EFFECT OF INTEGRATED NUTRIENT MANAGEMENT ON GROWTH, BULB YIELD AND STORABILITY OF ONION (Allium cepa L.) UNDER IRRIGATION AT SELEKLEKA, NORTHERN ETHIOPIA

Onion is an important crop both as a condiment and income generation for smallholder farmers in North western Zone of Tigray. However, Continuous use of inorganic fertilizers and inappropriate soil fertility management practices are among the major factors limiting onion productivity in the North Western Tigray. Therefore, a field experiment was undertaken in Selekleka district from October 2015 to June 2016 to assess the effects of integrated nutrient management on growth, bulb yield, and storability of onion (Allium cepa L.). The treatments consisted of combinations of two rates of farmyard manure (FYM) (10 and 20 t ha-1) and two rates of vermicompost (VC) (2.5 and 5 t ha-1) each combined with three rates of nitrogen (25, 50 and 75) of recommended N fertilizers, RDF. In addition, 100% RDF N (69 kg N ha-1), 100% (5 t ha-1) of VC, 100% (20 t ha-1) FYM and zero rates (unfertilized treatment) were used for comparison. The experiment was laid out in a randomized complete block design with three replications. Data were collected for growth, bulb yield and yield attributes and storability of onion bulb. Analysis of variances (ANOVA) revealed that combined application of 5 t ha-1 VC+50% inorganic N fertilizers recorded the highest plant height (71.67 cm), leaf number (16.15), leaf length (45.19 cm), nick thickness (1.51 cm), bulb length (5.51 cm), bulb diameter (5.90 cm), mean bulb weight (92.64 g), biological yield (131.42 g), harvest index (82.18%), marketable yield (35.13 t ha-1), bulb dry weight (35.46%), total dry biomass (40.27 g), and total yield (35.25 t ha-1). Integrated use of 2.5-5 t ha-1 VC with 25-75% of N resulted in higher total nitrogen, available K, available P, CEC, EC, OC, and organic matter of the soil over the control treatments. In case of bulb storage life, bulb weight loss during the entire storage was highly significant influenced by the combined application of organic and inorganic N fertilizers. The maximum bulb weight loss (36.16%) was recorded during 12th week of storage under the application of 100% RDF N. On the other hand, application of 5 t ha-1 VC + 50% RDF N recorded the lowest onion bulb weight loss throughout the storage period. Plots treated under nil fertilizer showed the least % bulb rotting and sprouting, hence, the lowest % bulb rotting (1.67, 2.27, and 4.06) were recorded during the 8th, 10th, and 12th week storage period respectively, in bulbs from the control treatment. From the economic point of view, it was found that, the treatment combination of 5 t ha-1 VC +50 % RDF N gave the highest net return (246,354 Birr ha-1), followed by 2.5 VC t ha-1 + 75 % RDF N (226,014 Birr ha-1). On the other hand, the lowest net return (143,018 Birr ha-1) was obtained from the control. It could, thus, be concluded that, based on the partial budget analysis and result of soli analysis after harvest the application of 5 t ha-1 vermicompost and 50 % recommended inorganic nitrogen was the appropriate combination for better onion production with minimum weight loss in the study area