抄録
The growth and yields of crop plants on deeply tilled upland fields are not always better than those on ordinarily treated fields. Such a failure may be due to various unfavorable factors induced by deep tillage, among which the leading one should be that the some inferior characters of the subsoil is admixed with the top soil by deep tillage. We studied how to improve such bad characters of subsoil in these experinLents on a volcanic ash soil. The subsoil researched was found to be deficient in nutritive elements, especially in P2O5 and in N. In order to bring good yields of plants on such a subsoil, it was necessary to fertilize with increased amounts of P2O5 and N. On the other hand, weathering practices of the subsoil such as freezing and melting or air drying were very useful for improving the subsoil. And good yields were considered to be expected by tillage of the field in autumn and weathering during a cold winter.
