Research Note: The use of Lolium multiflorum and uninoculated Trifolium subterraneum as reference crops in nitrogen fixation studies

Abstract

The ¹⁵N natural abundance and¹⁵ N dilution methods were used to determine the viability of using either Lolium multiflorum (annual ryegrass) or uninoculated Trifolium subterraneum (subterranean clover), as non‐fixing reference crops in N₂‐fixation studies. The δ¹³N values for the¹⁵ N natural abundance method and atom% ¹⁵N values for the ¹⁵N dilution method for plant and soil samples are presented. The ryegrass pastures showed the least variation in δ¹⁵N and atom% ^I5N values between experimental plots. This crop appeared to be a more appropriate choice in such studies, but further investigation is needed to confirm this observation. The use of uninoculated subterranean clover as a reference crop seemed problematic, since inoculation with effective rhizobia could not be prevented. Relatively high variation in δ¹⁵N values for inoculated subterranean clover was obtained compared to the atom% ¹⁵N values. This result indicated that the use of the ¹⁵N natural abundance method should be evaluated for other pasture legume species.

Additional index words:

• Nodulation
• ryegrass
• subterranean clover
• Woogenellup
• ¹⁵N