Abstract
It is important to know the characteristics of temporal change and spatial distribution of water content and infiltration rate of surface soil layer for remote sensing and unsaturated flow analysis. In this paper, we examined the water content change caused by rainfall and infiltration at 24 points (depth=0-10cm) surrounding a single tree by reflectometers. Results showed that the water content.Θ at the points near the stem had bigger average and smaller standard deviation than that at distant points. The relationship between Θ and its differential calculus immediately after rainfall differed in different water content. At lower content dΘ/dt was proportional to (Θ-Θr) n suggesting gradient of hydraulic head is 1. At higher content, the absolute value of dΘ/dt was bigger than that estimated by dΘ/dt=k (Θ-Θr) n. At the highest content, dΘ/dt suggested that the water was supplied from tree to surface soil after rainfall or that thegradient of hydraulic head is smaller than 1 because of high water content below 10 cm layer. The surface supply water estimated by using dΘ/dt=k (Θ-Θr) n corresponded with rainfall intensity but there is a time lag between them.
