Title: Greenhouse gas flux from western U.S. agroecosystems: Synthesis of mitigation opportunities Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2013
Publication Date: July 23, 2013
Citation: Liebig, M.A., Halvorson, A.D. 2013. Greenhouse gas flux from western U.S. agroecosystems: Synthesis of mitigation opportunities. Meeting Abstract. P. 67. In Abstracts of technical papers, 2013 joint meeting of the Canadian Soil Science Society, Manitoba Soil Science Society, and Canadian Society of Agricultural and Forest Meteorology, Winnipeg, MB. 22-25 July 2013. Canadian Soil Science Society, Pinawa, MB. Technical Abstract: Maintaining critical agroecosystem functions will require proactive management responses that concurrently mitigate greenhouse gas (GHG) emissions and adapt to impacts from climate change. In the western U.S., numerous strategies currently exist to mitigate GHG emissions from cropland and rangeland, though the quantification of their effectiveness has remained elusive due to the large diversity of climatic/edaphic conditions and management practices throughout the region. Given this need, we sought to summarize management effects on carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) flux using recently published data for western U.S. agroecosystems as a means to infer mitigation effectiveness while identifying critical research gaps. Conversion from conventional tillage (CT) to minimum-till (MT) or no-till (NT) resulted in net CO2 uptake in most, but not all, cropping systems. Most rangelands were net CO2 sinks, with assimilation rates ranging from 0.2-1.1 Mg C ha-1 yr-1. Cropland management had a negligible effect on CH4 flux, while rangelands were minor CH4 sinks (with the notable exception of prairie wetland). Fertilizer rate and N source were found to have overarching effects on cropland N2O emissions, with some practices decreasing emissions by as much as 50% compared to conventional fertilization practices. Nitrous oxide flux from rangelands were small (1.4-3.2 g N2O-N ha-1 d-1), and increased with N fertilization, invasion of non-native grasses, and woody plant encroachment, but not grazing intensity. While significant progress has been made in recent years to better understand GHG dynamics in western U.S. agroecosystems, numerous deficiencies persist that undermine the development of robust estimates of mitigation potential for most management practices. Such deficiencies stem from a lack of measurements across all major agroecosystem categories in the region, as well as limitations associated with a basic understanding of mechanistic processes related to GHG flux. Amidst this pressing opportunity, recommendations will be offered.