Erosion and Self-Restoration of Soils on the Central Russian Upland

The article presents an analysis of the thickness of humus horizons in chernozems and gray forest soils measured at more than a thousand survey sites on three plots with an area of about 10000 ha each in the northern (Orel oblast), central (Kursk oblast), and southern (Belgorod oblast) forest-steppe on the Central Russian Upland. The measured thicknesses of the humus horizons were compared with the model thicknesses. The thickness of humus horizons was simulated with the consideration of the rates of soil erosion and self-restoration. We used erosion models WaTEM/SEDEM (rainfall erosion) and that of the State Hydrological Institute modified by Larionov (snowmelt erosion) and Krasnov, which were previously verified on small catchments on the studied plots or near them. Land use history was reconstructed using historical maps. The approach enabled us to model with sufficient accuracy mean erosion losses of soils and calculate the mean modern thickness of the humus horizon. The obtained results of comparisons of measured and simulated thicknesses of the humus horizon clearly indicate the significant role of soil self-restoration in formation of erosion–accumulation patterns of the soil cover. Insufficient consideration of soil self-restoration results in a significant underestimation of the calculated thickness of the humus horizon and, as a consequence, in an overestimation of the degree of soil erosion. The rate of self-restoration of chernozems and (Luvic Retic Greyzemic Phaeozems) about 0.4 mm/yr, which corresponds to published data of case studies. There is an increase in differences between the model and measured thicknesses of the humus layer in the sequence chernozem–dark gray forest soil–gray forest soil–(Luvic Greyzemic Phaeozems). Plowing of gray forest soils obviously favors an increase in the flow of dissolved humus, as well as pedoturbation, which could potentially contribute to errors in the measurement of the thickness of the humus horizon in terrain conditions and to underestimation of the degree of degradation of the soil cover in the northern forest-steppe.