NITROUS-OXIDE AND CARBON-DIOXIDE FLUXES FROM A BARE SOIL USING A MICROMETEOROLOGICAL APPROACH

Increasing atmospheric carbon dioxide (CO2) and nitrous oxide (N2O) le vels have prompted research on management of the soil C and N pools. T he impact of C and N fertilizer addition on N2O and CO2 field emission s is not clear. We determined N2O and CO2 fluxes from a 1-ha bare soil plot using micrometeorological methods with the objective of evaluati ng the effect of management practices (cultivation, irrigation, fertil izer, and sucrose applications) on the relative importance of both tra ce gases. Research was conducted at the flora Research Station (Typic Hapludalf) in Ontario, Canada, over 7 mo. The N2O concentration gradie nts were measured using a Tunable Diode Laser Trace Gas Analyzer and t he CO2 gradients using an Infra-Red Gas Analyzer. The transport coeffi cients were calculated using a Bowen Ratio Energy Balance and two wind profile approaches. These three approaches resulted in similar hourly fluxes. Daily N2O fluxes for nonevent periods were 12 ng m(-2) s(-1) in 1991, and 2 ng m(-2) s(-1) in the summer of 1992, while CO2 fluxes before treatments in 1991 were 0.18 mg m(-2) s(-1). Sucrose addition ( 420 kg C ha(-1)) resulted in the highest N2O and CO2 daily emissions m easured during the experiment at 3100 ng m(-2) s(-1) and 0.5 mg m(-2) s(-1), respectively. Peak emissions of 250 ng N2O m(-2) s(-1) were mea sured after wetting of dry soil (WFP < 0.4) through irrigation in 1991 , and rain in 1992, Application of ammonium sulfate (100 kg N ha(-1)) and irrigation increased N2O emissions to 75 ng m(-2) s(-1), with a sm aller effect caused by two subsequent irrigations on wet soil (WFP > 0 .6). Carbon dioxide fluxes varied between 0.01 and 0.5 mg m(-2) s(-1) being the predominant gas contributing to an equivalent CO2 global-war ming potential, but addition of sucrose increased the contribution of N2O to twice the contribution of CO2. The combined effect of C and N a dditions (e.g. manure and legume) on the N2O emissions in irrigated or high rainfall areas should be considered in the efforts of atmospheri c C sequestering.