The cow as killer of the climate: this more recent portrayal of our bovine friends is because their digestion causes them to produce methane almost continuously and pound for pound methane has a much larger impact on global warming than carbon dioxide.
Now a team of German and Czech scientists say these animals also boost the production of methane from soil.
Grass lands that are not used for crops generally act as sinks for greenhouse gases like methane, carbon dioxide and nitrous oxide. However, once these grasslands become pastures for cattle a change occurs. This was especially noticeable in the winter, when cows stayed in a smaller area, reducing the spread of waste and increasing the density of the soil due to the animals' weight.
The researchers found that methane-producing micro-organisms from the gastro-intestinal tract of the animals were established in the soil while methane oxidation was restrained. Methane increased.
The investigation was carried out on an farm in south Bohemia consisting of approximately four hectares that has been used since 1995 for the over-wintering of about 90 cows from October till the beginning of May. According to Schloter, “At the end of this season, we could clearly see the consequences of the over-wintering on the soil.”
Unlike typical summer grazing, where the animals spread out evenly, the animals on the winter pastures prefer to stay near the feed house. As a result, no vegetation was visible and the ground was strongly compressed. In addition, this area was marked by a very high incidence of organic matter from the excrement of the animals. In more distant areas, the consequences were far less drastic.
The intensive grazing in the areas close to the barn led to a clear increase of methane emissions throughout the winter, 1,000 times more than the control areas where no bovine animals were kept. The classical process of methane oxidation, which is related to aerobic conditions, was restrained in the intensely grazed areas.
According to Schloter, this is explained by the high quantities of urea in the ground. The scientists were able to show further that methane producing micro-organisms from the gastro-intestinal tract of the cattle could survive in the soil and suppress parts of the autotchtone microflora. The newcomers profited from the environmental conditions in these soil, namely the extensive organic material.
Although in summer and autumn the animals were kept on other pastures, the composition of the microflora barely changed in the strongly over-grazed areas. Indeed, the methane production rates clearly decreased during these months, because the continuous supply of organic material was absent.
“We shall continue the project, because we also suspect consequences for the nitrogen cycle,” adds Schloter. “In addition, we have possibly proved a very rare process in the strongly compounded areas, namely the anaerobic oxidation of methane. All in all, it can be said that just about every agricultural measure has its positive and negative consequences. What weighs more in each case, however, is a social, rather than a scientific question.”
Article: Radl, V., Gattinger, A., Chronoakova, A., Nemcova, A., Cuhel, J., Simek, M., Schloter, M., Elhottova., D.: Effects of cattle husbandry on abundance, diversity and activity of methanogenic archaea in upland soils, Nature - ISME 1, 447 - 452 (2007).