在农田周围营造防护林带,是改善农田水分循环、防止风沙干旱的一个极为有效的措施,防护林带会使农田小气候发生显著变化。一般来说,在辐射型天气条件下,防护林带减弱了近地空气层的乱流交换作用,白天比旷野温度低,夜间则稍高。林带内白天虽然土壤蒸发比旷野小些,但农作物蒸腾量比旷野大,总的蒸散量比旷野大,可使温度降低。夜间,林带內蒸发量比较小,相旷野的热量差异不大。此外,林带与农田的空气交換,促使田间白天降温,夜间升温。早上和傍晚由于林带的遮阴,还可降低靠近林带农田的温 The construction of shelterbelt around farmland is an extremely effective measure to improve the farmland water cycle and prevent the wind and sand from droughts. The shelterbelt will make a significant change in the farmland microclimate. In general, under radiation weather conditions, shelterbelt attenuates the turbulent exchange of the near-Earth air layer, with lower temperatures during the day than in the wilderness and slightly higher at night. Although the soil evaporates more during the day in the forest than in the wilderness, the crop transpiration is larger than that in the wilderness and the total evapotranspiration is larger than in the wilderness, which can lower the temperature. In the night, the evaporation in the forest belt is relatively small, and there is not much difference between the heat in the wilderness. In addition, the exchange of air between the forest belt and the farmland led to a decrease in the temperature during the day and a warming during the night. Morning and evening shelter due to the forest, but also can reduce the temperature near the forest belt farmland