Increasing diversity of warm- and cool-season species enhances aboveground and root carbon and nitrogen accumulation in subtropical forage mixtures

Abstract Background and aims This study evaluated how increasing forage species diversity affects herbage and root mass, associated C and N accumulation, and soil particulate organic matter (POM). Methods Over three years a field experiment compared a baseline system of warm-season perennial bahiagrass ( Paspalum notatum ) annually overseeded with black oat ( Avena strigosa ) to eight mixtures containing 3 to 6 species, including legumes and grasses, differing in seasonal growth (warm vs. cool season) and life cycle (annual vs. perennial). Added legumes included warm-season forage peanut ( Arachis pintoi ) and cool-season white clover ( Trifolium repens ), while added grasses included warm-season limpograss ( Hemarthria altissima ) and cool-season annual ryegrass ( Lolium multiflorum ). Results Increasing diversity from the two-species baseline to mixtures containing 3–6 species increased herbage accumulation, root mass and respective C and N accumulation under cool and warm seasons. The addition of legume species consistently increased herbage and root N accumulation. The addition of warm-season species increased annual herbage accumulation, while cool-season species increased both herbage and root mass during the cool-season. Only annual ryegrass contributed to greater soil POM-C and POM-N after three years. Conclusions Increasing diversity in forage mixtures from two to 3 − 6 species had a positive effect on herbage, roots and C and N accumulation in a subtropical environment in Southern Brazil. The contribution of species varied depending on whether they were cool or warm-season species, or whether they belonged or not to the legume family. Selecting complementary species based on functional characteristics is therefore key to obtaining benefits from diverse forage swards.