 
Nevertheless, the sector is still a major source of employment as the 28 000 small planters, 
who are self-employed and operate on a part-time basis, are mainly involved in sugar cane 
cultivation and in the production of fresh vegetables. In most cases, their plot size does not 
exceed one ha. 
 
3.7.2.3 Organizations 
 
The milling and miller-planting companies of the sugar cane industry are grouped into the 
Mauritius Sugar Producers' Association to deal more effectively with problems such as 
those relating to employment, occupational health and safety in cane fields and mills, and 
training. As a result the industry has benefited from an improved operational efficiency and a 
safer work environment. Growers are grouped into several associations, namely the Mauritius 
Cane Growers' Association, the Mauritius Sugar Cane Planters' Association/Mauritius 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 56 
Planters' Association, and the Mauritius Co-operative Agricultural Federation Ltd. All these 
associations form part of the Mauritius Chamber of Agriculture, founded in 1853 to 
promote and safeguard their interests. The Mauritius Sugar Syndicate, created to be the sole 
marketing agency for Mauritius sugar, contributes to make financial resources available on 
time to the planting community and ensures that the industry meets its obligation to supply 
the sugar to the European Union. As stated previously, all research and development work 
pertaining to the sugar industry is conducted by the Mauritius Sugar Industry Research 
Institute, which is funded by a cess levied on all sugar produced. 
 
Government organizations dealing with the sugar cane industry comprise The Mauritius 
Sugar Authority established in 1984 to promote and maintain the efficacy, development and 
viability of the sugar cane industry and thus to advise the Government on policies to be 
followed with regard to the sugar cane industry. The Cane Planters' and Millers' Arbitration 
and Control Board controls the milling of canes and the manufacture of sugar and assesses 
the quantity of sugar and by-products accruing to growers and millers. It should be 
remembered that, like any other agricultural venture, sugar cane production stands vulnerable 
to the vagaries of climate. To ensure that planters are not left totally resourceless in case of 
crop failure, the Sugar Insurance Fund Board was created in 1946 to guard against losses 
due to cyclones, droughts, excessive rainfall and fire. The Sugar Industry Development 
Fund provides funds for the formulation and execution of projects aimed at increasing cane 
productivity. There is also a Sugar Planters' Mechanical Pool Corporation that hires out 
agricultural equipment to growers at reasonable rates. 
 
3.7.2.4 Sugar markets 
 
Mauritius is signatory to the Sugar Protocol since 1975 and to the Special Preferential Sugar 
(SPS) Agreement since 1995. These two agreements regulate sugar trade between ACP 
countries and the EU and form an integral part of the EU Sugar Regime. The Sugar Protocol 
provides duty free access to the EU market for fixed quantities of sugar exported from 19 
ACP suppliers, at a guaranteed price of 523.70 Euros c.i.f. per t. While the Protocol is of 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 57 
indefinite duration and has a “legal life of its own”, the SPS Agreement has a limited duration 
and will last until the expiry of the existing EU Sugar Regime in June 2006. The guaranteed 
price obtained under the SPS Agreement represents 95% of that under the Sugar Protocol, i.e 
496.80 Euros per t. Practically all the sugar production of Mauritius is exported to the EU 
under the Sugar Protocol (507 000 t yr-1 till 2008) and the SPS Agreement (around 25 000 t 
in 2003). The latter quantity is expected to decrease in the following years until it is 
completely eliminated by 2008. 
Next to the EU market is the United States market. Mauritius exports some 12 000 to 15 000 
t yr-1 under the US Tariff Rate Quota (TRQ), which is opened to some forty countries. The 
share of Mauritius under the US TRQ represents 1.2% of the total US yearly import. 
Domestic consumption of sugar in Mauritius is about 40 000 t yr-1 of which some 15 000 t 
are for industrial use and 25 000 t for direct consumption. The little that remains is sold on 
the world market (Figure 3.5). 
 
EU
USA
Local
World
 
 
Figure 3.5 Markets for sugar produced in Mauritius (Mauritius Chamber of Agriculture, 
2003). 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 58 
3.7.3 The future 
 
In the context of the new world economic order, the sugar industry of Mauritius needs to be 
competitive to survive. Indeed, in view of the threats and challenges ahead, namely the real 
risk of Mauritius sugar exports losing their competitive edge in a liberalized trade 
environment, a 5-year Sugar Sector Strategic Plan (SSSP) was launched by the Ministry of 
Agriculture, Food Technology and Natural Resources (2001), with the aim of providing the 
industry with the appropriate framework to improve its competitiveness and ensure its very 
survival. The sugar industry of Mauritius has embarked in major reforms at all levels, with 
centralization of milling activities, cost reduction, enhanced productivity, manpower 
rightsizing, the optimal use of cane sugar resources, well-planned diversification activities 
and the creation of new opportunities. Several targets need to be achieved by the end of the 
implementation period, the main ones being: 
 Ensuring that export market commitments are fulfilled. 
 Maintaining the sugar production target of 620 000 t yr-1. 
 Achieving substantial reduction in costs of production. 
 Generating as much electricity from renewable sources, in particular bagasse. 
 Adding value to the industry’s output through product diversification such as special 
sugars, electricity, ethanol, molasses and “rhum agricole”. 
 Ensuring a more efficient and judicious use of land and water resources. 
 Developing research, so as to fully tap the benefits deriving from biotechnology, biotics 
and cane biomass. 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 59 
3.7.4 Research and development 
 
The successful achievement of the objectives as spelt out in the SSSP will depend for a large 
part on research development. In this respect, the role of Mauritius Sugar Industry Research 
Institute (MSIRI) will be crucial. Autrey (2004) has reviewed the contribution of this body to 
the advancement of the sugar industry in Mauritius, and mapped out the way for its future. 
The MSIRI was established as a Statutory Body by Government Ordinance no. 9 of 1953, and 
has been responsible for all research associated with the sugar industry since that date. In 
terms of the Ordinance, its function was “to promote by means of research and investigation 
the technical progress and efficiency of the sugar industry”. It has been in existence for more 
than half a century and is well recognized for its achievements, a few of which will be 
detailed hereafter: 
 MSIRI’s cane breeding program has led to the production of some 59 new varieties, i.e. 
an average of more than one new variety per year. 
 An understanding of the stages of floral development at cellular level and factors 
controlling flowering has been achieved, thereby revolutionizing sugar cane breeding 
worldwide. 
 The foliar diagnosis technique developed at MSIRI has been adopted worldwide for the 
monitoring of fertilizer recommendations. 
 All pest and disease outbreaks have been controlled by biological or genetic means, 
without resort to pesticides, except in a few limited circumstances. 
 In environment protection, it has been proven that fertilizers and herbicides used in the 
sugar industry do not contaminate the country’s rivers and groundwater. 
 
For the future, Autrey (2004) believes that MSIRI’s expertise will be needed to help the sugar 
industry achieve its twin objectives of raising productivity and reducing production costs. Its 
main activities will focus on biotechnology, irrigation, mechanization, resource management, 
food technology and co-products, as well as some non-sugar crops. It will have to use new 
technologies to achieve these goals, while continuing to produce new varieties and ensuring 
that adverse factors do not compromise the development of the industry. The long-term 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 60 
vision of MSIRI is to help transform the sugar industry of Mauritius into an industry of 
renewable biomass, with the valorization of all the components of the biomass produced by 
the cane plant. 
 
3.8 Conclusion 
 
Mauritius is a small island of volcanic origin, but with great diversity in terms of climate and 
soil. Most of its original vegetation has disappeared as its increasing population has made 
optimum use of the available land. Today, the island is covered with sugar cane fields and the 
sugar industry remains a major component of the national economy, even though its influence 
has been waning. The land is still fertile and can keep on producing sugar cane with the 
correct application of water and fertilizers, and with the use of proper cultural operations. 
 
However, several challenges lie ahead for the sugar industry. It must increase its productivity 
and reduce its costs to remain economically viable in the long-term. To achieve this goal, it 
must reduce its manpower and rely more heavily on the use of machinery. It must find other 
sources of income, which can be achieved through the sale of electricity produced from 
bagasse, through an optimized use of its available land, or even through the enhancement of 
the value of its by-products. 
 
Should the sugar industry lose its economic viability, a major problem would arise with 
respect to land use. About half of the island is currently devoted to sugar cane cultivation. 
The cultural practices associated with this crop mean that the soil is kept under some form of 
cover for the better part of eight years, thereby protecting it from erosion. If cane were to be 
removed, what would be the effects on the environment? Alternative uses for the land would 
have to be found and the consequences of such changes cannot be foreseen. Cane has been 
grown in Mauritius for more than 350 years and is still the one crop that has stood the test of 
time. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 61 
CHAPTER 4 
 
MATERIAL AND METHODS 
 
4.1 Comparative studies 
 
In order to establish the effects of manual sugar cane production practices on soil quality, the 
properties of pristine land must be compared to those of sugar cane land. Fields have to be 
selected to represent these two conditions, namely fields that have never undergone any form 
of cultivation and those that have been cropped manually with sugar cane for a relatively long 
period. Fields of this nature were selected carefully based on reliable information obtained 
from sugar estates. 
 
Given that sugar cane production is expected to be economically viable only where 
mechanized production practices are introduced, these kind of land can be considered to be 
representative of the future for sugar cane production. Mechanized harvest requires the land 
to be relatively flat and rock-free, which is often not the case in several areas of Mauritius. In 
such cases, fields are subjected to derocking and land grading to render them suitable to 
mechanized harvesting. Thus, with respect to establishing the effects on soil quality of 
adopting sugar cane production practices such as derocking, land grading and mechanized 
harvesting, a comparison must be made between non-mechanized sugar cane fields, and 
fields which have been derocked, land graded and where sugar cane is mechanically 
harvested. Based on reliable information supplied by sugar estates, these kind of fields were 
selected. 
 
The two types of comparisons, between native and sugar cane cultivated lands where the 
operations are still manual, and between mechanized and non-mechanized sugar cane fields, 
need to be extended to all five major soil groups of Mauritius. In this way, an indication can 
be obtained whether any change in soil quality as a result of sugar cane production would 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 62 
differ among the major soil groups used for sugar cane production. The five soil groups do 
not all occur in each of the three climatic zones of the island. 
 
4.2 Choice of sites 
 
There are five important soil groups in Mauritius based on the 1962 Soil Map (Parish and 
Feillafé, 1965) of the island, namely the Low Humic Latosol, Humic Latosol, Humic 
Ferruginous Latosol, Latosolic Reddish Prairie and Latosolic Brown Forest soils. These five 
major groups make up 87% of sugar cane lands in Mauritius and cover most of the range of 
soils and climate that exist over the island. One representative site per soil group has been 
selected for the study (Table 4.1). 
 
Table 4.1. Study sites representing the five major soil groups of Mauritius 
Study site Climatic zone Soil group Area (ha) 
Richeterre Sub-humid Low Humic Latosol (L) 30 455 
Beau Champ Humid Humic Latosol (H) 9 640 
Mon Désert Alma Super-humid Humic Ferruginous Latosol (F) 21 220 
Médine Sub-humid Latosolic Reddish Prairie (P) 37 010 
Savannah Super-humid Latosolic Brown Forest (B) 30 615 
 
For each soil group, fields with different cropping histories were identified, each cropping 
history being deemed to be equivalent to a treatment. Thus, for the five soil groups, there 
were between three and five treatments under study, depending on cropping history (Table 
4.2). 
 
There were only three sampling categories within the H, B and F soil groups at Beau Champ, 
Savannah and Mon Désert Alma respectively. At Richeterre, the soils that had not been 
prepared for mechanized operations were further sub-divided into “old” (> 50 years) and 
“new” (< 25 years) fields, thus giving four treatments in the L soil group. This sub-division 
between “old” and “new” fields was also possible at Médine where soils under mechanized 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 63 
treatments were sub-divided into two categories, namely recent derocking and grading 
(within the last 3 years) or early derocking and grading (at least 10 years ago). Five treatments 
were thus identified in the P soil group. 
 
 
Table 4.2. Treatments studied for five soil groups 
Soil group Treatment 
 1 2 3 4 5 
L      
H      
F      
P      
B      
 
Treatment 1: Pristine soil (natural forest or pasture) 
Treatment 2: Old cane soil (>50 years under cane), no derocking or land grading 
Treatment 3: New cane soil (<25 years under cane), no derocking or land grading 
Treatment 4: Cane soil recently derocked and graded for mechanization (<3 years) 
Treatment 5: Cane soil derocked and graded for mechanization (>10 years) 
 
 
4.3 Sampling procedure 
 
To account for possible spatial variability, four samples were taken from three fields with the 
same cropping history, thus giving twelve replicates per treatment. For each selected field, a 
one-ha zone was earmarked, within which four representative 50 m2 sampling plots were 
chosen, at least 20 m distant from the edge of the field and other possible unrepresentative 
sites, e.g. close to irrigation risers. Two trenches were dug within each plot, thus giving a 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 64 
total number of eight trenches for each field. Soil samples from the same depth for each pair 
of trenches were bulked to give a representative sample for each plot (Figure 4.1). 
 
 
 
 
 
Plot No. 1 
 Plot No. 3 
 
 
 
 
 
Plot No. 2 Plot No. 4 
 
 
 
 
 
 Trench 
Figure 4.1. Pairing of trenches for bulking of samples (plan view) 
 
Each trench was 150 cm long, 30 cm wide and 50 cm deep. Since cane rows are spaced 150 
cm apart, this procedure ensured that soil underneath both cane row and inter-row was 
available for sampling. Soil was sampled from each trench in 4 layers, namely 0-5, 5-15, 15-
30 and 30-50 cm. For each layer, two sub-samples were taken from both faces of the trench 
so as to cover as large an area as was possible (Figure 4.2). The four sub-samples obtained in 
this way were mixed to give a composite sample representative of the trench, and as stated 
before, the composite samples from each pair were mixed to give the sample for the plot. 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 65 
 
 
 
 
 
 
 
 
Sampling points
 
Figure 4.2. Soil sampling procedure from trench wall (plan view) 
 
4.4 Soil quality parameters 
 
Research work in sugar cane-producing countries such as Australia and South Africa has 
shown that a range of biological, chemical and physical soil properties are affected by sugar 
cane production. These properties are thus indicators that must be monitored to determine 
whether soil quality is affected. The following are the quality parameters for the sugar cane 
soils of Mauritius, namely: 
1. Biological parameters - Organic matter and microbial biomass 
2. Chemical parameters - pH, cation exchange capacity and concentration of exchangeable 
bases 
3. Physical parameters - particle size distribution, aggregate size distribution, water stability 
of aggregates, bulk density, plant available water and stabilized infiltration rate. 
 
4.5 Methodology for determination 
 
4.5.1 Organic matter 
 
The organic carbon and total nitrogen contents of the soils were measured as indicators of 
organic matter. A concise description of the procedures used follows. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 66 
 
As basalt is the parent material for most of the soils in Mauritius, the latter are non-calcareous 
and the measured amounts of carbon are solely of organic origin. The organic carbon content 
of the soils was determined in the laboratory through partial oxidation using the modified 
Walkley-Black procedure as described by Anderson and Ingram (1993). In this procedure, 
soil organic carbon was partially oxidized by treating 0.5 g of finely ground (<0.25 mm) air-
dried soil with 10 ml of 5% potassium dichromate solution acidified with 20 ml concentrated 
sulphuric acid. After completion of this oxidation reaction, 50 ml of barium chloride solution 
was added and the mixture was centrifuged at 2500 rpm for 10 minutes. The supernatant was 
removed and the concentration of chromium ions in the reduced state within that supernatant 
was measured colorimetrically at 600 nm using a spectrophotometer. Since this concentration 
is directly proportional to the amount of organic carbon in the sample, the organic carbon 
content was deduced from chromium ion concentration. 
 
The total nitrogen content of the soil was determined by Kjeldahl digestion followed by 
steam distillation and titration against sodium borate as described by Bremner and Mulvaney 
(1982). A 0.3 g sample of finely ground (<0.25 mm) air-dried soil was gradually heated to 
150oC in a block digestor with a mixture of concentrated sulphuric acid, salicylic acid and 
sodium thiosulphate till it reached a brownish green colour. Thereafter, 2 g of a catalytic 
mixture of Na2SO4, CuSO4.5 H2O and Se was added, and the whole mixture heated to 325
oC. 
Through this process, the nitrogen in the soil was mineralized to ammonium-nitrogen, which 
was then steam distilled under alkaline medium, using 30 ml of 50% NaOH. Ammonia gas 
was produced and was trapped into a mixture of 10 ml 2% boric acid and Conway-Omalay 
indicator. The concentration of nitrogen was then determined by titration with standard 
0.0025 M sulphuric acid. 
 
4.5.2 Microbial biomass 
 
The microbial biomass was measured in the laboratory using the chloroform fumigation-
extraction method of Voroney et al. (1993). A 40 g sample of fresh soil, sieved through a 4 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 67 
mm mesh, was fumigated with 25 ml chloroform (CHCl3), sealed and placed under vacuum 
for 1 minute. Subsequently, the sample was placed in the  dark at 25oC for 24 hours. The 
CHCl3 vapour caused a flush of decomposition of the soil microbial population. The 
microbial biomass constituents released by CHCl3 fumigation, in this case microbial C and N, 
were then extracted directly using 60 ml of 0.5 M K2SO4 solution on a sub-sample of 12 g 
soil. The amounts of C and N dissolved in the K2SO4 extract were determined by dichromate 
and Kjeldahl digestion respectively. The amount of microbial biomass C and N present in the 
soil sample were calculated by comparing extracted values of C and N from fumigated soil 
samples to values from unfumigated soil samples. 
 
4.5.3 pH 
 
The pH was determined electrochemically in the laboratory using a pH meter by measuring 
the potential of the hydrogen ion electrode in a suspension of 20 g soil in 50 ml distilled 
water against that of a calomel reference electrode (STASM, 2003). The pH meter was first 
calibrated using buffer solutions of pH 4 and 7. 
 
4.5.4 Cation exchange capacity 
 
The cation exchange capacity (CEC) of the soils was determined in the laboratory using 
unbuffered ammonium acetate (Peech, 1945). As a first step, 5 g of air-dried soil, sieved 
through 2 mm mesh, was leached with 1 M unbuffered ammonium acetate solution to 
displace its exchangeable cations, namely Ca, Mg, K and Na. The exchange sites of the soil 
were filled with ammonium ions while the excess ammonium acetate was leached out of the 
soil by passing 125 ml of 96% ethyl alcohol. The sorbed ammonium ions were finally 
displaced by eluting the soil with 200 ml of acidified sodium chloride solution (10% NaCl in 
0.1 M HCl) and were determined quantitatively by back titration with standard 0.0025 M 
sulphuric acid. The soil CEC was calculated from the amount of ammonium sorbed in the 
soil. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 68 
4.5.5 Exchangeable bases 
 
The concentration of individual exchangeable bases in the soil samples was determined using 
the leachate obtained in the first step of the procedure described for CEC determination in 
Section 4.5.4 (Peech, 1945). As stated in Section 4.5.4, the 1 M unbuffered ammonium 
acetate solution displaced the exchangeable bases present in the soil sample and these 
elements, namely Ca, Mg, K and Na, remained dissolved in the leachate. An atomic 
absorption spectrophotometer was used to measure the concentration of Ca and Mg in the 
solution. The concentration of K and Na was determined using a flame photometer. 
 
4.5.6 Particle size distribution 
 
The size distribution of individual particles in the soil was determined in the laboratory by 
particle size analysis. In this procedure, the soil aggregates were destroyed or dispersed into 
discrete units by chemical and mechanical means as described by Gee and Bauder (1986). 
The particles were then separated according to size limits by sieving (sand fraction) and 
sedimentation (silt and clay fractions). The sedimentation analysis relies on the relationship 
between settling velocity and particle diameter (Stokes’ Law), the smaller particles taking 
longer to fall to the bottom of a suspension. 
 
As organic matter is a powerful aggregating agent in the soil, the first step was to chemically 
remove it by heating 10 g of air-dried soil, sieved through 2 mm mesh, with 2 g sodium 
metabisulphite and 50 ml 10% H2O2. The oxidation process using H2O2 was repeated twice 
to ensure that all organic matter had been removed. Once this oxidation process was 
complete, the soil was dispersed by shaking with sodium hexametaphosphate and maintained 
in the dispersed state until sedimentation was completed. 
 
The silt content was determined at 20oC in a constant temperature room by pipetting a 20 ml 
sample from the suspension after the critical time required for the silt fraction. Similarly, the 
clay content was determined through pipetting at the critical time required for the clay 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 69 
fraction. All the remaining silt and clay were then removed from the suspension by siphoning 
and the remaining sand material was dried and passed through a 150 μm sieve to obtain the 
coarse sand and fine sand fractions. 
 
4.5.7 Aggregate size distribution 
 
The size distribution of the aggregates was determined in the laboratory by dry sieving of air-
dried soil samples using a nest of sieves. Although a rotary sieve with multiple sieve sizes is 
the recommended technique (Kemper and Rosenau, 1986), a sieve shaker (Retsch AS200 
Digit analytical sieve shaker) with a flat nest of sieves was used in this case since no rotary 
sieve was available. 
 
The bulk soil was sampled and placed on a large tray, and allowed to air-dry in the shade. 
Prior to placing in the sieve shaker, the aggregates were gently passed through an 8 mm sieve. 
Thereafter, a 1.5 kg sample was shaken for 10 minutes on the sieve shaker to pass through 
sieve sizes of 4, 2, 1, 0.5 and 0.25 mm. The respective amounts of soil retained in the 
different sieves were then weighed, and the index of aggregate size distribution calculated as 
the geometric mean diameter, or GMD (Kemper and Rosenau, 1986). 
 
4.5.8 Water stability of aggregates 
 
The stability of aggregates in water was determined in the laboratory by determining the soil 
moisture characteristics of weathered and unweathered soil samples using the technique 
described by Haines (1930). A 20 g sample of air-dried soil aggregates in the size range 1 to 2 
mm were placed on the ceramic plate of a Haines apparatus (a sintered glass Buchner funnel 
connected to a burette), and soil moisture characteristics derived through desorption curve of 
a saturated sample (Figure 4.3). The desorption process was repeated with a weathered 
sample, the weathering process consisting of a sudden saturation of the sample, which was 
left submerged for 24 hours prior to air-drying. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 70 
Differential curves (Figure 4.4) derived from the soil moisture characteristics were obtained 
to reflect the pore size distribution within the soil sample. An aggregate stability index was 
thereafter calculated from the respective slopes of moisture characteristics of the weathered 
and unweathered samples as outlined by Childs (1940). 
50.0
45.0
40.0
35.0
30.0
25.0
20.0
50.0 60.0 70.0 80.0 90.0
Volume (ml)
Unweathered Weathered 
 
Figure 4.3 Desorption curves obtained using Haines apparatus 
 
2.50
2.00
1.50
1.00
0.50
0.00
50.00 60.00 70.00 80.00 90.00
Head (cm)
Unweathered Weathered
 
Figure 4.4. Differential curves derived from desorption curves 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Gradient (ml/cm) Head (cm)
 71 
4.5.9 Bulk density 
 
Bulk density determinations were undertaken in situ using the excavation method, essentially 
because the presence of stones within the profile at several locations prevents the use of the 
core method. In this procedure, a certain quantity of soil was excavated from the required 
depth in a 10 cm diameter hole, dried and weighed. A sand-funnel apparatus was used to 
measure the volume of the excavated material by filling the hole with sand of known volume 
per unit mass (Blake and Hartge, 1986). The volume of the excavation was then taken to be 
equal to the volume of sand dispensed. 
 
The excavated soil samples were oven-dried at 105oC for 24 hours and weighed. Thereafter, 
they were washed through a 2 mm sieve and any remaining stone was again oven-dried at 
105oC for 24 hours and weighed. Bulk density was calculated as the oven-dried weight of soil 
per unit volume. A correction was applied to this calculation when stones were found in the 
soil sample. The stone weight and volume were subtracted from the total weight and volume 
to give corrected values of the two parameters. The calculation for stone volume required the 
use of a standard bulk density of 2.65 g cm-3 for stones. The corrected bulk density was 
calculated as the corrected soil weight per unit corrected soil volume. 
 
 
4.5.10 Plant available water 
 
Soil moisture contents at field capacity (FC) and permanent wilting point (PWP) were 
determined in the laboratory on sieved air-dried soil samples using pressure plate and 
pressure membrane extractors as indicated by Klute (1986). A 25 g air-dried soil sample, 
sieved through 2 mm mesh, was placed on a pressure plate and saturated with water. It was 
then placed inside pressure extractors and a pressure of 15 kPa was applied for 24 hours, 
when equilibrium was reached and all excess water had been removed. The procedure was 
repeated with another sample, but under a pressure of 1500 kPa. The soil moisture content at 
equilibrium with 15 kPa was deemed to be the FC moisture content, while that at 1500 kPa 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 72 
was taken as the PWP moisture content. Plant available water (PAW) was then calculated 
based on values of FC, PWP, bulk density (BD) and soil depth using equation 4.1: 
 
PAW = 0.1 x (FC – PWP) x BD x soil depth      (4.1) 
where PAW is in mm; FC is in % in gravimetric terms; PWP is in % in gravimetric terms; 
BD is in g cm-3; and soil depth is in cm. 
 
 
4.5.11 Stabilized infiltration rate 
 
The stabilized infiltration rate of the soil was determined in the field using the CSIRO disk 
permeameter described by Perroux and White (1988). After clearing a flat piece of land, 
some sand was placed as contact material and the permeameter placed on the sand. The 
apparatus was set such that a zero head was applied. The volume of water being absorbed by 
the soil was read off the scale of the permeameter at standard time intervals taken from a 
stopwatch, initially every minute for the first ten minutes, and subsequently every five 
minutes until the rate had stabilized. The volume reading was then converted to a height of 
water by dividing with the contact area. Infiltration rate was calculated as the difference in 
height of water (mm) per unit time (hour). The soil absorbed the water at a fast rate initially, 
the rate declining gradually to reach a constant value, namely the stabilized intake rate, as 
illustrated by Figure 4.5. 
 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 73 
700
600
500
400 Stabilized intake rate 
300
200
100
0
0 20 40 60 80 100 120
Time(min.)
 
 
Figure 4.5. Infiltration curve derived from CSIRO disk permeameter test 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Rate(mm/h)
 74 
CHAPTER 5 
 
INFLUENCE OF SUGAR CANE PRODUCTION ON SOME SOIL BIOLOGICAL 
PARAMETERS 
 
5.1 Introduction 
 
The organic matter (OM) content in topsoil usually declines when land under native 
vegetation is cropped with sugar cane. This reflected in lower contents of either organic 
carbon (OC) and total nitrogen as reported by Van Antwerpen and Meyer (1996) for three 
different soil types at several sites in KwaZulu–Natal, South Africa. Henry and Ellis (1996) 
reported 8% and 26% decreases in OC and total nitrogen respectively in two soil types in 
North East Swaziland. In Australia, McGarry et al. (1996) noted that OC content was only 
1.0% in the cane row as compared to 1.5% in an uncultivated soil. The SOM decline under 
sugar cane production was mainly caused by enhanced aggregate disruption to expose 
physically-protected organic material to microbial action when cultivated, and enhanced 
decomposition rates due to more favourable conditions of aeration, temperature and water 
content (Dominy et al., 2001). There were however also cases where SOM was found to 
increase under sugar cane. Such an increase had been observed in Australia by Bramley et al. 
(1996) and was restricted to the topsoil. They measured an OC content of 2.8% in the upper 5 
cm of an “old” cane land, compared to 1.6% in the equivalent layer of a newly-converted 
cane land and suggested that it was the result of the beneficial effect of green cane harvesting 
/ trash blanketing adopted at the site. 
 
Where SOM content decreased after introduction of sugar cane, the rate of decline was found 
to be initially fast before becoming much slower after a few years prior to attaining a new 
equilibrium situation. This has been illustrated by Dominy et al. (2001) who showed that in 
South Africa, soil OC content went through a fast decline during the first ten years and 
attained an equilibrium level within thirty to fifty years. They hypothesized that the 
equilibrium level was dependent on the soil’s ability to stabilize OM and on the amount, 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 75 
quality and distribution of the plant residues. Measurements of the fast initial decline in 
Papua New Guinea showed a rate of 0.14% per year over the first seven years of cultivation 
(Hartemink, 1998b). The slower long-term decline rate was found to be 0.04% per year over 
fifty years for one soil and 0.01% per year over thirty years for another soil in South Africa 
(Qongqo and Van Antwerpen, 2000). Even though topsoil OC content tended to fall with the 
introduction of sugar cane, very little change has been observed in its chemistry (Skjemstad et 
al., 1999). 
 
A downward transfer of OC has been noted with sugar cane cropping, this process being 
ascribed to the secondary effects of OC-rich topsoil being mixed with the subsoil during land 
preparation (Masilaca et al., 1986). A similar OC-enriching effect of the subsoil could be 
achieved by ploughing in the residues of break crops (McGarry et al., 1996). However, 
subsoil OC content has not always been reported to increase with sugar cane cropping. There 
were instances where there was no change (Henry and Ellis, 1996) or even a drop (Van 
Antwerpen and Meyer, 1996) in subsoil OC content. Residue management seemed to play a 
major part in the evolution of soil OC content. Trash burning removed crop residues and has 
been proven to substantially reduce SOM content (Wood, 1985), while green cane harvesting 
and trash blanketing had an opposite effect (Bramley et al., 1996, Graham et al., 1999). 
Furthermore, even if total OC decreased, the light carbon fraction remained in proportion 
with total OC in soil with cane trashing (Skjemstad et al., 1999). 
 
In parallel with the decrease in SOM content, sugar cane cultivation also led to a marked 
decline in soil microbial biomass, possibly because of pesticide usage (McGarry et al., 1996). 
This decrease in microbial biomass was even more pronounced than that of OC, but the trend 
was similar, a fast rate during the first ten years and a new equilibrium level being attained 
within twenty years (Dominy et al., 2001). This trend was explained by the fact that the labile 
fraction of the OM was preferentially lost when the soil was cultivated; as a result, a long-
term cultivated soil was able to support only a proportionately smaller microbial community 
than an undisturbed one, in spite of the crop residues that were added. Upon sugar cane 
cultivation, microbial quotient was thus shown by Dominy et al. (2001) to decrease to 1.37% 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 76 
and 1.46% in two soils from a common initial level of 2.60%. However, this trend could be 
reversed under specific circumstances, for instance when trash was conserved at harvest 
(Graham et al., 1999). The annual fertilizer applications in the cultivated fields led to an 
increased return of organic residues to the soil, which in turn led to a higher soil microbial 
population. 
 
In this chapter, the effects of sugar cane cropping on some biological properties of the major 
soil groups of Mauritius are reported. Two indicators of biological quality, organic matter and 
microbial biomass, were assessed through three parameters, namely carbon, nitrogen and C/N 
ratio. The changes resulting from manual and mechanized sugar cane cropping practices on 
all five major soil groups are presented.  In addition, the effects of time under manual and 
mechanized sugar cane cropping practices for selected soil groups are also dealt with. 
 
5.2 Procedure 
 
5.2.1. General 
 
The soil biological quality parameters that have been measured were organic carbon, total 
nitrogen, biomass carbon and biomass nitrogen. A complete description of the methodology 
used to determine these four parameters was given in Chapter 4. All organic matter 
measurements were made in the laboratory on samples sieved through a 2 mm mesh since 
this fraction is defined as soil (Soil Survey Staff, 1975). Air-dried samples were used for the 
organic C and total N determinations. Hence the concentration of organic C and total N were 
directly derived from laboratory measurements and expressed in terms of percentage on a dry 
weight basis. However, fresh samples sieved through a 4 mm sieve were used for the biomass 
C and biomass N determinations. Thus for microbial biomass C, the amounts present were 
calculated from Equation 5.1 after determination of biomass C concentration, and were 
expressed in t ha-1 over 15 cm depth only, since sampling for biomass parameters was 
confined to the upper 15 cm zone. As shown by Dominy et al. (2001), microbial biomass 
content was negligibly small below 15 cm and changed very little with cropping, so there was 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 77 
no need to measure biomass deeper than 15 cm. Equation 5.1 was also applied to biomass N 
to calculate the amounts of N present in the microbial biomass. 
 
MbiomC = 0.1 x [biomC] x BD x (1- stone fraction) x depth of layer   (5.1) 
where MbiomC is biomass carbon in kg ha
-1; [biomC] is concentration of biomass carbon in mg 
kg-1; BD is bulk density in g cm-3; Stone fraction is non-dimensional; and depth of layer is in 
cm. 
 
Furthermore, the relative concentrations of C and N have been used to derive the carbon to 
nitrogen (C/N) ratio for both the whole soil and the microbial biomass as per Equation 5.2. 
 
C/N ratio = [C] / [N]          (5.2) 
where [C] is % concentration of carbon and [N] is % concentration of nitrogen. 
 
5.2.2 Data processing and analysis 
 
Since any individual measurement would lack precision, multiple measurements were 
required, even though none of the measurements was likely to be more precise than the 
others. However, it was expected that this group of values would cluster around the true value 
being measured. A single data point, the mean, or average value, was thus computed to 
represent this distribution of data values. It described a middle point, or central tendency, 
about which the data points varied. The variation in the data was described by the standard 
error of the mean, normally abbreviated to SE, which was effectively the standard deviation 
of the means (Streiner, 1996). This standard error was calculated from Equation 5.3. 
 
SE = SD /  N          (5.3) 
where SE is standard error; SD is standard deviation; and N is the number of samples. 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 78 
To obtain the SE value, the SD had first to be calculated. This was achieved by using 
Equation 5.4. 
 
SD =   (Xi – M)
2 / (N – 1)        (5.4) 
where SD is standard deviation; Xi is an individual data point; M is the mean; and N is the 
number of data points. 
 
At all sites, a total of twelve individual samples or measurements were taken per treatment. 
Furthermore, these twelve replicates were repeated for each of the sampling depths. Thus, 
each group of twelve individual data points was used to compute the average value and its 
standard error, i.e. N = 12 in Equations 5.3 and 5.4. The computation of the standard error of 
the soil and biomass C/N ratio had required additional calculations using Equation 5.5. 
 
SE = (avC/avN) x [(se /av )
2 
C C + (seN/av )
2
N ]
½      (5.5) 
where SE is standard error of C/N ratio; avC is average value of C concentration; avN is 
average value of N concentration; seC is standard error of C concentration; and seN is standard 
error of N concentration. 
 
 
5.2.3 Data presentation 
 
The data sets were processed using the Microsoft Excel program in Windows XP. This 
program was used for both calculations of mean and standard error, and for subsequent 
graphical presentation of the data. Thus, the standard deviation was calculated using the 
STDEV function in the program. Standard error was calculated by dividing the standard 
deviation obtained by 3.46, i.e. 12. The graphical functions of Microsoft Excel were then 
used to plot the average value and standard error of each treatment. 
 
For concentration of organic C, total N and C/N ratio in the soil at different depths, the soil 
layer was on the y-axis while the measured parameter was on the x-axis. The data for each 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 79 
soil layer has been represented as one single point, taken to be in the middle of the layer 
concerned, giving a line graph with horizontal error bars showing the standard error for each 
point. On the other hand, the microbial biomass C and N content, and its C/N ratio, have been 
represented by bar charts, with vertical error bars representing the standard error. 
 
The graphs have been interpreted in the following way: where the error bars for two 
treatments did not overlap, the difference between the two treatments has been taken to be 
significant. Otherwise, there was no significant difference. The advantage of this form of 
representation was that it summarized the whole data set together with its existing variability 
in one graph, and any significant difference was immediately visible. There were three sets of 
graphs for each parameter. The first set included the native, manual and mechanized 
situations. Effects of sugar cane cropping have been discussed by comparing the native with 
the manual situation, while those of mechanization were discussed by comparing the manual 
with the mechanized situation. The second set pertained to the comparison between “old” (> 
50 years) and “new” (< 25 years) cultivations, as defined in Section 4.2, and made it possible 
to determine the effects of time under cultivation. The third and final set compared 
mechanized soils that have undergone recent derocking and grading (within the last 3 years) 
with those that were subjected to early derocking and grading (at least 10 years ago) to 
determine the effects of time under mechanization. 
 
5.3 Results and discussion 
 
5.3.1 Organic matter 
 
5.3.1.1 Effects of manual and mechanized sugar cane cropping practices on organic 
matter 
 
The humid H soil had the highest OC concentration under native vegetation while the L soil 
had the lowest concentration (Figure 5.1). Compared to the P, L, B and F soils, the H soil had 
a much higher OC concentration in its topsoil (defined as the 0 - 15 cm layer). However, the 
difference in concentration became smaller in the subsoil (defined as the 15 - 50 cm layer). 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 80 
The H soil also had the highest total nitrogen concentration under native vegetation (Figure 
5.2). There were major differences with respect to total N in the four other soils since the sub-
humid P and L soils had higher topsoil total N contents than the super-humid F and B soils. 
The C/N ratio of the soil was dependent on the climatic zone. Thus, the sub-humid P and L 
soils had a lower C/N ratio under native vegetation than the humid H and super-humid B and 
F soils (Figure 5.3). The highest C/N ratio was found in the super-humid F soil, where it 
reached 14 for the whole profile. 
 
In the rocky soils, there was a significant fall in OC concentration with sugar cane cropping 
in the P topsoil and a significant rise in the B subsoil. In the rock-free H, F and L soils, OC 
concentration decreased with sugar cane cropping in the topsoil, but was counter-balanced by 
an increase in the subsoil. The decrease in SOM with sugar cane cropping in the P soil was 
confirmed by the significant fall in total N in its topsoil, while the SOM-enhancing effect of 
sugar cane cropping was confirmed in the B soil by a significant rise in total N in both topsoil 
and subsoil. In the H and F soils, total N followed the same trend as OC, with its 
concentration decreasing with sugar cane cropping in the topsoil and increasing in the 
subsoil. In the L soil, total N decreased with sugar cane cropping in the topsoil but remained 
unchanged in the subsoil. The effects of sugar cane cropping on C/N ratio in soil were 
influenced by climatic zone. In the sub-humid zone, cultivation tended to raise C/N ratio as it 
was higher in sugar cane-cultivated soils than in virgin soils, even though the change was not 
significant in most cases. The opposite trend occurred in the humid and super-humid zones, 
where the cropped H, F and B soils had a lower C/N ratio than their virgin counterparts. The 
fall in C/N ratio was significant in the H topsoil, and in most of the profile of the F and B 
soils. 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 81 
B soil P soil
0.00 2.00 4.00 6.00 8.00
0.00 2.00 4.00 6.00 8.00
0
0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Organic C concentration (%) Organic C concentration (%)
F soil L soil
0.00 2.00 4.00 6.00 8.00 0.00 2.00 4.00 6.00 8.00
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Organic C concentration (%) Organic C concentration (%)
H soil
0.00 2.00 4.00 6.00 8.00
0
-10
Figure 5.1 Effects of manual and 
-20 mechanized sugar cane cropping 
practices on organic carbon 
-30
concentration of the five major soil 
-40 groups of Mauritius
-50
Organic C concentration (%)
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm)
Soil depth (cm)
Soil depth (cm)
Soil depth (cm)
 82 
B soil P soil
0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Total N concentration (%) Total N concentration (%)
F soil L soil
0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Total N concentration (%) Total N concentration (%)
H soil
0.0 0.1 0.2 0.3 0.4 0.5
0
-10
-20
Figure 5.2 Effects of manual and 
-30 mechanized sugar cane cropping 
practices on total nitrogen concentration 
-40 of the five major soil groups of 
Mauritius
-50
Total N concentration (%)
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 83 
B soil P soil
0 5 10 15 20 0 5 10 15 20
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
C/N ratio C/N ratio
F soil L soil
0 5 10 15 20 0 5 10 15 20
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
C/N ratio C/N ratio
H soil
0 5 10 15 20
0
-10
-20
Figure 5.3 Effects of manual and 
-30 mechanized sugar cane cropping 
practices on carbon:nitrogen ratio of the 
-40 five major soil groups of Mauritius
-50
C/N ratio
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 84 
The OC and total N concentrations in the mechanized fields of the super-humid F soil were 
not significantly different from those where manual operations were practised. In the super-
humid B soil, adoption of mechanized practices led to a decrease in total N concentration 
while OC concentration remained unchanged. On the other hand, OC concentration decreased 
significantly with mechanized practices in the rock-free H and L soils. Total N concentration 
also declined significantly with mechanized practices in the H soil and in the L topsoil. The P 
soil was the only one whose OC and total N concentrations tended to increase as a result of 
the introduction of mechanized practices. The C/N ratio increased significantly with the 
adoption of mechanized practices in the P, H, B and F topsoils. C/N ratio decreased, but not 
significantly, in the sub-humid L soil. 
 
One would normally expect SOM content to fall with sugar cane cropping for the reasons put 
forward by Dominy et al. (2001), namely enhanced exposure of hitherto protected SOM to 
microbial action and higher decomposition rates as a result of more favourable conditions. 
While this was true for the topsoil, there was also a trend for a higher OC and total N 
concentration in the subsoil by way of compensation. These observations have demonstrated 
that sugar cane cropping promoted the downward transfer of SOM in the profile as reported 
by Masilaca et al. (1986). This was a long-term process as soil tillage led to the mixing of the 
OM-rich topsoil with the subsoil and residues were further added to the deeper layers when 
the fields were prepared for planting. The higher OC and total N contents in the subsoil of the 
super-humid B and F soils were probably brought about by the return of OM to the soil as a 
result of green cane harvesting in the super-humid region. All the old leaves and green tops 
were retained in situ after harvest and arranged in alternate inter-rows, thereby providing a 
ready source of OM for the soil. In contrast, the fields from the sub-humid and humid zones 
were normally harvested after the cane had been burnt to get rid of the trash, a common 
practice in those areas for improving the harvesting efficiency of the labour. Hence, there was 
a lower return of carbonaceous material in the humid and sub-humid soils and the latter were 
therefore likely to have lower OM contents. This was the case with the P soil, which was the 
only one whose subsoil OC and total N contents did not increase. On the other hand, the L 
and H soils had increased amounts of subsoil OC with sugar cane cropping, showing that 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 85 
sufficient organic inputs had been produced to compensate for the losses. However, while 
total N concentration also increased with sugar cane cropping in the H subsoil, there was no 
difference in the L subsoil. Since OC increased and total N did not change, the effect of 
cropping was to increase the C/N ratio in the L subsoil. The fact that C/N ratio decreased with 
sugar cane cropping in the super-humid zone indicated that there was less undecomposed 
plant material than under virgin conditions. A likely explanation was that, with tillage, the 
turnover rate of OM was increased as the soil disturbance put the microbial population in 
better contact with the residues. In addition, tillage favoured aeration and exposure to 
sunlight, thereby increasing the rate of residue breakdown. In contrast, the higher C/N ratio in 
the sub-humid zones showed an increase in undecomposed residue with cultivation. As OM 
turnover rate would be expected to increase, the only explanation for such an observation was 
that there were more residues for decomposition in these cultivated soils than under virgin 
conditions. This higher residue content was caused by the additional biomass produced under 
irrigated sugar cane production as opposed to the sparse natural vegetation in these dry 
regions. 
 
With the introduction of mechanization, particularly mechanized harvesting, the soil was 
often subjected to more disruption as the main objective in the land preparation was to 
smooth the field surface to create ideal conditions for operating the harvester. Given the 
disturbance, it was very likely that OM was affected negatively by the land preparation. This 
is what was noted in the L and H soils. On the other hand, there was likely to be much less 
disturbance in the super-humid F and B soils as land preparation was much less drastic in 
those soils. In fact, the time opportunity for large-scale mechanical operations is extremely 
limited in the super-humid region on account of the prevailing wet conditions. The OM 
content of these two soils was therefore not affected by the adoption of mechanized practices. 
The P soil was exceptional compared to the other four soils in that its OM concentration 
increased following the adoption of mechanized practices. This was not surprising if one 
considers the organic amendments that the sugar estate had added to its P soil following land 
preparation for mechanization. Indeed, substantial amounts of stillage slop and scum compost 
had been applied prior to planting, at rates of 20 and 5 t ha-1 respectively. The scum compost 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 86 
application was equivalent to 15 t ha-1 of fresh scum. Stillage slops contained 7 – 10% solids, 
of which 71% were organic in nature, such as reducing sugars, proteins and gums (Paturau, 
1989). The scum compost also contained OM, such as sucrose, wax fat and fibre. These made 
up 10.0 to 17.7 % by weight of fresh scum (Paturau, 1989). Consequently a very large 
amount of OM was being applied to the P soils, resulting in an increased SOM content. 
 
 
5.3.1.2 Organic matter and length of time during which sugar cane has been cropped 
manually 
 
The concentrations of OC and total N were significantly higher in the P soil cropped with 
sugar cane for a long time compared to the recently cultivated one (Figure 5.4). In the L soil, 
OC concentration increased with time under cropping in the topsoil. Its total N concentration 
was mostly unaffected by time under cropping (Figure 5.4). The C/N ratio was slightly higher 
in the soils cropped with sugar cane for a long time compared to the recently cultivated ones 
in both P and L soils (Figure 5.4). However, this increase in C/N ratio was non-significant in 
the whole profile of the two soils. 
 
These results indicate that OM content rapidly reached an equilibrium situation under sugar 
cane cropping in the L soil. In the P soil, the high degree of SOM accumulation with time 
was presumably a consequence of accumulation of OM from dry leaves and old roots after 
harvest, even with sugar cane burning. The provision of irrigation must have played a part in 
this accumulation, as the cultivated fields produced more biomass and therefore more 
residues to contribute to the build-up with time. The increase in OM concentration noted in 
the L topsoil was also probably caused by a temporal accumulation of residues. 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 87 
P soil L soil
0.00 1.00 2.00 3.00 4.00 0.00 1.00 2.00 3.00 4.00
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Organic C concentration (%) Organic C concentration (%)
0.0 0.1 0.2 0.3 0.4 0.5 0.0 0.1 0.2 0.3 0.4 0.5
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Total N concentration (%) Total N concentration (%)
0 5 10 15 20 0 5 10 15 20
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
C/N ratio C/N ratio
Old (> 50 years) New (< 25 years) Old (> 50 years) New (< 25 years)
Figure 5.4 Effects of length of time under manual sugar cane cropping on 
organic C concentration, total N concentration and carbon:nitrogen ratio of the 
two major soil groups in the sub-humid zone of Mauritius
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm) Soil depth (cm)
 88 
5.3.1.3 Organic matter and length of time during which mechanized practices have been 
adopted 
 
The OC and total N concentration of soils tended to fall under long-term mechanized 
conditions as the two parameters were significantly lower in early mechanized fields than in 
fields recently mechanized (Figure 5.5). The C/N ratio stayed constant with time. 
 
Such an OM decrease with time under mechanized conditions in the P soil was not surprising 
as the estate initially added very large amounts of OC-rich amendments to its soils 
immediately after land preparation. Afterwards, the soil slowly reached an equilibrium 
condition as there were no further external OM additions. There was thus an initial flush of 
OM in the recently mechanized fields, but OM content later decreased naturally as the 
microbial population attacked the more labile organic material. Eventually, the old 
mechanized fields reached a stabilized condition with the OC and total N concentration much 
lower than the initial values. 
 
5.3.2 Microbial biomass 
 
5.3.2.1 Effects of manual and mechanized sugar cane cropping practices on microbial 
biomass 
 
Under native vegetation, the rocky P and B soils had the lowest amount of biomass C, 
slightly less than 500 kg ha-1 in the upper 15 cm (Figure 5.6). The rock-free L and F soils 
contained sligthly more biomass C, some 600 kg ha-1 in the upper 15 cm, but the highest 
content occurred in the humid H soil, where it attained 1.0 t ha-1. The H soil also contained 
the highest amount of microbial biomass nitrogen, some 160 kg ha-1 (Figure 5.7). The super-
humid F soil had a biomass N content in the order of 100 kg ha-1, while the B, P and L soils 
had a biomass N content in the order of 40 to 60 kg ha-1. The microbial C/N ratio was highest 
in the B soil, followed by the L soil, while the other three soils had very similar lower values 
(Figure 5.8). The relatively high values of the B and L soils could be attributed to their lower 
microbial biomass N. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 89 
0.00 1.00 2.00 3.00 4.00
0
-10
-20
-30
-40
-50
Organic C concentration (%)
0.0 0.1 0.2 0.3 0.4 0.5
0
-10
-20
-30
-40
-50
Total N concentration (%)
0 5 10 15 20
0
-10
-20
-30
-40
-50
C/N ratio
Early (> 10 years) Recent (< 3 years)
Figure 5.5 Effects of length of time for which mechanized practices have been 
implemented on organic C concentration, total N concentration and 
carbon:nitrogen ratio of P soil of Mauritius cropped with sugar cane
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
 90 
B soil P soil
1500 1500
1000 1000
500 500
0 0
Virgin Manual Mechanized Virgin Manual Mechanized
practices practices practices practices
F soil L soil
1500 1500
1000 1000
500 500
0 0
Virgin Manual Mechanized Virgin Manual Mechanized
practices practices practices practices
H soil
1500
1000 Figure 5.6 Effects of manual and mechanized 
sugar cane cropping practices on biomass 
carbon content (kg/ha over 15 cm soil depth) 
500 of the five major soil groups of Mauritius
0
Virgin Manual Mechanized
practices practices
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Biomass C (kg/ha) Biomass C (kg/ha) Biomass C (kg/ha)
Biomaas C (kg/ha) Biomass C (kg/ha)
 91 
B soil P soil
200 200
150 150
100 100
50 50
0 0
Virgin Manual Mechanized Virgin Manual Mechanized
practices practices practices practices
F soil L soil
200 200
150 150
100 100
50 50
0 0
Virgin Manual Mechanized Virgin Manual Mechanized
practices practices practices practices
H soil
200
150 Figure 5.7 Effects of manual and 
mechanized sugar cane cropping 
100 practices on biomass nitrogen content 
(kg/ha over 15 cm soil depth) of the 
five major soil groups of Mauritius
50
0
Virgin Manual Mechanized
practices practices
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Biomass N (kg/ha) Biomass N (kg/ha) Biomass N (kg/ha)
Biomass N (kg/ha) Biomass N (kg/ha)
 92 
B soil P soil
20 20
15 15
10 10
5 5
0 0
Virgin Manual Mechanized Virgin Manual Mechanized
practices practices practices practices
F soil L soil
20 20
15 15
10 10
5 5
0 0
Virgin Manual Mechanized Virgin Manual Mechanized
practices practices practices practices
H soil
20
15 Figure 5.8 Effects of manual and 
mechanized sugar cane cropping practices on 
10 biomass carbon:nitrogen ratio of top 15 cm 
of the five major soil groups of Mauritius
5
0
Virgin Manual Mechanized
practices practices
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Biomass C/N ratio
Biomass C/N ratio Biomass C/N ratio
Biomass C/N ratio Biomass C/N ratio
 93 
 
Sugar cane cropping either had no effect, or led to a substantial fall in microbial biomass. 
Thus, the biomass C and N contents of the B and L soils did not change significantly upon 
conversion to sugar cane cropping, these soils already having low biomass C and N under 
native vegetation. The biomass C content of the P soil was not significantly affected by 
cropping, as opposed to its biomass N, which was significantly reduced. A highly significant 
decrease in microbial biomass occurred with sugar cane cropping in the H and F soils. The 
biomass C and N contents of the H soil fell to about a third of the values found under native 
vegetation. In the F soil, biomass N content also fell to a third of its initial value, while 
biomass C content was almost halved with sugar cane cropping. Sugar cane-cropped soils 
either had a higher, or an unchanged, biomass C/N ratio compared to soils under native 
vegetation. The increase in biomass C/N ratio with sugar cane cropping was significant in the 
P and F soils. 
 
With the adoption of mechanized practices, biomass C content increased significantly in the 
sub-humid L and P soils, but decreased significantly in the humid H and super-humid F soil, 
whereas the biomass C content of the rocky B soil was not significantly affected. On the other 
hand, the adoption of mechanized practices enhanced the microbial biomass N in the P and H 
soils. In the B, F and L soils, the biomass N increase with mechanization was not significant. 
Biomass C/N ratio decreased with the adoption of mechanized practices in the rock-free H 
and F soils. There was no change in biomass C/N ratio in the P, L and B soils. 
 
As carbon in the microbial biomass is energy stored for microbial processes, microbial 
biomass C content is therefore an indication of potential microbial activity (Rice et al., 1996). 
The decline in biomass C and N observed with sugar cane cropping in the H and F soils was 
expected in view of the decline in OC concentration in the upper 15 cm of these soils (Figure 
5.1). In contrast, there was a much less marked decrease in OC concentration in the top 15 cm 
of the L and B soils. It was therefore not surprising that the biomass C content was little 
affected by cultivation in these soils. However, it was not possible to draw any firm 
conclusion regarding the P soil as its biomass C and biomass N contents were affected 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 94 
differently by cropping. The C/N ratio of micro-organisms is much narrower than that of 
plant residues, varying usually between 4 and 9 (Brady, 1974) as compared to 128 for cane 
trash in Mauritius (Ng Kee Kwong et al., 1987). Bacterial tissue is generally richer in 
proteins than fungi and has consequently a narrower C/N ratio. The increased biomass C/N 
ratio of the sugar cane cultivated P and F soils was an indication that there had been a shift in 
the composition of the microbial population in these two soils, for instance with a relative 
increase in the fungal population at the expense of the bacterial one. 
 
The increase in biomass C content in the mechanized fields of the sub-humid soils was 
probably caused by different factors. There was an increase in the microbial population in the 
P soil as a result of the large amount of OM introduced after mechanization. On the other 
hand, there was no such build-up in OM in the L soil and its microbial population might be 
related to a difference in the nature of the SOM present in its mechanized fields compared to 
the manually cultivated ones. This was illustrated by the lower C/N ratio of the SOM in the 
mechanized fields, indicating that the residues were easier to decompose, hence the higher 
microbial population. In the soils from the humid and super-humid zones, biomass C tended 
to decrease with the adoption of mechanized practices but the opposite was true for biomass 
N. This reversal in trend obviously impacted on their biomass C/N ratio. No definite 
conclusion could therefore be drawn on the effects of adopting mechanized practices on the 
biomass content of the B, F and H soils. However, the reduced microbial C/N ratio under 
mechanized conditions in the H and F soils indicated that there was a possible increase in the 
bacterial population relative to the fungal one. 
 
 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 95 
5.3.2.2 Microbial biomass and length of time during which sugar cane has been cropped 
manually 
 
The effect of length of time under sugar cane cultivation was to increase the biomass C 
content in the two sub-humid soils (Figure 5.9). The L soil cultivated for a longer time with 
sugar cane had a significantly higher value than the recently cultivated soil. On the other 
hand, the difference between the two treatments was too small to be significant in the P soil. 
The evolution of biomass N with time under sugar cane cultivation differed for the P and L 
soils (Figure 5.9). In the rocky P soil, there was more biomass N in the recently cultivated 
fields and it thereafter declined with time. The rock-free L soil, on the contrary started with a 
low biomass N, which like biomass C, increased significantly with time under sugar cane 
cropping, an indication that microbial biomass accumulated with time in this soil. There was 
no significant effect of time under sugar cane cropping on the biomass C/N ratio of the L soil 
(Figure 5.9). On the other hand, biomass C/N ratio increased significantly with time in the P 
soil. 
 
This trend towards higher biomass C and N content with time in the manually cultivated L 
soil followed a similar trend in higher OC concentration in its topsoil. There was thus a 
biomass accumulation with time as the microbial population increased in parallel with the 
rise in SOM. On the other hand, the decline of microbial N with time in the P soil was 
contrary to the evolution of its biomass C, which remained unaffected, thereby demonstrating 
that the decline in biomass N occurred through changes in the biomass C/N ratio. 
 
 
 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 96 
1500
1000
500
0
Old (> 50 New (< 25 Old (> 50 New (< 25
years) years) years) years)
P soil L soil
200
150
100
50
0
Old (> 50 New (< 25 Old (> 50 New (< 25
years) years) years) years)
P soil L soil
20
15
10
5
0
Old (> 50 New (< 25 Old (> 50 New (< 25
years) years) years) years)
P soil L soil
Figure 5.9 Effects of length of time under manual sugar cane cropping on biomass C 
and N contents (kg/ha over 15 cm soil depth), and biomass carbon:nitrogen ratio of the 
two major soil groups in the sub-humid zone of Mauritius
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Biomass N (kg/ha) Biomass C (kg/ha)
Biomass C/N ratio
 97 
5.3.2.3 Microbial biomass and length of time during which mechanized practices have 
been adopted 
 
The microbial biomass C content of the P soil was higher in the fields recently-mechanized 
than in those where mechanized practices have been adopted for a longer period (Figure 
5.10), but the difference was not significant. Contrary to biomass C, the biomass N content of 
the P soil increased significantly with time under mechanization (Figure 5.10). Furthermore, 
the longer mechanized practices have been adopted in the P soil, the lower was its biomass 
C/N ratio (Figure 5.10). Thus, under long-term mechanization, the ratio decreased 
significantly to less than half its original value. This change as explained above indicated an 
evolution in the composition of the microbial population, most probably because the nature 
of the SOM had changed with time. Under recently mechanized conditions, there was an 
initial breakdown of the more easily decomposed organic material by a particular group of 
micro-organisms. In the long term, these subsided as they ran out of food and a different type 
of micro-organisms would then predominate, having to decompose the remaining, more 
resistant SOM. The change in C/N ratio of the microbial population would thus reflect this 
type of microbial evolution. 
 
 
5.4 Conclusion 
 
The effects of sugar cane cultivation on the biological properties of the major soils of 
Mauritius were variable, with a clear dependence upon the climatic zone in which these soils 
occur. This association of biology with climatic zone was related to the cultural practices that 
predominated in the different zones and which impacted on the return of organic residues to 
the soil. The practice of burning before harvest in the drier zone compared to green cane 
harvesting in the wetter zone was probably the one element that had the greatest influence on 
SOM and the microbial population. Sugar cane cultivation did not necessarily degrade the 
soil’s biological properties. In the dry zone, irrigated agriculture boosted biomass production 
and enhanced residue return to the soil. It was true that mechanization tended to impact 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 98 
1500
1000
500
0
Early (> 10 years) Recent (< 3 years)
200
150
100
50
0
Early (> 10 years) Recent (< 3 years)
20
15
10
5
0
Early (> 10 years) Recent  (<3 years)
Figure 5.10 Effects of length of time for which mechanized practices have been 
implemented on biomass C and N contents (kg/ha over 15 cm soil depth) and biomass 
carbon:nitrogen ratio of P soil of Mauritius cropped with sugar cane
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Biomass N (kg/ha) Biomass C (kg/ha)
Biomass C/N ratio
 99 
negatively on both SOM and microbial properties, except for the P soil. The latter did not 
follow the same trend as the other sites since the estate had taken the precaution of alleviating 
the negative effects of land preparation and rock removal by the addition of large amounts of 
organic amendments. It was therefore not surprising that the P soil should have had better 
biological properties after mechanization. 
 
It was difficult to draw clear conclusions regarding the effect of time under sugar cane 
cultivation on the biological properties of the sub-humid soils. Nevertheless, it can be stated 
that these properties were not systematically degraded under long-term cultivation in both L 
and P soils. It was under long-term mechanized practices that the soil biological quality was 
clearly depressed. This resulted from the practice of applying large amounts of organic 
amendments to the soil during land preparation and of letting them be used up, so that the soil 
started with initially high contents of SOM and microbial biomass and ended up with much 
lower contents in the long-term. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 100 
CHAPTER 6 
 
INFLUENCE OF SUGAR CANE PRODUCTION ON SOME SOIL CHEMICAL 
PARAMETERS 
 
6.1 Introduction 
 
The soil chemical parameter that had been the subject of most studies is pH. In addition to 
changes in the topsoil and subsoil, measurements were made on its evolution with time and 
possible causes for its change have been discussed. The other chemical parameters that had 
been considered to be sufficiently important to warrant study include cation exchange 
capacity (CEC), levels of plant nutrients such as calcium, magnesium, potassium and 
phosphorus, and the salinity and sodicity of soils as expressed by their electrical conductivity 
(EC) and sodium adsorption ratio (SAR). 
 
In general, soils became more acid under sugar cane (Haynes and Hamilton, 1999) and had a 
higher exchangeable aluminium level (Wong You Cheong and Chan, 1977) than under native 
vegetation. Topsoil pH was found to decrease immediately after planting of sugar cane by a 
maximum of 0.8 pH unit, but to rise again in the long term (Masilaca et al., 1986). Cropping 
under sugar cane also leads to a simultaneous drop in pH in the topsoil and a rise in the 
subsoil, as bases were leached from the topsoil into the subsoil following irrigation (Henry 
and Ellis, 1996). Acidification in both topsoil and subsoil was also shown to occur 
(Hartemink, 1998c), while there were also cases where no significant change happened when 
native soils were put under sugar cane production (Van Antwerpen and Meyer, 1996). 
 
The most frequent finding was that acidification occurred when soils under native vegetation 
were converted to sugar cane. Schroeder et al. (1994) believed that such an acidification was 
the most important yield-limiting factor in the KwaZulu-Natal region of South Africa, while 
Noble et al. (1997) concluded that a continual decline in soil pH would affect the long-term 
sustainability of sugar cane production systems. In such a case, corrective measures such as 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 101 
liming were necessary, or else soil acidification would ultimately become a threat to the long-
term fertility of the soil and therefore to the sugar industry. The rate of this process could be 
quite fast, since almost a six-fold increase in hydrogen ion activity was noted over 15 years in 
one instance (Meyer et al., 1998), while the rate of decline of soil pH could range from 0.025 
pH unit year-1 (Qongqo and Van Antwerpen, 2000) to 0.047 pH unit year-1 (Hartemink, 
1998c). 
 
Oxidation of ammoniacal fertilizers to nitrate, mineralization of organic matter and leaching 
of basic cations were identified as the three main causes for acidification of soils under sugar 
cane (Meyer et al., 1998). The most pronounced effect on pH was ascribed to ammonium 
sulphate fertilizer (Wood, 1965; McLean, 1975; Wood, 1985), which had twice the acidifying 
power of the most commonly used N fertilizer, i.e. urea (Noble et al., 1997). For both forms 
of fertilizer, nitrification by the soil microbial population was the driving force behind the 
acidification process (Haynes and Hamilton, 1999). This direct involvement of fertilizers was 
confirmed by the much lower soil pH values in fertilized treatments compared to unfertilized 
ones (Graham et al., 1999). 
 
CEC was also affected by sugar cane cultivation and its changes tended to reflect changes in 
SOM content as the latter was a major contributor to exchange sites. In general, sugar cane 
soils had lower CEC than soils under native vegetation on account of their lower OM 
contents (Wood, 1985; Henry and Ellis, 1996; Hartemink, 1998b). Nevertheless, the value of 
topsoil CEC could also remain unaffected by sugar cane cultivation (McLean, 1975), whereas 
subsoil CEC could increase as a result of downward transfer of OM when the soil was mixed 
and rotovated during land preparation at planting (Masilaca et al., 1986). 
 
The levels of plant nutrients in sugar cane soils were estimated by the balance of fertilizer 
inputs against crop removal, plus other losses such as leaching (Haynes and Hamilton, 1999). 
Contents of two important exchangeable bases, namely calcium and magnesium, tended to 
decrease under sugar cane cultivation (Wood, 1985; Masilaca et al., 1986; Van Antwerpen 
and Meyer, 1996; Meyer et al., 1998; Qongqo and Van Antwerpen, 2000) because 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 102 
insufficient amounts of bases had been added to compensate for crop removal and leaching 
(Masilaca et al., 1986). Exchangeable potassium levels followed a similar decreasing trend 
(Hartemink, 1998b; Henry and Ellis, 1996), even though potassium build-up could also occur 
in soils under sugar cane as a result of overuse of potassium fertilizers by growers (Meyer et 
al., 1998) or by disposal of stillage slop in the cane fields. The amounts of extractable 
phosphorus in sugar cane soils also depended on nutrient balance and could therefore either 
increase (McLean, 1975; Wood, 1985; Henry and Ellis, 1996) or decrease (Van Antwerpen 
and Meyer, 1996; Meyer et al., 1998; Hartemink, 1998a). These changes were mostly 
confined to the topsoil and very little phosphorus was removed from soil horizons below 30 
cm. 
 
Indicators of salinity and/or sodicity, such as EC and SAR, were affected essentially under 
irrigated conditions and depended on irrigation water quality. For instance, these parameters 
could be greatly improved if sugar cane was irrigated with good quality water associated with 
surface and subsurface drainage and the application of gypsum to replace sodium ions with 
calcium (Henry and Ellis, 1996). However, the opposite could also occur in irrigated sugar 
cane soils compared to virgin soils if no appropriate corrective measure was taken (Van 
Antwerpen and Meyer, 1996). 
 
Changes in some chemical properties of the major soils of Mauritius, as a result of sugar cane 
cropping, are reported in this chapter. Four indicators of chemical quality, namely pH, CEC, 
exchangeable bases and base saturation, were assessed following manual sugar cane cropping 
on all five major soil groups. On the same soil groups, the effects of adopting mechanized 
practices were also measured. In addition, the effects of time under manual and mechanized 
sugar cane cropping practices for selected soil groups are also dealt with. 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 103 
6.2 Procedure 
 
6.2.1. General 
 
Chemical quality parameters that have been studied in the major soil groups of Mauritius 
were pH, cation exchange capacity, exchangeable bases (Ca, Mg, K and Na) and base 
saturation. A complete description of the methodology used to measure pH, CEC and 
concentration of individual bases is given in Chapter 4. 
 
All measurements have been made in the laboratory on the soil fraction of the samples, as 
defined in Section 5.2.1. The concentration of the four individual exchangeable bases was 
determined on air-dried soil samples in the laboratory and expressed in g kg-1. These values 
were then converted to cmol  kg-1c , the same unit as for CEC, by using a conversion factor 
derived from the relative atomic mass of each element and their valency (Table 6.1). 
 
Table 6.1 Weight in gram of one cmol  kg-1c  of exchangeable chemical elements (adapted 
from Baize, 1993) 
 
Exchangeable chemical Weight (g) 
1 cmol  kg-1 of K+c  0.03910 
1 cmol  -1c kg  of Ca
2+ 0.02005 
1 cmol  kg-1 of Mg2+c  0.01215 
1 cmol  c kg
-1 of Na+ 0.02300 
 
Since the concentration of individual bases and the CEC were both in cmol  -1c kg , these 
parameters were used directly to derive the base saturation (BS) of the soil samples in 
percentage using Equation 6.1. 
 
BS = 100 x {[Ca] + [Mg] + [K] + [Na]} / CEC     (6.1) 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 104 
 
6.2.2 Data processing and analysis 
 
The same procedure as described in Section 5.2.2 has been adopted to calculate the average 
value of the measurements and their standard error, giving a single representative point per 
parameter while encompassing all the variability of the result. 
 
 
6.2.3 Data presentation 
 
A similar procedure as described in Section 5.2.3 has been used to present the data sets, 
namely the average values and their standard errors were plotted on graphs. For each 
chemical parameter the soil depth was on the y-axis while the parameter concerned was on 
the x-axis. Again, the data for each soil layer were represented in one single point in the 
middle of the layer concerned. The evolution of every parameter with depth for each 
treatment was thus expressed in the form of a line graph, and horizontal error bars showed the 
standard error for each data point. 
 
 
6.3 Results and discussion 
 
6.3.1 Soil pH 
 
6.3.1.1 Effects of manual and mechanized sugar cane cropping practices on soil pH 
 
Under native vegetation, the sub-humid P and L soils were close to neutral, with pH values of 
7.0 for the P soil and 6.3 for the L soil (Figure 6.1). The lower pH of the L soil compared to 
the P soil was related to the longer period during which the former had been subjected to 
leaching, since it was derived from older parent material. The humid H soil and the super-
humid F soil were acidic, in the pH range of 5.0, as expected for soils whose formation had 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 105 
B soil P soil
4.0 5.0 6.0 7.0 8.0
4.0 5.0 6.0 7.0 8.0
0
0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
pH pH
F soil L soil
4.0 5.0 6.0 7.0 8.0 4.0 5.0 6.0 7.0 8.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
pH pH
H soil
4.0 5.0 6.0 7.0 8.0
0
-10
Figure 6.1 Effects of manual and 
-20
mechanized sugar cane cropping practices on 
-30 pH of the five major soil groups of Mauritius
-40
-50
pH
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 106 
occurred under conditions of heavy rainfall with most bases having been leached out of the 
profile. However, the other soil from the super-humid zone, the rocky B soil, was surprisingly 
close to neutrality, whereas it should at best have been slightly acidic (Parish and Feillafé, 
1965). In terms of individual soil layers, pH tended to increase slightly with depth in the 
rocky P and B soils, but to decrease in the rock-free L, H and F soils. 
 
The abnormally high pH of the B soil under native vegetation shows that the site had not 
been under virgin conditions at sampling time. Since soils from this group normally have a 
pH varying between 5.0 and 6.3, with an average value of 5.5 (Parish and Feillafé, 1965), the 
measured values of 6.6 to 7.0 indicate that some form of amendment had been made to the 
site. This zone was under a vegetation of grass and coniferous trees and had obviously not 
been cultivated for a long time. However, this does not preclude the possibility that it could 
have received chemical amendments and in view of the high pH, it is probable that some 
liming agent had been applied. The site was definitely not under virgin conditions in 
chemical terms, and it would be unwise to compare this soil with the sugar cane cultivated 
soil. This means that no conclusion should be drawn on the effect of sugar cane cultivation on 
the pH of the B soil. 
 
Excluding the B soil, sugar cane cropping had variable effects on soil pH. In the sub-humid L 
and P and humid H soils, cultivation was generally beneficial as it led to higher pH, the 
increase being significant in most of the profile of the three soils. On the other hand, the pH 
of the super-humid F soil decreased with sugar cane cropping in the topsoil, but increased in 
the subsoil. 
 
Changes in soil pH with the adoption of mechanized practices were not as marked as those 
resulting from sugar cane cropping. There is very little effect in the L and P soils, but the pH 
of the H soil decreased significantly with mechanization in most of the profile. In the super-
humid soils, the effects differed according to rock content. The pH dropped significantly by 
some 0.2 units in the whole profile in the rocky B soil, but increased in the topsoil of the 
rock-free F soil. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 107 
 
The higher pH in the L, P and H soils with sugar cane cropping goes against the established 
pattern noted in most other sugar cane producing countries. It is well established in the 
literature that acidification followed sugar cane cultivation but in the case of these three soils, 
this expected acidification did not take place in spite of using fertilizer N. For the H soil, the 
reason appeared simple enough. It has been common practice to apply liming agents to raise 
soil pH in the acidic soils in the humid and super-humid zones. Historically, lime was applied 
at planting at the rate of 150 to 500 kg per arpent, equivalent to 0.36 to 1.2 t ha-1, in the early 
1900’s (North-Coombes, 1993). MSIRI (1990) recommended that soils under sugar cane 
should be limed if their pH was well below 5.0, the dose for raising pH by one unit 
amounting to 8.5, 4.8 and 2.4 t ha-1 of coral sand, lime and cement respectively. In the case of 
the H soil at Beau Champ, the pH of the virgin soil was effectively less than 5 and lime and 
sand were regularly applied to the sugar cane fields at planting at the recommended rates. As 
far as the L soil was concerned, there was still evidence of the presence of coral sand in the 
Richeterre soil samples, mainly small white pieces of coral debris. Sanding had been 
systematically practiced in areas such as Richeterre in the 1930’s, with normal rates of 1 to 5 
t per arpent, equivalent to 2.4 to 12 t ha-1 (North-Coombes, 1993), and heavier applications 
had even been made in some instances, up to 15 t per arpent, equivalent to 36 t ha-1. The 
situation is different for the P soil, where no evidence of sanding had been uncovered. In this 
case, the pH increase was caused by the practice at Médine of supplementing its mineral 
fertilizers at planting with 5 t ha-1 of composted filter mud and poultry litter. The application 
of filter mud is a common practice on all estates as it contains about 1% by weight of 
phosphate (Paturau, 1989), but it is not normally composted. This organic material raises soil 
pH as it contains some 1% CaO by weight. Poultry litter has a similar pH-enhancing effect in 
the long-term (MSIRI, 2006). The combined effect of these two organic amendments has 
probably raised the pH of the P soil, particularly as composted filter mud has again been 
added in the two subsequent ratoons. 
 
The acidification with sugar cane cropping in the topsoil of the super-humid F soil was 
probably due to the acidifying effect of ammoniacal fertilizers as noted by Wood (1965), 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 108 
McLean (1975) and Wood (1985). These fertilizers have been applied on a seasonal basis, at 
the bottom of the furrow in plant cane and at the soil surface in the subsequent ratoons. If 
they had any acidifying effect, it should have been felt close to the soil surface and 
acidification therefore occurred mainly within the topsoil. In this case the addition of 25 t ha-1 
of filter mud in the cane furrow at planting was not sufficient to counteract the acidifying 
effects of the fertilizers. Further acidification of the topsoil could have occurred through 
leaching of basic cations as described by Meyer et al. (1998). This leaching process could 
also explain why pH tended to increase in the F subsoil. 
 
The adoption of mechanized practices ought to have had little effect on chemical properties, 
since the practices that affect the latter, such as fertilization, application of organic manure 
and pH-enhancing amendments, were not modified with mechanization. This was what 
effectively happened with the pH of the sub-humid L and P soils, which remained essentially 
unaffected by mechanized practices. However, there was an acidifying trend with 
mechanization in the humid H soil and the super-humid F and B soils, which could be 
correlated with the lower calcium content of these soils under mechanized conditions (Figure 
6.8). This acidification was probably an artifact rather than a consequence of mechanization. 
 
6.3.1.2 Soil pH and length of time during which sugar cane has been cropped manually 
 
There was a slight, but insignificant, acidification with time under sugar cane cropping in the 
rock-free L soil (Figure 6.2), showing that a balance in pH had been struck early on when the 
virgin L soil was put under sugar cane cultivation. Conversely, there was a significant pH 
drop with time in the topsoil of the rocky P soil, accompanied by a small rise in the subsoil. 
 
The process driving this pH change was probably the same as that described by Henry and 
Ellis (1996), whereby acidification of the topsoil with time was caused by leaching of bases 
down the profile because of irrigation, with surface banding of fertilizers in ratoons as a 
possible additional cause. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 109 
P soil L soil
4.0 5.0 6.0 7.0 8.0 4.0 5.0 6.0 7.0 8.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
pH pH 
Old (> 50 years) New (< 25 years) Old (> 50 years) New (< 25 years)
Figure 6.2 Effects of length of time under manual sugar cane cropping on 
pH of the two major soil groups in the sub-humid zone of Mauritius
 
6.3.1.3 Soil pH and length of time during which mechanized practices have been adopted 
 
The pH of the P soil tended to be higher when mechanized practices had been adopted for a 
longer period (Figure 6.3), but the difference was not significant. It thus appears that the soil 
pH had reached an equilibrium value very rapidly following the introduction of mechanized 
practices. 
4.0 5.0 6.0 7.0 8.0
0
-10
-20
-30
-40
-50
pH 
Early (> 10 years) Recent (< 3 years)
Figure 6.3 Effects of length of time for which mechanized practices have been 
implemented on pH of P soil of Mauritius cropped with sugar cane
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
Soil depth (cm)
Soil depth (cm)
 110 
 
6.3.2 Cation exchange capacity 
 
6.3.2.1 Effects of manual and mechanized sugar cane cropping practices on cation 
exchange capacity 
 
Under native vegetation, the rocky P and B soils had a comparatively higher CEC than the 
rock-free L, H and F soils. The CEC value of these first two soils was in the order of 30 
cmol  kg-1 c in the topsoil and 26 cmol
 
c kg
-1 in the subsoil (Figure 6.4). The lowest values were 
found in the rock-free L and F soils, where they decreased with depth from 20 cmol  kg-1c  to 
12 cmol  -1c kg . The humid H soil had intermediate CEC values, with 25 cmol
 -1
c kg  in the 
topsoil and 18 cmol  kg-1c  in the subsoil. For all soil groups, CEC decreased with depth, 
showing that organic matter content was a major source of this property. 
 
In most cases, CEC values tended to be higher with sugar cane cropping compared to native 
vegetation, with the H topsoil as the only exception. The rise in CEC was not systematically 
significant in the other soils and there was indeed no significant effect of cropping in the 
rocky P and B soils. The effects were also not significant in the topsoil of the rock-free L and 
F soils. 
 
With the adoption of mechanized practices, the changes in CEC were variable and were 
related to climatic zone. Thus, the sub-humid L and P soils had an unchanged or increased 
CEC depending on soil depth, while the humid H soil and super-humid F and B soils had 
significantly lower CEC throughout the profile. The increase was quite substantial in the 
subsoil of the P soil, but was less pronounced in the L soil. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 111 
B soil P soil
0.0 10.0 20.0 30.0 40.0 0.0 10.0 20.0 30.0 40.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50
-50
-1
CEC (cmolc kg ) -1CEC (cmolc kg )
F soil L soil
0.0 10.0 20.0 30.0 40.0 0.0 10.0 20.0 30.0 40.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1
CEC (cmolc kg ) -1CEC (cmolc kg )
H soil
0.0 10.0 20.0 30.0 40.0
0
-10
-20
Figure 6.4 Effects of manual and 
-30 mechanized sugar cane cropping practices 
on cation exchange capacity of the five 
-40
major soil groups of Mauritius
-50
-1
CEC (cmolc kg )
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm)
Soil depth (cm)
 112 
CEC depends essentially upon organic matter content and soil texture, particularly the 
amount and the kind of clay present (Brady, 1974). The significant CEC increase noted with 
cropping in the L and F subsoil and the drop in the H topsoil could not be ascribed to textural 
changes as mechanical analysis had not shown any significant change in their clay content 
(Figure 7.2). It is most likely that these changes were related to changes in SOM content as 
the OC concentration of the H topsoil fell from 5.9 to 3.4% while that of the L and F subsoil 
increased by some 0.3 and 0.5% respectively (Figure 5.1). 
 
The adoption of mechanized practices led to lower CEC values under humid and super-humid 
conditions and higher ones under sub-humid conditions. It is difficult to relate this 
observation to a precise cause since SOM content did not systematically decline with 
mechanization in the humid and super-humid regions, nor did it significantly increase in the 
sub-humid region. In such instances, it would appear that the changes were caused by a 
combination of the various factors that influence CEC, namely SOM and nature and amount 
of clay, as well as the effect of pH increase in the sub-humid soils, given that CEC tends to 
increase with soil pH in most soils (Brady, 1974). 
 
6.3.2.2 Cation exchange capacity and length of time during which sugar cane has been 
cropped manually 
 
The longer the rocky P soil had been cropped with sugar cane, the higher the CEC rose 
(Figure 6.5). However, the opposite trend was found in the rock-free L soil, where length of 
time under cropping led to lower CEC values in the subsoil. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 113 
P soil L soil
0.0 10.0 20.0 30.0 40.0 0.0 10.0 20.0 30.0 40.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1
CEC (cmolc kg )
-1
CEC (cmolc kg )
Old (>50 years) New (<25 years) Old (>50 years) New (<25 years)
Figure 6.5 Effects of length of time under manual sugar cane cropping on cation 
exchange capacity of the two major soil groups in the sub-humid zone of Mauritius
 
The increase in CEC with time in the P soil was again linked to OM, since its OC content 
increased significantly with time (Figure 5.4). In the L soil, OC content did not change with 
time, so that the lower CEC values in the subsoil could not be directly attributed to a lower 
OM content. The exact cause for this observation could not be ascertained, but was probably 
the result of a combination of factors, namely SOM, nature and amount of clay, and pH as 
discussed previously. 
 
6.3.2.3 Cation exchange capacity and length of time during which mechanized practices 
have been adopted 
 
The fields that have been mechanized during a long period had a much lower CEC than those 
that have only recently been mechanized (Figure 6.6). This significant CEC decrease with 
time was observed throughout the whole soil profile and could be directly attributed to the 
significant fall in OM content with time in the mechanized fields (Figure 5.5). 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
Soil depth (cm)
 114 
0.0 10.0 20.0 30.0 40.0
0
-10
-20
-30
-40
-50
-1
CEC (cmolc kg )
Early (> 10 years) Recent (< 3 years)
Figure 6.6 Effects of length of time for which mechanized practices have been 
implemented on cation exchange capacity of P soil of Mauritius cropped with sugar cane
 
 
6.3.3 Exchangeable bases 
 
6.3.3.1 Effects of manual and mechanized sugar cane cropping practices on exchangeable 
bases 
 
Of the four exchangeable bases under study, Na is of little agronomic importance, even 
though it plays a major part wherever there are salinity problems. As there were no salinity 
problems in the soils of Mauritius, only K, Ca and Mg have been discussed. 
 
Under native vegetation, the sub-humid L and P soils contained more exchangeable bases 
than the wetter H and F soils (Figures 6.7, 6.8 and 6.9). This trend was expected as soils were 
subjected to greater leaching in the wet zones and thus to higher losses of bases. However, 
the B soil went against this trend as it had a high Ca content, an anomaly that also explained 
its unexpectedly high pH. The exchangeable base values of the virgin B soil should therefore 
not be considered as they were unreliable. 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
 115 
B soil P soil
0.0 0.2 0.4 0.6 0.8 1.0 0.0 1.0 2.0 3.0 4.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1
K concentration (cmolc kg ) -1K concentration (cmolc kg ) 
F soil L soil
0.0 0.2 0.4 0.6 0.8 1.0 0.0 1.0 2.0 3.0 4.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1
K concentration (cmol  kg ) -1c K concentration (cmolc kg ) 
H soil
0.0 0.2 0.4 0.6 0.8 1.0
0
-10
Figure 6.7 Effects of manual and 
-20 mechanized sugar cane cropping 
practices on potassium concentration 
-30
of the five major soil groups of 
-40 Mauritius
-50
-1
K concentration (cmolc kg )
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 116 
B soil P soil
0 10 20 30 0 10 20 30
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50
-50
-1
Ca concentration (cmolc kg ) -1Ca concentration (cmolc kg )
F soil L soil
0 10 20 30 0 10 20 30
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50
-50
-1
Ca concentration (cmolc kg ) -1Ca concentration (cmolc kg )
H soil
0 10 20 30
0
-10
Figure 6.8 Effects of manual and 
-20 mechanizad sugar cane cropping 
-30 practices on calcium concentration of 
the five major soil groups of Mauritius
-40
-50
-1
Ca concentration (cmolc kg )
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm)
Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 117 
B soil P soil
0.0 5.0 10.0 15.0 0.0 5.0 10.0 15.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1
Mg concentration (cmolc kg ) -1Mg concentration (cmolc kg )
F soil L soil
0.0 5.0 10.0 15.0 0.0 5.0 10.0 15.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1 -1
Mg concentration (cmolc kg ) Mg concentration (cmolc kg )
H soil
0.0 5.0 10.0 15.0
0
-10
Figure 6.9 Effects of manual and 
-20 mechanized sugar cane cropping practices 
-30 on magnesium concentration of the five 
major soil groups of Mauritius
-40
-50
-1
Mg concentration (cmolc kg )
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 118 
 
In general, sugar cane cropping did not have negative effects on exchangeable bases. 
Potassium, the most important base in agronomic terms, increased significantly with cropping 
in the P, F and H soils (Figure 6.7). The L soil was the only one where K concentration 
decreased with cropping. Calcium decreased in the topsoil of the L, P and F soils, but 
increased in the subsoil of the L and F soils and in the whole profile of the H soil (Figure 
6.8). Magnesium increased in the sub-humid L and P soils, but decreased in the H and F soils 
(Figure 6.9). 
 
The adoption of mechanized practices also did not depress the exchangeable base status in all 
the soils. In fact, K, Ca and Mg concentration increased in the P soil, but Mg concentration 
generally decreased with the adoption of mechanized practices in the other soils. The F and H 
soils were the only ones to experience a fall in K and Ca concentration respectively. 
 
The sugar cane crop requires large amounts of K (Clements, 1980). The exact amount of 
nutrient extracted is not constant and depends on soil type, climate and fertilization method. 
Thus, in India, a crop of 125 t ha-1 removed some 130 kg K ha-1 (Yadav and Prasad, 1992) 
whereas 1.33 to 1.97 kg K were extracted by 1 t stalk in Mexico, (Naranjo de la F. et al., 
2006) and 2.0 kg K was taken up per t of millable cane in Mauritius (MSIRI, 2005). The 
natural K fertility of the soils of Mauritius is low and economic crop production requires an 
input of K fertilizers. Based on the results of soil analysis, K fertilizer is recommended in 
order to meet plant demand. K fertilization was therefore the probable cause for K increase in 
the P, F and H soils. The high K value of the P soil is attributable to the practice of the sugar 
estate, which supplemented its mineral fertilizers with filter mud and poultry litter in 
manually harvested fields. Filter mud contained 0.017% K on a fresh weight basis (Paturau, 
1989) while fresh poultry litter contained some 19 kg K per t (Zublena et al., 1996). 
 
It is a recommended practice under sugar cane cropping in Mauritius to add products 
containing Ca to correct pH should the latter be lower than 5.0. In highly leached regions, 
calcium silicate is also recommended to correct for silicon deficiency, since silicon has a 
beneficial effect on sugar cane yield (Wong You Cheong, 1970). Further sources of Ca 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 119 
include fertilizers, such as calcium ammonium nitrate, a source of N, and tricalcium 
phosphate, used for phosphorus fertilization (Wong You Cheong, 1969), and filter mud. 
Overall, relatively high amounts of Ca are applied regularly to the fields. It is therefore not 
surprising that Ca contents should increase or at least stay at similar levels under sugar cane 
cropping, particularly in super-humid soils. Even in sub-humid soils, where there was a lesser 
need for Ca compounds, there was no significant net loss, a clear sign that its removal by the 
sugar cane crop or by leaching had been adequately compensated for. 
 
Unlike Ca, Mg is not added intentionally to the soil through fertilizers or amendments, but is 
found in some of the organic material that is applied. The most common source is filter mud, 
where it is present in the range of 0.3 to 0.9% Mg (Paturau, 1989). This filter mud is added to 
the fields at planting at rates varying between 12 and 28 t ha-1. Where Mg levels increased 
with sugar cane cropping, as in the L, P and B soils, it is most likely that Mg additions via 
filter mud were higher than its removal by the crop and losses by leaching. The increase in 
Mg was more pronounced in the P soil. This was due to the addition of poultry manure and 
litter to manually-harvested fields at rates of 5 t ha-1 in the P soil. As there were about 4 kg 
Mg t-1 of fresh broiler house litter (Zublena et al., 1996), this additional source further 
contributed to the Mg pool of the P soil. The absence of significant effect with cultivation in 
the F soil shows that additions were sufficient to balance losses, whereas the significant drop 
in the H soil means that the Mg added in the filter mud was not sufficient to offset removal 
by crops and leaching losses. 
 
No change in K content was expected with the adoption of mechanized practices, since the 
same soil testing principle as for the manual treatment had been applied. This was true for the 
H, L and B soils, which had similar K contents in both manual and mechanized situations. 
The much lower K concentration in the F topsoil clearly indicates that K removal by the crop 
and leaching had not been adequately compensated for by fertilization. This difference could 
not therefore be attributed to mechanization per se. The much higher K content of the P soil 
under mechanized condition was probably due to rock-crushing and the application of filter 
mud and stillage slop by the estate upon land preparation. The in situ basalt dust produced 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 120 
with rock crushing contains about 0.57% K (D’Hotman de Villiers, 1947), while filter mud 
and stillage slop contain on average 0.017% K (Paturau, 1989) and 6.5 g K l-1 (Booth and 
Lightfoot, 1990) respectively. The major source of K in this case was most probably the 
stillage slop, applied at rates of 20 t ha-1 at planting. 
 
The significant increase in Ca with the adoption of mechanized practices in the P soil had the 
same likely causes as for the increase in K. The stillage slop which had been added contained 
on average 3.8 g Ca l-1 (Booth and Lightfoot, 1990), while filter mud contained between 0.6 
and 0.8% Ca (Paturau, 1989). A further source of Ca lies in the rock dust that was produced 
by crushing the stones in situ. Basalt dust of this type has been shown to contain some 6.6% 
Ca (D’Hotman de Villiers, 1947). These practices were not commonplace on other sugar 
estates, except the routine application of fresh filter mud at planting, and consequently the 
other soils studied did not show such an increase in Ca concentration. 
 
As with K and Ca, Mg levels increased significantly with the adoption of mechanized 
practices in the P soil. Large amounts of this exchangeable base had been applied to the soil 
during land preparation through stillage slop, containing on average 4.3 g Mg l-1 (Booth and 
Lightfoot, 1990), and composted filter mud. There was a further addition of Mg from the 
doleritic basalt dust produced by stone crushing, with some 6.9% Mg in the dust (D’Hotman 
de Villiers, 1947). Since there was no similar addition of Mg-containing material in the other 
soils, except through filter mud, the L, H, F and B soils had much less Mg than the P soil 
with the adoption of mechanized practices. 
 
 
 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 121 
6.3.3.2 Exchangeable bases and length of time during which sugar cane has been cropped 
manually 
 
The exchangeable base concentration of the L soil was not affected by the duration under 
which it had been under sugar cane cultivation (Figure 6.10). It therefore appears that 
removal of exchangeable bases by the plant or by leaching had been compensated for 
adequately in the L soil by addition of fertilizers and filter mud. On the other hand, the K and 
Mg concentration of the P soil increased with time, while its Ca concentration was not 
significantly affected. The initial K concentration in the virgin P topsoil was about 1.3 cmol  c
kg-1, it increased to 1.5 cmol  kg-1 c when the soil was initially cropped with sugar cane and it 
finally reached a value of 2.5 cmol  c kg
-1 in the soil cultivated for a long period with sugar 
cane. This upward tendency is a clear sign that there had been a slow build-up of K with time. 
This build-up in the P soil was probably the result of an excessive application of K in organic 
amendments. The same explanation is applicable to the increase with time of the Mg 
concentration. 
 
 
6.3.3.3 Exchangeable bases and length of time during which mechanized practices have 
been adopted 
 
The concentration of exchangeable bases in the P soil was lower in the fields where 
mechanized practices had been adopted for a long period than those with more recent 
mechanized practices (Figure 6.11). There had been an initial flush of K, Ca and Mg when 
the land was prepared for mechanization since substantial amounts of stillage slop and 
composted filter mud were applied to the soil, coupled with in situ rock crushing. Afterwards, 
the amount of bases declined as they were exported by the crop and lost by leaching, with 
little further addition to counter-balance these losses. 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 122 
P soil L soil
0.0 1.0 2.0 3.0 4.0 0.0 1.0 2.0 3.0 4.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1
K concentration (cmolc kg )
-1
K concentration (cmolc kg )
0 10 20 30 0 10 20 30
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1
Ca concentration (cmolc kg )
-1
Ca concentration (cmolc kg )
0 5 10 15 0 5 10 15
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-1 -1
Mg concentration (cmolc kg ) Mg concentration (cmolc kg )
Old (> 50 years) New (< 25 years) Old (> 50 years) New (< 25 years)
Figure 6.10 Effects of length of time under manual sugar cane cropping 
on potassium, calcium and magnesium concentrations of the two major 
soil groups in the sub-humid zone of Mauritius
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm) Soil depth (cm)
 123 
0.0 1.0 2.0 3.0 4.0
0.0
-10.0
-20.0
-30.0
-40.0
-50.0
-1
K concentration (cmolc kg )
0 10 20 30
0
-10
-20
-30
-40
-50
-1
Ca concentration (cmolc kg )
0 5 10 15
0
-10
-20
-30
-40
-50
-1
Mg concentration (cmolc kg )
Early (> 10 years) Recent (< 3 years)
Figure 6.11 Effects of length of time for which mechanized practices have been 
implemented on potassium, calcium and magnesium concentrations of P soil of 
Mauritius cropped with sugar cane
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm)Soil depth (cm)
 124 
 
6.3.4 Base saturation 
 
6.3.4.1 Effects of manual and mechanized sugar cane cropping practices on base 
saturation 
 
The base saturation of the soils under native vegetation mirrors what has been described for 
the exchangeable bases: a high value for the sub-humid L and P soils and a low value for the 
humid H and super-humid F soils (Figure 6.12), but not in the B soil. As discussed with 
respect to soil pH, data for the B soil under native vegetation were not reliable and could not 
be compared with the cropped situation. 
 
With the exception of the B soil, the base saturation generally increased with sugar cane 
cropping, but the rise was more noticeable in the subsoil. Thus, significant improvements in 
base saturation occurred in the L, P, H and F subsoil. There was generally no significant 
change in the topsoil. 
 
The base saturation changes caused by the adoption of mechanized practices did not seem to 
be related to rock content or climatic zone. There was very little change in the rock-free L and 
F soils, but the H soil was affected by mechanized practices as its base saturation fell in the 
subsoil. Positive effects occurred with mechanized practices in the P soil, where there was a 
significantly higher base saturation value in the topsoil. 
 
The higher base saturation associated with cropping in the subsoil of the L, P, H and F soils is 
a clear indication that the addition of bases through fertilizers and other forms of amendments 
has improved the conditions compared to the soil’s original status. Furthermore, since the 
amendments and fertilizers were most often applied to the soil surface, the accumulation of 
bases in the subsoil indicates that there has been a migration of these elements down the 
profile. The probable causes for such a downward movement were leaching with percolation 
and mixing through soil tillage. The lack of significant change in base saturation within the 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 125 
B soil P soil
0 30 60 90 120 150 0 30 60 90 120 150
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Base saturation (%) Base saturation (%)
F soil L soil
0 30 60 90 120 150 0 30 60 90 120 150
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Base saturation (%) Base saturation (%)
H soil
0 30 60 90 120 150
0
-10
Figure 6.12 Effects of manual and 
-20 mechanized sugar cane cropping 
-30 practices on base saturation (%) of the 
five major soil groups of Mauritius
-40
-50
Base saturation (%)
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm)
Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 126 
topsoil indicates that, in this zone, the removal of bases by the crop has been effectively 
counter-balanced by additions. 
 
The adoption of mechanized practices has had little effect on base saturation. The positive 
effects noted in the P topsoil were again associated with the heavy organic amendment under 
mechanized conditions at the sugar estate, especially the addition of large amounts of filter 
mud and stillage slop, and the practice of stone crushing. 
 
6.3.4.2 Base saturation and length of time during which sugar cane has been cropped 
manually 
 
The base saturation values were quite high in the sub-humid L and P soils, approaching 100% 
in some soil layers (Figure 6.13). There has been no significant change in base saturation 
brought about by the length of time under cropping in the two topsoils. However, base 
saturation increased significantly with time in the two subsoils. 
P soil L soil
0 30 60 90 120 150 0 30 60 90 120 150
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Base saturation (%) Base saturation (%)
Old (> 50 years) New (< 25 years) Old (> 50 years) New (< 25 years)
Figure 6.13 Effects of length of time under manual sugar cane cropping on base 
saturation (%) of the two major soil groups in the sub-humid zone of Mauritius
 
In spite of the general increase in CEC with time in the P soil, its base saturation still 
increased in the subsoil. This was essentially due to the high increase in K, and to a lesser 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
Soil depth (cm)
 127 
extent in Ca and Mg. There was thus an accumulation of bases with time in the subsoil that 
exceeded the parallel increase in CEC. As far as the L soil is concerned, CEC decreased with 
time only in the subsoil. In addition, its Ca, Mg and K concentration did not change with time 
in the whole profile. The net result was that its base saturation increased in the profile but the 
increase was significant only in the subsoil. 
 
 
6.3.4.3 Base saturation and length of time during which mechanized practices have been 
adopted 
 
Irrespective of the length of time under mechanized practices, the base saturation was high, 
even exceeding 100% in the topsoil of the recently-mechanized fields (Figure 6.14). As 
opposed to what was found with respect to time under cropping, the base saturation of the P 
soil decreased with time under mechanized conditions, the change being significant in the 
whole profile except the lower part of the subsoil. 
 
0 30 60 90 120 150
0
-10
-20
-30
-40
-50
Base saturation (%)
Early (> 10 years) Recent (< 3 years)
Figure 6.14 Effects of length of time for which mechanized practices have been 
implemented on base saturation (%) of P soil of Mauritius cropped with sugar cane
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
 128 
The very high base saturation values in the recently-mechanized fields demonstrate that there 
were large amounts of bases, essentially from the organic amendments added during land 
preparation. Thereafter, bases were lost from the topsoil through crop removal and leaching, 
leading to a decrease with time in the upper 30 cm. 
 
6.4 Conclusion 
 
The changes that occurred in the chemical properties of the major soils of Mauritius as a 
result of sugar cane cropping were in line with those occurring in their biological properties. 
The differences tended to be related to the climatic zone, since cultural practices that affect 
the soil’s chemistry, such as liming, vary depending on prevailing climatic conditions. As 
noted with respect to the biological properties of the soil, sugar cane cropping did not degrade 
the soil. In fact, the addition of agrochemicals and amendments often improved the soil, even 
though such additions did not always adequately compensate for the removal of nutrients by 
the crop or by natural agents such as water. The adoption of mechanized practices did not 
have a negative impact on most soil chemical properties. In fact, chemical properties were 
improved with mechanization in the P soil of Médine. The latter stands apart from the other 
sites as innovative soil treatments and amendments were used to negate the impact of land 
preparation and rock removal, leading to a better chemical status. 
 
With respect to time under cropping, the results indicate that the changes in chemical 
properties were not the same for the rock-free soil and the rocky one. Again, the innovative 
soil treatments and amendments at Médine have impacted positively on the chemistry of the 
rocky soil in the long term whereas there has been a general degradation with time in the 
rock-free soil. Under long-term mechanized practices, the situation was also one of inevitably 
lower soil chemical quality as a result of the policy of adding large amounts of chemical 
amendments to the soil at the time of land preparation to rapidly boost its quality, followed by 
a depletion of the bases with time, so that the soil became chemically poorer in the long-term. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 129 
CHAPTER 7 
 
INFLUENCE OF SUGAR CANE PRODUCTION ON SOME SOIL PHYSICAL 
PARAMETERS 
 
7.1 Introduction 
 
Industrial sugar cane production is not possible today without modern husbandry practices, 
particularly through the use of machines such as tractors and tillage implements for land 
preparation and harvesters for cane cutting. Machinery traffic is common within sugar cane 
fields and this, as expected, has affected the physical properties of the soil mainly through 
compaction (Ng Cheong et al., 1999), which led to an increase in bulk density and a 
reduction in soil porosity. There was previously little change in bulk density in the cane soils 
of Mauritius (Wong You Cheong and Chan, 1977) as cropping practices were exclusively 
manual. Compaction as a consequence of mechanization is consistent with what was found 
elsewhere (e.g. McLean, 1975; Wood, 1985; Van Antwerpen and Meyer, 1996). As would be 
expected, it was more pronounced in the sugar cane inter-row (McGarry et al., 1996, 
Hartemink, 1998b) where most compacting forces are applied to the soil. Moreover, 
compaction was also observed in the subsoil (Henry and Ellis, 1996), indicating that 
machinery traffic was not the only contributing factor. 
 
Besides compaction, the mechanized practices in sugar cane production could lead to the 
physical degradation of the soil surface, resulting in lower macro-porosity and permeability. 
As a result, the stabilized infiltration rate of a soil planted with sugar cane tended to be lower 
than that of a soil under native vegetation (Garside et al., 1997, Hartemink, 1998b). The 
adverse effect of traffic in this respect was further highlighted by observation that the 
stabilized infiltration rate in parts of sugar cane fields not subjected to traffic was no different 
from that of areas under native vegetation (Hartemink, 1998b). In Mauritius, stabilized 
infiltration rate was also much lower for sugar cane inter-rows subjected to harvester traffic 
compared to inter-rows that had been traffic-free (Ng Cheong et al., 1999). 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 130 
 
While the stabilized infiltration rate of water into the soil was undoubtedly reduced by the 
machinery traffic associated with sugar cane cultivation, there was no such clear-cut effect 
with respect to the soil’s plant available water. There could be significant increases (Van 
Antwerpen and Meyer, 1996), or significant decreases (Garside et al., 1997, McGarry and 
Bristow, 2001) or no difference at all (Masilaca et al., 1986, Henry and Ellis, 1996). As far as 
Mauritius is concerned, sugar cane cultivation had variable effects on this soil property 
(Wong You Cheong and Chan, 1977). In general, plant available water decreased with sugar 
cane cultivation in soils in dry areas, but increased for a soil in a wet area. These differences 
could have been caused by changes in soil texture. 
 
The effect of sugar cane cultivation on aggregate stability was more obvious. The evidence 
suggests that aggregates found close to the soil surface became less stable when soils were 
cropped with sugar cane, be it in Mauritius (Wong You Cheong and Chan, 1977) or 
elsewhere (McGarry et al., 1996). Furthermore, soil aggregates tended to become less stable 
the longer the soil was cultivated with sugar cane (Qongqo and Van Antwerpen, 2000). 
 
It appears on the other hand that sugar cane cultivation did not affect soil texture, given that 
the particle size distribution of sugar cane-planted soils did not differ greatly from that of 
soils under native vegetation in Australia and South Africa (McLean, 1975; Van Antwerpen 
and Meyer, 1996, McGarry and Bristow, 2001). This was not the case in Mauritius where 
sugar cane cropping led to significant, but opposing, effects on clay content in two zones with 
marked differences in rainfall and temperature (Wong You Cheong and Chan, 1977). 
However, no explanation was found to explain those differences. 
 
A review of the literature has thus shown that sugar cane production had mostly detrimental 
effects on soil physical properties in Mauritius and in other sugar cane producing countries. 
The main cause appeared to be in-field traffic, whose disrupting effects have impacted 
negatively on the soil’s matrix and porosity. The demands of modern agriculture necessitate 
the use of high inputs, particularly in terms of energy. The downside of this practice appears 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 131 
to be a physical degradation of the soil when this energy is applied on its surface. 
 
In this chapter, the effects of sugar cane cropping on some physical properties of the major 
soils of Mauritius are reported. The six indicators of physical quality were particle size 
distribution, aggregate size distribution and stability, bulk density, plant available water and 
stabilized water infiltration rate. The changes resulting from manual and mechanized sugar 
cane cropping on all five major soil groups are presented. In addition, the effects of time 
under manual and mechanized sugar cane cropping practices for selected soil groups are also 
dealt with. 
 
7.2 Procedure 
 
7.2.1. General 
 
Physical soil quality parameters under study were particle size distribution, aggregate size 
distribution, water stability of aggregates, bulk density, plant available water and stabilized 
infiltration rate. A complete description of the methodology used to determine these six 
parameters has been given in Chapter 4. 
 
All the measurements of physical soil quality parameters had required the removal of the 
non-soil fraction by sieving through a 2 mm mesh prior to analysis, except for the stabilized 
infiltration rate which was measured in situ. For particle size distribution, aggregate size 
distribution and water stability of aggregates, the results derived from the sieved material 
needed no further data manipulation since these three parameters were concerned solely per 
size fraction. On the other hand, the bulk density and plant available water parameters needed 
to be calculated on a bulk soil basis. In these two cases, the non-soil fraction had to be taken 
into account as gravel and cobbles occupied a certain proportion of the whole soil volume. As 
far as bulk density was concerned, a correction factor was already applied in the 
determination procedure, as described in Section 4.5.9. With respect to PAW, it has been 
assumed that though the stone fraction of the sample did not retain water, it occupied a given 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 132 
volume making it necessary to apply a correction factor. This volume of stones was taken to 
be the volume measured in the course of bulk density determination. Thus, in samples where 
stones were present, Equation 4.1 to calculate PAW was modified to Equation 7.1 to take into 
consideration the stone content of the bulk soil sample. 
 
PAW = 0.1 (FC – PWP) x BD x (1- stone content) x soil depth   (7.1) 
where PAW is plant available water in mm; FC is field capacity in % in gravimetric terms; 
PWP is permanent wilting point in % in gravimetric terms; BD is bulk density in g cm-3; 
stone content is a non-dimensional fraction; and soil depth is in cm. 
 
7.2.2 Data processing and analysis 
 
The same procedure as described in Section 5.2.2 has been adopted to calculate the average 
value of the measurements and their standard error, giving a single representative point per 
parameter encompassing all the variability of the result. 
 
7.2.3 Data presentation 
 
Particle size distribution differed substantially from the other physical parameters in that it is 
made up of relative proportions of sand, silt and clay, and was therefore expressed as relative 
percentages rather than absolute values. It was first represented as vertical bar charts for the 
total 50 cm of soil, calculated as a weighted average of the samples from the four different 
layers. It has also been presented as horizontal bar charts layer-wise, with the soil layer on the 
y-axis and particle size distribution on the x-axis. Given the nature of the graphs, it has not 
been possible to present the standard error with the average percentage values. For aggregate 
size distribution, water stability of aggregates and bulk density, the data have been displayed 
in a line graph, the evolution of each parameter with depth being shown on the x-axis with 
soil depth on the y-axis. The horizontal error bars showed the standard error at each data 
point. On the other hand, the plant available water and the stabilized infiltration rate have 
been displayed in the shape of vertical bar charts with vertical standard error bars. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 133 
7.3 Results and discussion 
 
7.3.1 Particle size distribution 
 
7.3.1.1 Effects of manual and mechanized sugar cane cropping practices on particle size 
distribution 
 
The evolution of the particle size distribution of the five major soil groups of Mauritius 
following sugar cane cropping and the adoption of mechanized practices are shown in Figures 
7.1 per bulk soil and in Figure 7.2 per soil layer. Average values with their standard errors are 
presented in Appendix 1. 
 
In general, the soils contained relatively high proportions of clay (Figure 7.1). In fact, they all 
had a texture that could be classified as silty clay according to the USDA system (Gee and 
Bauder, 1986), irrespective of treatment. The exceptions were the F soil, which was classified 
as clay loam in all treatments and the B soil under native vegetation, which also fell in this 
textural class. The L soil contained the highest, and the F soil the lowest, proportion of clay, 
some 70% and 30% respectively. The highest silt content, which was around 30%, was found 
in the F soil, which was the only one with almost equal proportions of the three particle sizes. 
The textural classes of the soil layers were similar to those of the bulk soil. There was no 
abrupt change in the relative proportions of the three particle sizes down the profile in all five 
soils (Figure 7.2). However, even though these changes were gradual, the trends were 
different depending on soil group. Thus, in the soils under native vegetation, there was a 
small increase in clay content down the profile for the P, L and H soils. The opposite was true 
for the F soil, while the texture of the B soil was uniform throughout the profile. 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 134 
B soil P soil
100% 100%
80% 80%
60% 60%
40% 40%
20% 20%
0% 0%
native manual mechanized native manual mechanized
F soil L soil
100% 100%
80% 80%
60% 60%
40% 40%
20% 20%
0% 0%
native manual mechanized native manual mechanized
H soil
100%
80%
60% Figure 7.1 Effects of manual and 
mechanized sugar cane cropping 
40% practices on particle size distribution of 
the five major soil groups of Mauritius 
20%
0%
native manual mechanized
sand silt clay
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 135 
Native Manual Mechanized
P soil
0 - 5 cm
5 - 15 cm
15 - 30 cm
30 - 50 cm
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
L soil
0 - 5 cm
5 - 15 cm
15 - 30 cm
30 - 50 cm
0% 20% 40% 60% 80% 100%
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
B soil
0 - 5 cm
5 - 15 cm
15 - 30 cm
30 - 50 cm
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
F soil
0 - 5 cm
5 - 15 cm
15 - 30 cm
30 - 50 cm
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
H soil
0 - 5 cm
5 - 15 cm
15 - 30 cm
30 - 50 cm
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
sand silt clay
Figure 7.2 Effects of manual and mechanized sugar cane cropping practices on particle size 
distribution of soil layers of the five major soil groups of Mauritius
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil layer Soil layer Soil layer Soil layer Soil layer
 136 
The effect of sugar cane cropping on particle size distribution was variable. In the bulk soil, it 
led to a marked increase in clay content and concomitant decrease in sand content in the B 
soil, but had an opposite effect on the P and L soils, whereas the F and H soils were not 
affected. Silt contents did not change with cropping, except for an increase in the L soil. The 
reduction in clay content that occurred within the bulk of the P and L soils was associated 
with a general reduction in all layers. In the B soil, the highly significant increase in clay 
content noted in the bulk soil also reflected itself in all layers but the change was more 
pronounced in the deeper layers. In the F and H soils, there were small, but sometimes 
statistically significant, variations in texture across the soil layers, with a certain degree of 
clay enrichment in the deeper layers of both soils. 
 
Effects of mechanized practices on particle size distribution were also variable. There was a 
slight increase in clay content and decrease in sand content with mechanization in the B and 
L soils, and a similar, but more pronounced, effect on the P soil. No difference was noted 
with the F soil, but there was a marked decrease in clay content in the H soil, with a 
simultaneous increase in both silt and sand contents. Layer-wise, clay content increased in a 
regular way across the profile of the P soil. Similarly, there was a small but regular increase 
in clay content and decrease in sand content throughout the profile of the B and L soils. As 
with bulk soil, the layers of F soil were not affected. However, the marked decrease in clay 
and increase in silt and sand contents in the H soil were more pronounced in the deeper 
layers. 
 
The reduction in clay content in the sub-humid P and L soils as a result of sugar cane 
cropping could have been caused by wind erosion of the fine-textured material when the soil 
was left bare and dry after harvest, particularly if residues were burnt (Brye, 2003). The other 
possible explanation is associated with intensive irrigation under cropped conditions, which 
could lead to preferential clay loss in surface eroded sediments (Lal, 1976). The fact that this 
reduction in clay particles was more important in the lower horizons probably showed the 
effects of tillage, with clay being brought up from the lower horizons into the upper ones, 
where it became more susceptible to the loss process described. Furthermore, the increase in 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 137 
clay content associated with mechanized practices in both soils of the sub-humid zone 
indicates that there was a beneficial effect from the trash blanketing that resulted from 
mechanized harvest. This protective trash blanket has shielded the soil surface against the 
loss of fine material, directly by its covering effect, and indirectly by preserving soil moisture. 
Clay increase associated with mechanized practices in the B soil was probably caused by the 
production of particles of smaller size fractions from larger ones as a result of physical 
breakdown from repeated mechanical disturbance (Brye, 2003) whereas clay decrease in the 
H soil could have been caused by its illuviation down the profile (Lal, 1997). 
 
 
7.3.1.2 Particle size distribution and length of time during which sugar cane has been 
cropped manually 
 
The effects of length of time under cultivation on the particle size distribution of the two 
major soil groups of the sub-humid zone of Mauritius are shown in Figure 7.3 for the bulk 
soils and Figure 7.4 for the soil layers. The clay content in the P soil decreased and its sand 
content increased significantly with time, while the opposite trend was observed for the L 
soil, but without any significant difference. The proportion of silt remained unchanged for 
both soils. Layer-wise, the same trends have been noted. Thus, the texture of the L soil was 
not affected by time under cultivation while the P soil accumulated more coarse particles with 
time at the expense of the finer ones. As sugar cane cultivation itself has already been shown 
to significantly reduce clay content in both sub-humid soils (Figure 7.1), it can be concluded 
that the process leading to loss of clay took place in the P soil when native vegetation was 
replaced by sugar cane. However, the loss was a slow process as indicated by the similar clay 
percentage in the soil cultivated for less than 25 years. The processes involved in this gradual 
loss of clay have already been discussed in the preceding Section. 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 138 
P soil L soil 
100% 100%
80% 80%
60% 60%
40% 40%
20% 20%
0% 0%
Old (> 50 years) New (< 25 years) Old (> 50 years) New (< 25 years)
sand silt clay sand silt clay
Figure 7.3 Effects of length of time under manual sugar cane cropping on particle size 
distribution of the two major soil groups in the sub-humid zone of Mauritius
 
Old (> 50 years) New (< 25 years)
0 - 5 cm
5 - 15 cm
P soil 
15 - 30 cm
30 - 50 cm
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
0 - 5 cm
5 - 15 cm
L soil 
15 - 30 cm
30 - 50 cm
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
sand silt clay sand silt clay
Figure 7.4 Effects of length of time under manual sugar cane cropping on particle size distribution 
of soil layers of the two major soil groups in the sub-humid zone of Mauritius
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil layer
Soil layer
 139 
 
 
7.3.1.3 Particle size distribution and length of time during which mechanized practices 
have been adopted 
 
The effects of time under mechanized practices on the particle size distribution of the P soil 
are shown in Figure 7.5 for the bulk soil and Figure 7.6 for individual soil layers. Overall, 
clay content decreased with time while sand content increased and silt content remained 
unchanged. However, only the increase in the sand fraction was significant. The relatively 
insignificant nature of the changes has been further confirmed by the measurements from 
individual soil layers, where a slight decrease in clay and increase in sand fraction were found 
in all soil layers, but these differences were not significant. There has therefore been little 
change in soil texture with time with mechanized operations. 
 
100%
80%
60%
40%
20%
0%
Early (> 10 years) Recent (< 3 years)
sand silt clay
Figure 7.5 Effects of length of time for which mechanized practices have been implemented 
on particle size distribution of P soil of Mauritius cropped with sugar cane
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 140 
 
 
Early (> 10 years) Recent (< 3 years)
0 - 5 cm
5 - 15 cm
15 - 30 cm
30 - 50 cm
0% 20% 40% 60% 80% 100% 0% 20% 40% 60% 80% 100%
sand silt clay sand silt clay
Figure 7.6 Effects of length of time for which mechanized practices have been implemented on  
particle size distribution of soil layers of P soil of Mauritius cropped with sugar cane
 
 
7.3.2 Aggregate size distribution 
 
7.3.2.1 Effects of manual and mechanized sugar cane cropping practices on aggregate size 
distribution 
 
Under native vegetation, the size of aggregates in the sub-humid L and P soils increased with 
depth. The geometric mean diameter (GMD) values increased from 0.8 mm in the topsoil to 
1.1 and 1.3 mm in the subsoil of the L and P soils respectively (Figure 7.7). These aggregates 
were smaller than those of the H and F soils, the latter having a relatively constant average 
GMD of some 1.5 mm. The B soil had intermediate aggregate sizes, its GMD decreasing 
from 1.5 mm in the topsoil to 1.0 mm in the subsoil. As opposed to the sub-humid L and P 
soils, the aggregates from the wetter areas tended to become smaller down the profile, this 
evolution being more pronounced in the B than the F or H soils. 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil layer
 141 
B soil P soil
0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
GMD (mm) GMD (mm)
F soil L soil
0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
GMD (mm) GMD (mm)
H soil
0.0 0.5 1.0 1.5 2.0 2.5
0
-10
-20
-30
Figure 7.7 Effects of manual and mechanized 
sugar cane cropping practices on aggregate size 
-40
distribution (geometric mean diameter in mm) 
-50 of the five major soil groups of Mauritius
GMD (mm)
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 142 
 
Changes in aggregate size distribution as a result of sugar cane cropping were not consistent 
in all soils. Cropping led to aggregates of higher GMD in the sub-humid soils and to 
aggregates of lower GMD in the H and F soils while the GMD of the aggregates in the B soil 
evolved differently going down the profile. The greatest change occurred in the P soil where 
the GMD increased significantly across the profile by some 50% when it was cropped with 
sugar cane. The increase to a much smaller extent was also significant in the L topsoil. On the 
other hand, there were relatively small but significant drops in aggregate size in the F and H 
topsoil. Finally, cropping significantly decreased aggregate size in the B topsoil, but increased 
it significantly deeper in the profile. 
 
The adoption of mechanized practices led to variable changes in aggregate size distribution. 
Thus, higher GMD values were found in the topsoil in the mechanized treatments of both P 
and B soils, but there was no significant effect deeper in the profile. On the other hand, there 
was a significant decrease in GMD in the whole soil profile for the L and H soils. As for the 
F soil, the trend was for an increased aggregate size distribution. 
 
No reported work of the effects of sugar cane cropping on aggregate size distribution was 
found in the literature because it is difficult to relate aggregate size to field phenomena, most 
investigators preferring to use aggregate stability rather than aggregate size distribution as an 
index of soil structure in the field (Kemper and Rosenau, 1986). Nevertheless, the 
simultaneous determination of these two parameters was desirable to provide a more 
complete picture of the soil structure. In the present study, sub-humid L and P soils that were 
cropped with sugar cane using manual practices had larger aggregates than the same soils 
under native vegetation. Apart from the usual cultural practices associated with cultivation, 
i.e. tillage, fertilization and crop protection measures, the main difference between virgin and 
cultivated soils in the sub-humid L and P soils was the provision of irrigation. Without 
irrigation, sugar cane could not be profitably produced in the sub-humid zone, as lack of 
water is the main obstacle to plant growth. Irrigation is therefore a pre-requisite for rendering 
the L and P soils suitable for sugar cane production (Arlidge, 1973). With irrigation, there has 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 143 
been an increased production of plant biomass, and in the case of sugar cane, the combined 
effect of cane roots and residue return must have promoted the formation of larger 
aggregates. Roots enmesh and realign soil particles, release exudates, and aggregation is 
enhanced with the increasing root length density, microbial associations and ground cover 
(Bronick and Lal, 2005). In contrast to the irrigated soils of the sub-humid zones, the humid 
H and the super-humid F and B soils had a naturally high plant cover under native vegetation, 
thanks to the high rainfall prevailing in those regions. Sugar cane cultivation was therefore 
unlikely to have produced substantially more roots or residues than the amount already 
present under natural conditions. This was substantiated by the higher OM content under 
native vegetation in those soils (Figure 5.1). One would not therefore expect to note an 
increase in aggregate size in those soils. In fact, aggregates were relatively smaller with sugar 
cane cropping in the top 30 cm of the H and F soils, probably because they had been broken 
by soil tillage within this zone and were left exposed to the vagaries of weather. A regular 
wetting and drying cycle occurs under natural conditions in these regions and this wet-dry 
cycle has probably led to disruption of the aggregates as reported by Singer et al. (1992). 
 
With respect to the adoption of mechanized practices, it appeared that, irrespective of 
climatic zones, rock content played a part in changes of aggregate size distribution as the 
rocky P and B soils were affected in very similar ways. There was no significant difference in 
their subsoil but aggregates were bigger following mechanization in their topsoil, presumably 
on account of superficial soil consolidation with harvester traffic. For the rock-free L and H 
soils, the presence of smaller aggregates when mechanized practices were adopted could be 
ascribed to aggregate degradation caused by harvester and in-field loader traffic, exacerbated 
by a significant fall in OM content. For the F soil, the increased aggregate size with 
mechanization was probably due to the increase in OC content within the topsoil of this 
treatment compared to the manually cropped soil (Figure 5.1). 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 144 
7.3.2.2 Aggregate size distribution and length of time during which sugar cane has been 
cropped manually 
 
The aggregates of the P soil were much larger than those of the L soil, irrespective of time 
under cultivation (Figure 7.8). Aggregates became smaller the longer the soils had been under 
sugar cane cultivation. This change was not significant in both topsoil, but became significant 
in the subsoil. 
P soil L soil 
0.0 0.5 1.0 1.5 2.0 2.5 0.0 0.5 1.0 1.5 2.0 2.5
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
GMD (mm) GMD (mm)
Old (> 50 years) New (< 25 years) Old (> 50 years) New (< 25 years)
Figure 7.8 Effects of length of time under manual sugar cane cropping on aggregate size distribution 
(geometric mean diameter in mm) of the two major soil groups in the sub-humid zone of Mauritius
 
 
7.3.2.3 Aggregate size distribution and length of time during which mechanized practices 
have been adopted 
 
The P soil where mechanized practices had recently been implemented had aggregates of 
lower GMD than the soil where mechanization had been adopted for a longer period (Figure 
7.9). However, the changes in aggregate size distribution were not significant. It is therefore 
clear that, as with time under cropping, it does not matter how long the P soil has been under 
mechanized practices, as its aggregate size distribution would be unaffected. 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
Soil depth (cm)
 145 
0.0 0.5 1.0 1.5 2.0 2.5
0
-10
-20
-30
-40
-50
GMD (mm)
Early (> 10 years) Recent (< 3 years)
Figure 7.9 Effects of length of time for which mechanized practices have been 
implemented on aggregate size distribution (geometric mean diameter in mm) of P 
soil of Mauritius cropped with sugar cane
 
 
7.3.3 Water stability of aggregates 
 
7.3.3.1 Effects of manual and mechanized sugar cane cropping practices on the water 
stability of aggregates 
 
The index for water stability of aggregates ranges from 0 to 1. A zero value indicates total 
aggregate breakdown when flooded, while an index of 1 refers to the aggregate remaining 
completely stable in water. Under native vegetation, the aggregate stability index of the sub-
humid L and P soils was much lower than that of the humid H and super-humid F and B 
soils. Thus, for the P and L soils, the peak index value was of the order of 0.6 and 0.7 
respectively, compared to about 1.0 for the other three soils (Figure 7.10). In addition, their 
aggregate stability decreased with depth, values as low as 0.2 being noted for the P and L 
subsoil. On the other hand, the stability index of the super-humid B and F soils stayed 
constant at about 1.0 for the whole profile. The humid H soil resembled the sub-humid soils 
in that it displayed a gradual decrease in stability index down the profile. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) 
 146 
B soil P soil
0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Aggregate stability index Aggregate stability index
F soil L soil
0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Aggregate stability index
Aggregate stability index
H soil
0.0 0.5 1.0 1.5 2.0
0
-10
-20
Figure 7.10 Effects of manual and 
-30
mechanized sugar cane cropping 
-40 practices on  aggregate stability index of 
the five major soil groups of Mauritius
-50
Aggregate stability index
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 147 
When sugar cane was planted, the only significant effect was an increase in aggregate 
stability in the P, L, B and H subsoil. The F soil was the only one to be affected negatively by 
cultivation, with significant decreases in stability index in parts of the topsoil and the subsoil. 
 
With the adoption of mechanized practices, the stability index of the P soil was not 
significantly affected whereas that of the L soil was significantly reduced in most of the soil 
profile. There was also a general trend towards lower stability in the B soil with the adoption 
of mechanized practices, but this decrease was significant only in the subsoil. The opposite 
was true for the F and H soils, where the general trend was for a higher stability index, with a 
significant increase in the subsoil. 
 
As reviewed by Bronick and Lal (2005), aggregate stability can be used as an indicator of soil 
structure. Aggregation results from flocculation, cementation and rearrangement of particles. 
It is mediated by soil organic carbon, biota, ionic bridging, clay and carbonates. As far as 
sugar cane is concerned, the evidence from the literature is that aggregate stability of the soils 
decreased with long-term cultivation as a consequence of their declining organic matter 
content (Wong You Cheong and Chan, 1977; Qongqo and Van Antwerpen, 2000; Dominy et 
al., 2001). The results from this study contradict these literature findings since aggregate 
stability did not seem to be susceptible to changes upon cultivation. On the contrary, 
aggregate stability tended to increase, as were the case in the subsoil of the P, L, B and H 
soils. This enhancing effect could be ascribed to the fact that, with soil tillage, OM tended to 
be incorporated deeper in the profile (Figure 5.1), thereby increasing the stability of the 
aggregates in the lower layers. On the other hand, the significant decrease noted in the F soil 
could be ascribed to a marked decline in OM in its topsoil, but no such OM depletion was 
observed to explain the lower stability of its subsoil. In this instance, the decrease in stability 
had to be ascribed to a different cause, such as the action of cultivation impacting on 
aggregate stability by breaking up aggregates via roots and fungal hyphae and by direct 
shattering of aggregates. It must also be remembered that organic carbon is not the only 
element influencing aggregate stability, as demonstrated by Blair (2000). 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 148 
The adoption of mechanized practices had relatively small effects on aggregate stability, apart 
in the L soil where the topsoil was degraded. Of all the soils of Mauritius, this soil group had 
the lowest OM content, which was further reduced with mechanization. It is possible that its 
OM content had fallen below a critical threshold beyond which stability was impaired, 
whereas in the other soils, a sufficiently high OM content persisted to maintain their 
aggregate stability. Added to this SOM factor was the additional stress created by the passes 
of harvesters and associated traffic. 
 
7.3.3.2 Water stability of aggregates and length of time during which sugar cane has been 
cropped manually 
 
Even though aggregate stability values remained relatively low, the length of time under 
sugar cane cropping clearly led to a higher stability index in the sub-humid zone (Figure 
7.11). 
 
P soil L soil
0.0 0.5 1.0 1.5 2.0 0.0 0.5 1.0 1.5 2.0
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
Aggregate stability index Aggregate stability index
Old (> 50 years) New (< 25 years) Old (> 50 years) New (< 25 years)
Figure 7.11 Effects of length of time under manual sugar cane cropping on aggregate 
stability index of the two major soil groups in the sub-humid zone of Mauritius
 
 
Both P and L soils displayed higher stability values near the surface of the old cultivated 
treatment, which had been under cane for more than 50 years. The increase with time was 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
Soil depth (cm)
 149 
significant in part of the P topsoil and its subsoil, and in part of the L topsoil. Such changes 
could be directly related to the OM content of the respective layers in the two soils, since the 
old cultivated treatments had a higher OC content in the topsoil of both P and L soils, while 
the P soil also had a higher content in its subsoil, compared to the new fields, which had been 
under cane for less than 25 years (Figure 5.4). 
 
 
7.3.3.3 Water stability of aggregates and length of time during which mechanized practices 
have been adopted 
 
The aggregate stability index of the P soil irrespective of depth was not significantly affected 
by the number of years during which mechanized operations had been practised (Figure 7.12). 
0.0 0.5 1.0 1.5 2.0
0
-10
-20
-30
-40
-50
Aggregate stability index
Early (>10 years) Recent (<3 years)
Figure 7.12 Effects of length of time for which mechanized practices have been 
implemented on aggregate stability index of P soil of Mauritius cropped with sugar cane
 
 
 
However, there was a trend whereby the aggregate stability decreased in the deeper horizons, 
mirroring a similar decline in SOM (Figure 5.5). 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
 150 
7.3.4 Bulk density 
 
7.3.4.1 Effects of manual and mechanized sugar cane cropping practices on bulk density 
 
In general, all the soils were more compact with increasing depth under native vegetation 
(Figure 7.13). There was a marked increase in topsoil bulk density, below which bulk density 
values tended to be relatively constant. Values were relatively low, as would be expected 
with silty clay soils, and did not exceed 1.3 g cm-3. The rocky soils had a lower bulk density 
than the rock-free ones. The bulk density of the B soil ranged from 0.6 to 0.8 g cm-3, while 
that of the P soil ranged from 0.9 to 1.0 g cm-3. In contrast, the value for the F soil ranged 
from 0.8 to 1.2 g cm-3, while that of the L soil lay between 1.0 and 1.3 g cm-3. 
 
The changes in bulk density induced by cropping were variable and seemed to be influenced 
by rock content. In the rocky P and B soils, the general trend was for a higher bulk density 
with cultivation, i.e. soil compaction. Thus, in the P soil, bulk density increased significantly 
in the subsoil. The compaction was even more pronounced in the B soil where there was a 
significant increase in bulk density down the profile. The extent of compaction was much 
higher than in the P soil, with maximum bulk density increases of the order of 0.4 g cm-3, 
while the corresponding maximum increase in the P soil did not exceed 0.2 g cm-3. For the 
rock-free L soil, the trend was for loosening in part of the topsoil and of the subsoil. The F 
soil, for its part, displayed both compacting and loosening effects with sugar cane cropping. 
Indeed, while there were significant increases in bulk density in the topsoil, significant bulk 
density decreases were noted in the subsoil. The H soil was similar to the rocky P soil, with 
no change in bulk density in the topsoil, but significant compaction deeper in the profile. 
 
Adopting mechanized practices led to compaction in the whole profile of the H soil. The P 
soil was also compacted, even though a significant increase in bulk density was noted only in 
the topsoil. For the super-humid B and F soils, the general trend was for a lower bulk density 
with mechanized operations in the subsoil, while the topsoil was not affected. The effects of 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 151 
B soil P soil
0.40 0.60 0.80 1.00 1.20 1.40 0.40 0.60 0.80 1.00 1.20 1.40
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-3
Bulk density (g cm ) -3Bulk density (g cm )
F soil L soil
0.40 0.60 0.80 1.00 1.20 1.40 0.40 0.60 0.80 1.00 1.20 1.40
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-3 -3
Bulk density (g cm ) Bulk density (g cm )
H soil
0.40 0.60 0.80 1.00 1.20 1.40
0
-10
-20 Figure 7.13 Effects of manual and 
mechanized sugar cane cropping 
-30
practices on bulk density of the five 
-40 major soil groups of Mauritius
-50
-3
Bulk density (g cm )
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm) Soil depth (cm) Soil depth (cm)
Soil depth (cm) Soil depth (cm)
 152 
mechanized practices on the L soil were not uniform, as bulk density was significantly higher 
in the topsoil, but lower in the deeper layers. 
 
Soil compaction is the process by which soil grains are rearranged to decrease void space and 
to bring them into closer contact with one another, thereby increasing the bulk density. As 
reviewed by Hamza and Anderson (2005), bulk density is the most frequently used parameter 
to characterize the state of soil compactness. With respect to sugar cane cultivation, the 
available evidence was that soils were compacted when they were cropped with sugar cane 
(e.g. Wood, 1985; Van Antwerpen and Meyer, 1996), the main cause being the pressure 
applied to the soil upon traffic by wheeled farm machines. This process was probably the 
main cause of compaction in the P, B and H soils. Tillage has also been identified as another 
possible cause for subsoil compaction, with more significant effects if the soil was tilled 
under wet conditions (Hamza and Anderson, 2005). The lower bulk density in some subsoil 
layers of the rock-free L and F soils upon sugar cane cultivation was probably due to the use 
of subsoilers and other soil loosening equipment at the time of land preparation, a practice 
that was more difficult to implement in the rocky P and B soils. 
 
The effects of mechanized practices on soil bulk density corresponded to observations from 
other sugar cane producing countries, namely that the introduction of mechanized harvesting 
has led to topsoil compaction. The fact that compaction occurred with mechanized harvesting 
down to a depth of about 20 cm, beyond which the soil remained relatively unscathed, had 
already been noted in Mauritius (Ng Cheong et al., 1999). This topsoil compaction was 
related to the contact pressure applied to the ground by the axles of the harvesters and their 
accompanying sugar cane bins, which got more and more loaded as harvest progressed. On 
the other hand, the subsoil loosening in the rock-free L and F soils was probably caused by 
subsoiling, as additional subsoiler passes were often made in mechanically-harvested fields to 
alleviate any perceived compaction. 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 153 
7.3.4.2 Bulk density and length of time during which sugar cane has been cropped 
manually 
 
In the rock-free L soil, the bulk density decreased the longer the field has been under cane 
cropping (Figure 7.14). This significant loosening effect as a function of time occurred 
throughout the whole profile. Possible causes for this decrease could be physical, e.g. 
enhanced wetting and drying because of intensive irrigation, or biological, e.g. increased 
earthworm activity and root growth thanks to wetter soil conditions. However, it is more 
likely that it was caused by human intervention. Indeed, bulk density decreased in this soil on 
account of tillage when native vegetation was replaced by the sugar cane crop. The 
cumulative effects of tillage over time probably resulted in a lower bulk density in the older 
cultivated fields. On the other hand, there was no effect of time in the rocky P soil, whose 
bulk density remained very similar irrespective of the length of time it had been under sugar 
cane cultivation. The presence of rocks in the profile of the P soil was the probable cause for 
this unchanged situation, as only mild loosening work was possible to alleviate compaction 
under such conditions. 
 
P soil L soil 
0.40 0.60 0.80 1.00 1.20 1.40 0.40 0.60 0.80 1.00 1.20 1.40
0 0
-10 -10
-20 -20
-30 -30
-40 -40
-50 -50
-3
Bulk density (g cm ) -3Bulk density (g cm )
Old (> 50 years) New (< 25 years) Old (> 50 years) New (< 25 years)
Figure 7.14 Effects of length of time under manual sugar cane cropping on bulk 
density of the two major soil groups in the sub-humid zone of Mauritius
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
Soil depth (cm)
 154 
 
7.3.4.3 Bulk density and length of time during which mechanized practices have been 
adopted 
 
The bulk density of the P soil was not significantly affected, whether mechanized practices 
had been adopted in the long-term or only recently (Figure 7.15). However, the trend was for 
the subsoil to be more compact with time. This lack of significant effect on bulk density is 
similar to what was noted when fields under long-term cropping were compared to those 
under recent cropping. It therefore appears that the effects of cropping or mechanization on 
bulk density expressed themselves at an early stage in the P soil and an equilibrium had been 
rapidly reached, so that bulk density no longer changed significantly with time. 
 
0.40 0.60 0.80 1.00 1.20 1.40
0
-10
-20
-30
-40
-50
-3
Bulk density (g cm )
Early (> 10 years) Recent (< 3 years)
Figure 7.15 Effects of length of time for which mechanized practices have been 
implemented on bulk density of P soil of Mauritius cropped with sugar cane
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Soil depth (cm)
 155 
7.3.5 Plant available water 
 
7.3.5.1 Effects of manual and mechanized sugar cane cropping practices on plant 
available water 
 
Under native vegetation, the plant available water (PAW) of the soils of Mauritius varied 
between 40 and 60 mm for the top 50 cm layer (Figure 7.16). The highest values were found 
in the rock-free L and F soils, where some 55 mm of water were available, compared to about 
45 mm for the rocky P and B soils and the rock-free H soil. 
 
The effects of sugar cane cropping on PAW were variable. Thus, PAW values were 
significantly higher when P soil was cropped by sugar cane than when under native 
vegetation, were similar in the L and B soils, and were significantly lower in the F and H 
soils. The adoption of mechanized practices either had no significant effect, as in the B, F and 
L soils, or led to an increase in PAW as in the P and H soils. 
 
Klute (1986) has reviewed factors affecting water retention, this parameter being dependent 
on two major soil properties, namely texture or particle-size distribution of the soil, and 
structure or arrangement of the particles. Organic matter has also been identified as playing a 
role in determining PAW, either directly through its hydrophylic nature, or indirectly as a 
result of structure modification. In Mauritius, there was another factor that needed to be 
considered, namely the rock content of the soil. Thus, upon derocking and land preparation 
prior to cropping, a higher volume of soil material became available within the profile. It is 
therefore not surprising that the P soil had a higher PAW when cropped with sugar cane than 
when it was under native vegetation. In the case of the F and H soils, where no derocking has 
taken place, the decrease in PAW associated with sugar cane cropping could be ascribed to 
the decline in aggregate size and lower SOM content in the top layers (Figures 7.7 and 5.1). 
 
As expected, there was a further increase in PAW in the P soil when mechanized treatment 
was adopted, given that further derocking had been undertaken prior to the introduction of 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 156 
B soil P soil
80 80
60 60
40 40
20 20
0 0
Native Manual Mechanized Native Manual Mechanized
F soil L soil
80 80
60 60
40 40
20 20
0 0
Native Manual Mechanized Native Manual Mechanized
H soil
80
60
Figure 7.16 Effects of manual and 
40 mechanized sugar cane cropping 
practices on plant available water 
20 (mm of water in 50 cm soil) of the 
five major soil groups of Mauritius
0
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
PAW (mm) PAW (mm) PAW (mm)
PAW (mm) PAW (mm)
 157 
mechanized harvesters. The fact that PAW also increased in the H soil with the adoption of 
mechanized practices could be ascribed to the higher bulk density upon the soil compaction 
introduced by mechanization. The effect of compaction on a soil is to decrease its total 
porosity, particularly the volume of the existing large inter-aggregate pores (Hillel, 1980). On 
the other hand, the total volume of intermediate size pores would tend to increase in a 
compact soil since some of the originally large pores have been squeezed down to this size by 
compaction, while the intra-aggregate pores remain unaffected. The net effect would 
therefore be to increase the total volume of pores that retain water at the expense of those that 
conduct water, hence the higher PAW under mechanized conditions. 
 
7.3.5.2 Plant available water and length of time during which sugar cane has been cropped 
manually 
 
The trend was for recently cultivated fields to have a higher PAW than those that have been 
under cultivation for a longer period (Figure 7.17). However, this PAW decrease with time 
was significant only in the rock free L soil. This difference could again be explained by the 
fact that a higher bulk density in the newly cultivated L soil led to a higher volume of water-
retaining pores (Figure 7.14). Similarly, the lack of effect on bulk density explains why PAW 
remained unchanged in the P soil. 
80
60
40
20
0
Old (> 50 New (< 25 Old (> 50 New (< 25
years) years) years) years)
P soil L soil
Figure 7.17 Effects of length of time under manual sugar cane cropping on plant available water 
(mm of water in 50 cm soil ) of the two major soil groups in the sub-humid zone of Mauritius
Effects of sugar cane production practices on soil qual ity in Mauritius 
PAW (mm)
 158 
 
7.3.5.3 Plant available water and length of time during which mechanized practices have 
been adopted 
 
The PAW of the P soil was lowered when mechanized practices have been adopted over a 
long period (Figure 7.18). Compaction was not the reason for the decrease in PAW. In this 
case, the recently mechanized fields had much higher clay contents than the fields where 
mechanized operations had been adopted earlier. The reverse was however true for aggregate 
size. In fact, the most plausible explanation for the much higher PAW of the recently 
mechanized fields lay in their much higher SOM content, as a result of the practice of 
applying large amounts of organic matter, particularly compost, when fields had undergone 
extensive land preparation for mechanization. 
 
 
80
60
40
20
0
Early (> 10 years) Recent (< 3 years)
Figure 7.18 Effects of length of time for which mechanized practices have been 
implemented on plant available water (mm of water in 50 cm soil) of P soil of 
Mauritius cropped with sugar cane
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
PAW (mm)
 159 
7.3.6 Stabilized infiltration rate 
 
7.3.6.1 Effects of manual and mechanized sugar cane cropping practices on stabilized 
infiltration rate 
 
In general, the stabilized infiltration rate of the soils was relatively high under native 
vegetation, exceeding 100 mm h-1 in all of them (Figure 7.19). The infiltration rates in the 
sub-humid L and P soils were actually lower than that of the humid H soil, while the super-
humid F and B soils were the most permeable. 
 
With sugar cane cropping, the stabilized infiltration rate of the sub-humid L and P soils 
increased significantly to more than double their original value. On the other hand, the rate 
for the cultivated soils from the humid and super-humid zones, i.e. the H, F and B soils, were 
significantly lower than those of the virgin soil. Finally, there was no ambiguity concerning 
the effects of mechanized practices on the infiltration rates of the soils: there was a significant 
decrease in stabilized infiltration rate in all five soils when shifting from manual to 
mechanized conditions. 
 
As noted by Hartemink (1998b), it was not the presence of sugar cane which had a direct 
effect on infiltration rate, but rather the traffic associated with the crop, particularly the 
mechanized cultural operations, such as fertilizer and herbicide applications. If such 
operations were conducted under wet soil conditions, various phenomena such as 
compaction, surface crusting and other forms of physical deterioration were liable to happen 
and impact negatively on stabilized infiltration rate. The decrease in infiltration rate that was 
associated with sugar cane cropping in Mauritius was found only in soils in the humid and 
super-humid zones, where cultural operations were frequently undertaken under wet 
conditions. In contrast, there was no such decreasing effect in the two soils of the sub-humid 
zone, which were subjected to traffic under drier conditions and in fact, sugar cane cropping 
actually increased stabilized infiltration rate in these two soils. A possible cause for this 
increase was that there were more roots and associated soil macro-fauna in the sugar cane 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 160 
B soil P soil
400
400
300 300
200 200
100 100
0 0
Native Manual Mechanized Native Manual Mechanized
F soil L soil
400
400
300
300
200
200
100
100
0
0
Native Manual Mechanized
Native Manual Mechanized
H soil
400
300 Figure 7.19 Effects of manual and 
mechanized sugar cane cropping 
practices on stabilized infiltration rate of 
200
the five major soil groups of Mauritius
100
0
Native Manual Mechanized
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Infiltration rate (mm/h)
Infiltration rate (mm/h) Infiltration rate (mm/h)
Infiltration rate (mm/h)
Infiltration rate (mm/h)
 161 
cultivated soils thanks to the input of irrigation, giving rise to more numerous large inter-
aggregate pores, as shown by the decrease in bulk density in the topsoil of the L and P soils 
caused by sugar cane cropping. This increased macro-porosity was obviously favourable to 
surface infiltration of water, since the largest pores were the most conductive as demonstrated 
by Poiseuille’s law (Hillel, 1980). 
 
On the other hand, the traffic associated with harvesting had already been shown to lead to 
topsoil compaction in all soil groups because of the high axle loads of both harvesters and in-
field cane bins. In this case, the total porosity was reduced when a proportion of the existing 
macro-pores was converted to micro-pores under the compressing forces. As the stabilized 
infiltration rate depends on the number of macro-pores in the soil, the topsoil compaction was 
bound to reduce its water intake capacity. Thus, the decrease in infiltration rate with 
mechanized harvest in all soils was related to the increase in bulk density within the topsoil, 
particularly in the 0 – 5 cm layer. 
 
 
7.3.6.2 Stabilized infiltration rate and length of time during which sugar cane has been 
cropped manually 
 
Fields that had been cultivated for a longer period had a higher stabilized infiltration rate than 
fields recently planted with sugar cane (Figure 7.20). However, while the increase in 
infiltration rate was not significant in the rocky P soil, the difference was large enough to be 
significant in the rock-free L soil. In both cases, the stabilized infiltration rate of the recently 
cultivated fields was also higher than that of the virgin fields. There has thus been a gradual 
improvement in this parameter from the moment sugar cane was introduced. This positive 
effect of cultivation on infiltration rate was probably induced by the build-up with time of 
macro-pores from roots and activities of the soil meso- and macro-fauna, such as earthworms. 
In the L soil, it could also be related to the decrease in bulk density that occurred when sugar 
cane had been cultivated for a longer period. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 162 
400
300
200
100
0
Old (> 50 New (< 25 Old (> 50 New (< 25
years) years) years) years)
P soil L soil
Figure 7.20 Effects of length of time under manual sugar cane cropping on stabilized 
infiltration rate of the two major soil groups in the sub-humid zone of Mauritius
 
 
 
 
 
7.3.6.3 Stabilized infiltration rate and length of time during which mechanized practices 
have been adopted 
 
The duration of P soil exposure to mechanized practices had no effect on its stabilized 
infiltration rate (Figure 7.21). It is likely that any change in macro-porosity would have 
actually taken place in the first years of implementation of mechanized practices, with no 
further effect in subsequent years. This observation was again supported by the observation 
that bulk density in the mechanized treatments had not been affected with time. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Infiltration rate (mm/h)
 163 
250
200
150
100
50
0
Early (> 10 years) Recent (< 3 years)
Figure 7.21 Effects of length of time for which mechanized practices have been 
implemented on stabilized infiltration rate of P soil of Mauritius cropped with sugar cane
 
 
7.4 Conclusion 
 
As opposed to what has been observed in other sugar cane producing countries, the major soil 
groups of Mauritius were not very susceptible to change as a result of sugar cane cropping or 
following the introduction of mechanized practices. Changes occurring in the soil physical 
quality parameters investigated were in general relatively small and variable and could 
sometimes be related to the climatic zone in which the soils were found, or to their rock 
content. The effects of cultivating sugar cane might occasionally be detrimental to the 
physical properties of the soil, as generally observed in the literature, but beneficial effects 
were also found, even though it could not be said that the positive effects outweighed the 
negative ones. The only case where a totally significant negative impact has been 
demonstrated occurred with respect to the stabilized infiltration rate of water when 
mechanized practices were introduced. 
 
As to the effects of time under cultivation on soil physical quality, the results indicated that 
there was hardly any regular evolution with time for most parameters. In most cases, there 
was either no effect or only small and variable changes, indicating that the soil reached an 
Effects of sugar cane production practices on soil qual ity in Mauritius 
Infiltration rate (mm/h)
 164 
equilibrium rapidly once the native vegetation has been replaced by sugar cane. Similarly, the 
impact of mechanization was much more obvious in the short-term than in the long-term. If 
there was any effect of mechanization on soil physical properties, such an effect was 
observed right from the onset. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 165 
CHAPTER 8 
 
SUMMARY AND RECOMMENDATIONS 
 
8.1 Summary 
 
8.1.1 Purpose of the study 
 
Though the sugar industry in Mauritius contributes only 3.5% to the national GDP, it is an 
important component of the national economy as sugar exports represent some 19% of total 
foreign exchange earnings. Sugar is by far the most important agricultural product of 
Mauritius and sugar cane covers some 40% of the island or about 85% of the total cultivated 
area. The sugar industry directly employs about 4% of the total manpower of the island and 
sugar cane remains a source of revenue to some 28 000 small planters owning less than 10 ha. 
 
Comparative studies elsewhere in South Africa, Australia, or Papua New Guinea, have shown 
that sugar cane cropping leads to soil degradation. As a result, there is an apprehension that it 
would no longer be possible to produce sugar cane in a sustainable manner if current 
production practices are maintained. A preliminary study undertaken in the 1970’s has in fact 
shown that soil degradation occurred in Mauritius with sugar cane cropping. If there has been 
further degradation of the soil since that study was carried out, then the long-term 
sustainability of the sugar industry will be threatened. Furthermore, the industry has to adapt 
to a more competitive international environment, which entails the rapid replacement of 
manual practices by mechanized ones. These new mechanized practices, which include land 
preparation and leveling, rock removal, and mechanized harvest, could further exacerbate soil 
degradation. 
 
In the light of the above statements, it is therefore essential to ascertain whether sugar cane 
cropping and the adoption of mechanized practices have had negative effects on soil quality. 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 166 
Recommendations can then be formulated to maintain or restore soil quality, and future 
research avenues identified. 
 
 
8.1.2 Results evolved from study 
 
This study was implemented to determine the effects of sugar cane cropping, and the 
adoption of mechanized practices after land preparation, on soil quality in Mauritius. In 
addition, the effects of length of time under sugar cane cropping and following 
implementation of mechanized practices were assessed. To determine the effects of cropping, 
pristine soils were used in comparison with sugar cane soils cultivated in a conventional 
manner. The latter were then compared to soils where land preparation and mechanized 
practices had been implemented to assess the effects of adopting mechanized practices. For 
temporal effects, old cane soils (> 50 years) were compared to new cane soils (< 25 years) 
and early mechanized soils (> 10 years) were compared to recently mechanized soils (< 3 
years). Biological, chemical and physical soil quality parameters were measured in the course 
of the study. The biological quality parameters were soil organic matter and microbial 
biomass, while the chemical ones included pH, cation exchange capacity, exchangeable bases 
and base saturation. The physical parameters studied were particle size distribution, aggregate 
size distribution and stability to water, bulk density, plant available water and stabilized water 
infiltration rate. The main results evolved from the study are summarized below. 
 
1. Cropping with sugar cane is shown to have had both positive and negative effects on 
the quality of the major soils of Mauritius. These effects were associated with the 
cultural practices that were adopted in the crop production process. In some instances, 
cultural practices differed because of differences in climate, and these have produced 
contrasting effects on soil quality. The cultural practices that have had the greatest 
effects on soil quality were identified as tillage, organic amendments, fertilization, 
and trash management after harvest. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 167 
2. Topsoil OM generally decreased with cropping. The probable cause was soil tillage, 
which exposed the SOM to accelerated decomposition. However, tillage also 
produced mixing of topsoil with subsoil, resulting in enhanced OM in the subsoil. In 
addition, topsoil microbial biomass declined with sugar cane cropping as there was 
less material available for decomposition. The downward transfer of OM had a 
positive effect in the subsoil by increasing the stability of its aggregates. 
 
3. Soil pH, exchangeable bases and base saturation generally improved with sugar cane 
cropping due mainly to the organic amendments that were added to the soil at planting 
and just after harvesting. Soil acidification was also observed in one instance, 
probably as a result of the application of nitrogenous fertilizers. On the other hand, the 
higher plant biomass produced by fertilization meant that more OM, mainly in the 
form of plant roots and trash, was returned to the soil, thereby enhancing SOM 
content. The management of trash at harvest played an important role in the evolution 
of soil quality. Burning of trash before harvest lowered the return of carbonaceous 
material to the soil, whereas trash conservation under green cane harvesting had a 
positive effect through an improved return of OM to the soil. 
 
4. The adoption of mechanized practices had relatively little effect on the chemical 
quality of the major soils of Mauritius, as soil pH, CEC, exchangeable cation content 
and base saturation were mostly unaffected. This was not surprising as soil 
disturbance for land preparation and rock removal was the major activity in the 
implementation of mechanized practices and was not expected to impact on the soil’s 
chemistry. There was more soil disturbance under humid to dry conditions than under 
very wet conditions. SOM consequently decreased with the adoption of mechanized 
practices in the dry zones. In one soil where chemical quality was affected by 
mechanization, the changes were positive and could be ascribed to the large amounts 
of organic amendments that had been added to the soil after land preparation and rock 
removal. As expected, the adoption of mechanized practices had a greater influence 
on soil physical properties. Compaction invariably occurred in the topsoil and can be 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 168 
directly related to traffic associated with mechanized harvesting. Compaction also led 
to a reduced water infiltration rate as a result of the reduction in topsoil macro-
porosity, and to an increase in plant available water. 
 
5. No clear conclusion could be drawn regarding the effect of time under sugar cane 
cropping on the quality of the sub-humid soils of Mauritius. Soil properties were not 
systematically aggraded or degraded under long-term cultivation and changes were 
mainly small and variable. 
 
6. Soil quality declined with time after the adoption of mechanized practices. This 
decline resulted from the policy of adding large amounts of amendments to the soil 
when mechanized practices were implemented, and allowing the built-up SOM and 
nutrients present to be depleted with time. In physical terms, the impact of adopting 
mechanized practices was observed right from the onset and did not evolve with time. 
 
To sum up, sugar cane cropping had variable effects on soil quality in Mauritius. Negative 
effects were mainly confined to the topsoil in the instances where soil degradation was 
observed. The biological quality of the topsoil decreased with cropping as OM and microbial 
biomass declined whereas chemical quality generally improved with higher pH and 
exchangeable base content. On the other hand, topsoil physical quality decreased following 
the adoption of mechanized practices, through the compacting effect of heavy agricultural 
machinery traffic which also reduced the water intake rate. The quality of the soil was not 
systematically affected by the length of time during which it has been cropped, but it did 
decline with time after the adoption of mechanized practices. 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 169 
8.2 Implications and recommendations for the sugar industry of Mauritius 
 
8.2.1 Application of research results 
 
From the agronomic viewpoint, the OM depletion in the topsoil with cropping of sugar cane 
will impact negatively on the long-term yield. A direct consequence of this depletion is the 
reduction in soil N content (Sumner, 1997) as N is released through mineralization by soil 
micro-organisms into inorganic forms which are available to the sugar cane. This process 
supplies a significant portion of the N needs of the crop, as studies have shown that 85% of 
the N in sugar cane is derived from the N mineralized in the soil (Ng Kee Kwong et al., 
1983). As total N content and soil microbial biomass generally decreased with sugar cane 
cropping, N mineralization and availability will also decrease. The organic pool will thus 
provide less N to the sugar cane crop, and more fertilizer N will be needed to maintain crop 
productivity. The OM depletion in the topsoil is also expected to have negative consequences 
for the sustainability of the sugar industry by rendering the soils more susceptible to erosion. 
An OC value of 2% has been quoted as the threshold below which the soil can be considered 
erodible (Morgan, 1986). The OC content of the major soils of Mauritius is still above this 
threshold value under sugar cane cropping, but the L soil could be at risk since its OC content 
is close to this threshold, making it the soil most susceptible to erosion in Mauritius 
(Seeruttun, 2006). 
 
To ensure that the topsoil OM level does not decrease any further under cropped conditions, 
trash retention through green cane trash blanketing, addition of large amounts of organic 
wastes and green manuring should be favoured. Trash delivers only negligible amount of N to 
the next sugar cane crop, but contributes significantly to raising the OM level of the soil (Ng 
Kee Kwong et al., 1987). In fact, the N liberated from the trash is mainly immobilized in the 
soil, reflecting that it is an N source of slow availability to the crop (Basanta et al., 2003). For 
trash to be retained, the sugar cane must be harvested green, leaving a trash blanket on the 
soil surface. However, as trash blanketing affects soil water and temperature, its 
implementation should be restricted to the sub-humid and humid zones since the mulch 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 170 
lowers soil temperature by 1 to 2oC and reduces yield in the super-humid zone (Seeruttun et 
al., 1998). On the other hand, the mulching effect conserves soil water by reducing 
evaporation and has been shown to lead to a higher sugar cane yield in the sub-humid zone 
(Mc Intyre et al., 1996). 
 
Application of organic waste to sugar cane fields is already a common practice in Mauritius. 
The main organic waste is filter mud, but its application rates vary depending on the 
producers. Poultry litter is another possible form of organic waste that could be used. It is as 
effective as mineral fertilizers in increasing sugar cane yields and has the added advantage of 
improving the nutrient status of the soil (MSIRI, 2006). A third possible source of organic 
waste is stillage slop, a waste product from the fermentation process when molasses are 
converted to ethanol. According to the multi-annual adaptation strategy for the sugar industry 
of Mauritius for the years 2008 to 2013 (Government of Mauritius, 2006), 30 million l of 
ethanol will be produced when this strategic plan is fully implemented. As 13 l of slop are 
produced for every l ethanol (Paturau, 1989), some 390 million l of stillage slop would 
become available, part of which could be applied to sugar cane fields in a concentrated form 
known as condensed molasses solubles or CMS. Applications of slop at a rate of 80 m3 ha-1 
year-1 have been shown to lead to an accumulation of OM in the soil in the long-term with a 
strongly positive N balance, while increasing pH and exchangeable bases and decreasing 
exchangeable Al levels (de Resende et al., 2006). On the other hand, the multi-annual 
adaptation strategic plan from 2008 to 2013 promotes sugar mill centralization and the 
concurrent adoption of more efficient milling technologies such as the use of diffusers. As no 
filter mud is produced with this technology, the main source of organic waste of the sugar 
cane fields will disappear and alternative sources need to be found. One definite possibility is 
to use sewage sludge, a ready and constant source of organic waste. Its application to 
agricultural land represents the most sensible economic option for its disposal (Beck et al., 
1995), the more so as trials have shown that sewage sludge in Mauritius has extremely low 
levels of main organic pollutants (Soobadar et al., 2004) and its application to the soil carries 
little risk of contaminating groundwater by heavy metals (Toory et al., 2004). Furthermore, it 
has been shown that application of composted sewage sludge did not increase Mn, Cu, Fe, or 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 171 
Zn concentrations in sugar cane leaf tissue beyond acceptable limits (Viator et al., 2002). The 
main obstacle to its use in sugar cane fields could be a certain reticence from farmers, 
considering the source of this organic waste product. 
 
The incorporation of a rotation break in the sugar cane monoculture holds considerable scope 
for improving its biological status (Pankhurst et al., 2003). In addition to increasing SOM 
content, these green manures enhance sugar cane yield. In this respect, a well-managed single 
rotation crop of soybeans or peanuts has been shown to contribute substantial amounts of 
fixed N into the soil, to increase sugar cane yields and to impact on soil health (Garside and 
Bell, 2001). Trials in Mauritius have shown that higher yields are indeed obtained when 
legume green manure crops are incorporated into the soil and that lablab (variety Rongai) was 
the best species, fixing between 170 and 200 kg N ha-1 from the atmosphere (MSIRI, 2005). 
However, as the experience from Garside et al. (2004) has shown, the amount of green 
manure produced is highly dependent on a good input of water for growth. To reap the 
highest benefit from this practice, the green manure must therefore either be planted during 
the wet season under rainfed conditions or be regularly irrigated. As the growing season of 
lablab lasts some three months, that much time will have elapsed between the last sugar cane 
harvest and the replanting of the next crop. Thus, if green manuring is adopted under short 
season planting, the previous crop must be harvested early to allow time for the legume to 
grow under irrigated conditions, before ploughing in and replanting. Alternatively, under 
rainfed conditions, the legume should be planted in the wet season and the next sugar cane 
crop planted in the long season. 
 
The soil physical degradation in the form of compaction that results from the adoption of 
mechanized practices appears inevitable. Compaction is an unavoidable consequence of 
mechanized agriculture and should therefore be considered as a factor of the crop production 
system (Torres and Rodriguez, 1996). It has detrimental effects on sugar cane yield, Swinford 
and Meyer (1985) having shown that yield was negatively correlated with bulk density 
values. The consequence of compaction on the environment is a lower infiltration rate, 
increased runoff, higher risk of soil erosion, greater loss of agrochemicals and therefore more 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 172 
pollution. While mechanization of cultural practices must be implemented for economic 
reasons, strategies need to be developed to alleviate its drawbacks. 
 
Inter-row decompaction in ratoons is an option for eliminating compaction. Torres and 
Pantoja (2005) showed that one pass of a double-shank subsoiler was sufficient to restore soil 
physical properties in ratoons while Swinford and Boevey (1984) observed increases in cane 
yield following ripping of the inter-row in machine-compacted plots. However, this practice 
cannot be contemplated for Mauritius since the decompacting implements cannot be operated 
properly in the presence of trash. In the management of compaction, prevention is therefore 
the best strategy. To minimize, offset or eliminate compaction, Torres and Rodriguez (1996) 
have recommended that vehicles be kept off the fields when soil conditions were too wet, 
tyres be run at lowest possible inflation pressure, field operations be combined to reduce 
traffic, row spacing be matched to machine tracks (or vice-versa) and controlled traffic paths 
be implemented. Braunack (2004) also recommended that the number of passes by fully laden 
haulouts be reduced in mechanized harvesting, and that super single tyres be used rather than 
dual ones. In addition, Braunack (2004) suggested that lowering the pressure in the tyres 
might provide an additional benefit in reducing compaction, but at the expense of tyre life. Of 
these measures, in-field trailers fitted with low-pressure tyres have already been 
recommended for use in the super-humid zone of Mauritius (MSIRI, 2000). Unfortunately, 
the imperatives of industrial production have also meant that mechanized operations are often 
undertaken under wet conditions and this trend could even be accentuated with mill 
centralization. Other possible measures, particularly controlled traffic, seem promising but 
need to be tested prior to implementation. 
 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 173 
8.2.2 Suggestions for future research 
 
The most pertinent soil quality parameters to emerge from this study are OM, pH, bulk 
density and water infiltration rate. The evolution of the OM was the main indicator of the 
soil’s biological quality. On the other hand, measurements of microbial biomass were less 
important since there was a general correlation between microbial biomass and topsoil OM, 
and the latter parameter gave a clear indication of the evolution of the microbial population. 
A similar reasoning could be applied to CEC, a chemical quality parameter that is highly 
dependent on OM. The evolution of the soil’s chemical quality is best monitored through pH, 
as its evolution influences micro-organism activity and availability of plant nutrients, rather 
than through changes in exchangeable base status and base saturation. As far as physical 
quality is concerned, the indicators of compaction (bulk density) and water movement 
(infiltration rate) were more pertinent than the indicators of texture (particle size distribution), 
structure (aggregate size distribution and stability) or water retention (plant available water). 
 
An additional soil quality parameter that deserves investigation in the short-term is the labile 
C within the total OM pool, since it is the most labile pool that is the key determinant of soil 
properties (Moody et al., 1999). Under sugar cane, key soil properties such as CEC, aggregate 
stability and microbial biomass are more strongly related to the labile C fraction than to total 
organic C per se. Total C measures both labile C and the inert charcoal fraction of the SOM, 
and is therefore not a sensitive indicator of changes in labile C (Moody et al., 1999). 
Research on regeneration of OM in sugar cane soils should therefore include the 
determination of the labile C pool. 
 
There are different possibilities for regenerating SOM. It has already been mentioned that one 
possible source of OM is the legume fallow. Experimental work in Mauritius on legume 
green manure crops has shown that lablab was a more effective N fixer than cowpea, soybean 
and crotalaria, and has provided conclusive evidence that incorporation of these crops into the 
soil prior to replanting sugar cane can significantly increase yield (MSIRI, 2006). However, 
additional work needs to be done to determine whether the positive effects of incorporating a 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 174 
leguminous crop between two crop cycles has long lasting effects on the OM and aggregation 
status of the soil. In addition, only about 25% of the N fixed by the legume is absorbed by the 
ensuing sugar cane crop. The fate of the remaining fixed N needs to be investigated in 
subsequent ratoons to verify whether it becomes available to the crop at a later stage. 
 
Experimentation at MSIRI using sewage sludge has shown conclusively that there is no risk 
to public health if this waste is applied to sugar cane fields. However, the use of sewage 
sludge also requires the simultaneous application of chemical fertilizers to avoid loss in cane 
production (MSIRI, 2004). There is scope for work to determine the correct dose of this 
product for building up the organic C status of the soil in conjunction with optimum N 
fertilizer application. 
 
With respect to trash management, it has been shown that most cane trash decomposes within 
a year after harvest (Robertson and Thorburn, 2007a). However, decomposition rate was 
partially dependent on temperature and rainfall, among other factors. This indicates that there 
are possible differences in the rate of trash decomposition between the soils of the sub-humid 
zone and those of the super-humid zone, and their relative effects on soil quality should be 
investigated. Furthermore, Robertson and Thorburn (2007b) have suggested that some 10 to 
20% reductions in N fertilizer applications might be possible after 15 to 25 years of trash 
blanketing, provided that crop yields and N losses to the environment under trash blanketing 
were similar to those under the burnt system. The quality of the soils that have been long 
enough under trash blanketing of Mauritius needs to be investigated to verify this assertion, 
which if proven, will impact positively on production costs. 
 
As far as managing soil compaction is concerned, controlled traffic is a system that could 
help maintain a zone better adapted for sugar cane growth by restricting soil compaction to 
inter-row traffic lanes (Braunack et al., 1995), leaving a loose rooting zone in the cane row. 
McGarry et al. (1997) have shown that, after five ratoons, soil in the row was less dense and 
had better porosity than soil in the inter-row which had become a hard traffic zone with 
potential for increased traction and improved wet-weather access. However, the benefits of 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 175 
controlled traffic cannot be fully realized in Mauritius, as in Australia, unless the current 
mismatch between row spacing (1.5 to 1.6 m) and equipment track width (1.8 m) is 
eliminated (Braunack and McGarry, 2006). The effects of controlled traffic on row and inter-
row bulk density and water infiltration rate should be investigated, particularly in relation to 
efforts for adapting row spacing to equipment track width. 
 
Even though it is not deemed to alleviate compaction, reduced or minimum tillage can lead to 
substantial cost savings with environmental benefits without yield penalty if it is adopted in 
conjunction with row spacings that match harvester and in-field transport wheel spacings 
(Bell et al., 2001). Work on minimum tillage practice in Mauritius needs to be revisited, as 
recommendations for its adoption were based essentially on trials using manual harvesting 
practices, which led to little change in soil physical properties (McIntyre and Barbe, 1990). 
Trials combining controlled traffic and minimum tillage strategies need to be undertaken as a 
means for minimizing soil degradation and maintaining productivity in the long-term, as 
suggested by Braunack and McGarry (2006). 
 
In the long-term, research will have to focus on the changes in soil quality as new farming 
systems are adopted. Braunack and McGarry (2006) have suggested that the combination of 
controlled and reduced traffic could form the basis of a farming system to protect the soil 
resource and maintain long-term productivity in Australia. Similarly, the combination of 
raised beds, dual row planting, minimum tillage, controlled traffic and legume fallows in the 
sugar cane farming system has already been touted as a means of improving profitability, 
sustainability and environmental responsibility (Garside et al., 2004). The perceived 
advantages of this new system are that it replaces inorganic nitrogen fertilizer in the plant 
crop, improves soil health, reduces compaction in the cultivated area, and virtually eliminates 
offsite movement of soil, fertilizer and chemicals (Milford, 2005). Dual row planting has 
already been shown to give higher yields in Mauritius (MSIRI, 2006), with the additional 
benefit of a considerable improvement in harvester efficiency, while minimum tillage has 
long been recommended on sloping lands as a soil conservation measure (McIntyre et al., 
1984). However, the proponents of this new farming system have tended to focus essentially 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 176 
on biomass production and on the economic aspects of the system (Garside et al., 2004). The 
effects of integrating all these different practices on soil quality remain unknown because 
they have not been adopted long enough whereby their impact on soil quality can be stressed. 
If the sugar industry of Mauritius follows the same trend as in Australia, this new farming 
system needs to be tested locally, while including into it an aspect that is specific to 
Mauritius, which is the removal of stones from the permanent beds using either a stone 
aligner or a stone crusher. To conclude, it is foreseeable that cultural practices will change as 
the sugar industry of Mauritius adapts to its new economic environment, but the effects of 
these changes on soil quality must be determined to ensure that the new systems adopted are 
agronomically viable and environmentally sustainable. 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 177 
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APPENDIX 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 195 
Appendix 1.1 Average values and standard errors of particle size distribution of five major 
soil groups of Mauritius as affected by sugar cane cropping and mechanized practices 
 
B soil 
  Treatment 
Layer (cm) Particle size Virgin Manual Mechanized 
 Sand 42.7±1.9 29.2±2.0 20.6±1.5 
0 - 5 Silt 27.1±1.6 25.9±0.7 27.3±0.6 
 Clay 30.2±1.7 44.9±1.7 52.1±1.1 
 Sand 42.9±1.5 27.2±1.9 19.9±1.5 
5 - 15 Silt 28.7±1.6 25.5±0.7 27.4±0.5 
 Clay 28.4±2.1 47.3±1.9 52.7±1.1 
 Sand 42.7±1.9 24.0±2.1 19.6±1.9 
15 - 30 Silt 29.9±1.8 25.1±0.6 24.8±0.5 
 Clay 27.4±2.6 51.0±2.3 55.6±1.7 
 Sand 43.3±2.0 28.9±2.1 25.1±3.3 
30 - 50 Silt 29.5±1.7 26.4±0.9 23.3±0.9 
 Clay 27.3±2.3 44.7±2.1 51.6±3.9 
 Sand 43.0±1.8 27.1±1.4 22.0±2.2 
0 - 50 Silt 29.2±1.6 25.8±0.5 25.0±0.4 
 Clay 27.8±2.2 47.1±1.7 53.1±2.2 
 
 
P soil 
  Treatment 
Layer (cm) Particle size Virgin Manual Mechanized 
 Sand 21.5±1.4 29.0±2.8 20.6±1.5 
0 - 5 Silt 19.6±0.8 18.0±2.3 21.7±1.9 
 Clay 57.9±1.6 53.1±4.4 57.8±2.8 
 Sand 22.0±1.8 28.4±2.9 20.0±1.8 
5 - 15 Silt 17.0±0.6 21.1±0.9 20.9±0.5 
 Clay 61.0±2.1 50.5±3.3 59.1±2.1 
 Sand 19.1±2.0 28.2±2.9 19.5±2.2 
15 - 30 Silt 17.5±0.8 21.6±0.8 21.2±0.5 
 Clay 63.5±2.4 50.2±3.2 59.3±2.4 
 Sand 17.6±1.6 30.0±3.6 20.3±3.1 
30 - 50 Silt 18.0±0.7 21.6±0.8 21.7±1.5 
 Clay 64.4±2.1 48.4±3.6 58.1±3.8 
 Sand 19.4±1.6 29.0±3.1 20.0±2.3 
0 - 50 Silt 17.8±0.6 21.2±0.7 21.4±0.9 
 Clay 62.9±2.0 49.8±3.3 58.6±2.8 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 196 
Appendix 1.1 (continued) Average values and standard errors of particle size distribution of 
five major soil groups of Mauritius as affected by sugar cane cropping and mechanized 
practices 
 
F soil 
  Treatment 
Layer (cm) Particle size Virgin Manual Mechanized 
 Sand 28.2±0.6 33.8±1.6 34.4±1.1 
0 - 5 Silt 30.2±0.3 28.9±0.7 31.0±0.6 
 Clay 41.6±0.4 37.3±0.9 34.5±0.7 
 Sand 30.2±0.6 32.5±1.7 32.7±0.9 
5 - 15 Silt 31.2±0.8 29.3±0.6 31.6±0.8 
 Clay 38.6±1.1 38.3±1.1 35.7±0.5 
 Sand 38.6±2.1 34.3±2.3 33.8±1.4 
15 - 30 Silt 27.8±1.4 28.6±0.7 32.9±1.1 
 Clay 33.5±1.5 37.0±1.6 33.3±1.5 
 Sand 51.1±2.1 44.9±2.7 46.3±2.3 
30 - 50 Silt 23.9±1.0 25.2±1.4 28.3±1.5 
 Clay 25.0±1.4 29.9±1.8 25.5±1.5 
 Sand 40.9±1.3 38.1±1.8 38.6±1.3 
0 - 50 Silt 27.2±0.7 27.4±0.7 30.6±0.9 
 Clay 32.0±1.2 34.5±1.3 30.8±1.1 
 
L soil 
  Treatment 
Layer (cm) Particle size Virgin Manual Mechanized 
 Sand 16.7±1.6 15.3±1.3 14.3±1.5 
0 - 5 Silt 15.2±1.2 18.6±1.8 18.6±3.1 
 Clay 68.1±2.8 66.5±2.9 67.1±3.7 
 Sand 14.1±0.9 14.7±1.2 13.3±1.1 
5 - 15 Silt 15.5±1.4 20.3±1.9 19.4±2.0 
 Clay 70.3±2.3 65.0±2.6 67.4±2.6 
 Sand 10.6±0.9 14.1±1.4 12.8±1.1 
15 - 30 Silt 13.9±1.0 20.7±2.0 18.6±2.0 
 Clay 75.5±1.7 65.2±2.7 68.7±2.7 
 Sand 8.5±0.6 12.7±1.7 10.2±1.1 
30 - 50 Silt 12.6±0.5 19.2±1.8 16.7±2.6 
 Clay 78.8±1.0 68.1±2.7 73.1±3.0 
 Sand 11.1±0.6 13.8±1.4 12.0±1.1 
0 - 50 Silt 13.8±0.8 19.8±1.8 18.0±1.7 
 Clay 75.1±1.3 66.4±2.6 70.0±2.3 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 197 
Appendix 1.1 (continued) Average values and standard errors of particle size distribution of 
five major soil groups of Mauritius as affected by sugar cane cropping and mechanized 
practices 
 
H soil 
  Treatment 
Layer (cm) Particle size Virgin Manual Mechanized 
 Sand 16.5±1.5 18.6±1.0 23.9±1.4 
0 - 5 Silt 22.9±0.5 20.8±1.4 31.5±0.9 
 Clay 60.6±1.5 60.6±1.2 44.6±2.2 
 Sand 16.2±1.6 18.1±1.0 23.1±1.4 
5 - 15 Silt 22.4±0.7 20.6±0.3 31.5±0.9 
 Clay 61.4±2.2 61.3±1.2 45.5±2.2 
 Sand 16.4±2.0 16.7±1.0 23.0±1.9 
15 - 30 Silt 20.9±0.5 19.2±0.3 32.5±1.6 
 Clay 62.8±2.3 64.1±1.2 44.6±3.3 
 Sand 16.6±2.5 11.3±0.6 32.8±4.0 
30 - 50 Silt 20.4±0.7 17.1±0.9 30.4±1.6 
 Clay 63.0±2.9 71.6±1.3 36.9±5.4 
 Sand 16.5±2.1 15.0±0.7 27.0±2.5 
0 - 50 Silt 21.2±0.6 18.8±0.4 31.0±1.4 
 Clay 62.4±2.5 66.2±0.9 41.7±3.8 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 198 
Appendix 1.2 Average values and standard errors of particle size distribution of two soil 
groups of the sub-humid zone of Mauritius as affected by time under sugar cane cropping 
 
 
  Médine (P soil) Richeterre (L soil) 
Layer (cm) Particle size Old New Old New 
 Sand 29.0±2.8 19.7±0.9 15.3±1.3 16.7±1.0 
0 – 5 Silt 18.0±2.3 20.2±0.7 18.6±1.8 20.7±1.4 
 Clay 53.1±4.4 60.1±1.2 66.5±2.9 62.6±2.0 
 Sand 28.4±2.9 18.8±1.0 14.7±1.2 17.0±1.2 
5 – 15 Silt 21.1±0.9 19.2±0.7 20.3±1.9 20.9±1.4 
 Clay 50.5±3.3 62.0±1.2 65.0±2.6 62.1±2.2 
 Sand 28.2±2.9 21.1±2.2 14.1±1.4 16.0±1.5 
15 – 30 Silt 21.6±0.8 19.5±0.8 20.7±2.0 20.7±1.4 
 Clay 50.2±3.2 59.5±2.4 65.2±2.7 63.3±2.4 
 Sand 30.0±3.6 22.9±3.9 12.7±1.7 15.0±1.8 
30 – 50 Silt 21.6±0.8 19.9±1.4 19.2±1.8 21.5±1.1 
 Clay 48.4±3.6 57.2±4.4 68.1±2.7 63.5±2.4 
 Sand 29.0±3.1 21.2±2.4 13.8±1.4 15.9±1.4 
0 – 50 Silt 21.2±0.7 19.7±0.9 19.8±1.8 21.1±1.2 
 Clay 49.8±3.3 59.1±2.7 66.4±2.6 63.1±2.1 
 
Effects of sugar cane production practices on soil qual ity in Mauritius 
 199 
Appendix 1.3 Average values and standard errors of particle size distribution of P soil of 
Mauritius as affected by time for which mechanized practices have been adopted 
 
  Treatment 
Layer (cm) Particle size Old mechanized New mechanized 
 Sand 22.8±1.3 20.6±1.5 
0 - 5 Silt 20.7±0.8 21.7±1.9 
 Clay 56.4±1.8 57.8±2.8 
 Sand 23.2±1.7 20.0±1.8 
5 - 15 Silt 20.2±0.6 20.9±0.5 
 Clay 56.7±1.9 59.1±2.1 
 Sand 25.8±2.9 19.5±2.2 
15 - 30 Silt 21.5±1.8 21.2±0.5 
 Clay 52.7±3.1 59.3±2.4 
 Sand 26.4±3.6 20.3±3.1 
30 - 50 Silt 20.4±0.8 21.7±1.5 
 Clay 53.2±3.7 58.1±3.8 
 Sand 25.2±2.7 20.0±2.3 
0 - 50 Silt 20.7±0.9 21.4±0.9 
 Clay 54.1±2.9 58.6±2.8 
 
 
 
 
 
 
 
Effects of sugar cane production practices on soil qual ity in Mauritius