Composition of Organic Matter and Biological Properties of Eroded and Aggraded Soils of a Small Catchment in the Forest-Steppe Zone of the Central Russian Upland

The impact of land use and erosion-deposition processes on some physical, chemical, and biological soil properties in a small agricultural catchment in Kursk oblast is analyzed. Plowed Haplic Chernozems and stratozems (Fluvic Chernic Phaeozems (Loamic, Pachic)), as well as unplowed stratozems of a dry valley bottom have been studied. The proportion of large soil aggregates (clods) >10 mm in soils is high on plowed land and low in the dry valley bottom. Differences in the carbon and nitrogen content and in the C/N ratio have not been detected. The analytical pyrolysis has revealed 26 pyrolysates in the composition of soil organic matter (SOM). The relative abundances of pyrrole, pyridine, toluene, and indan among SOM pyrolysates are higher in plowed soils as compared to the soils at the dry valley bottom. Proportions of furfural and methyl furfural among SOM pyrolysates are higher in soils of the dry valley bottom than in plowed soils. Differences in the content of alkanes and phenol are absent. The biomass of microorganisms is mainly formed by fungi (97–99%), and their abundance is greater in soils of the dry valley bottom than in soils of the plowland. Differences in the respiratory activity of the studied soils have not been revealed. The significant influence of erosion-deposition processes and soil cultivation on the spatial heterogeneity of the SOM composition and microbiological parameters is shown. Plowed soils are characterized by the high relative abundance of nitrogen-containing SOM components, while soils at the dry valley bottom have a relatively high abundance of carbohydrate components of mature SOM. The accumulation of fungal biomass and an increase in the structure coefficient in soils of the dry valley bottom indicate the participation of material redeposited from slopes in soil aggregation.