Solute transport through soil may affect groundwater and surface water quality. The convection-dispersion equation has been widely used to describe soil solute transport processes. Dispersion coefficient (D) and retardation factor (R) are two important transport parameters in the model. Earlier researchers used boundary layer methods to estimate the soil solute transport parameters based on assumptions of parabolic or cubic polynomial concentration profiles. In this article, boundary layer theory is used to calculate solute concentration distributions and the boundary layer distances, based on assumptions of quartic and quintic concentration profiles. Equations describing soil solute concentration profiles are evaluated by comparing them with an exact solution. Equations for estimating D and R are developed, and the effects of instrument sensitivity on determining D and R are analyzed. The results indicate that all of the boundary layer equations may be used to estimate soil solute transport parameters, but the instrument sensitivity required by each equation is different. Therefore, instrument sensitivity should be evaluated before selecting the boundary layer equation used to estimate D and R
