Nitrous oxide emissions from a Northern Great Plains soil as influenced by nitrogen fertilization and cropping systems

Abstract

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.