Chapter 3: Cropland agriculture

Authors: OGLE, STEPHEN - Colorado State University; Del Grosso, Stephen - Steve; MARX, ERNIE - Colorado State University; GURUNG, RAM - Colorado State University; SPENCER, SHANNON - Colorado State University; WILLIAMS, STEVEN - Colorado State University

Submitted to: Government Publication/Report
Publication Type: Government Publication
Publication Acceptance Date: 12/1/2021
Publication Date: 1/19/2022
Citation: Ogle, S.M., Del Grosso, S.J., Marx, E., Gurung, R., Spencer, S., Williams, S. 2022. Chapter 3: Cropland agriculture. In: Hanson, W.L., Del Grosso, S.J., Gallagher, L., editors. U.S. Agriculture and Forestry Greenhouse Gas Inventory: 1990–2018. Technical Bulletin No. 1957. Washington, D.C.: United States Department of Agriculture, Office of the Chief Economist. p. 59-158.

Interpretive Summary: In 2018, cropland agriculture resulted in total greenhouse gas emissions (GHG) of approximately 297 MMT CO2 eq. which is almost half (48%) of all emissions from the agricultural sector. Nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from cropland soils totaled 239, 45, and 14 MMT CO2 eq. in 2018. However, that amount was partly offset by carbon (C) storage of 46 MMT CO2 eq. in cropland mineral soils during 2018. Cropland mineral soils in the U.S. are a net CO2 sink due to adoption of management practices such as: conservation tillage, perennial grass and legume hay rotations, manure amendments, and enrollment in CRP. When carbon sequestration is considered, net emissions of GHG from cropland agriculture amount to approximately 251 MMT CO2 eq. Greenhouse gas emissions from agricultural soils, primarily N2O, were responsible for the majority of total emissions (80%). Nitrous oxide emissions are largest in the corn belt region where extensive row crop production entails high nitrogen (N) inputs from fertilizer additions and legume cropping. Drained organic soils, mainly in southeastern and Great Lakes States, are the second largest source (12%).

Technical Abstract: In 2018, cropland agriculture resulted in total greenhouse gas emissions (GHG) of approximately 297 MMT CO2 eq. which is almost half (48%) of all emissions from the agricultural sector. Nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) emissions from cropland soils totaled 239, 45, and 14 MMT CO2 eq. in 2018. However, that amount was partly offset by a storage, or carbon sequestration, of 46 MMT CO2 eq. in cropland mineral soils during 2018. When carbon sequestration is considered, net emissions of GHG from cropland agriculture amount to approximately 251 MMT CO2 eq. The 95% confidence interval for net emissions in 2018 is between 117 and 384 MMT CO2 eq. In 2018, net emissions from cropland agriculture were about 11% higher than the baseline year (1990), mainly due to an increase in N2O emissions associated with increased crop production and a reduction in the CO2 sink associated with cropland mineral soils. Greenhouse gas emissions from agricultural soils, primarily N2O, were responsible for the majority of total emissions (80%). Nitrous oxide emissions are largest in the corn belt region where extensive row crop production entails high nitrogen (N) inputs from fertilizer additions and legume cropping. Soil CO2 emissions from cultivation of organic soils (12%), from liming (1%), and from urea fertilization (2%) and CH4 emissions from rice (4%) are the remaining major sources. Cropland mineral soils in the United States are a net CO2 sink for various reasons, including increased carbon inputs from improved crop varieties and residues, as well as other practices that reduce the decomposition of soil organic matter and subsequent losses of carbon from the soil. For example, adoption of conservation tillage, which began to increase in the 1980s, leads to an increase in soil carbon due to lower rates of decomposition of soil organic matter with less soil disturbance. Lands that are used for perennial grass and legume hay production, as well as increased manure amendments contribute more carbon to the soil and lead to larger amounts of carbon in soils. The magnitude of the mineral soil carbon stock varies annually in response to weather and land conversion such as to and from forest land and grazing land uses.