Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2006
Publication Date: 7/6/2006
Citation: Parkin, T.B., Kaspar, T.C. 2006. Nitrous oxide emissions from corn/soybean systems in the Midwest. Journal of Environmental Quality. 35:1496-1506. Interpretive Summary: Changing agricultural practices may offer solutions to reducing greenhouse gases in the atmosphere to mitigate global warming. One practice that has been considered is no tillage. No-till systems have been shown to increase soil organic carbon, thus removing carbon dioxide from the atmosphere. However, another potent greenhouse gas, nitrous oxide, may be released due to changing soil conditions. This study was performed in order to quantify the amount of nitrous oxide release from soils under chisel plow and no-till management. We observed no significant difference in nitrous oxide emissions in soils under these two management regimes over a two-year period. However, we did determine that the protocol recommended by the International Panel on Climate Change for predicting nitrous oxide emissions can severely underestimate actual emissions. This information will be useful to farmers and agencies engaged in trading carbon credits, as well as policy makers who are interested in predicting management effects on greenhoue gas emissions.
Technical Abstract: Soil nitrous oxide emissions from corn/soybean cropping systems in central Iowa were measured from the spring of 2003 through February 2005. 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 (N2O) 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 rings (30 cm diameter) were installed in each plot (in and between plant rows) and supported soil chambers during the gas flux measurements. Flux measurements were performed by placing vented chambers on the PVC anchors and collecting gas samples at 0, 15, 40 and 45 min following chamber deployment. N2O fluxes were computed from the change in N2O concentration with time, after accounting for diffusional constraints. We observed no significant tillage or cover crop effects on N2O flux in either year. In 2003 mean N2O fluxes were 2.8, 2.4, and 2.5 kg N2O-N ha**-1 y**-1 from the soybean plots under chisel plow, no tillage and no tillage + cover crop, respectively. Nitrous oxide fluxes from the chisel plow, no-till, and no-till + cover crop plots planted to corn averaged 10.4, 8.7, and 8.2 kg N2O-N ha**-1 y**-1 , respectively. In 2004 fluxes from both crops were higher. Fluxes from the corn plots were significantly higher than from the soybean plots in both years. Comparison of our results with estimates calculated using the IPCC guidelines, along with known N inputs from fertilizer and crop residues, indicated that the IPCC estimates underestimate actual fluxes by a factor of 3 at our sites.