Change in aggregate structure of various soil types during the succession of abandoned lands

A comparative analysis of the changes in the aggregate structure in various types of soils (Sod-podzolic, Gray forest, and Chernozems) during their postagrogenic evolution was carried out. The study plots included: sod-podzolic soils -plowland, laylands abandoned 8, 13, 35 years ago and a secondary forest (~100 years); gray forest soils -plowland, laylands abandoned 6,15 and 30 years ago and a secondary forest of 60 years; сhernozems-plowland and layland abandoned 10, 15, 26 and 81 years ago. The geobotanical studies have shown that the withdrawal of soils from agricultural use causes changes in species composition, increase of biodiversity, and a gradual recovery of climax communities, which are attributed for specific natural climatic zones. Along with vegetation succession, we observed the increase in the total carbon content in the upper part of the former arable layer (0-10 cm) in all studied soils. However, the trend becomes weaker from northern to southern climatic zones in the following sequence: Sod-podzolic soil > Gray forest soil >Chernozems ordinary. It was found that the content of macroaggregates increases authentically in the surface layers of all of the investigated soils from cropland to abandoned and forest soils during the self-restoration of Gray forest soils and Chernozems while the number of micro-aggregates, on the contrary, decreases. In all studied chronosequences, we observed the increase of the weighed mean diameter of the aggregates and the structure coefficients. The most pronounced changes in the aggregate structure were observed in the chronosequence, formed on Gray forest soils, while the weakest alterations were typical for the Sod-podzolic soils of the southern taiga.