SHORT-TERM NITROGEN FERTILIZATION EFFECTS ON CARBON DIOXIDE PRODUCTION AND SURFACE EMISSIONS

An investigation on short-term nitrogen fertilization effects on carbon dioxide (CO₂) production in soil profiles and surface flux emissions to the atmosphere was conducted in Eastern Nova Scotia. Temperature and moisture factors were also measured in this study to determine if they have any influence of CO₂ production and emissions. Collection of carbon dioxide surface flux and subsurface concentration data spanning a four month period (July-November) in 2002 were recently completed. Two 4-by-4 metre plots were monitored, one in a grass field and one in a mixed hardwood stand along with the existing control plots in Northeastern Nova Scotia. Nitrogen fertilizer (NH₄NO₃) was applied twice in July and August at a rate of 25 kg N/ha/application. In September and October the application rate was quadrupled to 100 kg N/ha/application. Carbon dioxide concentrations were measured in the soil profile once a week at depths of 0, 5, 10, 20, 50 and 100 centimetres using 3 multiport gas wells installed at each plot. Carbon dioxide fluxes to the atmosphere were measured twice a week with 10 vented surface flux chambers. Temperature and moisture readings were measured and averaged over five minute intervals by automated weather stations located at both sites. Five millilitre vials were evacuated in the lab and samples were drawn in the field. The samples were analyzed in the lab on a Shimadzu GC14a. Initial results from the surface flux data indicate that there is no significant difference in CO₂ emissions between the fertilized plots and the control plots over the short term. The spatial variability of measured CO₂ fluxes is high, typically around 1 g C-CO₂/m²/day, and may partially explain the lack of detection of a clear effect of nitrogen fertilization on CO₂ emissions. There appears to be some relationship between surface fluxes, temperature and moisture but the results are still very preliminary. These subsurface profiles are being used, in conjunction with a soil diffusivity estimate, to calculate subsurface production.