Livestock reduces nitrous oxide emissions

Emissions over 72 percent overestimated

Nitrous oxide emissions, especially from agriculture, contribute significantly to the anthropogenic greenhouse effect. However, in contrast to previous assumptions livestock farming in steppe and prairie areas does not lead to increased nitrous oxide emissions. On the contrary, it reduces the release of nitrous oxide into the atmosphere. This was determined by researchers of the Institute for Meteorology and Climate Research - Atmospheric Environmental Research (IMK-IFU) of KIT in investigations in China. The results of the project funded by the German Research Foundation (DFG) have now been published in the journal Nature.

After carbon dioxide (CO2) and methane, laughing gas (N2O) is one of the main causes of climate change. One kilogram of N2O has around 300 times more greenhouse effect than the same amount of CO2. Around 60 percent of the emissions of trace gas caused by humans occur in agriculture, for example during the microbial breakdown of nitrogenous excrement from grazing sheep or cattle in the soil. So far, scientists have assumed that keeping large herds of livestock in steppes and prairie areas also contributes to the steadily growing concentration of laughing gas in the atmosphere - corresponding calculations were included in the reports of the Intergovernmental Panel on Climate Change (IPCC), known as the Intergovernmental Panel on Climate Change.

"A big mistake," says Professor Klaus Butterbach-Bahl from the Institute for Meteorology and Climate Research - Department of Atmospheric Environmental Research (IMK-IFU) of KIT in Garmisch-Partenkirchen. "In fact, areas not used for livestock emit larger amounts of nitrous oxide on an annual basis than grazed steppe areas." This was determined by the scientists funded by the German Research Foundation (DFG) in Inner Mongolia, China. For a whole year, they maintained several measuring stations in the deserted steppe region, which can be as cold as -40 degrees Celsius in winter. Support came from scientists from the Chinese Academy of Sciences and the Scottish Center for Ecology and Hydrology in Midlothian.

"Previous short-term studies have overlooked the fact that the release of significant amounts of nitrous oxide from steppe soils into the atmosphere is a natural process and that a large part of the natural nitrous oxide emissions occur during the spring thaw period," explains Butterbach-Bahl the new results. Livestock farming causes precisely these emissions to decrease significantly. The reduced grass height due to grazing means that snow is transported more easily by the wind and the snow depth therefore remains lower than on ungrazed grass areas. On the one hand, grazed soils are poorly insulated in the long and cold winter and are therefore up to 10 degrees colder. On the other hand, grazed steppe soils remain drier due to the reduced snow cover in the thaw period in March. Cold and drought then inhibit microbial activities in the thaw period. As a result, the soil gives off significantly less nitrous oxide.

Emissions over 72 percent overestimated

These "savings" clearly exceed the "normal" stimulation of the nitrous oxide emissions by the excrement of the animals - with far-reaching consequences: The scientists assume that previous calculations the nitrous oxide emissions of huge areas - about one fifth of the total area of ​​the landmass of the temperate latitudes are grasslands - overestimated by around 72 percent.

However, the results are not a positive signal for climate change. The constantly increasing nitrous oxide concentration in the atmosphere is a fact. "Our work only shows that a lot of research is still needed to really understand the sources of atmospheric nitrous oxide," says Butterbach-Bahl. Extensive grazing by livestock may not be a viable approach either. Livestock farming releases large amounts of climate-impacting methane, which the study did not take into account. Nevertheless, the KIT study shows a way to improve the greenhouse gas balance of grass steppes: making hay in autumn could reduce the grass height and thus the winter snow depth as well as the nitrous oxide emissions in the dew period.

Literature:

Benjamin Wolf, Xunhua Zheng, Nicolas Brüggemann, Weiwei Chen, Michael Dannenmann, Xingguo Han, Mark A. Sutton, Honghui Wu, Zhisheng Yao, Klaus Butterbach-Bahl: "Grazing-induced reduction of natural nitrous oxide release from continental steppe" (Nature Issue No. 7290 Vol. 464, page 881-884)

Source: Karlsruhe [KIT]