First-Cut Yield and Forage Quality of Grass–Legume Mixtures Differing in Composition and Intended Use Across Two Years

Grass–legume mixtures can improve forage productivity and quality, but their performance may vary between years. This study evaluated grass–legume mixture types differing in composition and intended use (forage, universal, and grazing) across two growing seasons, focusing on the first cut. Mixtures were assessed for dry matter yield, botanical composition, chemical composition, and plant height, and principal component analysis (PCA) was used to describe multivariate trait patterns. The year strongly affected mixture performance. Mean dry matter yield decreased from 6949 ± 212 kg ha−1 in 2023 to 1588 ± 94 kg ha−1 in 2024, corresponding to an approximately 76% reduction. In 2023, forage mixtures produced the highest yield, followed by universal and grazing mixtures, whereas in 2024, differences among mixture types were not significant. Botanical composition shifted toward a higher legume proportion in 2024, while mixture type differences in chemical composition largely converged, except for DMD. PCA showed clearer separation among mixture types in 2023, with PC1 and PC2 explaining 64.9% and 17.6% of variance, respectively, whereas separation weakened in 2024. These results indicate that mixture composition and intended use influenced productivity and quality mainly under more favorable growing conditions, while year-to-year variation strongly constrained first-cut mixture performance.