Soil combinations as an object of digital soil mapping: forest-steppe of the Oka-Don lowland

A 0.5 million-hectare study area of the Bityug-Saval-Tsna interfluve of the Oka-Don lowland demonstrates the potential of digital mapping of soil combinations in the forest-steppe zone. The gently rugged topography of the interfluve and deposits with low permeability have resulted in restricted surface and subsurface runoff, leading to a predominance of semihydromorphic and hydromorphic chernozem soils in the soil structure, with some solonetzic soils at the northern boundary of their range. The region's soil cover characteristics are expressed by the dependence of the proportion of soils in soil combinations on the morphological features of the mesorelief, which is the leading factor in their organization. Soil diversity and intralandscape variability are determined by a set of 2,200 soil descriptions of 12 soil types/subtypes. The most significant factors of their spatial organization are slope steepness (°), topographic position index with radius 2,000 m (m), channel network base level (m), LS-factor, topographic wetness index (TWI), depth (m), and density (ha/100 ha) of closed depressions. Regional soil cover diversity is reduced to ten types of soil combinations, taking into account their component composition. A comparison of their boundaries with the contents of archival soil survey data demonstrated the comparability and advantages of the digital soil cover organization model compared to a regional generalization of large-scale soil maps of land use (southern Tambov Oblast). The approach used appears promising for solving fundamental and applied problems related to the study and inventory of soil cover as a component of the resource potential of agricultural land use.