Parkin, Tim (USDA-ARS, National Soil Tilth Lab., 2150 Pammel Dr., Ames, IA, 50011; Phone: 515 294-6888; Email:


Nitrous Oxide Emissions from Midwest Corn/Soybean Cropping Systems


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.