Simulating yield and water productivity of onion in response to deficit irrigation and mulching in Koga Irrigation Scheme, North West Ethiopia.

Abstract Optimization of crop water productivity is critical in water-scarce areas. The aim of this study was to evalute effects of deficit irrigation (DI) and wheat straw mulch on yield and water productivity of onion in Koga irrigation scheme, North Western Ethiopia. The factorial Randomized Complete Block Design with three replications, were performed. Three levels of DI (Full irrigation, 25% DI, and 50% DI) at all crop growth stages except for the mid-stage and two mulch levels (wheat straw mulch and without mulch), were applied as treatments. The effects of treatments on onion yield and water productivity were statistically evaluated, and the applicability of AquaCrop model was tested. The main and interaction effects of DI and mulch were significantly affecte yield, yield components and the water productivity of onion. The highest bulb yield (32.1 ton/ha) was obtained from full irrigation with wheat straw mulch. The lowest bulb yield (26.4 ton/ha) was obtained from 50% DI without mulch. The highest (7.07 kg/m3) and the lowest (5.9 kg/m3) water productivity were recorded at 50% DI with wheat straw mulch and full irrigation without mulch, respectively. The AquaCrop model accurately simulated canopy cover, biomass, and yield for the given climate. Average value of R2 0.98, NRMSE 11.5%, and d 0.98 were obtained for canopy cover. Biomass was simulated with values of R2 of 0.98, NRMSE 2.46%, and d 0.95; yield was simulated with values of R2 0.98, NRMSE 3.96%, and d 0.95. Therefore, adopting 50% DI at all stages except mid-stage in combination with wheat straw mulch is the best alternative for higher water productivity and yield of onion, in the area where water is scarce.