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Crop-livestock systems in sub-Saharan Africa (SSA) are mostly rainfall-dependent and based on fragmented marginal lands that are vulnerable to soil erosion, drought and variable weather conditions. The threat of water scarcity in these systems is real, due to expanding demand for food and feed, climate variability and inappropriate land use (Amede et al., 2009). According to recent estimates, farming, industrial and urban needs in developing countries will increase water demand by 40% by 2030 (FAO, 2009). Water shortage is expected to be severe in areas where the amount of rainfall will decrease due to climate change. The lack of capacity of communities living in drought-prone regions to respond to market opportunities, climatic variability and associated water scarcity also results from very low water storage facilities, poverty and limited institutional capacities to efficiently manage the available water resources at local, national and basin scales. The spiral of watershed degradation causes decline in water budgets (Awlachew and Ayana, 2011), decreases soil fertility and reduces farm incomes in SSA (Amede and Taboge, 2007) and reduces crop and livestock water productivity (Descheemaeker et al., 2011). In areas where irrigated agriculture is feasible, there is an increasing demand for water and competition among different users and uses.

This study uses georeferenced community-level data to study the adoption of improved cowpea (Vigna unguiculata) in northern Nigeria. One objective of the study is to find out which factors at the community or village level are significant determinants of adoption of improved dual-purpose (DP) cowpea varieties and management techniques. The implications for those attempting to catalyse dissemination of the new varieties and related management techniques are explored. A second objective is to estimate the amount of cowpea currently being grown in the two Nigerian states included in the study (Kano and Jigawa) and to extrapolate to a wider area suggested by the study findings (i.e., places with similar agricultural potential, population density and market access across West Africa). Results suggest that, for improved cowpea varieties to become and remain popular in all locations, they must first be high-grain yielding; secondly, pest resistant; and, thirdly, yield enough fodder to support the crop-livestock enterprises in which each and every family in the study area is involved. The adoption of improved DP varieties appears to be a 'win-win' situation with respect to improvements in natural resource management in intensive, integrated crop-livestock systems, particularly soil fertility. Those more market-oriented producers more interested in selling the cowpea grain leave the residues to rot in the fields, adding nutrients to the soil. Those that prefer the DP types and feed the residues to their animals return a significant amount of nutrients to the soil via the manure.

Relative palatability and some agronomic traits were studied for nine legumes including Aeschynomene histrix, Centrosema brasilianum (two accessions), Centrosema pascuorum, Chamaecrista rotundifolia, Stylosanthes guianensis (two accessions) and Stylosanthes hamata (two accessions). All species were consumed by cattle but the relative palatability varied according to season. Only the two S. guianensis accessions were positively selected throughout the year. A positive relationship was established between the ability to retain green leaves in the dry season and palatability. Once established, the two C. brasilianum accessions out-performed the other legumes in their ability to stay green and retain leaves in the dry season; related to the ability to retain green leaves under drought conditions, C. brasilianum ILRI 155 was among the most palatable legumes in the dry season. S. guianensis accessions had the highest dry matter (DM) yields and one of them (ILRI 15557) had the highest nutritive value. In contrast with earlier results in the same environment, C. rotundifolia and A. histrix performed poorly in terms of DM productivity. The implications of the agronomic characteristics of the legumes for the management of legume-based pastures in crop/livestock systems are discussed and the concept of legume±legume mixtures, composed of several compatible species, is advocated.