Response of onion (Allium cepa L.) bulb to the combined effect of vermicompost and mineral fertilizer under irrigated soil condition in Raya Azobo and Kilte-Awulaelo districts south and eastern Tigray, Ethiopia

In Ethiopia, onion (Allium Cepa L.) is a major vegetable crop. However, due to erratic cultivation, rising mineral fertilizer prices and inadequate soil fertility management, its productivity is declining. Integrated nutrient management is a cost effective approach to fertilizing soil. If used properly, the combination of vermicomposting with mineral fertilizers is one of the most promising options. Nonetheless, in the study areas, the appropriate application rate of vermicompost and NPSZn fertilizer on onion production has not been well examined.

A field experiment was conducted in the irrigated soil conditions of Kilte-Awulaelo and Raya Azobo districts. The study used a randomized complete block design with three replications and twelve experimental treatments (4.5, 3 and 1.5 t ha^-1 vermicompost rates combined with NPSZn 75, 50 and 25 kg ha^-1). Full recommended 6 t ha^-1 vermicompost, 100 kg ha^-1 NPSZn fertilizer and absolute control were used. The collected agronomic data were subjected to ANOVA using SAS statistical software (SAS 9.0) and mean separation was done using LSD.

Most of the measured onion growth and yield parameters were significantly affected by the joint application of vermicompost and NPSZn. It varies among districts. Maximum bulb yields of 51.2 t ha^-1 in Kilte-Awulaelo and 42.5 t ha^-1 in Raya Azobo district were obtained from the application of 4.5 t ha^-1 vermicompost with 50 kg ha^-1 NPSZn and 4.5 t ha^-1 vermicompost with 75 kg ha^-1 NPSZn respectively. The combined application of vermicompost with NPSZn fertilizer enhanced onion growth and yield.