Assessing the effects of grazing and land use change on soil carbon stocks in pastures of the Virginia Blue Ridge
Date
2013
Authors
Bowen, Eric C., author
Conant, Richard, advisor
Kelly, Eugene, committee member
Hansen, Neil, committee member
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Abstract
The impact of livestock on our climate and the environment has been a hot topic since the 2006 FAO report "Livestock's Long Shadow" (Steinfeld et al., 2006) which estimated that livestock are responsible for 18% of anthropogenic greenhouse gas emissions and stimulated a great stir in the popular press. Numerous life cycle assessments have studied the environmental costs of various livestock species and have found beef and dairy to have particularly high greenhouse gas emissions (de Vries and de Boer, 2010). These assessments are often unable to include soil carbon changes caused by land-use change or management, perhaps because these data are limited and vary widely by region. The results of this study present data from the first known long-term study of grazing impacts on soils along the Virginia Blue Ridge. In this study, I sampled nine pastures on five farms to study both management and land-use change. I found significant increases in soil organic carbon on eight of the nine pastures with evidence that land-use and management change drove these increases. A portion of these data were an in-depth chronosequence on one farm, within which, data from our preferred approach (repeated measures) conflicted with the results of the chronosequences that we collected in 1999 and 2010. This conflict should serve as a cautionary tale to ecologists using space-for-time substitution. Averaged across all sites (all of which are grazed), we found soil carbon in the top 20 cm of soil increased 1.2±0.2 Mg/ha/yr for the 11 years between 1999 and 2010. This provides clear evidence that pasture-raised beef and dairy production can offset at least part of its environmental impact. These results are valuable to policy makers and consumers that are interested in reducing the impacts our food system has on climate change and the environment.
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Subject
grazing
livestock
pastures
rotational grazing
soil carbon
soil organic matter