published_or_final_version / abstract / toc / Botany / Doctoral / Doctor of Philosophy

Agricultural scientists are faced with the challenge of producing enough food for the increasing world population. Hence the need to develop tools for managing soil and plant systems to increase food production in order to meet the world food demand in the future. Crop simulation models have become promising tools in predicting yield and related components fi'om a set of weather, soil, plant and management data inputs. This study describes the estimation of solar radiant density, a crucial input in crop simulation models; calibration and validation of a soil-plant growth simulator, CropSyst, for management purposes; and generation of weather data for assessment of crop production under possible climate changes in the future. Daily solar radiant density, an input required by most crop simulation models, is infiequently observed in many stations. This may prevent application of crop simulation models for specific locations. Long-term data records of daily minimum and maximum air temperatures, precipitation, sunshine hours and/or solar radiant density were obtained for Cedara, Durban, Seven Oaks and Ukulinga in KwaZulu-Natal, South Africa. Solar radiant density was estimated fi'om sunshine hours using the Angstrom equation and ten other models that involved daily minimum and maximum air temperatures and/or precipitation along with extratelTestrial radiant density. Coefficients for the Angstrom equation and one of the other ten models were specifically developed for South African conditions; the remaining models required fitting coefficients using the available data for all locations. The models were evaluated using (i) conventional statistics that involved, root mean square elTor (RMSE) along with its systematic and unsystematic components, slope, intercept, index of agreement (d), and coefficient of determination (R\ and (ii) a fuzzy expert system that involved a single modular indicator (Ira d) aggregated from the modules of accuracy (aggregation of the indices relative RMSE, model efficiency and I-student probability), con'elation (Pearson's correlation coefficient) and pattem (aggregation of pattem index vs day of year and pattem index vs minimum air temperature). For each index, two functions describing membership to the fuzzy subsets Favourable (F) and Unfavourable (V) were defined. The expelt system calculates the modules according to both the degree of membership and a set of decision rules. Solar radiant density estimated from sunshine hours for the Durban station resulted in R2 , RMSE (MJ m,2) and d index of 0.90, 2.32 and 0.97 respectively. In the absence of observed solar radiant density data, estimations from sunshine hours were used for derivation of coefficients as well as evaluation of the models. For Durban, the performance of the models was generally poor. For Cedara, Seven Oakes and Ukulinga two of the models resulted in a high d index and smallest systematic RMSE. The solar radiant density estimated from each model was also used as an input to simulate maize grain yields using the soil-plant growth simulator, CropSyst. The models were ranked according to their ability to simulate grain yields that match those obtained from using the observed solar radiant density. The rankings according to crop simulation, conventional statistics and expert system were compared. The CropSyst model was also evaluated for its ability to simulate crop water-use of fallow and cropped (oats, Italian ryegrass, rye and maize) plots at Cedara, KwaZulu-Natal, South Africa. Soil characteristics, initial soil water conditions, irrigation and weather data were inputted to CropSyst. Crop input parameters for oats, Italian ryegrass and rye were used, with little modifications, as determined from field experiments conducted at Kromdraai open cast mine, Mpumalanga province, South Africa. Crop input parameters for maIze were either determined fi'om field experiments or taken from CropSyst crop input parameters documentation and adjusted within a narrow specification range of values as dictated by CropSyst. The findings indicated that CropSyst was generally able to simulate reasonably well the water-use of fallow and cropped (oats, Italian ryegI°ass, rye and maize) plots; leaf area index and crop evapotranspiration of rye; and grain yield and developmental stages of maize. The validated CropSyst model was also used to simulate timing and amount of irrigation water, and investigate incipient water stress in oats, Italian ryegrass and rye. The CropSyst model was used to investigate potential effects of future climate changes on the productivity of maize grain yields at Cedara, KwaZulu-Natal, South Africa. The effect of planting date (local planting date, a fortnight earlier and a fortnight later) was also included in the study. A 30-year baseline weather data input series were generated by a stochastic weather generator, ClimGen, using 30 years of observed weather data (l971 to 2000). The generated weather data series was compared with the observed for its distributions of daily rainfall and wet and dry series, monthly total rainfall and its variances, daily and monthly mean and variance of precipitation, minimum and maximum air temperature, and solar radiant density. Four months of the year failed to reproduce distributions of wet and dry series, daily precipitation, and monthly variances of precipitation of the observed weather data series. In addition, Penman-Monteith reference evaporation (ETa) was calculated using the observed and generated data series. Cumulative probability function of ETa calculated using the generated weather data series followed the observed distribution well. Moreover, maize grain yields were simulated using the generated and observed weather data series with local, a fortnight earlier and a fortnight later planting dates. The mean simulated grain yields for the respective planting dates were not statistically different from each other; the grain yields simulated using the generated weather data had significantly smaller variance than the grain yields simulated using the observed weather data series. When the generated weather data series was used an input, the early planting date as compared to the locally practiced and late planting dates resulted in significantly greater simulated grain yields. The grain yields simulated using the observed weather data for the early and local planting dates were not statistically different from each other. The baseline period was modified by synthesized climate projections to create future climatic scenarios. The climate changes considered corresponded to doubling of [C02] from 350 to 700 ~t1 ,-I without air temperature and water regime changes, and doubling of [C02] accompanied by increases in mean air temperature and precipitation changes of 2 (lC and 10%, 2 (le and 20%>, 4 °c and 10%, and 4 (lC and 20% respectively. Solar radiant density was also estimated from daily air temperature range for all scenarios that involved change in mean air temperature. In addition, input crop parameters of radiation-use and biomass transpiration efficiencies were modified for maize, in CropSyst, to accommodate changes in elevated levels of [C02]. Equivalent doubling of [C02], without air temperature or water regime changes, resulted in increased simulated grain yields as compared to the baseline period. Adding 2 QC to the mean daily temperature and 10% to the daily precipitation of a [C02] elevated atmosphere reduced the grain yield but still kept it above the level of the baseline period grain yield. Adding 4 QC to the mean daily temperature and 10% to the daily precipitation fLllther decreased the yield. Increasing the daily precipitation by 20% instead of 10% did not change the simulated grain yield as compared to the 10% increments. Early planting date, for all scenarios, also resulted in higher yields, but the relative increment in grain yield was higher for the late planting dates with scenarios that involved increment in mean air temperature. In general, this study confi1l11ed that doubling of [C02] increases yield but the accompanied increase in mean air temperature reduces yield. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 337-367.

Thesis (Ph.D.)--University of Western Australia, 2006.

Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2009. / Full text also available online. Scroll down for electronic link.

The object of this research was follow up the cumulation of nitrates in individual kinds of vegetables. Analysed was 240 samples of root crops, cole crops and potatoes distributed in the trade network in Humpolec in the years 2008 - 2010. The measurement results show that all the vegetables went beyond the nitrate permitted limit, according to a law n. 53/2002. The most frequently it was in potatoe samples (50 % samples). The next was a carrot (27 %), kohlrabi (25 %), broccoli (24 %) and celery (17 %). From aspect cumulation of nitrates is parsley unchallenged kind of vegetable. Permitted limit was transcendent in 10 % about less than 1 %. The origin of the vegetables was detected as well. Czech republic had the worst results (52,5 %) because of the high nitrate concentration in potatoes. It is grown by a domestic growers. Spain had 20 % in broccoli and kohlrabi. It is imported to our market. Although the high nitrate concentration in some vegetable samples the vegetable influence the human health in a positive way and it doesn?t make health hazard.

Having appreciated the changes in global markets that offer lucrative opportunities for highvalue crops like baby vegetables; the dire need to diversify the Swaziland agricultural sector; and the versatility of value chain finance, this study takes the Swaziland baby vegetable industry as a case study to determine the applicability of value chain finance to infant highvalue horticultural industries lacking guaranteed markets. This study focused on the NAMBoard value chain, employing both qualitative and quantitative methods of inquiry through a desktop study; case study reviews; and in-depth interviews. This study adapted the UNIDO (2011) VCF analytical framework. This study found that NAMBoard provides direct VCF to its producers, financial institutions provide formal finance, farmer group members provide informal finance to each other, farmers that have some other sources of income self-finance the baby vegetable enterprise, and that there is inter-financing between the baby vegetable and conventional vegetable value chains. Indirect VCF is absent in this value chain. On the other hand, Sdemane enterprise provides direct VCF to its outgrowers and data collectedEmpirical evidence on a sample constituting about 30% of the target population shows that seeds/seedling costs contribute 56.1% to total average production costs. This shows a big financing challenge now that NAMBoard is reluctant to give seeds on credit, while the rest of v the 43.9% still require financing. In addition to that, there is no capital finance loans provided to smallholder producer, but only operational finance is accessible from formal financial institutions. This study discovered that all baby vegetable producers also produce conventional vegetables, and these businesses are inter-linked. There is financing between the baby vegetable and conventional vegetable businesses and thus value chains, sourced from product proceeds. Individual producers, farmer groups and farmer associations form the producer base. A financial analysis on the production stage revealed that that there are informal financial relationships within farmer groups. Also, farmer groups use formal finance suggests that these don’t use other financing mechanisms except self-finance VCF. Empirical evidence on a sample constituting about 30% of the target population shows that seeds/seedling costs contribute 56.1% to total average production costs. This shows a big financing challenge now that NAMBoard is reluctant to give seeds on credit, while the rest of the 43.9% still require financing. In addition to that, there is no capital finance loans provided to smallholder producer, but only operational finance is accessible from formal financial institutions. This study discovered that all baby vegetable producers also produce conventional vegetables, and these businesses are inter-linked. There is financing between the baby vegetable and conventional vegetable businesses and thus value chains, sourced from product proceeds. Individual producers, farmer groups and farmer associations form the producer base. A financial analysis on the production stage revealed that that there are informal financial relationships within farmer groups. Also, farmer groups use formal finance more than individual producers who mostly prefer self-finance VCF. A VCF analysis of NAMBoard discovered that there is direct VCF between the SAS input shop and also the NAMBoard input shop, and between producers and the NAMBoard input shop. NAMBoard, in addition to the input shop and provision of extension services, performs three distinct post-harvest services namely: transportation; processing; and marketing, for which a handling fee of 35 percent to the final produce value is charged and deducted from product proceeds. The Swaziland financial system has no financial products specifically for this industry, as there is a very small number of participants borrowing funds from financial institutions. The loan processing procedures are cumbersome and take too long thus formal finance is currently ill suited to producers. This study rated the risks to the financial transaction reflecting the qualitative interpretation of available information and that obtained in the field through interview schedules with all value chain actors. Risks identified as high are: insufficient production; poor quality produce; failure to meet food quality ands safety standards; lack of guaranteed market; and ignorance on price. Catastrophic weather; loss of quality; lack of technical know-how; and failure to manage business profitably were categorised as medium risk. Inefficiency; lack of market demand; and unreliable water sources & electricity are seen as low risk to the financial transaction. This study also explored the Sdemane value chain, where Sdemane enterprise is the lead firm. It was examined and interpreted as an institutional success story that holds the solution to the NAMBoard value chain ailments. It also has out grower producers to supplement its production. Findings of this research show that a financial bailout ensured the survival and growth of this emerging value chain, which now has secured markets with a market demand more than achieved output. The model used is able to minimise and diversify risk for both Sdemane and the out grower producers. The manner in which this value chain is organised makes it competitive and exhibits potential which attracted donor funding, and today is an infant value chain that is achieving tremendous growth. This study concludes that VCF is applicable to infant industries lacking guaranteed markets to a limited extent. Minimising risk increases the availability of finance due to the resultant increase in financial attractiveness and the chain becomes able to produce competitively and meet the strict market conditions. At the end, the value chain would operate as if the market were guaranteed, just by being competitive and successfully delivering products to end markets. With regard to policy, rethinking the underlying NAMBoard business model and learning from success stories including the local Sdemane enterprise is one way to avoid the imminent collapse in exports from this value chain. / Dissertation (MSc Agric)--University of Pretoria, 2014. / gm2014 / Agricultural Economics, Extension and Rural Development / unrestricted

The coal industry of Mpumalanga Province is faced with the problem of developing cost effective ways of using large volumes of calcium and magnesium sulphate enriched waste waters. Use of the waste waters for agricultural production may contribute as a stabilising factor with regard to yields in this high potential agricultural area. The objectives of this study were to determine the effect of such waste waters on yield and to compare crop response to calcium and magnesium sulphate salinity at different nutrient levels. Two separate glasshouse experiments were conducted. Wheat (Triticum aestivum L. cv. SST 825) was grown in calcium and magnesium sulphate salinised nutrient solutions (Ca:Mg 2: 1) with differential levels of NO3, NH4, P and K. A soil pot experiment was subsequently conducted with maize (Zea mays, cv. PAN 6256), three gypsum and magnesium sulphate salinity levels and a 6 x 2 x 3 factorial combination of N, P and K. Calcium and magnesium sulphate salinity decreased the biomass production of both crops. This was mainly due to interactions of Mg with the uptake of essential nutrients in wheat and a Mg toxicity andlor Ca deficiency induced by high levels of Mg andlor SO4 in maize. The application of NO3, NH4, and K at rates different from the level considered beneficial for non-saline conditions improved wheat growth under sulphate saline conditions. Strongly inhibitory salinity levels controlled the maize yield of the highest salinity treatment regardless of the level of fertiliser application. A beneficial effect of higher NH4 supply was observed in both experiments. This can be ascribed to the antagonistic effect that NH4 exerted on Mg concentrations in plants (both experiments) and SO4 (soil pot experiment) and/or to a higher N-utilization efficiency where N was supplied as NH4 compared to NO3. Differential application levels of P had no effect on the yield of wheat. Phosphorus concentrations in maize were marginal to low, even at extremely high soil Bray I-P levels. This was probably caused by the precipitation of P as insoluble calcium phosphate complexes in the soil andlor between the free space of the cortex cells of plant roots. These results could also indicate that the Bray I extraction method does not give a true reflection of plant available P in sulphate saline soil. Further experimentation is needed to verify these results under field conditions and determine the optimal rate, method and timing of especially NH4 and PO4 fertilisers when irrigating crops with these calcium and magnesium sulphate enriched waste waters. / Dissertation (MSc (Plant Production and Soil Science))--University of Pretoria, 2007. / Plant Production and Soil Science / unrestricted

Winter rotational cover crops (WRCC) are often used to boost soil fertility and plant nutrition. However, selection and use of WRCC for soil physical improvement is usually overlooked. The objective of this study was to determine the effects of WRCC on soil strength, aggregate stability and water conservation of a hardsetting soil. The soil physical properties were determined after four rotations of growing monocultures of vetch (Vicia dasycarpa cv. Max), lupin (Lupinus angustifolius cv. Tanjil) and oats (Avena sativa cv. Sederberg) and after two rotations of growing bicultures of oats (Avena sativa cv. Pallinup) and vetch (Vicia dasycarpa cv. Max) across two soil layers, 0 to 15 cm and 15 to 30 cm. The individual WRCC and a weedy fallow constituted the treatments in the monoculture study whilst in the biculture study the various combinations of WRCC namely; 90% oat plus 10% vetch (O90V10); 70% oat plus 30% vetch (O70V30) and 50% oat plus 50% vetch (O50V50) and a weedy fallow constituted the treatments. After four rotations with cover crop monocultures, oats significantly (P ≤ 0.05) reduced penetration resistance (PR) whilst vetch increased PR in both soil layers compared to the weedy fallow control. The effect of the biculture treatments was only experienced within the 15 to 30 cm depth. The treatments O50V50 and O70V30 increased the PR compared to the control. The WRCC in monoculture significantly increased the soil aggregate stability relative to the control in both soil layers. Vetch, lupin and oats resulted in a 41.7%; 20.4% and 15.7% increase in MWD in the 0 to 15 cm soil layer and 47.2%; 44.2% and 39.7% in the 15 to 30 cm depth, respectively. An increase in aggregate stability was associated with increased macro-aggregation. Under the biculture, WRCC slightly increased, non- significantly, the aggregate stability. Both hot water and dilute acid extractable polysaccharides showed no significant correlation with aggregate stability in the two studies. Oats monoculture resulted in a significant difference (P ≤ 0.05) on cumulative infiltration compared to the control. However, after 2 h vetch and lupin showed no significant difference from the control on cumulative infiltration. Oats resulted in a 7.8% increase in final infiltration rate (FIR) whilst vetch and lupin reduced FIR by 9% and 16.7% respectively, compared to the control. Bicultures of oats and vetch significantly (P ≤ 0.05) increased cumulative infiltration compared to the weedy fallow control. A similar significant increase in FIR was also observed under bicultures. The treatments O50V50; O90V10 and O70V30 resulted in a 163.3%; 113.3% and 105.4% increase in FIR respectively, compared to the control. Cover crop monocultures significantly (P ≤ 0.05) increased plant available water (PAW) compared to the weedy fallow, with vetch, oats and lupin resulting in a 28.3%; 22% and 23.9% increase respectively, in PAW. However, no significant differences were observed on PAW after two rotations with bicultures. Compared with winter weedy fallow, WRCC improved most of the soil physical properties under study, with the most suitable results expected under bicultures compared to monocultures. Under CA, selection of WRCC like oats, vetch and lupin, one should therefore take into consideration their effects on soil physical properties as a selection criterion and not biomass and fertility alone.

There are many technologies being developed for crop breeding. Two interesting technologies are genetic modification and genetic editing. Competitive pressures and changing consumer preferences are forcing organizations to invest heavily in these two technologies. Organizations must decide which traits they want to target and must commit significant time a money to the project. Traditionally, firms would decide which project to embark on if the project is net present value positive. Throughout the research and development process managers have flexibility to abandon the project once new information is received. That flexibility has value and real option analysis must be performed to value that flexibility. Once the value of a GM and GE project is determined, how might an organization decide which project to do? The concept of minimum required acreage (MRA) is developed in this study, allowing organizations to compare GM and GE technologies and decide which project to invest it.