Abstract
In the paddy fields of medium- and coarse-textured Gray Soils subsoiling was carried out at 2 m distance in a half area of a 34 a plot, and pasture plants were cultivated for two years. After one crop season, soil structures in the plowed layers changed into grain states, in the subsoil layers, especially in the subsoiler passing strips, small cavities and soil cracks were highly developed. In the non-subsoiler areas, regrowth of the grass was hindered by excessive water damage. In the field of Gravelly Lowland Soils, subsurface drainage systems were prepared in 36 a × 2 plots by installing a drain pipe connected with 5 trenchs filled with rice husks at 20 m distance and subsoiling at 2 m distance. After the passing of winter, eddoes were cultured. This soil had high clay content, Andorols, and a traffic pan layer, but the drainage systems worked effectively. Soil water mainly percolated to the depth below the drain pipe and was partially collected by the pipe at the time the snow melted. After cultivating the eddoes, the soil structures of the plowed layers changed into grain and clod states, but the colors of the soils profile did not change. In the subsoil layer, cavities and soil cracks increased, and fine soil cracks were formed along the strips of subsoiling. The growth of eddoes was related to the gas phase ratio of the plowed layers. Chemical components of the plowed layers were almost unchanged by the subsurface drainage and upland use ; the contents of NH_4^+ and Ca^<2+> were somewhat lowered.
