Abstract

Every soil has a limited capacity to physical-chemically protect organic matter from biodegradation in its clay and silt particles. Thus, the rates at which carbon (C) and nitrogen (N) are mineralized in soil should be related to the degree of C saturation in those particles. In this study the authors investigated the hypothesis that the decline in the amount of C in clay and silt particles from coarse to fine textured soil is due to a reduction of the specific surface area of clay and silt fractions in clay soils. The relation between the mineralization rates of C and N to the degree of C saturation in the clay and silt particles was also investigated. Six cultivated soils (cereal) and three non-cultivated soils (Medicago sativa L.) were sampled at 0-20 cm depth. All soils were ultrasonically treated and gravimetrically separated into fractions > 50