This paper presents an approximate analytical method for describing irreversible kinetics in soil columns. The method, which produces exact results for the limiting cases of zero- and first-order kinetics, uses an interpOlation technique between those two orders and can be applied to an arbitrary kinetic rate. Using Michaelis-Menten kinetics as an example, we apply the method to near zero- order kinetics, near first-order kinetics, and an intermediate case for a wide range of possible experimental conditions. The results are checked by comparison with a numerical solution. Conditions under which accurate results can be expected are given. Also, results are compared with a previous approximation, which is simpler to implement but less accurate when the effect of dispersion is considerable. Practical use of the method to determine kinetic rales, is illustrated using an experimental breakthrough curve.