Emissions of N2O from Alfalfa and Soybean Crops in Eastern Canada
2004
Rochette, Philippe | Angers, Denis A. | Bélanger, Gilles | Chantigny, Martin H. | Prévost, Danielle | Lévesque, Gabriel
There is considerable uncertainty relative to the emissions of N₂O from legume crops. A study was initiated to quantify N₂O fluxes from soils cropped to alfalfa (Medicago sativa L.) and soybean (Glycine max L.), and to improve our understanding of soil and climatic factors controlling N₂O emissions from these crops. Measurements were made on three soils cropped to alfalfa, soybean, or timothy (Phleum pratense L.), a perennial grass used as a control. In situ soil-surface N₂O emissions (F N₂O) were measured 47 times during the 2001 and 2002 growing seasons. Soil water, NH₄–N, NO₃–N, and N₂O contents, and soil temperature were also determined to explain the variation in gas fluxes. Emissions of N₂O were small under the grass where very low soil mineral N content probably limited denitrification and N₂O production. Soil mineral N contents under legumes were up to 10 times greater than under timothy. However, soil mineral N contents and F N₂O were not closely related, thus suggesting that the soil mineral N pool alone was a poor indicator of the intensity of N₂O production processes. Higher F N₂O were measured under legume than under timothy in only 6 out of 10 field comparisons (site-years). Moreover, the emissions associated with alfalfa (0.67–1.45 kg N ha⁻¹) and soybean (0.46–3.08 kg N ha⁻¹) production were smaller than those predicted using the emission coefficient proposed for the national inventory of greenhouse gases (alfalfa = 1.60–5.21 kg N ha⁻¹; soybean = 2.76–4.97 kg N ha⁻¹). We conclude that the use of the current emission coefficient may overestimate the N₂O emissions associated with soybean and alfalfa production in eastern Canada.
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