Gray soils with a second humus horizon in the mixed forests of the Vyatka-Kama region

The article presents the results of studying the problem of the genesis of gray soils with the second humus horizon (SHH) of broad-leaved and coniferous forests of the east of the Russian Plain on the territory of the lower right bank of the Vyatka River, within the Urzhumsky and Mari-Tureksky plateaus. The AEl[hh] horizon is located at a depth of about 25–50 cm from the surface and differs significantly from the above-lying humus horizons in terms of its external and internal properties, which indicate a complex history of soil development with a binary humus profile. The work is based on a set of methods of morphological, genetic and analytical paleosurface studies. For the first time, data on the morphology, conservative and relevant substantive properties, genesis and main stages of evolution of soils with problematic profile structure have been obtained for the region. The polygenetic nature of the soils and the relict (residual in origin) age of the humus of the SHH with the Early Holocene, Atlantic formation time – about 8.5–6.5 thousand years ago – under vegetation more corresponding to the forest-steppe paleolandscapes are substantiated. Two different stages of soil development are distinguished: developing evolution with elements inheriting in the Boreal-Atlantic optimum; inheriting evolution with elements erasing in the second half of the Postglacial. Conclusions are drawn about the inconsistency of these soils with the modern bioclimatic conditions of the mixed forests of the Vyatka Kama region, the degradation trend of their development in the second half of the Holocene and the prospects for further transformation into sod-podzolic soils from the soils with SHH. These objects are considered as a rare soil heritage corresponding to the status of rare and endangered soils recommended for inclusion in the network of protected natural territories of Vyatka land.