Overseeding aeschynomene and N fertilization effects on forage characteristics, N fixation, and N2O-N emissions of bahiagrass pastures

Aeschynomene (Aeschynomene americana L.) is a warm-season annual legume forage used in tropical and subtropical regions; however, there is limited information on agronomic and environmental benefits of aeschynomene when overseeded into bahiagrass (Paspalum notatum Flugge) swards. The objective of this study was to evaluate the effects of overseeding aeschynomene or applying N fertilizer to existing bahiagrass on forage characteristics, atmospheric N fixation, and N2O-N emissions. The study was conducted in Ona, FL, from April 2019 to March 2021. Treatments were the split-plot arrangement of bahiagrass-aeschynomene or bahiagrass monoculture (main plot) and N fertilization level (0 or 60 kg N ha(-1); subplot), distributed in a randomized complete block design with four replicates. Nitrogen fixation was estimated in plots receiving no N fertilization. The static chamber technique was used to estimate N2O-N emissions. Overseeding aeschynomene did not increase forage accumulation (mean = 1300 kg dry matter [DM] ha(-1) harvest(-1)) or N2O emissions (mean = 15 g N2O-N ha(-1) per day), but increased forage crude protein (CP) concentration (from 98 to 108 g kg(-1)) when compared to bahiagrass monoculture. Nitrogen fertilization increased forage accumulation (from 1200 to 1400 kg DM ha(-1) per harvest) but it did not affect aeschynomene N fixation (84% N derived from atmospheric fixation [Ndfa]). Nitrous oxide emissions had significant temporal variability across all treatments; however, there were no differences in accumulated N2O-N emissions among treatments (mean = 2.4 kg N2O-N ha(-1) per year). Overseeding aeschynomene is an effective management practice to increase forage CP concentration in pastures without increasing N2O-N emissions.