Combined Agronomic and Economic Modeling in Farmers’ Determinants of Soil Fertility Management Practices: Case Study from the Semi-Arid Ethiopian Rift Valley

Abstract

Studies on smallholders’ determinants of soil fertility management practices have become increasingly important for boosting agricultural productivity, particularly in cereal-based farming systems in sub-Saharan Africa. In these parts of Africa, farmers preferentially apply organic and inorganic fertilizers to the fields close to their housing compounds (infields). In addition, they prefer to use more fertilizers to grow cash crops rather than food crops. Many researchers suggested that farmers use limited nutrient resources in their hot-spot fields, e.g., infields and/or cash-crop fields. Recent econometric case studies have suggested using a model that considers a complementarity or substitutability between organic and inorganic fertilizers use. This study employed bivariate probit models to analyze 524 plot data collected from the northern semi-arid Ethiopian Rift Valley. A K-means cluster analysis divided the sample data into two subdatasets, representing food-crop-based cropping system (FCCS) and cash-crop-based cropping system (CCCS). Based on narrative inquiry interviews and the cluster analysis, this study considered reflecting the structure of the local farming system in modeling: a data segmentation approach and dummy variable method. Bivariate and univariate probit analyses showed that, first, the farmers’ determinants differed between the FCCS and CCCS. Second, the correlation between organic and inorganic fertilizers use was independent. Farmers’ determinants were primarily governed by the biophysical features of the plots (commuting distance to the plot, plot size, type of the plot, etc.), which narrowed down the feasible soil fertility management options in the plot to one or two; farmers’ more specific decisions on soil fertility management practices depend on individual farmers’ socioeconomic endowments (farm holding, livestock ownership, etc.).