A comparative study of conventional irrigation and CropWat model-based irrigation scheduling: effects on water productivity under onion and teff cultivation in the upper Blue Nile basin

Abstract Nevertheless, irrigation agriculture is expanding; therefore, evaluating the performance of existing irrigation schemes and introducing improved irrigation scheduling techniques that enhance water productivity (WP) becomes an important strategy. Thus, this study aimed to investigate the effect of furrow irrigation using both gravitational and motorized irrigation water applications on WP for onion and teff crops in the Gumara watershed, northwest Ethiopia. We conducted the field investigation in 2019/20 during the dry season. We utilized CropWat as a decision-making tool to estimate crop evapotranspiration and net irrigation requirement (NIR) and to inform irrigation scheduling. We measured the field irrigation water using pumping tests for motor pump users and a Parshall flume for gravity users. The measurements were taken from a total of 30 onions in Wanzaye and 25 in Jigna, as well as 5 teff crop farmers’ fields in Bebeks. When we examined the model estimates and field records for NIR on onions and teff, we observed that farmers used significantly more water than the crops required. Onions had a seasonal NIR of 360.1 mm, according to the model. However, farmers in Wanzaye, Jigna, and Bebeks used an average of 501.05 mm, 496.8 mm, and 468.7 mm for their applications. The model estimated a NIR of 364.0 mm for teff, while the farmers applied a mean of 459.7 mm of water. Consequently, farmers over-irrigated with water depths of 141, 136.7, and 104.1 mm at Wanzaye, Jigna, and Bebeks, respectively. In Wanzaye and Jigna, farmers charged an extra cost of 3728 birr/ha and 3146 birr/ha for fuel/kerosene, respectively. The onion WP was low in Wanzaye, Bebeks, and Jigna, respectively. The result also revealed that the benefit-cost ratio of the onion was low for Wanzaye, Jigna, and Bebeks, respectively. The WP of teff grain was also found to be low. But the result showed that teff’s benefit-cost ratio was higher than that of onion.