Defoliation Effects on Regrowth, Nodulation, and Nitrogenase Activity at Anthesis with Hairy Vetch
1980
Lynd, J. Q. | McNew, Ronald W. | Odell, George V.
Pasture legumes present a great potential to increase productivity of pastures. Little information is now available concerning quantitative evaluation of symbiotic N fixation with pasture legumes such as hairy vetch (Vicia villosa, Roth). Results from 3 years of study are summarized to determine the influence of defoliation and regrowth on tillering, nodulation, and nitrogenase activity (C₂H₂ reduction) at anthesis with ‘Madison’ hairy vetch inoculated with Rhizobium legumimsarum Frank, ATCC 10314. Plants were grown in a siliceous thermic Psammentic Paleustalf (Eufaula) of pH 6.1. Peak nitrogenase activity of field grown plants occurred at anthesis about 250 days after emergence. Highly significant increases in tillering resulted with three defoliations at 45, 90, and 180 days along with increased nodule fresh weight, nodule umbers, and nitrogenase levels. Abundant large cluster nodule types occurred on root systems of most plants regardless of defoliation treatment. Significant correlations were apparent for nitrogenase levels with top weight, number of tillers, nodule weight, and number of nodules for plants receiving the threedefoliation treatment. Nodule number was significantly correlated with top weight. Nodule number and nodule weight were nega. tively related probably due to an influence from frequent large nodule cluster development. No significant correlations were apparent with the nondefoliated plants. Multiple regressions indicated nitrogenase levels were influenced in decreasing order by nodule weight, tillers, top weight, and nodule number with R₂ = 0.775, C.V. = 29.1% P < 0.001. The pot culture technique used may be adapted for nondestructive evaluations with repotted plants utilized for plant breeding and further symbiotic N fixation research.
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