Nitrous oxide and carbon dioxide fluxes from a bare soil using a micrometeorological approach

Increasing atmospheric carbon dioxide (CO2) and nitrous oxide (N2O) levels have prompted research on management of the soil C and N pools. The impact of C and N fertilizer addition on N2O and CO2 field emissions is not clear. We determined N2O and CO2 fluxes from a 1-ha bare soil plot using micrometeorological methods with the objective of evaluating the effect of management practices (cultivation, irrigation, fertilizer, and sucrose applications) on the relative importance of both trace gases. Research was conducted at the flora Research Station (Typic Hapludalf) in Ontario, Canada, over 7 mo. The N2O concentration gradients were measured using a Tunable Diode Laser Trace Gas Analyzer and the CO2 gradients using an Infra-Red Gas Analyzer. The transport coefficients 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 measured 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 measured 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 smaller 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-warming potential, but addition of sucrose increased the contribution of N2O to twice the contribution of CO2. The combined effect of C and N additions (e.g. manure and legume) on the N2O emissions in irrigated or high rainfall areas should be considered in the efforts of atmospheric C sequestering.