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Factors Influencing Early Performance of Leguminous Plants in Forest Soils

USDA-Forest Serv., Southeastern Forest Exp. St., Research Triangle Park, NC 27709

R. J. Volk

Dep. of Soil Science

C. B. Davey

Dep. of Soil Science and Forestry, North Carolina State Univ., Raleigh, NC 27695-7619

*Corresponding author.

ABSTRACT

Subterranean clover (Trifolium subterraneum L.), a winter annual, and big trefoil(Lotus pedunculatus Cav.), a summer perennial, are being studied for use in forestry operations. Establishment and performance of these plants with their associated rhizobia (+RHIZ) are adversely affected by the infertile, acid conditions generally encountered in forest soils. Using the ¹⁵N isotope dilution technique, we investigated the effects of N fertilization and inoculation with the vesicular-arbuscular mycorrhizal fungus, Gigaspora margarita Becker and Hall (+VAMF) on early growth and N₂-fixing capabilities of these plants in a pasteurized acid forest soil containing low levels of both P and N. In clover, dual inoculation with + RHIZ, + VAMF at 10 kg N ha^–1 enhanced N derived from the atmosphere (Ndfa), both on a per-plant (350%) and a per-gram total N (151%) basis, as well as plant biomass (68%) and flower production (100%) over the corresponding values for + RHIZ plants. Increasing N to 100 kg N ha^–1 resulted in greater biomass (24%) in dual-inoculated clover, but concurrently decreased the amount of Ndfa while increasing the amount of N derived from the soil (Ndfs). Compared to + RHIZ trefoil, dual inoculation of trefoil (+ RHIZ, + VAMF) resulted in greater biomass production at 100 kg N ha^–1, but had no significant effect on Ndfa or Ndfs. Increasing soil N increased biomass production, but did not reduce Ndfa in dual-inoculated trefoil. The difference in response to G. margarita inoculation may be a reflection of the annual vs. perennial nature of subterranean clover and big trefoil, respectively. The shift in biomass production and Ndfa in nodulated plants at the higher N level demonstrates the need to modify site management practices in order to maximize tree growth and leguminous plant-biological N fixation benefit to the site.

Contribution from the Dep. of Forestry, North Carolina State Univ. Paper no. 11644 of the Journal Series of the North Carolina Agric. Res. Serv.

Received for publication June 14, 1988.