Parkin, Tim (USDA-ARS, National Soil Tilth Lab., 2150 Pammel
Dr., Ames, IA, 50011; Phone: 515 294-6888; Email: parkin@nstl.gov)
T.B. Parkin *, T.C. Kaspar
Soil nitrous oxide emissions from corn/soybean cropping
systems were measured from the spring of 2003 through December 2004. Two year corn-soybean rotations were
established in plots subjected to plow tillage (fall chisel plow, spring disk)
and no-till. A no-till corn/soybean/rye
cover crop system was also evaluated.
Four replicate plots of each treatment were established with both crops
of the rotation represented in each of the two growing seasons. Nitrous oxide fluxes were measured weekly
during the periods of April through October, bi-weekly during March and
November, and monthly in December, January and February. Duplicate PVC anchors (30 cm diameter) were
installed in each plot and supported soil chambers during the gas flux
measurements. Flux measurements were
performed by placing vented chambers on the anchors and collecting gas
samples 0, 15, 40 and 45 minutes
following chamber deployment. Nitrous
oxide fluxes were computed from the change in N2O concentration with
time, after correcting for diffusional constraints. We observed no significant tillage or cover crop effects on N2O
flux in either year. In 2003 mean N2O
fluxes were 9.2, 6.0, and 6.8 mM N2O m -2from the soybean plots under plow tillage,
no-tillage and no-tillage + cover crop, respectively. Nitrous oxide fluxes from the plow till, no-till, and no-till +
cover crop plots planted to corn averaged 36.1, 24.6, and 25.2 mM N2O m-2 , respectively. In 2004 fluxes from both crops were higher,
but the fluxes from the corn plots were significantly higher than from the
soybean plots. Comparison of our
results with estimates calculated using the IPCC guidelines using known N
inputs from fertilizer and crop residues indicated that the IPCC estimates
underestimate actual fluxes by a factor
of 5.