Field Investigation on Physical Properties of Reclaimed Soil in Oizumi Park

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(1) The Park was reclaimed by banking decomposed granite on paddy field, but in reclamation work the soil was compacted in excess. The physical properties of the soil, therefore, are not desirable for growing of trees on such points as three phases of soil, soil hardness, water permeability and retentivity, drainage and so on. (2) In order to make these properties of the soil better, soil improvement work was carried out. From the results of experiments on effects of the soil improvement, it is clear that subsoil improvement by heavy machinery is effective on dry density, porosity, soil hardness and water permeability, and soil amendment by soil conditioner is effective on also retentivity of available soil moisture. The practical way of improvement work will be given later on. (3) Moisture content was measured at four representative points where trees existed and their growing was rather good. As soil moisture is under the condition of excessive wetness, root growth is threatened to become week for air permeability in the soil is reduced. Consumptive use (ET) between pF 1.5 and 3.0 was estimated and the rate of about 2.0mm/day was given. But this rate was indicated to be small from the main reason that there seemed to be subsurface flow over the hard layer in the soil. As the above two problems are expected to be solved by the soil improvement, it is necessary to plan the irrigation system after considering the change of conditions of trees and the soil. (4) In the case of Oizumi Park, soil has been compacted very hard but it is able to carry out reclaiming by banking decomposed granite and to give the reclaimed soil good physical properties if original soil is selected carefully and construction management is done with sufficient care. It is, however, inevitable that the soil will be compact in excess. So it is necessary in the practical working process to carry out subsoil break by heavy machinery for immediate effects and then to mix soil conditioner for the slow effects. (5) Subsoil break must be done when the soil is dry and by a bulldozer with three rippers so as to decrease the running frequency of the bulldozer over the soil. Water retentivity of the soil was little improved by subsoil break itself in the Park. So if possible, it is necessary to mix soil conditioner. In this case mixing must be done uniformly during the banking (6) Also, planting grass, especially the leguminous, is effective for improving properties of the soil, as aggregate is formed by the action of organic material increased in the soil. The final working process is as follows; selection of original soil-banking for test-banking (if necessary, mixing soil conditioner)- modificatory banking for sight-deep plowing or subsoil breaking-planting trees-seeding grass.
大阪府立大学の論文
1977-03-31

Field Investigation on Physical Properties of Reclaimed Soil in Oizumi Park

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