Estimates of nitrous oxide emissions from agricultural fields over 28 months

Field studies conducted throughout the calendar year are needed to improve flux estimates for the greenhouse gas nitrous oxide (N 2 O). In this study, we report monthly N 2 O emissions measured using micrometeorological techniques and a Tunable Diode Laser Trace Gas Analyzer (TDLTGA). Nitrous oxide fluxes were measured at the Elora Research Station (20 km north of Guelph, Ontario) from July to November 1992, and from March 1993 to February 1995, giving a total of 2445 daily averages obtained during the full length of the experiment. The soil at the experimental site was a Conestogo silt loam (Gleyed melanic brunisol). Several fields were monitored including fallow, manured fallow, Kentucky bluegrass, alfalfa, barley, canola, soybeans and corn plots. Spring thaw emissions from fallow or ploughed plots measured from March to April ranged from 1.5 to 4.3 kg N ha −1 , corresponding to approximately 65% of the total annual emission. Similar effects were not observed on the vegetated (alfalfa and grass) plots. The lowest total annual N 2 O emissions were measured for second year alfalfa (1 kg N ha −1 yr −1 ) and bluegrass (0 to 0.5 kg N ha −1 yr −1 ). Higher annual emissions (2.5 to 4.0 kg N ha −1 yr −1 ) were observed for corn, barley, canola, and fallow plots. Highest annual emissions were measured after addition of nitrogen in the form of animal manure on a fallowed plot (5.7 to 7.4 kg N ha −1 yr −1 ), and alfalfa residue by fall-ploughing (6.1 kg N ha −1 yr −1 ). Plot management during the previous year affected N 2 O emissions, particularly on the soybean plot (5.9 kg N ha −1 yr −1 ) that followed a manured fallow treatment. The micrometeorological technique used in this study was successful at quasi-continuous monitoring of N 2 O fluxes from several plots, and therefore, useful for detecting long-term effects of management on emissions. Key words: Nitrous oxide, N 2 O fluxes, trace gases, agriculture, greenhouse gases