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

Adetomiwa Kolapo ^1* Temitope O Ojo ^1,2,3 Nolwazi Z Khumalo ⁴ Khalid M Elhindi ⁵ Hazem S Kassem ⁶ Olajide Julius Filusi ¹

• ¹ Obafemi Awolowo University, Ife, Nigeria
• ² Dalhousie University, Halifax, Nova Scotia, Canada
• ³ University of the Free State, Bloemfontein, Free State, South Africa
• ⁴ University of Zululand, KwaDlangezwa, South Africa
• ⁵ King Saud University, Riyadh, Riyadh, Saudi Arabia
• ⁶ Mansoura University, Mansoura, Dakahlia, Egypt

Improving bacterial nitrogen fixation in grain legumes is central to sustainable intensification of agriculture using rhizobia biofertilization. However, few studies have evaluated their joint impact with the use of improved soybean varieties on productivity. Using a household-level data from North Central Nigeria, this study explored the joint effects of improved soybean varieties adoption and use of rhizobium inoculant on soybean yield and farm income. Since 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 improved soybean varieties adoption. Furthermore, a selectivity-corrected Ordinary Least Square (OLS) model is applied to estimate the joint effects of improved soybean varieties adoption and rhizobium inoculant usage 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 result show that improved soybean varieties adoption increases the probability of using rhizobium inoculant by 25.2% as complementary technological package. Soybean yield and farm income is positively and statistically significantly impacted by adoption of improved soybean varieties (ISV). In the same vein, adoption of rhizobium inoculant shows a positive and statistically significant effect on the yield and income from soybean production. This implies that farmers' use of rhizobium inoculant helps them increase their farm yield while also improving their income. To provide more robust insights to this study, a robustness check, using unconditional quantile regression at different quantiles was estimated. The findings demonstrate the heterogeneous effects of rhizobium inoculant and improved soybean varieties adoption on soybean yield and farm income. Our finding generally confirms the significant role of improved soybean varieties adoption in facilitating farmers use of rhizobium inoculant as complementary package.