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.

Morphological and physicochemical properties of four pedons of paddy fields located on the northern and central areas of Mie prefecture, Japan were investigated, and the classification of them was examined. All of the four pedons were located on the alluvial plain, and they were classified into Fluvic soils in the Soil Classification System of Japan (Pedon M01: Gleyic Gray Fluvic soil, Pedon M02: Epi-gleyed Gray Fluvic soil, Pedon M03: Haplic Gray Fluvic soil, Pedon M04: Haplic Gray Fluvic soil), the Lowland soils in the Comprehensive Soil Classification System of Japan (Pedon M01: Fine-textured Gleyed Gray Lowland soil, Pedon M02: Fine-textured Epi-gleyed Gray Lowland soil, Pedon M03: Fine-textured Haplic Gray Lowland soil, Pedon M04: Coase-textured Haplic Gray Lowland soil), and Fluvisols in the World reference base for soil resources 2014 (Pedon M01: Eutric Gleyic Pantofluvic Fluvisol (Pantoloamic), Pedon M02: Eutric Pantofluvic Fluvisol (Anoloamic), Pedon M03: Eutric Pantofluvic Fluvisol (Pantoloamic), Pedon M04: Eutric Pantofluvic Fluvisol (Endoarenic)). In the pedons M01 and M02, gleyic properties which would be induced by reducing conditions under the influence of irrigation were observed in 14–20 cm and 13–20 cm (epi-gleyed layer). Such soils having epi-gleyed layers could give a negative impact on the growth of upland crops when they were managed and converted into upland fields. Therefore, a classification system which can appropriately express those characteristics would be useful. Pedons M03 and M04 had no diagnostic horizons other than paddy surface horizon, and they were classified into the same soil subgroup name in the Soil Classification System of Japan. On the other hand, they were classified into different soils at the level of Series Groups in the Comprehensive Soil Classification System of Japan by detecting differences in soil texture. Similarly, they were differentiated by giving different Supplementary qualifiers and subqualifiers related to soil texture and its distribution in the World reference base for soil resources 2014.