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Reflectance (R), polarized reflectance (Q) and degree of polarization (P) were measured for a mixed seeding pasture consisting of white clover and tall fescue in 8 spectral bands in the visible, near- and short-wave infrared wavelength ranges. Horizontal leaves in the white clover canopies generated more polarized light than vertical leaves of the tall fescue. Polarization (Q and P) increased as the ratio of legumes (ROL, leaf area ratio of white clover to the total) increased in the mixed sown canopies. A multiple regression model that used a Q and Rs of 3-bands that were all acquired at view zenith angle 60° explained 90% of the variation of ROL with RMSE 11%. The regression model was validated by a data set provided in the next growing season. The model including polarization information was comparatively more stable inter-annually than the model of reflectance only. It is effective to utilize the polarization information of reflected light as a method of estimating ROL of mixed seeding pastures where planophyll and erectophyll plant species coexist. Polarization is appropriate for ROL monitoring in pastures.