It is known that microwave emission for soil is partially polarized, whereas the polarization degree of radiation from crops is either very small or equal to zero. The effect of vegetation on the polarized emission from the soil is analyzed by means of a model based on the radiative transfer theory. A comparison between the values predicted by the model and the experimental data obtained at 10 and 36 GHz shows that the model is particularly adequate for corn at 10 GHz, in which case different values of leaf area index can be estimated. At 36 GHz, the polarization degree changes very rapidly as vegetation grows and it is possible to distinguish only bare soil from vegetated soil. >