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Livestock manure is an important source of nutrients for crop production in semi-arid West Africa. An assessment of the potential of manure to sustain crop production calls for an estimation of the amounts of manure that could be produced and captured and the feed resources required to maintain livestock used for manuring. This paper presents estimates of the amounts of manure produced by cattle, goats and sheep fed ad libitum under confinement. A model is presented to predict the yearly faecal output by grazing ruminants under fluctuating feed supplies. Statistics on livestock population and cultivated areas are used to evaluate the effects of livestock to cropped area ratios and the spatial location of livestock at manuring time, on the potential amounts of manure available for crop production. The number of cattle, sheep and goats needed to manure different proportions of a 10-ha farm and the amounts of feed required for herds used for manuring are estimated. Model results indicate that the potential of manure to continuously sustain crop production in semi-arid West Africa is limited by livestock population, spatial location of livestock at manuring time, manure excretion per animal, efficiency of manure collection, and the amounts of feed and land resources available. Since the relative importance of these limiting factors and the possibilities for realising this potential vary both spatialy and temporally, it is suggested that these technical factors should be taken in consideration when evaluating the potential of manure to support crop production at national, regional, or farm level.
