Assessing Biological N2 Fixation in a Perennial Warm-Season Grass/Legume System.

Incorporating perennial legumes into grasslands or into more urban settings, such as medians, road easements, or lawns, provides a more sustainable system requiring little to no maintenance N fertilizer inputs. Rhizoma peanut (Arachis glabrata Benth) is an attractive legume candidate with biological N₂ Fixation (BNF) ability that can be added to a subtropical perennial grass system. However, it is unclear if the actively growing legume contributes N to the grass component. A field plot study compared two rhizoma peanut cultivars, Ecoturf and experimental line Q6b grown at two Florida locations, in replicated field plots, as monocultures or mixed with either of two bahiagrass (Paspalum notatum Flüggé) cultivars, Argentine or experimental dwarf line, F9. Yield, soil fertility, plant nutrient composition, and natural abundance ¹⁵N were measured in 2014. Mixed plantings produced as much or sometimes more dry yield than the experimental dwarf bahiagrass in monoculture. The two sites differed in BNF patterns, where above-ground tissue from the legume plots at the central Florida location (Alorthod soil type) were much more depleted in 15N than the grass monoculture plots. Additionally, grasses from the mixed plantings more closely resembled the legume isotopic signatures than they did the grasses from monoculture plots. This was not the case at the northwest Florida location (Kandiudult soil type), where the isotopic signatures were more similar among all the treatments. Comparative differences among location conditions and cultivars will be discussed in terms of using natural abundance ¹⁵N for quantifying BNF in warm-season, grass/legume plantings.