Soil Carbon Sequestration and Nitrous Oxide Fluxes in Organic, NO-till and Chisel-till Cropping Systems in the Mid-Atlantic Region

Organic cropping systems may have the potential to increase soil C sequestration and reduce soil nitrous oxide (N2O) fluxes compared to conventional systems but organic systems are not well studied. As part of the GRACEnet project we are measuring soil C sequestration and greenhouse gas fluxes in organic (ORG), no-till (NT), and chisel-till (CT) corn-soybean-wheat/legume cropping systems at the USDA-ARS Beltsville, Maryland Farming Systems Project, a long-term field trial. Soil carbon to a depth of 1 m is 9 and 23% greater in NT and ORG than in CT. Greater soil C sequestration in ORG than NT is likely due to greater C inputs in ORG than NT and possibly to reduced C decomposition rates in ORG due to burial of C inputs. Seasonal flux patterns and cumulative annual fluxes of N2O vary considerably by year, reflecting differences in weather, especially rainfall, patterns. The largest N2O fluxes in 2005 and 2006 occurred after N fertilization in NT and CT and after green manure plowdown in ORG. N2O flux in 2007, an extremely dry year, was about 10-fold lower than in 2005 and 2006 in all systems. While there were no differences in cumulative N2O flux among systems in 2005, cumulative N2O flux in 2006 was lower in CT and ORG than in NT (2.3 ug N2O-N m-2 h-1) by 15 and 61%, respectively. Results indicate that organic cropping systems may result in lower global warming potential than conventional systems but additional research and synthesis are needed to fully assess this hypothesis.