Acknowledgements: This research was supported by the USDA-ARS Specific Cooperative Agreement Biologically Based Weed Management for Organic Farming Systems (project number ). We thank Dave Wilson, Dwight Lingenfelter, John Teasdale, William Curran, Richard Smith and the Penn State Weed Ecology Laboratory for their critical input. Conclusion: In our analysis, the ORNT system had the smallest carbon footprint. Despite the conservatively low yields assigned to the ORNT system, it was 30% more efficient than the CNV system and had the greatest potential to sequester soil C. Recent field trials from across the US have demonstrated that ORNT systems can produce yields that are comparable to conventional systems. However, more research is needed to improve pest management and performance consistency. Methods: We used the Farm Energy Analysis Tool (FEAT) (Camargo, 2009) to simulate and evaluate 5 corn-soybean-wheat management systems (Table 1). FEAT is a static, deterministic model that is parameterized using literature values for cropping system inputs (see references supplement). Data from the USDA-ARS Farming Systems Project in Beltsville, MD and the Rodale Farming Systems Trial in Kutztown, PA were used to estimate yield and soil C sequestration potential. Herbicide programs simulated in the 3 non-organic systems were based on typical usage for PA (Lingenfelter, personal communication). Assumptions include: 1) farm was 150 ha and located in southeastern PA; 2) manure used in the organic systems was transported 10 km; 3) equipment had a 10-year lifespan. Labor, electricity, and insecticides (seed treatments) were excluded from the analysis. Because of the similarity between energy usage and carbon emissions, only energy results are presented. In this study we consider the carbon footprint to be a combination of the system efficiency and soil C sequestration potential. Results: Energy usage was lower in the organic systems, primarily because of the energy associated with N fertility (mineral fertilizer vs. manure). Mineral N fertilizer was the largest energy input in the CNV, NT, and CCNT systems (33% of total). The CCNT system was more efficient than the CNV and NT systems, because hairy vetch offset the need for N fertilizer. Diesel fuel was the largest energy input in the two organic systems (37-44% of total). The ORNT required 26% less diesel fuel than the ORG system as a result of less tillage. The ORNT system was the most efficient and had the greatest potential to sequester soil C. Introduction: No-till and organic management systems reportedly produce crops with lower input energy requirements and provide more ecosystem services, such as soil carbon (C) sequestration. Despite the similarity in benefits of no-till and organic systems, research on hybrid systems is limited. Integrating cover crops in no-till systems and reducing tillage in organic systems will likely provide further benefits than are currently realized. Although nascent and potentially more variable than standard systems, competitive yields in organic rotational no-till systems have been demonstrated. Organic farmers are interested in these systems because they can save time and no-till farmers see potential for accessing lucrative organic grain markets. In this study, we simulated 5 organic and conventional corn-soybean-wheat management systems with varying levels of soil tillage and cover cropping to: 1) compare energy usage, 2) identify the largest energy inputs in each system, and 3) assess the soil C sequestration potential of each system. Rotational No-Tillage Management for Reducing the Carbon Footprint of Organic Corn-Soybean based Cropping Systems Matthew R. Ryan, David A. Mortensen, Gustavo G. T. Camargo, and Thomas L. Richard. Dept. of Crop and Soil Sciences, The Pennsylvania State University, University Park, PA ( Figure 2. Crop yield output to energy input ratio (black bar, left y-axis) and annual soil C sequestration potential relative to the CNV system (grey bar, right y-axis). Yields were assumed to be identical for the CNV, NT, and CCNT systems (150, 50, 60 bu/a for corn, soybean, and wheat, respectively) and 10 and 20% lower for the ORG and ORNT systems, respectively. The NT soil C sequestration rate was based on West and Post (2002), the CCNT rate was based on the assumption that adding winter cover crops would increase sequestration by 8.6% (Villamil et al. 2006), and the rate for the ORG system was based on Marriott and Wander (2006). Because of the large amount of cover crop residue and the relative decrease in tillage, the ORNT system was assumed to sequester 10% more C than the ORG system. Figure 1. Annual energy usage across cropping systems. Parameter values used and references are available (see supplement). Organic no-till planted corn in hairy vetch residue Organic no-till planted soybean in rye residueRolling hairy vetch cover crop Rolling cereal rye cover crop Please visit us at: Table 1. Details on tillage, cover crop, soil fertility, weed management, and planting differences between the 5 management systems that were evaluated. P fertilizer K fertilizer Manure Lime Seed Herbicide Input transportation Grain drying Equipment Diesel fuel N fertilizer Photo credit: Jeff Mitchell Photo credit: William CurranPhoto credit: Matthew Ryan Photo credit: David Mortensen