Nitrogen Dynamics in Bahiagrass-Rhizoma Peanut Mixtures in Contrast with Their Monocultures.

Nitrogen fertilization is an important management practice to increase forage growth. Cost and environmental impacts of N fertilizer, however, may reduce its use. In this study, we evaluated biological N₂-fixation (BNF), % of nitrogen derived from the atmosphere (%Ndfa), and N losses (NH₃ and NO₃^-) to the environment for mixtures and monocultures of bahiagrass (Paspalum notatum Flüggé) and rhizoma peanut (RP; Arachis glabrata Benth.). Treatments consisted of two bahiagrass entries (‘Argentine’ and an experimental entry; DF9), which received 90 kg N ha^-1 after each harvest, two RP entries (Ecoturf and an experimental entry; Q6B), and the mixture of each bahiagrass with each RP. Plots were harvested every 6 wk. Nitrate concentration in leachate did not differ among treatments (P > 0.05), averaging 0.09 mg L^-1. Loss due to NH₃ volatilization for bahiagrass plots was greater compared with the mixtures and RP monocultures (P < 0.05), with no differences among grasses (P > 0.05). Ammonia volatilization for DF9 and Argentine was 0.170 and 0.136 kg N ha^-1 d^-1, respectively, while the means for the mixtures and RP monocultures were 0.016 and 0.020 kg of N ha^-1 d^-1, respectively. The %Ndfa for Q6B increased when mixed with Argentine (92.5%), and differed (P < 0.05) from its monoculture (78%) and the association with DF9 (76%). Ecoturf %Ndfa did not differ among treatments (P > 0.05) and averaged 87%. The BNF contributed more to biomass production in the monocultures when accounting the rhizoma peanut portion of the stand (P < 0.05). Ecoturf and Q6B fixed 39 and 43 kg N ha^-1 harvest^-1, respectively, while their corresponding mixtures fixed 17 and 21 kg N ha^-1 harvest^-1. Mixtures of bahiagrass-RP required less external input of N fertilizer, leading to lower N losses to the environment while providing similar or greater amounts of forage than fertilized bahiagrass.