Optimizing Spacing and Nutrient Sources for Enhanced Yield and Quality of Summer Onion (Allium cepa L.)

Onion (Allium cepa L.) is a crucial crop in Bangladesh, but current winter-only cultivation fails to meet national demand. This study aims to optimize summer onion production through proper plant spacing and nutrient management. The field experiment was conducted during the period from March to June 2016 in the Horticultural Farm of Sher-e-Bangla Agricultural University, Sher-e-Bangla Nagar, Dhaka to find out the effect of spacing and nutrient sources on yield of summer onion. The experiment consisted of two factors: Factor A: Three levels of spacing. Viz., S1: 10 cm x 15 cm, S2: 15 cm x 15 cm, and S3: 20 cm x 15 cm. Factor B: Four levels of nutrient sources. viz., F0: (control); F1: Vermicompost (7 t/ha); F2: Mustard oil cake (6 t/ha) and F3: Inorganic fertilizer (N-110 + P-50 + K-125 Kg/ha). There were 12 treatment combinations. The experiment was laid out in Randomized Complete Block Design (RCBD) with three replications. Results indicated that 15x15 cm spacing significantly enhanced plant height, bulb diameter, and yield, achieving 22.03 t/ha. Vermicompost (7 t/ha) yielded the highest plant height, bulb size, and overall yield (20.61 t/ha). Combined treatment of 15x15 cm spacing with vermicompost resulted in the highest yield (24.06 t/ha). These findings suggest that optimized spacing and organic nutrient application can significantly improve summer onion production, potentially reducing dependency on imports and enhancing food security in Bangladesh.