Tillage may affect the microstructural organization of soil, including the distribution of microaggregates with different mechanical strengths. We quantified the impact of tillage treatment on the amount and distribution of free organic matter, microaggregates (unstable and stable under low intensity sonification) and their components, in the upper horizons of zonal soils of the Center of the Russian Plain. Under plowing, the carbon content decreases, both in unstable and stable microaggregates. The loss of carbon in unstable microaggregates was ~24%, whereas in stable microaggregates, it was ~37%, relative to native soils. The carbon content of organic (LFoc
) and organo-clay (Clayrd
) fractions in unstable microaggregates (CLFoc
) was almost identical in the upper horizons of native soils: the ratio of these components is for Albeluvisols (1.1), Phaeozem (0.8) and Chernozems (1.0). Under plowing, these decrease to: Albeluvisols and Chernozems (0.6) and Phaeozem (0.5). The shares of carbon accumulated within the unstable and stable microaggregates (Cunstable
) are constant under equilibrium conditions and show a tendency to decrease from north to south on the order of: Albeluvisols and Phaeozem (2.2) > Chernozems (1.0). Under plowing, they increase to: Albeluvisols (3.0) and Phaeozem (3.2) > Chernozems (1.5).
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