Influence of Nitrogen Rates on Growth, Yield and Quality of Onion (Allium cepa L.) Varieties in West Dembia District, North Western Ethiopia

Onion (Allium cepa L.) is highly important vegetable in the daily diets of Ethiopians as flavoring of dishes, sources of important carbohydrate, protein and several nutrient elements. However, its productivity is low mainly due to low soil fertility, improper fertilizer application and limited use of improved onion varieties. Hence, a field experiment was conducted under irrigation to evaluate the effects of nitrogen rates on growth, yield, and quality of onion varieties. The treatment consisted of a factorial combination of six levels of nitrogen rates (0, 46, 69, 92, 115 and 138 kg N ha-1) and two improved onion varieties (Adamared and Bombayred), which were laid out in a randomized complete block design in three replications. The collected data were analyzed using SAS software. The analysis of variance showed that the main effect of nitrogen rates on all tested parameters was significant while the main effects of varieties had significant effect on all parameters except plat height, number of leaves and unmarketable yield. Adamared variety gave higher marketable bulb yield (15.56 t ha-1) than Bombayred (13.89 t ha-1). The application of 138 kg N ha-1 gave the highest marketable bulb yield (19.23 t ha-1) and the maximum net benefit (253965 birr ha-1) with acceptable marginal rate of return (2804%). However, application of 138 kg N ha-1 reduced quality parameters of onion bulbs. It increased neck diameter, decreased dry matter content and total soluble solids. It also caused the highest percent rots, sprouts and weight losses of bulbs during the eight month storage life. It can be concluded that application of 138 kg N ha-1 for Adamared variety can be used for better productivity in the study area.