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Title: Free-air CO2 enrichment of sorghum: Soil carbon and nitrogen dynamics

item Prior, Stephen - Steve
item Torbert, Henry - Allen
item Runion, George
item Rogers Jr, Hugo
item Kimball, Bruce

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/13/2007
Publication Date: 5/1/2008
Citation: Prior, S.A., Torbert III, H.A., Runion, G.B., Rogers Jr, H.H., Kimball, B.A. 2008. Free-air CO2 enrichment of sorghum: Soil carbon and nitrogen dynamics. 37:753-758.

Interpretive Summary: The increasing level of CO2 in the atmosphere has led to concerns regarding future changes in the global environment. One important issue is whether the often reported increase in crop growth by elevated atmospheric CO2 will lead to organic matter buildup in soil. Our results suggest that more soil C storage could be expected in sorghum production systems under elevated CO2 conditions. Accumulation of more soil carbon could potentially reduce the level of CO2 in the atmosphere as well as increase soil productivity.

Technical Abstract: The positive impact of elevated atmospheric CO2 concentration on crop biomass production suggests more carbon inputs to soil. Further study on the effect of elevated CO2 on soil carbon and nitrogen dynamics is key to understanding the potential for long-term carbon storage in soil. Soil samples (0-5, 5-10, and 10-20 cm depths) were collected after two years of grain sorghum [Sorghum bicolor] (L.) Moench.] production under two atmospheric CO2 levels [370 (ambient) and 550 ppm (free-air CO2 enrichment) (FACE)] and two water treatments (ample water and limited water) on a Trix clay loam (fine, loamy, mixed (calcareous), hyperthermic Typic Torrifluvents) at Maricopa, AZ. In addition to assessing treatment effects on soil organic C and total N, potential C and N mineralization and C turnover were determined in a 60 day laboratory incubation study. After two years of FACE, soil C and N were significantly increased at all soil depths. Water regime had no effect on these measures. Increased total N in the soil was associated with reduced N mineralization under FACE . Results indicated that potential C turnover was reduced under water deficit conditions at the top soil depth. However, C turnover was not impacted under FACE, thus implying that the observed increase in soil C with elevated CO2 may be stable relative to ambient CO2 conditions. Results suggest that, over the short-term, a small increase in soil C storage could occur under elevated atmospheric CO2 conditions in sorghum production systems with differing water regimes.