IATP Hog Report - Institute for Agriculture and Trade Policy

Section 4
out carbon dioxide. Plants take in carbon dioxide, photosynthesize the
carbon into plant tissue, and release oxygen. Some carbon is released
when plants die or it can be stored in live plants and trees or in soil.
Research by the Center for Rural Affairs finds that agriculture can reduce
its carbon dioxide emissions and manage productive land in a way that
removes carbon from the atmosphere and stores it in the soil and living
plants. 52 Farmers can (1) plant trees as windbreaks, (2) plant grass on
previously cultivated land, (3) reduce soil erosion to levels that are offset
by natural soil formation, (4) reduce fossil fuel use, and (5) rebuild organic
matter (carbon) in cultivated soils.
Organic matter can be rebuilt in cultivated soils by returning crop residues
to the soil, reducing tillage intensity, minimizing fallowing, and rotating
row crops with grasses and deep-rooted legumes. Returning manure to the
land is most beneficial if the carbon and nitrogen nutrients in the manure
have been stabilized by composting. 53
Methane
Methane is a highly potent greenhouse gas. Nearly half of all methane
emissions are from agriculture. 54 Other sources include lakes, wetlands,
oceans, and tropical forests. Bacteria produce methane in the absence of
oxygen (anaerobically). Hence, anaerobic digestion of liquid manure is a
major source of agriculturally produced methane into the atmosphere. The
other major agricultural source is fermentation of food organic matter
during ruminant digestion. It is estimated that nearly 63 million tons per
year, of the 88 million tons produced by digestion in all animals, is
produced by cattle. 55
The waste characteristics of the animal species and the animals' diets
affect how much methane is emitted by manure. But the key factor is the
way in which the manure is handled once it has been excreted. 56
Nearly half the manure methane emissions from cattle and hogs in the
United States before 1992 came from anaerobic lagoon waste management
systems. 57 Since then, the number of factory farms using anaerobic lagoon
systems has increased as hog and dairy cattle factories have proliferated
across the United States. The number of smaller farms operating anaerobic
lagoon systems has increased dramatically as well. Hence, manure
methane emissions from anaerobic lagoon systems account for a much
greater proportion of the total livestock emissions today.
Unstable organic matter in liquified manure also can have negative effects
on the physical properties of the soil, filling cavities between soil particles,
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