ANTHROPOGENIC CHANGES OF TAIGA SOILS ON VARVED CLAYS IN NORTHWEST RUSSIA

The plow horizon of soddy-podzolic surface and deep gley soils on varv ed clays in northwest Russia attains cultivation status within a 5- to more than 10-year period (the whole period of observations was 20-25 years); however, this status may be defined as just ''semi-cultivation .'' Along with positive changes in some soil properties, adverse featu res are preserved or accentuated in the plow and underlying horizons. Thus, strong gleying develops in the subplow layer, whose impermeabili ty increases. The degradation of soil structure and the mobility of hu mus substances are enhanced, as well as the formation of nodules and s oil claying (dispersion of silty particles in the plow horizon). Also, the descending migration of fine particles increases in agrogenic soi ls. Two trends in the evolution of cultivated soddy-podzolic soil are revealed-surface gleying and restoration of the original profile of na tural soil. The cultivation of these soils does not seem to be feasibl e.