NITROUS-OXIDE RELEASE FROM SPRUCE FOREST SOIL - RELATIONSHIPS WITH NITRIFICATION, METHANE UPTAKE, TEMPERATURE, MOISTURE AND FERTILIZATION

The spatial variability in a homogeneous 63 yr old spruce forest stand was investigated with respect to potential release of N2O in relation to nitrification rate, N mineralization rate, CH, uptake, organic C, total N and pH in soil under standardized laboratory incubation conditions. Soil samples were taken at random within a 100 m2 forest stand, and gas fluxes at three temperatures (3, 10 and 15-degrees-C) and two soil moisture contents (35 and 45% v/v) were measured. In addition, a number of other relevant factors was measured in each soil sample. There was large spatial variation in N2O release [coefficient of variation (CV)=up to 152%], nitrification rate (CV=65%) and N-mineralization rate (CV=137%). Comparatively low spatial variations in organic C (CV=31%), total N (CV=29%), CO2 evolution (CV=38%), CH4 uptake (CV=37%) and pH (CV=4.4%) were observed. The rate of N2O release was positively correlated with nitrification rate and negatively correlated with pH. The rate of CH4 uptake was negatively correlated (r=-0.61) with nitrification rate. No significant correlation was observed between the N-mineralization rate and any of the variables measured. N2O fluxes measured at 10 and 3-degrees-C were 76% (+/-14%) and 17% (+/-4%) of that measured at 15-degrees-C, respectively. We found a significant increase in N2O accumulation by increasing the moisture content from 35 to 45%. Ammonium sulphate additions stimulated N2O release but not the nitrification. The investigation demonstrated large spatial variation in the rates of nitrification, N2O release, but it was difficult to identify regulating factors for this spatial variability.