Manures in African Smallholder Farming Systems: A Review

Abstract

Agricultural development in Sub Saharan Africa (SSA) is faced with a growing soil productivity crisis due to deterioration of the soil capital base, which is caused by among other reasons, greater removal of nutrients in crop harvests than those returned each year. Unlike other continents where intensification of crop production has been made possible through increased fertilizer usage, widespread use of fertilizers in Africa is still hampered by high commodity prices, poor infrastructure, a lower proportion of irrigated land compared to other continents, reliance on traditional crop varieties that are less responsive to fertilizers and increasingly unpredictable weather patterns due to climate change. Soil fertility replenishment therefore relies heavily on application of organic resources (where available), which benefit soil primarily by building up soil organic matter. Animal Manures though widely used by smallholder farmers are of low and variable quality, and bulky. This restricts application to homestead fields, in the process, aiding the creation of within-farm soil fertility gradients after repeated applications. On the other hand, green manures though effective have a high demand for labour, compete for land and moisture with crops, and seeds are scarce. Experts however, advocate combined use of organic and inorganic nutrient sources usually referred to as Integrated Soil Fertility Management (ISFM) because the relative nutrient compositions of organic resources do not normally match crop requirement ratios and neither do their nutrient release patterns commonly synchronize with crop demand. Future research needs should focus on increasing organic resource use efficiency through synchronization of nutrient release patterns with crop demand, increasing the concentration of nutrients in animal manures through innovative management techniques that improve efficacy and reduce bulkiness, developing whole-farm soil fertility recommendations to diminish formation of within-farm soil fertility gradients, and on studying the long-term effects of organic resources on soil properties, crop. Productivity and the environment within the context of climate change in SSA.