Late sowing with high seeding rate increases wheat water use efficiency under deficit irrigation

In the North China Plain (NCP), drought and groundwater overdraft threaten winter wheat (Triticum aestivum L.) production. The objective of this study was to improve water use efficiency (WUE) under deficit irrigation. A three-year field experiment was conducted with four sowing dates (SD; SD1: October 10, SD2: October 20, SD3: October 30, and SD4: November 10) using two cultivars (Jimai22 [JM22] and Shimai15 [SM15]). As SD was delayed, seeding rate (SR) increased from 450 seeds m(-2) in SD1 to 600, 700, and 800 seeds m-2 in SD2, SD3, and SD4, respectively. Relative to the normal SD (SD1), moderately delaying SD to SD2 with increased SR did not reduce yield (SD1: 8.79 Mg ha(-1) and SD2: 8.72 Mg ha(-1)). Delaying SD to SD3 and SD4 reduced yield by 9% and 11.3% (SD3: 8 Mg ha(-1) and SD4: 7.74 Mg ha(-1)). Delaying SD increased WUE from 1.83 kg m(-3) in SD1 to 2.07 kg m(-3) in SD4. The increase in WUE associated with delayed SD was attributed to shorter vegetative stage and decreased preanthesis evapotranspiration (ET). Under deficit irrigation, soil water availability and photosynthetic rate (Pn) during grain filling were higher as SD was delayed. As SD was delayed, the ratios of spike number to maximum stem number, postanthesis ET to seasonal ET, spike biomass to biomass at anthesis, and postanthesis biomass to total biomass all increased, resulting in higher harvest index and WUE. The yield reduction on SD4 was attributed to a reduced number of grains per spike due to decreased preanthesis biomass and thousand-grain weight (TGW). Comparing two cultivars, JM22 had higher Pn, postanthesis biomass, and TGW, but lower biomass remobilization (BMR) during grain filling. On SD4, JM22 had higher yield and WUE than SM15. In conclusion, under deficit irrigation in the NCP, moderately delaying sowing (SD2) with increased SR can obtain both high yield and high WUE. Extremely late sowing (SD4) with increased SR can maximize WUE and minimize yield loss, especially in cultivar JM22.