The Big Sky Carbon Sequestration project sponsored terrestrial carbon sequestration field studies at “farm-managed sites” in northern Montana near Fife, Chester, Power, Dutton, and Conrad during Phase III. The overall objective of these studies was to determine whether adoption of tillage reduction (i.e. no-till) and annual cropping practices would result in soil C sequestration, and if so, at what rate. A 10 year study (2002-2012) was conducted at five farm-managed sites in northern Montana and on the property of the MSU-Post Farm near Bozeman. The MSU-Post farm trial was conducted with funds from the Montana Agricultural Experiment Station. Soil cores were collected in 2012, processed, and then analyzed for organic C. Estimates of SOC mass for different profile depths were calculated for the farm-managed sites (i.e. 0-20 cm and 0-50 cm) and MSU-Post Farm (0-30 cm). Estimates of SOC mass were contrasted with baseline numbers in 2002 (or 2004) where comparison could be reliably made. This study found that terrestrial C sequestration was possible in Montana’s dryland cropland soils by replacing fallow-wheat with more intensive cropping practices such as annual, pulse-wheat rotations. The impact of a reduction in tillage on C sequestration was somewhat unclear but it appeared to be considerably less important than cropping intensity. Estimated SOC sequestration response averaged 0.32 MT C ha-1 yr-1, or 1.17 MT CO2 equivalent ha-1 yr-1 over five sites where responses to increasing cropping intensity were observed. As anticipated there was considerable variance (0.18 to 0.60 MT C ha-1 yr-1) in soil C sequestration rates among the responsive sites. The largest C sequestration was response to cropping intensity was observed at Fife which was characterized by high soil clay content (60%). Current, Montana ag-statistics indicate that approximately 1.29 million hectares of farm land (3.19 million acres) are in fallow on an annual basis. Approximately, 72% of the fallow-wheat acreage (or 925,000 hectares) is found in Montana’s Golden Triangle plus three other neighboring counties. If we apply our mean soil C sequestration rate to this acreage, then the potential of terrestrial C sequestration in Montana following conversion of fallow-wheat to annual cropping equates to approximately 1.0 million MT of CO2 per year.
