Quality and Storage Life of Onion (Allium cepa L.) as Influenced by Applications of Nitrogen, Phosphorus and Potassium Fertilizer, at Jimma, South Western Ethiopia

Abstract

Onion (Allium cepa L.) is one of the most important vegetable crops produced in Ethiopia. Yield and productivity of the crop has been far below the regional and national standards owing to several factors; absence of location specific fertilizer recommendation being the major among others. In Ethiopia, post harvest loss of vegetables contributed up to 30% yield reduction on vegetables and fruits. Thus, a field experiment was conducted at Jimma University College of Agriculture and Veterinary Medicine Research field in dry season to study the effects of Nitrogen (N), Phosphorus (P) and Potassium (K) fertilizer on quality and storage life of irrigated onion under Jimma condition, South Western Ethiopia. The treatments consisted of factorial combinations of four levels of Nitrogen (0, 50, 100 and 150 kg N ha^-1), three levels of Phosphorus (0, 46, and 92 kg P₂O₅ ha^-1) and four levels of Potassium (0, 40, 80, and 120 kg K₂O ha^-1) laid out in Randomized Incomplete Block Design with three replications. Data on yield, bulb quality and storage life parameters were recorded and analyzed using GenStat 12.1 version computer soft ware packages. Results of the study revealed that; N, P and K had shown a highly significant effect on quality parameters like TSS (^oBrix), DMC (%) and bulb shape index. Similarly, keeping quality of the Onion bulbs like bulb sprouts (%), weight loss (%), weeks to 50% bulb sprouts and storage rots (%) are highly influenced by application of N, P and K at different levels. The higher total bulb yield per hectare (18.78 ton) was recorded with combined application of 150:92:120 kg of N-P-K ha^-1 and it is statistically the same with the results obtained in the combined applications of 150:46:120 and 150:46:80 kg of N-P-K ha^-1 which were significantly superior over the rest of other treatments. Excessive Nitrogen caused higher bulb rots (%); bulb sprouts (%) and weight loss (%); while, potassium significantly decreased the bulb rots (%), bulb sprouts (%) and weight loss (%) during the two month storage time at ambient temperature. However, according to the partial budget analysis; the highest economic benefit was obtained at 150:46:80 kg of N-P-K ha^-1 where as the lowest net benefit was obtained from the control treatment. This can be recommended for use by potential onion investors or farmers with high initial capital in the study area. Nevertheless, more researches are needed in different locations and on different soils to come up on general recommendation.

Keywords: Nitrogen, Onion, Phosphorus, Potassium, Quality, Storage life.