Nitrous oxide emission by nitrification and denitrification in different soil types and at different soil moisture contents and temperatures

Nitrous oxide is produced from denitrification and nitrification processes in soils, and contributes to global warming and stratospheric ozone depletion. Laboratory experiments with six soils ranging in clay content between 4-12% were designed to investigate the effect of water and temperature on the partitioning of N2O from denitrification and nitrification. The nitrification rates at 70% field capacity (FC) were significantly higher in the loamy soils (980-1440 mu g N kg(-1) soil day(-1)) than in the sandy soils (60-460 mu g N kg(-1) soil day(-1) ). The nitrous oxide produced by nitrification differed similarly between the soil types resulting in ratios of N2O-N relative to NO3--N, which were only ranging from 0.28 to 0.48% with an average of 0.39%, indicating a rather constant relationship between nitrifrcation and nitrous oxide emission. Maximum nitrification rates occured at 20 degrees C and 100% fired capacity (FC) and was 1/3 at 40% FC. At lower temperatures only small responses to changes in soil moisture were observed. The percentage of N2O-N produced by nitrification increased with increasing soil moisture (0.49% at 40% FC and 0.93% at 100% FC) and decreased with increasing temperature (0.49% at 5 degrees C and 0.17% at 20 degrees C). The denitrification activity (N-2 + N2O) in the sandy loam soil responded significantly to both increased soil moisture and increased temperature, whereas the coarse sandy soil only reacted to increased temperature. In the coarse sandy soil the Q(10)-values were in the range from 1.9 to 3.4, and the values were ranging from 4.9 to 8.9 in the sandy loam soil. As for the denitrification activity also the N-2 to N2O ratio increased exponentially with increasing temperature, which implies a linear relationship between the Iog(N-2 to N2O ratio) and the temperature. The N-2 to N2O ratios were lower in the coarse sandy soil than in the sandy loam soil, and were in the range from 0 to 16.