Nitrous oxide is a 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. Four cropping systems with varying N fertilizer regimes were sampled through the year. The greatest activity of N2O emissions occurred during a 10 week period following N fertilization (April 13) and a two week period following spring thaw (Mar 2). Emissions over these periods averaged 26-67% 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%. In 2004, total season losses were lower in the continuous wheat rotation than the fallow-wheat and pea-wheat rotation. Measured losses of N2O-N ranged from 34 to 347 g ha-1 for all cropping systems. Fertilizer N induced losses ranged 0.09 to 0.23% of the applied N rate. Fertilizer induced losses were frequently greater than one order of magnitude below IPCC predicted losses using the 1.25% default value.
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