Potential for Climate Change Mitigation of Cropping Systems in Eastern Washington: A Simulation Study.

Agriculture is the second global source of GHG emissions after the power sector, and it is also the largest land use category worldwide. Although much research has focused on agriculture’s impact on global climate change, the evaluation of how agriculture might help mitigate climate change through improved management practices is needed. One important management practice with potential to increase carbon sequestration is the conversion from conventional tillage (CT) to reduced (RT) or no-tillage (NT) management.  We applied a cropping systems simulation model to examine the long-term effects of tillage intensity on soil organic carbon (SOC) conservation and nitrous oxide emissions at 3 dryland and 1 irrigated locations in eastern Washington State. In addition, life-cycle assessment-based calculations were made to establish the net Global Power Warming (GWP) of the different cropping systems and locations. The largest benefit to SOC was obtained from converting from CT to NT in Pullman (high rainfall), with benefit declining with less intensive rotations and lower rainfall.  Overall, the potential SOC sequestration for these systems in eastern Washington appeared lower than for much of the rest of the country. The net Global Warming Power (GWP) was positive for all cropping systems/locations except for RT management and low precipitation (GWP~0). Carbon sequestration was the only GWP mitigating factor, while on-farm N₂O emissions contributed 60-70% of the emissions in high and middle rainfall locations and 30-40% in low rainfall locations. Production of fertilizers contributed 13±3 % of the emissions. Emissions from fuel consumption varied across sites due to differences in machinery use. Potential carbon credits represent a small income stream, with NT or RT being economically feasible in high rainfall but not in lower rainfall zones.