ИСТИНА

After ceasing of agricultural use, degraded arable lands undergo self-restoration and development towards natural ecosystems involving the full range of physicochemical and biological processes of pedogenesis. We studied the linkage between microbial properties and density fractions of soil organic matter during post-agricultural restoration of former arable lands and estimated the duration of full recovery of soil properties after ceasing agricultural use depending on climate. The chronosequence study was conducted in two contrasting bioclimatic zones of European Russia: deciduous forest (Albic Phaeozems) and dry steppe (Haplic Chernozems). Each chronosequence included an arable soil, 3–4 soils with increasing periods since abandonment (from 7 to 35 yrs), and reference sites with native or completely recovered soils. Soils were sampled from the toplayer 0–5 cm. The basal respiration (BR) and microbial biomass (Cmic) were correlated with the content of soil organic carbon (Corg), total nitrogen (TN), and SOM density fractions: free particulate organic matter (fPOM), occluded particulate organic matter (oPOM), and mineral fraction (mineral–SOM). The greatest increase was found for fPOM and oPOM fractions (by 1.5–2.5 times), Cmic (1.9 times), and BR (1.5–2.5 times). Generally, the full restoration of all properties was faster in dry steppe (Chernozems) compared to deciduous forest (Phaeozems). To restore Corg, TN, and Cmic contents in 0–5 cm layer after the ceasing of agricultural use ca. 40–120 and 20–30 yrs are required for Phaeozems and Chernozems, respectively.