关键词: 绿洲, 春小麦, 蒸腾, 蒸散, 日变化

Abstract:

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 m² 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.

Key words: oasis, spring wheat, transpiration, evapotranspiration, diurnal variation