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Agricultural management practices and environmental drivers of nitrous oxide emissions over a decade for an annual and an annual-perennial crop rotation

Mario Tenuta, Brian D. Amiro, Xiaopeng Gao, Claudia Wagner-Riddle, Matt Gervais
Agricultural and forest meteorology 2019 v.276-277 pp. 107636
Fabaceae, alfalfa, ammonium, annuals, barley, carbon, carbon dioxide, corn, crop rotation, environmental factors, faba beans, fertilizer rates, grasses, greenhouse gas emissions, greenhouse gases, manufacturing, nitrates, nitrogen fertilizers, nitrous oxide, nitrous oxide production, perennials, rapeseed, soil, soybeans, spring, spring wheat, Manitoba
Nitrous oxide (N2O) emissions were measured over 4 fields in Manitoba, Canada, continuously from 2006 to 2016 using the micrometeorological flux-gradient technique. The fields were divided into 2 treatments: 2 fields with a rotation of annual crops (corn, faba bean, spring wheat, rapeseed, barley, spring wheat, corn, soybean, spring wheat, soybean, soybean); while 2 fields had a four-year period with a leguminous perennial crop in the rotation (corn, faba bean, alfalfa/grass, alfalfa/grass, alfalfa/grass, alfalfa/grass, corn, soybean, spring wheat, soybean, soybean). Nitrogen fertilizer was applied according to local practice, and was typically not applied in years when a legume was planted. N2O was emitted from the field in episodes during spring thaw and following nitrogen fertilizer application. Emissions were less during the perennial phase of the comparison (mean 1 kg N ha−1 y−1 from perennial fields; 4.7 kg N ha−1 y−1 from the annual fields; P < 0.001). However, over the 11-year period, the treatments were not different (P = 0.3), averaging 5 kg N ha−1 y−1 because of large emissions of about 20 kg N ha−1 y−1 in the year following termination of the perennial crop. Nitrogen fertilizer application rate explained 69% of the variability in emissions (P < 0.001), with only a marginal advantage including other environmental variables such as soil nitrate exposure or soil ammonium concentrations. The N2O flux data were combined with carbon dioxide flux measurements, fertilizer N manufacturing, and potential product end uses to estimate the net greenhouse gas budget. Net emissions were a source of 1.7 Mg CO2 equivalents ha−1 y−1, driven by 3 Mg CO2 equivalents ha-1 y-1 source from N2O emissions, net carbon exchange of 3 to 5 Mg CO2 equivalents ha-1 y-1 sink, and a consumption source of 6 to 7 Mg CO2 equivalents ha-1 y-1. High inter-annual variability in fluxes resulted in no significant difference (P = 0.87) in overall greenhouse gas emissions between treatments over the full period including N fertilizer inputs and end uses of crop products.