Evapotranspiration Model Of Winter Wheat-Summer Maize Based On Canopy Air Temperature Difference Under Different Water Conditions

Research on Crop Water Deficit Based on canopy temperature can grasp the law of crop water demand,and then formulate a reasonable irrigation system,which can optimize the allocation of limited irrigation amount in different growth periods of crops,and provide the basis for the optimization of irrigation system.In this paper,winter wheat summer maize rotation experiment was carried out in Daxing District of Beijing from 2019 to 2020.Different water treatments were set up to measure the growth index,soil moisture change and final yield of the two crops in the main growth period.At the same time,the daily evapotranspiration of the two crops was obtained by weighing lysimeter,and the crop canopy temperature was continuously observed at different times every day The S-I model parameters of winter wheat and summer maize under different water conditions were determined,and the differences of different treatment parameters were analyzed.The calibration results in 2019 were verified by the data obtained from repeated experiments in 2020,and the crop evapotranspiration calculation suitable for Daxing District of Beijing was established The model provides a basis for estimating evapotranspiration,and is helpful to explore better irrigation system and alleviate the imbalance of agricultural water supply and demand.The main conclusions are as follows:(1)The results showed that the soil moisture of winter wheat and summer maize fluctuated with irrigation,and the change range of shallow soil moisture content was larger than that of deep soil layer;the temperature difference between canopy and air increased first and then decreased with time in 1 day,and the difference was obvious at noon between different water treatments;the time of reaching the peak value of Winter Wheat in different growth stages was different,but it was later than 14:00 in the whole growth period The relationship between plant height,leaf area index and canopy air temperature difference is quadratic trinomial,and the correlation between plant height and canopy air temperature difference of winter wheat is weak,and that of leaf area index and canopy air temperature difference is good;the correlation between plant height and canopy air temperature difference of summer maize is good,and that of leaf area index and water stress is good The results showed that there was a good correlation between the canopy air temperature difference and the three factors of production;(2)The crop coefficients of winter wheat were Kc ini=0.4,Kc mid=1.1,Kc end=-0.15;summer maize were Kc ini=0.35,Kc mid=1.4 and Kc end=0.45,respectively the daily evapotranspiration of the treatment with high water content is always greater than that of the treatment with low water content,and the daily evapotranspiration of the treatment with large irrigation amount is always greater than that of the treatment with small irrigation amount;(3)The variation range of model parameters a and b was different among different treatments of winter wheat and summer maize,but the highest R2 appeared at 13:00.At this time,the model parameters of the two crops were:winter wheat a=1.082,b=-1.127,summer maize a=1.588,b=-1.363;water stress had different effects on the range and trend of model parameters.Through the repeated test in 2020,the regression coefficient and R2 of different treatments are all above 0.7,the root mean square error(RMSE)is less than 1,and the consistency coefficient d is 0.9 The above shows that the model based on the data obtained in 2019 can better estimate the daily evapotranspiration,and the ETd calculated by the model is more accurate,which can be used to estimate the farmland evapotranspiration in Daxing District of Beijing,and provide the basis for evapotranspiration estimation.