| Rhizoma peanut (Arachis glabrata Benth.) is an important perennial forage and hay legume in the southeastern United States. The potential nitrogen (N) limitation on rhizoma peanut growth and options for enhancing the symbiotic N2 fixation inputs were explored in the current study.;The potential N deficit for maximum rhizoma peanut production was evaluated in two experiments. For Ecoturf and Florigraze, optimal N accumulation in two greenhouse studies was saturated by the 192 mg m-2 wk -1 treatment (21 kg ha-1). In the field significant differences in yield and N accumulation occurred only at the first harvest date. All three experiments confirm that N2 fixation does not fully provide the N necessary for optimal perennial peanut production.;Inoculant application to increase N2 fixation in rhizome peanut was explored in two experiments. In the greenhouse, four inoculants were applied to intact cores of rhizoma peanut growing in field soil. Yield, nodulation, nitrogenase activity, and N accumulation responses to the inoculants were not significant. Differences in yield and N accumulation were attributable to the core origins. This result raises further questions about interactions between management practices, soil characteristics and N2 fixation potential of this crop. Inoculation was further evaluated by DNA analysis. Rhizoma peanut was found to be nodulated with multiple strains indigenous bacteria that were very similar to the inoculants applied. Only three of 12 nodules evaluated contained either of the two inoculants, indicating low inoculant competitiveness.;Drought tolerance may limit rhizome peanut growth and N2 fixation. Transpiration rates and nitrogenase activity of Florigraze, Ecoturf, and Arbrook rhizoma peanut were evaluated under drying soil conditions. The normalized transpiration rate breakpoints versus fraction of tranpirable soil water were 0.32, 0.23, and 0.23, respectively, which indicates that rhizoma peanut is a relatively drought tolerant crop. Normalized nitrogenase activity of Florigraze and Ecoturf did not respond to drying soil, and Arbrook rates were too low to estimate.;Rhizoma peanut was N-limited under both controlled and field conditions. Available inoculants were not able to increase yield or N2 fixation, and rhizoma peanut is a drought tolerant crop with respect to both transpiration rate and nitrogenase activity. |
