Optimizing use of surface and groundwater for irrigation in lower reaches of the Yellow River Basin

【Background】 Combined use of surface water and groundwater for irrigation is a common practice in the lower reaches of the Yellow River Basin to control groundwater table at a desirable depth. In this paper, we investigate the optimal timing and quantity of irrigation using groundwater, based on crop water consumption and crop yields in the region. 【Method】 The analysis was based on modelling. A dissipative hydrological model was used to simulate water balance influenced by irrigation using different combinations of surface water and groundwater. The results were combined with the Jensen crop water production function to analyze the variation in the yields of winter wheat and summer corn with irrigation. 【Result】 ① Significant water deficits were identified in early April, mid- to late-May, early June, late July, and early August, which negatively impacted crop yields. Supplementary irrigation using groundwater in mid-October did not have a noticeable effect on crop yield, and the difference in crop yields between irrigations using surface and groundwater and irrigation using only surface water was minimal. ② The relative yield of winter wheat during the jointing stage and the relative yield of summer maize were sensitive to supplementary irrigation using groundwater, underscoring the importance of timing in irrigation using groundwater. ③ Supplementary irrigation of 40 mm using groundwater during the jointing stage of winter wheat notably increased its grain yield, with the optimal ratio of surface water to groundwater for irrigation being 5.25∶1. Irrigating 60 mm with groundwater for summer maize during the heading stage also boosted yield, with the optimal ratio of surface water to groundwater for irrigation being 4.4∶1. 【Conclusion】 Optimizing the timing and quantity of groundwater for irrigation is critical for improving crop yields in the lower reaches of the Yellow River basin. In our experimental study, irrigating 40 mm of groundwater for winter wheat during the jointing stage and 60 mm for summer maize during the heading stage can significantly improve their yields.