Study On Annual Evapotranspiration Of Mature Jujube Orchard Under Micro Sprinkler Irrigation In Arid Oasis

With the steady implementation of the Rural Revitalization Strategy,jujube has become the core of the characteristic forest and fruit industry in Aksu,Xinjiang,promoting farmers’income,expanding employment channels and improving the oasis ecological environment.At present,the shortage of water resources and the irrigation system with low water use efficiency limit the sustainable development of local jujube industry.Therefore,this study selects the micro spray jujube orchard in the southern suburb of Aksu City,Xinjiang as the experimental field,takes the mature gray jujube planted in 2000 as the research object,and collects the actual data of the jujube orchard through Eddy covariance system,needle stem flow meter,self-made micro lysimeter,soil moisture measurement system（TRIME）,intelligent moisture content,small automatic weather station and other instruments,The characteristics of water and heat flux and evapotranspiration law of jujube orchard in the whole year are analyzed,and the correlation model between stem flow rate of jujube tree and meteorological factors is constructed.The purpose is to study the correlation between annual evapotranspiration law at point（jujube tree）—area（jujube orchard）scale,determine the evapotranspiration of jujube orchard in growth period and dormancy period,and provide basis for efficient and water-saving irrigation system of jujube tree.The conclusions are as follows:（1）It was found that solar radiation had the most significant effect on stem velocity rate during growth period,and the correlation coefficients were R_D1=0.924,R_D2=0.939,R_D3=0.943 and R_D4=0.915.During dormancy period,air humidity had the most significant effect on stem velocity rate,and the correlation coefficients were R_C1=0.699,R_C2=0.923,R_C3=0.841,R_C4=0.918 and R_C5=0.618.The maximum duration of stem flow activity in the daytime of jujube trees in growth period and dormancy period was 14h and 9h.There were significant differences in the variation law of stem flow at night.The peak range of stem flow rate is 12:00-15:30 in growth stage.While the stem flow rate in dormancy stage shifts with each stage of dormancy.The peak range of stem flow rate is 3:00-6:00 in C1 and C2 stages.that range of stem flow rate is 7:00-10:00 in C4 and C5 stages.Water consumption in each period of growth periods:D3>D4>D2>D1.Dormancy periods:C1>C5>C3>C2>C4.（2）The accuracy of measuring evapotranspiration in jujube orchard is analyzed by Eddy covariance method and water balance method.The error of the two calculation methods are small and within the allowable range.Therefore,the data of evapotranspiration monitored by Eddy covariance system in each period of jujube orchard has high reliability.The annual energy closure of jujube orchard is 82.07%.Under the 0.5h scale and daily scale,the energy closure is 60%～100%.The relationship between energy balance and closure degree of jujube orchard in growth stage and dormancy stage is as follows:leaf bud stage>flowering>fruit maturity>fruit enlargement.Prophase of dormancy>breaking dormancy>dormancy transition period>mild dormancy>deep dormancy period.（3）The transpiration in the whole growth period is 403.2 mm,accounting for 75%of the evapotranspiration.The proportion of transpiration in each growth period is fruit maturity>fruit enlargement>flowering>leaf bud stage.The linear regression equations of stem flow system and Eddy covariance system for measuring evapotranspiration of jujube orchard at daily scale and irrigation cycle scale are Y₁=0.965X,R²=0.832,NSE=0.78,RSR=0.47;Y₂=0.964x,R²=0.674,NSE=0.67,RSR=0.57.The total difference of evapotranspiration measured by stem flow system and Eddy covariance system is 4.98 mm,and the relative error is 0.93%.There is a good correlation between jujube evapotranspiration measured by stem flow system at different time and space scales and jujube orchard evapotranspiration measured by Eddy covariance system.The evapotranspiration measured by stem flow system can be converted to jujube orchard scale evapotranspiration.