Empirical Analysis of the Effect of Integrated Soil Fertility Management on Sorghum Productivity and Soil Health in the Sahel Savanna

Integrated soil fertility management combining mineral fertiliser, organic matter, and biological nitrogen fixation has demonstrated significant yield improvement benefits in research trials, but empirical evaluation of its effect on both crop productivity and soil health parameters under farmers' conditions in the Sahel savanna remains insufficient for confident extension recommendation. This study empirically evaluated three integrated soil fertility management combinations (sole mineral NPK, mineral NPK plus poultry manure, and mineral NPK plus Striga-resistant cowpea intercrop) compared with a control in sorghum production at 24 on-farm sites in Borno and Yobe States over two seasons (2022 and 2023). Sorghum grain yield, stover yield, and total biomass were measured at harvest. Soil samples at season end were analysed for organic carbon, microbial biomass carbon, soil respiration, and aggregate stability. Results showed that ISFM with poultry manure produced the highest sorghum grain yield across sites (2.43 t ha-1 on average) and the largest improvement in soil organic carbon (+0.22 percent over two seasons). The sole mineral NPK treatment showed a marginal decrease in microbial biomass carbon over the two seasons, suggesting potential long-term soil health trade-offs from sole mineral fertilisation. Cowpea intercrop reduced Striga incidence by 48 percent in the second season. The study provides empirical evidence filling the farm-level ISFM evaluation gap in the Sahel savanna and recommends the ISFM plus manure combination as the priority system for North East extension programme promotion.

Keywords: integrated soil fertility management, sorghum, Sahel savanna, soil health, ISFM evaluation