The Role of Reduced Tillage and Organic Agriculture in Soil Nitrous Oxide Emissions.

A majority of the world’s anthropogenic nitrous oxide (N₂O) emissions come from agricultural soils. Because emissions levels depend on a combination of factors including soil organic matter (SOM) levels and mineral N availability, it is not clear how farm management strategies may affect net production of this potent greenhouse gas. Furthermore, it is vital to understand which of several diverse SOM pools is driving N₂O emissions. This research examines both organic and conventional farming methods as well as different rotations within each for their impact on soil N₂O emissions. Both organic and conventional annual cropping systems have been managed since 1999 in the Coastal Plain of North Carolina using reduced-till (RT), clean till (CT), or a 3 year rotation with pasture (LR). Data collected from field soil (0-15cm) include microbial biomass carbon and nitrogen (MBC/MBN), and dissolved organic carbon (DOC). Laboratory incubations were also conducted to quantify N₂O emissions, soil respiration, and N mineralization from the same samples. Preliminary results indicate that the farming systems differ in the size of the flush of N₂O that occurs following rewetting soils (70% WFPS) collected in early spring and at soybean harvest, but not during the growing season. Conventional CT soil N₂O emissions exceeded organic LR and CT at both time points.  MBN of organic LR also exceeded that of conventional CT in early spring, while organic RT MBN was higher than that of conventional NT at harvest.  No differences were found in MBN or DOC.