Engel, Richard (Montana State Univ., Dept. of Land Resources and Environmental Sciences, Bozeman, MT, 59717-3120; Phone: 406-994-5295; Fax: 406-994-3933;

Email: engel@montana.edu)

Nitrous oxide emissions from soils under cropping systems adapted for the semi-arid Northern Great Plains

M.P. Dusenbury, R.E. Engel *, P. Miller, R.L. Lemke

Nitrous oxide is powerful greenhouse gas and contributes to degradation of ozone in the atmosphere. Although, agriculture has been identified by the Intergovernmental Panel on Climate Change (IPCC) as the major anthropogenic source of N₂O emissions, field measurements of N₂O are limited for agricultural systems, particularly in the Northern Great Plains. This study was undertaken to learn more about N₂O seasonal emission patterns and levels from cropping systems adapted for the Northern Great Plains, and to determine if the IPCC methodology for estimating fertilizer N induced N₂O losses is accurate for this region. Five cropping systems with varying N fertilizer regimes were sampled from spring thaw in March until freeze up in December. The greatest activity of N₂O emissions for this sampling year occurred during a 10-week period following N fertilization (April 13). Emissions over the period averaged 73% of the sampling year total. Emission levels in the spring were influenced by soil moisture and N substrate. Nitrous oxide flux rates from fallow-wheat and pea-wheat rotations under high N fertility (200 kg ha^-1 available N) were related to water-filled pore space by a quadratic relationship. The relationship showed emissions increasing rapidly after water-filled pore space exceeded 50%. Total sampling year losses of N₂O-N were < 0.10 kg ha^-1 for all cropping systems. Fertilizer N induced losses ranged 0.02 to 0.12%, and were greater than one order of magnitude below IPCC predicted losses using the 1.25% default value.