Several studies have shown that organic farming systems can produce crops with low carbon footprint (CF). However, many important factors such as crop rotation, farm size, and location effect are commonly missed in comparative CF studies. Such inconsistencies limit our understanding of the factors behind the claimed differences between farming systems. This dissertation uses the OFoot tool to assess the CF of two organic farms in Washington State. This body of research focuses on the effect of farm size, location, and cover crops on CF estimation and aims to establish a consistent set of parameters to be used for CFs of other farming operations.

The dissertation consists of three main chapters: (1) a case study analyzing the CF of the two farms using broad and consistent system boundaries to identify hotspots of each farm's CF and the underlying reasons for differences in hotspots between the two farms; (2) an examination of how cover cropping practices impact net soil emissions, N-leaching and CF of the two farms; and (3) a commentary review calling for consistent and improved methodology for agricultural CF studies.

The case study found that critical hotspots differed between the two farms and identified farm size and site-specific soil and climatic conditions as factors influencing decision making that have a great impact on agricultural CF. Fuel use, electricity, fertilizers, and soil dynamics were the largest contributors to CF but both total and relative effects of these factors differed greatly between the two farms. The cover crop study found that use of cover cropping practices reduced net soil emissions and N-leaching in both farms but resulted in higher CF for the small-scale farm due to fuel used in managing the cover crop. The CF cost of cover cropping is beyond its effect on net soil emission or soil carbon sequestration. Finally, the commentary review recommended and defended that accurate and consistent assessments at a finer temporal and spatial scale are needed to support effective policy and individual decision-making that reduce GHG emissions and/or sequester more carbon.