Fertilizer use in sub-Saharan Africa (SSA) is low, averaging 16 kilograms (kg) of fertilizer per hectare (ha) of arable land. This does not imply that the average farmer uses 16 kg/ha. In reality, many farmers do not use any fertilizers, while commercial and smallholder farmers that apply fertilizers use much higher rates. While several factors, including accessibility, cost, and lack of output markets, constrain farmers' fertilizer use, a significant problem facing smallholders is the lack of diversity in fertilizer products to address soil-and crop-specific demands. The main fertilizers available to smallholder farmers are what are referred to as "commodity fertilizers," including diammonium phosphate (DAP), urea, calcium ammonium nitrate (CAN), 15:15:15 or similar NPKs, and occasionally NPKS products such as 10:20:10+65 or 23:21:0+4S. In many African countries, farmers can access only two or three commodity fertilizers, making it challenging to address crop-specific demands or secondary and micronutrient deficiencies. Lime products are often not available and seldom used when they are. In some cases, fertilizers are unavailable at the appropriate time due to logistical and procurement problems, resulting in late application. As a result, fertilizer use efficiencies are less than half of what is achieved in agriculturally developed countries. Poor response and high costs discourage fertilizer use. Relative to much of the world, African soils are poor, with most not being enriched by recent geological activity such as glaciation, volcanic processes, mountain outwash, or acid rain, which until recently provided considerable quantities of S in industrialized countries. As a result, NPK fertilizers do not address the suite of nutrient deficiencies present and, while they usually improve yields, do not result in optimal nutrient response. Vast tracts of secondary and micronutrient deficiencies (primarily sulfur [S], zinc (Zn), and boron [B]) and soil acidity constraints have been identified through various mapping initiatives, and superior responses to balanced fertilizers that supplement NPKs with appropriate secondary and micronutrients have been observed in several countries. Fertilizer blending companies, primarily serving commercial farmers, exist throughout the continent. Still, their products are only available to some smallholders, who often are impeded by cost considerations, lack of awareness and access, and subsidies on commodity fertilizers, which are persuasive in farmer purchasing decisions. A few commercially available balanced fertilizer compounds exist, but these are generally not targeted to soils or the food crops grown by smallholders. Delivering balanced fertilizers to smallholder farmers is a high development priority. A better fertilizer response is necessary to improve stagnant productivity (yield per hectare) and address human nutrition and farm income objectives.
Fertilizers, Soil mapping