Abstract
Differences in soil structure according to land-use and soil properties were examined visually using soft X-ray. Consequently, the following results were obtained.
(1) Differences in paddy field Soil structures in plow layers were different from the subsoil. In the plow layer, unique soil structures were formed in a year after spring puddling. After puddling, pores outside the aggregates were predominant to other structures, but in the lower plow layer, vertical tubular-pores were formed gradually according to rice root penetrating. In the subsoil, tubular-pores were predominant to other structurs and no structural variation was observed in the course of the year.
(2) Differences in soil type In Andosol, the pore diameter was larger than in Gray lowland soils and Brown lowland soils because of its aggregation. In sandy loam, tubular-pore structure was rarely formed because of its single-grained structure.
(3) Soil structure in upland field compared with paddy field The plow layer in the upland field was rich in pore structures but poor in tubular-pore structures. In the subsoil, however, tubular-pore structures were predominant as well as in the paddy field, but tubular-pores had no principal direction, which is different from the paddy field. In the upland field converted from paddy field, vertical tubular-pore structure which could be seen in the paddy field decreased in number with time as affected by drainage or drying.
