Common Bean (Phaseolus vulgaris L.) Yield Response to Coffee Husk Biochar and NPSB Fertilizer in Southwest Ethiopia

Abstract Common bean ( Phaseolus vulgaris L.) is an economically important pulse crop in Ethiopia, yet its productivity remains low due to soil acidity and poor nutrient management. A field experiment was conducted during the 2025 cropping season at Kayikela and Kicho Districts, Southwest Ethiopia, to evaluate the optimum combination of coffee husk biochar and NPSB blended fertilizer for maximizing yield and economic return. Treatments consisted of four CHB levels (0, 2.5, 5, and 7.5 t ha − 1 ) and four NPSB rates (0, 50, 100, and 150 kg ha − 1 ) arranged in a factorial randomized complete block design with three replications. Data were analyzed using SAS 9.4, and treatment means were separated using LSD at 5%. Results revealed that combined CHB and NPSB applications significantly (p < 0.01) affected most growth, phenology, and yield traits, except days to emergence and stand count. The highest mean values for days to flowering (50 and 48), days to maturity (91 and 89), branch number (7.9 and 6.3), plant height (44.2 and 38.3 cm), and pod length (41.3 and 33.6 cm) were recorded under 7.5 t ha − 1 BC with 150 kg ha − 1 NPSB at Kayikela and Kicho, respectively. Similarly, maximum pods per plant (35 and 26), seeds per pod (5.1 and 5), hundred seed weight (41 and 36 g), aboveground biomass (5724.6 and 5308.3 kg ha − 1 ), harvest index (43 and 52), and seed yield (2483.6 and 2373.3 kg ha − 1 ) were obtained from 5 t ha − 1 BC combined with 150 kg ha − 1 NPSB. This treatment also provided the highest net benefit (101,437 ETB ha − 1 at Kayikela and 95,989 ETB ha − 1 at Kicho). Therefore, application of 5 t ha − 1 BC with 150 kg ha − 1 NPSB can be tentatively recommended for enhancing common bean productivity in the study areas.