Integrating forage legumes reduces dependence on N fertilizer and increases the stability of grazing systems

Midst increasing global demand for livestock products, grassland-livestock systems face challenges including pasture degradation and climate change. The introduction of nitrogen (N)-fixing legumes into grass monocultures addresses these challenges and may sustain or increase livestock production with fewer off-farm inputs. This 10-yr study assessed N fertilization level and legume integration effects on cool- and warm- season herbage responses, animal performance, and system stability of bahiagrass ( Paspalum notatum Flügge) pastures. Including diverse legume species added a total of 139 kg N ha −1 yr −1 , 66 kg ha −1 during the cool season and 73 kg ha −1 during the warm season, via biological N fixation. The inclusion of rhizoma peanut (RP; Arachis glabrata Benth.) and clovers ( Trifolium spp.) resulted in similar animal performance to N-fertilized, grass-only systems. Cool + warm-season liveweight gain on Grass+N and Grass+RP systems averaged 635 and 626 kg ha −1 , respectively, with the legume integration reducing N fertilizer inputs by 85 % (224 vs. 34 kg N ha −1 yr −1 ). The proportion of RP in feces was 49.5 % compared with ∼35 % in pasture herbage mass, indicating the preference of grazing animals for RP. Cattle average daily gain was successfully predicted from fecal δ 13 C (‰) ( P < 0.001). Over a decade, the grass-legume mixture was more stable than the other grazing systems ( P = 0.07), and increasing the system biodiversity improved overall system performance. In conclusion, integrating forage legumes into bahiagrass pastures reduced dependence on N fertilizers without sacrificing cattle performance, potentially improving the economic return and stability of the system. Increased biodiversity in the Grass+RP enhances the stability of the system. The system’s biodiversity depends on the number of grass and legume species included, affecting herbage distribution and nutritive value. Including C 3 species improves the nutritive value of C 4 warm-season grasses, and legumes add atmospheric nitrogen to the system by biological nitrogen fixation (BNF). Animals consume forages and their responses depend on the herbage quantity and quality. The aboveground forage not consumed by livestock plus the belowground root rhizomes will return nutrients to the system, acting as a reservoir of nutrients. Likewise, the material ingested by animals is excreted, returning nutrients to the system. Soils act as a pool of nutrients for plant growth providing continuous from the soil organic matter (SOM). • Grass-legume mixtures produced similar animal gains compared to N-fertilized grass systems, with 85 % fewer off-farm inputs. • Including diverse legume species added a total of 139 kg N ha −1 yr −1 , being more efficient than N fertilizers. • Including different forage species in the system throughout the year enhances the grazing system stability. • The use of δ 13 C fecal samples can help predict the ADG, indicating a novel application of this technique.