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%).

No abstract

No abstract

Urea placement in band or nests has been shown to enhance N use efficiency, but limited work has been done to assess its affect on N(2)O emissions. This study compared N(2)O emissions from urea prills applied to an Amsterdam silt loam (fine-silty, mixed, superactive, frigid Typic Haplustolls) using broadcast, band, and nest placements. Experiments were conducted in greenhouse pots (200 kg N ha(-1)) and in canola (Brassica rapa L.) seeded fields using rates of 100 kg N ha(-1) (recommended) and 200 kg N ha(-1). Urea placement affected N(2)O emission patterns and cumulative N(2)O losses in the greenhouse and field. Urea prills placed in nests, and sometimes bands delayed N(2)O production with peak flux activity occurring later, and elevated emission activity being more prolonged than for broadcast applications. Differences were more obvious at 200 kg N ha(-1). These effects were attributed to a delay in urea hydrolysis and inhibition of nitrification. The fraction of applied urea-N lost as N(2)O for broadcast, band, and nest placements applied at the recommended rate averaged 2.0, 2.7, and 5.8 g N kg(-1) N, respectively. The fraction of applied urea-N lost as N(2)O averaged 2.9, 10.4, and 9.2 g N kg(-1) N for broadcast, band, and nest placements when urea-N rate was increased from 100 to 200 kg N ha(-1), respectively. Greater N(2)O production with nest placement may in part be due to significant soil NO(2)-N accumulations. Potential benefits to crop fertilizer use efficiency that come with placement of urea in concentrated zones may lead to enhanced N(2)O production.

Bulk optical characterization of dissolved organic matter from semiarid wheat-based cropping systems," Geoderma 306, (November 2017): 40-49. Made available through Montana State University's ScholarWorks scholarworks.montana.edu