Carex nigra Reichard is a relatively constant species typical of damp and inundated habitats. One of the species that gain the highest cover in meadow communities with common sedge is Ostericum palustre Besser. This work presented comparison of communities with predomination of C.nigra or O. palustre in phytocenotic and yieldforming aspects. In floristic terms, Pratocenoses with C. nigra or O. palustre refer to meadows from the alliance Molinion. Their sward contains small proportion of valuable meadow plants. Habitat differences of both variants determined based on the Ellenberg indices indicate more alkaline character of the subsoil of patches with O. palustre. Yields obtained from the studied areas dominated by C. nigra were on average by about 1 Mg·ha-1 lower and by C. nigra and O. palustre by about 1.5 Mg·ha-1 lower than the mean national meadow productivity. Phosphorus and potassium content was lower than that required in feeding standards. Phosphorus and potassium occurred in larger amounts in sward with O. palustre. Proportion of O. palustre improved calcium balance particularly in the second regrowth. In general agricultural evaluation studied communities should be regarded as low-value. Consequently the main reason for their maintenance is their natural values connected with protection of plant communities and natural habitats.

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