Mineralization kinetics of corn and clover residues in quartz sand, loam, sand + 15% bentonite, and sand + 30% kaolinite have been studied. A scheme has been proposed for the transformation of plant residues in mineral substrates. Kinetic parameters of mineralization have been calculated with the use of a first-order two-term exponential polynomial. It has been shown that the share of labile organic carbon pool in the clover biomass is higher (57–63%) than in the corn biomass (47–49%), which is related to the biochemical composition of plant residues. The mineralization constants of clover residues generally significantly exceed those of corn because of the stronger stabilization of the decomposition products of corn residues. The turnover time of the labile clover pool (4–9 days) in all substrates and that of the labile corn pool (8–10 days) in sands and substrates containing kaolinites and bentonite are typical for organic acids, amino acids, and simple sugars. In the loamy substrate, the turnover time of labile corn pool is about 46 days due to the stronger stabilization of components of the labile pool containing large amounts of organic acids. The turnover time of the stable clover pool (0.95 years) is significantly lower than that of the stable corn pool (1.60 years) and largely corresponds to the turnover time of plant biomass.