Determination of Optimum Nitrogen and Phosphorus Fertilizer Rates on Bulb Yield of Onion (Allium cepa L.) at Bako, Western Oromia, Ethiopia

Abstract

Field experiment was conducted to evaluate bulb yield of onion (Allium cepa L.) under different levels of nitrogen and P₂O₅ for two years (2013-2014) at Bako, Western Oromia. Treatments comprised of three levels of nitrogen (46, 92, 138 kgha^-1) and three levels of P₂O₅ (46, 92,138 kgha^-1) and including check 0, 50 and 0,100 kgha^-1 P₂O₅ and nitrogen respectively. The experiment was designed in RCBD and replicated three times. The variety bombe red is used as test material. Fertilizer rates were applied in split applications two times for nitrogen and once for P₂O₅. Combined analysis of variance showed as highly significant differences were observed among the treatments. So, an optimum fertilizer rates for nitrogen & P₂O₅ which gave the highest marketable bulb yield ha^-1 was recommended for the study area and for similar agro-ecologies. The result showed that application of nitrogen significantly increased the average bulb yield of red bulb onion after harvest but application of the main effect P₂O₅ alone, year * nitrogen, year * P₂O₅ and year * P₂O₅ * nitrogen has no significant effect on bulb yield of onion. The interaction of 138kgha^-1 P₂O₅ with 138kgha^-1nitrogen can significantly increases total bulb yield of onion (28.07 tha^-1) and recommended for the study area. Besides, it is possible to produce and obtain reasonable bulb yield of 20.58 tha^-1 bulb onion with the interaction of 92kgha^-1nitrogen and 92kgha^-1 P₂O₅. During vegetative growth stage and at its maturity it was observed that there is disease reaction of purple blotch recorded. Eventually, it is also possible to recommend from the result that onion bulb yield was more responsive to the main effect of nitrogen and its interaction with P₂O₅ but not much respond to the main effect P₂O₅ application alone. We can conclude that rather than application of 92 kgha^-1N*138kgha^-1 P₂O₅ and 46kgha^-1N*92kg ha^-1 P₂O₅, application of 100 kgha^-1 N alone gave remarkable bulb yield. This directly indicated that bulb yield of onion production is more responsive to nitrogen application than P₂O₅ fertilizer rates. As this experiment was conducted during the main rainy season disease infestation (purple blotch) was the main problem encountered especially in the second year followed the humid environment. So, application of chemical (Orious) 2 litha^-1 2-3 times with in fourteen days interval is very crucial to check/control this diseases.

Keywords: Bulb Yield, Nitrogen, Onion, Phosphorus

DOI: 10.7176/JNSR/13-8-01

Publication date: April 30^th 2022