重粘土水田の挙動と粘土
スポンサーリンク
概要
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In alluvial plains along the northern to central part of the Japan Sea Coast of the Main Island. Japan, namely West Tohoku- and Hokuriku Districts, paddy fields of heavy clay soils are widely distributed. Because of the extremely low water permeability of the subsoils, these paddy soils are characterized by ill-drainage and poor bearing capacity. Consequently, it is difficult to use large-sized farm machines and to practice crop rotation including upland crops, and the productivity of rice is naturally low. In addition, improvement of these low land heavy clay soils to well-drained paddy soils by the operation of underdrainage is difficult because of their poor water permeability and large water holding capacity. Techniques of their conversion to upland state and changes, of physical properties of the soil in the process of drying were studied. The results obtained are summarized. 1. Gley horizon of low water permeability of the ill-drained clayey paddy soils gradually cracked by drainage and subsequent drying, and finally, became to show a high water permeability. 2. After drainage and subsequent drying, a horizon of high bulk density was formed directly below the plow layer. This horizon obstructed the percoration of gravitational water as well as the upward movement of capillary water. 3. Conversion of an ill-drained paddy into an upland field was accompanied by an increase in the macro pores of the plowlayer and aeration was, therefore, improved. Although the holding capacity of available water was reduced in the early stage of the conversion, it gradually increased with the lapse of time. 4. As for the growth of a crop (corn), growth and yield were poor in the early stage of the conversion. This was attributed to a violent fluctuations in soil moisture tensions. Afterwards, however, the yields increased according to the improvement of the drainage. It took a few years to complete a conversion into the upland field. 5. It was found that a drainage system including mole drain and block drainage was required for conversion of an ill-drained clayey paddy soil to an upland state. In order to accelerate soil drying, growing crops having deeply penetrable root system and operation of sub-soiling are desirable. 6. Application of rice straw and aluminum chloride increased macro pores and holding capacity of available water, respectively, and these materials improved the soil consistency.
- 1980-06-25