The use of bioslurry for fodder production in sustainable crop and livestock production system by smallholder farmers.
Livestock play a major role in the livelihoods of smallholder farmers in the rural areas of South Africa. In these areas livestock are continuously grazed in the natural rangelands (veld) for most of the year. This exerts a high grazing intensity on the veld and can result in compaction, soil degradation, increased run-off, loss of palatable grass species, poor veld condition and affect long-term sustainable productivity. In the sour veld areas of the Upper Thukela grazing livestock in the veld in winter is a major problem because the nutritive quality of the grasses is low. The use of fodder crops could provide an alternative and also reduce the pressure on the rangeland to allow a rest period and ensure long-term sustainable productivity. Sorghum (Sorghum bicolor) and cowpea (Vigna unguiculata) are potential crops that could be produced by farmers because they grow under drought conditions and they are nutrient rich crops which can be intercropped. These fodder crops can be fed to livestock in winter and the animal-excreta can be used to produce biogas. Liquid effluent from the anaerobic digestion of the manure and water in the biodigester can be used as organic fertilizer to provide important plant nutrients such as nitrogen (N) and phosphorus (P). There is little information on the use of bioslurry for fodder production in South Africa and the effect on soil chemical properties. The aim of the study was to establish whether bioslurry could be used as a nutrient source for fodder production and secondly, to determine whether this could contribute to sustainable livestock-crop production systems among smallholder farmers in the Upper Thukela, South Africa. The specific objectives were (1) to conduct on-farm trials to determine the effect of bioslurry on growth, biomass and nutritive quality of cowpea and sorghum fodder; (2) to determine the N and P release patterns from bioslurry in two contrasting soils (acidic and non-acidic) sampled from two farms in the Upper Thukela and (3) to assess the impact of using cowpea and sorghum fodder for supplementary feeding on the current grazing carrying capacity (AU ha-1). On-farm trials were conducted at two rural homesteads (New Stand and Potshini) in the Upper Thukela. Growth and yield were measured for both sorghum and cowpea species .Nutritive quality was also analysed for soil and plant samples. No significant differences were observed between MAP, bioslurry and control treatment with respect to growth characters, yield components and nutritive quality in both on farm trials. Sorghum yield in New Stand ranged between 3.75 to 5.47 kg m-2 for the applied treatments (control, bioslurry and MAP), the highest yield was recorded for MAP. Cowpea yield ranged between 4.97 to 6.73 kg m-2 for the applied treatments in New Stand. In Potshini, there were no significant differences on yield. Sorghum yield ranged from 1.8 kg m-2 to 3.09 kg m-2 and cowpea ranged from 3.7 kg m-2 to 5.33 kg m-2. An incubation study was conducted to determine the N and P content and the release patterns from bioslurry in two contrasting soil types (acidic and non-acidic) which represent the soils of the study area. Ammonium-N concentration decreased for all the bioslurry application rates in all the soils (non-acidic, acidic unlimed and limed). There were no significant differences in ammonium-N concentration between the different bioslurry rates applied on the non-acidic soil samples during the 70 day incubation period. Similar results were observed for ammonium-N in the unlimed and limed acidic soils. Results showed that there were no significant differences in nitrate-N concentrations between bioslurry application rates during the incubation period for non-acidic soil. The major findings of this study show that phosphorus increased with the increased application rate of bioslurry. Phosphorus increased with the increase in pH indicating that phosphorus release to the soil is pH dependent. Ammonium-N decreased during the incubation study for all the bioslurry application rates. However, the nitrate-N concentration did not increase which suggests that ammonium-N was not converted to nitrate-N. The case study showed that sorghum and cowpea have potential for the implementation of a semi-zero grazing systems since the higher production of these crops can supplement the low production of the natural rangeland and reduce the grazing pressure on the natural rangeland. The study concluded that although there were no significant differences, bioslurry remain the potential source of organic fertilizer for fodder production in smallholder farming systems.
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