Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1998
Publication Date: N/A
Interpretive Summary: Some greenhouse gas (GHG) emissions have been attributed to agricultural activities, however as agricultural management changes it is important to adjust the accounting of these emissions. For example shifting form conventional tillage to reduced or no tillage may change the amount of GHG emissions that can be attributed to agriculture. In fact, some of these practices may mitigate GHG emissions which could have significant consequences since our nation has agreed to voluntary mitigation of GHG through international treaties. Previous estimates of GHG emissions were broad guesses because specific soil, weather, and crop data were not used. We used a detailed model that required specific data which we obtained from the Natural Resource Conservation service, the NRI data set. With over 2500 specific points nationwide we compared GHG emissions from different crops and soil management systems. We found that for the gas nitrous oxide (N2O) no-till produced more than conventional tillage. Also that soybeans, wheat, and corn contribute 68% of the total emissions. We found that converting cropland to grassland, such as in the Conservation Reserve Program (CRP) significantly reduces N2O emissions from agriculture. This mitigation could account for 4 to 13% of the total emissions due to fertilization. Our study shows that reducing the cropland area and reducing fertilizer use on soybeans, corn and wheat can significantly reduce GHG emissions from U.S. agriculture.
Technical Abstract: Even though agricultural soil management is the predominant anthropogenic nitrous oxide (N2O) source, little is known about the effects of alternative soil management practices on regional N2O emissions. We used a model to simulate annual N2O emissions from 2639 cropland sites in the US using both no-till and conventional tillage management scenarios. We also evaluated N2O emissions from 306 Conservation Reserve Program (CRP) grassland sites. Extensive soil and land use data for each site was obtained from the Natural Resource Inventory (NRI) database and weather data was obtained from NASA. The no-till scenario had greater overall N2O emissions than the conventional tillage scenario. Differences between the two tillage scenarios were strongly regional, however, and suggest that conversion of conventionally tilled soil to no-till may have a greater impact on N2O emissions in the drier regions. About 80 percent of the total emissions were from the Great Plains and Central regions mainly due to their large cultivated area. We estimate that agricultural lands in the U.S. produce 447 Gg N2O-N/yr under a conventional tillage scenario via emissions directly from agricultural fields. Our results suggest that CRP program conversion of 10.5 million hectares of cropland to grassland has a N2O mitigation potential of 31 Gg N2O-N/yr, (8.4 Tg carbon equivalents/yr). This value is similar to many of the major greenhouse gas (GHG) emission reduction strategies under consideration and has the potential to mitigate 4 to 13 percent of North and Central American fertilizer induced N2O emissions.