测定农田蒸发的试验研究*

本文阐述了中国科学院禹城综合试验站1986—1988年测定农田蒸发的联合观测试验概况,比较和评述所用的微气象学方法、水量平衡法、遥感技术和以Lysimeter为主的器测法等测试结果的优缺点及适用性。并给出了几种主要作物田的蒸发耗水量。

EXPERIMENTAL STUDY FOR DETERMINING EVAPOTRANSPIRATION OF THE FIELD

The author related the general situation about combined measurementt ex periment of the field evapotranspiration in Yucheng Experimental Station, Chinese Academy of Sciences during 1980-1988, and introduced the observation object, methods and the instrumentation, etc, in this paper. The author compared and evaluated the following methods. (1) Lysimeter's method,(2) Bowen ratio-energy balance approach (BREB), (3) energy balance-aerodynamic resistance method in relation to remotely sensed technique,(4) aerodynamic technique-layer gradient method. The results are as follows.1, The calculated value of evapotranspiration (ET) of the field by BREB method is 20% lower than the measured values with Lysimeter. The observed differences between BREB-estimated and lysimetrically-measurcd ET values may stem from four of the following causes. (1) underestimation or overestimation of Rn, G, △t and △e, (2) non-equality of Kb and Kw, (3) insufficient fetch, (4) overestimation of actural ET by Lysimeter. The author evaluated the applicability of the calculating ET values by BREB method.2. The author considers that Dr. Chen Jimin' s, excess resistance model and author's removed formula are better than other aerodynamic resistance-energy balance formulas, the relative error is about 11% in all stability conditions, compared with Lysimeter.3. The relative error of aerodynamic technique-layer gradient formnla is about 21% in stable condition, while in unstable condition, the error is larger.4. The author analysed the ET of some crop fields, the value of ET of the wheat field is more than 500 mm in the whole growing period (1987), the difference between ET and rainfall is about 400mm, the ET of wheat in spring is more than 300mm, but the rainfall only a few, the difference is over 200mm, so, the irrigation is necessary during the wheat growing season.Even though the ET of cotton and soybean are large (about 300-400mm), as it is rainy season in summer, yet the rainfall is large too, the difference between both ET and rainfall is only less than 100mm, If it is drought in summer (for example in 1986), the difference between ET and rain is more than 100mm and irrigation is necessary for these crops.