Amount of root mass created in soil profile of 0-100 mm of grasslands was investigated on the course of three years (1993-1995). Dynamics of root mass growth of grasslands was investigated under the three different types: 1. permanent grassland (TTP) 2. temporary grassland (DTP) 3. reseeded grassland (PTP) and four treatments of fertilization. Nitrogen fertilizers were applied to respective growth period of cuts in even doses, P and K by one-shot application in spring. The grasslands were exploited by mowing three times during growing season. Root increment of three types of grasslands fluctuated during growing season from 0.06 kg.m-2 to 0.30 kg.m-2 within investigated years. Significant effect of years on the accumulated root mass amount was confirmed when decisive driving factor seems to be sum of precipitation in growing season (r = 0.797+). In contrary, effect of both various mineral nutrition and type of grassland on root mass accumulation was not confirmed. Lower root mass increments in resown grassland (PTP) could be influenced by allelophaty effect.