农田休闲期作物留茬对近地表风场的影响

茬是防治农田休闲期土壤风蚀的有效措施。该文利用野外观测数据，通过比较不同高度的4种作物留茬及冰草覆盖地表的风速廓线，分析各种处理下近地面风速和空气动力学特征，揭示作物留茬防止土壤风蚀的机制。结果表明：作物留茬降低了地面以上2 m高度内的风速，降低幅度与留茬高度成正比，与观测高度成反比。高度相同时不同类型的留茬比较，莜麦和小麦茬下风速降低幅度较大，植株稀疏的油菜茬和秸秆较细的胡麻茬的防风效果较差。同类作物不同高度的留茬覆盖下，地表空气动力学粗糙度随留茬高度的增加而增大，在莜麦、油菜和小麦茬高度达到15、30和15 cm时显著增大，是3种留茬防风的有效高度。可见，高度适宜的作物留茬能降低近地面风速，削弱侵蚀力，有效防治土壤风蚀。

Effect of crop stubble on wind field above field surface during fallow period of cropland

Crop stubble is effective for soil wind erosion control during fallow period of cropland, whereas more studies are needed on the mechanism of different crop stubble treatments to prevent wind erosion. Through field test, wind profiles for four kinds of crop stubble and grassland covered with Agropyron cristatum were observed. Two items of aerodynamic roughness and wind velocity were analyzed comparatively on all the underlying surfaces. The results indicated that compared with grassland, crop stubble treatments decreased wind velocities from the height of 0 to 2 m, and the decrement increased with the increasing of stubble height, decreased with the increasing of observed height. For the sparseness of oilseed rape stubble and thin stem of benne stubble, their wind-breaking effects were worse than wheat stubble and naked oats stubble. In addition, aerodynamic roughness of stubble field increased with the increasing of stubble height, until the heights reached 15, 30, 15 cm for naked oats stubble, oilseed rape stubble and wheat stubble, respectively. So those heights were regarded as the effective stubble heights for wind erosion control. In conclusion, crop stubble with reasonable height could control wind erosion by decreasing wind velocity and reducing near surface wind shear stress.