Optimizing irrigation water levels to improve yield and water use efficiency of vegetables: case study of tomato

Optimizing irrigation water requirement is necessary to improve productivity of irrigated agriculture. Hence, adapting the knowledge of irrigation scheduling for specific crop and location is important. Field experiment was then conducted in Raya Alamata district of Tigray, Ethiopia to investigate the impact of different irrigation water levels on yield and irrigation water use efficiency (IWUE) of tomato. Eight treatments (50, 35, 25% above estimated crop water requirement (CWR), estimated CWR, 25, 35, 50% below the estimated CWR and farmers practice) were arranged in randomized complete block design under three replications. Tomato water requirement was estimated using CROPWAT 8 software and it was estimated to be 500 mm throughout the base period. The result indicates significant difference between marketable yield (MY), total yield (TY) and IWUE of tomato by the level of irrigation. The application of estimated CWR of tomato gave higher MY (36.37 ton/ha) and TY (38.58 ton/ha). Unmarketable fruit yield of tomato was unaffected by level of irrigation. Farmers' practice gave considerable MY (36.32 ton/ha). But, the depth of water applied by farmers throughout the growing season was 561 mm which was 12.2% above the estimated CWR. The yield obtained per unit of applied water (IWUE) ranges from 0.357 to 0.876 kg/m(3) for the different irrigation water levels. This shows that IWUE increases with decreasing depth of water application. In conclusion, deficit irrigation practice could be successful in saving irrigation water up to 35% of tomato CWR without significant reduction in fruit yield of tomato in regions where water is a limiting factor for vegetable production.