Ensiling capacity and quality of silage were studied as a part of ecosystem research of seminatural, oversown and temporary grasslands. The ensiling capacity was influenced especially by a level of fertilizer nitrogen (N) application and frequency of cuts. The highest content of water-soluble carbohydrates (WSC) and the lowest content of crude protein (CP) was recorded at the 1st cut, but the silage quality was very poor at this cut. Therefore, wilting is necessary at low dry matter (DM) content in herbage. With rising cutting frequencies, CP content increased (r = 0,8221⁺⁺) and WSC content decreased (r = - 0,6689⁺⁺). The lowest WSC content was recorded in oversown grassland and the highest one in temporary sward. Intensive application of N fertilizer showed impact on chemical com position of sward. The content of CP was rising and WSC content decreased (r = - 0,4040⁺). As a result, ensilage capacity deteriorated (Table 1). Silage from the 1st cut had the poorest quality characterized by the highest content of ammonia, free amino-acids and high concentration of butyric acid. The best quality of silage was recorded at the 3rd cut.