Simulation of Winter Wheat Yield in Response to Irrigation Level at Critical Growing Stages in the Huang-Huai-Hai Plain

Water deficiency is recognized as a major problem in winter wheat production in the Huang-Huai-Hai Plain. This study
aimed to assess the impact of drought stress on winter wheat yield and raise irrigation proposals for water-saving production in
this area. With reference to the fact of water deficits in major growth stages of wheat and the local irrigation practice, we input
different irrigation levels (volumes) required by the DSSAT crop model to simulate yield variations in response to irrigation levels
at critical growing stages in four typical sites during the past three decades. The cumulative probability for yield reduction was
concluded based on irrigation at jointing–heading and filling stages. The greatest yield reduction was found under jointing–
heading drought stress, and the relative change rate in yield was two folds to that under drought stress at filling stage. This
relative yield change was primarily attributed to the relative change in grain number per square meter caused by water deficiency
during jointing–heading stage. Under high-strength drought stress, medium yield reduction dominantly resulted from water deficiency
during jointing–heading, with a two-fold probability to that under drought stress at filling stage (except for Yanzhou site);
whereas, slight and severe yield reductions at Shijiazhuang and Tianjin sites resulted from early (jointing–heading) drought stress
and those at Yanzhou and Xinxiang sites were attributed to either early (jointing–heading) or late (filling stage) drought stress. At
Yanzhou and Xinxiang sites, the probabilities of slight yield reduction were similar under early and later drought stressed; however,
water deficiency at filling stage resulted in severe yield reduction. These results indicate that irrigation is important not only
from jointing to heading but also at filling stage of winter wheat in the southern area of the Huang-Huai-Hai Plain.