Humic substances in agro-stratozems of Leningrad oblast

Chemical properties and some parameters of the humus status of agro-stratozems developed in Leningrad oblast from different parent materials and with different histories of agricultural use were studied. The stability of the elemental composition of humus in the studied soils was found. The group and fractional composition of humus was more sensitive to agricultural impacts. In response to the application of manure, lime, and mineral fertilizers, humate-fulvate humus changed into fulvate-humate humus and the content of the agronomically most valuable HA-2 fraction increased, in some cases, to predominance. Exclusion from land use for 15 years decreased the humus content and changed its composition; it became more similar to that in zonal soddy-podzolic soils, which are the natural analogues of the agro-stratozems studied.