Drought, Nutrition and N2-Fixation Effects On Perennial Peanut Production.

Perennial peanut (Arachis glabrata) is an important forage and hay crop in the southeastern United States.  In many instances, however, the productivity has not been as high as expected.  The objective of the current study was to investigate the possible limitation of nitrogen fixation activity of two common cultivars of rhizoma peanut, Florigraze and Ecoturf.  The possibility of a nutrient limitation was studied using fertigation to apply Fe and KNO₃ in a factorial combination of 300 and 150 kg N ha^-1 yr^-1 and 70 and 140 kg ha^-1 Fe sequestrene.  Shoot mass was significantly increased by both the low and high N dosages, indicating a N limitation to production.  In follow-up studies, perennial peanut shoot production also increased significantly in response to very low NO₃ dosage rates (20 kg N ha^-1 yr^-1) and three Bradyrhizobium inoculants versus unfertilized and uninoculated controls, respectively.  The possibility that soil water-deficit might be a significant constraint on nitrogen fixation of perennial peanut was studied by subjecting plants to gradual soil drying.  Relative to well-watered control plants, transpiration rates of plants grown on drying soil reached a breakpoint at approximately 0.3 fraction of transpirable soil water.  On the other hand, nitrogen fixation activity of these plants displayed no consistent decrease even at very low soil water contents.