326-7 Estimation of Nitrogen Fixation Rates of Common Versus Hairy Vetch and Seeding Rates Needed for Interseeding Into Established Switchgrass Stands.



Wednesday, October 19, 2011
Henry Gonzalez Convention Center, Hall C, Street Level

Kara Warwick1, Fred Allen2, Patrick Keyser1, Gary Bates1, Donald Tyler1, Paris Lambdin1 and Amanda Ashworth3, (1)Plant Science, University of Tennessee, Knoxville, TN
(2)University of Tennessee, Knoxville, TN
(3)Department of Forestry, Wildlife and Fisheries, Universty of Tennessee, Knoxville, TN
Interest in alternative sources to synthetic N fertilizer for switchgrass (Panicum virgatum) production continues to grow. Nitrogen fixing legumes interseeded into switchgrass may be one alternative. Common vetch (Vicia sativa) is a N-fixing legume that occurs naturally throughout the Southeast as well as other parts of the U.S. It has less hard seed than hairy vetch, making it less of a weed problem and common may fix N at similar rates to hairy vetch (Vicia villosa). The objectives of this study were to: a) determine and compare nitrogen fixation rates of common  and hairy vetch when seeded into established stands of 'Alamo' cv. switchgrass and b) estimate stand densities needed to fix the recommended N rate (67 kg ha-1) for switchgrass biomass production.  In this study, N-fixation rates via the N-difference method were determined to be 59.3 and 43.3 kg N ha-1 for common and hairy vetch, respectively when seeded at 6.7 kg ha-1.   At these rates, neither common nor hairy vetch significantly affected switchgrass yields. Based on the N fixation rates and vetch plant masses determined in this study, we estimate that minimum seeding rates of 7.6 and 10.4 kg PLS ha-1 of common and hairy vetch will be required to obtain plant stands needed to fix the current recommended rate of N for switchgrass biomass production.
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