Prior, Stephen A. (USDA-ARS National Soil Dynamics Laboratory, Global Change Research, 411, South Donahue Drive, Auburn, AL, 36832; Phone: 334-844-4741 ext.143
Fax:  334-887-8597; Email:,


Elevated Atmospheric CO2 Effects on Residue Decomposition of Different Soybean Varieties


Stephen A. Prior *, H.A. Torbert, G.B. Runion, H.H. Rogers, D.R. Ort, R.L. Nelson


Elevated atmospheric CO2 can result in larger plants returning greater amounts of residues to the soil.  However, the effects of elevated CO2 on carbon (C) and nitrogen (N) cycling for different soybean varieties has not been examined.  Aboveground residue of eight soybean varieties (Glycine max [L.] Merr.) was collected from a field study where crops had been grown under two different atmospheric CO2 levels [370 ppm (ambient) and 550 ppm (free-air carbon dioxide enrichment) (FACE)].  Senesced residue material was used in a 60-day laboratory incubation study to evaluate potential C and N mineralization. Residue N concentration was usually increased by FACE, but residue C concentration was not altered. Varietal differences were observed with the oldest variety having the lowest residue N concentration and highest residue C: N ratio. Residue C: N ratio was lower under FACE, which could be attributed to increased N fixation. Mineralized N was usually increased by FACE, except for a non-nodulating variety, suggesting that increased N fixation impacted residue decomposition. Mineralized N was lowest in the oldest variety illustrating the influence of high residue C: N ratio. Across varieties, mineralized C was increased slightly by FACE, however, differences in varieties suggest that the impact of elevated CO2 on C mineralization could be influenced by soybean variety selection