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.

三重県北中部に位置する水田土壌4断面を対象に，断面形態，理化学性および土壌分類について調査した。4断面はいずれも沖積平野に位置し，日本土壌分類体系では沖積土大群（ペドンM01：グライ化灰色沖積土，ペドンM02：表層グライ化灰色沖積土，ペドンM03：普通灰色沖積土，ペドンM04：普通灰色沖積土），包括的土壌分類第１次試案（包括１次試案）では灰色低地土大群（ペドンM01：細粒質グライ化灰色低地土，ペドンM02：細粒質表層グライ化灰色低地土，ペドンM03：細粒質普通灰色低地土，ペドンM04：粗粒質普通灰色低地土），World reference base for soil resources 2014（WRB 2014）ではFluvisols（ペドンM01：Eutric Gleyic Pantofluvic Fluvisol (Pantoloamic)，ペドンM02：Eutric Pantofluvic Fluvisol (Anoloamic)，ペドンM03：Eutric Pantofluvic Fluvisol (Pantoloamic)，ペドンM04：Eutric Pantofluvic Fluvisol (Endoarenic)）に分類された。ペドンM01では14～20 cm深，M02では13～24 cm深において灌漑水由来と考えられるグライ特徴が確認された。表層にグライ特徴をもつ土壌は，水田高度利用における畑作において作物への悪影響が懸念されるため，分類名においてその特徴を適切に表現できる分類体系は有用と考えられる。ペドンM03とM04は水田表層以外の特徴層位を持たず，日本土壌分類体系では同じ分類名となった。一方，包括１次試案では統群において土性の違いを組み込むことによって，WRB 2014では土性とその分布の違いについてSupplementary qualifiersならびにSubqualifiersを付すことによって区別された。