The examinations were carried out on samples of soils derived from loess, representing diversified land use areas: cultivated, fallow lands, voluntary afforesting, scheduled afforestation aimed at re-naturalisation of post-arable objects. In soil samples measurements of grain size distribution, pH in KCl, Corg content, CO2 release and dehydrogenase activitiy were carried out. The following phenomena were observed – a reduction in the biological activity of the soils in period of 3 and 5 years after abandoning cultivation, an increase in biological activity indicators with entering of the tree flora to the post arable areas, and increasing dehydrogenase activity in re-naturalised objects in relation to those remaining in cultivation.