耕作地表土块状况及其对近地表风场的影响

为深入理解非可蚀性土块吸收风能、降低侵蚀力的机制,利用野外风速资料,对半干旱区农田传统耕作模式下犁耕、耙耱及抹平等的地表土块大小、土壤表面粗糙度、近地表风速及空气动力学特征进行了研究。结果表明,犁耕后农田土块长、宽、高均在15 cm以上,盖度为27.67%,耙耱、抹平后土块大小和盖度显著降低,抹平地表土块盖度仅为2.13%;土块的破碎导致土壤表面粗糙度降低,近地表风速增大;与犁耕地表比较,耙耱后土壤表面粗糙度降低34%~64%,抹平后降低幅度甚至在90%以上;耙耱抹平后地表以上0.5 m高度内风速显著增大,空气动力学粗糙度由1.1 cm降低至0.05 cm,侵蚀力增强。因此认为,合理选择犁耕、耙耱和抹平的时间对农田风蚀防治有实际意义。

Dynamic change of soil clods and its influence on wind field above field surface

Soil clods caused by plowing are the main roughness elements for wind erosion control in cropland of arid and semiarid regions, especially while no crop straw left on soil surface in fallow. However, the following operation of harrowing and milling destroy soil clods, which make its benefit of wind erosion control disappeared. Through field test, the size and cover fraction of soil clods under three kinds of soil surface, including just after plowing, harrowing, and milling respectively, were observed. Roughness of soil surface, decrement of wind velocities in the height of 0--3 m, aerodynamic roughness and friction velocity were calculated through analyzing soil surface fluctuation and wind velocity data. The results indicated the length, width, height of soil clodswere all larger than 15 cm, and its cover fraction reached 27.67% after plowing operation, while after harrowing and milling operation the size and cover fraction of soil clods decreased significantly, especially after milling operation the cover fraction of soil clods was only 2.13 %. Compared with after plowing, soil surface roughness decreased by 34 % --64 % after harrowing and by more than 90 % after milling, and wind velocities in the height of 0-- 0.5 m increased significantly. Aerodynamic roughness was reduced from 1.1 cm to 0.05 cm after plowing surface of soil was milled, which made its benefits on wind erosion control obviously decreased. So choosing the time of plowing, harrowing and milling reasonably was important for wind erosion control on cropland of arid and semiarid regions.