State‐conditional Fertilizer Yield Response on Western Kenyan Farms
基于西肯尼亚小农玉米地块数据，发现土壤有机质低会限制氮肥的产量响应，约三分之一地块因土壤退化导致施肥不盈利，且肥料干预可能对贫困农民不利，加剧收入不平等。
Abstract 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.