| 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 of0～3m?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 clods were all larger than15cm?and its cover fraction reached27．67％ 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 by34％～64％ after harrowing and by more than90％ after milling?and wind velocities in the height of0～0．5m increased significantly．Aerodynamic roughness was reduced from1．1cm to0．05cm 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． |