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United States Department of Agriculture

Agricultural Research Service

Research Project: Mitigating Agricultural Sources of Particulate Matter and Greenhouse Gas Emissions in the Pacific Northwest

Location: Land Management and Water Conservation Research

Title: Dryland agriculture’s impact on soil carbon in the Pacific Northwest

Authors
item Brown, Tabitha -
item Huggins, David

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 30, 2012
Publication Date: September 1, 2012
Citation: Brown, T.T., Huggins, D.R. 2012. Dryland agriculture’s impact on soil carbon in the Pacific Northwest. Journal of Soil and Water Conservation. 67:(5)406-415.

Interpretive Summary: Soil carbon (C) sequestration is an important greenhouse gas mitigation strategy. Knowledge of how different agricultural practices impact changes in soil C is needed for policy makers as well as for carbon marketing. Our objective was to provide information and assessment tools that quantify agricultural impacts on soil C sequestration for dryland cropping systems of the Pacific Northwest. We found that the soil C data were quite variable and that developing cumulative probabilities of soil C change could be a useful method for policy makers and marketers to assess the influence of land management changes on soil C. These analyses showed that 75% of the converted native ecosystems have lost at least 0.14 to 0.70 metric tons (Mg) of C per hectare (2.471 acres) per year depending on agroclimatic zone. Converting from conventional tillage to no-tillage was predicted to increase soil organic carbon (SOC) from 0.12 to 0.21 Mg of C produced by hectare per year for 75% of situations depending on the climatic zone where the conversion occurred. Compared to annual cropping systems, mixed perennial-annual systems would be expected to have SOC gains of at least 0.55 Mg C per hectare per year for 75% of sites. The variability found among studies suggests that a well validated C model for the region would aid evaluation of SOC changes due to management particularly for specific farms and sites with unique SOC history and circumstances. The research findings will be useful for federal and state agencies such as the NRCS, Washington Department of Agriculture, and the Idaho Soil Conservation Commission, who are assessing agricultural mitigation strategies to address climate change. Also, these data will be useful to carbon marketers and aggregators such as the Chicago Climate Exchange, and the Pacific Northwest Direct Seed Association.

Technical Abstract: Agricultural practices have the potential to restore soil C that was lost following conversion of native lands to cropland. The soil C marketing requirement for additionality establishes the need to evaluate SOC changes under alternative managements to determine net benefits. Our objective was to provide science-based information and assessment tools that quantify agricultural impacts on soil C sequestration for dryland cropping systems of the Pacific Northwest. One hundred and thirty one data sets of soil organic carbon (SOC) were analyzed to assess the influence of land management changes on SOC including the conversion of native ecosystems to agricultural crops, the conversion from conventional tillage (CT) to no-tillage (NT) and the use of alternative crop rotations and management practices. Cumulative probabilities of SOC change were developed that could be used for marketing of SOC. These analyses showed that 75% of the converted native ecosystems have lost at least 0.14 to 0.70 Mg C ha-1 yr-1 depending on agroclimatic zone. Converting from CT to NT was predicted to increase SOC from 0.12 to 0.21 Mg C ha-1 yr-1 for 75% of situations and was also agroclimatic zone specific. Compared to annual cropping systems, mixed perennial-annual systems would be expected to have SOC gains of at least 0.55 Mg C ha-1 yr-1 for 75% of sites. There was an overall lack of existing SOC data for wheat-fallow regions of the Pacific Northwest. Furthermore, the impact of soil erosion processes on SOC was identified as a needed research area. The variability among studies suggests that a well validated C model for the region would aid evaluation of SOC changes due to management particularly for specific farms and sites with unique SOC history and circumstances.

Last Modified: 9/2/2014
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