Modeling the impacts of climate, soil, and cultivar on optimal irrigation amount of winter wheat in the North China Plain

Improving winter wheat (Triticum aestivum L.) productivity and water use efficiency (WUE) in the North China Plain (NCP) is critical to maintain grain security and ease the water shortage in this region. This study was conducted to examine the optimal irrigation amount (OI) for winter wheat across the NCP and analyze its responses to the climate, soil, and cultivar. We applied a novel approach with the Agricultural Production Systems sIMulator (APSIM) during 1961–2010 to estimate the OI by considering the trade-off between yield and WUE. Our results suggested that the optimum irrigation amount determined by climate (OI_c) ranged from 3–342 mm for simulation experiments considering climate impacts alone. When soil conditions were additionally considered, the optimal irrigation amount (OI_cs) showed an average decrease of 45 mm across 19 sites in the northern NCP but an average increase of 42 mm across 29 sites in the southern NCP. When all three factors were included, the estimated optimal irrigation amount (OI_csc) fell within the range of 3–286 mm across the NCP, lower than OI_c and OI_cs. Climate, soil, and cultivar explained 54, 27, and 19% of the spatial variation in the optimal irrigation amount, respectively. Further analysis indicated relatively higher optimal irrigation amounts for late-maturing cultivars, but their inter-annual variations and decadal changing rates were lower relative to the early- and medium-maturing cultivars. Our study demonstrated the incorporation of the genotypes and environmental factors, and recommended the optimal irrigation amount of 3–286 mm for winter wheat in the NCP.