This study evaluated the effects of calcium-based soil amendments and pasture composition on forage productivity, nutritional quality, and livestock carrying capacity in high-Andean grassland systems. A field experiment was analyzed using linear mixed-effects models to assess the effects of soil amendments (limestone, dolomite, and gypsum), pasture types (Lolium multiflorum, Trifolium pratense, and their mixture), and their interaction on productivity, nutritional composition, derived nutritional indicators, and feed-related performance. Soil amendments significantly increased forage productivity and feed availability, improving dry matter production, crude protein yield, energy yield, and livestock carrying capacity. Limestone and gypsum showed the most consistent positive effects across productivity-related variables. Pasture composition mainly influenced forage nutritional quality. Trifolium pratense increased crude protein concentration, protein-derived energy, and protein:fiber ratio, while Lolium multiflorum showed higher fiber and carbohydrate concentrations. Mixed pastures exhibited intermediate values, reflecting functional complementarity between species. Although total energy concentration remained unaffected by treatments, calcium-based amendments increased the proportion of protein-derived energy, improving the nutritional efficiency of the forage. Multivariate analysis confirmed clear differentiation between amended and non-amended systems, with legumes associated with improved nutritional quality and productivity-related indicators. In conclusion, calcium-based soil amendments enhance forage production and feed availability, while legume inclusion improves forage protein value. The combined use of soil fertility management and pasture diversification represents an effective strategy to improve feed resources and livestock production efficiency in high-Andean systems.