Benchmarking water use efficiencies of agricultural and horticultural crops under various management strategies in an arid region

Based on a 30-year available data during 1980-2010, water saving potentials consumed in the irrigated agriculture of Khuzestan province was investigated. To this end and based on FAO classification system, all agricultural and horticultural crops were divided into 8 groups of cereals, vegetables, legumes, oil crops, sugar crops, root and tubers, nuts and fruits. Then, different management scenarios were defines by combining three planting dates of on time cultivation (local date), early and late plating dates, and furrow, sprinkler and drip irrigation systems, and four levels of supplying crop water demand (100, 85, 70 and 55 percent). The best scenario and cropping pattern were determined based on water use efficiency and irrigation water productivity indices, and then, the corresponding indices under the selected scenarios were considered as the benchmark levels. The highest values of water use efficiencies were obtained for sugar crops had the highest water use efficiencies due to their high crop productivity, root and fiber due to their low water requirement, and vegetables due to their low water requirement and high yield. While taking the fifth place regarding water use efficiency, cereals were the largest fresh water consumer in the province due contributing more than 70% in total irrigated harvested lands. Substituting one hectare of irrigated lands under cereals with root and tuber productions, results in an average 3.8 thousand cub meter (63%) saving in net crop water consumption. substituting surface irrigation system with drip irrigation system led to an increase in water sue efficiency in sugar crops, legumes and oil, while such substitution caused a reduction in the amount of produced crop per unit consumed water. A 15% water stress results in a negligible change in water use efficiency due to maintaining crop water requirement at the favorable rates and reducing crop yield by only 1.4-8.3%. Increasing the water stress level up to 30% result in a maximum reduction of 5.6% in crop production per net consumed water. Regardless of the irrigation systems and water stress levels, early planting will increase water use efficiency up to 20%. Hence, a mild water stress and adjusting planting date as well as prioritizing the cultivation of agricultural and horticultural crops based on their water use efficiency could be considered as favorable management scenarios for alleviating pressure on blue water resources in Khuzestan province.