An experiment was conducted in plastic pots filled with loamy sand and inserted into the soil. Half of the pots were sown with one species, orchard grass, and half with a mixture of six grass species. Every year at the end of May, half of the pots in each variant was enriched with 300 g DM of earthworm casts per pot. To estimate the abundance of Enchytraeidae, Acarina and Collembola, soil samples were taken three times per season. The abundance of enchytraeids was significantly higher in the orchard grass monoculture and in pots enriched with earthworm casts, especially at high population densities. No unequivocal effect of vegetation and earthworm casts on the Acarina and Collembola density was observed.