Embodiments of the present invention provide estimates of soil moisture by measuring the change in electrical conductivity near the surface of the earth using surface-propagated electromagnetic fields. A method is provided for estimating near-surface soil moisture, including measuring signals from an electromagnetic ground wave propagating between one or more receiving element locations, determining a transfer characteristic proportional to an average electrical conductivity between pairs of locations; and determining estimated soil moisture in one or more regions derived from analyzing the determined electrical conductivity between pairs of locations and a predetermined regional relationship between electrical conductivity and soil moisture.