Soil fertility investments in sub-Saharan Africa, where budgetary resources are scarce, must be well targeted. Using a causal forest algorithm and an experimental maize trial dataset matched with geocoded rainfall, temperature and soils data, we modelled site-specific, ex ante distributions of yield response and economic returns to fertilizer use. Yield response to fertilizer use was found to vary with growing season temperature and precipitation and soil conditions. Fertilizer use profitability—defined as clearing a 30% internal rate of return in at least 70% of the years—was robust to growing season climate and the fertilizer-to-maize price ratio in several locations but not in roughly a quarter of the analysed area. The resulting profitability-assessment tool can support decision makers when climate conditions at planting are unknown and sheds light on the profitability determinants of different regions, which is key for effective smallholder farm productivity-enhancing strategies.

在预算资源稀缺的撒哈拉以南非洲，土壤肥力投资必须有针对性。使用因果森林算法和与地理编码降雨量、温度和土壤数据相匹配的实验性玉米试验数据集，我们对特定地点的产量响应和化肥使用的经济回报的事前分布进行了建模。产量对肥料使用的反应随生长季节温度、降水量和土壤条件而变化。化肥使用盈利能力——定义为在至少 70% 的年份中清除 30% 的内部回报率——在几个地方对生长季节气候和化肥与玉米的价格比率是稳健的，但在大约四分之一的分析中不是这样区域。