• Authors:
    • McLaughlin, N. B.
    • Reynolds, W. D.
    • Yang, X. M.
    • Drury, C. F.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 2
  • Year: 2008
  • Summary: t is well established that nitrous oxide (N2O) and carbon dioxide (CO2) emissions from agricultural land are influenced by the type of crop grown, the form and amount of nitrogen (N) applied, and the soil and climatic conditions under which the crop is grown. Crop rotation adds another dimension that is often overlooked, however, as the crop residue being decomposed and supplying soluble carbon to soil biota is usually from a different crop than the crop that is currently growing. Hence, the objective of this study was to compare the influence of both the crop grown and the residues from the preceding crop on N2O and CO2 emissions from soil. In particular, N2O and CO2 emissions from monoculture cropping of corn, soybean and winter wheat were compared with 2-yr and 3-yr crop rotations (corn-soybean or corn-soybean-winter wheat). Each phase of the rotation was measured each year. Averaged over three growing seasons (from April to October), annual N2O emissions were about 3.1 to 5.1 times greater in monoculture corn (2.62 kg N ha-1 ) compared with either monoculture soybean (0.84 kg N ha-1) or monoculture winter wheat (0.51 kg N ha-1). This was due in part to the higher inorganic N levels in the soil resulting from the higher N application rate with corn (170 kg N ha-1) than winter wheat (83 kg N ha-1) or soybean (no N applied). Further, the previous crop also influenced the extent of N2O emissions in the current crop year. When corn followed corn, the average N2O emissions (2.62 kg N ha1 ) were about twice as high as when corn followed soybean (1.34 kg N ha-1) and about 60% greater than when corn followed winter wheat (1.64 kg N ha-1). Monoculture winter wheat had about 45% greater CO2 emissions than monoculture corn or 51% greater emissions than monoculture soybean. In the corn phase, CO2 emissions were greater when the previous crop was winter wheat (5.03 t C ha-1) than when it was soybean (4.20 t C ha-1) or corn (3.91 t C ha-1). Hence, N2O and CO2 emissions from agricultural fields are influenced by both the current crop and the previous crop, and this should be accounted for in both estimates and forecasts of the emissions of these important greenhouse gases.
  • Authors:
    • Wallander, R.
    • Lemke, R. L.
    • Miller, P. R.
    • Engel, R. E.
    • Dusenbury, M. P.
  • Source: Journal of Environmental Quality
  • Volume: 37
  • Issue: 2
  • Year: 2008
  • Summary: 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 -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%).
  • Authors:
    • Worth, D.
    • Desjardins, R. L.
    • Verge´, X. P. C.
    • Dyer, J. A.
  • Source: Canadian Journal of Soil Science
  • Volume: 88
  • Issue: 5
  • Year: 2008
  • Summary: Estimates of the efficiency of mitigation measures on reducing greenhouse gas (GHG) emissions from the agricultural sector are required. In this paper, recently calculated dairy GHG emissions for 2001 were extrapolated back to 1981 for census years using an index. The index was verified by comparing it with estimates based on the Intergovernmental Panel on Climate Change (IPCC) methodology for 1991. The index agreed with the IPCC estimates within 1% for methane and 4% for nitrous oxide on a national scale with no region having a difference of more than 5% for methane. For nitrous oxide, all regions were within 10%, except British Columbia, where the index was 19% too high. The index indicates that GHG emissions from primary milk production within the Canadian dairy industry have decreased by about 49% since 1981, mainly due to a 57% reduction in the dairy cow population during that period. The GHG emissions per kilogram of milk decreased by 35%, that is from 1.22 kg CO2eq kg-1 milk to 0.91 kg CO2eq kg-1 milk. Because this study took into account the energy-related CO2 emissions from all the major farm inputs (fertilizer and fossil fuel), there was little risk of hidden GHG emissions in the emission intensity calculation. This study demonstrates that where lack of input data restricts historical application of simulation models, a semi-empirical index approach can yield valuable results. Key words: Greenhouse gas, dairy industry, index, intensity indicator
  • Authors:
    • Alberta Environment and Water
  • Year: 2008
  • Authors:
    • Alberta Environment
  • Year: 2008