Carbon footprint of organic and conventional arable crop production systems in a long-term trial

Abstract Agriculture is a major contributor to climate change, and there is an urgent need to reduce greenhouse gas (GHG) emissions from agriculture for mitigation purposes. Modern industrial agriculture has been recognized as a significant source of agricultural GHG emissions, whereas the adoption of regenerative organic agriculture has been proposed as a solution with the potential to reduce GHG emissions from agricultural production. However, there is a lack of on-the-ground studies reporting on the climate impacts of organic agriculture. To remedy this, a carbon footprint (CF) analysis was conducted comparing regionally representative organic and conventional arable cropping systems at Rodale Institute’s Farming Systems Trial in Pennsylvania, USA. Two separate modeling approaches were used to construct CFs for three agricultural systems (two organic and one conventional). The baseline CF analyses used an Intergovernmental Panel on Climate Change Tier 3 model (COMET-Farm) and Tier 2 model (Cool Farm Tool) for comparison purposes. Secondary analyses were conducted on the effects of CO 2 emissions from composting manure on CFs. Emission metrics were generally higher (+27%) using the Tier 3 model compared with the Tier 2 model. In the baseline analysis, absolute area-scaled emissions were highest in the conventional system, ranging from 1.25 to 1.72 tons CO 2 -eq ha −1 yr −1 . In comparison, emissions in the organic manure-based system were 25%–37% lower (0.94–1.09 tons CO 2 -eq ha −1 yr −1 ), while the organic legume-based system had the lowest emissions, which were 52%–74% lower (0.33–0.83 tons CO 2 -eq ha −1 yr −1 ). Yield-scaled emissions of maize in the baseline analyses were highest in the conventional system (0.19–0.26 kg CO 2 -eq kg −1 ), followed by the organic manure (0.13–0.16 kg CO 2 -eq kg −1 ) and organic legume (0.07–0.17 kg CO 2 -eq kg −1 ). Yield-scaled emissions on a feed digestible energy basis were highest in the conventional system (0.014–0.020 kg CO 2 -eq MJ −1 ) but were similar between organic manure (0.009–0.010 kg CO 2 -eq MJ −1 ) and organic legume (0.006–0.015 kg CO 2 -eq MJ −1 ). Including estimates of CO 2 emissions due to composting increased emissions for the manure-based organic system substantially (+103%–122%). Our results imply that regenerative organic farming can help mitigate climate change. Future research should focus on more accurately measuring emissions from compost production and other sources of organic fertility, conducting a full life-cycle assessment of these systems, and verifying the results using in-situ field measurements.