Paswel Phiri Marenya

State-conditional Fertilizer Yield Response on Western Kenyan Farms

Fertilizer interventions have attained prominence in rural poverty reduction programs in Africa. Using data from maize plots operated by small farmers in western Kenya, we find a von Liebig-type relationship between soil organic matter (SOM) and maize yield response to nitrogen application. Low SOM commonly limits the yield response to mineral fertilizer application. Although fertilizer is, on average, profitable in our sample, on roughly one-third of the plots degraded soils limit the marginal productivity of fertilizer such that it becomes unprofitable at prevailing prices. Moreover, because poorer farmers most commonly cultivate soils deficient in SOM, fertilizer interventions might be less pro-poor than is widely assumed and may instead reinforce ex ante income inequality. Copyright 2009, Oxford University Press.

Farmers’ Perceptions of Soil Fertility and Fertilizer Yield Response in Kenya

To develop soil fertility techniques that respond to farmers’ actual concerns, researchers and agricultural development practitioners in developing countries need to identify how farmers in those regions form perceptions on soil quality and crop response to inputs. Using survey and farm soils data collected in 2002 and 2005 from smallholder farmers in western Kenya, we study whether farmers’ subjective perceptions of soil fertility and impacts of fertilizer vary statistically with objective estimates generated by laboratory and statistical procedures. Our results show that farmers’ perceptions of soil fertility on their plots are largely determined by observed crop yields. By contrast, farmers’ perceptions on the impacts of fertilizer on yields vary rather closely with estimated returns to fertilizer application. This suggests that farmers’ perceptions of soil fertility and the impacts of fertilizer are driven by observed yields. Implications for fertilizer use (the focus of current soil fertility management policies) and long term and integrated soil fertility management are drawn.