Background/Question/Methods
To analyze the greenhouse gas effect of land-use conversion from CRP grasslands to a biofuel cropping systems, we conducted a full carbon accounting of land conversion of three such systems. The systems were converted to no-till soybean management. Additional CRP grassland served as control. The analysis included measured fluxes of greenhouse gases (N₂O, CH₄), net ecosystem productivity measured by eddy-covariance technique, and agricultural chemical and fuel use during the year of conversion.

Results/Conclusions
Conversion of CRP grasslands caused net emission of 1.4 ± 0.1 kg CO_2eq m^-2 y^-1 including 95.6 ± 3.6 g CO_2eq m^-2 y^-1 fossil fuel offset credit. An additional 4 to 93 years of biofuel cultivation would be required to offset this initial debt. The CRP reference site had a negative GWP impact of -282.5 ± 102.9 g CO_2eq m^-2 y^-1. Were the CRP grasslands biomass used for cellulosic ethanol production, an additional mitigation of 322.0 ± 10.9 g CO_2eq m^-2 y^-1 would be provided by fossil fuel offset, together with as much as 45.2 ± 1.5 GJ ha^-1y^-1 of energy in liquid fuels worth. Using established grasslands as cellulosic feedstock production systems rather than converting to grain-based biofuel systems will avoid the carbon cost and resulting debt of land conversion.