Meat Eaters Guide: Methodology - Environmental Working Group

Meat Eaters Guide: Methodology
E. Modeling Emissions from Feedstock and Crop Production
Our GHG life cycle analysis of crop production for animal feed (grains and forage crops), beans, vegetables
and nuts was based on one or two representative conventional production systems from one
or two geographic locations. Table below indicates geographic region and primary data source. While
input data varied considerably across crop types, the general assumptions regarding the farm structure
remained the same.
1. General Production and Modeling Details
• The farm receives manufactured inputs – including fertilizers (both synthetic and organic),
pesticides, lime, gypsum, etc. – from sources that are not typically local. Locally procured
inputs included compost and manure.
• Other inputs to the farm include fuel – such as gasoline, diesel, and propane – and electricity
from the local power grid.
• Water for irrigation is required in many but not all crop production systems. Water may come
from various sources, including groundwater, district-supplied water and natural sources such
as rivers. Most irrigation requires energy use, which may be accounted for directly as part of
the on-farm energy use and/or indirectly as the energy used by the water district to supply the
water.
• On-farm emissions are generated by fuel combustion, application of lime and urea to the soil,
application of nitrogen fertilizers to the soil, flooding of rice fields and other factors such as
crop residues left on the ground.
• In the case of nut crops, our analysis accounts for carbon that is absorbed and sequestered in
the biomass of perennial crops, considering the full production life cycle spanning many years
or decades. As explained previously, carbon sequestration benefits and losses due to soil
management practices are not considered in the calculations.
• Some farm operations may include certain food processing steps. For example, the LCA
model includes refrigerated potatoes that are stored on farm; all of these energy-consuming
operations are included in the fuel and electricity requirements for the farm.
2. Specific Modeling Details for Feedstock Production
a. Corn Production
Our LCA calculated GHG emissions for corn and corn silage based on the production input data in
Table 40 (below) for a hectare of Iowa corn production, with an estimated yield of 10.7 metric tons
of corn and 42.2 metric tons of corn silage. The original input data were presented as a supplement
to “Comparative Life Cycle Environmental Impacts of Three Beef Production Strategies in the Upper
Midwestern United States” and, according to the authors, were initially gathered from several sources
including NASS, ISU extension, and other university sources. 67 In this model, 1 kg of corn and 1 kg of
corn silage generates .23 kg CO 2 e. and .08 CO 2 e respectively.
40
Environmental Working Group Meat Eaters Guide: Methodology 2011