河西绿洲区春小麦蒸腾蒸散的变化研究

Research on Variations of Evapotranspiration and Transpiration from Spring Wheat Fields in Hexi Oasis Areas

在甘肃张掖绿洲区利用浮力称重式蒸散仪对春小麦蒸散量进行了测定，对蒸散量的日变化和季节变化特征进行了论述。研究结果表明：小麦田的日蒸散量在白天１２∶００～１６∶００达到最大，夜间２０∶００～０８∶００最小甚至呈负值。灌溉前后蒸腾强度出现峰值的时间有所变化。但灌溉以后，蒸腾与蒸散量均呈增大趋势。日蒸散量随着净辐射的增加而加大。在小麦不同的生育阶段，蒸散量有所不同，小麦拔节以前较小，拔节以后开始增大，灌浆期达到最大。

During the periods of observations on interaction processes between atmosphere land (HEIFE), the rate of evapotranspiration( ET ) from oasis spring wheat fields has been measured by a hydraulic evapotranspirometer(small lysimeter). The area cross section of a column of undisturbed soil inside the instrument is 0 2 m 2 with a depth of 1 5 m. This instrument can accurately measure the ET more than 0 1 mm. The ET of spring wheat is small before the elongation stage, however it obviously increases after irrigation. And it increases from the elongation to milk ripe stage. The irrigation at these stages has less effect on the ET because of the extensive growth of root system downward and the increase of water absorbed by the root system. The ET decreases with getting close to the mature stage. At night (20∶00～08∶00) the ET of spring wheat is small or negative throughout the growing season. In the daytime, the ET increases from 08∶00 and reaches a maximum value between 12∶00 and 16∶00, then decreases. The peak values at different stages are not the same. Generally the ET is small before the elongation and gets to the maximum at around the heading stage. The net radiation has large influence on the ET that increases with net radiation. The ground surface, air and leaf temperatures exert their influence on the diurnal variation of the ET . The soil moisture influence greatly on the transpiration of spring wheat that increases with the soil moisture in the daytime. When the soil moisture was high, the transpiration rate went up to maximum with only one peak value(about 13∶00). When the soil moisture was small, for a obvious decrease in the rate of transpiration at 12∶00～13∶00, there were two peaks of transpiration at 12∶00 and 16∶00, but the second peck was small than the first. The diurnal variations of transpiration of spring wheat before and after irrigation were not equal to each other. The transpiration reached a maximum value on the period from 11∶00 to 13∶00 before irrigation, however the peak is delayed until 15∶00 after irrigation. In addition, the transpiration in the period from 15∶00 to 21∶00 becomes larger obviously by irrigation. At the elongation stage the peak values of ET and transpiration before irrigation did not appear at the same time. This implies that the soil surface evaporation in this period dominates the ET .