Elevated Atmospheric CO2 in Agroecosystems: Residue Decomposition in the Field

Elevated atmospheric CO2 concentration can increase biomass production and alter tissue composition. Shifts in both quantity and quality of crop residue may alter carbon (C) and nitrogen (N) dynamics and management considerations in future CO2-enriched agroecosystems. This study was conducted to determine decomposition rates of the legume soybean [Glycine max (L.) Merr.] and nonlegume grain sorghum [Sorghum bicolor (L.) Moench.] residue produced under two levels of atmospheric CO2 (ambient and twice ambient) on a Blanton loamy sand (loamy siliceous, thermic, Grossarenic Paleudults) in Auburn, Alabama, USA, managed using no-till practices. At maturity, harvested plants were separated into component parts for dry weight determination and tissue analysis. Mass, C, and N losses from residues were determined using the mesh bag method. Biomass production was significantly greater for soybean compared to sorghum and for elevated versus ambient CO2-grown plants. The CO2 level had little affect on the C/N ratio of residue (probably because the tissue used was senesced). Elevated CO2 concentration did not affect percent residue recovery; however, greater biomass production observed under elevated CO2 resulted in more residue and C remaining after overwintering. The higher total N content of soybean residue, particularly when grown under elevated CO2, indicated more N may be available to a following crop with lower N inputs required. Results suggest that in a high CO2 environment, greater amounts of residue may increase soil C and ground cover, which may enhance soil water storage, improve soil physical properties, and reduce erosion losses.