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...