by Greenhouse gases act like a layer of window glass in the atmosphere: they prevent heat from being radiated from the earth’s surface into space. Methane does that 28 times as well as carbon dioxide – it’s (to stick with the metaphor) a kind of invisible double glazing.
In the last 200 years, the concentration of methane in the atmosphere has more than doubled. This is mainly due to human meat consumption: on the one hand, cows and other ruminants produce methane during digestion. Another important source is the excrement of the animals. “A third of the world’s man-made methane comes from livestock,” explains Felix Holtkamp, who is doing his doctorate at the Institute for Crop Science and Resource Conservation INRES at the University of Bonn. “It is estimated that up to 50 percent of this comes from fermentation processes in the liquid manure.”
Researchers all over the world are therefore looking for ways to suppress these processes. Holtkamp, his academic supervisor Dr. Manfred Trimborn from the Institute for Agricultural Engineering at the University of Bonn and Dr. Joachim Clemens from fertilizer manufacturer SF-Soepenberg GmbH have now presented a promising solution to the problem. “In the laboratory, we combined liquid manure from a farm with calcium cyanamide, a chemical that has been used as a fertilizer in agriculture for more than 100 years,” says Holtkamp. “As a result, methane production almost came to a complete standstill.”
Emissions fell by 99 percent
Overall, emissions fell by 99 percent. This effect started just under an hour after the addition and lasted half a year later until the end of the experiment. The long-term effectiveness is important because liquid manure is not simply disposed of. Rather, it is stored until the beginning of the following growing season and then applied to the fields as a valuable fertilizer. Months of storage are therefore quite common.
During this time, the slurry is transformed by bacteria and fungi: they break down undigested organic matter into smaller and smaller molecules. Methane is produced at the end of these processes. “Calcaneous cyanamide interrupts this chain of chemical transformations at different points at the same time, as we could see in the chemical analysis of the manure treated in this way,” explains Holtkamp. “The substance suppresses the microbial breakdown of short-chain fatty acids, an intermediate product in the chain, and their conversion into methane. Exactly how this happens is still unknown.”
But the substance has even more advantages: It enriches the liquid manure with nitrogen and thus improves its fertilizing effect. It also prevents the formation of so-called floating layers – these are deposits of organic substances that form a solid crust on the liquid manure and impede gas exchange. This crust usually has to be broken up and stirred in regularly.
The procedure also has advantages for the animals themselves: They are often kept on so-called slatted floors. Their excrement falls through openings in the floor into a large container. Due to the microbial conversion, the stool-urine mixture foams up over time and rises again through the gaps. “The animals then stand in their own excrement,” says Holtkamp. “Calcium cyanamide stops this foaming.” The costs are also manageable – they are around 0.3 to 0.5 cents per liter of milk for cattle farming.
Slurry Purity Law currently prohibits use
It is still unclear how the process will affect the release of ammonia from the liquid manure. Ammonia is a toxic gas that is not harmful to the climate itself, but can be converted into dangerous greenhouse gases. “We have initial indications that the amount of ammonia will also be reduced in the long term,” says Dr. Manfred Trimborn from the Institute for Agricultural Engineering at the University of Bonn. “But we can’t say for sure at this point.”
In Germany, an environmental law is currently preventing the addition of calcium cyanamide: there is currently a strict purity requirement for conventionally stored liquid manure.
