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Soil Organic Carbon and Nitrogen Accumulation in Plots of Rhizoma Perennial Peanut and Bahiagrass Grown in Elevated Carbon Dioxide and Temperature

^a USDA-ARS, Crop Genetics & Environmental Research, Building #350, P.O. Box 110965, University of Florida, Gainesville, FL 32611-0965
^b USDA-ARS, Columbia Plateau Conservation Research Center, P.O. Box 370, Pendleton, OR 97801-0370
^c Agronomy Department, 304 Newell Hall, P.O. Box 110500, University of Florida, Gainesville, FL 32611-0500. Y.C. Newman, current address: TAMU, 1229 North U.S. Hwy 281, Stephenville, TX 76401

^* Corresponding author (LHAJR{at}ifas.ufl.edu)

Received for publication May 1, 2005. Carbon sequestration in soils might mitigate the increase of carbon dioxide (CO₂) in the atmosphere. Two contrasting subtropical perennial forage species, bahiagrass (BG; Paspalum notatum Flügge; C₄), and rhizoma perennial peanut (PP; Arachis glabrata Benth.; C₃ legume), were grown at Gainesville, Florida, in field soil plots in four temperature zones of four temperature-gradient greenhouses, two each at CO₂ concentrations of 360 and 700 µmol mol^–1. The site had been cultivated with annual crops for more than 20 yr. Herbage was harvested three to four times each year. Soil samples from the top 20 cm were collected in February 1995, before plant establishment, and in December 2000 at the end of the project. Overall mean soil organic carbon (SOC) gains across 6 yr were 1.396 and 0.746 g kg^–1 in BG and PP, respectively, indicating that BG plots accumulated more SOC than PP. Mean SOC gains in BG plots at 700 and 360 µmol mol^–1 CO₂ were 1.450 and 1.343 g kg^–1, respectively (not statistically different). Mean SOC gains in PP plots at 700 and 360 µmol mol^–1 CO₂ were 0.949 and 0.544 g kg^–1, respectively, an increase caused by elevated CO₂. Relative SON accumulations were similar to SOC increases. Overall mean annual SOC accumulation, pooled for forages and CO₂ treatments, was 540 kg ha^–1 yr^–1. Eliminating elevated CO₂ effects, overall mean SOC accumulation was 475 kg ha^–1 yr^–1. Conversion from cropland to forages was a greater factor in SOC accumulation than the CO₂ fertilization effect.

Abbreviations: BG, bahiagrass • PP, rhizoma perennial peanut • SOC, soil organic carbon • SOM, soil organic matter • SON, soil organic nitrogen • TGG, temperature-gradient greenhouse