Soil Dressing with Alluvial Soil Materials: “Dorotsuke”

Abstract

Dorotsuke was a winter off-season chore of the farmers in the Omiya upland area alongside the Arakawa River from November to May. Farmers transported alluvial soil material onto the uplands by horse, left it to mature around their fields, and then used it a few years later. The application of alluvial soil materials to Andosol fields had the effect of supplying available phosphates, and increasing yields of barley. Periodic long-term application of Dorotsuke, together with ploughing, created thick anthropogenic epipedons consisting of a mixture of alluvial soil material and Andosol topsoil. The soil profile exhibits vertical weakening of the andic properties, such as low bulk density, high content of short-range-order minerals, and high phosphate retention. The contents of acid-oxalate-soluble aluminum (Al_ox) and iron (Fe_ox), derived from short-range-order minerals and organo-mineral complexes, were lower in the upper horizons. Phosphate retention (P ret) also decreased from the Andosol horizons to the present topsoil. The soil profile was rich in exchangeable calcium (Ex_Ca) mainly derived from the alluvial soil material receiving the water of the Arakawa River. Base saturation (BS) was higher than 80% and soil acidity was mild in most of the profile, but acidification has progressed in the present topsoil through calcium leaching. In the field where the anthropogenic epipedon is thicker than 50 cm and its base saturation is higher than 50%, the soil can be classified as Terric Anthrosols. When the BS in topsoil dips below 50% through calcium leaching, however, the taxa of the soil may change.