US agricultural nitrous oxide emissions: context, status, and trends

The use of commercial nitrogen (N) fertilizers has led to enormous increases in US agricultural productivity. However, N losses from agricultural systems have resulted in numerous deleterious environmental impacts, including a continuing increase in atmospheric nitrous oxide (N 2 O), a greenhouse gas (GHG) and an important catalyst of stratospheric ozone depletion. Although associated with about 7% of total US GHG emissions, agricultural systems account for 75% of total US N 2 O emissions. Increased productivity in the crop and livestock sectors during the past 30 to 70 years has resulted in decreased N 2 O emissions per unit of production, but N 2 O emissions from US agriculture continue to increase at a rate of approximately 0.46 teragrams of carbon dioxide equivalents per year (2002–2009). This rate is lower than that during the late 20th century. Improvements in agricultural productivity alone may be insufficient to lead to reduced emissions; implementing strategies specifically targeted at reducing N 2 O emissions may therefore be necessary.