| Wheat is one of the three most important grain crops in China,and an adequate supply of water is a prerequisite for the normal growth of winter wheat and ensuring crop yield and quality.The Yellow Huaihai Plain is one of the major grain producing areas in China,and it is necessary to investigate the water demand pattern of winter wheat in the region with the increased risk of drought and flooding under the general trend of climate change.Based on the measured hourly evapotranspiration of a large-scale weighing evapotranspiration meter,this study divided the whole winter wheat fertility period into five typical fertility stages,and investigated the evapotranspiration characteristics and trends during the winter wheat fertility period,as well as the hourly evapotranspiration patterns of different winter wheat fertility periods under different weather conditions.The meteorological data provided by the weather stations in the experimental area were used to analyze the changes of meteorological elements during the fertility of wheat and to investigate the dominant factors affecting the evapotranspiration of winter wheat at different fertility stages.A representative reference crop evapotranspiration estimation model was selected and compared with the measured evapotranspiration values,and statistical indicators were used to evaluate each model and investigate the applicability of the reference evapotranspiration model in the winter wheat growing area in the huang-huai-hai plain.Finally,the accuracy of crop coefficient models for estimating winter wheat evapotranspiration under different soil moisture conditions and the status of winter wheat water use efficiency were investigated.Based on the weighing type evapotranspiration meter,three water deficit irrigation treatments were set,single crop coefficient and double crop coefficient models were selected,and leaf area index and soil evapotranspiration coefficient were analyzed under different irrigation treatments of winter wheat during the crop reproductive period to explore the accuracy of crop coefficient models for The simulation accuracy of crop coefficient model on evapotranspiration of winter wheat was investigated.The following main results were obtained:(1)In the three years of winter wheat fertility from 2016-2017,2017-2018 and 2018-2019,the total accumulated evapotranspiration was 614.97,647.79 and 598.85 mm,respectively,and the average daily evapotranspiration was 2.70,2.84 and 2.64 mm/d.The daily evapotranspiration of winter wheat in the three years showed a trend of increasing first and then decreasing throughout the fertility period.The daily evapotranspiration of winter wheat showed a trend of increasing and then decreasing throughout the whole growing period,and the differences in evapotranspiration at different stages of fertility were significant.The average evapotranspiration value of winter wheat from tillering to nodulation was the lowest in the entire reproductive period,with a three-year average value of 1.39 mm/d.The highest evapotranspiration value of 7.24 mm/d was observed from tasseling to filling stage,when the leaves were growing strongly.(2)Within each reproductive period,the daily transpiration of winter wheat was highest on sunny days(1.38-9.25 mm),followed by cloudy days(1.37-4.79 mm)and lowest on rainy days(0.57-2.97 mm).The evapotranspiration of the crop occurred mainly during the daytime,while the nighttime evapotranspiration was weak and the trend was stable with some negative values.From sowing to tillering,the evapotranspiration values of winter wheat leaves were the lowest in all weather conditions,with the mean hourly evapotranspiration values of 0.08,0.06 and 0.02 mm/h for sunny,cloudy and rainy days,respectively;from tasseling to filling,the highest evapotranspiration values in all weather conditions were 0.39,0.20 and 0.12 mm/h for sunny,cloudy and rainy days,respectively.ET in all weather conditions started to increase roughly at 07:00(standard solar time)and gradually decreased at about 18:00.(3)The correlation between meteorological factors and crop evapotranspiration was high in the early stage of winter wheat fertility,while in the late stage of fertility,crop factors gradually became the dominant factor affecting evapotranspiration.The correlation between meteorological factors and evapotranspiration of winter wheat was the highest,with R~2 reaching 0.624 and 0.618,respectively;the correlation between leaf area index and evapotranspiration of crop factors was the highest,with R~2 reaching 0.583.(4)A representative reference evapotranspiration model based on meteorological factors was selected for the study design of fully irrigated winter wheat treatment.Overall,the correlation between the measured daily crop evapotranspiration and the simulated evapotranspiration values obtained using the evapotranspiration meter was high throughout the winter wheat reproductive period.The models significantly underestimated evapotranspiration during the I to IV stages of winter wheat growth,while all models overestimated it during the V stage of winter wheat.The R2 values of evapotranspiration from the FAO-56 PM,H-S,P-T,Turc and D-K models ranged from 0.402-0.898,0.376-0.904,0.307-0.861,0.330-0.843 and 0.353-0.657,respectively,during the whole winter wheat growing period.56 PM>Turc>P-T>D-K.(5)The mean daily evapotranspiration measurements of winter wheat under T70,T60 and T50 treatments were 2.80,2.45 and 2.18 mm/d,respectively,and the simulated daily mean evapotranspiration values were 2.27,2.05 and 1.98 mm/d for the single-crop coefficient model and 2.68,2.34 and 2.07 mm/d for the double-crop coefficient model,respectively,during the whole reproductive period.In the early stage of winter wheat growth,both single and double crop models were able to simulate evapotranspiration accurately under wet irrigation;for deficit irrigation,the simulation accuracy of double crop model was higher,but there was still some error in the late stage of crop growth.(6)Under different irrigation treatments,the differences between leaf area indices were not significant in the early growth stage of winter wheat,and the differences in leaf area indices were the largest and reached a significant level in the period of vigorous growth of winter wheat.With the decrease of irrigation water,the yield composition index of winter wheat showed a decreasing trend.Compared with CK,T70,T60 and T50 reduced the water use efficiency of winter wheat by2.94%,7.35%and 11.76%,respectively,but the differences between CK and T70 were not significant,while both T60 and T50 treatments differed significantly from CK and T70. |
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