Meat Eaters Guide: Methodology - Environmental Working Group

d. Feed Production
The four main feed stocks modeled in the LCAs are domestic corn, soybeans, orchard grass and
alfalfa. 19 Feed production requires significant fuel, water and energy to produce and apply pesticides
and fertilizer and to grow and feed crops. CleanMetrics estimated fertilizer, pesticides, fuel, irrigation
and electricity quantities used in feed production based on input data cited in Table 27 and 28. Section
E2 provides further details about the sources of emissions from the production of corn, soybean,
and alfalfa, the three primary animal feed stocks.
CleanMetrics used IPCC Tier 1 methods in modeling emissions from agricultural soils from fertilizer
application for growing feed (including grazing, where appropriate). These emissions include direct
and indirect nitrous oxide emissions generated from synthetic and organic nitrogen fertilizers and crop
residues, as well CO 2 from the application of lime and urea.
The model also includes indirect nitrous oxide emissions from aquaculture systems as a function of
nitrogen added or released into the water.
e. Enteric Fermentation and Manure Management
Ruminant animals such as sheep and cows emit methane from enteric fermentation, a digestive process
in which microorganisms break down carbohydrates into simple molecules for better absorption.
All animals generate methane and nitrous oxide from manure deposits.
CleanMetrics used IPCC tier 2 methods to model emissions from livestock production. Calculations
for methane from enteric fermentation are based on the kind of feedstuffs ingested by livestock species
and the quality of the ingredients in the feed mix. For example, feedstuffs with higher fiber content,
such as grass and hay, generate higher emissions than a higher quality, grain-based diet. 20
Methane emission estimates from manure management are based on the type of manure management
system (pasture, solid storage, liquid), the average temperature of the geographic location, and
the amount of volatile solids excreted (in turn based on feed energy content and digestibility). Direct
and indirect nitrous oxide emissions from manure are calculated based on nitrogen balance (in turn
based on crude protein content in the diet) and the quantities of nitrogen excreted. Emission factors
vary depending on the actual manure management system (such as pasture, dry lot, solid storage,
liquid/slurry, poultry manure with/without litter, etc.). 21
f. Soil Carbon Emissions and Sequestration
Net carbon can be emitted from or sequestered in soil depending on the kinds of agricultural practices
employed on the land and whether the system is in transition or steady state. While certain types of
management practices, such as tillage and intensive grazing, are known to generate a loss of carbon,
other practices such as rotational grazing and organic fertilization are known to build up carbon in the
soil (see Best Management Practices section below).
Rates of soil carbon sequestration and emissions from soils differ under different land management
Environmental Working Group Meat Eaters Guide: Methodology 2011 13