Life cycle assessment of the potential carbon credit from no- and reduced-tillage winter wheat-based cropping systems in Eastern Washington State

Abstract

Integrated environmental and economic assessment studies are required to support tillage reduction decisions. In this paper, carbon sequestration and nitrous oxide emissions from winter wheat-based cropping systems were evaluated in eastern Washington, USA, using computer simulation. System boundaries were expanded to consider fertilizer production and use of machinery in a standard life cycle assessment (LCA) study. Variations in rainfall, tillage intensity and crop rotation were considered. Potential earnings from carbon credits obtained by converting to reduced and no-till management were evaluated and compared with the corresponding changes in farm budgets. No-till increased the average soil carbon sequestration by 0.5, 0.3, 0.2Mg-Cha−1yr−1 (30-year average) in high, middle and low rainfall zones, respectively. On-farm N2O emissions contributed 60–70% of the total CO2-equivalent emissions (CO2eha−1yr−1) in high and middle rainfall scenarios and 30–40% in low rainfall scenarios. Production of fertilizers contributed 13±3% of total emissions. Emissions from fuel consumption varied across sites due to differences in machinery use with different topography, tillage, soils and number of fallow years. Reduced tillage systems are more profitable in the moderate and high rainfall zones with 2011 crop price and input cost assumptions but they are less profitable in the drier rainfall zone. Even a more inclusive accounting with LCA that includes credits for reductions in N2O emissions, fuel usage and fertilizer production was insufficient to compensate for the lower returns. With the net market price assumption of 2.48$CO2e−1ha−1yr−1, the CO2e credits for reducing tillage ranged from 0.27 to 1.63$CO2e−1ha−1yr−1 across the region.