Abstract
We studied the effect of hairy vetch planting on changes in soil physical properties and soybean early growth in a heavy clayey soil field. Hairy vetch (Vicia villosa Roth) was planted in an upland field converted from a paddy field from October, 2004 to June, 2005. Then soybean (Glycine max [L.] Merr.) seeds were sown in the field after cutting and incorporating of the hairy vetch plant. Hairy vetch grew vigorously and its roots elongated into the subsoil (about 40cm in depth). In the surface layer, the soil aggregate structure was developed by hairy vetch root growth compared with the control. There were large soil cracks from the surface to deep layer (until 50cm in depth) where the hairy vetch root elongated along with the soil cracks. In hairy vetch treatment, the water retention capacity of the soil was increased especially at surface layer by forming micro-pores or interaggregate pores. The rate of the soil drying after precipitation was faster than that in the control caused by the high water permeability of the soil with large soil cracks and transpiration of the hairy vetch plant. At 30d after soybean seed sowing, the dry weight of each part of soybean in hairy vetch treatment was higher than that in the control. The root activity of N absorption and N_2 fixation activity of the nodules in hairy vetch treatment were higher than those in the control. Therefore, it is concluded that soybean early growth is promoted in hairy vetch treatment where the physical properties of the heavy clayey soil are improved by planting hairy vetch.
