3Chair of Agricultural Systems

Agricultural use of land on hydrogenic soils is associated with lowering the groun-dwater level, which intensifies the processes of organic matter mineralisation and, in ef-fect, releases large amounts of mineral nitrogen. The aim of the study was to determine the seasonal variability of the concentrations of nitrogen mineral compounds (N-NO2, N-NO3 and N-NH4) in groundwater under extensively managed peat-muck soils, situated in Wrocikowo in the Olsztyn Lakeland and in the Dymerskie Meadows in the Mrgowo Lakeland. Peat-muck soil, found at the study sites, had varied physical properties. The hi-ghest content of mineral particles (69.3%) in the muck layer was found in soil marked as MtI 120gy under turf-covered wasteland, and in the peat layer (51.5%) – in soil marked as MtII 60gy under extensively managed meadow. Groundwater taken from piezometers in-stalled in hydrogenic soils was used as the study material. Water for chemical determina-tions was taken during four seasons: spring – in May, summer – in August, autumn – in November and winter – in January. The concentration of mineral forms of nitrogen in groundwater of peat-muck soil was found to depend on its type, the depth where the gro