## 3 Results and Discussion
### Discussion  
In order to further analyze the reliability of the research results, the irrigation date determined by the study was compared with the actual local situation. From the research results, the reasonable irrigation of subregion I and II is mainly at the beginning of November and April. The irrigation of subregion I at the beginning of April is more important than that of the beginning of November of the previous year, while subregion II is the opposite. This is because the water shortage in the growth period accounts for 3/5 of the total water requirement, and the annual change is large. The precipitation in most years can not meet the water requirement of wheat growth. The water shortage stages are mainly in the seedling stage and the filling stage. Precipitation during the seedling period (from tillering to jointing) continued to decrease from July and August in the rainy season, which was very unfavorable for the development of tillering and jointing. From the perspective of precipitation in the growth period, July and August are rainy seasons, with relatively large rainfall. The water requirement for wheat seedling can be basically guaranteed, while the rainfall in early November and early April of the next year is not guaranteed. Therefore, irrigation should be carried out during these two stages. By comparing the effects of irrigation in winter and spring, it can be found that the effect of irrigation in spring on winter wheat yield in subregion I is more significant, while that in subregion II is the opposite, which may be due to the more drought in subregion I and the serious water shortage in jointing stage of winter wheat. According to the research results, subregion III and subregion IV should be irrigated at the beginning of December or the beginning of January of the next year. This is because winter irrigation can promote the growth of tillering, the growth of roots, and meet the water demand of initial wheatear development. Timely winter irrigation can stabilize the ground temperature, reduce the temperature difference between day and night, and play an important role in cold prevention and seedling protection. From March to May of the next year, the precipitation in these two subregions is higher than that in subregions I and II, so irrigation is generally not required. Compared with the reasonable irrigation in winter in subregion III and subregion IV, it can be seen that the period of irrigation in subregion IV is relatively early, which may be due to the fact that subregion IV is in the west of subregion III, the temperature in winter is lower than that in subregion III, and if the irrigation period is late, it is easy to cause freezing on the surface of soil in the coldest January, and then cause freezing damage to winter wheat. The above analysis results are basically consistent with local farmers' agricultural proverbs and irrigation habits of local farmers, and can be used to guide the irrigation of local winter wheat [23; 24]. The supplementary effect of precipitation on soil water content is the same as that of irrigation, but the solar radiation value on the rainy day is smaller than that on the non-rainy day, and the temperature is slightly lower than that on the non-rainy day. Therefore, there will be a slight error in the optimal irrigation period determined by this method, but it will not affect the determined optimal irrigation period on the whole. The method for determining the regional irrigation period proposed in this paper has the advantages of fewer data required, robust and reliable results, and simple and practical, although it is still unable to determine the corresponding exact irrigation amount in each period, there are certain limitations, but considering the fact that the amount of available water for irrigation in many dry areas is limited, only a small amount of available water can be used for irrigation. Therefore, the results of this study have important application value to determine the deficit irrigation period with small amount of water in large regions.