Low and inappropriate use of nutrient inputs by smallholder farmers is a major factor underlying low crop productivity in sub-Saharan Africa. Current fertilizer recommendations were mostly developed to maximize production and ignore the financial limitations faced by various categories of farmers, and fail to address the high uncertainty of the returns on investment in fertilizer associated with variable soil fertility conditions and rainfall variability. A feasible option for ensuring sustainable crop production intensification is the use of simple but robust decision support tools that provide guidelines for fertilizer use and expected yield levels at various spatial and temporal scales. In SSA, a number of QUEFTS (Quantitative Evaluation of the Fertility of Tropical Soils)-based decision support tools have been successfully developed for exploring responses to fertilizers across heterogeneous farms. The same concepts underpinning these models were also used to develop the Nutrient Expert, a simple decision tool for use by extension services to develop and disseminate site-specific nutrient management recommendations. The proposed research aims to use existing long-term trials in Eastern Kenya to evaluate the added agronomic and economic value of using simple decision support tools over current blanket recommendations and recommendations based on soil testing.
The candidate is expected to: (1) to analyze data sets on soil fertility and maize yields; (2) use these data to calibrate and test the decision support tool Nutrient Expert; and (3) write down the findings of the study in a paper to be published in a peer-reviewed journal.