Stabilization Mechanisms of Decomposition Products of Plant Residues by Density Fractions of Loam

The distribution of decomposition products of corn and clover residues by density fractions of noncalcareous mantle loam was studied under controlled conditions. Two light ( 2.2 g/cm3 (HF)) fractions were isolated using sodium polytungstate. The LF-1 mainly consisted of incompletely decomposed plant residues; the LF-2, of their decomposition products bound with clay minerals (kaolinite, illite, smectites); and the HF, of the organic matter discretely sorbed on the surface of large grains of quartz and feldspars. It was demonstrated that during stabilization of newly formed organic matter (OM) by different density fractions, they are separated as a result of selective specific adsorption. In this case, the LF-2 is enriched in compounds that do not contain nitrogen, whereas the HF is enriched in nitrogen-containing compounds, including those of microbial nature. As a result, the C/N ratio decreases in the series: LF-1 > LF-2 > HF. The sizes of free and bound to mineral particles organic matter pools were calculated, and a scheme describing the mechanisms of stabilization of decomposition products of plant residues by organo-mineral fractions of different densities was suggested.