Abstract
A method to determine the vertical distribution of the volumetric water content, θ, -pressure head, _??_, relationship of forest soils using a large-size sample (diameter 19.5 cm, length 75.0cm) are described (usually, the θ-_??_G relationship is determined by using a small-size sample). This can be defined as the instantaneous profile method of determining the θ-_??_ relationship when the hydraulic conductivity, K, -_??_ relationship is known. By this method, the θ-_??_ relationship is determined based on the equation of continuity for unsaturated infiltration from the vertical distribution of flux and the time-sequential change of the pressure head under a unsteady-state condition. The vertical distribution of flux is calculated from the K-_??_ relationship and the distribution of the pressure head obtained by the saturated-unsaturated hydraulic conductivity test which was proposed in the first paper. The method was applied to two types of forest soil samples whose parent materials were weathered granitic rock; (1) undisturbed and (2) disturbed in which macropores were broken. The results are compared with those of the measurements using a small sample and the observations of the forest soil-layer in situs. It is concluded that the method can measure the θ-_??_ relationship influenced by the macropores in forest soils, and that a large-size sample is more effective than a small-size sample in determining the relationship.
