Abstract
The aim of this paper is to show the morphology of macropores in the root zones under the permanent meadow. The structure of macropores was studied by examining the physical conditions of the soil, the morphology of macropores by X-ray and contrast media, and the root system. Soil samples were collected from the root zone shallower than 55 cm in a meadow composed mainly of orchardgrass seeded fourteen years ago. The samples were classified by surface soil layer (0-10 cm), sub-surface soil layer (10-35 cm), and subsoil layer. Each layer was composed of volcanic sandy soil. The physical condition of the surface soil layer was dense and solid, the micropores and the effective pores were small, and the permeability was low. Because of the low density of the soil, the macropores and the effective pores increased in the sub-surface soil layer, but the subsoil layer was higher in permeability. The macropores of the above soils were mainly tubular root pores formed by the grass roots. In the surface soil layer, the pores developed irregularly in the horizontal and the slanting directions along the crack rather than in a vertical direction because of the dense soil. In the sub-surface soil layer thicker pores developed in a vertical direction at a constant distance, but the thinner pores clearly developed in the horizonal direction from these thick ones. In the subsoil layer, the pore morphology was not formed by the grass root, but instead originated from previously planted grasses. Most of these radiographic images were formed by the contrast media. They permeated into pores as follows in the surface soil layer and the sub-surface soil layer, the pores formed between the grass root and the soil but in the subsoil layer, the pores were formed by the root system of the previously planted grasses. The diameter of the radiographic pore ranged between 0.37 and 0.85 mm, but it was larger in the lower layers. In contrast, the diameter of the grass roots was larger in the shallower layer, and ranged from 0.30 to 0.19 mm. Since the pore morphology showed a good correspondence with the soil's physical conditions, it is concluded that the morphology of the micropore of the root system in the drainage zone of the permanent meadow forms mostly by tubular root pore which originates from the grass roots.
