MSCAGR (Soil Science) / Department of Soil Science / The application of organic manures as alternatives to reduce the use of mineral fertilizers is considered a good agricultural practice for smallholder farmers. However, the effect of organic manure on soil properties and crop yield depends upon its application rate and chemical composition. Climatic seasonal variability within the study area could adversely affect crop production. The amount of rainfall and temperature are among the most important factors that determines crop production. This field experiment was carried out during the 2013/2014 and 2014/2015 cropping seasons at the University of Venda experimental farm which is located about 2 km west of Thohoyandou town in the Vhembe District, Limpopo Province. The main objective of this study was to determine the effect of three types of organic manure (cattle, poultry and their combination (1:1)) on yield and water use efficiency of sunflower (Helianthus annuus L.) and selected soil physical and chemical properties under rainfed conditions. The experiment was a randomized complete block design (RCBD) with four treatments and four replications (control (C0), cattle manure (CM), poultry manure (PM) and their combination (CM + PM)). All organic manures were applied 21 days before planting at a rate equivalent to 20 t ha-1. The manures were incorporated in the soil using a hoe to an approximate depth of 10 cm. Crop water use (WU) and water use efficiency (WUE) were determined using the water balance equation. Rainfall was measured using three standard rain gauges installed on the experimental site. Change in soil moisture storage was determined by monitoring soil moisture content weekly using a neutron water meter (NWM), calibrated on the experimental site. Data on sunflower dry matter and leaf area index (LAI) was collected at flower bud stage, flowering stage and at grain maturity stage. Plant height and stem girth were also determined at the same developmental stages. Grain yield was measured at physiological maturity. xv Analysis of variance (ANOVA) was carried out using SPSS software. Due to seasonal variability encountered during the two cropping seasons, particularly in terms of rainfall, further analysis of two factors (viz. cropping season and organic manure) and their interaction were performed. The differences between treatment means were separated using the least significant differences (LSD) procedure. The results showed that organic manure application had no significant effect on soil physical properties. Poultry manure application resulted in lowest bulk density (BD) with a decrease of 32% in the top layer (0 – 20 cm) compared to control. Cattle manure + PM and CM application decreased BD in the top layer by 14% and 9% compared to control, respectively. Poultry manure and CM recorded almost the highest similar stable aggregate fractions at all soil depths. Poultry manure recorded the highest final infiltration rate and cumulative infiltration followed by CM and CM + PM. The control treatment retained the highest mean water content compared to other treatments at both field capacity (FC) and wilting point (WP). Cattle manure + PM and PM recorded the least mean water content among others at FC and WP respectively. This could be as a result of increased micropores by organic manure application on a clayey soil which allowed an ease movement of water that control treatment which had no manure application. Total N, Ca, and Zn were significantly different between treatments in the first cropping season while K, Na, CEC and Zn were significantly different in second cropping season. pH recorded no significant difference in all treatments in both cropping seasons. CM + PM recorded the highest OC at top layer (0 – 20 cm) in both cropping seasons compared to other treatments. Dry matter yield and LAI at flower bud, flowering and maturity stages increased with the application of different manures compared to the C0. Organic manure application showed a significant (p<0.05) effect on dry matter at all growth stages in the second cropping season. Organic manure had a significant effect on LAI only at flower bud stage of the first cropping season, with PM and CM + PM recording the highest similar value of 1.31. The manure xvi application also showed a significant (P<0.05) effect on plant height and stem girth at all growing stages in the second cropping season, whereas in the first cropping season the significant effect was only in the flower bud stage for both parameters. Grain yield was significantly affected by the manure application in the second cropping season. Manure application in the second cropping season resulted in an increase in the grain yield compared to the first cropping season, except for PM where the grain yield decreased significantly by 167.92% from the first cropping season. Then high grain yield in the second cropping season could be as a result of high WUE reported. The manure application had a significant effect (p<0.05) on water use efficiency (WUE) in the second cropping season. The WUE recorded the highest values under CM and CM + PM treatments in second cropping season than in first cropping season, while PM recorded the highest WUE value in the first cropping season. Generally, organic manures used obtained higher grain yield and WUE compared to control. Keywords: Organic manure, smallholder farmers, sunflower and water use efficiency

MSCAGR (Soil Sciece) / Department of Soil Science / In most parts of Limpopo Province of South Africa, crop yields are low and continue to decrease due to decline in soil fertility, which has been identified as a major constraint to crop production. Therefore, there is a pressing need for soil amendments such as the application of biochar, which has the potential to improve soil fertility due to its physical and chemical properties. Biochar is the product of incomplete combustion of biomass in the absence of oxygen. The overall objective of the study was to determine the effects of biochar and NPK fertilizer on maize performance and selected soil nutrient levels. A 3x2 factorial experiment was conducted at the School of Agriculture Experimental Farm for two consecutive seasons (2015/16 and 2016/17 seasons). Treatments consisted of biochar applied at three levels, viz. 0, 10 and 20 t/ha and NPK inorganic fertilizer applied at two rates viz. NPK0 (zero NPK fertilizer) and NPK1 {N (150 kg/ha) P (50 kg/ha) K (20 kg/ha)}. The treatments were laid out in a randomized complete block design (RCBD) and replicated three times. Maize cultivar (DKC 2147) was used as the test crop. Maize growth and yield measurements assessed included: plant height (cm), stem diameter (cm), number of leaves, leaf area, dry biomass (kg/ha), nutrient uptake, cob yield, grain yield and harvest index. Soil samples were collected from 0-10 cm and 10-20 cm soil depths at the end of each season to determine total N, P, K nutrient levels in the soil. Data collected was subjected to two-way analysis of variance using the general linear model (GLM) procedure of Genstat software version 17. Comparison of means was done using the Standard Error of Deviation (SED) method at 5% level of significance (p<0.05). Biochar and NPK fertilizer had no effect on total N and exchangeable K at all soil depths in 2015/16 and 2016/17 seasons. Biochar had no effect on phosphorus at all soil depths in 2015/16 and at 0-10 cm soil depth in 2016/17 season. The effect of biochar and NPK fertilizer was highly significant (p<0,001) on available P at 10-20 cm soil depth in 2016/17 season. Significant interactive effect of biochar and NPK fertilizer on soil total N at 10-20 cm (in 2015/16 season), available P and exchangeable K at 10-20 cm soil depth in 2016/17 season was also observed. Plant growth parameters increased with biochar addition at 20 t/ha and NPK1 (150 kg N/ha, 50 kg P/ha, 20 kg K/ha) fertilizer. The results of this study showed that biochar application at the rate of 10 and 20 t/ha has the potential to influence selected soil nutrient levels, maize growth, yield and yield components with and without NPK fertilizer application. Since this study was conducted over two seasons and biochar properties changes over a long-term period, more research is needed to evaluate the effect of biochar on soil nutrient levels and maize growth, nutrient uptake and yield over a long period of time. / NRF