Method for measuring laughing gas production in soils is not working

The method that has been used for the last twenty years to measure the production of laughing gas (nitrous oxide) from different natural sources is not working. Due to this, the size of some of the sources of this greenhouse gas has locally probably been underestimated. This conclusion is drawn by Nicole Wrage in her PhD thesis that she is going to defend at Wageningen University (Netherlands) on February 28.

The research of the PhD student at Wageningen University focussed on the production of laughing gas (N2O) in fertilized soil. This greenhouse gas is produced by different groups of soil bacteria. These bacteria convert ammonia to nitrate (nitrification) or they use nitrate (a soil compound containing nitrogen) to make nitrogen gas (denitrification). During these processes, laughing gas can be produced. To investigate along which biochemical way the laughing gas is produced, researchers have used since 1979 a relatively simple method based on the separation of some soil (incubation). To different incubations, some (0.02 %) acetylene gas, a lot of (100 %) oxygen or a combination of both gases is added. The acetylene is supposed to stop nitrification, whereas oxygen should inhibit the denitrification processes.

According to the study, this method does not work for all bacteria. Thus, the addition of acetylene gas did inhibit the production of laughing gas by the bacterium Nitrosomonas europaea. The bacterium Nitrosospira briensis, however, known from agricultural soils, was not influenced. According to the researcher Nicole Wrage, acetylene probably inhibits only some of the nitrifying bacteria in the soil. Oxygen, which should only stop denitrification processes in the incubations, was found to also inhibit part of nitrification. Due to these problems of the method, it is likely that nitrifying bacteria are an underestimated source of laughing gas.
Laughing gas is responsible for approximately six percent of global warming. Roughly seventy percent of the laughing gas is produced in the soil, especially after fertilization. Carbon dioxide is the largest cause of global warming.