Agriculture Reference
In-Depth Information
Figure  12.2 . Emissions of carbon dioxide equivalents (CO 2 e) from agricultural fuel and
chemical inputs in the Conventional and No-till corn-soybean-wheat and the Alfalfa systems
of the Main Cropping System Experiment (MCSE). Emissions from N fertilizer represent
production costs only, not the resultant emission of nitrous oxide after fertilizer application.
an important source of strong acid in fertilized soils. The relative significance of
these reactions with liming materials in most soils and environmental settings is
not well known.
Pesticides have high CO 2 e production costs (4-5 kg CO 2 e kg −1 ) but a dispropor-
tionately low impact on ecosystem CO 2 e fluxes because usually only a few grams
of active ingredient are applied per hectare; they thus represent only ~10% of total
agricultural inputs, except in the No-till system, where they represent ~20% of
total inputs (Fig. 12.2). Seeds have a larger impact on GWI due to their high pro-
duction costs and seeding rates of ~20, 70, and 170  kg ha −1 for corn, soybean,
and wheat, respectively (Gelfand et  al. 2013). Estimates of GWI for seeds vary
widely, however, depending on how seed production costs are estimated: West and
Marland (2002) used a dollar value method to estimate a cost of 0.25 kg CO 2 e kg −1
soybean seed (Table 12.5); and Sheehan et  al. (1998) estimate a cost of 2.62  kg
CO 2 e kg −1 soybean seed based on 150% of the soybean energy content of 23.8 MJ
kg −1 (Rathke et  al. 2007). Based on average actual production costs for irrigated
soybean, we estimate a cost of 0.31 kg CO 2 e kg −1 soybean seed (Table 12.5; West
and Marland 2002).
Other inputs not common to KBS cropping systems can also have signifi-
cant GHG costs. Most notable among these is irrigation. Pumped irrigation uses
energy to move water from lower landscape positions or groundwater to the crop,
and the electricity or diesel used for this can readily become the dominant com-
ponent of the GWI of irrigated systems (Mosier et al. 2005). Irrigation scheduling
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