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2	Big Sky Regional Partnership: MT, SD, ID Phase I assessment of terrestrial potential Modeled using CENTURY, GIS Agriculture is currently a net C sink MT has greatest land base but SD has most cropland No-till in SD offers most potential
3	Climate data National Climatic Data Center (NCDC) monthly average precip, min/max temperature since 1895 by station and climate division.
4	Generation of soil texture grids SSURGO/STATSGO map unit data extracted into sand/silt/clay % grids. Bulk density from texture ENVI processing to generate soil classes Distributed soil classes within counties
5	Historical and current agricultural management: I Historical data from extension survey (SD), NASS crop databases, Census of Agriculture, anecdotal sources (types of crops, fertilizer use, irrigation) Conservation tillage and CRP data for 2002 from CTIC. No-till = ZERO tillage For point simulations, represent spatial proportions of crops as temporal series 6 timeblocks: 1900-35, 1936-45, 1946-65, 1966-82, 1983-89, 1990- Assume grassland for baseline period
6	Historical and current agricultural management: II Assume no fertilizer before 1965 Assume no irrigation unless >50% of crop was irrigated Scenarios ct2ct: continuous conventional tillage since 1900 ct2nt: conventional, change to no-till in 1990 ct2crp: conventional, change to CRP in 1990 grz2grz: continuous grazing since 1990 grz2crp: removal of grazing in 1990
7	Historical and current agricultural management III No public lands in simulation Runs to 2030 (stochastic weather after 2003) For each state: 8-10 climate divisions 17-19 soil classes 5 scenarios = up to 900 separate simulations Distribute results over county/soil class cells, sum for county-level output
8	Results: Land use distribution
9	Carbon stock changes since 1990
10	State-level C stock trends
11	Role of Ag Soil C in State GHG Budgets
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