Greenhouse Gas Emissions from U.S. Agriculture and Forestry: A ...

manure‐N immobilization by the crop; (2) adjusting the amount of manure based on crop N needs to
prevent overfertilization with its associated N losses; (3) adjusting commercial N application rates to
account for N addition in the manure; and (4) injecting liquid manure below the soil surface rather than
surface application to prevent ammonia loss and reduce indirect N2O emissions. Other studies have
indicated the importance of the ‘form’ of manure that is being applied to the field. Reduced N2O
emissions were found upon application of solid manure compared to liquid manure (e.g., Gregorich et
al., 2005). The use of nitrification inhibitors can also reduce N2O losses following manure application to
land (Saggar et al., 2004).
CH4 emissions from feces and urine of grazing animals are less than 1% of enteric CH4 emissions and
much smaller than emissions from liquid manure storage. However, dung and urine deposits in grazed
pastures have been shown to be rather important sources of N2O. The most important management
option to minimize N2O emissions from grazing animals is by ensuring that pastures are not
overfertilized with N added by the animals themselves and by maximizing the likelihood for plant uptake
of added N (CAST, 2004).
Other useful papers on manure management:
Facility type: Philippe et al., 2007; Amon et al., 2007; Fabbri et al., 2007
Liquid manure management: Sharpe et al., 2002; Berg et al., 2006; Amon et al., 2006, 2007; Martinez et
al., 2003; Dinuccio et al., 2008
Composting: Fukimoto et al., 2003, 2006; Yamulki, 2006; Hao et al., 2001, 2004, 2005; Lopez‐Real and
Baptista, 1996; Sommer and Moller, 2000
III.c. Enteric fermentation
(Boadi et al., 2004; Johnson and Johnson, 1995; Ominski and Wittenberg, 2004; Kebreab et al., 2006,
2008; Sejian et al., 2010; Ogle et al., 2010; CAST, 2004; Smith et al., 2007)
Livestock, in particular ruminants, lose a significant proportion of their ingested energy as CH4 (2‐12 % of
GE intake) due to methanogenic activity within their digestive tract (Johnson and Johnson, 1995).
Research on mitigating CH4 emissions from livestock has been mainly driven by the need to reduce this
loss of energy to animals, but has recently also been spurred by the important contribution of the
livestock sector to global greenhouse gas emissions and the large opportunities in this sector for climate
change mitigation (e.g., Steinfeld et al., 2006). Several reviews have been published in the last decade
on the mechanisms controlling CH4 emissions and mitigation strategies to reduce enteric CH4 emissions,
with a focus on ruminants (e.g., cattle, sheep, goat) (Boadi et al., 2004; Ominski and Wittenberg, 2004;
Kebreab et al., 2006; Ogle et al., 2010). The dominant factors that control enteric CH4 production are the
availability of hydrogen (H2) and the proportion of volatile fatty acids (VFA), specifically acetate:
propionate produced in the rumen as a result of microbial fermentation. Dietary factors that influence
the ratio of acetate:propionate include the residence time of the feed in the rumen, the type of
carbohydrates consumed by the animals and diet digestibility (Ominski and Wittenberg, 2004).
Hydrogen availability for CH4 production can be reduced through the addition of fats, in particular
Contract # GS‐23F‐8182H, Project Technical Report 35