Submitted to: International Soil Tillage Research Organization Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 14, 2003
Publication Date: July 14, 2003
Citation: Prior, S.A., Runion, G.B., Torbert, H.A., Rogers, H.H., and Reeves, D.W. 2003. Effects of elevated atmospheric CO2 on biomass production and C sequestration: Conventional and conservation cropping systems. In: Soil Management for Sustainability, International Soil Tillage Research Organization, 16th Triennial Conference Book of Abstracts, University of Queensland, Brisbane, Australia, July 14-18. p. 943-948. Interpretive Summary: Increased CO2 in the atmosphere has led to concerns regarding potential environmental changes and how crops will be managed. Our goal was to determine how elevated CO2 would affect crop production and soil C storage under different management conditions (conventional and conservation). Cover crop residue production can be expected to be increased by high CO2 in conservation systems. But, the variable response of weeds to CO2 in the conventional system suggest more work is required to clarify management implications. Rising CO2 levels can be expected to increase soybean residue more than that of sorghum regardless of management systems used. Grain yield will likely be increased (due to high CO2) for soybean followed by wheat and sorghum. Total residue production was increased by high CO2 and conservation management. This resulted in increased soil carbon in the soil profile, suggesting that in a future elevated CO2 world, agroecosystems could store more C, especially with conservation management. Results also suggest that with conservation management in a high CO2 environment, more crop residue will increase ground cover (thereby improving water infiltration and soil water storage, and reducing soil erosion).
Technical Abstract: Increasing atmospheric CO2 concentration may impact production agriculture's role in sequestering carbon (C). This study was initiated (fall 1997) to compare the effects of elevated CO2 on two cropping systems (conventional and conservation). The experiment was a split-plot design replicated three times with two cropping systems as main plots and two CO2 levels (ambient and twice ambient) as subplots using open top field chambers on a Decatur silt loam (clayey, kaolinitic, thermic Rhodic Paleudults). The conventional system consisted of a grain sorghum [Sorghum bicolor (L.) Moench.] and soybean [Glycine max (L.) Merr.] rotation using conventional tillage practices and winter fallow. In the conservation system, sorghum and soybean were rotated and three cover crops (also rotated) were used [crimson clover (Trifolium incarnatum L.), sunn hemp (Crotalaria juncea L.), and wheat (Triticum aestivum L.)] using no-tillage practices. The conservation system had either cash or cover crops grown throughout the year with no fallow periods (in order of: clover, sorghum, sunn hemp, wheat, and soybean). Biomass responses over two complete 2-year cropping cycles (total of 4 years) and the effect of these two contrasting management systems on C sequestration were evaluated. In the conservation system, cover crop residue production (clover, sunn hemp, and wheat) was increased by high CO2, but CO2 effects on weed residue were variable in the conventional system. Elevated CO2 had a greater effect on increasing soybean residue compared to sorghum. Grain yield increases due to added CO2 were greater for soybean followed by wheat and sorghum. Differences in sorghum and soybean residue production within the different management systems were small and variable. Cumulative non-yield residue inputs (both 2 yr cycles) were increased by elevated CO2 and conservation management. Greater inputs resulted in a substantial increase in soil C concentration at the 0-5 cm depth increment in the conservation system under CO2-enriched conditions. Conservation management increased soil C concentration at lower depths (5-10 and 15-30 cm) and CO2-induced increases also occurred at the 5-10 cm depth (similar trend at15-30 cm) in both management systems. Results suggest that with conservation management in a high CO2 environment, greater amounts of crop residue could increase soil C storage as well as increase ground cover, improve water infiltration and soil water retention, and reduce erosion.