LABORATORY STUDY OF THE EMISSION OF N(2)O AND CH(4) FROM A CALCAREOUS SOIL

The emission of N2O and CH4 from a calcareous soil was studied, in the laboratory, with the addition of inorganic N at different soil water levels. On the whole, the addition of NH4+ led to significantly higher N2O emissions than the addition of NO3-. At 2/3 and 1.5 times field capacity, the N2O production was caused mainly by nitrification. At 3 and 6 times field capacity, nitrification and denitrification produced N2O simultaneously, in spite of low nitrification rates. The highest N2O emission was obtained at the more intermediate soil water levels (1.5 and 3 times field capacity) at which marginal oxygen conditions are likely to occur rather than at the soil water levels that had the highest nitrification (2/3 field capacity) or denitrification (6 times field capacity) process rates. This indicates that the effect of O2 on the relative N2O production was more important in determining the N2O emission than the process rate. The C2H2 inhibition of the reduction of N2O to N2 failed at 6 times field capacity, probably because of insufficient C2H2 diffusion into the soil. The CH4 emission increased with increasing water content of the soil, but it was not significantly affected by the addition of inorganic N. No inhibitory effect of the presence of NO3- on the CH4 production could be detected. This has led to the hypothesis that electron acceptors such as NO3- may only have an inhibiting effect on methane production when organic carbon is limiting the methane production.