The study, carried out on a Czech farm in southern Bohemia, proved that two factors are vital for this process to take place. These were the amount and quality of organic material from the excrement and the heavy compaction of the soil by the weight of the cattle. These changes result in methane-producing microorganisms from the gastro-intestinal tract of the animals becoming established in the soil while, simultaneously, the process of methane oxidation, which leads to its breakdown, is restrained.
'The over-wintering of bovine animals is quite widespread at least in the ecological agriculture of Central Europe as a whole, ' says Dr Michael Schloter, the leader of the study. 'The reasoning is that the animals are less susceptible to infectious disease, thanks to the movement outside and, therefore, fewer antibiotics need to be used. However, this connection has not been proved.'
The area studied comprised approximately four hectares and has been used since 1995 for the over-wintering of about 90 cows from October till the beginning of May. According to Dr 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, cattle on the winter pastures prefer to stay near the feed house. This resulted in no vegetation being visible and the soil becoming compacted. In addition, the area was marked by a build up of organic matter from the animals’ excrement. In areas further from the feed house the consequences were less drastic.
The intensive grazing in the area near the cowshed led to an increase of methane emissions throughout the entire winter. These were 1 000 times more than the control areas, where no cattle were housed. The researchers further demonstrated that methane producing microorganisms from the animals’ gastro-intestinal tract could survive in the soil and suppress parts of the native soil microflora, the newcomers benefiting from the extensive organic material.
In summer and autumn, when the cattle were kept on other pastures, the composition of the microflora barely changed in the heavily over-grazed areas. In fact, the methane production rates clearly decreased during this period, 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. '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.'