Enhancing bulb yield through nitrogen fertilization and the use of hybrid onion (Alluim cepa L.) varieties in northwest Ethiopia

Onions are among the most important cash crops in developing countries, including Ethiopia. However, its production and productivity are very low, which is associated with inappropriate fertilization and the use of low-yielding varieties. Therefore, the present study was conducted to evaluate the effects of the nitrogen fertilizer rate on the growth, yield, and quality of hybrid onion varieties in northwest Ethiopia. The experiment was conducted at three locations (Koga, Woreta, and Woramit) during the 2021/2022 cropping season under irrigated conditions. The treatments consisted of three hybrid onion varieties (Russet, Jambar, Red Coach) and one open-pollinated onion variety (Bombay Red) and four nitrogen rates (0, 41, 82, and 123 kg ha-1), which were laid out in a randomized complete block design with a factorial arrangement of 4*4 in three replications. The results of the present study revealed that onion growth, yield and quality were influenced by the nitrogen fertilizer rate and onion variety across all locations. Compared with the open pollinated Bombay Red variety, the hybrid varieties (Russet and Jambar) performed well in terms of bulb diameter, bulb weight, total yield, marketable bulb yield, and pungency. Nitrogen fertilizer applied at a rate of 82 kg ha-1 resulted in the highest growth and yield parameters of onion. The Russet and Jambar varieties recorded the highest marketable bulb yields of 26.50 t ha-1 and 24.57 t ha-1, respectively. Onion varieties treated with the highest nitrogen fertilizer dosage of 123 kg ha-1, particularly the Bombay Red variety, exhibited the longest duration to reach maturity. Onion plants supplied with 82 kg ha-1 nitrogen presented the highest marketable bulb yields, with a value of 26.77 t ha-1. Too much nitrogen above 82 kg ha-1 leads to decreased yield; hence, excess nitrogen is lost to the environment. Furthermore, the Jambar and Russet hybrid varieties and the application of 82 kg ha-1 nitrogen fertilizers provided the highest net benefit. The hybrid varieties Jambar and Russet and the application of 82 kg ha-1 nitrogen fertilizer can be recommended for onion production in the study area and areas with similar agroecosystems. Since this study is the first of its kind, considering other hybrid onion varieties and optimizing agronomic practices such as spacing and phosphorus fertilizer are also recommended in future research.