Nitrous oxide emissions from a Northern Great Plains soil as influenced by nitrogen fertilization and cropping systems
Dusenbury, Matthew Paul
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Agriculture has been identified by the Intergovernmental Panel on Climate Change (IPCC) as the major anthropogenic source of N₂O emissions. Field measurements of N₂O emissions are limited for cropping systems in the semi-arid Northern Great Plains (NGP). The study objectives were to determine temporal N₂O emission patterns for NGP cropping systems, and estimate fertilizer N induced emissions (FIE) and contrast with IPCC default methodology. No-till (NT) wheat (Triticum Aestivum L.)-fallow, wheat-wheat, and wheat-pea (Pisum sativum L.), and a conventional till (CT) wheat-fallow all with three N regimes (200 and 100 kg N ha-1 available N, unfertilized N control); plus a perennial grass system (CRP) were sampled over two years (15 Apr 2004 - 14 Apr 2006) using static chambers. Nitrous oxide emissions over two years were 209 to 1310 g N ha-1 for the cropping systems. Greatest N₂O emission activity occurred following urea-N fertilization (10-wk) and freeze-thaw cycles. The sum for these periods comprised 73-84% of total emissions. Emissions were positively correlated with urea-N fertilization rates and increased rapidly when water-filled pore was > 50%.Total N₂O-N emissions were greater (P < 0.10) from the fertilized (high and moderate N regimes) wheat-wheat system (1193g ha-1) than fertilized wheat-fallow systems (CT and NT) (475 g ha-1), and fertilized wheat-pea (711 g ha-1) systems. Emissions from unfertilized cropping systems (209 to 329 g ha-1) were not different from CRP (284 g ha-1). Tillage (CT vs. NT) did not (P greater than or equal to 0.10) affect N₂O emissions in the wheat-fallow systems. Fertilizer loss coefficients ranged from 0.08 to 0.45% of the applied N rate and were well below the IPCC loss coefficient of 1.25%. A more realistic estimate of fertilizer-induced losses for this region is suggested at 0.24% ± 0.5 (± 1.0 SE) of the applied N rate, or 0.26% if 10% NH₃(g) loss from fertilizer N is assumed. Despite modest emissions compared to more humid regions, there was some evidence emissions could be reduced by efficient N management. Broadcast applying urea-N to established stands of winter wheat in the spring resulted in lower N₂O emissions than band applications at seeding.