Effect of Combined Application of Organic Manure and Inorganic Nitrogen on Marketable Yield, Shelf Life of Onion and Soil Fertility Status after Harvest

Low soil fertility is one of the most important constraints limiting onion production in Eastern Africa. Farmers northern Ethiopia should tackle this problem through combined application of organic and mineral fertilizers, which amend the soil environment. An investigation was carried out to study the effect of combined application of organic manure and inorganic nitrogen on marketable yield, shelf life of onion and soil fertility status after harvest from, October 2015 to June 2016. The treatments consisted of combinations of two rates of farmyard manure (FYM) (10 and 20 t ha-1), two rates of vermicompost (VC) (2.5 and 5 t ha-1), and three rates of recommended N fertilizers (RDF) (25, 50 and 75%). 100% RDF N (69 kg N ha-1), 100% (5 t ha-1) of VC, 100% (20 t ha-1) FYM and (absolute control) were used for comparison. Results from the experiment revealed that onion storage life significant influenced by the combined application of organic and inorganic N fertilizers. Application of 5 t ha-1 VC + 50% RDF N recorded the highest marketable yield and lowest onion bulb weight loss throughout the storage period. While, maximum bulb weight loss (36.16%) was recorded during 12th week of storage under the application of 100% RDF N. The absolute control 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. On the other hand combined 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. Applications of organic inputs in combination with chemical fertilizer were found better option than application of organic manure or chemical fertilizer alone for better onion yield, shelf life and soil fertility replenishment. Therefore, it is concluded that the application of organic fertilizer (vermicompost) along with inorganic fertilizer (nitrogen) could be better for onion yield, shelf life and soil fertility replenishment.