The residual effect of fertilizer in soil: Can crop rotation practices combat soil fertility loss and increase crop yield?

Abstract

The depletion of soil nutrients is a global problem with a tendency to increase under climate change leading to degraded soils and decreasing crop yields. Various initiatives aim at the restoration of soils and the ecosystem services they provide. Studies investigating the effects of fertilizer application on soils have found positive long-term effects on soil nutrient content and crop yield even in the season after the fertilizer application. The utilization of this so called fertilizer residual effect has been suggested as a possible solution to prevent decreasing soil fertility. This study investigates the residual effects of NPK fertilizer on the fertility of agricultural soil in the Sudanian Savannah of the Republic of Benin in West Africa. Smallholder farmers in the study area commonly practice crop rotations and apply NPK fertilizer for the cultivation of cotton. Many of those farmers have claimed to benefit from fertilizer application in terms of higher crop yields in subsequent seasons even without the application of further fertilizer. In this study soil samples were taken and analyzed for soil nutrient content and smallholder farmers of associated agricultural fields were interviewed to understand farmer’s motivations to adopt the agricultural practice of crop rotation. The collected data was combined with spatial information derived from satellite imagery and compared to farmer interview responses. The results provide information on crop rotation cycles, soil N, P and K content and farmer’s motivation for 120 agricultural fields in Dassari, Benin. Data shows no significant correlation between year of fertilizer application, soil nutrient content or crop cycle used for rotation. This study therefore contradicts the hypothesis of the positive effect of residual fertilizer on crop yield and questions the application of chemical fertilizer for sustainable ecosystem restoration. Results of this study can be used by projects in development cooperation to train smallholder farmers in more sustainable agricultural practices to restore soil fertility and increase crop yield in order to strengthen food security and fight land degradation in the West African Sudanian Savanna belt and get closer to achieving SDG2 and SDG15.