Doctoral Degrees (Soil, Crop and Climate Sciences)
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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 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, GodfreyMaize 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.Item 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 Hydrogeology of the Table Mountain sandstone aquifer - Klein Karoo(University of the Free State, 2001) Kotze, Johanita Christelle; Van Tonder, G. J.; Verhagen, B. T. H.Abstract not availableItem 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.Item 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.Item 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.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 The growth, yield and physiological response of rain fed maize to foliar applied fertilizer(University of the Free State, 2012-01) Buitendag, Roelof Adriaan; Pretorius, J. C.; Grobbelaar, J. U.; Allemann, J.English: Regardless of past research, great uncertainty still exists amongst the research community, fertilizer agents and farmers alike with regard to the benefits of foliar inorganic fertilizer application for crop production. This supplied a rationale for investigating foliar nutrition as an agricultural practice, with the main aim of increasing maize kernel yield, under standard farm management practices. Fertilizer salts used in this study included potassium nitrate (KNO3), mono potassium phosphate (MKP) and mono ammonium phosphate (MAP). Three objectives were set in order to obtain information about i) the optimal application growth stage (2004/05 season), ii) the optimum concentration rate (2005/06 season) and iii) the contribution of either the P or K moiety (or both) contained in foliar applied salts towards growth, physiological and yield responses measured in maize (2006/07 season). During the 2004/05 season a 4% solution of MKP and a 3% solution of KNO3 were applied at growth stages V3 and V8. MKP applied at V8 was the best treatment as it increased plant height significantly (11%) as well as plant fresh and dry mass markedly, compared to the control, when measured at the end of the vegetative growth period at V19. The higher yield (+23%) obtained with MKP applied at V8 during season one, compared to treatment at V3, corresponded with an increase in grain filling of the second ear (+16%), total ear mass (+20%), kernel mass (+20%) and number of kernels (+16%) as well as higher total sugar and starch that accumulated in kernels. During the 2005/06 season, vegetative growth and yield parameters showed no significant differences between the single and double rates for both salts applied at V8. However, MKP applied at both the single and double rates contributed to marked yield increases of 12% and 14% respectively. Although neither KNO3 nor MKP significantly influenced chlorophyll content or photosynthesis efficacy (chlorophyll a fluorescence), higher sugar levels were detected in kernels at the milk and soft dough stages as well as starch at harvest of plants treated with both salts and at two different concentrations. This strongly indicated that improvement of sucrose translocation from the leaves to kernels was rather causative of higher carbohydrate content measured in harvestable parts than sugar production per se. During the 2006/07 season MAP had either no significant effect or suppressed both growth and yield eliminating its purpose to verify P or K involvement. Further, the third season was significantly drier compared to the first two seasons further complicating the use of third season data to distinguish between P and K in terms of its involvement in causing the vegetative and yield responses measured in maize. Overall, it was only MKP applied at 4% and at V8 that tended to increase kernel yield over the first two seasons.Item Open Access Induction of defence responses and resistance to wheat leaf rust by plant extracts(University of the Free State, 2008-05) Cawood, Maria Elizabeth; Pretorius, J. C.; Van der Westhuizen, A. J.English: Information on the induced disease resistance mechanism in wheat against leaf rust (Puccinia triticina) by two natural bio-stimulants (ComCat® and the seed suspension of Lupinus albus; SS) and two extracts with antifungal activity (Tulbaghia violacea and Agapanthus africanus) may be of great value both in designing new agrochemicals that stimulate plant resistance responses and in developing genetically engineered plants with enhanced disease resistance. The potential of these extracts to control leaf rust in vivo in susceptible (Thatcher) and resistant (Thatcher / Lr15) wheat was investigated. ComCat® and SS had no direct effect while the A. africanus extract resulted in the reduction of pustule and necrotic lesion formation in a susceptible and resistant wheat cultivar. T. violacea and A. africanus significantly inhibited the germination of P. triticina spores and prevented further germ tube development. Foliar application of the different plant extracts on resistant infected wheat plants activated β-1,3-glucanase, chitinase and peroxidase enzyme activities. However, it was only the A. africanus treatment that increased the in vitro activities of these three apoplastic PRproteins significantly in both susceptible and resistant wheat cultivars, whether uninfected or infected. As a result it was decided to concentrate the rest of the study on the A. africanus extract only. The induction pattern of apoplastic proteins from infected susceptible and resistant wheat treated with an A. africanus extract as well as a control treated with distilled water was followed using SDS-PAGE. Clear differences between SDS-PAGE profiles of intercellular proteins from resistant and susceptible as well as untreated and treated plants were observed throughout the 144 h period after treatment with the extract. In general, resistant plants contained higher amounts of a 31 kDa protein and the protein was also present at much higher detectable levels in plants treated with the A. africanus extract. The molecular mass corresponded to that of β-1,3-glucanase. A Western blot using a polyclonal antibody against β-1,3-glucanase from wheat confirmed the identity of the 31 kDa protein to indeed be that of β-1,3-glucanase. This overwhelmingly excluded the A. africanus extract from the rest in terms of its potent ability to induce a defence response in wheat towards leaf rust. RT-PCR was used in the analysis of the expression of the three defence related genes. Timecourse experiments confirmed that they were induced in resistant as well as susceptible wheat after infection. In this study, when resistant and susceptible wheat were treated with an extract of A. africanus 48 h prior to infection, a more pronounced induction of PR2, PR3 and PR9 gene expression occurred. Two different sized fragments were amplified when using PR9 specific primers and both were induced by infection and by treatment with A. africanus extract in susceptible and resistant wheat. After sequencing, the larger fragment was confirmed to be peroxidase, while the smaller fragment shared very high sequence similarity to a retrotransposon gene. It can, therefore, be claimed that A. africanus is responsible for the induction of PR genes and a retrotransposon gene in wheat. From the results obtained thus far, it was obvious that A. africanus must contain an active compound(s) that act as an elicitor(s) in the mechanism of the defence reaction of wheat against leaf rust infection. Subsequently, activity directed isolation and purification of the active compound lead to the isolation of a saponin, identified by means of 1H-NMR and 13CNMR spectroscopy as (25R)- 5α spirostane-2α, 3β, 5α-triol 3-O-{O-α-L-rhamnopyranosyl- (1α2)-O-[β-D-galactopyranosyl- (1α3)]- β-D-glucopyranoside}.Item Open Access Response of crops on shallow water table soils irrigated with deteriorating water qualities(University of the Free State, 2007-11) Ehlers, Louis; Bennie, A. T. P.; Van Rensburg, L. D.This study was undertaken to investigate a number of issues regarding the effect of using saline irrigation water for crop production on soils with shallow water tables. The experiments were conducted in large drainage lysimeters, filled with a yellow sandy soil and a red sandy loam soil in which shallow saline water tables were maintained at a constant depth of 1.2 m. Wheat, beans, peas and maize were grown under controlled conditions using irrigation water with salinities that ranged from 15 to 600 mS m-1. This facility was used to determine the effect of irrigation water and water table salinity on crop yield and water uptake, as well as salt accumulation in the root zone during growing seasons. The field experiments simulated conditions of adequate water supply to the crops through irrigation in the presence of a shallow saline water table. Except for wheat that gave better yields in the more clayey soil, the growth of the other three crops was similar on both soils for comparative irrigation water salinity treatments. The above-ground biomass of wheat, maize, peas and beans started to decline when irrigated with water of 600, 450, 300 and 150 mS m-1, respectively. The water use of all four crops, as indicated by evapotranspiration, declined with deteriorating irrigation water salinity. On a relative basis the evapotranspiration of peas, beans, maize and wheat decreased at rates of 0.0007, 0.0005, 0.0004 and 0.0001 mm per unit increase of soil water salinity measured in mS m-1. A decrease in the osmotic potential of the soil water to -300 kPa, which is equivalent to an electrical conductivity of 750 mS m-1, reduced evapotranspiration in comparison to the control by 7, 30, 38 and 53% for wheat, maize, beans and peas, respectively. The water use efficiency of the crops, expressed in above-ground biomass produced per unit mass water used, started to decline only when the threshold ECe-values were exceeded. Water uptake from the shallow water tables decreased with an increase in irrigation water salinity for all four crops on both soils. The relative water uptake from the capillary zones above the water tables declined linearly when the soil water salinity in these zones exceeded certain threshold values. These values varied between 57 mS m-1 for beans to 279 mS m-1 for maize, with an average value of 136 mS m-1. The crops less affected by the increase in salinity, were wheat followed by maize, beans and peas. Salts accumulated at or just below the capillary fringe in both soils, with maximum accumulation at 700 mm from the soil surface or 500 mm above the water table. Equations were derived from the accumulation of salts in the root zone to calculate the salt accumulation in soils with restricted drainage during a crop growing season. These equations were incorporated in proposed procedures for salinity management on irrigated soils. The procedures made provision for five different conditions: i) where added salts to the root zone accumulate without any possibility for leaching and the mean root zone salinity is lower than the crop ECe-threshold value; ii) where added salts to the root zone accumulate without any possibility for leaching and the mean root zone salinity is higher than the crop ECe-threshold value; iii) where added salts can leach naturally from the root zone, but with not enough irrigation water to supply in the crop water demand; iv) where the natural leaching of added salts can be accelerated by irrigating more than the required crop water demand; and v) to irrigate according to the crop water demand in order to utilize rainfall for leaching. The different salinity management procedures were compared on the two soil types by means of computer simulations for a range of irrigation water qualities and long-term climatic conditions. The simulated results indicated that under conditions with zero drainage, sustainable production could be maintained for only 25 to 40 years if good quality water was used for irrigation. Irrigation water with an ECi > 50 mS m-1 resulted in severe soil salinisation and crop losses within 5 to 10 years. On freely drained soils additional leaching was required within 5 years, even with the use of good quality irrigation water. It was clear from the simulated results that an increase in root zone salinity in soils with shallow water tables, necessitate adaptations in the normal approaches to irrigation scheduling and irrigation water management.Item 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.Item 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.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 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 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.Item Open Access The relationship between the water regime and morphology of soils in the Weatherley catchment, northerly Eastern Cape(University of the Free State, 2003-11) Van Huyssteen, Cornelius Wilhelm; Le Roux, P. A. L.; Hensley, M.English: The Weatherley catchment is situated close to Maclear in the northern Eastern Cape Province. Soil water contents have been measured regularly, as part of a long-term project, at 28 sites in the catchment for six years to quantify the soil water regime. For this study tEm of these sites were selected, described and analysed in detail to characterize the soil properties. This data was used to determine the relationship between soil water regime and soil profile morphology. A correlation was found to exist between mean annual duration of water saturation above 0.7 of porosity (ADs>o.7, days year") and other soil properties. CECsoil increases from 3.5 to 11.5 crnol, kg-1 , base saturation increases from 25 to 44 %, and the underlying unspecified material with signs of wetness or G horizons occur closer to the soil's surface as mean ADs>o.7 increases. Orthic A horizons that occur in seeps are wetter, with mean ADs>o.7 212 - 365 days year", than orthic A horizons that occur on ridges with mean ADs>o.7 of < 25 days year". The former have common and many Fe oxide mottles, whereas the latter lack clear mottling. ADs>o.7 data.shows that orthic A horizons overlying red apedal B, yellow-brown apedal B or neocutanic B horizons are well drained, while those overlying E, soft plinthic Band G horizons are wetter. It is proposed that orthic A horizons can be subdivided into wetness classes using the occurrence of mottles, as well as the nature of the underlying horizon. The Longlands (P201 and P207) and Westleigh (P204) soils, characterized by the occurrence of a soft plinthic B horizon, have intermediate mean ADs>o.7. They increase from 84 to 157 days year" in orthic A horizons, to 231 days year" in soft plinthic B horizons and 360 days year" in the underlying unspecified material with signs of wetness. The chromatic soils, including Pinedene (P202), Tukulu (P203) and Bloemdal (P210) soil forms, defined as having yellow-brown apedal B, neocutanic B or red apedal B horizons as the second horizon in the profiles respectively have the driest water regime of the soils studied. The A and B1 horizons have mean ADs>o.7 < 40 days year'", the B2 horizons 88 days year", and the underlying unspecified material with signs of wetness 130 to 350 days year" . Pooling the data from all the profiles studied produces the following mean ADs>o.7 for the different diagnostic horizons: G horizons = 324 ± 20 days year": unspecified material with signs of wetness = 243 ± 40 days year": E horizons = 163 ± 56 days year": soft plinthic B horizons = 148 ± 45 days year": orthic A horizons = 144 ± 40 days year'"; and chromatic (red apedal B, yellow-brown apedal Band neocutanic B) horizons = 88 ± 51 days year". There is an association between mean ADs>o.7 and other soil properties. For example clay content, CEC, basic cations and pH are highest in G horizons and lowest in chromatic horizons. CBD extractable Fe and Mn are found to be roughly twice as much in soft plinthic B, chromatic B and unspecified material with signs of wetness horizons compared to orthic A, E or G horizons. Digital soil horizon photographs were quantified and classified into diagnostic red, yellow-brown, grey and black colours, using the Red and Green values of RGBnotation in ArcView SpatialAnalyst. This methodology produced promising results, as proven by classification of photographed Munsell colour sheets. Colour classification of horizon photographs generally supports the field colour classification of these horizons using Munsell colour sheets. In general, the profiles described for this study are dominated by diagnostic grey and yellow-brown colours, with the exception of the Bloemdal (P210) which is diagnostic red.Item 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.Item Open Access Improvement of SAPWAT as an irrigation planning tool(University of the Free State, 2015-06) Van Heerden, Pieter Schalk; Walker, S.; Stevens, J. B.English: In a world with a continuous reduction in per capita availability of fresh water, the increase in the efficiency of irrigation water use becomes more important as a means to postpone the time when water shortages will restrict crop production. Irrigation uses 62% of South Africa’s fresh water resources; therefore a saving in irrigation water through an increase in efficiency could have a large impact on total water use. Informed irrigation requirement planning is one way in which irrigation water use efficiency could be increased. Associated to efficient irrigation water use, is the effective use of irrigation soil as a resource. Problems such as waterlogging and salinity are found on 19% of irrigated soil in South Africa. Increasing the efficiency of irrigation water use could reduce the rate of increase of these problems and it might even decrease the occurrence. With the eye on the efficient planning of irrigation areas, research in crop irrigation water requirements has been done over time. Various approaches and planning aids have been developed for the estimation of irrigation requirements. During the second half of the 20th century products like the FAO’s CROPWAT and the South African SAPWAT were developed. Both these programs had shortcomings which made their use somewhat difficult. Development of SAPWAT3 followed with the objective to develop a user-friendly program that could be used as widely as possible. The estimation of irrigation water requirements by SAPWAT3 is based on the internationally accepted Penman-Monteith approach. The former links the climate data of a specific weather station with crop characteristics to determine a water requirement for a specified place and time. The growth and development of crops are influenced by temperature; therefore the crop growth characteristics have been linked to the Köppen climate system as a means of growth and development periods for warm and cool areas. About 5 100 weather stations in 144 countries with either daily or monthly values are included in SAPWAT3. A large number of crops are also included in the data files. If enough daily climate data are included, SAPWAT3 does consecutive year-on-year irrigation requirement calculations, which are then used to determine different levels of nonexceedance of the irrigation requirement. This enables the designer of systems or the water use planners to plan for different levels of risk. A linkage between enterprise budgets and estimated irrigation requirements is also built into SAPWAT3. This enables the user to plan crop combinations which will provide a potential income while also considering water supply constraints. The crop growth characteristics included in SAPWAT3 and in similar programs, are the weak point of such programs because they are based on calendar time and not on thermal time. A computerised methodology has been developed that uses measured crop water requirements and temperature data to link crop growth and development to thermal time. This methodology will be included as a module in the next version of SAPWAT3. SAPWAT was accepted by the South African irrigation fraternity. To determine why this was so, and to determine future upgrade approaches that need to be considered, the level of adoption of SAPWAT was investigated. Good and bad points about SAPWAT which had been identified through verbal feed-back from users were kept in mind and confirmed during the development of SAPWAT3. The feedback on SAPWAT indicated the need to improve the functionality of SAPWAT as an irrigation planning tool, to evaluate and to verify its output and to test its potential for adoption by users. The feedback also indicated that SAPWAT3 is easy to use and that it gives credible results, two aspects that enhance adoption. Therefore it can be expected that future improved versions will also be well received, acceptable and used by the irrigation planning community.Item Open Access Quantifying rainfall-runoff relationships on selected benchmark ecotopes in Ethiopia: a primary step in water harvesting research(University of the Free State, 2006-12) Welderufael, Worku Atlabatchew; Le Roux, P. A. L.; Hensley, M.Large areas of cultivated land in Ethiopia frequently suffer from drought, causing low crop yields and food insecurity. It was hypothesized that it may be possible to alleviate this problem by employing infield rain water harvesting (IRWH). Three representative semi-arid ecotopes in the Rift Valley were selected to test this hypothesis. They were the Melkassa Hypo Calcic Regosol, The Dera Calcic Fluvic Regosol and the Mieso Hypo Calcic Vertisol. The climate, topography and soils of the ecotopes were characterized in detail. Rainfall runoff studies were carried out over two rain seasons on replicated plots on these ecotopes comparing two soil surface treatments. They were conventional tillage (CT), simulating the initially fairly rough surface which results after normal tillage; and no tillage (NT), simulating the flat crusted surface expected on the runoff strip of the IRWH system. Rainfall amounts, rainfall intensity at one minute intervals, and runoff, were measured for each storm during the two rain seasons on each ecotope. The results were used to calibrate and validate the Morin & Cluff runoff model in order to enhance the extrapolation capability of the study results to other similar ecotopes. The study yielded the following useful results. · The rainfall pattern on all the ecotopes was characterized by occasional storms with fairly high amounts and high intensities (Pi) which greatly exceeded the final infiltration rates of the soil, causing a high proportion of the rain (P) to runoff (R), i.e. producing a high R/P ratio. For the NT treatment final overall R/P values for the two seasons on the Melkassa, Dera and Mieso ecotopes were 0.45, 0.52 and 0.32, respectively. These high values indicate that IRWH should produce a significant increase in yield due to its ability to reduce R to zero while concentrating the runoff in the basin area and increasing the water available for transpiration and therefore increasing yield. · Because of the textural and mineralogical properties of the topsoils, particularly the two Regosols soils; they disperse and form crusts easily when impacted by high intensity rain. The result was that after cultivation at the start of the rain season the surface of the CT treatment soon became very similar to that of the NT treatment. Accordingly no significant difference was found between the runoff from the NT and CT plots on the Melkassa Regosol and Dera Regosol. There was, however, a significant difference in this respect on the Mieso Vertisol with a more stable surface. · Runoff prediction in all the ecotopes were well done by the M & C model. · Two separate strategies were developed to estimate the maize yield increase that could be expected on the Melkassa Regosol by employing IRWH. From the nearby Melkassa Research Station it was possible to obtain maize yields for 15 seasons (1989-2003). These were used together with climate data, the CROPWAT model, and the runoff measurements, to estimate the benefit of IRWH. The two strategies produced yield increase estimates of 33% and 40% compared to CT.
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