Water-saving irrigation regime for winter wheat in county areas under water resources constraints

High-efficiency water-saving irrigation engineering technology is facing a difficult situation to be extended popularly covering the field crops. A feasible way can be to optimize the water-saving irrigation regime, thereby to improve the efficiency of irrigation water. In this study, an optimization design was conducted to develop a water-saving irrigation regime in Xinzheng City, Henan Province, China. Three scenarios were set, including non-irrigation, average irrigation, and insufficient irrigation. The specific procedures were: First, Penman-Monteith formula was used to calculate indirectly the water volumes that the winter wheat required in the full and every growth stages. Second, the collected parameters were selected, such as meteorological data, the field moisture capacity, wilting coefficient of different types of soil texture, and hydro-geological data, thereby to estimate the total water resource that supplied in the full growth stage of winter wheat, including atmospheric precipitation, soil water content, and available water resource for irrigation. Third, the water sensitivity index of winter wheat was used to monitor the water demand of winter wheat in the different growth stages. Taking the maximum yield of winter wheat as a goal, a Jensen-model was selected to optimize the total supply water, and further distribute to the different growth stages of winter wheat. Finally, the obtained parameters were used, including the actual evapotranspiration, atmospheric precipitation, and soil water content, to calculate the irrigation water quota in different growth stages of winter wheat. The results showed that: 1) The total supply water was less than that in normal and dry years in Xinzheng City, Henan Province, China. Therefore, it was necessary to implement deficit irrigation regime. 2) Since the Jensen-model cannot be used to calculate directly the irrigating quota in different growth stages, the actual evaporation can be achieved for the weight coefficient of sensitivity index in different growth stages of winter wheat. Specifically, the allocation proportions of evaporations were 15.8%, 5.4%, 23.4%, 34.9%, 20.5% in seedling, over-wintering, booting, heading, and filling stages. 3) In Xinzheng City, the key irrigation periods of winter wheat were the heading and filling stages. In filling stages, the irrigating quota accounted for 73.3%-96.7% of the total irrigation amount in high flow years. In heading and filling stages, the irrigating quota accounted for 60.8%-68.5% and 32.2%-38.0% in normal flow years. In heading stages，the irrigating quota accounted for 53.9%-71.9% in dry years. In Jensen-model estimation, the yield of winter wheat under insufficient irrigation was 20.6%-40.9% higher than that under non-irrigation or average irrigation in normal flow year, and 23.8%-58.9% higher in dry year. Therefore, the amount of water resources available for irrigation in Xinzheng City was only 640-1225 m3/hm2, 28.8%-55.0% of the quota given in Henan Province local standard-agricultural water. Nevertheless, the insufficient irrigation can be recommended for the field crops. The finding can offer the basic counties (cities) data for extending a deficit irrigation regime to other counties.