3.3 Irrigation Scheduling Scenarios

3.4 Three irrigation scheduling scenarios analysis
3.4.1 Irrigation scheduling scenarios setting
There have been some water-saving irrigation field experiments conducted in the HID. Such as in the shahaoqu experimental station (SHQ) and shuguang experimental station (SG), water-saving irrigation experiments on spring wheat showed that irrigation at jointing and heading for spring wheat, compared with four irrigations, could improve water use efficiency without affecting crop yield significantly (Dong et al., 2011; Zhang et al., 2013). For spring maize, experiments showed that irrigation on non-critical water demand stage (seedling and filling stage) had little effect on crop yield in the SHQ and SG (Hou and Shen, 2001). Experiments on sunflower
In scenario 1, the irrigation amount of sunflower was reduced by 28.3%, whereas the crop yield increased by 3.5%, and the WP increased by 3.0%，compared with the basic scenario. The sunflower yield increased significantly in WQQ, but decreased a little in DK and HH (Figures 8c and 8f). In scenario 2, the irrigation amount of sunflower was reduced by 24.9%, whereas crop yield increased by 3.3%, and the WP increased by 3.1% compared with the basic scenario (Figures 8c and 8f). This indicated that moderate reduction in the irrigation amount at seeding and filling stages would not negatively affect sunflower yield and WP in the HID, similar observations were reported by Ma and Zhang (2009) and Yang et al. (2009). During 2000-2010, the groundwater depths of the five counties in scenario 1 and 2 were lower than those in the basic scenario, but not by much. Based on above analysis, scenario 1 was suggested for LH, WY and WQQ, scenario 2 was suggested for DK, and the basic scenario was suggested for HH during 2000-2010 (Table 7), in order to ensure efficient and high-yield crop production without seriously decreasing the groundwater depth in a normal year and to save as much water as