Andrey Petrovich Zhidkin

The article presents an analysis of the thickness of humus horizons of chernozems and gray forest soils, measured at more than a thousand survey points in three areas with an area of about 10 thousand hectares each in the northern (Oryol region), central (Kursk region) and southern (Belgorod region) forest-steppe on the Central Russian Upland. Th e measured thicknesses of the humus horizons was compared with the modeled thicknesses. Modeling of the thickness of humus horizons was carried out based soil erosion modelling and taking into account soils development. An assessment of soil erosion rates was carried out by WaTEM/SEDEM (rainfall erosion) and State Hydrological Institute in the Larionov modifi cation (snowmelt erosion), previously verifi ed on small catchments within or in close proximity to the study sites. Land use history was reconstructed using historical maps. Th e approach made it possible to model with suffi cient accuracy the average erosion losses of soils and calculate the average current thickness of the humus horizon. The obtained results of comparisons of measured and modeled thicknesses of the humus horizon clearly indicate the signifi cant role of soil development in the formation of erosion-accumulative structures of the soil cover. Insuffi cient consideration of soil development leads to a signifi cant underestimation of the calculated thickness of the humus horizon and, as a consequence, to an overestimation of the degree of soil degradation. The rate of development of chernozems and dark gray forest soils is about 0.4 mm∙year–1, which is consistent with literature data from case studies. An increase in diff erences between the modeled and measured thicknesses of the humus layer was noted in the series: chernozem - dark gray forest soil - gray forest soil - light gray forest soil. Perhaps the plowing of gray forest soils contributes to an increase in the fl ow of dissolved humus, as well as pedoturbations, which could potentially contribute to a measurement distortion of the thickness of the humus horizon and an underestimation of the degree of degradation of the soil cover in the northern forest-steppe.

The dynamics of sedimentation in the bottoms of small catchments in the forest–steppe zone of the Central Russian Upland was assessed using the soil–morphological, radiocesium and magnetic tracer methods, which made it possible to calculate the rate of soil loss 1) since 1986, 2) since 1954, 3) since the launch and active operation of the railway, 4) since the mass plowing the entire catchment area. Two groups of small dry valleys have been identified: the catchment area of the first group includes tributaries of larger dry valleys, where the average rate of loss during the agricultural period is 2,1–2,4 t∙ha-1 per year and exceeds modern ones (since 1986) by 0,6–0,7 t∙ha-1 per year. The catchments of the second group include the sources of larger valleys, where the average rate of loss during the agri- cultural period is 0,6–0,9 t∙ha-1 per year and less than modern ones (since 1986) by 0.3–0.8 t∙ha-1 per year. The max- imum rates within all catchments were observed in the period 1954–1986, which is associated with soil compaction by heavy agricultural machinery, as well as the contribution of snowmelt runoff, which was regular for this period.