Influence of macro-mineral and biological fertilization on the botanical composition and quality of natural grassland in the Central Balkan Mountains

The aim of this study was to evaluate the effects of mineral and biological fertilizers on the botanical composition, structural fibre characteristics, and in vitro dry matter digestibility (IVDMD) of forage biomass from two mountain grassland communities: an Agrostis capillaris-Festuca fallax meadow and a Nardus stricta pasture. Mineral fertilization consisted of calcium ammonium nitrate combined with phosphorus, whereas the biological treatments included Panamin Agro and the sapropel-derived products Blago, Blago 3 and Blago 5. Botanical composition was expressed as the proportion of grasses, legumes and forbs in total fresh biomass. Mineral fertilization increased the proportion of grasses in both grassland types, with the strongest response observed in the meadow, where the highest N-P-Ca treatment increased grass proportion from 60.0% to 79.1%. Biological fertilizers generally increased legume participation and reduced the proportion of forbs, particularly under Blago treatments and the lowest Panamin Agro rate. Fertilization also modified several forage-quality parameters. In both grassland types, the combined Blago 5 + Blago treatment resulted in the lowest NDF, ADF and cellulose concentrations and the highest numerical IVDMD values. Compared with the corresponding controls, IVDMD increased by 19.6% in the meadow and 22.9% in the pasture. The results demonstrate that fertilization effects depended on grassland type, fertilizer product and application rate. Mineral fertilization primarily promoted grass development, whereas selected biological fertilizer treatments, particularly the combined Blago 5 + Blago application, produced a broader response involving greater legume participation, reduced forb contribution, and improved measured forage-quality characteristics.