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United States Department of Agriculture

Agricultural Research Service

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2012 Annual Report

1a. Objectives (from AD-416):
To assist ARS in producing the U.S. Agriculture and Forestry Greenhouse Gas Inventory and assess the impacts of different crop management practices at the national scale. These efforts will facilitate collaborative efforts between ARS and CSU to continue simulation model development, testing, and refinement of input data to predict the impacts of changing climate and management on greenhouse gas (GHG) emissions, crop yields and soil carbon content.

1b. Approach (from AD-416):
Major products so far include the 2nd edition of the USDA GHG inventory published in 2008 and development of the GRACEnet data entry template. Major improvements in the 2nd edition of the inventory include more refined partitioning of GHG sinks and sources, better quantification of uncertainty and more accurate emission estimates, and quantification of mitigation potentials. Model improvements, tests, and applications used to generate data for the inventory have been reported in 12 journal and several presentations at meetings and symposia. The DAYCENT model was used to perform life cycle analysis for different biofuel cropping systems and initial tests were conducted to implement high resolution NRI data for future GHG inventory simulations. In addition to producing and improving future editions of the USDA GHG Inventory, general goals for the next 5 years include evaluating biofuel cropping systems and investigating how changes in land use and climate impact crop yields and GHG fluxes. Production and improvement of the U.S. Agriculture and Forestry Greenhouse Gas Inventory requires applying and improving the models used to calculate emissions and their associated uncertainty ranges. Use of more refined model input data, further comparison of model outputs with field measurements, and increased computing capacity lead to more accurate national scale estimates and better characterization of the regional and temporal patterns of emissions. ARS will interact with CSU to incorporate programming expertise, high capacity computing clusters, and data collection into the inventory analyses. CSU will assist ARS in evaluating the impacts and feasibility of different cropping systems, including biofuels by implementing and testing the ability of models to represent the impacts of improved N management technologies and perform regional analysis to identify local best management practices.

3. Progress Report:
ARS and Colorado State University have incorporated database, programming, and computer systems and improved methodologies into GHG inventory and mitigation analyses. These improved methodologies resulted in more reliable emission estimates and are described in the 2012 EPA Inventory of U.S. Greenhouse Gas Emissions and Sinks and in the 3rd edition of the U.S. Agriculture and Forestry Greenhouse Gas Inventory published by USDA in 2011. The DayCent and CENTURY models were used to help develop Technical Guidelines for Quantifying Greenhouse Gas Sources and Sinks in the Forest and Agriculture Sectors mandated in the 2008 Farm Bill. The DayCent model has been shown to accurately represent biomass yields for biofuel cropping systems and was used to perform regional simulations to assess the potential of biofuels to mitigate greenhouse gas emissions from the Mississippi basin (Davis et al. 2012). The model has also been used to assess the impacts of winter season biofuel crops on greenhouse gas emissions and nitrate leaching in the Chesapeake Bay watershed. In addition, the model was used to investigate the impacts of historical land use change in the U.S. Great Plains and results are reported in a recently published journal article (Hartman et al. 2011).

4. Accomplishments
1. Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2010 published by EPA: Compared to other economic sectors, estimates of greenhouse gas emissions from agriculture are highly uncertain. Thus, more accurate methods to quantify greenhouse gas emissions from the agricultural sector are required. The recently published Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2010 published by EPA features emissions calculated from model simulations of over 300,000 cropped and grazed areas across the US. The report partitions emissions spatially and by source category so policy makers can identify where mitigation efforts should be targeted. Results from this inventory are reported to The United Nations Framework Convention on Climate Change (UNFCCC).

2. Development of Technical Guidelines for Quantifying Greenhouse Gas Sources and Sinks in the Forest and Agriculture Sectors: Development of these guidelines was mandated in the 2008 Farm Bill. During a series of in person and teleconference meetings the working group decided that the CENTURY model would be used to quantify changes in soil carbon stocks in response to different land management options. For nitrous oxide emissions, the working group decided to use the DayCent model to estimate emissions from cropped and grazed systems under typical land management and then developed adjustment factors to quantify how emissions would change in response to different mitigation practices. Model simulations will be conducted during the summer of 2012 and the document describing the guidelines will be released for peer review in December.

3. Environmental Impacts of Biofuel Feedstock Production Systems: The Energy Independence and Security Act of 2007 mandates the production of 36 billion gallons of biofuel by 2022 and that the greenhouse gas emissions associated with producing this fuel are 20 to 60% lower than petroleum based fuel. Field data from biofuel feedstock plots in the central and eastern US were used to verify the ability of the DayCent ecosystem model to represent the ethanol yields and greenhouse gas emissions for corn, switchgrass, and miscanth systems. The model was then used to quantify yields and greenhouse gas emissions for lands currently used for corn ethanol production and to project yields and emissions if this land was converted to cellulosic ethanol production using perennial crops. Results suggest that if land currently used for corn ethanol production were converted to perennial crops, ethanol production could increase from 7 to 12 billion gallons while greenhouse gas emissions from soil would decrease by approximately 400% (Davis et al. 2012).

4. Peer-reviewed government report: EPA. Inventory of US greenhouse gas emissions and sinks: 1990-2010. Environmental Protection Agency, Office of Atmospheric Programs. 2012. Washington, D.C.

Last Modified: 06/27/2017
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