The rate of washout and formation of the humus horizon in the eroded soils of the agro-landscapes of the forest-steppe and steppe zones in the European part of Russia

Erosion is one of the most common factors of soil degradation. There are various ways to estimate the maximum erosion rate at which a high level of crop productivity is maintained. In this paper, the permissible erosion rate is proposed to be estimated by comparing the ratio of humic acid carbon to fulvic acid carbon (CHA/CFA) in non-eroded soils and in their eroded analogues. When the values of the CHA/CFA ratio in similar eroded and non-eroded soils are similar, it can be assumed that the erosion rate approximately corresponds to the humus formation rate. The study of arable zonal soils of the European part of Russia: dark gray forest soil (Haplic Greyzems) of the northern part of the forest-steppe zone; leached chernozem (Haplic Chernozems) of the forest-steppe zone; southern chernozem (Calcic-Glossie Chernozems) of the steppe zone and chestnut soil (Haplic Kastanozems) of the dry steppe zone and their moderately eroded analogues showed that in the moderately eroded dark gray forest soil and leached chernozem there was a more pronounced decrease in the CHA/CFA ratio compared with non-eroded analogues than in ordinary chernozem and chestnut soil, which suggests that in eroded dark gray forest soil and leached chernozem, the erosion rate significantly exceeded the humus formation rate compared with southern chernozem and chestnut soil. This assumption is also confirmed by a more significant decrease in the content of the light fraction of organic matter and a deterioration in the aggregate state and density as a result of water erosion in dark gray forest soils and leached chernozems than in southern chernozems and chestnut soils. The proposed approach enables to compare the erosion rate and the soil formation rate and assess the danger of erosion processes for specific areas.