Abstract
The purpose of this study is to examine the morphology of macropores in the root zones of grassland on the weathered granitic soil. The soil was sampled in Houzyou city of Shikoku. The structure of macropores was studied three-dimensionally examining the physical condition of the soil and the morphology of macropores by stereoscopic-radiography. The soil samples were collected from four layers of root zones shallower than 45cm on a 10-year old pasture. The physical condition of each soil layer was sandy loam, dense and solid, and the solid phase rate was 52-58%. The macropores and the effective pores were small, and permeability was low in the surface soil layer. The macropores and the effective pores increased in the sub-surface soil layer and the subsoil layer, and permeability was higher in both. The morphology of the non-capillary pores (pF≦1.5) observed on each soil layer. The first soil layer (0-10cm) consisted of pores formed by grass roots. The second to the third soil layer (10-45cm) consisted of pores formed by roots, and pores of inter-particles and inter-aggregates. The morphology of the capillary pores (pF1.8, pF2.0) is shaped by pores formed by roots in the surface layer. In the subsoil layers they were consisted of pores formed by roots, and pores of inter-particles and inter-aggregates. These results on the pore morphology of the weathered granitic soil showed that the shape of almost all macropores is formed by roots. This is the same as that described for the Andosols (volcanic sandy soil) and Steppe soil (chestnut sandy soil) cases. It was concluded that the macropores of the grassland soil consisted mainly of the tubular pores formed by plant roots.
