Exposure at 1 m above the ground from isotropic gamma-ray point sources in the soil has been studied by the Monte Carlo method for source energies from 40 keV to 5 MeV. Source depths from 0.1 down to 30 cm and horizontal distances out to 5 mfp have been considered. Considerable deviations were found in the results of different buildup factor methods since such methods do not account for geometric effects at the interface. Moreover, exposures from infinite and finite plane sources have been calculated. It is shown that, for source energies <662 keV, the buildup factor methods underestimate the kerma considerably. It is shown how surface roughness conditions can be accounted for by the introduction of an effective source depth in the soil. The validity of approximations used to describe the exposure from finite or inhomogeneous plane sources with values for infinite homogeneous plane sources was examined.