Final Vermont Greenhouse Gas Inventory and Reference Case Projections, 1990-2030 Page: 1
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Final Vermont GHG Inventory and Reference Case Projection, 1990-2030
CCS, September 2007
Appendix F. Agriculture
Overview
The emissions discussed in this appendix refer to non-energy methane (CH4) and nitrous oxide
(N20) emissions from enteric fermentation, manure management, and agricultural soils.
Emissions and sinks of carbon in agricultural soils are also covered. Energy emissions (fossil
fuel combustion in agricultural equipment) are included in the residential, commercial, and
industrial (RCI) sector estimates (see Appendix B).
There are two livestock sources of greenhouse gas (GHG) emissions: enteric fermentation and
manure management. Methane emissions from enteric fermentation are the result of normal
digestive processes in ruminant and non-ruminant livestock. Microbes in the animal digestive
system breakdown food and emit CH4 as a by-product. More CH4 is produced in ruminant
livestock than in other animals because of digestive activity in the large fore-stomach to break
down grasses and other high-fiber feeds. Methane and N20 emissions from the storage and
treatment of livestock manure (e.g., in compost piles or anaerobic treatment lagoons) occur as a
result of manure decomposition. The environmental conditions of decomposition drive the
relative magnitude of emissions. In general, the more anaerobic the conditions are, the more CH4
is produced because decomposition is aided by CH4 producing bacteria that thrive in oxygen-
limited (or oxygen-free) anaerobic conditions. Under aerobic conditions, N20 emissions are the
dominant GHG emissions of concern. Emissions estimates from manure management are based
on estimates of the volumes of manure that are stored and treated in livestock operations.
Emissions from manure that is applied to agricultural soils as an amendment or deposited
directly to pasture and grazing land by grazing animals are accounted for in inventories of
emissions from agricultural soils.
The management of agricultural soils can result in N20 emissions and in fluxes of carbon
dioxide (CO2) that make soils net emitters or net sinks of carbon. In general, soil amendments
that add nitrogen to soils can also result in N20 emissions. Nitrogen additions drive underlying
soil nitrification and de-nitrification cycles, which produce N20 as a by-product. The emissions
estimation methodologies used in this inventory account for several sources of N20 emissions
from agricultural soils, including decomposition of crop residues, synthetic and organic fertilizer
application, manure and sewage sludge application to soils, nitrogen fixation, and cultivation of
histosols (high organic soils, such as wetlands or peat lands). Both direct and indirect emissions
of N20 occur from the application of manure, fertilizer, and sewage sludge to agricultural soils.
Direct emissions occur at the site of application and indirect emissions occur when nitrogen
leaches to groundwater or in surface runoff and is transported off-site before entering the
nitrification/denitrification cycle. Methane and N20 emissions also result when crop residues are
burned. Methane emissions occur during rice cultivation; however, rice is not grown in Vermont.
The net flux of CO2 in agricultural soils depends on the balance of carbon losses from
management practices and gains from organic matter inputs to the soil. Carbon dioxide is
absorbed by plants through photosynthesis and ultimately becomes the carbon source for organic
matter inputs to agricultural soils. When inputs are greater than losses, the soil accumulates
carbon and there is a net sink of CO2 into agricultural soils. In addition, soil disturbance from theVermont Department of F-1 Center for Climate Strategies
Environmental Conservation www.climatestrategies.us
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Center for Climate Strategies. Final Vermont Greenhouse Gas Inventory and Reference Case Projections, 1990-2030, text, October 2007; Washington, DC. (https://digital.library.unt.edu/ark:/67531/metadc226803/m1/77/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .