Grass ecosystems perform productive functions and significant non-productive functions – ecological and environmental. The sod (root biomass and tillering zone), with a dominant share of 80 % in primary grass swards production, ensures these functions. The production of root biomass and above ground phytomass was examined on three grass swards types - permanent grass swards (PGS), over-sown grass swards (OGS), temporary grass swards (TGS) with four variants of mineral nutrition. The experiment was carried out in the research area of GMARI in Banská Bystrica (Slovak Republic). Root sampling was realized from the soil profile 0-100 mm by the method of monoliths. The lowest root biomass production was observed on TGS (7.3 t.ha^-1), the highest production on PGS (8.27 t.ha^-1). The root biomass production is highly influenced with mineral nutrition and with climate change. The significantly highest amount of root biomass (8.3 t.ha^-1) was produced on grass swards fertilized at highest doses of nutrients (180 kg N + 30 kg P + 60 kg K.ha^-1) and amount of root biomass was significantly higher during the dry years than climatically normal and wet years. Parameter for the evaluation of drought effect on the grass swards is the ratio of the root mass to the above ground mass ratio (R/S). The results of R/S (4.02 - 5.16) demonstrate the significant ecological stability of the grass swards to the drought stress factor. The accumulation of biogenic elements in roots and in above ground phytomass of grass swards was also determined. The total grass sward biomass accumulate: 362.7 kg.ha-1 N, 41.8 kg.ha^-1 P, 252.1 kg.ha^-1 K, 115.5 kg.ha^-1 Ca, 49.7 kg.ha^-1 Mg on average. Root biomass has considerable importance in protection of the environment and food chain, because accumulates heavy metals from soil and prevents excessive release to the above ground biomass using as forage for livestock.