Optimization of Nitrogen and Phosphorus Fertilizer Rates for Improved Snap Bean (Phaseolus vulgaris L.) Growth, Yield and Quality

Abstract

Snap bean (Phaseolus vulgaris L.) is a significant vegetable crop in Ethiopia, serving as both an exportable commodity and a vital protein source for consumers. However, its current national productivity of 4.12 t ha^-1 falls below its potential due to inadequate soil fertility. To address this issue, a field experiment was conducted at Melkassa Agricultural Research Center and Bishola in 2020 and 2021, respectively, with the objective of assessing the impact of nitrogen and phosphorus fertilizer rates on the growth, yield, and quality of snap bean. The experiment employed a 5x4 factorial design within a Randomized Complete Block Design (RCBD) framework, comprising five nitrogen fertilizer rates (control, 46, 92,138 and 184 N kg ha^-1) and four phosphorus fertilizer rates (control, 46, 92, and 138 P₂O₅ kg ha^-1). Statistical analysis revealed significant (p≤ 0.05) interactive effects of nitrogen and phosphorus fertilizer rates on marketable and total yield at the Bishola location. In 2020, at the Melkassa site, nitrogen fertilizer rates exhibited significant (P ≤ 0.05) variations in total yield. However, neither nitrogen nor phosphorus fertilizers, nor their interaction, showed significant differences in pod weight per plant, pod length, and pod diameter at both Melkassa and Bishola. Notably, nitrogen fertilizer application demonstrated a significant impact on chlorophyll content and plant height at the Bishola location. The highest marketable and total yields were observed with nitrogen fertilizer rates of 46 and 138 N kg ha^-1 at the Bishola location. Economic analysis, as reflected in the partial budget assessment, identified the application of a 46 N kg ha^-1 fertilizer rate as the optimal treatment, resulting in the highest net benefits of 234,480 ETB ha^-1 and an acceptable marginal rate of returns for snap bean production in the central rift valley of Ethiopia, where similar soil properties exist. In conclusion, optimizing nitrogen and phosphorus fertilizer rates can significantly enhance the growth, yield, and quality of snap bean crops. The findings of this study provide valuable insights for farmers and policymakers alike, with the potential to improve snap bean productivity and contribute to the agricultural development of Ethiopia's central rift valley region.