ESTIMATES OF NITROUS-OXIDE EMISSIONS FROM AGRICULTURAL FIELDS OVER 28MONTHS

Field studies conducted throughout the calendar year are needed to imp rove flux estimates for the greenhouse gas nitrous oxide (N2O). In thi s study, we report monthly N2O emissions measured using micrometeorolo gical techniques and a Tunable Diode Laser Trace Gas Analyzer (TDLTGA) . Nitrous oxide fluxes were measured at the flora Research Station (20 km north of Guelph, Ontario) from July to November 1992, and from Mar ch 1993 to February 1995, giving a total of 2445 daily averages obtain ed during the full length of the experiment. The soil at the experimen tal site was a Conestogo silt loam (Gleyed melanic brunisol). Several fields were monitored including fallow, manured fallow, Kentucky blueg rass, alfalfa, barley, canola, soybeans and corn plots. Spring thaw em issions from fallow or ploughed plots measured from March to April ran ged 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 v egetated (alfalfa and grass) plots. The lowest total annual N2O emissi ons were measured for second year alfalfa (1 kg N ha(-1) yr(-1)) and b luegrass (0 to 0.5 kg N ha(-1) yr(-1)). Higher annual emissions (2.5 t o 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 h a(-1) yr(-1)). Plot management during the previous year affected N20 e missions, particularly on the soybean plot (5.9 kg N ha(-1) yr(-1)) th at followed a manured fallow treatment. The micrometeorological techni que used in this study was successful at quasi-continuous monitoring o f N2O fluxes from several plots, and therefore, useful for detecting l ong-term effects of management on emissions.