Study On The Field Evapotranspiration Measurement And Calculation

Corp evapotranspiration is a continuous process which happened in soil-plant-atmosphere-continuum, is the main form of water consumption on farmland, it is the basic basis of guiding agricultural drainage and irrigation, monitoring agricultural drought, and improving the efficiency of water use. Determine and estimate crop evapotranspiration accurately have been highly appreciated by the domestic and overseas. This paper uses measured dates of spring corn and winter wheat between2010and2011by large-scale weighting lysimeter, dates form automatic weather station at the same time, and the meteorological datas between2006and2007form Nanjing station. The airticle analyzed Penman-Monteith model and its radiative item. the crop evapotranspirations of spring corn and winter wheat which measured by lysimeter were also analyzed.Crop coefficients were estimated in view of measured dates.The airticle researched.The influence factors of evapotranspiration, established some simple crop estimating models on the supported condition of some datas. The oonclusions are as follows:(1)The radiative item occupied a large porprotion in the reference crop evapotranspiration, and the good correlation can be found between the reference crop evapotranspiration and the radiative item. Estimating the radiative item accurately is very important.(2) According to the different values of as and bs, which are derived form Nanjing station and FAO56, the result of the net radiation and the reference crop evapotranspiration were greatly different.So in allowable areas, we should revise the parameter values of as and bs according to the local actual radiation data, in order to get higher precision of the reference crop evapotranspiration.(3)On the condition of the deficiency of the daily average meteorological data, we can use the monthly average meteorological data to estimate reference crop evapotranspiration instead of it; especially in high temperature, strong radiation, long sunshine of the second half year, the difference between the calculated values will greatly decrease.(4) The diurnal variation of spring corn evapotranspiration in the whole growth period showed unimodal. The diurnal variation of winter wheat evapotranspiration in the whole growth period showed the trend of a twin peaks. The crop coefficient of spring corn in the whole growth period which was estimated in Nanjing area is0.94, and the crop coefficient of winter wheat in the whole growth period is0.93. As regards to the spring corn and winter wheat, net radiation affects evapotranspiration mostly. The influence of air temperature, relative humidity, soil moisture content and soil temperature to evapotranspiration are different because of the different type of the crop. The influence of wind speed to evapotranspiration is not obvious mostly.