The Study on Crop Evapotraspiration and Crop Coefficient in Hetao Irrigation District of Inner Mongolia

Crop evapotranspiration and crop coefficient is an important basis for reasonable irrigation and water resources management, and agricultural significance. In this paper, the Bowen ratio energy balance method, evapotranspiration and crop coefficient of different methods of calculation of the water balance method and FAO56 recommended crop coefficient method Hetao different crops (corn, sunflower, wheat and bare land). By analyzing, draw the following conclusions: 1) the application of five different methods to calculate the reference crop evapotranspiration results essentially similar results closest to the FAO Penman method and the Penman-Monteith (PM) method, followed Priestley-Taylor (PT) Law and Hargreaves-Samani (HS) method, PT method calculation result of majority is greater than the PM method, while the majority of HS method results is less than the PM method IA method calculated results are relatively stable. Derived through the analysis, the five kinds of methods the ET0 in the dry season is relatively stable, and each method of calculation results of absolute deviation is small. FAO Penman method is basically similar FAO56 PM method applies to most climatic conditions; the HS method applicable in smaller temperature difference between the regions ET0; the IA Act applies to relative humidity, radiation small areas; PT method is suitable humidity than small regions. 2) period Sunflower fertility (in addition to the early seedling stage), the total water demand of 252mm, wheat throughout the growing period (except the seedling stage outside) the total water demand 512.2mm; peak water demand period in late May in late June; overall corn throughout the growing period of water requirement rules parabolic 607.9mm total water demand throughout the growing period. 3) different crops crop coefficient differences at the same stage, this major crop plant height and soil moisture conditions and other factors. In the early stage of crop growth, the average crop coefficient values ??of different crops were: corn 0.5, sunflower 0.3, wheat 0.4; mid-average crop coefficient for crop growth were: corn 1.15 Sunflower 1.17 wheat 1.13; late to crop growth, due to the aging crop, yellow leaves, transpiration rate decreased crop coefficient in decline. 4) application of single and double crop coefficient method to calculate the actual evapotranspiration results sometimes close, sometimes large deviations, but the overall trend is more consistent. The two methods have a high correlation, R2 is greater than 0.7. Dual crop coefficient approach BREB method calculated throughout the growing period of maize, wheat and sunflower average relative error of 20%, 4%, 2%; water balance method to calculate the relative error of the results with BREB law sometimes large and sometimes small, generally the crop into the growth of the late results of large deviations. 5) in corn throughout the growing period, soil evaporation changes with the degree of crop cover and soil moisture content. Inversely related to soil evaporation and leaf area index overall leaf area index between 0 to 3, with higher E / ETc, both power function. Surface soil moisture and E / ETc's correlation coefficient highest when of LAI gt; 3, the E / ETc with the increase of the surface soil moisture content increases, and the moisture content was quadratic polynomial relations. 6) Surface Evaporation diurnal variation curve showed a single peak the maximum two o'clock in the afternoon. Positively related to soil evaporation and air temperature and relative humidity were negatively related, was positively correlated with the soil temperature at 1cm. Soil evaporation and temperature, relative humidity and soil temperature correlation, multiple correlation coefficient of 0.95.