Incorporating County-Level Spatial Resolution in Maize Life Cycle Emissions Analysis in Illinois, USA

Abstract

Maize is a major biofuel feedstock, accounting for 64% of the global share of ethanol production. Recent improvements in life cycle analyses (LCAs) have accounted for temporal changes in the improved efficiency of farming practices, with reductions in the carbon intensity (CI) of maize grain production over time. There has been little progress on understanding the spatial variation of the CI of maize grain production. The average life cycle CI of US maize production at the farm gate converts to a contribution of 251 g CO₂e/kg of maize produced, used in policy calculations related to biofuel production. The objective of this work was to understand the spatial variation in CI scores using Illinois, USA as a case study to conduct life cycle analysis for modeling county-level CI score. The average CI score of maize produced in Illinois has a range of 9%–12% lower than the national average CI when averaged across the state using county-level yield and fertilizer application data. Maize grown within 56 km of ethanol facilities in Illinois has scores 14%–17% lower than the national average, when adjusted for ethanol output. This is mainly due to the high yields in Illinois and more efficient use of fertilizer across counties delivering to ethanol plants. There was spatial variation in the impact of cover crop seeding and conservation tillage across a transect of counties. Further refinement of life cycle models will provide more accurate assessments of the carbon intensity of maize production at smaller spatial scales than national averages.