William R. Osterholz, Agronomy, University of Wisconsin - Madison, Madison, WI and Joshua Posner, 1575 Linden Drive, University of Wisconsin-Madison, Madison, WI
Nitrous oxide (N2O) emissions measurements were taken for two growing seasons at the Wisconsin Integrated Cropping Systems Trial (WICST). WICST is a 20 year experiment comparing 6 realistic Midwestern cropping systems varying in diversity, perenniality, and input intensivity. Season-long measurement revealed that N2O emissions were lowest in the grass-legume pasture system and the 3 year organic grain system, and were greatest in the continuous corn system and the 3 year organic manured forage based system. The conventional corn-soy system and the 4 year conventional manured forage system were intermediate. Within the systems, the organic corn and organic and conventional soy phases were associated with the least emissions. N2O emission factors (EFs) for the cropping systems ranged from 0.9% to 1.8% of N additions to the systems, and for individual crop phases EFs ranged from 0.6% to 6.3% of N additions. The IPCC default EF of 1% of N additions resulted in underestimation of emissions from grain-based cropping systems, and overestimation of emissions from forage-based cropping systems. IPCC default EFs were inaccurate for the individual cropping phases. We conclude that the main driver of N2O emissions from our diverse range of cropping systems is the magnitude of organic and inorganic N inputs, and that management systems that minimize external N inputs can reduce N2O emissions. Extended grain rotations that incorporate leguminous crops, as well as pasture-based forage systems, could substantially lower N2O emissions from agriculture in the Midwest.