RESUMO
The U.S. Corn Belt area has the capacity to generate high nitrous oxide (NO) emissions due to medium to high annual precipitation, medium- to heavy-textured soils rich in organic matter, and high nitrogen (N) application rates. The purpose of this work was to estimate NO emissions from cornfields in Iowa at the county level using the DeNitrification-DeComposition (DNDC) model and to compare the DNDC NO emission estimates with available results from field experiments. All data were acquired for 2007 to 2011. Weather Underground Network and the Iowa State University Iowa Soil Properties and Interpretation Database 7.3 were the data sources for DNDC inputs and for computing county soil parameters. The National Agriculture Statistic Service 5-yr averages for corn yield data were used to establish ex post fertilizer N input at the county level. The DNDC output suggested county-wide NO emissions in Iowa ranged from 2.2 kg NO-N ha yr in south-central to 4.6 to 4.7 kg NO-N ha yr in north-central and eastern Iowa counties. In northern districts, the average direct NO emissions were 3.2, 4.4, and 3.6 kg NO-N ha yr for west, central, and east, respectively. In central districts, average NO emissions were 3.5, 3.9, and 3.4 kg NO-N ha yr for west, central, and east, respectively. For southern districts, NO emissions were 3.5, 2.6, and 3.1 kg NO-N ha yr for west, central, and east, respectively. Direct NO emissions estimated by the DNDC model were 1.93% of N fertilizer input to corn fields in Iowa, with values ranging from 1.66% in the northwest cropping district to 2.25% in the north-central cropping district. These values are higher than the average 1% loss rate used in the IPCC Tier 1 approach.