he quantitative aspects of mineralization and humification of organic residues in soil were analyzed on the basis of the experimental curves of their transformation and using three conceptual approaches. Ågren's and Bosatta's concept of the continuum of substrate quality loss accentuates the gradual reduction of the availability of the decomposable material for microorganisms. The discrete succession concept emphasizes the existence of morphologically and biochemically distinguishable stages (a fraction cascade) of transforming the organic debris into humus. According to the biochemical concept, the organic debris transformation is represented as the mineralization of individual organic substances with different rates, more often without taking into account the influence of humus formation. The testing of these concepts led to the conclusion that the discrete succession and biochemical concepts should be integrated for the elaboration of the theoretical basis for assessing the rate of organic debris transformation in the soil.