Unlocking soybean potential: Enhancing smallholder farmers' yields through rhizobia inoculation and phosphorus fertilizer in Ethiopia

Abstract Despite the promising potential of soybean [ Glycine max L. (Merrill)] production in Ethiopia, smallholder farmers face challenges such as low yields and nutrient deficiencies, which limit their productivity and economic stability. Thus, the objectives of the input diagnosis/demonstration trials were to enhance the yields of smallholder soybean farmers, to explore the interaction and variations of soybean yield responses to phosphorus (P) and/or inoculant (I) applications across multiple locations, and to identify the economic benefits from phosphorus (P) and/or inoculant (I) use on the fields of many smallholder farmers, representing diverse agroecological conditions. The application of P, I, P + I, and control was evaluated on 78 farmers’ fields in 10 districts. The result indicated that the combined use of I + P and P alone enhanced grain yield by 42% and 21%, respectively. The use of the inoculant only also increased the yield by 5% over P alone. Although P + I showed the highest yield and 80% of the farmers observed positive yield, the variability was very large (0.3–5.3 t ha −1 ). Moreover, the inoculant was more profitable compared to P. Notably, 15% of the total farmers experienced relative yield increases of 142%–368% under the combined use of P and I. In addition, about 52%, 50%, and 15% of farmers achieved at least 5000 ETB ha −1 (where ETB is Ethiopian Birr) of an economic benefit with the application of corresponding P + I, I, and P. Considering price fluctuation of variable cost by assuming 30% inflation after some years, use of the of inoculant alone and then integrated use of P and I were relatively more stable as 46% and 60% of the total farmers could respectively attain benefit to cost ratio ≥2. While most smallholder farmers benefited from the use of P + I or I only, a few of them still did not benefit from the technologies. This may need further investigation, particularly for nonresponsiveness soils. Therefore, understanding the causes of yield variability helps to cluster the best bet packages to groups of farmers who are expected to benefit most, reduce yield gain instability across the farm plots, and minimize higher risk for technology adoptions.