Tree Foliage Polyphenols and Nitrogen Use in Crop–Livestock Systems of Southern Africa: Strategies for Increasing Efficiency

In southern Africa and Sahelian West Africa, livestock and cropping systems are inextricably linked together. Livestock manure is perhaps the most important soil amendment for crop production. Crop residues provide feed resources during the 7-month dry period. Livestock also provide a source of nutrients, draft power, transport, and is a source of capital for crop production inputs. The potential to increase crop and livestock production in mixed crop—livestock farming systems in these regions is limited by low and erratic rainfall, poor soil fertility, and very limited use of external nutrient sources in the form of inorganic fertilizers and feed supplements. Organic materials consisting of crop residues and vegetation from fallow land and rangeland are the most important sources of nutrients for agricultural production in these farming systems. In managed tropical agroforestry systems large amounts of fresh biomass are harvested and fed to animals or applied to soil. The cycling of plant biomass through livestock faeces and urine, which will be referred to as manure, enhances both livestock and crop production (Powell et al. 1999). For these low input systems to remain viable, plant biomass must be either fed to livestock and manure applied to soils or plant biomass applied directly to soil as amendments.