1. Institute for the Study of Society and Environment
A Comprehensive Environmental and Economic Assessment Method Applied to the Southwest Michigan Greenhouse Gas Mitigation Cropping Experiment
Third USDA Symposium on Greenhouse Gases & Carbon Sequestration
in Agriculture and Forestry
March 21-24, Baltimore MD
Susan Subak, Ph.D.
Institute for the Study of Society and Environment

2. Expanded Assessment for Alternative Practices:
Environmental Comparison
- greenhouse gas emissions
- nitrogen loadings
chemical applications
Question: Do herbicides applied for No-Till represent a significant pollution trade-off for greenhouse gas abatement?
Does the benefit of nitrogen reduction for low-input agriculture surpass greenhouse gas benefits for No-Till?
Economic Comparison
- direct input cost savings
- greenhouse gas reduction value
(value of reducing nitrogen and chemicals not assessed)
- crop value (price x yield)

4. Corn/wheat/soybean rotation
Kellogg Biological Station Cropping Experiments
NSF – LTER; Michigan State University
Data logs:
Corn/wheat/soybean rotation
T1: Conventional Tillage
T2: No-Till
T3: Low Input with Legume Cover
T4: Organic with Legume Cover
Robertson, G.P., Paul, E.A, Harwood, R.R. Greenhouse Gases in Intensive Agriculture: Contributions of Individual Gases to the Radiative Forcing of the Atmosphere. Science 289(5486):

5. Greenhouse Gases: Nitrogen Loadings: Toxicity Index:
From Robertson et al 2000:
Soil C
CO2 inputs to fertilizer, lime, fuel
N2O
CH4
Nitrogen Loadings:
Compiled from logbooks from KBS for fertilizer applications
Toxicity Index:
Derived by author based on logbooks from KBS for herbicide and pesticide applications

6. Toxicity Index: I = a x b x 1/c x d x 1/e
a = volume chemical applied (liter/hectare/year)
b = % active ingredient
c = lethal concentration half life (LC50) for trout (mg/liter)
log 10 scaled 1 to 5
d = groundwater ubiquity index (GUS)
e = water degradation half life (days)

12. Value of alternative practices compared with Conventional Tillage:
Input Costs
Greenhouse Gas Emissions Abatement ($10 t CO2e)
Crop Value

14. Conclusions from KBS Example:
Environmental:
- Chemical impact (Toxicity Index) of CT, NT and Low Input/legume were similar
- Nitrogen loadings were very different for the low-input practices (compared with CT and NT) but importance depends on estimated local impact
- Environmental benefit from reduced GHG and/or nitrogen loadings compared with CT is clear
Economic:
- Higher crop yields from NT were canceled out by higher direct input costs
- Lower crop yields from Low-Input/legume were canceled out by lower input costs
- Greenhouse gas abatement value is low, under current assumptions, but can change the incremental value from negative to positive when comparing these alternatives to CT