Analysis of Drivers of Adoption and Effects of Fertilizer Management Practices on Yield in Maize-based Systems of Embu County, Kenya

Abstract

Fertilizers play a critical role in maize production and global food security. However, continuous rise in fertilizer prices has resulted in inflated costs, leading to unaffordability and suboptimal utilization, while excessive application poses environmental risks. Additionally, farmers' limited awareness and knowledge have resulted in insufficient and imbalanced application. Recognizing the limitations on fertilizer use, the International Fertilizer Industry Association (IFA), in collaborative efforts with other stakeholders, formulated an innovative approach to best fertilizer management known as the “4R-Nutrient Stewardship” of applying fertilizers from the right source, using the right fertilizer rate, applying fertilizers at the right time and the right place, for enhanced economic, social and environmental outcomes. Practices in this study including soil testing, split application, side banding application, combined manure plus inorganic fertilizer use, and moist soil fertilizer application are inherently embedded within the “4R-Nutrient Stewardship”. Despite widespread promotion of these practices, the extent, factors influencing adoption, and adoption effects remain largely unknown. This study therefore sought to assess drivers of adoption and resulting effects on yield in maize-based systems of Embu County. Data was collected using structured questionnaires from a sample of 371 households. Descriptive statistics were employed to delineate the profile of farmers, characterizing specific features of their farms, socio-economic factors, and institutional factors hypothesized to influence adoption. The Multivariate Probit Model (MVP) was used to assess drivers of adoption while the Instrumental Variable (IV) regression model was used to evaluate the nuanced effects of adoption. The analysis revealed complementarity and varying levels of adoption, with manure plus inorganic fertilizer use, side banding application, and split application emerging as the most adopted practices. It was also revealed that most farmers do not test their soils. Gender disparities in adoption were evident, with

female-headed households exhibiting higher adoption across most practices. The study revealed several factors that positively influenced adoption, including training on soil fertility, years of formal education, farm visits and demonstrations, on-farm experimentation, and individual land ownership. Impediments to adoption included farm size, reliance on household labour, and male-led households. The Heckman model`s initial results yielded insignificant Inverse Mills Ratios (IMR), prompting the use of Instrumental Variable (IV) regression. The validity of instruments was confirmed through Sargan-Hansen and Cragg-Donald tests. Results of the IV regression revealed that adoption of manure plus inorganic fertilizer, split application, soil testing, and side banding application positively influenced yield. Furthermore, practices such as intercropping, soil moisture conservation, crop rotation, and agroforestry positively influenced yield, whereas minimum tillage reduced yield. The study recommends designing and implementing soil health training initiatives tailored to the needs of farmers. Implementing on-farm experimentation initiatives, and promoting collaborative learning through field demonstrations are important in facilitating adoption. Efforts should be directed towards accelerating adoption of fertilizer management practices under the “4R- Nutrient Stewardship” to increase maize yields among smallholder farmers in Embu