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In the chronological sequence of postagrogenic soils, the restoration of the original differentiation of the soil profile and its horizons proceeded with different rates depending on the fallow age and the horizon depth. The layer sampling (at 5-cm intervals) showed that the plow horizon began to differentiate into a system of subhorizons in all the fallow soils. The zonal pedogenesis showed clear signs of manifestation already in the 15-year-old fallow. The upper part of the former plow horizon in the 15- and 60-year-old fallows under herbaceous plants was transformed into a soddy horizon, while a postagrogenic soil 90 years old already developed under a zonal type of vegetation and approached the control soil in its morphological features. The content and reserve of carbon in the soils showed a stable tendency of increasing (especially in the upper part of the plow horizon) during the entire postagrogenic period under study. The water permeability of the soils gradually increased and approached that of the virgin soil. However, the compacted subsurface horizon (the plow pan) disappeared only after 90 years. The assessment of the physicochemical properties of the soils and the structural and functional parameters of the humic acids indicated the expansion of the layer differentiation primarily within the homogeneous plow horizon. From the elemental analysis and 13C NMR spectroscopy data, the degree of aromaticity in the molecular structure of the humic acids gradually decreased, and the aliphatic part developed with the age of the fallow.
Kechaikina et al. (Sat,) studied this question.