Chemical Structure of Organic Matter of Water-stable Macroaggregates of Agrochernozems of Different Positions on the Slope

The chemical structure of pools of organic matter (OM) in the 2–1 mm water-stable macroaggregates, isolated from air-dry aggregates of the same size in arable horizons of non-eroded, eroded and deposited agrochernozems has been studied by solid-state ¹³C-NMR spectroscopy. An assessment is made of the alteration of their chemical structure in the denudative-accumulative landscape. It was revealed that the overwhelming majority of water-stable macroaggregates in the erosion zone are newly formed due to the dynamic replacement of OM in situ, which is clearly evidenced by the integral indicators of the chemical structure of all pools of OM macroaggregates. Analytical data indicate the predominant transport of newly formed macroaggregates. The destruction of macroaggregates during the transport phase is accompanied by the release of previously physically protected aggregated OM, which undergoes partial mineralization (predominantly its most labile part – hydrolyzable), and its stable part remains little/non-changed. Mineral-associated OM (Сlay and Residue) changes little, maintaining relative freshness, which may be indirect evidence of the transportation of predominantly newly formed macroaggregates from the erosion zone. The greater degree of freshness of free OM of macroaggregates in deposited agrochernozem is due to the predominance in of fresh remains of cultivated vegetation of the accumulative zone, together with those transported from the erosion zone.