环境因子对土壤水分蒸散的影响

EFFECTS OF ENVIRONMENTAL FACTORS ON THE EVAPOTRANSPIRATION OF THE SOIL WATER

在有作物生长的条件下,土壤散失到大气中的水分主要通过土壤表面蒸发和作物叶面蒸腾两种方式进行,二者之和称为土壤水分蒸散。由于作物冠层的遮荫作用,作物覆盖下土壤水分的蒸发强度与裸土情况下显然不同。本文建立了土壤水分蒸散率的计算公式,并对几个环境因子的影响进行了讨论。计算结果表明,冠层净辐射强度和空气饱和差对蒸散率影响较大,而气温和风速的影响相对较小。当冠层净辐射强度和空气饱和差增大时,蒸散率和日蒸散总量的增加均较为明显。另外,作物的叶面积指数对蒸散也有较大的影响,同时它对蒸发和蒸腾在蒸散中所占的比重影响很大,叶面积指数增大时,叶面蒸腾所占的份额增大,而蒸发所占的份额相应地减小。

There are two ways for the soil water to diffuse into the atmosphere when the soil surface is covered with crops. The one through the soil surface is called evaporation; the other through the surfaces of the crop leaves is called transpiration. The total of evaporation and transpiration is usually defined as the evapotranspi-ration of the soil water. With crops growing in the soil, the evaporation is quite different from that of the bare soil due to the shading effect of the crop canopy. The calculation formula of the evapotranspiration rate of the soil water was deduced and some discussions on the influences of several environmental factors were conducted. The calculation results showed that the neat radiant intensity Rn and the saturation difference of the atmosphere Da exert significant influences on the evapotranspiration while the effects of the atmospheric temperature Ta and wind speed Vz are relatively small. With the increase of Rn or Da, an obvious rise in the evapotranspitation rate and the total evapotranspiration of the day occurs. Moreover, the bigger the leaves area index(LAI), the bigger the proportion of the transpiration and the smaller the proportion of the evaporation.