Chemical Structure of Organic Matter of Agrochernozems in Different Slope Positions

摘要

Chemical structure of organic matter (OM) pools in the arable layers of agrochernozems (non-eroded, eroded, and depositional has been studied by solid-state C-13-NMR spectroscopy. As has been shown, two competing processes simultaneously take place in the erosional zone: decomposition of the OM of the underlying horizon exposed due to erosion, and the stabilization of fresh OM having entered with the crop residues (OM dynamic replacement). Analytical data suggest that the OM dynamic replacement in the erosional zone efficiently compensate for the OM decomposition, as is evidenced by the highest C/N ratio of all studied OM pools in the eroded agrochernozem along with the absence of statistically significant differences in the integral characteristics of their chemical structure. However, a continuous removal of the upper soil layer from the eroded agrochernozem with each erosion event does not fully compensate for the quantitative OM losses there. The most labile OM part can be mineralized during transportation of the eroded material to the depositional zone. Accordingly, the OM entering the depositional zone is to a greater degree transformed as compared with that of the eroded agrochernozem. Nevertheless, characteristic of the depositional agrochernozem is an increased accumulation of organic carbon in the bulk soil and all examined OM pools. Correspondingly, the continuous OM inputs from the slope position subject to erosion with its subsequent burial after each consecutive erosion event, as well as the repacking/aggregation of the newly deposited OM, efficiently contribute to the deposition of organic carbon in the depositional zone.