Doctoral Degrees (Soil, Crop and Climate Sciences)

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Open Access
Agroclimatological risk assessment of rainfed maize production for the Free State Province of South Africa
(University of the Free State, 2010-12) Moeletsi, Mokhele Edmond; Walker, Sue; Landman, Willem A.
English: The risks associated with climate and its variability over the Free State Province is the major determining factor for agricultural productivity, and has a major impact on food security across the province. To improve productivity of agricultural lands, producers and decisions makers have to be provided with relevant agrometeorological information that will enable them to make appropriate decisions. This has lead to the investigation of this agroclimatological risk assessment for maize production in the Free State. The ultimate goal was to characterize the agroclimatological risks impacting negatively on dryland maize production and develop a climate risk tool that will assist the stakeholders in their management of agricultural lands. First, meteorological data needed to perform this study was prepared by looking specifically at filling the missing data gaps and using alternative data in cases where measured data was not available to obtain good spatial distribution of weather stations. Frost was identified as one of the climate hazards affecting the maize plant in the Free State. Three frost severity categories were analysed, namely 2°C, 0°C and -2°C representing light, medium and heavy frost respectively. The onset of frost for all the thresholds was earlier over the northern, eastern and far southeastern parts of the Free State province while places over the western and southwestern parts of the province the first frost dates are later. The northern and eastern parts are also marked by late cessation of frost giving a shorter frost-free period (220-240 days at medium frost severity). The western and southwestern areas mostly have earlier cessation of frost resulting in relatively long frostfree period with ranges from 241 to 300 days at medium frost severity level. Cessation of frost occurring later than normal over the Free State can impact negatively on the maize crop if planted in October and early November, especially over the highlands. Productivity of the crops can also be hampered by earlier than normal onset of frost that affects maize at silking and grain-filling stages. The onsets and cessation of rains together with the duration of the rainy season also play an important role in agricultural planning. Over 300 stations across the Free State were analysed to characterize the rainy season. The onsets of rains were found to be early over the eastern parts of the province with median onsets on or earlier than 10 October. In most areas over the Fezile Dabi and Motheo districts, onsets are between 11 to 30 October while over the Lejweleputswa onsets are mostly between 21 October and 10 November. Most of the western parts of Xhariep experience later than 21 November at 50% risk level. The cessation of rains does not vary much over the Free State with most places having their median last rains between 21 April and 30 April. Rainy season lengths are longer over the Thabo Mofutsanyane district with over 200 days in some places. The ENSO episodes are related to Free State seasonal rainfall variability but only have slight effect on the cessation of rains while onsets of rains showed no differences between El Niño or La Niña phases as compared to all the years. In El Niño years the seasonal rainfall amount is lower than normal, being higher than normal in La Niña years which support findings from other studies. The cessation of rains occurs earlier in El Niño years and later than normal in La Niña years. Agricultural drought is one of the most devastating hazards affecting maize production in most growing periods depending on the location. It is important to plant during periods which minimise drought conditions. In this study a simple water balance model developed by FAO called WRSI was used to quantify drought risk. When using the 120-day maize cultivar as a reference, drought index over most parts of the Lejweleputswa, Xhariep and eastern parts of the Motheo district show high vulnerability (WRSI<40) for October planting dates while other areas have relatively low risk of drought. In December and January planting dates drought index over most parts of the province showed much improvement but places that showed low risk are over the Thabo Mofutsanyane, Fezile Dabi and pockets of northern Lejweleputswa district. Poone AgroClimatic Suitability Index (PACSI) was introduced to integrate all the climate hazards affecting maize production in the Free State. The index in made from the combination of frost probability over the growing period, non-exceedence probability of onset of rains and agricultural drought index. The index was further used to delineate the suitable areas across the Free State for planting maize variety requiring 1420 growing degree days (heat units) to maturity. The findings obtained from the resulting maps show areas of high maize production suitability over the Thabo Mofutsanyane district for mid-October to early November planting dates. Places over Fezile Dabi and northern parts of the Lejweleputswa district also showed high suitability of maize especially for planting from mid-November to end of December. The western and southern Xhariep district area is not suitable for planting maize while other marginal dryland maize production areas include western Motheo, southwestern Lejweleputswa and most parts of the central and eastern Xhariep. To conclude the study, the Free State Maize Agroclimatological Risk Tool (FS-MACRT) was developed to provide agroclimatological risk information important to the production of rainfed maize in the Free State Province. The tool is to be used by the farmers, extension officers, policy-makers and agricultural risk advisors. The tool has two main parts, 1) climatological risk and 2) forecasting. The climatological risk enables the user to obtain drought stress risk for the 100-day, 120-day and 140-day maize cultivars for planting window starting in October to January. The best planting dates based on the risk associated with the climatology onset and cessation of both rains and frost can be determined. Using climate forecasts obtained from the national forecasting centres, drought index can be predicted for different planting dates giving the farmer valuable information when planning for the coming season. The tool also has the functionality of predicting onsets of rains using weather and climate forecasts.
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
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
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
Characterization and modelling of water use by amaranthus and pearl millet
(University of the Free State, 2013-01) Bello, Zaid Adekunle; Walker, Sue
Amaranthus (Amaranthus spp) and pearl millet (Pennisetum glaucum [L.] R. Br.) are drought tolerant crops with much potential that has not been well exploited as they can be cultivated under semi-arid climatic conditions. This study was carried out to characterize their water use and model their growth and yield in response to water. Experiments were carried out under a field line source sprinkler irrigation system for both crops for two seasons, as well as in a greenhouse with a pot experiment for amaranthus and in the lysimeter facility for pearl millet studies, each for one growth cycle. One genotype of amaranthus (Amaranthus crentus ex Arusha) and two lines of pearl millet (GCI 17, improved line and Monyaloti, local variety) were used in the trials with these crops in a semi-arid area near Bloemfontein, South Africa. The influence of water application on growth of amaranthus was contrary to the expectation that fully irrigated plants will perform better than the plants receiving less water. Fully irrigated plants produced shorter plants with less leaves and branches. However, irrigation improved the plant height in both lines of the pearl millet. A large amount of irrigation resulted in taller plants for both lines while the shortest plants were found in the rainfed plots. Another millet crop parameter that was affected by irrigation was flower emergence. Flower emergence was earlier in irrigated plots of both lines of pearl millet and during the two seasons. In both lines of pearl millet, irrigation increased leaf area index and biomass accumulation during both seasons. The two crops were able to exhibit the ability to tolerate water stress with different coping mechanisms and this influenced their water uptake and invariably also water use. Amaranthus was able to manage water stress in rainfed plots through the closure of stomata in the field and during the pot trials. Stomatal closure reduces water loss as a response to water deficit in the soil-crop-atmosphere continuum. Daily water use of amaranthus ranged from 1.2 to 6.5 mm day-1 while the seasonal water use was 437 mm for the first season and 482 mm for the second season. Higher water use in the second season was attributed to higher atmospheric evaporative demand recorded during the second amaranthus growing season compared to the first. It was observed that while water application can increase the production of amaranthus, it should also not be too much or it could have a detrimental effect on biomass production of the crop. This conclusion is due to the fact that the lowest irrigated plots produced higher fresh and dry mass of amaranthus during both seasons while production in the fully irrigated plots was low for the two seasons. The response of pearl millet to water deficit stress was to lower the leaf water potential (more negative) and also gradually decrease the leaf stomatal conductance. Pearl millet demonstrated a response to the water stress condition by closing of the stomata as leaf water potential declined (towards more negative) so as to conserve water and prevent water loss. This minimized water loss through transpiration when the soil water available is limited. The crop adjusted to severe water stress conditions by maintaining a leaf water potential that keeps the leaf turgid in order to avoid wilting when the stomata closes so as to prevent excessive water loss. The daily evapotranspiration of the two lines of pearl millet for the two seasons were between 2 and 8 mm day-1 for the first season and 1 and 6 mm day-1 for the second season. The difference could also be attributed to a higher atmospheric evaporative demand in the first pearl millet growing season than the second season. Overall, the improved (GCI 17) and the local variety (Monyaloti) of pearl millet had water use of 309 and 414 mm in 2008/2009 season. The water use for the two lines was higher in the 2009/2010 season with GCI 17 having water use of 401 mm and Monyaloti 457 mm which was probably due to high availability of water. High soil water content coupled with a higher amount of rainfall in the second season than the first season could be the reason for difference of the water use of the two lines of pearl millet for the two seasons. However, the water use of the plants of the two lines of pearl millet from the rainfed plots and water stressed treatments showed that the crop was able to reduce water use under water stress conditions as a coping mechanism and hereby increase water use efficiency of the crop. With the aid of the data from the field experiment, greenhouse and lysimeter trials, calibration and validation of AquaCrop crop model was performed successfully for both crops. Simulation of biomass production and cumulative evapotranspiration of both crops were performed adequately. The good performance in simulating these crop parameters were illustrated with a high index of agreement that was higher than 0.9 except for 2 cases of CC excluding the soil water comparisons. However, it was observed that more effort is needed to accurately simulate early canopy cover in amaranthus and also the soil water content and depletion patterns for both crops. Following successful validation, the model was also applied to predict the performance of both crops under a range of proposed planting dates and choice of varieties in pearl millet as possible adaptation strategies under two climate change scenarios. The model was able to predict the production of the two crops under predicted climate change for the period between the year 2046 and 2065 and the most appropriate adaptation strategy as a recommendation is to delay planting for two months until the first half of January for both crops under the two future climate change scenarios (A2 and B1). In conclusion, the two crops under investigation can adjust to water limited conditions but through different mechanisms. Amaranthus can avoid water stress through restricting growth, while the pearl millet crop escapes water stress through speedy completion of growth stages before the water stress condition sets in. It was also revealed that there are possibilities of cultivating these crops in central South Africa. However, more studies should be carried out on the effect of interaction of nutrient and irrigation on amaranthus production to reveal the reasons for the unexpected response of amaranthus to water application. Studies on root development of the two crops are hereby recommended to aid in accurate simulation of water balance of the two crops in the field situations. The calibration and validation of AquaCrop for these two crops can also be improved by using datasets of more varieties or genotypes of the crops and from other agro-ecological regions. In general, underutilised crops provide means of food security and source of income for farmers. Due to the fact that they are drought tolerant, they require minimum amount of input which is a desirable quality for low resource farmers and can be used as alternative crops in semi-arid areas.
Open Access
Developing a digital soil mapping protocol for southern Africa using case studies
(University of the Free State, 2013-06) Van Zijl, G. M.; Le Roux, P. A. L.
English: Although there is an increasing need for spatial soil information, traditional methods of soil survey are too cumbersome and expensive to supply in that need. Digital soil mapping (DSM) methods can fulfil that need. Internationally, DSM is moving from the research to the production phase. As soil-landscape interaction and availability of data varies between locations, local DSM research is needed to make its application practical. This research aims to produce a working DSM protocol which can be used for mapping large areas of land in southern Africa. The protocol must meet soil surveyors where they are at, being easy enough to follow, while also allowing for the creation of products needed by industry. To keep the link with industry’s needs, a case study approach was followed. Four case studies were done in succession, with the protocol being improved with every case study. The case studies cover an array of challenges faced by soil surveyors. In the first case study a baseline protocol was created when two land types near Madadeni were disaggregated in a series of soil maps. With each map, more information was incorporated when creating the map. For Map 1 only the land type inventory and terrain analysis were used. A reconnaissance field visit with the land type surveyor was added for the second map. Field work and a simplified soil association legend proved to improve the map accuracy for Maps 3 and 4, which were created using 30% and 60% of the observations points as training data respectively. The accuracy of the maps increased when more information was utilized. Map 1 reached an accuracy of 35%, while Map 4 achieved a commendable accuracy of 67%. Principles which emerged was that field work is critical to DSM, more data input improves the output and that simplifying the map legend improves the accuracy of the map. An unrealistic demand for a soil survey of 37 000 ha of land in the Tete Province, northern Mozambique, possibly infested with land mines, in 8 working days by two persons, created an opportunity to apply the soil-land inference model (SoLIM) as a digital soil mapping tool. Dividing the area into smaller areas where unique soil distribution rules would apply (homogeneous areas, HA’s) was introduced. A free survey was conducted along the available roads of the area. The final soil map for 15 000 ha had an accuracy of 69%. A principle which emerged was that inaccessible areas can be mapped, provided that they occur within surveyed HA’s. Near Namarroi, Mozambique, the potential of DSM soil survey methods to rapidly produce land suitability maps for a large area with acceptable accuracy was evaluated. Conditioned Latin hypercube sampling (cLHS) was introduced to determine field observation positions. SoLIM was used to run an inference with soil terrain rules derived from conceptual soil distribution patterns. A restriction of the expert knowledge based approach was found in that only six soil map units (SMU’s) could be determined per HA. The map achieved an overall accuracy of 80%. Land suitability maps were created based on the soil class map. In the Kruger National Park a soil map was used to create and extrapolate 2-dimensional conceptual hydrological response models (CHRM’s) to a 3-dimensional landscape. This is a very good example on how value could be added to a soil map. An error matrix convincingly identified problem areas in the map where future work could focus to improve the soil map. The current data indicates that at least 28 soil observations are necessary to create a soil map to an acceptable standard. When minimum observation criteria are met, observation density is irrelevant. The cLHS method to pre-determine observation positions improved the usability of observations. Although more research is needed to accurately determine the minimum observation criteria, an observation strategy is suggested. A 15 step protocol is produced with which it was shown that soil surveyors could produce a variety of maps in diverse situations. The protocol relies on the expert knowledge of the soil surveyor, combined with field observations. It has the advantages that fewer observations are necessary, map accuracy assessment is possible, problem areas are identified and under certain conditions unsurveyed areas can also be mapped. On the down side, there is a limitation of six SMU’s per HA. Further research needs to be done to determine the minimum criteria for soil observations, and soil distribution relationships between soil and remotely sensed covariates.
Open Access
Developing an index for phosphorus loss from sugarcane soils in Mauritius
(University of the Free State, 2015-01) Mardamootoo, Tesha; Du Preez, C. C.; Ng Kee Kwong, K. F.
Sugarcane is the major crop cultivated in Mauritius and currently occupies some 53,500 hectares of land with an average cane productivity of 74 t ha-1. Phosphorus (P) fertilization on deficient soils can increase annual cane production up to 24 t ha-1. Currently the sugarcane industry consumes some 3,350 tonnes of P2O5 in the form of soluble mineral fertilisers with an additional 1,110 tonnes P2O5 coming from filter muds. While the application of P to agricultural land is essential in maintaining crop productivity, non-point sources of P leaving the agricultural landscape can cause accelerated eutrophication of surface waters, thereby impairing water quality. Although these losses may not always be of economic importance to farmers, only small amounts of P can trigger eutrophic conditions in freshwaters. Past studies in Mauritius have shown that runoff P concentrations of limnological significance (> 0.1 mg P L-1) can occur, particularly during high flow events. Hence, this study was initiated to provide a better understanding of P mobilization from cane fields and to integrate factors influencing P movement into a P risk assessment tool. To achieve these objectives, rainfall surface runoff simulations were conducted on 20 sites representing the main soils under which sugarcane is cultivated. The tests were done on runoff plots (2.1m by 0.75m in duplicate) at three slope categories (0 to 8%, 8 to 13%, 13 to 20%) and under three different rainfall intensities (50, 100, 150 mm hr-1) for a duration of 30 minutes each. In an attempt to evaluate the impact of continuous fertilizer application on the environmental soil P status of sugarcane soils in Mauritius, it was found that 0.01M CaCl2-P of surface soils was linearly correlated to dissolved runoff P losses (r2= 0.92). Thus simple laboratory soil extractions with 0.01M CaCl2 is a suitable estimate for dissolved P losses when field experimentation is not possible. Since the use of the routine agronomic soil test (0.1M H2SO4 soil extraction) for sugarcane in Mauritius provided a more accessible analytical tool for P management, the relationship between the 0.01M CaCl2-P and 0.1M H2SO4-P was established and it was found that soils with 0.1M H2SO4-P above 160 mg kg-1 can potentially impair runoff water quality. While soil testing provides a reliable pointer of desorbable P in surface soils, it gives no indication of its potential for transport during runoff and erosion. Results from the simulation studies showed that runoff and erosion potential varied across the different soil types. It was also observed that with increasing rainfall intensities and field slopes, P mobilisation was enhanced due to increases in runoff and erosion rates. The results further showed that total runoff P was more strongly correlated with suspended sediments (r2=0.92) present in runoff waters than with runoff volume (r2=0.49) indicating that a greater proportion of the P transported in runoff occurred mostly as particulate P rather than dissolved P. Actually, about 90% of total P loss in runoff waters was mobilised in particulate forms regardless of field soil type, rainfall intensity and field slope. Using these research findings and historical data, the P index was developed to rank site vulnerability to P loss by accounting for source (dissolved P, particulate P, P application rate, method of application and application timing) and transport factors (soil erosion, surface runoff potential and precipitation) such that site-specific management practices can be implemented to critical source areas to minimize offsite P export. The proposed improved management practices to reduce P loss from fields in the P index include terracing, construction of diversions, field borders, field strips, grassed waterways, forest buffers and herbaceous cover. Sensitivity analysis and edge-of-plot field testing were used to assess the behavior and performance of the P index. The results indicated that further evaluations at a watershed scale would be more insightful about the strengths and weaknesses of the P index as a risk assessment tool. Besides, further evaluations of this tool will eventually lead to improvements in estimating the impacts of agricultural P management on downstream water quality.
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
Dissemination of climate information to small-holder farmers: a case study for Mujika area, Zambia
(University of the Free State, 2010-11) Nanja, Durton Hamooba; Walker, Sue; Musvosvi, Denford
Most scientists globally agree that human activities are causing global climate change resulting in pressures on Africa‟s agriculture systems and economies. Knowledge gaps still exist in coping with climate change and adaptation, regardless of the increasing country level research on the agricultural systems. With climatic information dissemination and appropriate policy development as major global themes, literature and knowledge on dissemination of climatic information is still limited in Zambia. This study was undertaken in Mujika area of Monze district, southern province of Zambia from 2007 to 2010. Faced with climate change challenges, the Mujika community opted to investigate the possibility of developing an agrometeorological extension strategy. This strategy was to respond to community needs for routine dissemination of climatic information, serving as a warning as well as guide to improving the local agricultural decision making. This study addressed the following specific objectives: To analyze long-term rainfall data for two stations as a basis for developing climate risk approaches for Mujika area; To establish the current status of climatic risk information and dissemination practices in Mujika area; To document the social/institutional aspects that enable farmers to adopt appropriate alternative interventions; and To operationalise the community agrometeorological participatory extension service (CAPES) so as to evaluate its effectiveness. Data collection used both quantitative and qualitative methods. The quantitative approach analyzed long-term rainfall data while the qualitative approach used Participatory Rural Appraisal (PRA). Community members from three villages (Nkabika, Bulimo and Malomo) participated in PRA exercises by presenting spatial data (in community sketch maps, farm sketches and transect walks), time related information (by historical time and trend lines) and social data (from household interviews, daily calendar according to gender and institutional analysis) throughout the study. They organized their problems and opportunities into a priority order at the village level, resulting in the creation of a community information dissemination plan (CIDP). The implementation of the CIDP included weekly local radio broadcasts of specially prepared programmes which were then recorded by local club representatives. The farmers organized themselves into five small radio listening clubs where they listened and discussed the re-recorded programmes. Their learning by doing was around the mother field trial managed by the other PhD student, Prospard Gondwe and baby field trials conducted by 16 local farmer volunteers in their own fields. Monitoring and evaluation was incorporated into the project by these volunteer farmers keeping records of most project activities. A community agrometeorological participatory extension service (CAPES) developed out of these interactions between stakeholders, including community members, agriculture extension officers, an agrometeorologist and agronomist during all these activities. CAPES is an agrometeorogical extension service including monitoring, developed together with a community to give tailor-made climatic information for improved agricultural decision making. Stories of five selected Mujika farmers were used to evaluate the effectiveness of CAPES in disseminating climatic information to smallholder farmers in Mujika. This assisted understanding the influence of CAPES on individuals across a range of different types of farmers that are present in Mujika, according to status, education and influence of authority. The study findings led to the following conclusions: Although long-term rainfall data analysis was useful in understanding smallholder farmers‟ environment, it was also instrumental in characterising available annual and seasonal rainfall trends. Detailed intra-seasonal information (start and end of rain, dry spell length) used together with seasonal forecasts helped improve agricultural decision making. Indigenous forecast knowledge plays a major role in smallholder farmers‟ agricultural decision making and planning of crop management options for every unfolding season when access to seasonal climate forecast information is limited. The fact that the community had a good knowledge of the natural resources enabled them to recognize that the use of climate information was a viable opportunity to improve crop productivity. The lack of credibility of researchers and Zambia Meteorological Department (ZMD) within the community to produce and disseminate seasonal climate forecasts had a negative influence on farmers‟ acceptance and usage of seasonal climate forecasts. A sustainable community agrometeorological participatory extension strategy depends on smallholder farmers‟ contributions during planning as users because farmers know what climatic information is required for addressing their problems and the best dissemination modes for effective information utilization. It is possible to develop an effective and appropriate community agrometeorological participatory extension service with a community when appropriate participatory approaches to community interactions are used. The stories of the identified farmers used in the qualitative approach provided the visible evidence of the influence of the CAPES on the farming systems in Mujika. All this information was combined into a practical handbook on CAPES to be used to train agrometeorological intermediaries. Recommendations that follow from this thesis and that may also help as starting points for future research are: Participatory dissemination of climatic information should be based on a well-researched community baseline so as to address actual community problems. The participatory multi-disciplinary climatic information dissemination plan should be develop together with farmers and other stakeholders for an effective information flow in the community. In order to improve smallholder farmers‟ agricultural decision making and crop management options in rainfed systems, an effective dissemination of seasonal climate forecast and a detailed long-term rainfall analysis for their respective area is required. The community agrometeorological extension strategy (CAPES) developed during the dissemination of climatic information to smallholder farmers in Mujika area is a model of success and is recommended for application to other areas. Use of stories about selected farmers in evaluating the effectiveness of community interactions is a useful approach and is recommended. The CAPES handbook, developed during this project, is a useful guide and is recommended for use by anyone intending to interact with communities for the dissemination of climatic risk information. The community agrometeorological participatory extension strategy should be evaluated in future in five or ten years after it establishment.
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
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
Establishing optimum plant populations and water use of an ultra fast maize hybrid (Zea Mays L.) under irrigation
(University of the Free State, 2014-07-18) Yada, Gobeze Loha; Ceronio, G. M.; Van Rensburg, L. D.
English: For each grain production system, there is an optimum row spacing and plant density that optimises the use of available resources, allowing the expression of maximum attainable grain yield in that specific environment. Introduction of the ultra-fast maize hybrids raised the question whether existing guidelines for row spacing and plant density were still applicable. This necessitated the integration of optimum row spacing by plant density to maintain productivity and sustainability the yields with the intention to increase water use efficiency. Field experiments were conducted for two successive cropping seasons (2008/9 to 2009/10) at Kenilworth Experimental Station of the Department of Soil, Crop and Climate Sciences, University of the Free State to evaluate the growth, agronomic performance, phenological development and water use efficiency of an ultra-fast maize hybrid at varying row spacing and plant densities under irrigation. The treatments involved in this study were three row spacings (0.225, 0.45 and 0.90 m) and five plant densities (50 000, 75 000, 100 000, 125 000 and 150 000 plant ha-1). The treatments were arranged in a factorial combination and laid out in a randomized complete block design (RCBD) with four replications. The largest block was used for periodic destructive sampling for growth analysis where a completely randomized design was adopted and replications consisted of five (5) single plants randomly selected. Regarding soil water monitoring, twenty neutron probe access tubes were installed prior to planting in the center of each plot in one of the three blocks of the agronomic study. Soil water content was measured at 0.3 m intervals to a depth of 1.8 m using a calibrated neutron probe. Measurements were made at weekly intervals from planting to crop physiological maturity where the volumetric reading was converted into depth of water per 1.8 m. Seasonal ET (water use) was determined by solving the ET components of the water balance equation. From this water use efficiency was computed as the ratio of total biomass/grain yield to seasonal ET. In each season crop growth, agronomic, phenologic and water use efficiency parameters were measured and the collected data were combined over seasons after carrying the homogeneity test of variances. Growth parameters, agronomic traits, phenology and water use efficiency of maize reacted differently to row spacing and plant density and the combination thereof. In general a slow increase in growth parameters during establishment was followed by an exponential increase during the vegetative phase. At the reproductive phase growth ceased following the onset of flowering. Photosynthetic efficiency (NAR) and CGR, averaged over row spacing, were highest at a plant density of 100 000 plants ha-1 at all growth phases. Reducing row spacing from 0.45 to 0.225 m and a plant density below or above 100 000 plants ha-1 showed LAI outside the optimum with respect to NAR for optimum seed yield. Row spacing, plant density and its interaction affected yield and yield components of maize significantly. Narrowing rows from 0.45 to 0.225 m and plant densities above 100 000 plants ha-1 as main or interaction effects led to the formation of smaller ears, a shorter ear length and diameter, low seed mass, favored plant lodging and development of barren plants with an obvious negative impact on grain yield. On other hand, plant densities below 100 000 plants ha-1 were insufficient to utilise growth-influencing factors optimally. Thus, growth analysis provided an opportunity to monitor the main effects and interaction effects of row spacing and plant density on crop growth at different growth and development phases. Row spacing and plant density combinations affected the phenological development of maize. Increasing row spacing from 0.225 to 0.90 m relatively prolonged the number of days to anthesis and silking. Regarding anthesis-silking interval (ASI), the lowest plant density had the shortest ASI while the higher plant densities had relatively longer ASI. Wide row spacing coupled with low plant density increased the number of days to physiological maturity and vice versa. Row spacing and plant density and their interaction affected water use efficiency of maize. Highest water use was observed at a plant density of 125 000 plants ha-1. Biomass WUE was highest at a row spacing of 0.45 m with a plant density of 125 000 plants ha-1 while the highest grain yield WUE recorded was at a row spacing of 0.45 m with a plant density of 100 000 plants ha-1. The overall combined effect of row spacing and plant density revealed that a combination of 0.45 or 0.90 m with 100 000 plants ha-1 to be the optimum for the selected ultra-fast maize hybrid under irrigation.
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
Evaluating in-field rainwater harvesting with a sunflower - cowpea intercrop on a semi-arid ecotope in Limpopo province
(University of the Free State, 2012-12) Mzezewa, Jestinos; Van Rensburg, L. D.
A field study was conducted during the 2007/2008 and 2008/2009 cropping seasons in order to evaluate the in-field rainwater harvesting (IR WH) production technique with sunflower (Helianthus annuus L.) X cowpea (Vigna unguiculata L.) intercrop. The IRWH is a special crop production technique that promotes runoff on 2 m wide no-till strip between crop rows and collects the runoff water in basins where it infiltrates into the soil profile. The IRWH was tested against the conventional tillage (CON). The study was carried out at the University of Venda (22°58' S, 30°26' E at 596 m above sea level) in Thohoyandou in the Limpopo Province of South Africa at the University of Venda- Shortlands ecotope. The potential for food production in the Limpopo Province is limited by low and erratic rain fall. The smallholder farmers in the province are the most vulnerable because they depend on dryland agriculture for livelihood. Crop yields in the province are typically low. It was therefore hypothesized that (i) IR WH will increase crop yields compared to the CON system, and (ii) cowpea intercropped as living mulches with sunflower will increase water use (WU), water use efficiency (WUE), PUE and grain yield of sunflower. The relationship between soil water content (8) and matric suction (h) or soil water release curve (SWRC) was obtained using the hanging water column (h :s 800 mm water). The drainage patterns as well the relationship between 8 and unsaturated hydraulic conductivity (K) for each diagnostic soil horizon was evaluated using the internal drainage method (IDM). Field saturated hydraulic conductivity (Ks) of each diagnostic soil horizon was determined using a double ring infiltrometer. Results from this study indicated that soil hydraulic properties were unique for each diagnostic horizon. The saturated hydraulic conductivity in the orthic A and structured Bhorizons was 30 mm h-' and 12 mm h-', respectively. The difference was largely attributed to the crumb microstructure observed in the orthic A-horizon. The results of the study also indicated that Shortlands the soil had good water retention properties as 19% (average for the profile) of the water was released between saturation and 8 kPa. It was further concluded that the plant available water (PA W) (267 mm) in the root zone was high and surpassed the soils tested for IRWH, making the University of Vend a-Short lands ecotope suitable for this production strategy. Rainfall on the ecotope was characterized using historical data (1983 - 2005) in Chapter 3. The statistical analysis of rainfall at the study site revealed that the annual rainfall was highly variable (CV of 315% for annual rainfall). Further analysis revealed that the probabil ity of receiving high rainfall amounts was low with small storms «20 mm) accounting for a large proportion of rainfall The field experiment to evaluate the IRWH with sunflower X cow pea intererop production is reported in Chapter 4. The experiment was laid out as a split plot design. Tillage systems formed main plots with cropping systems (CRS) as sub-plots. The treatments in the CRS consisted of a sole crop (sunflower or cowpea) and an intererop (sunflower x cowpea). The IRWH led to a significant (P < 0.05) increase in sunflower grain yield in the second season but cowpea grain yield was not influenced by tillage systems (TS). IRWH resulted in significantly higher water use (WU), water use efficiency (WUE) and precipitation use efficiency (PUE) of both crops compared to the CON system. The CRS had significant effects on sunflower grain yield in both seasons, but none on the cowpea grain yield. The effect of IRWH production on runoff was studied using a rainfall simulator in Chapter 5. Results of this study indicated that IRWH was superior in runoff generation compared to the CON system and it could supply I% of maize water requirements under the conditions of this ecotope. The Crop Yield Prediction for Semi-arid Areas (CYP-SA) model was applied to assess risk associated with IRWH on the ecotope. Using cumulated probability functions (CPFs), the results indicated that simulated sunflower yield was significantly influenced by initial profile water content. The IRWH was significantly better than CON at all levels of initial profile water content.
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
Evaluation of selected industrially manufactured biological amendments for maize production
(University of the Free State, 2012-09) Baloyi, Tlangelani Cedric; du Preez, C. C.; Kutu, F. R.
The soaring prices of inorganic fertilisers among other reasons has persuaded companies to commence producing biological enhanced substances herein refers as industrially manufactured biological amendments (IMBAs) with claims that they could increase crop growth and yield, and also revitalize the soil. Such claims are often without substantial empirical agronomic data to proof the efficacy of these IMBAs. A glasshouse pot trial was conducted during 2008/09 season to assess the effects of graded rates of nine IMBAs (Biozone, Gliogrow, Gromor, Promis, Growmax, Crop care, K-humate, Lanbac and Montys) on maize seedlings establishment and growth over six-weeks. These were assessed at 50, 75 and 100% of the recommended rates together with optimum inorganic NPK fertiliser and a control as check. The IMBAs exerted in many instances a deleterious effect on percent maize seedling emergences when applied at 100% rate. Application rates of 50 and 75% appeared sufficient amongst most IMBAs for encouraging better growth and phenological development of maize, although the most appropriate rate is dependent on the IMBA type. Rainfed trials were conducted for three seasons (2006/07-2008/09) at four localities (Bethlehem, Bothaville, Ottosdal and Potchefstroom) to assess the effects of the same nine IMBAs used above on maize performance and on soil health in a randomised completely block design. The IMBAs were applied based on product manufactures and/or supplier recommendations along with optimum inorganic NPK rate and the unamended control as check. All trial sites were planted to one maize cultivar PAN 6479. Every season, observations on phenological growth traits, grain yield and yield components, nitrogen and phosphorus content, uptake, and agronomic use efficiency, soil chemical and microbial properties and on grain quality traits were measured. The manure-based IMBAs like Gromor, Promis and Growmax generally raised pH (H2O) to between 6.0 and 7.0 which was not always the case with the other IMBAs that coincided with inorganic NPK fertiliser. Generally, Gromor and Gliogrow recorded most cases of significant pH increases compared to the NPK treatment. The frequency of significant increases in organic C, mineral N and extractable P were only four instances and less of all 12 potential cases in relation to the NPK check. Gromor resulted in no cases of significantly higher mineral N and extractable P than the NPK check. The IMBAs promoted higher microbial biomass-C immobilisation at 4-weeks after planting while biomass-C mineralisation was predominant at flowering and crop harvest, although it tended to decline at crop harvest. The different IMBAs exerted in many instances no significant effect on biomass-C and -P compared to the NPK check. The IMBAs had no positive effect on maize growth and phenological traits compared with the NPK treatment. Application of Gliogrow resulted in constant reduction in plant phenological growth in the 9th leaf and silking growth stages due to poor emergence, particularly from soils with higher clay content. Gromor and Promis exerted no significant positive effect on grain yield and yield components compared to the NPK check. Despite the consistent poor stand count, Gliogrow resulted in significant increases for all the yield parameters measured than any other IMBA. Compared to the NPK check, the IMBAs resulted also in few cases of significant increases on harvest index while no positive significant effect was observed on cob length. Treatments with Biozone, Gliogrow and Promis at 9th leaf, Gliogrow and K-humate at silking, and Biozone and K-humate at harvesting significantly increased plant N content and uptake at the respective growth stages. None of the IMBAs exerted a significant effect on the agronomic use of the applied N compared to the applied N from the NPK check, except in one case with Promis. The P content and uptake recorded at 9th leaf, silking, and harvesting increased significantly in three to four instances due to the application of Promis, Growmax and Montys. The efficiency of applied P from the IMBAs was not in one case significantly better than the applied P from the NPK check. Application of Gliogrow, Crop care and Lanbac significantly increased thousand kernel mass in two to three cases, and milling index in two to seven cases in comparison with the NPK check. Gliogrow gave solely significantly higher percentage of >11 mm, and 10-11 mm kernels than the NPK check. Equally, Gromor gave significantly higher percentage of 8-9 mm kernels, and Growmax of 7-8 mm kernels.
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
Genetic analysis of resistance to maize lethal necrosis with emphasis on strategies for improvement of host resistance
(University of the Free State, 2021-11) Kwemoi, Daniel Bomet; Labuschagne, Maryke T.; Herselman, Liezel; Gowda, Manje; Asea, Godfrey
Maize lethal necrosis (MLN) is a new disease in Sub-Saharan Africa (SSA) caused by double infection by maize chlorotic mottle virus (MCMV) with any of the many viral agents in the Potyviridae family. It has become one of the key constraints to maize production in the region due to the significant crop losses caused since its emergence in 2011. Sustainable management of MLN is achievable through genetic improvement and replacement of old susceptible varieties with farmer-preferred varieties that combine MLN resistance with tolerance to other prevailing biotic and abiotic stresses. To effectively breed for MLN resistance, it is important to identify sources of resistance, determine the genetic nature of resistance and employ efficient breeding techniques that will result in high genetic gains from selection. This study aimed to dissect the genetic nature of MLN using elite and introduced inbred lines from tropical and temperate maize genetic pools, new biparental populations and potential hybrids. The genetic analysis was conducted in five studies representing the major stages of maize breeding, from pre-breeding to variety development. In the pre-breeding study, the breeding potential for MLN resistance among 18 tropical and temperate inbred and doubled haploid (DH) lines was conducted to identify the best parents for population development. The second study on the genetic potential and usefulness of new pedigree populations was conducted using nine segregating biparental populations derived by crossing susceptible elite and recycled DH lines to two introduced MLN resistant lines from the KS23 pool. The third study, using a section of these populations, selected three sizable populations, which were phenotyped, genotyped and used to validate quantitative trait loci (QTL) linked to MLN resistance in the KS23 genetic background. The fourth study, moving towards product development, entailed determining the potential of new lines and single crosses for use as MLN resistant testers and hybrid parents. In this study, the combining ability for MLN resistance and agronomic traits was estimated among tropical MLN resistant maize lines and prospective single cross testers. Finally, MLN-resistant three-way test cross hybrids (potential new varieties) were evaluated to determine the magnitude of genotype by environment interaction (GEI) and yield stability of hybrids under stress and optimum conditions. Results indicated overall high genetic variation for MLN resistance among introduced and adapted inbred lines, segregating populations and test cross hybrids. High heritability estimates were also observed among the diverse germplasm categories. With the high heritability estimates observed, significant gains from selection can be achieved for both MLN resistance and agronomic traits. The pre-breeding assessment identified good inbred lines suitable for formation of new MLN resistant populations. Testcross analysis led to identification of two resistant inbred lines and seven potential single cross testers that could be used for routine MLN resistance breeding. Multi-location experiments on three-way testcross hybrids identified 11 potential hybrids stable under MLN pressure and disease-free conditions. These hybrids could be further tested, released and commercialised. Genetic analysis and QTL mapping using biparental populations led to the validation of one major recessively inherited QTL located on the long arm of chromosome 6, consistently linked to three Kompetitive allele-specific polymerase chain reaction (KASP) markers across three mapping populations. This major candidate QTL needs to be fine-mapped and high-quality markers linked to the QTL selected and used for routine MLN resistance breeding in SSA and globally.
Open Access
Growth and yield response of selected crops to treatment with ComCat
(University of the Free State, 2011-12) Hüster, Thomas; Pretorius, J. C.; Swart, W. J.
English: A recently commercialized natural bio-stimulant, ComCat®, that contains three active brassinosteroids (BRs) of which two were identified previously, was scrutinized in this study for its potential to be applied in the agricultural industry. Concerning objective (1), seven biotests were employed to quantify the bio-stimulatory activity of ComCat® under laboratory and glasshouse conditions. The product was tested at different concentration levels and the 0.5 mg ℓ-1 application repeatedly emerged as the optimum concentration in terms of contributing towards increases in all of the parameters measured. Treatment with ComCat® had little or no effect on seed germination, but especially root growth of seedlings from different crops was significantly and consistently induced. Concerning objective (2), two cultivars for each of five test crops were treated with ComCat® over two growing seasons under field conditions in order to ascertain their yield response. Some of the test crops, but not all, showed cultivar sensitivity to treatment with ComCat®. However, overall the significant yield increases measured in one or both cultivars of the five different test crops and in one or both seasons confirmed the potential of ComCat® to be applied in agriculture and to contribute to economic prosperity for a farmer. Concerning objective (3), gas chromatographic analyses of a crude extract of the product as well as semi-purified fractions thereof by, using internal BR standards, were employed to identify an unknown BR contained in ComCat®. This was confirmed to be 24-epi-brassinolide. The latter as well as the previously identified 24- epi-castasterone and 24-epi-secasterone are known to be active BRs of the brassinosteroid group. In conclusion, the bio-stimulatory characteristic of ComCat® was confirmed both in vitro and in vivo under laboratory, glasshouse and field conditions in this study. Significant yield increases in all of the test crops over two seasons in some instances, confirmed the potential of ComCat® to be applied sustainably in the agricultural practice. Based on the results obtained in this study, three possible application methods of ComCat® are suggested. These include 1) seed treatment, 2) foliar application or 3) soil application.
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.