Location: Dale Bumpers Small Farms Research CenterTitle: N2 fixation of common and hairy vetches when intercropped into switchgrass
|ALLEN, FRED - University Of Tennessee|
|WARWICK, KARA - University Of Tennessee|
|KEYSER, PATRICK - University Of Tennessee|
|BATES, GARY - University Of Tennessee|
|TYLER, DONALD - University Of Tennessee|
|LAMBDIN, PARIS - University Of Tennessee|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2017
Publication Date: 6/8/2017
Citation: Ashworth, A.J., Allen, F.L., Warwick, K.S., Keyser, P.D., Bates, G.E., Tyler, D.D., Lambdin, P.L., Pote, D.H. 2017. N2 fixation of common and hairy vetches when intercropped into switchgrass. Agronomy Journal. 7(2):39. doi:10.3390/agronomy7020039.
Interpretive Summary: For farmers seeking economical ways to produce a forage/biomass crop on marginal lands, switchgrass (a native North American forage grass) has shown potential for providing high yields when supplied with adequate nitrogen inputs. Commercial inorganic nitrogen fertilizers are expensive and tend to acidify soil, so vetch and other legume crops that deposit atmospheric nitrogen to the soil can provide an attractive alternative method for fertilizing switchgrass. Researchers seeded two vetch species (each at 6 pounds of pure live seed per acre) into switchgrass plots to determine the ability of vetch to survive, deposit atmospheric nitrogen, and increase switchgrass yields. Hairy vetch deposited an average of 39 pounds of nitrogen while common vetch supplied 53 pounds of nitrogen per acre and seemed to increase switchgrass yield; but these were less than the target rate of 60 pounds per acre recommended for switchgrass production. Researchers estimated that planting 7 pounds (common vetch) or 9 pounds (hairy vetch) of pure live seed per acre could produce sufficient vetch densities to significantly increase switchgrass yield. This study is of interest to scientists, extension personnel, agricultural producers, and the biomass industry because it shows that vetch can be successfully intercropped with switchgrass to increase nitrogen inputs, but vetch seeding rates should be greater than 6 pounds of pure live seed per acre if the producer hopes to significantly increase switchgrass yield.
Technical Abstract: Interest in alternatives to synthetic nitrogen (N) fertilizer for switchgrass (Panicum virgatum L.) forage and bioenergy production continues to increase, and interseeding legumes into swards may be one such prospect. Common vetch (Vicia sativa L.) occurs naturally throughout the U.S. and has fewer hard seed than hairy vetch (Vicia villosa L.), thus reducing potential weed issues. Consequently, objectives were to: i) test physical and chemical seed scarification techniques (10 total) for common vetch germination; ii) determine whether or not switchgrass yields are increased by vetch N2-fixation under optimum primary seed dormancy suppression methods; and, iii) determine N2-fixation rates of common and hairy vetch via the N-difference method. Results suggest among all scarification methods tested herein, chemical seed scarification (sulfuric acid) and mechanical pretreatment [0.7 kg of pressure for one minute (31% germination)] improved common vetch germination by 60 and 50%, respectively, relative to controls. Assuming a bioavailability rate of 50%, N2-fixation rates via the N-difference method were 59.3 and 43.3 kg N ha-1 for aboveground plant matter when chemically scarified and seeded at a rate of 7 kg pure live seed (PLS) ha-1 for common and hairy vetch, respectively. This seeding rate for common and hairy vetches did not affect cv. ‘Alamo’ switchgrass yields after the first year’s production (P>0.05). However, based on atmospheric N2-fixation rates and vetch plant densities, seeding rates of 8 and 10 kg PLS ha-1 for common and hairy vetch, respectively, would be required to obtain plant densities sufficient for biological N2-fixation at the current recommended rate of 67 kg N ha-1 for switchgrass biomass production in the Southeast.