Research On The Decision-making Method Of Winter Wheat Irrigation Time Under Limited Water Supply

The severe shortage of water resources not only affects human life,but also limits the development of agriculture.For agricultural development,the effective use of limited water is a measure of water-saving agriculture and an important way to improve the efficiency of crop water use.In this paper,the dynamic change process of water,soil temperature and yield of winter wheat is simulated based on the soil hydrothermal coupling model and crop growth model based on the winter wheat of Huoquan Experimental Station in Shanxi Province.Based on a long series of meteorological data,five typical years were selected to optimize the irrigation system,and evapotranspiration models under different irrigation quotas were established to compare with empirical irrigation methods for irrigation forecasting.The yield and benefit of winter wheat in the past ten years were analyzed,and the optimal irrigation decision-making method of winter wheat was finally determined.（1）A relational formula including cumulative evapotranspiration and cumulative effective precipitation is proposed.This formula can be used for limited water supply irrigation forecasting,and can also be used to determine the irrigation time in the forecast of adequate water supply irrigation,which is called the evapotranspiration method.This method is called the evapotranspiration method.The parameter values of three irrigation quotas（45mm,75mm and 120mm）determined based on the evapotranspiration irrigation method are given.When the irrigation quota is 45mm,the parameters K=0.6741,M=27.158,c₁=0.1639 and c₂=0.0985;When the irrigation quota is 75mm,the parameters K=0.8425,M=39.348,c₁=0.2728 and c₂=0.1155;When the irrigation quota is 120mm,the parameters K=1.3481,M=74.917,c₁=0.4501and c₂ 0.1237.The parameters K、M、c₁ and c₂ all show an increasing trend with the increase of irrigation quotas.Parameter c₁ increases significantly.（2）The calibration and test of soil water-heat coupling model and PS123 crop growth model showed that the obtained determination coefficient was high,indicating that the parameters were reasonable.Taking winter wheat at Huoquan Experimental Station in Shanxi Province as the research object,the soil moisture content and yield were simulated and calculated by using the soil hydrothermal coupling model and the crop growth model,and the model parameters were determined.The fitting effect between the measured value and the simulated value of soil moisture content is good,and the coefficient of determination is 07662.The coefficients of the simulated and measured values of dry matter weight of panicles and aboveground dry matter weight were 0.9695 and 0.9433,respectively.The coefficient of determination between the simulated dry weight value and the measured value of the grain of winter wheat was 0.9621.The coefficient of the soil hydrothermal coupling model parameter verification result can reach more than 0.6.The determination coefficient of the validation results of crop growth model parameters can reach above 0.9,and the results show that the calibration parameters are reasonable.（3）Based on the long series of meteorological data of Linfen City（1958-2019）in Shanxi Province,the frequency analysis of irrigation water demand during the growth period of winter wheat was carried out,and five typical years of 5%,25%,50%,75%and 95%were determined.（4）In order to find the optimal irrigation time,seven different sets of initial values of the irrigation time were selected and the evolution algorithm in the Excel Programming Solution Tool was used.The irrigation time of a certain irrigation quota in five typical hydrological years is optimized and calculated.The optimal irrigation system for winter wheat is finally determined by taking the maximum benefit as the target function until the maximum benefit is stopped.（5）Considering the randomness of the interannual meteorological factor changes,the meteorological data of Linfen City in Shanxi Province for nearly ten years was selected.The evapotranspiration method model is compared with the production increase benefit determined by the empirical irrigation method model.The results show that the irrigation quota is 45mm,75mm and 120mm.When irrigating water once,the evapotranspiration model increased by0.6%,6.7%and 7.9%respectively compared with the average ten-year increase benefit of the empirical irrigation model.When irrigating secondary water,the evapotranspiration model increased by 27.1%,27.3%and 21.6%respectively compared with the average ten-year increase benefit of the empirical irrigation model.When irrigating tertiary water,the evapotranspiration model increased by 25.3%,16.8%and 4.6%respectively compared with the average ten-year increase benefit of the empirical irrigation model.