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Nitrous Oxide Emissions from a Northern Great Plains Soil as Influenced by Nitrogen Management and Cropping Systems

^a Dep. of Land Resources and Environmental Sciences, Montana State Univ., P.O Box 173120, Bozeman, MT 59717-3120
^b Agriculture and Agri-Food Canada, 51 Campus Drive, Saskatoon, SK S7N 5A8

^* Corresponding author (rengel{at}montana.edu).

Received for publication September 22, 2006. Field measurements of N₂O emissions from soils are limited for cropping systems in the semiarid northern Great Plains (NGP). The objectives were to develop N₂O emission-time profiles for cropping systems in the semiarid NGP, define important periods of loss, determine the impact of best management practices on N₂O losses, and estimate direct N fertilizer-induced emissions (FIE). No-till (NT) wheat (Triticum Aestivum L.)-fallow, wheat-wheat, and wheat-pea (Pisum sativum), and conventional till (CT) wheat-fallow, all with three N regimes (200 and 100 kg N ha^–1 available N, unfertilized control); plus a perennial grass-alfalfa (Medicago sativa L.) system were sampled over 2 yr using vented chambers. Cumulative 2-yr N₂O emissions were modest in contrast to reports from more humid regions. Greatest N₂O flux activity occurred following urea-N fertilization (10-wk) and during freeze–thaw cycles. Together these periods comprised up to 84% of the 2-yr total. Nitrification was probably the dominant process responsible for N₂O emissions during the post-N fertilization period, while denitrification was more important during freeze–thaw cycles. Cumulative 2-yr N₂O-N losses from fertilized regimes were greater for wheat-wheat (1.31 kg N ha^–1) than wheat-fallow (CT and NT) (0.48 kg N ha^–1), and wheat-pea (0.71 kg N ha^–1) due to an additional N fertilization event. Cumulative losses from unfertilized cropping systems were not different from perennial grass-alfalfa (0.28 kg N ha^–1). Tillage did not affect N₂O losses for the wheat-fallow systems. Mean FIE level was equivalent to 0.26% of applied N, and considerably below the Intergovernmental Panel on Climate Change mean default value (1.25%).

Abbreviations: CT, conventional till • FIE, fertilizer-induced emissions • IPCC, Intergovernmental Panel on Climate Change • NGP, northern Great Plains • NT, no-till • WFPS, water-filled pore space