Integrated application of nitrogen, phosphorus, and lime for boosting faba bean (Vicia faba L.) yield on acidic nitisols of Ethiopia

Combining nitrogen (N) and phosphorus (P) fertilizers with lime (CaCO₃) significantly enhances faba bean yields in central Ethiopia by mitigating soil acidity and bridging existing productivity gaps. During the 2023 cropping season, a field trial was conducted at Welmera and Ejere districts to evaluate the effects of N, P, and lime on grain yield and economic returns. The treatments comprised three levels of N (0, 18, 36 kg ha⁻1), P₂O₅ (0, 46, 92 kg ha⁻1), and lime (0, 4.5, 9 t ha⁻1),with three replications arranged in a randomized complete block design in a factorial arrangement. Results showed that the soil pH at the two sites is strongly acidic; however, after harvest, the pH dramatically increased from 5.08 and 5.11 to 5.8 and 5.6 at Welmera and Ejere, respectively. Application of 36 kg N ha⁻1, 92 kg P₂O₅ ha⁻1, and 9 t lime ha⁻1 significantly improved plant height, nodule number, number of pods per plant, and harvest index. Notably, N and P interactions alone (p ≤0.001) also increased the number of effective nodules and nodule dry weight. Maximum number of seeds per pod (3.63) increased by 44.9% and pod number (36.3,), hundred-seed weight (123 g), Above-ground dry biomass (13.88 t ha⁻1) and straw yield (7.4 t ha⁻1 at Ejere) was recorded with 92 kg P₂O₅ ha⁻1 and 4.5 t lime ha⁻1. Grain yield (7.10 t ha⁻1, an 84.65% increase over the control), was achieved at Welmera, yielding a net economic return of ETB 251,335.3 and a marginal rate of return (MRR) of 165%. under the highest N-P-lime combination. In conclusion, the integrated application of N, P, and lime increased grain yield by 77.6% compared to the control, and effectively addressed soil fertility and acidity issues that hinder faba bean productivity, promoting sustainable food security in an economically and environmentally safe manner.