Evaluation of Water Use Efficiency and Optimal Irrigation Quantity of Spring maize in Hetao Irrigation District using Noah-MP Land Surface Model

The Hetao Irrigation District (HID) has low rainfall and high evaporation and is one of the main grain-producing areas in China. As the increasing competition between industrial water, agricultural water and urban domestic water, agricultural water is facing severe challenges. Improving the efficiency of agricultural water use is the most appropriate way to achieve sustainable agricultural development in irrigation areas and obtain high returns. In this study, the Noah-MP Land Surface Model (LSM) with dynamic crop growth and irrigation schemes was used to jointly simulate the maize yield and irrigation amount of spring maize in the HID from 2003 to 2012 under rain-fed condition. Sensitivity test was conducted for ten sets of irrigation setup with different soil moisture triggering thresholds (IRR_CRI=0~1). Water use efficiency (WUE) and irrigation water use efficiency (IWUE) are introduced to define the ratio of crop transpiration to available water (precipitation plus irrigation) and the ratio of maize yield to the corresponding irrigation water, respectively, during the maize growing season. The WUE and IWUE of the above ten scenarios were evaluated and analyzed. The results show that under the rain-fed scenario, the severe soil moisture deficit during the growing season lead to a significant decrease in maize yield in the HID, with almost no grain harvest in 2011.When IRR_CRI>0.7, both WUE and IWUE decrease and decline with the increase of IRR_CRI. When IRR_CRI < 0.7, WUE decreases while IWUE increases. Under the traditional flood irrigation pattern (IRR_CRI>0.9), the irrigation amount per unit area exceeds 950mm in the HID, WUE and IWUE are both at a very low level, and more than 25% of irrigation water is wasted as runoff. When IRR_CRI is between 0.6 and 0.7, IWUE achieves the maximum value, and the corresponding irrigation amount is about 400-500mm. In this scenario, most of the irrigation water becomes soil moisture and transpiration, and less than 5% becomes runoff. Fully considering the maize yield, water use efficiency, ecological health, and the availability of water resources of the Yellow River in the HID, the recommended irrigation amount is about 450~550mm to achieve the optimal maize yield and the water use efficiency.