Enhancing land nutrient through rhizobia biofertilization: modeling the joint effects of rhizobium inoculants and improved soybean varieties on soybean productivity in North Central, Nigeria

Improving bacterial nitrogen fixation in grain legumes is central to the sustainable intensification of agriculture using rhizobia biofertilization. However, few studies have evaluated their joint impact on productivity using improved soybean varieties. Using household-level data from North Central Nigeria, this study explored the joint effects of the adoption of improved soybean varieties and the use of rhizobium inoculants on soybean yield and farm income. As both observed and unobserved factors may affect farmers’ decisions to adopt improved soybean varieties, a recursive bivariate probit (RBP) model is used to address the selection bias issue associated with the adoption of improved soybean varieties. Furthermore, a selectivity-corrected ordinary least square (OLS) model is applied to estimate the joint effects of the adoption of improved soybean varieties and usage of rhizobium inoculants on soybean yield and farm income. The results of the RBP model reveal a negative selection bias due to unobserved factors. After controlling for this selection bias, the results show that the adoption of improved soybean varieties increases the probability of using rhizobium inoculant by 25.2% as a complementary technological package. Soybean yield and farm income are positively and statistically significantly impacted by the adoption of improved soybean varieties (ISV). In the same vein, the adoption of rhizobium inoculants shows a positive and statistically significant effect on the yield and income from soybean production. This implies that farmers’ use of rhizobium inoculants helps them increase their farm yield while also improving their income. To provide more robust insights into this study, a robustness check, using unconditional quantile regression at different quantiles, was estimated. The findings demonstrate the heterogeneous effects of rhizobium inoculants and the adoption of improved soybean varieties adoption on soybean yield and farm income. Our finding generally confirms the significant role of the adoption of improved soybean varieties in facilitating farmers’ use of rhizobium inoculants as a complementary package.