Effects of time of spring one irrigation on the grain filling characteristics and water use efficiency of winter wheat

There is a serious contradiction between water resources and grain production in the Hebei Plain; therefore, this study aimed to investigate the optimal time of once irrigation in spring for winter wheat to provide a technical basis for regional food security and groundwater overdraft control. A field positioning experiment was conducted from 2018 to 2020, with the water-saving winter wheat cultivar 'Heng 4399' under five treatments of spring one irrigation time (0 d after jointing, AJ0; 5 d after jointing, AJ5; 10 d after jointing, AJ10; 15 d after jointing, AJ15; and 20 d after jointing, AJ20) and two control treatments (no spring irrigation, CK1; and spring two irrigations, CK2). The effects of different treatments on the grain filling characteristics, yield, and water use efficiency of winter wheat were analyzed. The results showed that the delay of one spring irrigation time increased the duration of grain filling and the theoretical maximum 1000-grain weight, and decreased the average grain filling rate. Compared with AJ0, the duration of grain filling was prolonged by 3-7 d, the average grain filling rate decreased by 2.40%-13.51%, and the theoretical maximum 1000-grain weight increased by 1.61%-18.62% in the other spring one irrigation treatments. Under the spring one irrigation condition, the spike number per unit area, grain number per spike, and grain yield of winter wheat first increased and then decreased with the delay of irrigation date, whereas the 1000-grain weight gradually increased. Grain yield in the AJ5 treatment was the highest, followed by AJ10, and there was no significant difference between AJ5 and AJ10 (P>0.05), but both were significantly higher than those of AJ0, AJ15, and AJ20 (P < 0.05). The yields of AJ5 and AJ10 increased by 96.04% and 52.18% in 2018-2019, and 90.15% and 49.84% in 2019-2020, respectively, compared to CK1. However, compared to CK2, the same treatments decreased by 0.80% and 16.75% in 2018-2019, and 3.79% and 18.03% in 2019-2020, respectively. In the two experimental years, the water use efficiency of spring one irrigation treatments was higher in AJ0, AJ5, and AJ10, and there was no significant difference among the treatments (P>0.05). AJ15 and AJ20 significantly decreased the water use efficiency compared to the above-mentioned treatments (P < 0.05). Compared to CK1 and CK2, the water use efficiency of AJ5 increased by 20.78% and 18.47% (P < 0.05) in 2018-2019, and by 41.07% (P < 0.05) and 5.33% (P>0.05) in 2019-2020, respectively; AJ10 increased by 12.34% and 10.19% (P>0.05) in 2018-2019, and by 37.50% (P < 0.05) and 2.67% (P>0.05) in 2019-2020, respectively. In summary, under spring one irrigation conditions of winter wheat in the experimental area, the optimal irrigation date is 5-10 days after jointing, which resulting in a higher yield and water use efficiency.