Doctoral Degrees (Soil, Crop and Climate Sciences)
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Browsing Doctoral Degrees (Soil, Crop and Climate Sciences) by Advisor "Du Preez, C. C."
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Item 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.Item 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.Item 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.Item 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.Item 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.Item Open Access Nitrogen dynamics in agro-ecosystems of Uasin Gishu district, Kenya(University of the Free State, 2015-01) Chemei, David Kipleting; Du Preez, C. C.; Okalebo, J. R.Abstract not availableItem Open Access Quantifying soil fertility parameters with electromagnetic induction, infrared reflectance spectroscopy and conventional chemistry procedures for wheat and maize under irrigation in arid climate(University of the Free State, 2021-04) Gura, Isaac; Du Preez, C. C.; Van Rensburg, L. D.; Barnard, J. H.Current global challenges, such as food security and soil quality, cannot be solved without up-to-date, high-quality, high-resolution, spatio-temporal, and continuous soil and environmental data that characterize soil and cropping ecosystems. Therefore, accurate and precise assessments of soil and crop characteristics are critical for site-specific management, vibrant soil condition and environmental sustainability. The inability to evaluate soil and crop characteristics quickly and inexpensively remains one of the main challenges of precision agriculture. Therefore, the ultimate aim of this study was to evaluate the use of soil sensors, viz the mid-infrared (MIR) sensor and the apparent electrical conductivity (ECa) sensor, in quantifying multiple soil fertility properties and their variability under irrigation. The study also attempted to apply the sensor data fusion approach to improve the assessment of multiple soil quality indicators and the overall soil quality under irrigation using the Soil Management Assessment Framework (SMAF). The established international ECa-directed soil sampling design approach was employed at each of the seven fields of interest by measuring apparent soil electrical conductivity (ECa) with a Geonics EM38-MK2 sensor (non-invasive geophysical electromagnetic induction, EMI). A “Response Surface Sampling Design” (RSSD) sampling methodology in the “Electrical Conductivity Sampling Assessment and Prediction” (ESAP) software was used to direct soil and crop sampling based on the degree of ECa variability. This methodology reduced sampling points from each field to 12 sampling points after an initial ECa survey. Soil samples from each field were analysed in the laboratory for various soil properties that are related to soil fertility. Wheat and maize were also sampled from the ECa directed sampling points at each field at the end of the winter 2016 season and 2016/17 summer season, respectively. The MIR spectra was obtained in the laboratory from the soil and crop samples from each field using a sensor iS50 Nicolet Fourier Transform Infrared (FTIR) (Thermo Fisher Scientific Inc., Waltham, MA) equipped with an accessory for attenuated reflectance acquisition (iS50 FTIR-ATR). The MIR sensor and EM38 sensor showed different levels of accuracy with respect to predicting soil fertility properties under irrigation. The study results demonstrated the effectiveness and usefulness of the MIR attenuated total reflectance (ATR) technique coupled with partial squares least regression (PLSR) in quantitative analysis of soil fertility properties. In contrast, the EM38 sensor modelled accurately only a few soil properties per site at a given sampling time. Comparatively, the model results from both sensors show that the MIR sensor produced better prediction models for most of the measured soil fertility properties than the EM38 sensor. For quantifying nutrient accumulation in wheat and maize, the MIR sensor technique produced more excellent predictive models for the nutrient concentrations in wheat samples than in maize. The results from the in-field spatial characterization of plant nutrient levels and crop yields at the study sites showed that although ECa readings may be useful for the spatial characterization of some soil fertility properties in non-saline and non-sodic soils in South Africa, the results showed many inconsistencies between sites and between the centre pivots. The limitations of quantifying soil properties and overall soil quality using a single soil sensor can be overcome by integrating data from conceptually different sensing techniques to improve model accuracy and robustness. The findings in this study demonstrated that models for most of the soil properties obtained based on step-wise multiple linear regression (SMLR) fusion of data from MIR sensor and EM38 sensor measurements were more robust as compared to models from individual sensors. The SMLR sensor fusion technique failed to improve the models of some soil properties at the selected fields as well as the overall SMAF soil quality index at the Douglas 40 ha field. A more robust fusion technique such as PLSR can be used to implement the data fusion for these properties. The sensor data fusion results demonstrate the superiority and efficiency of the sensor data fusion approach in the measurement of soil fertility properties and overall soil quality in irrigation systems of South Africa. Based on the findings of this study, for soil fertility evaluation and quantification, it is recommended to use the MIR technique coupled with PLSR and alternatively, the ECa measurements as complementary information to provide extended attribute coverage and increased capacity of the sensor data fusion.Item Open Access Refining of nitrogen fertilization guidelines for irrigated cotton (Gossypium hirsutum L.) in South Africa(University of the Free State, 2023) Haumann, Eduard Johannes; Du Preez, C. C.Thirteen randomised block nitrogen fertilization field trials were done in five irrigated cotton producing areas of South Africa: Bela Bela, Rustenburg, Vaalharts, Rietriver and Groblersdal, with the aim to refine the existing nitrogen fertilization guideline. At Rustenburg cotton was preceded by harvested oats, harvested soybean, ploughed in soybean and babala in order to create varying soil nitrogen contents. Soil samples (0–300, 300–600 and 600–900 mm soil depths) were taken at least two weeks after irrigation for land preparation to determine total nitrogen. Leaf petiole samples were collected at two-week intervals, starting one week before first flowering for measurement of total nitrogen. After ripening, seed cotton yield was determined. The yield was subjected to analysis of variance and correlated with the nitrogen application rate to quantify an optimal nitrogen fertilization rate per site for each trial year. The estimated optimal nitrogen fertilization levels were correlated with the residual soil nitrogen content for each depth resulting in four guidelines for either maximum yield or maximum profit. Therefore, the cotton grower has eight different options for the calculation of an appropriate nitrogen application level based on the residual nitrogen content of the soil.Item Open Access Response of Ethiopian field pea (Pisum sativum L.) cultivars to phosophorus fertilization of Nitosols(University of the Free State, 2003-12) Amanu, Amare Ghisaw; Du Preez, C. C.; Bekele, TayeField pea (Pisum sativum L.) is the third most important grain legume in Ethiopia where its productivity is constrained by several biotic, abiotic and socioeconomic factors. The crop is grown mainly on a wide range of soil types throughout the highlands (1800 to 3200 m.a.s.l.) in well drained soils like Nitosols that developed from volcanic rocks. Nowadays the blanket recommendation of diammonium phosphate (DAP) at 100 kg ha" to this low input crop is questioned by the farmers and development workers. Hence, experiments have been conducted with the major objective of quantifying the response of Ethiopian field pea cultivars to phosphorus fertilization of Nito soIs under both glasshouse and field conditions. Glasshouse experiments: Topsoil from Ilala and Cheffa were used. Experiments were laid out in a split plot design with three phosphorus fertility levels (Extractable phosphorus: low = 5, medium = 15 and high = 30 mg kg-I) as the main plot treatments and factorial combinations of two pea cultivars (TIala soils: Holetta and G22763-2C; and Cheffa soils: Tegegnech and Cheffa local) and six phosphorus application rates (0, 7.5, 15, 30, 60 and 120 mg P kg") as the sub-plot treatments in a randomized complete block design with four replications. The phosphorus fertility levels together with the phosphorus application rates had positive influences on the growth and development of the pea crop as manifested in the biomass yield of the different cultivars. Critical phosphorus levels were estabilished by relating relative biomass yield to extractable soil phosphorus. In the case of the Bray 2 extractions, the critical phosphorus levels for TIala soils were 14 and 15 mg P kg" for cvs. G22763-2C and Holetta respectively, for Cheffa soils 17 and 20 mg P kg" for cvs. Cheffa local and Tegegnech respectively. However, in the case of Olsen extractions the critical phosphorus levels for TIala soils were 17 and 27 mg P kg" for cvs. Holetta and G22763-2C respectively, and for Cheffa soils 20 and 22 mg P kg" for cvs. Cheffa local and Tegegnech respectively Field experiments: Two sets of experiments were conducted, viz. the first set at Holetta (1996 to 1999) and Bekoji (1996 to 1998) and the second set in 2001 at TIalaand Cheffa. For the first set of experiments a factorial combination of five phosphorus rates (0, 10, 20, 40 and 60 kg P ha") and three pea cultivars (Holetta site: Tegegnech, G22763-2C, Holetta local; and Bekoji site Tegegnech, G22763-2C and Cheffa local) were laid out in a randomized complete block design with four replications. On the other hand, for the second set of trials a split plot design was used with three phosphorus fertility levels (Extractable phosphorus: low = 5, medium = 15 and high = 30 mg kg") as the main plot treatments and the factorial combinations of five phosphorus application rates (0, 10, 20, 40 and 80 kg ha") and two pea cultivars (llala site: G22763-2C and Holetta; and Cheffa site: Tegegnech and Cheffa local) as the sub-plot treatments which were replicated four times. At the Holetta and llala sites, grain yield response of the pea crop to phosphorus a.pplication was poor regardless of the phosphorus application rates or the cultivars . As a result, low marginal rate of returns (MRRs) were computed which implicated that phosphorus fertilization is not economically viable. On the contrary, at the Bekoji and Cheffa sites, the grain yield response of the pea crop to the application of phosphorus was good with significant differences between phosphorus fertility levels and cultivars. The interaction of phosphorus application rate and cultivars was significant (p < 0.05). A MRR of 100% was obtained at an application of21 kg P ha-I for cv. Tegegnech, 10 kg P ha" for cv. G22763-2C and 5 kg P ha-I for cv. Cheffa local. The 100% MRR computed implicated that phosphorus fertilization to all cultivars at the low phosphorus fertility level was economically viable with the current prices of grain and fertilizer in the zone. Unfortunately, no critical soil phosphorus levels could be estabilished under field conditions. The critical soil phosphorus levels that were established under glasshouse conditions should therefore still be validated in the field. However, the fact that the pea crop did respond to phosphorus application mainly at the low phosphorus fertility levels in the field confirms already to some extent their validity. In general, the improved pea cultivars responded better to phosphorus fertilization than the local cultivar. A thorough investigation on phosphorus use efficiency of pea genotypes to' identify low phosphorus requiring ones should be considered to benefit resource poor farmers. The aspect of soil pH modifications through liming, and the use of non-nitrogenous phosphorus fertilizer sources for field peas are recommended.Item Open Access Response of soil properties to rangeland use in grassland and savanna biomes of South Africa(University of the Free State, 2015) Kotze, Elmarie; Du Preez, C. C.; Sandhage-Hofmann, AA significant portion of grassland and savanna ecosystems is over-utilized by livestock, due to inappropriate rangeland management. South Africa´s rangelands are increasingly threatened by overgrazing, followed by altered grassland composition and loss of vegetation cover in the grassland ecosystem, and by bush encroachment in the savanna ecosystem. Although not all land is overgrazed, there are some parts where signs of degradation can be found. Overgrazing has detrimental effects on soil and vegetation, but these changes can be reversed or prevented by proper rangeland management practices. The causes of and the processes involved in these changes and human interactions with them are poorly understood. Literature has indicated that rangelands can recover if managed accordingly, however scientists still have much to learn about how grazing affects soil properties. Sustainable utilization of the rangeland ecosystem is based on the appropriate application of rangeland management principles that will safeguard long-term productivity and profitability of the production system at the lowest possible risk. The main aim of this study was to investigate how soil chemical, physical and microbiological properties responded to different management systems in a clayey grassland and sandy savanna ecosystem of South Africa. For this purpose we sampled rangeland management systems under communal (continuous grazing), commercial (rotational grazing) and land reform (mixture of grazing systems mentioned) farming. Within each of these systems a grazing gradient was identified with increasing grazing pressure, indicated by indicator grass species for the purpose of rangeland condition assessment. Different grass species exist in the clayey grassland and sandy savanna ecosystems, with Acacia shrub and tree species being dominant in the savanna ecosystem. Rangeland condition ranged from poor, moderate to good grazing conditions. The results revealed that soils in both ecosystems responded differently to increased rangeland degradation. In the grassland ecosystem bare patches and soil crusts lead to a degradation of the soils, whereas in the savanna ecosystem bush encroachment lead to a temporary improvement of the soil quality. As a consequence of management, soil degradation in the piosphere of continuous grazed rangeland of the clayey grassland ecosystem is driven by the deterioration of aggregates and associated SOM losses in the poor and moderate rangeland condition, as well as nutrient losses caused by lower plant cover and litter input in the sacrifice area of the piosphere. Rotational grazed camps, in contrast, showed little evidence of soil degradation, but they exhibited an early deterioration of the aggregate structures nearby the water points. Furthermore, aggregate fractionation is a sensitive indicator for detecting the beginning of soil degradation in this ecosystem. Soil degradation was less pronounced under rotational than under continuous grazing systems. Hence, soil analyses confirm that fences and appropriate grazing periods are needed to manage these rangelands sustainably. In the sandy savanna ecosystem, results also revealed that communal farms were affected negatively by continuous grazing, which exhausted most plant nutrients especially close to the water points, when compared to rotational grazing in commercial farms. In contrast, the communal farms had more plant nutrients than commercial farms when moving away from the water points, which coincided with an increase in Acacia species. Only near the water points, high grazing pressure had overridden the positive effects of Acacia species. Hence, and in contrast to the results from the grassland ecosystem, rangeland degradation in communal farms of the savanna ecosystem improved soil quality due to bush encroachment, but at the cost of palatable grass area. Our data also demonstrated that in both ecosystems a decrease in grazing pressure on a rangeland, such as by commercial farmers practicing rotational grazing, could stimulate microbial activity. There was a positive feedback between microbial mediated nutrient mineralization and plant growth, as all microbial biomass and activity as well as grass cover and biomass were elevated when grazing pressure changed. Results further showed that in the long-term, the sandy soils seem to be more resilient to soil degradation, indicated by less significant differences in all measured parameters between the rotational and continuous grazing systems. In the short-term, however, it were the clayey soils in the grassland ecosystem that showed evidence of resilience, as the resting times in the rotational grazing systems was obviously able to compensate or restore disturbances from high grazing pressure, which was not possible under continuous grazing management.Item Open Access The use of operational weather and climate information in farmer decision making exemplified for the South Western Free State, South Africa(University of the Free State, 2013-01) Zuma-Netshiukhwi, Gugulethu N. C.; Stigter, C. J.; Du Preez, C. C.This study demonstrates that participating commercial and resource poor farmers used weather forecasts and climate predictions for agriculture and other science-based agrometeorological advisories during most of the study period. The study took place in the south-western Free State, synonymously used in this study as Modder/Riet catchment, which encompasses two districts Motheo and Lejweleputswa. It was found that most farmers in the south-western Free State originally were not familiar with such agrometeorological products but relied on their experience and traditional knowledge for farming decision-making. Most commercial farmers, having more resources, performed better compared to the resource poor farmers. The thesis especially exemplifies case studies linking science-based products/advisories and problem solving in the agricultural production environment for various farmers, where applicable through extension intermediaries. This particularly contributed to increasing the useful operational applicability of weather science, climate science and various fields of agricultural sciences. This must be seen as a contribution to science itself. The analytical results from questionnaires conducted in 2008 and 2012, with partly overlapping farmers, indicated that farmers in the south-western Free State differ in agricultural practices, interests, needs, experience and skills. Therefore, provision of tailor-made products for respectively crop production, animal husbandry, agroforestry and veld management is needed. Such agrometeorological information/advisories and, where people can assist to establish them, services can be disseminated by sending them to key communication outlets that are readily used by most people such as television, freely available local newspapers, local radio, bulletins, ward committees, extension forums and early warning committees. Cell phones can be used where the message may have limited size. The agrometeorological details should entail relevant and specific products that are directly useful to the farmers, and the latter should be able to interact with the sources. For all farmers in the Free State to embrace the use of agrometeorological knowledge and understanding would ideally require the interaction with well-trained extension agents. The study groups presented a very diverse situation in terms of experiences, challenges and needs that are related to their farming. The consequences of increasing climate variability needed greater emphasis as to farmer's ability to develop on-farm coping strategies and interventions. A successful farmer should understand the local trends in climate change and how agricultural outcomes are influenced. For example, the concept of response farming prepares the farmer to be aware of past and future climatic conditions and of the extent of increasing climate variability and related dangers and interventions to reduce vulnerabilities. The study also identified potential production areas for vegetables, herbs/spices, grain food, oil seeds, fruits and other products such as cotton and other fibers. Application of crop models such as Ehler's model and Eco-Crop 2 revealed the thermal and water requirements of these crops which are either fully or partially met in various parts of the catchment. Agricultural production in some parts of the study area can be optimal under supplementary irrigation and where soil requirements are suitable. Analyzed long term rainfall data assisted the farmers to select suitable crops for the area for diversification and sequential planting and determining the suitable planting dates and planting densities. Crop models were used to generate and evaluate a series of management practice scenarios. These outputs from the analyzed climate data and crop models were used to develop advisories that were tailor-made for the farmers. The decision trees handled in the last Appendix were also used to develop alternatives of agricultural management practices for different seasonal climatic conditions. The majority of farmers in the south-western Free State prior to this study regularly experienced devastating disasters that were weather and climate related, such as rainfall scarcity and rainfall irregularity, floods, untimely frost events, wind storms that also perpetuated destructive wildfires, outbreaks of diseases and pests, uncontrollable weeds which required intensive labour, severe drought conditions and overgrazed grazing lands. Weather forecasts and climate predictions for agriculture and other science-based agrometeorological advisories should be used to guide the farmers in terms of which response actions/decisions on agricultural activities to take under the above conditions and this way to reduce risks. Such agrometeorological products should serve a crucial role in strengthening sound decision-making and sustainable food security. Farmers used weather-related indicators in their traditional forecasting (mostly of rains and droughts) such as animal behavior, appearance of certain bird species, sprouting of aloe and other indigenous trees, accumulation of clouds, cloud types, appearance of certain insects, star constellation, shape of the moon and wind speed and direction. Agricultural decisions were made according to such traditional knowledge and understanding of environmental conditions of their local area obtained through years of experience. Understanding of the farmer's perception on climate is a critical step to facilitate effective communication on agrometeorological information/advisories/services. The tendency of scientists to develop knowledge for journals in the library that does not reach any end-users should be changed. It is therefore the responsibility of researchers and intermediaries to ensure that farmers have access to quality agrometeorological products for the betterment of agriculture in the Republic of South Africa at large. The study divulged a noticeable gap between the producers (universities/research institutes/weather services and other environmental services) and suppliers (broadcasters, extension officers, other intermediaries) of information/advisories/services while the users are in bitter need of agrometeorological products for improved on-farm decision-making. Participation of farmers in a series of monthly innovative workshops created a conducive environment for information exchange and training. It is advisable to conduct on-farm visits prior to the workshop/meeting days for proper preparations. This was to ensure that the monthly workshops were well-planned, productive and informative events. The manner in which this study was structured enhanced a bottom-up approach since it allowed participative approaches in close contact with the study groups, improving farming development by closing the gaps existing between developers, suppliers and users of agrometeorological knowledge and understanding. This study can recommend that participatory interaction with the farmers using focus groups, buzz questions, word of mouth, study groups and workshops allows two-way participation. This helps to understand the user's perception of the advisories, it allows a platform for constructive criticism that should lead to improvement of products and introduction of actual services, which are user friendly and translated into vernacular languages. The best outcome of this study was that farmers learnt new things and shared their information and experience. This farmer to farmer extension should be recommended for reaching the highest number of farmers in an area. The remaining challenge for agrometeorological advisories/services providers is to supply reliable and skilled forecasts/predictions and other science based information for agriculture through dissemination methods that suit the farmer such as already mentioned above.