Effect of Irrigation Scheduling and Nitrogen Levels on Yield and Water Productivity of Wheat (<i>Triticum aestivum</i>) at Ambo, West Shoa, Ethiopia

Excessive fertilizer use and improper irrigation scheduling can accelerate soil degradation and increase the nitrogen leaching rate. This study, conducted at the Ambo Agricultural Research Center during the 2021/22 and 2022/23 irrigation seasons, aimed to identify optimal nitrogen fertilizer rates for wheat production under irrigation. The experiment followed a randomized complete block design with three replications, utilizing a split-plot arrangement. The main plot tested three soil moisture depletion levels: 80%, 100%, and 120%, while the sub-plot involved five nitrogen levels with 0, 46, 69, 92, and 115 kg N/ha. Results showed that nitrogen levels significantly influenced grain yield, above-ground biomass, and water productivity but not the irrigation regimes or their interaction with nitrogen levels. The 115 kg N/ha rate produced the highest grain yield, 5213 kg/ha, and water productivity of 1.24 kg/m³, though these values were not significantly higher than those at 92 kg N/ha. Both 115 kg and 92 kg N/ha treatments significantly outperformed the 69 kg N/ha treatment and lower rates. Applying 120% allowable soil moisture depletion levels resulted in high net income and benefit-to-cost ratio values of 197,716.00 Ethiopian Birr (ETB) and 30.89%, respectively. At 120% allowable soil moisture depletion, the highest net income and benefit-cost ratio were observed (197,716 ETB and 30.89%, respectively). The 92 kg N/ha application resulted in the highest marginal rate of return (826.05%), well above the acceptable threshold of 100%, with a net income of 223,655 ETB. Based on grain yield, water productivity, and economic feasibility, we recommend applying 92 kg N/ha with 120% ASMDL for wheat production in this region.