Stocks of organic substance in post-agrogenic lands in Leningrad region

We have analysed factors affecting the formation of organic matter stocks in sod-podzolic soils and post-agrogenic lands in the south-western part of the Leningrad region. There are many factors influencing the process of humus formation, which does not allow to reliably simulate the process of transformation of organic residues and the accumulation of humus in areas previously used for agricultural production. There is a connection in the differences in the specific density of the soil and the unequal content of humus in the genetic horizons of fallow soil compared to the arable layer of the field, where these horizons are mixed into a homogeneous mass. The data obtained show a high correlation between the humus content in the former arable horizon of soil with a clay fraction and pHKCI. At different successional stages of accumulation of organic matter in post-agrogenic lands is not the same, as the formation of different species composition of vegetation makes adjustments to this process. When determining humus stock in post-agrogenic lands, an error can reach to 30%. The main reason is the differences in the specific density of the soil and the unequal content of humus in the genetic horizons of fallow soil compared to the arable layer of the field, where these horizons are mixed into a homogeneous mass. The conclusion was made about different methods of soil sampling from arable lands and from post-agrogenic lands.