Studies were carried out in a field experiment in the years 2009-2012 on a permanent productive meadow situated on peatmuck soil of the Biebrza Experimental Farm. The aim was to identify the effect of various types and intensities of fertilisation (with cattle manure and liquid manure) on botanical composition of the sward and the content of mineral nitrogen forms in soil. Mineral nitrogen was applied in three doses (N/I - 60, N/II - 90 and N/III - 120 kg N·ha^-1). The lowest N dose was accompanied by fertilization with phosphorus and potassium at a rate of 30 and 60 kg ha^-1, respectively. Nitrogen fertilisations II and III were supplemented with P (45 and 60 kg P ha^-1, respectively) and with K (90 and 120 kg ha^-1, respectively). Fertilization with cattle manure and liquid manure was also applied in amounts corresponding to those used with mineral fertilisation. Obtained results showed progressing floristic changes resulting from different forms of fertilisers and increased moisture, which affected yield forming potential in a range from 6 to 9 t dry mass ha^-1. Nitrogen fertilisation (with liquid manure or mineral N) at a rate of 90 kg N ha^-1 resulted in the increase in N-NO3 in soil layer below 20 cm depth in 2012. In the variant fertilised with 120 kg N ha^-1, irrespective of its form, a distinct increase in nitrate content was noted in all soil layers below 20 cm depth, which indicated the leaching of nutrient. Concentrations of mineral forms of N (N-NO3 and N-NH4) in ground water tended to increase in plots fertilised with mineral nitrogen irrespective of its does.