Determination of Irrigation Scheduling and Optimal Phosphorus Fertilizer Rate for Onion in Tiyo District, Arsi Zone, South Eastern Ethiopia

Abstract

The three-years consecutive study was carried out at the Kulumsa Agricultural Research Center (KARC), Tiyo, Arsi Zone, Southeastern Ethiopia. The objectives of the study were to determine optimal irrigation levels and phosphorus rates, as well as the interacting effect of nutrient and moisture levels on onion yield and yield quality. The experiment was arranged in a split plot Randomized Complete Block Design (RCBD) with three replications. The main plots received three irrigation levels, whereas sub-plots received five phosphorus fertilizer rates. Key growth parameters such as plant height, number of leaves per plant, bulb diameter, sugar content, average bulb weight, and marketable yield were subjected to evaluation. The results demonstrated that irrigation and phosphorus levels had a significant impact on onion growth and yield components. The study result of onion bulb yield revealed significant differences at (p<0.05). The highest marketable bulb yield of onion 28.08 tons ha-1 was obtained at 100% crop evapotranspiration (ETc) and 30 kg ha-1 of phosphorus application. The highest water productivity 10.38 kg/m3 result was recorded from the treatment receiving 50% ETc and 20 kg ha-1 of phosphorus. The economic analysis found that treatment 100% ETc with 30 kg ha-1 of phosphorus was more profitable, with better net benefits and significant marginal rates of return when compared to other treatments. As a result, a phosphorus rate of 30 kg/ha combined with irrigation levels of 100% and 75% ETc also gave over 100% MRR as a promising option for maximizing onion output in the study area.