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 P 2 O 5 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 P 2 O 5 (46, 92,138 kgha -1 ) and including check 0, 50 and 0,100 kgha -1 P 2 O 5 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 P 2 O 5 . Combined analysis of variance showed as highly significant differences were observed among the treatments. So, an optimum fertilizer rates for nitrogen & P 2 O 5 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 P 2 O 5 alone, year * nitrogen, year * P 2 O 5 and year * P 2 O 5 * nitrogen has no significant effect on bulb yield of onion. The interaction of 138kgha -1 P 2 O 5 with 138kgha -1 nitrogen 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 -1 nitrogen and 92kgha -1 P 2 O 5 . 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 P 2 O 5 but not much respond to the main effect P 2 O 5 application alone. We can conclude that rather than application of 92 kgha -1 N*138kgha -1 P 2 O 5 and 46kgha -1 N*92kg ha -1 P 2 O 5 , 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 P 2 O 5 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