Studies on the perfection of radiography for soil macropores and on the application to the soil physical problems.

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1. Perfection of the macropore imaging method. (1) Undisturbed sampling of cubic form soil. Cubic form soil samples are suitable for x-ray stereoradiography, and in this study the square cylindrical sampler method and knife cutting method have been developed. These two methods are followed by soil sample trimming in the laboratory, and 4.15cm cube sample of undisturbed soil is obtained. (2) Infiltrating method of contrast medium into the sample. Clay plate coating of cubic sample and water saturation of sample were standardized, and the method was named "Drying method". This standardization raised the efficiency of contrast medium infiltration and the accuracy of macropore imaging.2. Application of the macropore imaging method. (1) In the fields of volcanic ash soils, it was found that macropores having shape of plant roots developed densely through the whole depth of tephra horizon. Further, the plants opals of native plants were detected simultaneously in the soils of whole horizon. These results indicate that the macropores would have been formed by the old plants roots. (2) The shapes of macropores infiltrated with water in the compacted soils were investigated using above method. Namely, after permeability test the water was replaced with contrast medium, and the sample soil was radiographed. At the low water content of soil, the interspaces of granulated units developed. However at the high water content, the membrane-like voids grew into horizontal direction. (3) In the farmland, the rice paddy field, upland field and grass land, macropores formed by the c rop roots grew vigorously. Among them, grass land shows the most active and deepest (1 m) development of those macropores. (4) Initially air entering voids of volcanic ash soils were visualized by the above method, and they were most thick macropores formed by the plants roots.