HR: 1330h
AN: B42A-0942    [PDF]
TI: Total Carbon and Nitrogen Budget in Pasture Soils After 10 Years of Elevated CO$_{2}$
AU: Boots, B
EM: bas.boots@wur.nl
AF: Department of Agronomy and Range Science, One Shields Avenue University of California, Davis, CA 95616 United States
AU: Boots, B
EM: bas.boots@wur.nl
AF: Laboratory of Soil Science and Geology, Wangeningen University P.O. Box 37, Wageningen, 6700 AA Netherlands
AU: * Six, J W
EM: jwsix@ucdavis.edu
AF: Department of Agronomy and Range Science, One Shields Avenue University of California, Davis, CA 95616 United States
AU: van Breemen, N
EM: Nico.vanBreemen@wur.nl
AF: Laboratory of Soil Science and Geology, Wangeningen University P.O. Box 37, Wageningen, 6700 AA Netherlands
AU: Harris, D
EM: dharris@ucdavis.edu
AF: Stable Isotope Facility, One Shields Avenue University of California, Davis, CA 95616 United States
AU: Harris, D
EM: dharris@ucdavis.edu
AF: Institute of Plant Science, Swiss Federal Institute of Technology, Zurich, CH-8092 Switzerland
AU: Blum, H
EM: herbert.blum@ipw.agrl.ethz.ch
AF: Institute of Plant Science, Swiss Federal Institute of Technology, Zurich, CH-8092 Switzerland
AU: van Kessel, C
EM: cvankessel@ucdavis.edu
AF: Department of Agronomy and Range Science, One Shields Avenue University of California, Davis, CA 95616 United States
AB: The impact of elevated CO$_{2}$ and N-fertilization on soil C-cycling in {\it Lolium perenne} and {\it Trifolium repens} pastures were investigated under Free Air Carbon dioxide Enrichment (FACE) conditions. For ten years, swards were exposed to ambient or elevated CO$_{2}$ (35 and 60 Pa p CO$_{2}$) and received a low and high rate of labeled ($^{15}$N) N fertilizers. The CO$_{2}$ added in the FACE plots was depleted in $^{13}$C compared to ambient ($\delta$ $^{13}$C -40 per mille) thus the C and N inputs could be quantified. The maximum amount of labile C in the {\it T. repens} sward was estimated at 10.4$\pm$1.3 Mg ha$^{-1}$ and 9.7$\pm$ Mg ha$^{-1}$ in the {\it L. perenne} sward. Mean residence time (MRT) for newly sequestered soil C was estimated at 3.5 years for {\it T. repens} and 4.2 years for {\it L. perenne}. An average of 34 % and 7 % of total soil C in the 0-10 and the 10-25 cm depth respectively in the {\it T. repens} sward and 30 % and 8 % respectively in the {\it L. perenne} sward was derived from FACE after 10 years exposure. The majority of the change in soil $\delta$ $^{13}$ occurred in the first three years of the experiment. We found no treatment effect on total soil C and FACE derived C was not detected in the 50-75 cm depth layer. In the 0-10 cm depth, total N is similar under {\it L. perenne} and {\it T. repens} swards, regardless of CO$_{2}$ treatment. Whereas total $^{15}$N under {\it T. repens} is smaller than under {\it L. perenne}, due to symbiotic atmospheric $^{14}$N$_{2}$ fixation in the legume {\it T. repens}. Leached $^{15}$N was not observed in the 50-75 cm depth layer of all treatments. Although the rate of C and N cycling was affected by species, the soil in this intensively managed grassland ecosystem did not become a sink for additional C under elevated CO$_{2}$ conditions.
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting