The components of an object and the moisture in it can be estimated by measuring the degree of spectral polarization of scattered light from that object. In this paper the degree of spectral polarization of scattered light from CuSO(4), CuCl(2), Fe(2)O(3), SiC, S, NiCl(2), and CoCl(2) as models of soil was measured and compared with that of volcanic ash and natural soil. From these results it is estimated that Fe appears in natural soil and Si appears in volcanic ash. The field capacity point of soil was obtained from measurements of the degree of spectral polarization, and it was detected more clearly in a shorter wavelength region (about 400 nm).