Abstract Onion is one of the most important vegetable crops in Ethiopia, including in the Koga Irrigation Scheme. However, the limited availability of hybrid varieties and the inappropriate application of nitrogen fertilizer are major constraints to onion production. Therefore, a field experiment was conducted to evaluate the effects of nitrogen fertilizer on the growth, yield, and quality of hybrid onion varieties and to determine the optimum nitrogen fertilizer rate while identifying productive hybrid cultivars for economical onion production. The study consisted of four hybrid onion varieties (Red Coach, Russet, Jambar, and Bombay Red) and four levels of nitrogen fertilizer (0, 41, 82, and 123 kg ha⁻¹). The results indicated that the main effects of varieties and nitrogen fertilizer significantly influenced stand count percentage, days to bulb maturity, plant height, leaf length, leaf number, bulb neck diameter, bulb length, harvest index, total soluble solids, and bulb dry matter content. The highest marketable bulb yield (57.84 t ha⁻¹) was obtained from the Russet variety with 82 kg ha⁻¹ of nitrogen fertilizer. Based on the partial budget analysis, the highest net benefits (1,490,384.8 Birr ha⁻¹) and the highest marginal rate of return (3061.25%) were recorded from the treatment combination of the Russet variety with 82 kg ha⁻¹ of nitrogen fertilizer. Therefore, growing the Russet variety with 82 kg ha⁻¹ of nitrogen fertilizer is recommended for the economical production of onion in the study area and other areas with similar agro-ecological conditions.
Getaneh et al. (Tue,) studied this question.