Temporal Characteristics Of Transpiration And Evapotranspiration Rate For Winter Wheat On The Loess Tableland

Evapotranspiration which consists of crop transpiration and soil evaporation is animportant link of the water cycle and water balance among the Soil-Plant-Atmosphere system.Separately calculating crop evapotranspiration is critical for precise water resourcemanagement and reasonable irrigation scheduling design. In this work, the temporalcharacteristics of evapotranspiration and transpiration for winter wheat on the Loess Plateauwere studied using dynagage sap flow sensors and lysimeter. The main conclusions are asfollows:In this period, the transpiration rate of winter wheat was influenced by the weathercondition. The daily curve of transpiration rate for the winter wheat exhibited a single peakon a sunny day; however, it became more complicated on cloudy and rainy days withpolymodal curve. The transpiration rate was positively correlated with solar radiation, weedspeed, and air temperature, but had a negative correlation with relative humidity. At the earlystage, the transpiration rate increased with surface temperature, but decreased at the late stageowing to the shortage of soil water content. After jointing of winter wheat, the ratio oftranspiration to evapotranspiration ranged from80.23%to83.41%.The daily curve of evapotranspiration on both sunny day and rainy day exhibited a singlepeak, but the peak appeared later in a fine day than in a rainy day (at about15:00on sunnyday and12:00-13:00on rainy day). Through studying the variation characteristics of the dailyand monthly evapotranspiration over the whole growth stage of the winter wheat, we foundthat the evapotranspiration rate was lower at the initial stage, but increased rapidly afterentering the development season stage, and it got the highest in May. The evapotranspirationcalculated with the water balance methods was lower than that measured by lysimeter.The reference evapotranspiration was calculated using FAO-56Penman-Monteith formula.The difference between observed evapotranspiration (ETc) and reference evapotranspiration(ET0) ranged with the variation of the growth stage of winter wheat. The variation Theobserved evapotranspiration cumulant is larger than the reference crop evapotranspirationcumulant at the middle growth stage of winter wheat, but smaller than reference crop evapotranspiration at other stages.