Effects of root growth on physicochemical properties of soil profiles and komatsuna productivity in a wild oat cover-crop system

抄録

The root systems of cover crops have been reported to reduce soil erosion and N loss. However, the effects of cover crops on the physicochemical properties of the entire soil profile are less well known, particularly in Andisols. Therefore, we examined the effects of winter cover crop of wild oat (WO) on the soil profile physicochemical properties and main crop yields in comparison with conventional farming (CF) systems (i.e., without cover crops) as controls in Andisols, Japan. Vertical root distribution and soil physicochemical properties at 0–100-cm depths were determined for each depth. As the main crop, the yields of komatsuna (Japanese mustard spinach) were measured over 2 years. In the WO field, which exhibited a large number of cover-crop roots, bulk density and compactness were reduced in top and subsurface horizons, exchangeable K⁺ concentration was reduced in deeper horizons, and NO₃^--N and exchangeable K⁺ concentrations were increased in topsoil. These results suggested the WO roots improved the soil physical properties in subsurface horizons and reduced N and K loss. Furthermore, incorporating WO residues enhanced the topsoil physical properties and supplied it with N and K. The fresh komatsuna yields in the WO field were higher than those in the CF field. In addition, the soil horizons with a large number of komatsuna roots expanded to a 0–30-cm depth in the WO field, and was thinner in the CF field. These results suggested that the improvement of physical properties and N and K concentrations in the top and subsurface horizons (0–30-cm depth) by WO introduction contributed to the increased komatsuna yields. Overall, we concluded that the WO cover-crop system influenced physicochemical properties of the soil profile at a 0–100-cm depth through root growth and incorporation of WO residue, which improved productivity of the main crop.