Doctoral Degrees (Soil, Crop and Climate Sciences)

Permanent URI for this collection

http://hdl.handle.net/11660/466

Browse

Now showing 1 - 20 of 47

Open Access
Die geohidrologie in die opvanggebied van die Moloporivier in die Noordelike Kalahari
(University of the Free State, 1977) Smit, Petrus Jurgens; Grobler, N. J.
Afrikaans: Die gebied wat 58 153 km2 beslaan en waarvan ongeveer 75 persent met sand bedek is, is uitsluitlik van ondergrondse water afhankliko Die gesteentes le hoofsaklik in die westelike en suidelike dele blootgele Die Kalaharilae is tot 180 m dik en die geologiese formasies onder die Kalaharilae is volgens boorgatgegewena vasgestel Die diepte van die grondwatervlak varieer tussen 15 m in dagsoomgebiede en 150 m in gebiede waar die Kalaharilae die dikste is. In die westelike dele Is die Kalaharilae waterdraend. In stollingsgesteentes lewer 34 tot 50 persent van die boorgate meer as 450 l/h en in sedimentire geateenteep behalwe die Formasie Dwyka, 50 tot 80 perssnte Boorgate wat wetenskaplik op Voor-Kalaharigeeteentes gekies is lewer 10 persent hoer suksease (lewering meer Ba 450 1/h) 88 boorgate wat op ander metodes gekies is. In 38 boorgate is watervlakakommelinge sedert 1967 gereeld gemeeto Seisoensveranderinge is ongeveer 3 keer groter in boorgate in dagsoomgebiede aa in boorgate waar'die Kalaharilae tussen 0 en 15 m dik is. Waar die Kalaharilae dikker as 15 m is, is geen seisoensveranderinge waarneembaar nie. Die gebied kan volgens die hoogtekontoere van die grondwatervlak in 8 grondwatereenhede r ingedeel word wat elk 'n afsonderlike grondwaterkompartement vorm. Die temperatuur van die grondwater varieer volgens die diepte van die grondwatervlak. Die geotermiese gradient is hiervolgens bereken as 54 m/°C in graniet, 50 m/°C in dolomiet, 35 m/°C in jaspiliet, 30 m/°C in lawa en 45 rn/°C 1n Kalaharilae. In totaal ia 204 grondwatermonsters chemies ontleed en totale opgeloste stowwe ia In 655 monsters bepaelo Die konsentrasie van T.O.S. in die grondwater in Voor-Kalaharigesteentea word progressief hoer met 'n toename in die dikte van die Kalaharilae. Die Kalaharilae veroorsaak nie 'n verhoging in die konsentrasie van totale opgeloste stowwe in die grondwater nie maer ioonuitruiling vind wel plaas waar grondwater deur die kleilae beweeg. Die grondwater in die Voor-Kalaharigesteentes en in die Kaleharilae kan elk in 4 tipes ingedeel word volgens die chemiese samestelling en oorsprong. Die grondwateraanvulling in dagsoomgebiede varieer tussen 2,2 persent in die weste by ‘n reenval van 220 mm per jaar, tot 3,8 persent in die ooste, by ‘n reenval van 550 mm per jaar. In gebiede waar die bedekking tussen 0 en 15 m is, is aanvulling moontlik 0,5 persent van die jaarlikse reenval en waar die Kalaharilae dikker as 15 m is, vind geen direkte aanvulling plaas nie. Die totale jaarlikse aanvulling tot die grondwater in die hele gebied is 227,2 x 106m3• Die totale grondwaterverliese in die gebied is 52,498 x 106m3 per jaar, waarvan 70 persent uit boorgate en 30 persent uit fonteine afkomstig is. Die jaarlikse toename in die waterverbruik word beraam op 1,5 persent in Blanke gebiede en 8 persent in Tuialandgebiede. Die waterverbruik deur mense en diere verteenwobrdig 39 persent van die totale gl'ondwaterverliese, verbruik deur besproeiing 36 persent, deur dorpe en myne 20 persent en deur verdamping en transpirasie 5 persent. Net 62 persent van die totale fonteinvloei word direk benut. Die totale grondwaterverliese in, die gebied verteenwoordig 23 persent van die jaarlikse bruto aanvulling, maar varieer tussen 91 en 17 persent in die verskillende grondwatereenhede. Die totale hoeveelheid water wat uit boorgate onttrek word is 36,856 x 106m3/j of 16 persent van die totale jaarlikse aanvulling. Die toekomstige waterverbruik in die gebied word beraam op 114,l4 x l06m3/j vir die jaar 2000, wat ongeveer 50 persent van die jaarlikse potensiele aanvulling verteenwoordige Die benutting varieer egter tussen 31 en 132 persent in die' verskillende grondwatereenhede. Ten einde die grondwaterpotensiaal beter te bepaal is verdere navorsing nodig op die natuurlike aanvulling tot die grondwater in dagsoomgebiede, die optimale dikte van die bedekking in verhouding tot aanvulling, die ondergrondse vloei deur die dolerietgange in dolomiet en op die ondergrondse vloei uit sommige van die grondwatereenhede. Ondersoek is ook nodig op die ontginningspotensiaal en stoorkapaaiteit van die verskillende formasies insluitende die Kalaharilae wat oor groot gebiede ‘n belangrike akwifeer vorm. Die ontginning van grondwater vernaamlik in granietgelJiede is 'n wesenlike probleem en navorsing op metodes en tegnieke van boorplek aanwysing sowel as boorgatontwikkellng is nodig. In groot gebiede in die noordweste is die grondwater onbruikbaar sout en ontsouting van grondwater is ‘n baie belangrike aspek vir toekomstige benutting. Navorsing behoort ook gedoen te word op die ontwerp en beplanning van kunsmatige opvanggebiede ten einde reenwater in sekere gebiede direk te benut.
Open Access
Die verdraagsaamheid van wildehawer vir onkruiddoders
(University of the Free State, 1993-03) Smit, Hugo Amos; Human, J. J.; Du Toit, D.
No abstract available
Open Access
A system for drought monitoring and severity assessment
(University of the Free State, 1995-02) Lourens, Uys Wilhelm; De Jager, J. M.
English: The objectives of this study were: (i) to develop a near real-time crop-specific drought monitoring system that delimits drought stricken areas and assesses the severity of droughts in these areas, (ii) to produce products from the system which can be used for decision support by decision makers, and, (ii) to test the system for maize production using historical production seasons. Objectives (i) and (ii) An agricultural drought monitoring system was designed, which combined crop growth modelling and a Geographic Information System (GIS) . The use of crop models made it possible to assess the drought damage suffered by crops, in relation to their growth stage. As drought is a spatially related phenomenon, a GIS was used to present the geographic distribution of a drought situation. A grid based, spatially distributed, system was designed. The map units of the South African 1.:250 000 map series were used as the base units on which to present information. Each base unit was divided into cells covering an area of 2' by 2' minutes of latitude and longitude. There were thus 1.800 grid cells in one such unit. The models were run for each of these cells. The data inputs required by the crop models therefore had to be spatially distributed. Methods of creating spatially distributed weather data bases, were implemented or developed. Existing interpolation techniques were used to create the rainfall and temperature data bases. A technique developed for determining daily irradiance, from the Japanese Geostationary Meteorological Satellite, was adapted for use on METEOSAT data obtained over South Africa. A spatially distributed soil data base was also created. Maize was chosen as the crop to monitor in the initial evaluation of the system. Drought monitoring was undertaken at fortnightly intervals from the beginning of the crop production season. At each interval, observed weather data was used up to the present date, and the season completed with surrogate data. Three surrogate scenarios were used: a below normal rainfall year, a normal rainfall year, and, an above normal rainfall year. Surrogate data were created for each homogeneous climate zone (HCZ) within the study area. The HCZ within which the cell lay was determined and its data used to complete the season. A rainfall data generator, the accuracy of which had been proved, was used in establishing the surrogate data. The cumulative probability distribution function (CDF) of seasonal yield, was used as the norm against which to measure current season performance at the conclusion of each monitoring session. CDF's were established for all combinations of soil, climate, and planting dates used within the bounds of a particular 1:250 000 map unit. The yield simulated for each cell was compared with the appropriate CDF, and the probability range within which it lay, determined. A drought index value was assigned based on this comparison. The indices were: 1- Extreme Drought (CDF probability range 0- 10%), 2- Severe Drought (>10- 20%), 3- Moderate Drought (>20- 30%), 4- Mild Drought (>30- 40%), and, 5 - No Drought (>40 - 100%). Maps showing the distribution, and tables providing the extent of area classified, were produced. Objective (iii) The drought monitoring system was tested for three maize production seasons. The accuracy of the system was determined by comparing the average maize yield per magisterial district with measured yield data. Individual farm records were also evaluated. The system accurately portrayed the general maize production trends during a severe drought (91/92}, while an r 2 of 0.59 was obtained for the individual yields. The crop modelling approach to drought assessment takes the interaction of the soil, plant and atmosphere into account and is crop specific. The important influence of both the amount and timing of rainfall in relation to crop growth stages is therefore reflected in the drought index.
Open Access
Parametric analysis to describe genotype x environment interaction and yield stability in winter wheat
(University of the Free State, 1997) Purchase, John Luscombe; Van Deventer, C. S.
No abstract available.
Open Access
Hydrogeology of the Table Mountain sandstone aquifer - Klein Karoo
(University of the Free State, 2001) Kotze, Johanita Christelle; Van Tonder, G. J.; Verhagen, B. T. H.
Abstract not available
Open Access
Estimating water retention for major soils in the Hararghe region, Eastern Ethiopia
(University of the Free State, 2003-02) Tsehai, Kibeebw Kibret; Bennie, A. T. P.
English: Soil water retention IS a fundamental property controlling water storage and movement in the solurn. To determine the water retention characteristic curve is time consuming and expensive. Several attempts have been made to establish relationships between easily measurable soil properties, like particle size distribution, organic carbon content, and the water retention characteristic curve. Those relationships are referred to as pedotransfer functions (PTFs). More conveniently, it is described by analytical functions that are suitable in the solution of numerical flow equations as well as in implementation of closed-form methods for predicting other hydraulic properties, such as unsaturated hydraulic conductivity. The objectives of this study were to describe the water retention characteristics of soils from the Hararghe Region, eastern Ethiopia, in relation to certain soil properties; to identify water retention functions for describing the water retention characteristic curves of these soils and to develop a procedure for estimating water content either at certain matric potentials or the complete curve from readily available soil properties. Two approaches, point estimation and parametric estimation techniques, were used for estimating the water content at certain matric potentials and at any matric potential, respectively. To establish relationships between water retention and relevant soil properties, regression analyses were carried out. From the regression analyses, point PTFs that can be used to estimate the water content at certain matric potentials were developed. This was done firstly by using the complete data set consisting of 216 retention curves and secondly by dividing the complete data set into topsoil and subsoil samples. Due to observed differences in water retention characteristics, the subsoil samples were divided into two groups based on their silt (Si) to clay (C) ratio. The dividing line between these two groups was 0.75. The topsoil and the two subsoil groups were divided into classes based on their silt plus clay content. This resulted in 7 classes for topsoils and subsoils with Si:C ratios < 0.75 and 6 classes for the subsoils with Si:C ratios> 0.75. For all the point estimation PTFs, the silt plus clay content functions described the variability in water content best. The relationship between water content and silt plus clay content was curvilinear. In order to quantify the prediction accuracy of these equations, the mean of the mean absolute error (mMAE), the mean of the root mean square error (mRMSE), the mean of the mean bias error (mMBE), d-index of agreement and coefficient of determination (R2) were used. In some instances, the slopes and intercepts of the 1:1 lines, between measured and predicted values, were used. The silt plus clay content functions for the complete data set explained 78 to 87 % of the variability in water content at specific matric potentials. The mMBE ranged from -0.001 to -0.003 cm' cm", the mMAE 0.022 to 0.034 crrr' cm", the mRMSE 0.027 to 0.042 crrr' ern". The d-values ranged from 0.838 to 0.867. The silt plus clay content functions for the topsails explained 88 to 94 % of the variability in water retention with the mMBE ranging from 0 to -0.001 crrr' cm", mMAE 0.018 to 0.031 crrr' cm", mRMSE 0.024 to 0.036 cm3 ern" and the d-values 0.765 to 0.886. The silt plus clay content functions for the subsoils with Si:C ratios < 0.75 were able to explain 78 to 87 % of the variability in water retention with the mMBE ranging from -0.001 to -0.004 crrr' ern", mMAE 0.019 to 0.036 crrr' ern", mRMSE 0.023 to 0.045 cnr' cm" and d-values 0.793 to 0.884. The silt plus clay content function for the subsoils with Si:C ratios> 0.75 explained 86 to 98 % of the variability in water content with mMBE ranging from -0.001 to 0.004 cm' ern", mMAE 0.013 to 0.031 ern' cm", mRMSE 0.015 to 0.038 crrr' cm" and d-values 0.737 to 0.99l. Of the three groups, the mean values of the classes were used to develop PTFs with higher R2-values and lower errors compared with the PTFs developed from the complete data set in each respective group. From the six water retention functions tested, the Van Genuchten (1980) function, with the restriction m = 1 - lIn, gave the best description of the water retention curves, followed by the Smith (1992) and the ordinary power functions. Over all, the Brooks-Corey (1964) function gave the poorest description of the water retention curves studied. The parameters of the Smith (1992) and Hutson & Cass (1987) functions correlated better with relevant soil properties compared to the parameters of the Van Genuchten function. With the parametric approach the Smith (1992) function estimated water content for topsails and subsoils with Si:C ratios> 0.75 with a higher accuracy compared with the Van Genuchten and Hutson & Cass functions whereas the Hutson & Cass function was better for the subsoils with Si:C ratios < 0.75. Testing the functions derived from the point estimation and parameterization techniques on an independent data set indicated that both approaches estimated water content with a reasonable degree of accuracy, although the point estimation techniques gave slightly better results for the subsoils with Si:C ratios> 0.75.
Open Access
Changes in the phosphorus status of soils and the influence on maize yield
(University of the Free State, 2003-05) Schmidt, Christiaan Jan Jacob; Du Preez, C. C.; Adriaanse, F. G.
The principle objective of this study was to obtain P fertilizer guidelines for large maize producing areas west of the Drakensberg mountains according to a similar approach previously used in KwaZulu-Natal based on the sufficiency concept of soil extractable P. Data from 14 different P fertilizer trials at various localities in the Free State, Gauteng, Mpumalanga and North West provinces was used. Different phosphorus treatments were applied for all trials in order to establish differences in extractable soil P levels which were expected to have corresponding effects on maize yield. Long-term rainfall varied from 990 mm per annum for the Athole trial in the eastern maize producing region to 494 mm per annum for the Wolmaransstad trial in the western region. The duration of trials varied between one and nine seasons. Firstly, simple regression equations with high R²-values were obtained for relationships between Ambic 1 and Bray 1 extractions over soils, but since it was demonstrated that relationships for different soils differed significantly from each other the use of these equations may result in a very high degree of inaccuracy with respect to P fertilizer recommendations. Soil properties had a significant effect on the efficacy of the two extractants. Furthermore, slopes of relationships between Ambic 1 and Bray 1 could be predicted by using exchangeable Ca in simple regression relationships (R²-values of between 80 and 83%). Secondly, it was established that P requirement factors (PRF's) cannot be obtained over soils (R²-values varied between 10 and 54 %), but rather for different soils separately (R²-values varied between 75 and 99%). Differences between the PRF's in total soil volumes (1.7 to 63.2 for Ambic 1 concentrations and 0.8 to 27.3 for Bray 1 quantities) indicated that the soils used in this study differed in their behavior to applied P. Phosphorus requirement factors could be predicted by a simple regression equation using degree of leaching based on the clay content as input parameter (R²-values between 60 and 78 %) as well as six multiple regression equations using either one of exchangeable Ca, Mg, K, silt content or degree of leaching based on the clay content (R²-values between 52 and 99 %) as input parameters. The implementation of any of these regression equations should be practical since all the parameters are usually included in standard analysis. However, the simple regression with degree of leaching based on the clay content appears to be an obvious option above the multiple regression equations since it is based on five input variables, i.e. exchangeable Ca, K, Mg, Na and clay content. Lastly, threshold extractable P values were derived for 10 out of the 14 localities that have been included in this study with varying R²-values. These threshold extractable P values were related to soil properties and it was found that the degree of leaching and silt-plus-clay content were the parameters that explained most of the variation. However, it was decided to explore only the relationships between threshold extractable P values and silt-plus-clay contents in more detail. By excluding data from two localities of which the topsoil contained lime, the R²-values of the mentioned relationships improved substantially so that threshold extractable P values could be derived from the silt-plus-clay content range of the other eight localities. For example the threshold extractable soil P concentrations based on Bray I for the total soil volume to obtain 90 % relative yield varied from 33.5 mg kg-¹ at 13 % silt-plus-clay to 14.6 mg kg-¹ at 60 % silt-plus-clay. These P (Bray 1) thresholds are much higher on the sandy soils than the value of 19 mg P kg:' (Bray 1) for 95 % relative yield currently in use according to existing guidelines. This may not necessarily imply that more P fertilizers will be sold according to higher soil P thresholds obtained in this study, since the corresponding soil sampling procedure also measures more residual P from enriched zones over rows where P fertilizer was band placed. The soil sampling procedure according to existing guidelines excludes sampling from these zones.
Open Access
The relationship between the water regime and morphology of soils in the Weatherley catchment, northerly Eastern Cape
(University of the Free State, 2003-11) Van Huyssteen, Cornelius Wilhelm; Le Roux, P. A. L.; Hensley, M.
English: The Weatherley catchment is situated close to Maclear in the northern Eastern Cape Province. Soil water contents have been measured regularly, as part of a long-term project, at 28 sites in the catchment for six years to quantify the soil water regime. For this study tEm of these sites were selected, described and analysed in detail to characterize the soil properties. This data was used to determine the relationship between soil water regime and soil profile morphology. A correlation was found to exist between mean annual duration of water saturation above 0.7 of porosity (ADs>o.7, days year") and other soil properties. CECsoil increases from 3.5 to 11.5 crnol, kg-1 , base saturation increases from 25 to 44 %, and the underlying unspecified material with signs of wetness or G horizons occur closer to the soil's surface as mean ADs>o.7 increases. Orthic A horizons that occur in seeps are wetter, with mean ADs>o.7 212 - 365 days year", than orthic A horizons that occur on ridges with mean ADs>o.7 of < 25 days year". The former have common and many Fe oxide mottles, whereas the latter lack clear mottling. ADs>o.7 data.shows that orthic A horizons overlying red apedal B, yellow-brown apedal B or neocutanic B horizons are well drained, while those overlying E, soft plinthic Band G horizons are wetter. It is proposed that orthic A horizons can be subdivided into wetness classes using the occurrence of mottles, as well as the nature of the underlying horizon. The Longlands (P201 and P207) and Westleigh (P204) soils, characterized by the occurrence of a soft plinthic B horizon, have intermediate mean ADs>o.7. They increase from 84 to 157 days year" in orthic A horizons, to 231 days year" in soft plinthic B horizons and 360 days year" in the underlying unspecified material with signs of wetness. The chromatic soils, including Pinedene (P202), Tukulu (P203) and Bloemdal (P210) soil forms, defined as having yellow-brown apedal B, neocutanic B or red apedal B horizons as the second horizon in the profiles respectively have the driest water regime of the soils studied. The A and B1 horizons have mean ADs>o.7 < 40 days year'", the B2 horizons 88 days year", and the underlying unspecified material with signs of wetness 130 to 350 days year" . Pooling the data from all the profiles studied produces the following mean ADs>o.7 for the different diagnostic horizons: G horizons = 324 ± 20 days year": unspecified material with signs of wetness = 243 ± 40 days year": E horizons = 163 ± 56 days year": soft plinthic B horizons = 148 ± 45 days year": orthic A horizons = 144 ± 40 days year'"; and chromatic (red apedal B, yellow-brown apedal Band neocutanic B) horizons = 88 ± 51 days year". There is an association between mean ADs>o.7 and other soil properties. For example clay content, CEC, basic cations and pH are highest in G horizons and lowest in chromatic horizons. CBD extractable Fe and Mn are found to be roughly twice as much in soft plinthic B, chromatic B and unspecified material with signs of wetness horizons compared to orthic A, E or G horizons. Digital soil horizon photographs were quantified and classified into diagnostic red, yellow-brown, grey and black colours, using the Red and Green values of RGBnotation in ArcView SpatialAnalyst. This methodology produced promising results, as proven by classification of photographed Munsell colour sheets. Colour classification of horizon photographs generally supports the field colour classification of these horizons using Munsell colour sheets. In general, the profiles described for this study are dominated by diagnostic grey and yellow-brown colours, with the exception of the Bloemdal (P210) which is diagnostic red.
Open Access
Response of Ethiopian field pea (Pisum sativum L.) cultivars to phosophorus fertilization of Nitosols
(University of the Free State, 2003-12) Amanu, Amare Ghisaw; Du Preez, C. C.; Bekele, Taye
Field pea (Pisum sativum L.) is the third most important grain legume in Ethiopia where its productivity is constrained by several biotic, abiotic and socioeconomic factors. The crop is grown mainly on a wide range of soil types throughout the highlands (1800 to 3200 m.a.s.l.) in well drained soils like Nitosols that developed from volcanic rocks. Nowadays the blanket recommendation of diammonium phosphate (DAP) at 100 kg ha" to this low input crop is questioned by the farmers and development workers. Hence, experiments have been conducted with the major objective of quantifying the response of Ethiopian field pea cultivars to phosphorus fertilization of Nito soIs under both glasshouse and field conditions. Glasshouse experiments: Topsoil from Ilala and Cheffa were used. Experiments were laid out in a split plot design with three phosphorus fertility levels (Extractable phosphorus: low = 5, medium = 15 and high = 30 mg kg-I) as the main plot treatments and factorial combinations of two pea cultivars (TIala soils: Holetta and G22763-2C; and Cheffa soils: Tegegnech and Cheffa local) and six phosphorus application rates (0, 7.5, 15, 30, 60 and 120 mg P kg") as the sub-plot treatments in a randomized complete block design with four replications. The phosphorus fertility levels together with the phosphorus application rates had positive influences on the growth and development of the pea crop as manifested in the biomass yield of the different cultivars. Critical phosphorus levels were estabilished by relating relative biomass yield to extractable soil phosphorus. In the case of the Bray 2 extractions, the critical phosphorus levels for TIala soils were 14 and 15 mg P kg" for cvs. G22763-2C and Holetta respectively, for Cheffa soils 17 and 20 mg P kg" for cvs. Cheffa local and Tegegnech respectively. However, in the case of Olsen extractions the critical phosphorus levels for TIala soils were 17 and 27 mg P kg" for cvs. Holetta and G22763-2C respectively, and for Cheffa soils 20 and 22 mg P kg" for cvs. Cheffa local and Tegegnech respectively Field experiments: Two sets of experiments were conducted, viz. the first set at Holetta (1996 to 1999) and Bekoji (1996 to 1998) and the second set in 2001 at TIalaand Cheffa. For the first set of experiments a factorial combination of five phosphorus rates (0, 10, 20, 40 and 60 kg P ha") and three pea cultivars (Holetta site: Tegegnech, G22763-2C, Holetta local; and Bekoji site Tegegnech, G22763-2C and Cheffa local) were laid out in a randomized complete block design with four replications. On the other hand, for the second set of trials a split plot design was used with three phosphorus fertility levels (Extractable phosphorus: low = 5, medium = 15 and high = 30 mg kg") as the main plot treatments and the factorial combinations of five phosphorus application rates (0, 10, 20, 40 and 80 kg ha") and two pea cultivars (llala site: G22763-2C and Holetta; and Cheffa site: Tegegnech and Cheffa local) as the sub-plot treatments which were replicated four times. At the Holetta and llala sites, grain yield response of the pea crop to phosphorus a.pplication was poor regardless of the phosphorus application rates or the cultivars . As a result, low marginal rate of returns (MRRs) were computed which implicated that phosphorus fertilization is not economically viable. On the contrary, at the Bekoji and Cheffa sites, the grain yield response of the pea crop to the application of phosphorus was good with significant differences between phosphorus fertility levels and cultivars. The interaction of phosphorus application rate and cultivars was significant (p < 0.05). A MRR of 100% was obtained at an application of21 kg P ha-I for cv. Tegegnech, 10 kg P ha" for cv. G22763-2C and 5 kg P ha-I for cv. Cheffa local. The 100% MRR computed implicated that phosphorus fertilization to all cultivars at the low phosphorus fertility level was economically viable with the current prices of grain and fertilizer in the zone. Unfortunately, no critical soil phosphorus levels could be estabilished under field conditions. The critical soil phosphorus levels that were established under glasshouse conditions should therefore still be validated in the field. However, the fact that the pea crop did respond to phosphorus application mainly at the low phosphorus fertility levels in the field confirms already to some extent their validity. In general, the improved pea cultivars responded better to phosphorus fertilization than the local cultivar. A thorough investigation on phosphorus use efficiency of pea genotypes to' identify low phosphorus requiring ones should be considered to benefit resource poor farmers. The aspect of soil pH modifications through liming, and the use of non-nitrogenous phosphorus fertilizer sources for field peas are recommended.
Open Access
The effect of nitrogen, phosphorus and potassium fertilisation on the growth, yield and quality of Lachenalia
(University of the Free State, 2004-11) Engelbrecht, G. M.; Du Preez, C. C.; Spies, J. J.
English: Very little is known about the response of Lachenalia to fertilisation when cultivated in soil. The objective of this study was therefore to quantify the effect of fertilisation on the growth, yield and quality of Lachenalia in both the nursery and pot plant phases. In order to achieve this two pot trials for the nursery phase and one pot trial for the pot plant phase were conducted in the glasshouse. For the first trial in the nursery phase the combined effect of nine nitrogen levels and three application times on the Lachenalia cultivars, Rupert and Ronina, were studied. The nitrogen was applied at levels equivalent to 0, 30, 70, 120, 180, 250, 330, 420 or 520 kg N ha -1 . Three different nitrogen application times were used namely: one third with planting and the rest 10 weeks after planting (T1); one third with planting and the other two thirds after planting (T 2) or one quarter with planting and the other three quarters after planting (T3). The leaf area of Ronina plants was larger than that of Rupert plants irrespective of nitrogen levels and application times. However, Ronina bulbs were larger and softer than Rupert bulbs. The nutrient (N, P, Ca and Mg) and carbohydrate (D-glucose, sucrose and starch) content of Rupert bulbs were higher than that of Ronina bulbs. Application of nitrogen had a positive influence on the leaf area, bulb fresh mass and circumference of both cultivars. Bulb firmness was negatively influenced by nitrogen application. The best results for most parameters were obtained when nitrogen was applied in four equal applications. In the second trial for the nursery phase the response of Rupert and Ronina to five nitrogen (0, 70, 180, 330 or 520 kg N ha -1 ) and five phosphorus (0, 10, 30, 50 or 80 kg N ha -1 ) or five potassium (0, 70, 180, 330 or 520 kg N ha -1 ) levels were studied. Neither the interaction between nitrogen and phosphorus levels nor the interaction between nitrogen and potassium levels had a large influenced on the growth and development of Lachenalia. Results obta ined in this trial with respect to the effect of nitrogen levels on the different parameters mainly confirm with the results obtained with the first trial. In the trial for the pot plant phase the effect of seven nitrogen levels (0, 30, 70, 120, 180, 250, 330, 420 or 520 kg N ha -1 ) on Lachenalia grown from 7-8 cm bulbs, whereof the fertilisation history in the nursery phase differed, was investigated. The fertilisation history of the bulbs in the nursery phase consisted of three nitrogen levels (0, 70, 250 or 520 kg N ha -1 ) combined with two nitrogen application times (T1, T2 or T3 as described earlier). The leaf area of Ronina plants was larger than that of Rupert plants. Nitrogen applied in the nursery phase promoted the leaf area of both Rupert and Ronina. Application of nitrogen in the nursery phase and in the pot plant phase increased the number of inflorescence per plant and the number of florets per inflorescence. The peduncle length increased with higher nitrogen levels in the nursery phase wherea s the peduncle diameter increased with higher nitrogen levels in the pot plant phase.
Open Access
Bio-stimulatory properties of a Lupinus albus L. seed suspension
(University of the Free State, 2005-05) Van der Watt, Elmarie; Pretorius, J. C.; Van der Westhuizen, A. J.
English: The sustainable increase in crop yields on available land, in light of an ever growing world population, remains an issue of importance for agronomists and plant physiologists alike. With this in mind, the underlying study was aimed at investigating the bio-stimulatory properties of a Lupinus albus L. seed suspension (SS) as well as its potential to be applied as a natural plant growth regulator in the horticultural and agricultural industries. Preliminary bio-tests, including the respiration rate of monoculture yeast cells, seed germination and seedling growth, strongly indicated that the rather crude seed suspension possessed the ability to manipulate these aspects when applied exogenously. SS significantly increased the respiration rate of monoculture yeast cells and, although it did not have a significant effect on seed germination, stimulated seedling growth in terms of coleoptile and root length in a number of crops at an optimal concentration of 5 mg L-1. Subsequently, the effect of SS on the yields of a variety of vegetable crops, flowers and cash crops was tested under field conditions at a concentration of 5 mg L-1. This concentration proved to be optimal for most vegetables, flowers, maize and wheat as either flower formation or yield of different crops were significantly enhanced. The most significant yield increases, after a foliar spray treatment with SS at an early growth stage, was observed in beetroot, lettuce and carrots under drip irrigation by increasing the yield with 9.3, 20.0 and 24.3 ton ha-1 respectively. This supplied the rationale for activity directed isolation and purification of the active bio-stimulatory compounds involved using standard chromatography techniques. By means of NMR spectroscopy and mass spectrometry the active compound was identified as a triglyceride, glycerol trilinoleate, and its structural formula elucidated. It was concluded from this study that the development of a natural product with growth regulating and yield enhancing properties should be considered strongly from a commercial perspective.
Open Access
Using seasonal climate outlook to advise on sorghum production in the Central Rift Valley of Ethiopia
(University of the Free State, 2005-12) Diga, Girma Mamo; Walker, Sue
English: Seasonal rainfall is an important source of water for rainfed farming in the semi-arid regions of the world, where rainfall is marginal and variable. However, as rains are unpredictable in terms of onset, amount and distribution, there is a need to understand the variability and other basic rainfall features in order to use the information in agricultural decision making. More specifically, combining the seasonal rainfall prediction with crop water requirement and soil water information is the core component to successful agriculture. The ultimate objective of this study was to characterize and obtain a better understanding of the most important rainfall features that form the basis for classifying the areas into homogenous rainfall zones and then to develop a seasonal rainfall prediction model for the Central Rift Valley (CRV) of Ethiopia. The source data for the analyses was primarily obtained from the National Meteorological Services Agency (NMSA) and partly from Melkassa Agricultural Research Centre (MARC) and the web site of the International Research Institute for Climate and Society (IRI). Rainfall variability and time series analyses were done using INSTAT 2.51 and coded time method, respectively. Rainfall onset and March-April- May (MAM) rainfall totals are the two most variable features both at Miesso and Abomssa. For both stations, rainfall end date displays the least variability. Rainfall onset date at Miesso ranges from the lower quartile (25 percentile) of DOY 61 to the upper quartile (75 percentile) of DOY 179 with a 42% coefficient of variation (cv). At Miesso, the main rainy season terminates during the last days of September (DOY 272 - 274) once in four years and terminates before DOY 293 in three out of four years. At Abomssa, the c.v for the lower quartile (DOY 61) to the upper quartile (DOY 134) was found to be 40.5%. At both locations, planting earlier than 15 March (DOY 75) only proves successful once in every four years. Further, at Miesso this upper quartile statistic can extend up to the DOY 179, whereas at Abomssa planting earlier than 15 April (DOY 134) is possible in three out of four years (75 percentile). At Abomssa, rainfall terminates by DOY 286 and the end of October (DOY 305) for the 25 and 75 percentile points respectively. From the time series analyses, there was no conclusive evidence for the existence of a trend for both Miesso and Abomssa, information which is useful for long-term research and development planning, as well as seasonal rainfall prediction for the study area. The classification study for the spatial rainfall pattern resulted in four homogenous rainfall zones that form distinct development and research units, using the FORTRAN- 90 based NAVORS2 program. The south facing Alem Tena-Langano zone has a better rainfall pattern than drier zones and thus formed zone 1. The southern, southwestern and southeastern area has formed the wet zone (zone 2), the northwestern to northeastern facing part (Debre-Zeit-Nazerth-Dera) that receives a higher rainfall amount than zone 1 has formed zone 3 and finally, the drier northeastern part constituted zone 4. Twenty seven seasonal rainfall prediction models with varied performance skills that can be used for the operational farming were developed for the March-September monthly rainfall using the Climate Predictability Tool (CPT v.4.01) from IRI. It was understood that with increased observing networks and data availability, useful operational climate prediction could be achieved for a smaller spatial unit and with a short lead-time. The tempo-spatial water requirement satisfaction pattern analyses were conducted using AGROMETSHELL v.1.0 of the FAO. Fourteen concurrent sorghum-growing seasons that give a general picture of crop water requirement satisfaction were mapped. The southern, southwestern and southeastern parts (zone 2) of the CRV constitute the most favourable location for growing a range of sorghum maturity groups. The northwestern and central (zone 3) parts constitute the next most suitable zone. The wide northeastern drylands (zone 4) of the study area, except the pocket area of Miesso-Assebot plain, does not warrant economic farming of sorghum under rainfed conditions. From the growth stage-based Water Requirement Satisfaction Index (WRSI) analyses, mid-season / flowering stage of the sorghum cultivars was found to be three times more sensitive to changes in sorghum yields for both cultivars and experimental sites as compared to the WRSI from the rest of growth stages. The results from the water production function analyses (WPF) also indicated the potential of WRSI for prediction of the long-term sorghum yields. The cumulative density function (CDF) and stochastic dominance analyses for the 120-day grain sorghum cultivar grown at Miesso show the June planting to be the most efficient set by first degree stochastic dominance (FSD), while May was found efficient for Melkassa. The CDF for Arsi Negele shows April planting date to be the best set. Therefore, these planting dates are to be preferred by farmers seeking ‘more’ yield at the respective locations, regardless of their attitude towards risk. The sensitivity analyses conducted using different levels of the seasonal rainfall related input variable combinations (sorghum planting date, maturity date, number of rainy days and WRSI) for Miesso, Melkassa and Arsi Negele provide useful information. By keeping input variables other than WRSI at the most preferred level (i.e. early planting date, extended maturity date, and greater number of rainy days) and only changing WRSI from 100% to 75% resulted in a 49.7% yield reduction in case of Miesso, 40.8% in case of Melkassa and 24.3% in case of Arsi Negele. Further, when WRSI was reduced down to 50%, there was a total crop failure in the case of Miesso and Melkassa, while the reduction was 48.6% for the Arsi Negele case. Similar results were found when WRSI was varied across other input level combinations. Visual Basic v.6.0 was used to write the algorithm for the decision support tool (DST) relating sorghum planting dates in CRV, to which the name ABBABOKA 1.0 was given. By using the rainfall prediction information from three different sources (the new prediction model developed in chapter 3, NMSA and ICPAC), ABBABOKA suggests the best possible planting alternatives for a given homogenous rainfall zone and planting season. When decision making under this predictive information alone is not sufficient, soil water parameters need to be consulted for more reliable decision making. This simple and briefly constructed ABBABOKA is expected to provide a suite of guidelines to the users. Certainly, this constitutes a significant departure from the fixed ‘best bet’ recommendations I learned from research systems in the past. It is recommended that the time-space classification of agricultural areas into homogeneous zones needs to be extended to the rest of the country together with the tailored rainfall prediction information. Research needs to be geared towards crop water requirements, climate risks and simulation modelling aspects. A network of weather stations and soil database needs to be developed in order to promote the soilcrop- climate research in Ethiopian agriculture. More importantly, the use of decision support tools and the well-established models (like APSIM) need to be included in agricultural research and development efforts.
Open Access
Effect of tillage system, residue management and nitrogen fertilization on maize production in western Ethiopia
(University of the Free State, 2006-05) Dilallessa, Tolessa Debele; Du Preez, C. C.; Ceronio, G. M.
English: The sustainability of maize production in western Ethiopia is in question despite of favorable environmental conditions. A major reason for this phenomenon is severe soil degradation in maize fields. This soil degradation manifested often in low soil N fertility which inhibited maize yields. The situation is worsened by the financial inability of most farmers to purchase N fertilizer for supplementation. In these conditions two basic approaches can be followed to improve maize productivity in a sustainable way. Firstly, integrated cropping practices can be developed for maize to make better use of N from organic and inorganic sources. Secondly, maize genotypes can be selected that are superior in the utilization of available N, either due to enhanced uptake efficiency or because of more efficient use of the absorbed N. In this context, experiments were conducted to determine the integrated effects of tillage system, residue management and N fertilization on the productivity of maize, and to evaluate different maize genotypes for N uptake and use efficiency. The experiments on integrated cropping practices were done from 2000 to 2004 at five sites viz. Bako, Shoboka, Tibe, Ijaji and Gudar in western Ethiopia. They were laid out in a randomized complete block design with three replications. Three tillage systems (MTRR = minimum tillage with residue retention, MTRV = minimum tillage with residue removal and CT = conventional tillage) and three N levels (the recommended rate and 25% less and 25% more than this rate) were combined in factorial arrangement. Every year yield response, usage of applied N and changes of some soil properties were measured. In 2004 the same experiments were used to monitor the fate of applied N in the soil-crop system. Labeled urea was applied at the recommended rate to micro plots within the MTRR and CT plots for this purpose. During the initial two years of the experiments, there was no significant difference in grain yield between MTRR and MTRV and both were significantly superior to CT. However, during the final two years of the experiments, there was no significant difference between MTRV and CT and both were significantly inferior to MTRR. On average, the grain yield of MTRR was 400 and 705 kg ha-1 higher than that of MTRV and CT, resulting in consequent increases of 6.6 and 12.2%, respectively. The application of N increased the grain yield regardless of tillage system. An application of 92 kg N ha-1 was significantly superior to 69 kg N ha-1, but on par with the 115 kg N ha-1 application. Hence, the recommended fertilization rate of 92 kg N ha-1 for conventional tilled maize was also found adequate for minimum tilled maize in western Ethiopia. This rate remained economically optimum with a 20% decrease in the maize price and a 20% increase in fertilizer cost. The grain differences resulted from the tillage systems and concomitant residue management were attributed to significant changes in some soil fertility parameters, especially in the 0-7.5 cm layer. After five years both indices of organic matter, viz. the organic C and total N contents were significantly higher in the MTRR soils when the CT soils serve as reference. Similarly, the extractable P and exchangeable K contents of the MTRR soils were also higher than that of the CT soils. The only negative aspect of MTRR in comparison with CT was a decline in soil pH. A significantly higher grain N content was recorded with MTRR than with MTRV and CT. The stover N content was not significantly affected by the three tillage systems. However, grain, stover and total N uptake were consistently superior with MTRR compared to MTRV and CT. The NAE, NRE and NPE of maize for the same tillage system were consistently higher at the lower N level range of 69-92 kg ha-1 than at the higher N level range of 92-115 kg ha-1. At the lower N level range NAE and NRE were larger with CT than with the other two tillage systems. Both indices were higher with MTRR than with the other two tillage systems at the higher N level range. The NPE was not significantly affected by the tillage systems. However, the trend at both N level ranges was higher with MTRR than with MTRV and CT. The labeled urea study showed that the grain, stover and total biomass N derived from fertilizer was consistently higher for CT than MTRR. Conversely, grain, stover and total biomass N derived from soil was consistently higher with MTRR than CT. Therefore, the fertilizer N recorded in the MTRR soils was higher with MTRR than CT and mainly confined to the upper 45 cm. The fate of fertilizer N was in MTRR: 47% recovered by maize, 17% remained in the soil and 36% unaccounted for and in CT: 54% recovered by maize, 12% remained in the soil and 34% unaccounted for. The experiments on genotype comparison for N uptake and use efficiency were also done at Bako, Shoboka, Tibe, Ijaji and Gudar. In 2004 the response of five open-pollinated and five hybrid genotypes were evaluated at six N levels from 0 to 230 kg ha-1 with 46 kg ha-1 intervals. Only two out of the ten genotypes evaluated qualify as N use efficient. They were the openpollinated Ecaval 1 and the hybrid CML373/CML202/CML384. These two CIMMYT genotypes showed consistently higher NAE, NRE and NPE at low and high N applications as required. This was not the case with the two local genotypes that were included, viz. the open-pollinated Kulani and the hybrid BH 540. Based on the results that evolved from this study it is clear that: 1. Farmers should be encouraged to practice MTRR instead of CT since this change in tillage system could improve the productivity of maize on Nitisols in western Ethiopia. 2. On these Nitisols the conversion from CT to MTRR need not coincide with an adaptation in the recommended fertilization rate of 92 kg N ha-1. 3. The planting of N use efficient maize genotypes on Nitisols must be advocated to farmers, especially those who can not afford proper fertilization. Aspects that need to be investigated in future are: 1. Quantification of N mineralization and immobilization in the Nitisols when subject to MTRR and CT for maize production. 2. Losses of fertilizer N through volatilization, leaching and denitrification from the Nitisols when subject to MTRR and CT for maize production. 3. Suitability of other soil types which are used for maize production in western Ethiopia for MTRR instead of CT. 4. Performance of the N use efficient genotypes on other soil types which are used for maize production in western Ethiopia. 5. Crop rotation with N fixing crops.
Open Access
Causes and impact of desertification in the Butana Area of Sudan
(University of the Free State, 2006-11) Elhag, Muna Mohamed; Walker, S.
English: Desertification is one of the most serious environmental and socio-economic problems of our time. Desertification describes circumstances of land degradation in arid, semi-arid and dry sub-humid regions resulting from the climate variation and human activities. The fundamental goal of this thesis was to monitor the extend and severity of the land degradation and examine climate variability and change in the Butana area of northeastern Sudan. To explore the climate variability and climate change in terms of rainfall, temperature and the aridity index for the period from 1941 to 2004, the monthly and annual time series for four weather stations (El Gadaref, Halfa, Wad Medani and Shambat) across the Butana area were analysed. The trend of the rainfall at Wad Medani and Shambat shows significant decline, while that of Halfa and El Gadaref does not show a significant decrease or increase. The Cumulative Rainfall Departure (CRD) was used to detect the periods of abrupt changes in the rainfall series. A significant decrease in the annual rainfall was observed at Shambat (p = 0.00135) and Wad Medani (p = 0.0005) from 1968 to 1987, there after the rainfall amount is close to the long-term mean. In El Gadaref there was a decline in the annual rainfall from 1971 to 1974 (p = 0.35) but it was not significant, with a recovery from 1975 to 1982 to a value higher than the long-term mean, followed by another downward turn from 1983 to 1994. In Halfa there was a significant decrease (p = 0.0304) from 1982 to 1993. The trends of maximum and minimum temperature were examined for the summer (March-May), autumn (June-October) and winter (November-February) seasons for the four weather stations. At Halfa and Shambat the trend of maximum and minimum summer and winter temperature was increasing but vi not significant, while in Wad Medani there was a significant increase for summer and winter minimum temperatures. El Gadaref station showed a significant increase in maximum and minimum temperature (p = 0.00005, p = 0.00016) respectively. The miimum autumn temperature for Halfa increased significantly, while this was the case for both the minimum and maximum autumn temperature at Shambat and Wad Medani. This significant increase in temperature, associated with autumn, is partly due to dry conditions observed during the late 1960s. The relationship between 8 km2 AVHRR/NDVI and rainfall data (1981-2003) was tested in the Butana area. The relationship was strong between the peak NDVI (end of August through the beginning of September) and cumulative July/August rainfall, but weak relationships resulted when annual rainfall and cumulative NDVI were used. The Departure Average Vegetation method showed that the area had a high percentage of departure, reaching about 40% of the long-term average during the drought years and the NDVI recovered during the following year if the rainfall was above average. There were increased trends in NDVI in the study area during the period from 1992 to 2003, despite some years during this period having higher departure although that departure was less than for the period 1981-1991. To monitor the impact of human activities on land degradation it is essential to remove the effects of rainfall on vegetation cover. Using the Residual Trend Method the differences between the observed peak NDVI and the peak NDVI predicted by the rainfall was calculated for each pixel. This method identified degraded areas that exhibit negative trends in NDVI. The human impact is more clear in the northern part. Satellite imagery provides an opportunity to undertake routine natural resource monitoring for mapping land degradation over a large area such as Butana over a long time period. This facilitates efficient decision making for resource management. Five classes of land use were achieved using unsupervised classification, whereafter an image difference technique was applied for 1987-1996 and 1987-2000. This analysis showed that the bare soil and eroded land increased by 3-7% while the vegetated area decreased by 3-6%. Also when comparing the aerial photographs (1960s and 1980s) for Shareif vii Baraket, Kamlin and El Maseid with Landsat images (2000) severe degradation of the vegetation cover was visible at all the three sites. The Moving Standard Deviation Index (MSDI) is calculated by performing a 3×3 moving standard deviation window across the band 3 Landsat images (1987, 2000). MSDI proved to be a powerful indicator of landscape condition for the study area. The MSDI increased considerably from 1987 to 2000, especially for Sufeiya, Sobagh and Banat areas, which are referred to as severely degraded sites in the literature. The Bare Soil Index (BSI) supports the finding from the MSDI. The BSI for the degraded sites Sufeiya, Sobagh and Banat increased from 0-8 in 1987 to 32-40 in 2000. The image difference of the BSI ndicated that the index increased by about 14-43 over the 13 years. A Microsoft Excel macro was used to write the algorithms for a decision support tool relating the factors that trigger and propagate desertification in arid and semi-arid areas. This was named “Tashur”. Rainfall, aridity index and NDVI were used to evaluate the condition of the landscape. If these three parameters alone were not sufficient to make a decision, then soil and human activity parameters need to be consulted for more reliable decision making. This simple and concise decision support tool is expected to provide guidelines to planners and decision makers. Different ecosystems in the Butana area are subjected to various forms of site degradation. The desertification has led to sand encroachment and to accelerated development of dunes and also increased the water erosion in the northern part of the area. The area has also been subjected to a vegetation cover transformation. Pastures have deteriorated seriously in quality and quantity, but in many parts the degradation is still reversible if land use and water point sites are organized.
Open Access
Evaluation of maize and sunflower production in a semi-arid area using in-field rainwater harvesting
(University of the Free State, 2006-11) Botha, John Jacobus; Van Rensburg, L. D.; Hensley, M.
English: Subsistence farmers occupy a large area east of Bloemfontein around Thaba Nchu in the Free State Province of South Africa. They do not enjoy food security because the area is marginal for crop production. There are three reasons for this: (a) low and erratic rainfall that amounts to a mean of 543 mm per annum; (b) a corresponding high evaporative demand of 2198 mm per annum; (c) dominantly duplex and clay soils on which rainwater productivity (RWP) is low due to high runoff (R) and evaporation (Es) losses. It was hypothesised that the in-field rainwater harvesting (IRWH) technique could improve crop yields compared to conventional tillage (CON), and thereby serve to improve food security. Field experiments were conducted on the Glen/Bonheim; Glen/Swartland (dark brown A horizon); Khumo/Swartland and Vlakspruit/ Arcadia ecotopes to study the benefits of the IR WH technique on maize and sunflower yields. This thesis distinguishes between ex-field (REx) and in-field runoff (RIn). RIn is transportation of water over the 2 m runoff strip in the IR WH technique. REx occurs on CON and represents a loss of water and soil. Runoff and sedimentation results indicate that IR WH stops REx completely and has the ability to harvest extra rainwater in the basins through RIn and minimize sedimentation. The results also indicate that mulch on the runoff area decreases RIn and sedimentation. The Es process with different surface coverings was studied on two ecotopes viz. Glen/Bonheim and Glen/Swartland (red-brown A horizon). The soil coverings were as follows: bare soil; stone and organic mulch covering 50% of the surface; and organic mulch covering 100% of the surface. The studies were conducted during summer (69 days) and winter (52 days). Results indicated that the % cover affected Es more than mulch type, and that the influence of mulch on Es was more efficient when the drying-out period did not exceed 16 days. New terminology for the various Es stages was introduced. The role of Eo, water content and hydraulic conductivity during the Es process were clarified. Es measurements shallower than 300 mm were shown to be unreliable. Field experiments were conducted on four ecotopes over two to seven growing seasons during the period 1996/1997 to 2002/2003 with maize and sunflower. The treatments were CON; IRWH with a bare basin and bare runoff area (BbBr); IRWH with organic mulch in the basins and a bare runoff area (ObBr); IR WH technique with organic mulch in the basins, stones on the runoff area (ObSr); IRWH technique with organic mulch in the basins, organic mulch on the runoff area (ObOr); IRWH technique with stones in the basins, organic mulch on the runoff area (SbOr). Results showed that IR WH significantly increased maize and sunflower yields compared to CON. This was shown to be due to the ability of IR WH to stop REx completely; enhance RIn and its resulting beneficial redistribution of water in the soil profile; minimize Es/ET, and contribute towards higher transpiration. Both yield and RWP results showed that IRWH stabilises crop production on these ecotopes, compared to CON. Comparing the IR WH techniques revealed that there was a consistent trend in yield and RWP viz. ObSr> ObOr ~ SbOr > ObBr> BbBr. All the IR WH treatments with mulch on the runoff area produced higher RWP values and yield increased between 7 and 16% compared to ObBr. Although Es/ET results indicated that the IR WH treatments with mulch on the runoff area lost smaller portions of ET to Es than ObBr, mulch type on the runoff area and basins did not significantly affect Es in any of the years. The most reliable way to describe the effectiveness with which rainwater was converted into grain by various techniques was by using the parameter RWPn. It was computed by using long-term experimental and simulated yield data, which included rainfall during the fallow and growing seasons. An empirical crop water stress model "Crop Yield Prediction for Semi-Arid Areas" (CYP-SA) was developed. Model composition and validation results with maize and sunflower are described. CYP-SA was used to make long-term maize and sunflower yield predictions with long-term climate data (8I-year period). Cumulative probability functions of simulated long-term maize and sunflower yields have shown that IR WH is significantly superior to CON. The ObSr treatment was shown to be the best. It was also shown that it is advisable to plant maize or sunflower early in January, especially when the soil water profile is between ¾ full and full. The JRWH technique was introduced to rural communities In the target area to improve household food production. The thesis reports on the rapid spread of the application of JRWH amongst homesteads, and on its ability to eradicate poverty at household level. Selected case studies were reported. Very promising results were obtained showing that households can reduce poverty by selling the produce. The five pillars of sustainability, as defined by Smyth & Dumanski (1993) viz. agronomic productivity; crop production risk; conservation of natural resources; economic viability and social acceptability, were investigated in relation to JRWH. Results indicate that in the agro-ecological and socio-economic environment present in the rural communities around Thaba Nchu CON was non-sustainable and that JRWH was sustainable.
Open Access
Quantifying rainfall-runoff relationships on selected benchmark ecotopes in Ethiopia: a primary step in water harvesting research
(University of the Free State, 2006-12) Welderufael, Worku Atlabatchew; Le Roux, P. A. L.; Hensley, M.
Large areas of cultivated land in Ethiopia frequently suffer from drought, causing low crop yields and food insecurity. It was hypothesized that it may be possible to alleviate this problem by employing infield rain water harvesting (IRWH). Three representative semi-arid ecotopes in the Rift Valley were selected to test this hypothesis. They were the Melkassa Hypo Calcic Regosol, The Dera Calcic Fluvic Regosol and the Mieso Hypo Calcic Vertisol. The climate, topography and soils of the ecotopes were characterized in detail. Rainfall runoff studies were carried out over two rain seasons on replicated plots on these ecotopes comparing two soil surface treatments. They were conventional tillage (CT), simulating the initially fairly rough surface which results after normal tillage; and no tillage (NT), simulating the flat crusted surface expected on the runoff strip of the IRWH system. Rainfall amounts, rainfall intensity at one minute intervals, and runoff, were measured for each storm during the two rain seasons on each ecotope. The results were used to calibrate and validate the Morin & Cluff runoff model in order to enhance the extrapolation capability of the study results to other similar ecotopes. The study yielded the following useful results. · The rainfall pattern on all the ecotopes was characterized by occasional storms with fairly high amounts and high intensities (Pi) which greatly exceeded the final infiltration rates of the soil, causing a high proportion of the rain (P) to runoff (R), i.e. producing a high R/P ratio. For the NT treatment final overall R/P values for the two seasons on the Melkassa, Dera and Mieso ecotopes were 0.45, 0.52 and 0.32, respectively. These high values indicate that IRWH should produce a significant increase in yield due to its ability to reduce R to zero while concentrating the runoff in the basin area and increasing the water available for transpiration and therefore increasing yield. · Because of the textural and mineralogical properties of the topsoils, particularly the two Regosols soils; they disperse and form crusts easily when impacted by high intensity rain. The result was that after cultivation at the start of the rain season the surface of the CT treatment soon became very similar to that of the NT treatment. Accordingly no significant difference was found between the runoff from the NT and CT plots on the Melkassa Regosol and Dera Regosol. There was, however, a significant difference in this respect on the Mieso Vertisol with a more stable surface. · Runoff prediction in all the ecotopes were well done by the M & C model. · Two separate strategies were developed to estimate the maize yield increase that could be expected on the Melkassa Regosol by employing IRWH. From the nearby Melkassa Research Station it was possible to obtain maize yields for 15 seasons (1989-2003). These were used together with climate data, the CROPWAT model, and the runoff measurements, to estimate the benefit of IRWH. The two strategies produced yield increase estimates of 33% and 40% compared to CT.
Open Access
Response of crops on shallow water table soils irrigated with deteriorating water qualities
(University of the Free State, 2007-11) Ehlers, Louis; Bennie, A. T. P.; Van Rensburg, L. D.
This study was undertaken to investigate a number of issues regarding the effect of using saline irrigation water for crop production on soils with shallow water tables. The experiments were conducted in large drainage lysimeters, filled with a yellow sandy soil and a red sandy loam soil in which shallow saline water tables were maintained at a constant depth of 1.2 m. Wheat, beans, peas and maize were grown under controlled conditions using irrigation water with salinities that ranged from 15 to 600 mS m-1. This facility was used to determine the effect of irrigation water and water table salinity on crop yield and water uptake, as well as salt accumulation in the root zone during growing seasons. The field experiments simulated conditions of adequate water supply to the crops through irrigation in the presence of a shallow saline water table. Except for wheat that gave better yields in the more clayey soil, the growth of the other three crops was similar on both soils for comparative irrigation water salinity treatments. The above-ground biomass of wheat, maize, peas and beans started to decline when irrigated with water of 600, 450, 300 and 150 mS m-1, respectively. The water use of all four crops, as indicated by evapotranspiration, declined with deteriorating irrigation water salinity. On a relative basis the evapotranspiration of peas, beans, maize and wheat decreased at rates of 0.0007, 0.0005, 0.0004 and 0.0001 mm per unit increase of soil water salinity measured in mS m-1. A decrease in the osmotic potential of the soil water to -300 kPa, which is equivalent to an electrical conductivity of 750 mS m-1, reduced evapotranspiration in comparison to the control by 7, 30, 38 and 53% for wheat, maize, beans and peas, respectively. The water use efficiency of the crops, expressed in above-ground biomass produced per unit mass water used, started to decline only when the threshold ECe-values were exceeded. Water uptake from the shallow water tables decreased with an increase in irrigation water salinity for all four crops on both soils. The relative water uptake from the capillary zones above the water tables declined linearly when the soil water salinity in these zones exceeded certain threshold values. These values varied between 57 mS m-1 for beans to 279 mS m-1 for maize, with an average value of 136 mS m-1. The crops less affected by the increase in salinity, were wheat followed by maize, beans and peas. Salts accumulated at or just below the capillary fringe in both soils, with maximum accumulation at 700 mm from the soil surface or 500 mm above the water table. Equations were derived from the accumulation of salts in the root zone to calculate the salt accumulation in soils with restricted drainage during a crop growing season. These equations were incorporated in proposed procedures for salinity management on irrigated soils. The procedures made provision for five different conditions: i) where added salts to the root zone accumulate without any possibility for leaching and the mean root zone salinity is lower than the crop ECe-threshold value; ii) where added salts to the root zone accumulate without any possibility for leaching and the mean root zone salinity is higher than the crop ECe-threshold value; iii) where added salts can leach naturally from the root zone, but with not enough irrigation water to supply in the crop water demand; iv) where the natural leaching of added salts can be accelerated by irrigating more than the required crop water demand; and v) to irrigate according to the crop water demand in order to utilize rainfall for leaching. The different salinity management procedures were compared on the two soil types by means of computer simulations for a range of irrigation water qualities and long-term climatic conditions. The simulated results indicated that under conditions with zero drainage, sustainable production could be maintained for only 25 to 40 years if good quality water was used for irrigation. Irrigation water with an ECi > 50 mS m-1 resulted in severe soil salinisation and crop losses within 5 to 10 years. On freely drained soils additional leaching was required within 5 years, even with the use of good quality irrigation water. It was clear from the simulated results that an increase in root zone salinity in soils with shallow water tables, necessitate adaptations in the normal approaches to irrigation scheduling and irrigation water management.
Open Access
Induction of defence responses and resistance to wheat leaf rust by plant extracts
(University of the Free State, 2008-05) Cawood, Maria Elizabeth; Pretorius, J. C.; Van der Westhuizen, A. J.
English: Information on the induced disease resistance mechanism in wheat against leaf rust (Puccinia triticina) by two natural bio-stimulants (ComCat® and the seed suspension of Lupinus albus; SS) and two extracts with antifungal activity (Tulbaghia violacea and Agapanthus africanus) may be of great value both in designing new agrochemicals that stimulate plant resistance responses and in developing genetically engineered plants with enhanced disease resistance. The potential of these extracts to control leaf rust in vivo in susceptible (Thatcher) and resistant (Thatcher / Lr15) wheat was investigated. ComCat® and SS had no direct effect while the A. africanus extract resulted in the reduction of pustule and necrotic lesion formation in a susceptible and resistant wheat cultivar. T. violacea and A. africanus significantly inhibited the germination of P. triticina spores and prevented further germ tube development. Foliar application of the different plant extracts on resistant infected wheat plants activated β-1,3-glucanase, chitinase and peroxidase enzyme activities. However, it was only the A. africanus treatment that increased the in vitro activities of these three apoplastic PRproteins significantly in both susceptible and resistant wheat cultivars, whether uninfected or infected. As a result it was decided to concentrate the rest of the study on the A. africanus extract only. The induction pattern of apoplastic proteins from infected susceptible and resistant wheat treated with an A. africanus extract as well as a control treated with distilled water was followed using SDS-PAGE. Clear differences between SDS-PAGE profiles of intercellular proteins from resistant and susceptible as well as untreated and treated plants were observed throughout the 144 h period after treatment with the extract. In general, resistant plants contained higher amounts of a 31 kDa protein and the protein was also present at much higher detectable levels in plants treated with the A. africanus extract. The molecular mass corresponded to that of β-1,3-glucanase. A Western blot using a polyclonal antibody against β-1,3-glucanase from wheat confirmed the identity of the 31 kDa protein to indeed be that of β-1,3-glucanase. This overwhelmingly excluded the A. africanus extract from the rest in terms of its potent ability to induce a defence response in wheat towards leaf rust. RT-PCR was used in the analysis of the expression of the three defence related genes. Timecourse experiments confirmed that they were induced in resistant as well as susceptible wheat after infection. In this study, when resistant and susceptible wheat were treated with an extract of A. africanus 48 h prior to infection, a more pronounced induction of PR2, PR3 and PR9 gene expression occurred. Two different sized fragments were amplified when using PR9 specific primers and both were induced by infection and by treatment with A. africanus extract in susceptible and resistant wheat. After sequencing, the larger fragment was confirmed to be peroxidase, while the smaller fragment shared very high sequence similarity to a retrotransposon gene. It can, therefore, be claimed that A. africanus is responsible for the induction of PR genes and a retrotransposon gene in wheat. From the results obtained thus far, it was obvious that A. africanus must contain an active compound(s) that act as an elicitor(s) in the mechanism of the defence reaction of wheat against leaf rust infection. Subsequently, activity directed isolation and purification of the active compound lead to the isolation of a saponin, identified by means of 1H-NMR and 13CNMR spectroscopy as (25R)- 5α spirostane-2α, 3β, 5α-triol 3-O-{O-α-L-rhamnopyranosyl- (1α2)-O-[β-D-galactopyranosyl- (1α3)]- β-D-glucopyranoside}.
Open Access
Fertility recovery in sandy soils under bush fallow in southern Mozambique
(University of the Free State, 2008-05) Nhantumbo, Alfredo Bernardino Julio Da Costa; Du Preez, C. C.; Ledin, S.
English: Bush fallow under shifting cultivation is the most common practised subsistence farming system in southern Mozambique. This system is likely to persist due to the existence of large areas sparsely inhabited coupled with financial limitations preventing small scale farmers from buying fertilizers. The bush fallow is intended to recover naturally the productive capacities of soils lost during cropping. This study was conducted therefore to gain a better understanding on the composition and biomass of bush fallow vegetation, climatic factors affecting leaf litter decay of an important tree species and the dynamics of some soil fertility indicators. Five agroecosystems representing rainfall regions of <400 mm (AE6), 400-600 mm (AE5), 600-800 mm (AE3), 800-1000 mm (AE2), >1000 mm (AE1) and a transitional agroecosystem of 400-800 mm (AE4) were selected. Within each agroecosystem, five land uses (virgin, cultivated, < 5 years fallow, 5-15 years fallow and >15 years fallow) were identified. Descriptions and comparisons of vegetation were performed between land uses within agroecosystems and similar land uses across agroecosystems, except in cultivated land; effects of soil water content and soil temperature on decomposition of Brachystegia spiciformis leaf litter were evaluated in recently abandoned agricultural fields cleared of any vegetation (Bare) and in >15 years fallow fields (15F) at sites in a transect that covered AE2 to AE6; and at every combination of agroecosystem and land use the dynamics of organic C, total N, CEC, pH, P, Ca, Mg and K were determined in the 0-50 mm, 50-100 mm and 100-200 mm soil layers. A total of 204 species that including N-fixing species, belonging to 141 genera and 50 families divided into tree, shrub and herbaceous layers were identified. The tree layer was only found in virgin fields and in fields abandoned to bush fallow >15 years, whereas shrub and herbaceous layers occurred in all fields. The tree species in bush fallow fields of coastal and wetter AE1, AE2 and AE3 (dominated by B. spiciformis and Julbernaldia globiflora) outnumber those in inland and drier AE4, AE5 and AE6 (dominated by Birchemia discolour and Colophospermum mopane) and have larger diameter that result in greater biomass. Number of shrubs decreased from coastal an wetter to inland and drier agroecosystems. The herbaceous biomass declined from young to old fallow fields in coastal and wetter agroecosystems, while the converse was observed in inland and drier agroecosystems. Nitrogen-fixing species tended to occur more in bush fallow fields older than 15 years. In inland and drier agroecosystems the tree biomass in 15F fields tended to be higher than in virgin fields due to presence of succession species that differ from the original ones. In the wetter agroecosystems C loss from B. spiciformis leaf litter was faster, whereas in the drier ones it was more sensitive to rainfall pulses. Similarly, C loss was faster in 15F fields than in bare fields. In coastal and wetter AE1, AE2 and AE3 there was a declining trend in organic C and total N from virgin to cultivated fields. This trend proceeds to the <5 years fallow fields and thereafter the contents of the two indicators increased in older fallow fields. A different pattern was found in the dry AE4 and AE5 where organic C and total N tended to decline gradually even with longer fallow periods. In the severely dry AE6 no clear trend was found. The pH in all agroecosystems decreased from cultivated to fallow fields, an effect attributable to a gradual decrease in the basic cations released on the soil surface by the ash produced during slash and burn. A slight increase in the silt plus clay fraction from AE4 to AE5 was found, which resulted in increased CEC, P, Ca, Mg and K. From the coastal and wetter to inland and drier agroecosystems pH, P and Ca increased, except in AE4 and AE5, which had lower pH and Ca values. The lower values of pH resulted in lower contents of P in AE4 and Ca and Mg in both agroecosystems, which have the same vegetation, suggesting that this should be the determining factor. The results from this study showed that a bush fallow period of longer than 15 years is required for restoration of soil fertility in abandoned cultivated fields to the same level as in virgin fields. This aspect must be taken into account when strategies are developed to improve the sustainability of cropping on the sandy soils of southern Mozambique.
Open Access
Growth, yield and physiological response of carrot (Daucus carota L.) to different fertilizer levels and bio-stimulants
(University of the Free State, 2009-06) Sekoli, 'Mabataung Magdalena Sebina; Pretorius, J. C.; Engelbrecht, G.
English: Concerns regarding environmental pollution, emanating from agricultural effluent due to abusive use, have led to a paradigm shift in production technology. On the other hand, subsistence farmers in developing countries cannot afford fertilizer at the current prizes. Farmers, therefore, have to reconcile agronomic, economic, agricultural product quality and environmental aspects of crop. In view of these concerns this study evaluated the response of carrot (Daucus carota L. cv. Karina) to varying fertilizer levels, applied singly and in combination with two commercial bio-stimulants, ComCat® and Kelpak®. Both biostimulants are plant extracts, containing natural active compounds, and are applied exogenously to manipulate crop growth and yield. No reports on the use of either of the two products on carrot production could be found in literature. During both seasons of greenhouse studies, the incremental increase of NPK fertilizer contributed to increased vegetative growth and root fresh mass, though not significantly at all times. The application of bio-stimulants had an erratic effect on carrot growth under greenhouse conditions. However, both bio-stimulants in combination with the standard fertilizer level enhanced root fresh mass at harvest (Chapter 3). Under field conditions, especially during the 2007 growing season, foliar application of both bio-stimulants enhanced yield. Although the ensuing increases were not significant, a higher increase of 7 ton ha-1 was attained due to application of a combination of ComCat® with the standard fertilizer. A lower increase of 4 ton ha-1 was achieved with combinations of ComCat® and Kelpak® with the half-standard fertilizer level (Chapter 4). Growth and yield response of tap roots due to application of different fertilizer levels separately and in combination with bio-stimulants was verified through determination of selected physiological activities (Chapter 5). Sucrose content tended to increase, in concert with yield, as the fertilizer levels were incrementally elevated. Conversely, glucose and fructose content decreased in tap roots as maturity was attained, probably due to less sucrose being hydrolyzed at this development stage. ComCat® had a strong enhancing effect on sucrose translocation as evidenced by the positive relationship between sucrose content, radio-active translocation to the roots and final carrot root yield. The latter applied in both instances where the standard and half the standard fertilizer levels were applied in combination with ComCat®. This effect could be related to ComCat® enabling improved sucrose transport across membranes. The effect of Kelpak® on sucrose accumulation and translocation was less evident but, in combination with half of the standard fertilizer, its application led to a slight increase in yield. The accumulation of -carotene, a terpene associated with taste and quality of carrots, was not influenced by fertilizer application. The level, however, increased where ComCat® was combined with the half-standard fertilizer level. To further comprehend the manipulative effects of fertilizer and bio-stimulants on physiological processes influencing growth and yield of carrots, root respiration as well as activities of glycolytic and oxidative pentose phosphate pathway regulatory enzymes was determined. In all cases the activities were only measured at 30% plant development and 24 hours after second bio-stimulant application. Both ComCat® and Kelpak® increased the respiration rate as well as the activity of glycolytic and oxidative pentose phosphate pathway key enzymes during early carrot development under 25% and zero fertilization. The latter was probably due to nutrient stress during early development. However, as carrots matured nutrient acquisition and energy needs were probably reduced as indicated by the respiration rate remaining at a steady state during later development stages and at harvest across all fertilizer levels. This correlated positively with increased sugar levels at maturity and the final yield. In conclusion, the collective interpretation of growth and physiological data acquired during this study at different fertilizer levels, especially when considered in relationship with final yield data at harvest, does not supply a sufficient rationale to recommend either the use of sub-optimal levels on their own or in combination with the two bio-stimulants included in this study for the cultivation of carrots. However, it is recommended that this study be repeated under irrigation conditions but with plots far enough apart to prevent sideways movement of fertilizer and possible contamination of plots.