Soil organic carbon and nitrogen accumulation in plots of rhizoma perennial peanut and bahiagrass grown in elevated carbon dioxide and temperature

Carbon sequestration in soils might mitigate the increase of carbon dioxide (CO 2 ) in the atmosphere. Two contrasting subtropical perennial forage species, bahiagrass (BG; Paspalum notatum Fliigge; C 4 ), and rhizoma perennial peanut (PP; Arachis glabrata Benth.; C 3 legume), were grown at Gainesville, Florida, in field soil plots in four temperature zones of four temperature-gradient greenhouses, two each at CO 2 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 CO 2 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 CO 2 were 0.949 and 0.544 g kg -1 , respectively, an increase caused by elevated CO 2 . Relative SON accumulations were similar to SOC increases. Overall mean annual SOC accumulation, pooled for forages and CO 2 treatments, was 540 kg ha -1 yr -1 . Eliminating elevated CO 2 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 CO 2 fertilization effect.