Abstract

Onions are the second most valuable vegetables in the world, following tomato. Its production is constrained by a number of problems including declining soil fertility and inappropriate fertilizer application. A study was conducted to determine economical optimum rates of N and P fertilizers for onion seed production in Arsi area. The experiment was conducted at Kulumsa, South Eastern Ethiopia, using four different levels of N (0, 50,100 and 150 kg N ha-1) and four levels of P (0, 35, 70 and 105 kg P2O5 ha-1) fertilizers arranged in 4 X 4 factorial arrangements in randomized complete block design with three replications. The result of the study revealed that almost all growth parameters considered were significantly affected by the treatments. The crop phenology and growth components were significantly influenced by the rate of N and P fertilizers. The combination of N at 100 kg N ha-1 and P at 70 kg P2O5 ha-1 was promising combination that generated highest net benefit 488,878.5 ETB ha-1 with the highest marginal rate of return (36638%). Therefore, a combined application of N at 100 kg N ha-1 and P at 70 kg P2O5 ha-1 rates can be recommend for onion seed famers in the study area and areas of similar agro-ecology