Relationships between the Size of Aggregates, Particulate Organic Matter Content, and Decomposition of Plant Residues in Soil

The distribution of total organic matter (C-org), particulate organic matter (C-POM), and potentially mineralizable organic matter (C-0) in mega- (10-5 and 5-2 mm), macro- (2-0.25 mm), and microaggregates (<0.25 mm) isolated by dry sieving from gray and agrogray soils (Luvic Retic Greyzemic Phaeozems) of different land uses was studied. In the soils under forest and meadow, the highest C-org content was detected in the megaaggregates of 5-2 mm in size (43 and 37% of C-org in whole soil sample, respectively), whereas in the arable soil, it was found in macroaggregates (45%). In the uncultivated soil, the C-POM was mainly accumulated in megaaggregates (65-72% of the C-POM in the whole sample); in the arable soil, it was equally distributed between mega- and macroaggregates (46-45%). The fine (0.25-0.05 mm) C-POM subfraction in the uncultivated and arable soils contained 1.3- and 2.3-fold more carbon, respectively, as compared with the coarse (2-0.25 mm) C-POM subfraction. The C-0 content in the aggregates correlated with C-POM and C-org. Decomposition of plant residues with a wide C : N ratio in soil increased with a decrease in the aggregate size. However, aggregate size did not influence the decomposition of plant residues with a narrow C : N ratio. The effect of aggregate size on the decomposition rate mainly appeared at the early stages of transformation of plant residues.