N-FERTILIZATION AND SOIL ACIDIFICATION EFFECTS ON N2O AND CO2 EMISSION FROM TEMPERATE PINE FOREST SOIL

The fluxes and soil atmospheric concentrations of N2O were studied in field lysimeters containing reestablished soil profiles from 100-y-old Scots pine (Pinus sylvestris) forest of Norway. The experiment was designed as a full factorial with 3 N-fertilization rates [0 (Control), 30 kg (Medium) and 90 kg (High) N ha(-1) y(-1)] with NH4NO3 and 3 pH values of soil acidification (acid irrigation with pH 3, 4 and 5.5). The most acidic treatment (pH 3) significantly reduced both N2O fluxes and soil N2O concentrations. The highest N2O fluxes were observed in the intermediate pH treatment (pH 4). There was a significant increase in N2O release due to input of N. The average fertilizer-derived N2O-N emission during the summer period was 94 and 93 mg kg(-1) of added NH4NO3-N d(-1) for Medium N and High N, respectively. Surprisingly, despite a strong effect of acidification on the N2O flux, we could not find any significant interaction between acidification and N-fertilization. This means that N-deposition effects on the N2O fluxes will be more or less unaffected by previous acidification due to deposition of sulphuric acid. Soil acidification with the most acidic ''rain'' (pH 3) resulted in decreased CO2 fluxes and concentrations in soil.