Evaluation of the Impact of Combined Application of Inorganic Fertilizer and Plant Spacing on Onion ( <i>Allium cepa</i> L.) Production Under Irrigation Conditions in Central Ethiopia, Ethiopia

Abstract

A field experiment was conducted in the Enemor district during 2022 and 2023 under irrigated conditions to evaluate the combined effects of blended NPSB fertilizer and intra‐row plant spacing on onion production. The study employed a randomized complete block design (RCBD) in a factorial arrangement with three replications. Twelve treatment combinations were tested, consisting of four NPSB fertilizer rates (0, 122, 244, and 366 kg·ha −1 ) and three intra‐row spacings (7.5 cm, 10 cm, and 12.5 cm). Data, analyzed using SAS software, indicated that yield and yield‐related traits were significantly affected ( p &lt; 0.01) by the interaction of fertilizer rate and spacing. Across both years, the optimal combination of 244 kg·ha −1 NPSB fertilizer and 7.5 cm spacing produced the highest marketable yields—41.2 t ha −1 in 2022 and 39.67 t ha −1 in 2023—along with total bulb yields of 41.3 t ha −1 and 39.7 t ha −1 , respectively. This treatment also achieved the greatest net benefit (625,770 Birr·ha −1 ) and a remarkable marginal rate of return (54,140%). Seasonal differences had no significant effect. Therefore, applying 244 kg·ha −1 NPSB fertilizer with 7.5 cm intra‐row spacing is recommended to maximize onion yields under irrigation in the study area and similar environments.