Enhancing water productivity of different field crops using deficit irrigation in the Koga Irrigation project, Blue Nile Basin, Ethiopia

The population of Ethiopia is growing rapidly and consequently, the country may face aggravated food insecurity. Therefore, improving agricultural productivity is critical to feed its inhabitants. The occurrence of drought and poor irrigation systems lead to a real burden on water resources. Thus, optimal irrigation planning and management should be considered. In this study, the linear programming (LP) model was applied to optimally allocate water and land for different field crops at Koga irrigation scheme. The model was applied for an optimally defined cropping pattern and three levels of deficit (10%, 20%, and 30% of ET) irrigation. The objective function of the study was to maximize net benefit and water productivity. The model was developed using constraints of water, land and different field crop diversifications. CROPWAT 8.0 was used for the estimation of crop water requirements using local climate and soil data. The result showed that using 20% deficit irrigation for the identified optimal cropping pattern, 7361 ha of land (2018 ha additional land from the irrigated land of the scheme in 2016/17) could be irrigated. Under this scenario of deficit irrigation, a net benefit of 284.7 million Birr and water productivity of 5.3 Birr m(-3) have been achieved. This indicates that using 20% deficit irrigation, the net benefit increases by 23% and the water productivity by 55% as compared to the existing irrigation practice. Wheat, barley and pepper were not found to be attractive crops in the cropping pattern system. The actual irrigation system has been found poorly managed in addition; the cropping system and the irrigation activity were operated below the optimal. Therefore, the practice of deficit irrigation (recommended 20% deficit irrigation) can substantially increase the net benefit and water productivity of the scheme.