An impact of grass/clover mixtures (3 grass and 2 clover species) oversown to permanent grassland on dry matter production was carried out at five sites of different altitudes (200-960 m) and soil properties (Table 1) in Slovakia during 1993-95. At zero fertilizer application, the grass/clover mixture oversown to grassland increased annual production from 3.54 to 3.97 t ha⁻¹ (i.e. 19%). At application of PK and two rates of N fertilizer (90 and 180 kg N ha⁻¹ + PK), a relative increase in production was 12, 15 and 6%, respectively. The application of PK to sward without grass/clover mixture oversowing enhanced DM production by 29%. A veraged over the research years and sites, savings on fertilizer represented 60 kg N ha⁻¹ as a result of grass/clover mixture oversown to grassland.
Over a four-year period some microbiological aspects of soil subsystem and proportion of legumes were studied in permanent, oversown and temporary grassland under different level of fertilizer application. The research was carried out in Banská Bystrica, Slovakia, at the altitude of 460 m. The proportion of legumes markedly increased in temporary and oversown grasslands, but decreased with the fertilizer application. There was a positive relationship between CO₂ production in soil and the legume proportion in sward (Figures 1 and 3). However, the correlation between soil CO₂ production and the ratio of soil CO₂ with added N and glucose (NG) to basal CO₂ (B) production (NG/B) was negative. The ratio of NG/B is an indicator of soil organic matter quality (Figures 4 and 5). It was concluded that soil organic matter was more easily degradable in grassland with higher proportion of legumes.