|HIRSTOV, ALEXANDER - Pennsylvania State University|
|RICE, CHARLES - Kansas State University|
|BROWN, MOLLY - University Of Maryland|
|CONANT, RICHARD - Colorado State University|
|Del Grosso, Stephen - Steve|
|GURWICK, NOEL - US Department Of State|
|Rotz, Clarence - Al|
|WEST, TRISTRAM - US Department Of Energy|
|RUNKLE, BENJAMIN - University Of Arkansas|
|JANZEN, HENRY - Agriculture And Agri-Food Canada|
|REED, SASHA - Us Geological Survey (USGS)|
|CAVALLARO, NANCY - National Institute Of Food And Agriculture (NIFA)|
Submitted to: Government Publication/Report
Publication Type: Government Publication
Publication Acceptance Date: 9/24/2018
Publication Date: 11/23/2018
Citation: Johnson, J.M., Hirstov, A.N., Rice, C.W., Brown, M.E., Conant, R.T., Del Grosso, S.J., Gurwick, N.P., Rotz, C.A., Sainju, U.M., Skinner, R.H., West, T., Runkle, B.R., Janzen, H., Reed, S., Cavallaro, N. 2018. State of the Carbon Cycle Report -2 (SOCCR-2) Chapter 5: Agriculture. Government Publication/Report. https://doi.org/10.7930/SOCCR2.2018.Ch5.
Interpretive Summary: Agriculture is an important land use in the US and North America; consequently, agricultural lands significantly impact continental C fluxes. Trends in food production and agricultural management can fluctuate significantly with changes in global markets, diets, regional policies, and incentives, thereby affecting regional carbon budgets and net GHG emissions. Fertilizer additions, irrigation, tillage, cropping intensity and other practices influence soil C stock changes. In addition to C, Non-CO2 gases (N2O and CH4) are important agricultural GHG sources. Various mitigation strategies can affect soil N2O emissions and livestock enteric and manure methane (CH4) emissions. For example, promising and readily applicable technologies, such as a CH4 inhibitor, can reduce enteric CH4 emissions from ruminants by 20-30%. Other mitigation technologies, including solids separation, aeration, acidification, biofiltration, composting, and anaerobic digestion, can reduce manure CH4 emissions by 30-50% and up to 80%.
Technical Abstract: The total area of agricultural land in North America has remained essentially constant over the past decade (2003-2013). In the United States, these lands decreased slightly from 45.2% of the land surface in 2003 to 44.3% in 2013. In Mexico and Canada, the reported coverage remained almost constant: 54.8% and 54.9% and 7.4% and 7.2%, respectively. In comparison, the First SOCCR reported total agricultural and grazing lands in North America (as occupying 47% of ice-free land surface on the continent, accounting for 17% of global terrestrial carbon. Most of this carbon occurred in soils; less than 5% resided in cropland vegetation and 5-30% resided in grazing lands. While the annual U.S. soil carbon sequestration rate has decreased approximately 104% between 1990 and 2013, national reporting from 2013 estimated that approximately 9% of total annual U.S. greenhouse gas (GHG) emissions came from agriculture (including on-farm energy use), although this figure does not include emissions associated with food waste. Agricultural emissions totaled 595 MMT CO2 eq. (including 1.4 MMT CO2 eq. offset from soil carbon sequestration). The major agricultural non-CO2 emission sources were nitrous oxide (N2O) from cropped and grazed soils (44% of emissions in 2013) and enteric methane (CH4) from livestock (28% of emissions). Combined with forestry, the agricultural sector contributed to a total net carbon sequestration of 270 MMT CO2eq. Trends that drive GHG emissions from agriculture in North America include changes in: (1) the amount of N fertilizer applied, (2) numbers of ruminants, and especially beef cattle and dairy cows because they produce large quantities of enteric and manure methane; (3) trends in diet, because they drive changes in land use, numbers of livestock, (4) area of agricultural land opened by clearing forest, which converts large amounts of plant- and soil carbon to CO2, and (5) the amount of food wasted, which leads to methane emissions from landfills and also drives additional production with associated GHG emissions.