Are Kenyan farmers under-utilizing fertilizer? Implications for input intensification strategies and research

It is widely perceived that African farmers are under-utilizing inorganic fertilizer. However, very little long-term evidence from farmers' fields, accounting for variations in agro-ecological conditions, has been assembled to back this claim or determine the conditions under which it is true. Using five waves of nationwide household survey data from Kenya covering 13 years, we estimate the relative and absolute profitability of nitrogen application rates on maize fields and compare these profitability conditions to observed nitrogen use patterns over time. In general, we find that farmers are consistently and steadily increasing towards risk-adjusted economically optimal rates of fertilizer application over time and that, in the most agriculturally productive areas, farmers' application rates on maize sometimes exceed rates that maximize profitability. Fertilizer use rates may nevertheless be profitably raised in these areas, but doing so will require the adoption of complementary inputs and management practices that raise maize response rates to fertilizer application. This motivates a more holistic approach to input intensification strategies in the region.