作物系数是估算作物需水量的一个重要参数，科学地确定作物系数对准确计算农田作物耗水量、制定科学合理的灌溉制度及水利工程规划设计等具有重要的意义和实际应用价值。通过 Penmman-Monteith 公式、ENVIdata-DT草地蒸腾自动测量系统确定充分灌溉条件下毛乌素沙地青贮玉米及紫花苜蓿的逐日参考作物蒸散ET0与实际蒸散ETc，计算青贮玉米及紫花苜蓿的逐日作物系数，得出青贮玉米在整个生育期的作物系数均值为0.91，且在各生长阶段相差较小。苜蓿第一茬及第二茬作物系数随着时间的推进呈现递增的规律，且在6月27日第一茬收割之后，作物系数大幅减小，第一茬的作物系数均值为0.87，第二茬为0.85。并通过播后天数、累积积温逐日模拟苜蓿及青贮玉米生育期内的作物系数，结果显示，在以播种后天数、生育期累积积温为自变量的拟合模型中，决定系数 R2介于0.59~0.72，拟合效果较好。%Crop coefficient is an important parameter to estimate water requirement of crops. It has an important practical significance for agricultural production. The daily evapotranspirations of the reference crops of the silage maize and the alfalfa were determined in Maowusu sandy land using automatic measuring system of ENVIdata-DT for grassland transpiration. Then the daily crop coefficients of the silage maize and the alfalfa were calculated with Penmman-Monteith formula. Results showed that the mean of crop coefficient of silage maize in the whole growth period was 0.91. The difference of crop coefficient among different growth stages was small. Crop coefficient of alfalfa was increased with the increasing time in the first and second crops, and the crop coefficient sharply decreased after the first crop harvest on June 27, and average crop coefficient of the first crop was 0.87, and 0.85 for the second crop. A model was used to fit the crop coefficients of the silage maize and the alfalfa during growth period day by day with the number of days after sowing and accumulative temperature as independent variables. The results showed the model fitted the data of the crop coefficients well with the determination coefficient ofR2 in the range from 0.59 to 0.72.
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