Determination of Crop Water Requirements and Irrigation Scheduling of Wheat Using Cropwat at Koga and Rib Irrigation Scheme, Ethiopia

Population growth, high water competition, and the effect of climate change have caused water shortage problems in the Nile basin, Ethiopia. Proper water management improves water efficiency and determining the water requirement of field crops are options for improving water productivity. In this study, the CROPWAT 8.0 model, local climate, and soil data were used to determine crop water requirement (CWR) and irrigation scheduling of wheat at Koga and Rib irrigation scheme, Nile basin. The Penman-Monteith and United States Department of Agriculture (USDA) soil conservation service methods were used to compute the reference evapotranspiration (ETo) and effective rainfall. Five levels of water depth (50%, 75%, 100%, 125%, and 150%) of the model and two irrigation intervals (14 and 21 days) were arranged in a Randomized Completely Block Design. The Koga, irrigating 75% of CROPWAT simulated water depth (9.3, 22.9, 44.1 and 25.8 mm at initial, development, middle and late-stage respectively) gave 3.37 t ha⁻¹ wheat yield and 1.01 kg m⁻³ water productivity. The result at Rib showed that irrigating 75% of the model (9.1, 23.6, 47.2, and 34.2 mm at initial, development, middle, late-stage, respectively) gave 4.27 t ha⁻¹ yield and 1.81 kg m⁻³ water productivity of wheat. The reference evapotranspiration varied from 4.86 to 3.14 mm⁻¹ day at Koga and from 4.67 to 2.36 mm⁻¹ day at Rib scheme. The irrigation requirement of wheat at Koga was 376.9 mm⁻¹ dec while at Rib was 379.9 mm⁻¹ dec. The CROPWAT model is an important tool to compute the crop water requirement of field crops in irrigated agriculture.