Productivity of selected grasses in mixtures with Trifolium repens L. at two levels of nitrogen fertilization

The paper contains a compilation of results of field research conducted in 2007-2009 at the \nPlant Breeding Station-HBP in Skrzeszowice near Krakow (220 m a.s.l.). The investigations compared two grasses: hybrid ryegrass (Gala, c.v.) and perennial ryegrass (Solen c.v.) cultivated in mixtures with white \nclover (Romena c.v.) sown 50% each. Grasses in mixtures were evaluated against the background of diversified \nnitrogen fertilization rates of 50 and 100 N kg N/ha. The aim of the investigations was comparison of hybrid ryegrass and perennial ryegrass in view of gas exchange, chlorophyll level in leaves and yielding of two-species mixtures at two levels of mineral nitrogen fertilization. During the three-year period of investigations the hybrid ryegrass revealed greater intensiveness of photosynthesis and transpiration, as well as higher average number of chlorophyll pigments than perennial ryegrass. Both grasses assimilated best \nin the second and third re-growths at the rate of 50 N kg/ha. Increasing the rate to 100 N kg/ha caused a decline in photosynthesis. The lowest SPAD values were noted in plants fertilized with nitrogen dosed 50 N kg/ha and in the second place in plants from the control treatments. Higher values of this index were \nassessed in plants fertilized with a higher nitrogen dose. A mixture of white clover with hybrid ryegrass yielded better than the mixture with perennial ryegrass. Nitrogen fertilization had a significant effect on \nmixture yielding during the vegetation season only when applied at the rate of 100 N kg/ha.