Greenhouse Gas Emissions from U.S. Grain Farms

Abstract

ABSTRACTFarm-level environmental impact assessments for U.S. agriculture exist, but results are often not comparable because of different methodologies used. The objective of this research was to estimate the greenhouse gas emissions (GHG) levels for multicrop farms in the United States. A partial life cycle assessment (LCA) for 47 representative grain farms was performed, showing heterogeneous emissions across farm size, crops, and regions. Emissions of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) were estimated and transformed into CO2 equivalents (CO2e) per hectare and kilogram of production. The GHG emission intensity was affected by three characteristics: location, farm size, and cropping system. When crops were grown in different regions, they had different GHG intensities because of differences in soil quality, yields, and production efficiency. Emissions tended to be less per hectare and ton of the crop on larger farms. Crops grown outside their principal production regions were often more GHG-intensive than the same crops in their principal growing regions. The results of this study suggested that there was a correlation between production efficiency and GHG efficiency with higher yielding and/or larger operations having reduced emissions per unit of output.