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Thesis (Msc. (Agriculture)) --University of Limpopo, 2011 / The impact of agricultural chemicals on the environment has come under close scrutiny in the country of South Africa, for that reason, we are investigating alternative and appropriate methods for nutrients management. The objective of the study was to assess infield spatial variability of soil nutrients in a uniformly managed corn field, and (ii) to recommend method that can potentially help corn (Zea mays L.) producers in Limpopo Province to enhance grain yield with optimal utilization of resources. The study was conducted at Syferkuil agricultural experimental farm (23o50’ S; 29 o40’ E) of the University of Limpopo, in the northern semi-arid region of South Africa. Prior to planting of corn on this uniformly managed 7 ha portion of a 1 705 ha farm, the field was mapped with Ag132 Trimble differentially corrected global positioning system (DGPS) equipped with Field Rover II® GIS mapping software. Land suitability assessment for corn was conducted before planting and the field was classified for suitability as S1 based on FAO guidelines for irrigated agriculture and South African Binomial System of Soil classification. Soils and corn leaf sample parameters, including N were collected and measured from geo-referenced locations on a 40 x 40 m grid. Nutrient distribution spatial maps were produced with Surfer software 8.0. There was a significant variability (P≤0.05) of soil nutrients and pH across the corn field. Corn grain yield ranged from 2.7 to 6.3 Mg ha-1. For a land suitability class of S1 under linear irrigation in a semi-arid environment, these grain yields were considered lower. This lower grain yields can be linked to variability of soil nutrients, and pH because the field was classified suitable according to FAO guidelines. This field, with its significant variability of nutrients and pH that resulted in lower grain yields, is potentially a good field for precision agriculture IX methods of nutrient management such site-specific management zones for environmental quality and economic efficiency. Keywords: Maize, Small-scale farming, Soil nutrient management, and Spatial variability

MSCAGR (Animal Science) / Department of Animal Science / The objective of the study was to determine the effects of fertilisation with bio-digester slurry and the inclusion of carbohydrate additives at ensiling on the fermentation characteristics, chemical composition, ruminal degradability, and in vitro digestibility of Napier grass silage. Napier grass planted at the School of Agriculture Experimental Farm, University of Venda in 5 m x 4 m plots replicated three times in a completely randomised design and was irrigated with either biodigester slurry or no bio-digester slurry (tap water) for a period of 12 weeks. After 12 weeks, the Napier was freshly cut and ensiled for 90 days in 1 litre glass jars in a 2 (Control - tap water and slurry irrigation) x 4 (No additive, molasses, maize meal and brown sugar) factorial arrangement. Fermentation quality and nutritive composition were determined using standard protocols. The dry matter (DM) and crude protein (CP) ruminal degradability was determined in sacco by incubating feed samples in nylon bags (external dimension: 6 × 12 cm, pore size of 46 μm) in the rumen in three Bonsmara steers fitted with rumen cannulae for 0, 6, 12, 24, 48, 72, 96 and 120 hours (h). Parameters to describe the dynamics of ruminal degradability of DM and CP were obtained by fitting the data on the exponential equation P = a + b (1 - e-ct) using the NEWAY computer program, where “a” is the rapidly degradable fraction, “b” is the slowly degradable fraction and “c” is the outflow rate. The in vitro DM and CP degradability of rumen undegradable residue collected after 12, 24 and 48 h incubation was determined by sequential digestion in pepsin (abomasal) and pancreatin (small intestine) solutions. Fertilisation with bio-digester slurry increased (P <0.05) CP content of fresh cut Napier grass pre-ensilage. Bio-digester slurry fertilisation with molasses inclusion improved (P <0.05) the silage DM content which improved (P >0.05) fermentation characteristics with pH of 4.2 and lowest NH3-N of 13.3 g/kg. Other chemical compositions and fermentation characteristics were not affected (P >0.05) due to fertilisation x additives treatment combinations. No bio-digester slurry fertilisation with maize meal inclusion increased (P <0.01) DM degradability at 0 h incubation. As time progressed to 24 h, no biodigester slurry fertilisation with no additive included reduced (P <0.01) DM degradability with no difference (P >0.05) on other treatments. Potential DM degradability (a + b) of no bio-digester slurry fertilisation with no additive inclusion silage was reduced (P <0.01). The reduction was associated with low levels (P <0.01) of slowly degradable fraction “b”. In vitro DM and CP digestibility were not affected (P >0.05) due to fertilisation x additives treatment combinations. In conclusion, bio-digester slurry application improved the quality of fresh cut Napier grass, with the combination of bio-digester slurry fertilisation and molasses addition yielding the best silage quality.