Effect of Deficit Irrigation on Water Productivity of Onion (Allium cepal.)under Drip Irrigation

Abstract

Deficit irrigation (DI) improves water productivity and irrigation management practices resulting in water saving by maintaining soil moisture content below optimum level throughout growth season. Field study was carried out on clay loam soil at Melkassa Agricultural Research Center, Ethiopia with the objectives to estimate water productivity of onion and evaluate the effect of water deficit on onion yield and quality using drip irrigation. The experiment contained five DI treatments of 90%, 80%, 70%, 60%, and 50% Crop water use (ETc) and the control (100% ETc) laid out in RCBD design with three replications. Irrigation water was applied at allowable soil moisture depletion (p=0.25) of the total available soil moisture throughout the crops growth stage. Statistical analysis revealed that plant height was not affected by the level of DI while, leaf number, bulb diameter, marketable bulb yield and total bulb yield had shown a highly significant (P<0.01) differences among DI treatments. The highest bulb diameter was observed from a control treatment that was significantly different to all other treatments. The highest total bulb yield of 15,690 kg/ha was observed from a control treatment which was not significantly different with treatment receiving 90% ETc. Highest water productivity of onion bulb yield was observed from treatment receiving 70% ETc and better onion bulb diameter was observed from treatment receiving 100% ETc to 70% ETc. The yield response factor ranged between 0.8 and 1.7. Thus, DI practices should be avoided for Ky values that are less than unity. Considering yield response factors (Ky) is limiting factor, 80% ETc application was a marginal and beyond that yield losses are intolerable. Thus, the practice of DI application up to 20% saved 45 to 108 mm depth of water from the gross onion irrigation water requirement.