Quantifying the contribution of crop-livestock integration to African farming

Keywords: System analysis, modelling, smallholders, manure, diversity, feeding strategies, resource use efficiency, NUANCES Smallholder farming systems in Sub-Saharan Africa are often nutrient-limited systems that depend largely on the use of land resources for their subsistence. Crop-livestock integration is an effective means by which nutrients can be rapidly recycled within and between farms. However, there is great uncertainty over which are the critical stages of nutrient transfer through crop-livestock systems. Each transfer of nutrients within the farming system provides a risk of inefficiency, which depends on the type of system, its management practices and site conditions. Because livestock fulfil several functions in crop-livestock systems, and farmers manage their animals according to the weight assigned to each function, there are trade-offs between increasing animal productivity, and income from livestock and sustaining crop production through cycling nutrients from animal manure. This thesis is a contribution to development of an analytical tool, the NUANCES framework, to support the analysis of trade-offs in crop-livestock sys¬tems, with focus on opportunities for intensification and maximisation of the benefits from crop-livestock integration for smallholder farmers. The framework that was developed can be used to analyse options for intensification at different scales, from the cattle sub-system, farm scale to village scale. Efficient use of animal manures depends on improving manure handling and storage, and on synchrony of mineralisation with crop uptake. Model calculations with the HEAPSIM model show that manure management during collection and storage has a large effect on the efficiency of C and nutrient retention. Differences in nitrogen cycling efficiency (NCE) between farms of different wealth classes arise due to differ¬ences in resource endowment. Measures to improve manure handling and storage are generally easier to design and implement than measures to improve crop recovery of N. Covering manure heaps with a polythene film reduce mass and N losses considera¬bly. For the poor to increase overall NCE, investment in cattle housing and recycling of urinary-N is required. Direct application of plant materials to soil results in more efficient cycling of N, with lower losses than from materials fed to livestock and the applying manure to the soil. However, livestock provide many other benefits highly valued by farmers. Evaluation of lifetime productivity is a sensible strategy to target interventions to improve productivity of smallholder dairy systems. Model simulations with LIVSIM show that it is possible to maximise lifetime productivity by supplementing with con¬centrates to meet the nutritive requirements of cattle not only during lactation but also during early development to extend productive lifetime. Reducing mortality by implementing health care management programmes must be included in interventions to increase dairy outputs. Improving lifetime productivity has a larger impact on small¬holders’ income than interventions targeted to improving daily milk yields through feeding strategies. Indicators of network analysis (NA) are useful to support discussions on diversified and sustainable agro-ecosystems and allow assessment of the effects of farm management strategies to improve the system design. The amounts of N cycled in crop-livestock systems in the highlands of East and southern Africa were small and comparable in size at all sites (less than 2.5 kg N per capita per year). Dependency on external in¬puts to sustain current production was larger for poor than for wealthier households, who had larger soil N storages per capita. Because increases in size of the network of N flows and organisation of the flows lead to increases in productivity and food self-sufficiency, combination of both strategies may improve not only productivity but also adaptability and reliability of smallholder crop-livestock systems. An analysis of village scale interactions in a crop-livestock system of NE Zimbabwe using NUANCES-FARMSIM showed that the grasslands contribute to c. 75% of the annual feed intake of the herd of the village, and that the crop residues produced by the non-livestock owners sustained c. 30% of the intake of livestock during the critical dry season. The removal of carbon (0.3−0.4 t C y−1) resulted in a long term reduction of the yields of their farms. Impeding the access of livestock to the crop residues of non-livestock owners increases the quality of their soils modestly and improved yields in the mid- to long term. Adding mineral fertiliser to the whole (community) system con¬currently with changes to the current management of the crop residues and manures appears to be a promising strategy to boost the productivity of the community as a whole. There are benefits in terms of productivity and resource use efficiency of closer integration between crops and livestock. Opportunities seem to be small, but still may play an important role in rehabilitating soils together with other measures. However opportunities for intensification have to be explored in a broader context, taking into account that farmers face constraints at higher scales, constraints that need to be re¬laxed by proper policies and interventions.