The Crop Coefficient Approach For Estimating Evapotranspiration Of Maize Harvested Green In The Forage Base

It is very important for us to determine reasonably crop evapotranspiration which relates to determining irrigation schedule and efficiency coefficient of water use. Many kinds of approaches have been used for estimating crop evapotranspiration,here,we use crop coefficient approach recommended by FAO. Since 2003,I have attended the key project,A Study of Scientific Allocation of Water Resources for Vegetation Construction in The Sandy Area Between Beijing and Inner Mongolia(50139040),supported by National Committee of Natural Science Foundation and have in charge of the irrigation experiment of maize under guidance of professor Chaolunbagen. The maize evapotranspiration has been estimated by single and dual crop coefficient methods under non-water stress and have-water stress condition. The crop coefficient methods have more advantage behaviors than other approaches have. It is recommended here for applying in agricultural activities in terms of our experience. Main section of this paper as follows: First,Comparison of ET0 which were calculated by different net solar radiation,such as they are estimated from solar constant,solar radiation measured and the measuring net radiation data. The methods which calculate ET0 at missing climatic data region have been presented. Second,The maize evapotranspiration accounted by single crop coefficient method under non-water stress condition and by dual crop coefficient approach under have-water stress and non-water stress condition. The variation of evapotranspiration during growing season was analyzed. The validity of two approaches was discussed and usefulness conditions of them have been emphasized. The method for determining the threshold values of soil water content at the root zone is also presented. Third,the paper studied the relationship between the ratio (ETe/ETc) and leaf area index,the relationship between soil evaporation and wind speed,and relative humidity,and solar radiation,and sunlight hours,and atmosphere temperature,and saturation water vapor pressure deficit. Understand the relationship between maize evapotranspiration and climate condition and physiology condition initially. Fourth,The soil evaporation mechanism at the initial growing stage has been studied by Two Stage Model for Soil Evaporation.