Thesis (M.Sc. (Agronomy)) -- University of Limpopo, 2019 / Smallholder farmers are usually confronted with severe climatic conditions during summer growing seasons on production fields that are generally characterized by poor soil fertility and consequent low crop yields. Conservation agriculture could be a feasible local practice under such conditions to ensure a more sustainable and environmentally friendly system for cultivating crops. A rainfed field experiment was conducted at two diverse agroecological sites, Syferkuil and Ofcolaco during 2017 growing season in the Limpopo Province of South Africa to evaluate production, and symbiotic activities in soybean (Glycine max (L.) Merrill) and also to validate the performance of the Agricultural Production System Simulator (APSIM) model in simulating soybean biomass accumulation and grain yield under tillage and mulch practices. The experiment was established as a randomized complete block design in a split-plot arrangement with tillage (till and no-till) as the main plot treatment and four rates of grass mulch (0, 3, 6 and 9 tons ha-1) as the sub-plots treatment. The APSIMSoybean model was used to validate the result for simulated biomass and grain yield for the tillage practices at different mulching rates. A greenhouse experiment was also conducted during the 2017/2018 growing season to enhance the understanding of undulation potential in the selected soybean cultivar together with other cultivars. The greenhouse experiment was laid out in a randomized complete block design (RCBD) with four replications. Three soybean cultivars, commercial cultivar Donmario 8.6IRR (sourced from Agricol), Dundee commercial cultivar and Ibis 2000 (both sourced from Agricultural Research Council) were evaluated for their growth, phenological development, and symbiotic activities. Soybean growth was significantly (p≤0.001) affected by tillage at Syferkuil but not at Ofcolaco with the tilled soil having more pronounced growth than no-till at the former. Addition of mulch resulted in improved soybean growth relative to the control at both localities. Tillage and mulch as well as their interactive effects on soil moisture was significant at Syferkuil. Across tillage practices mulch application exhibited the highest moisture content than the control plots. At Ofcolaco tillage and mulch significantly (p≤0.001) affected soil water content but not the interaction effect, with more moisture recorded under the no-tilled condition and mulch application rate of 9 t ha-1 Soybean shoot and root nitrogen content was not influenced by tillage but was responsive (p≤0.001) to mulch application at both sites. The application of 9 t ha-1 mulch increased the shoot nitrogen content compared to the control plants at both locations. Soybean biomass and grain yield were also significantly influenced by tillage and mulch at Syferkuil but not at Ofcolaco (p≤0.001). A significant interaction effect of tillage and mulch (p≤0.001) on biomass and grain yield was also observed at Syferkuil but not Ofcolaco. At Syferkuil, higher biomass and grain yield was observed under the tilled condition when mulch at the rates of 6 and 9 tons were applied whereas, at Ofcolaco, soybean biomass and grain yield was higher under mulch application than the control with mulch application of 9 tons ha-1 at this location having the highest biomass and grain yield. The results of the APSIM model simulation showed the simulated biomass and grain yield to have a positive relationship. Hence, APSIM model can be used to guide alternate management practices to improve soybean production in the Limpopo Province. Findings from the greenhouse trial revealed that soybean cultivars significantly (p≤0.001) vary in symbiotic activities, growth, and physiological development. Across the cultivars, Ibis 2000 was superior in all studied parameters whereas Donmario, the cultivar used in the field trial was generally inferior among the three. KEYWORDS: Cultivars, Grain yield, Soybean, / Department of Science and Technology (DST) and National Research Foundation (NRF)

Thesis (M.Sc. (Pasture Science)) -- University of Limpopo, 2014 / Forage sorghum is widely grown in South Africa as annual summer forage to supplement pasture production for sheep, beef and dairy cattle. A number of sorghum cultivars are available commercially, and periodically some cultivars are added while others are withdrawn from the market. The potential yield figures and the nutritive value of these forage sorghum cultivars are generally not known. The management practices that improve forage sorghum production and quality include the time of planting and time of harvesting. The genetic makeup of different forage sorghum cultivars also accounted for a portion of the production and quality. A field experiment was conducted at Dewageningsdrift Experimental Farm (DWD), Moloto, Gauteng and Nooitgedacht Agricultural Development Center (NGD), Ermelo, Mpumalanga to study the influence of planting date on the growth potential of different forage sorghum cultivars. Three planting dates were used: mid-December 2006, mid-January 2007 and mid-February 2007. Thirteen different cultivars were incorporated in the trial to evaluate influence of the breeding history. The cultivars were defoliated at three different stages: cut repeatedly at six weekly intervals (Dt 1), cut repeatedly when it reached a grazing stage (± 800 mm high) (Dt 2) and once at the silage stage (soft dough) (Dt 3). At DWD the average total dry matter (TDM) productions, for the six week cutting treatment (Dt 1), were 10760 kg/ha, 5195 kg/ha and 1944 kg/ha for December, January and February planting date respectively. For the same treatment, at NGT, the average TDM productions were 6396 kg/ha and 1737 kg/ha for December and January respectively. The February planting resulted in the poor germination and seedling emergency. The seedlings did not survive due to low temperatures. The minimum of 13 ºC and 11.8 ºC as well as the maximum of 24.1 ºC and 23.0 ºC in February and March were below the required germination temperature (15 ºC). The highest producers that is available in the market were Jumbo, Sentop, Piper, Kow Kandy, and Sugargraze. Defoliated repeatedly at grazing stage (Dt 2), at DWD, resulted in average TDM productions of 8541 kg/ha, 4950 kg/ha and 2683 kg/ha for December, January and February, respectively. At NGT the average TDM productions were 7769 kg/ha and 3010 kg/ha for December and January respectively. The highest producers were Jumbo, Kow Kandy, Piper, Sentop and Sugargraze. The average TDM productions at the silage stage (Dt 3), at DWD, were 17923 kg/ha, 15015 kg/ha and 2529 kg/ha for December, January and February respectively. At NGT the average TDM production iii was 11856 kg/ha and 5350 kg/ha for December and January, The highest producers were Jumbo, Sugargraze, Kow Kandy, Sentop and Kow Kandy.December planting proved to be the best planting date for optimum DM production, compared to later plantings in January and February. Keywords Forage sorghum, cultivars, planting dates, defoliation stages, grazing stage, silage