Integrated NPSB fertilizer and vermicompost improve soil fertility, onion seed yield, and quality in North Shewa, Oromia, Ethiopia

Abstract Onion seed productivity, quality, and profitability in Ethiopia are constrained by declining soil fertility and inadequate fertilizer management, particularly due to a historical reliance only on blanket nitrogen-phosphorus-based recommendations for bulb production. Therefore, the study examined the impacts of NPSB fertilizer, vermicompost, and their integrated application on soil fertility, onion seed yield, and quality in Yaya-Gulele, Oromia, Ethiopia. Treatments comprised a factorial combination of four NPSB rates (0, 75, 150, 225 kg/ha) and four vermicompost rates (0, 1.25, 2.5, 3.75 t/ha), arranged in a randomized complete block design with three replications. Seed quality was evaluated under laboratory conditions using a completely randomized design with four replications. The integrated application of NPSB and vermicompost improved key soil chemical properties, prolonged vegetative growth, and enhanced seed yield and quality parameters of onions compared to sole applications and the control. The highest-performing integrated treatment increased seed yield by up to threefold relative to the control. The integration of 150 kg/ha NPSB with 3.75 t/ha vermicompost was identified as the most agronomically and economically optimal treatment, producing the highest seed yield and net returns. This first report from North Shewa shows that the synergistic integration of NPSB and vermicompost significantly increases onion seed productivity and quality by improving soil fertility. This approach offers a practical and sustainable nutrient management strategy for onion seed production systems in Ethiopia.