Abstract
In order to establish the optimum tilling methods in the areas of clayey soils, we have been investigated the physical properties of clayey soils from view-point of tillage. The clayey soils have the properties in high rates of clay contents of about 35%, large value of liquid limit of 71 to 88% and large value of plastic index of 38 to 55. In the fields of clayey soils, water permeability has become quite poor and tilling operation has became difficult. The main reason seems to be that the gley layer under the topsoil layer prevent the water permeability. Available day stage for tillage, which are based the calculation on soil moisture contents, are estimated at short periods from April 4 to November 15, and an available day rate for tillage is estimated at 64% in TAKADA (NIIGATA prefecture) which rate shows small value comparison with SAPPORO's, TOKYO's and FUKUOKA's. Especially, an available rate in autumn shows extremely small values. It seems that the precipitation in TAKADA is much in autumn.
