The Study On Crop Evapotraspiration And Crop Coefficient In Hetao Irrigation District Of Inner Mongolia

Crop evapotraspiration and crop coefficient is the important basis of rational irrigation and water resourse management, and there is important significance in the agricultural production. This study used Bowen ratio energy balance method, soil water balance and crop coefficient of FAO56 to calculate the evapotraspiration and crop coefficient of three kinds of main crops in Hetao irrigation area district of Inner Mongolia. According to analyse, got the main conclusion as following:1) The results of ET0 that were determined by five different methods were almostly similar. The results of Penman method was most similar to Peman-Monteith, the second was Priestley-Taylor and Hargreaves-Samani, the results of Priestley-Taylor was greater than Peman-Monteith, while Hargreaves-Samani was less than Peman-Monteith, the results of Irmark-Allen were stable. According to analyse we can know, five different methods are stable during less rainy seasons, and the error is less. Both FAO Peman and Peman-Monteith can be applicable to most climate condition; Hargreaves-Samani is adequate for the area of lesser difference in temperature; while Irmark-Allen can be used in the district of larger relative humidity and lower radiation; Priestley-Taylor is adapt to the district of lower relative humidity .2) The total water requirement of sunflower is 252mm during whole development stage except seedling stage, and wheat is 512.2mm, the peak time of water requirement is in the last of May and June; the total water requirement of maize is 607.9mm, and the tendency of water requirement regulation is parabola in shape.3) The value of crop coefficient has relationship with crop height and soil moisture. In the early stages of crop development, the mean value of crop coefficient of different crop is 0.5(maize), 0.3(sunflower), 0.4(wheat) respectively. In the middle stage, the mean value is 1.15, 1.17, and 1.13 respectively. In the anaphase, due to the crop aging and leaf wilting, the transpiration rate is descended, the crop coefficient is decline.4) The deviation value of actual evapotraspiration that calculated by single and dual crop coefficient is related to the time, but there is stranger correlation in the majority periods, and R2 is more than 0.7. The mean relative error of maize, wheat and sunflower that used dual crop coefficient and BREB is 20%, 4% and 2% respectively; the error between soil water balance and BREB is uncertain, and the amount of deviation becomes larger when the crop gets into the late stages of development.5) During the whole development stages of maize, the variation of soil evaporation has the relationship with crop coverage and soil moisture. It has inverse correlation between soil evaporation and leaf area index (LAI), and there is higher correlation between LAI and E/ETc when LAI is less than 3, and they are power fuction in shape. The related coefficient is maximal between the top soil moisture and soil evaporation, when LAI is more than 3, E/ETc is increased with top soil moisture'increase, and they are quadratic polynomial in shape.6) The daily variation curve of soil evaporation is single-peaked; the maximum value is in the 14:00, and it has positive correlation with temperature and soil temperature, while there is inverse correlation with relative humidity. There is good relationship between soil evaporation and temperature, relative humidity and soil temperatue, and R2 is 0.95.