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Title: Elevated atmospheric carbon dioxide effects on soybean and sorghum gas exchange in conventional and no-tillage systems

Author
item Prior, Stephen - Steve
item Runion, George
item Rogers Jr, Hugo
item Arriaga, Francisco

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/6/2009
Publication Date: 3/1/2010
Citation: Prior, S.A., Runion, G.B., Rogers Jr, H.H., Arriaga, F.J. 2010. Elevated atmospheric carbon dioxide effects on soybean and sorghum gas exchange in conventional and no-tillage systems. Journal of Environmental Quality. 39:596-608.

Interpretive Summary: Increasing atmospheric CO2 concentration may impact agriculture. This study examined the effect of elevated atmospheric CO2 level (ambient and twice ambient) under different crop management systems (conventional tillage and no-tillage). Row crops studied included grain sorghum and soybean. The no-till system included crimson clover, sunn hemp and wheat as winter cover crops. Over several seasons (three for each row crop), the effect of management and CO2 level on leaf level gas exchange during reproductive growth were evaluated. Findings were consistent across years with higher photosynthetic rates seen under high CO2 (more with soybean) regardless of management. Further, high CO2 decreased transpiration and increased water use efficiency. Results suggest that better soil moisture conservation and high rates of photosynthesis can occur in both tillage systems in CO2-world during reproductive growth.

Technical Abstract: Increasing atmospheric CO2 concentration has led to concerns about potential effects on production agriculture. In the fall of 1997, a study was initiated to compare the response of two crop management systems (conventional tillage and no-tillage) to elevated CO2. The study used a split-plot design replicated three times with two management systems as main plots and two atmospheric CO2 levels (ambient and twice ambient) as split-plots using open top chambers on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system was a grain sorghum [Sorghum bicolor (L.) Moench.] and soybean [Glycine max (L.) Merr.] rotation with winter fallow and spring tillage practices. In the no-tillage system, sorghum and soybean were rotated and three cover crops were used [crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)] under no-tillage practices. Over multiple growing seasons, the effect of management and CO2 level on leaf level gas exchange during row crop [soybean (1999, 2001, 2003) and sorghum (2000, 2002, 2004)] reproductive growth were evaluated. Treatment effects were fairly consistent across years. In general, higher photosynthetic rates were observed under CO2 enrichment (more so with soybean) regardless of residue management practice. Further, elevated CO2 led to decreases in stomatal conductance and transpiration, and water use efficiency was increased. Management had little effect on gas exchange measurements. These results suggest that better soil moisture conservation and high rates of photosynthesis can occur in both tillage systems in CO2-enriched environments during reproductive growth.