Przemiany materii organicznej gleb łąkowych w pierwszych latach po zalesieniu

The properties of humic substances in gley soils in the first years after afforestation were charac−terized. Study was performed in former meadow soils in Gostynin Forest District (central Poland). Four soil profiles were analysed. It was found that changes of soil organic matter in studied soils were closely associated with hydrologic properties of these soils. Establishment of forest plantation on gley soils greater violated the balance of mineralization and humification processes in mineral−organic soils than in mineral soils. This was reflected in substantial losses of organic carbon (Corg) and total nitrogen (Nog) in the upper layers mineral−organic soils and minor changes of Corg content and Nog in the upper horizons of the mineral soils. Fractional composition of humus was more sensitive indicator of changes than the analysis of the total quantity of carbon and nitrogen. Studies have shown that after afforestation labile compounds were mineralized at first. Transformations of other humus fractions depended on soil subtype. In soils with high initial content of Corg (93.7 g/kg) in addition to the loss of organic matter deterioration of humus quality were also recorded. In the soil of the average initial content of Corg (65.1 g/kg) loss of organic matter was found, but a better quality of humic substances with increased proportion of humic acids was recognized. In soils with the lowest initial content of Corg changes in the amount of organic matter were not statistically significant, but a larger share of humic acids in different humic compounds was evidence of the greater stability after afforestation.