Optimum plant density and inorganic fertilizer application improved selected soil chemical properties and common bean productivity in southern Ethiopia

Poor soil fertility and inappropriate plant density are the major factors that constrain the productivity of common bean (Phaseolus vulgaris L.) in tropical Africa, including Ethiopia. This problem necessitates improving soil fertility and optimizing agronomic practices. Therefore, we conducted field experiments from 2019 to 2021, integrating plant density and multinutrient fertilizer application to improve soil properties and common bean productivity in southern Ethiopia. The treatments included four plant densities (333,300 plants ha⁻¹, 250,000 plants ha⁻¹, 200,000 plants ha⁻¹, and 166,600 plants ha⁻¹) and five fertilizer rates (0, 50, 100, 150, and 200 kg NPS ha⁻¹). The application of NPS fertilizer reduced the soil pH while increasing the soil organic carbon, total nitrogen, and available sulfur and phosphorus contents but did not affect the cation exchange capacity. Similarly, at the lowest plant density, the available soil sulfur and cation exchange capacity improved. Increasing the NPS application increased common bean growth and yield components, particularly when the plant density was the lowest. An optimum grain yield of 3056.28 kg ha⁻¹ was obtained with the application of 150 kg NPS ha⁻¹ and a plant density of 200,000 plants ha⁻¹, with a net return of 80,132.56 ETB ha⁻¹ and a marginal return rate of 4169.10%. It was concluded that applying 150 kg of NPS at a common bean plant density of 200,000 ha⁻¹ resulted in an optimum grain yield. Using the stated amount of NPS and optimizing the density in the study area, smallholder farmers can improve common bean productivity and soil organic carbon, total nitrogen, sulfur, and phosphorus availability.