Nitrous Oxide Fluxes in Diverse Cropping Systems in the Mid-Atlantic Region.

Nitrous oxide emissions from organic cropping systems may be greater than from conventional systems since organic systems rely on organic materials (green and animal manures), which can increase denitrification rates compared to synthetic fertilizers.  On the other hand, lower soil nitrate levels in organic systems may reduce N2O emissions in organic compared to conventional systems.  There are few long-term data sets on N2O emissions from organic systems. We measured soil N2O fluxes in the corn phase of organic (ORG), no-till (NT), and chisel-till (CT) corn-soybean-wheat/legume rotations for five years at the USDA-ARS Beltsville, Maryland Farming Systems Project, a long-term field trial.  These systems differed in multiple factors, including fertility source for corn.  Hairy vetch and poultry litter were applied pre-planting in ORG.  UAN was applied at planting (~30 kg ha-1) and at sidedressing (~120 kg ha-1) in NT and CT.  N application rates were similar in all treatments. Seasonal N2O flux patterns and cumulative annual fluxes of N2O varied considerably by year, reflecting differences in weather, especially rainfall, patterns.  The largest N2O fluxes each year occurred after N fertilization in NT and CT and after soil incorporation of green plus animal manure in ORG when soils were wet (>27% VWC).  While there were no differences in cumulative N2O flux among systems in 2005, 2007, and 2008, 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 N2O fluxes in organic systems are similar to those from conventional systems when N input levels are similar.