Energy Flows and Carbon Budgets in a 30 Years Old Comparison of Conventional and Organic Systems.

Greenhouse gas emissions from the agriculture sector account for 6.1 Gt CO₂-equivalents annually (14 % of the total emissions) mainly due to emissions from fertiliser use and livestock. Storing atmospheric CO₂ in soil organic matter, and reducing the inputs produced at the expense of fossil fuels are proposed as improved agricultural techniques in order to mitigate climate change. A large proportion (57-78%) of the emissions of the agriculture sector may be set off by carbon sequestration that has also other benefits like soil stabilisation, and improved water storage capacity. Here we report results of a long-term comparison between conventional and organic farming, evaluated in a plot design for 30 years. While input of nutrients was reduced by 40 to 60% in the organic systems as compared to the conventional systems, mean yields achieved were 80% in the organic systems. Maize and soybean yields were equal in both farming systems, but grass-clover yields were reduced by 15% and wheat yields by 20% in the organic system. Energy use was reduced by 41% on a per hectare bases and by 30% on a yield bases in organic farming. Organic farming systems also showed a high potential to mitigate the global warming potential and to sequester organic carbon in the soil.