Methane from manure: improve measurements to save the climate

Climate-neutral agriculture and food production

Manure in barns emits methane, a greenhouse gas that contributes to global warming. Photo: Shutterstock

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Livestock farms are responsible for 70 per cent of methane emissions in the Netherlands. These levels need to come down. You can pull various levers, from feed to manure storage, but which has the biggest impact? Wageningen University & Research is collaborating with European partners in the M4Models research project to find better measurement methods and predictive models.

Every day slurry – the mixture of faeces and urine – lies under the barn floor fermenting, it emits more methane. We already know that, says André Aarnink, a Livestock & Environment researcher at Wageningen University & Research (WUR). But how exactly does that process work? And in particular, what is the role of various factors, such as the characteristics of the animal and the weather conditions?

That is why WUR researchers are reviewing the measurement methods together with Aarhus University in Denmark, Lund University and RISE research institute in Sweden and the Leibniz Institute for Agricultural Engineering and Bioeconomy in Germany in the M4Models (Manure management for methane mitigation) EU research project. The universities and institutes also have the support of Bioprocess Control, a Swedish company specialising in measuring equipment. Aarnink: “Methane is a greenhouse gas and a relatively large contributor to global warming – it is 27 times more harmful than CO₂. So we need to reduce emissions.”

Tool designed for taking samples from the manure pit under the slatted floor of pig farms and dairy farms. Photo: Paria Sefeedpari

The tool uses a small pump and can be adjusted to take samples at the desired height. Photo: Paria Sefeedpari

Sample preparation on location. The temperature is measured immediately and the samples are stored in thermos bottles until delivery to the LeAF lab in Wageningen. Photo: Paria Sefeedpari

To find better measurement methods, trials need to be carried out in the laboratory and on the farm. Bioprocess Control is developing measuring equipment for M4Models that will allow precise measurements of the methane emitted by manure in the lab. Aarnink: “We are quite advanced in that area in Wageningen, but there is too much variation in the measurement methods across Europe at present. In M4Models, we are developing a straightforward, unambiguous measurement method. There is an underlying scientific aim too, as it will allow us to compare results in future publications. Only then will we be able to reduce methane emissions from manure effectively.”

Don’t keep it so long

Ideally, you would do away with slurry pits in order to reduce methane emissions, because storing slurry under barn floors leads to higher methane emissions than the old-fashioned approach of manually scooping up solid manure and removing it from the barn every day. “But that is no longer a realistic option in intensive livestock farming”, says Paria Sefeedpari, a researcher and colleague of Aarnink at WUR. “Fortunately, more methods are being introduced for removing manure quickly and not leaving it there for so long – at present, the slurry may be left for up to six months.” One of the options is to use suction to extract the manure from the slurry pit every day and transport it to an anaerobic digester, says Aarnink. “The methane that is produced there in a controlled process can be used as biogas, replacing fossil fuels or for producing electricity and heat. However, biofermentation plants are only viable on large farms, or you need to have a central location as in Denmark. But we are not at that stage yet in the Netherlands.”

By storing manure outdoors, less methane is released than under the warm barn floor

Storing slurry under barn floors leads to higher methane emissions than the old-fashioned approach of manually scooping up solid manure and removing it from the barn every day. Photo: Wageningen Livestock Research

“What also helps,” adds Sefeedpari, “is storing manure outdoors as it is usually colder, and as a result less methane is released than under the warm barn floor. Another factor is what the animals eat. If you give them more digestible carbohydrates – for example from sugar beet – they will produce less methane during digestion.” Is less methane also emitted from their excrement? Sefeedpari: “Yes, but we are currently investigating the details.”

Tailor-made measurements

In the Netherlands, the farm measurements are being carried out in six barns for pigs and six barns for cows. Similar measurements are being carried out in Denmark, Sweden and Germany. That is because conditions can vary – take the weather, for example, and therefore the temperature indoors and outside. Sefeedpari: “Feed also varies between countries and between farms, especially with cows. There is more uniformity among pig farms at the national level because feed suppliers largely use the same raw materials. But cows often vary in how much maize and grass they get so that is an important variable to include in the models. In the second phase of the M4Models project, we will be studying the effect of diet on the degradability of organic matter in manure.”

Predicting farm-level emissions

Location-specific measurements in combination with research data from lab studies can then be used to build robust models that can predict a farm’s methane emissions. Farmers can use those models to set up a manure management system. Sefeedpari: “You want to know the effect of all the relevant factors, so also the sediment layer in the slurry pit, for instance. That sediment can contain bacteria that stimulate methane emissions. So regularly cleaning the slurry pit could be an important measure for reducing methane emissions.” In addition to livestock farmers, policymakers can also benefit from a good analysis of methane emissions, says Aarnink. “Sound standardised data is needed first to determine the effects of a climate policy. And a European approach is required because the problem of greenhouse gases does not stop at the border. We can only stop climate change by working together.”

European research context

Manure Management for Methane Mitigation (M4Models) addresses the following European policy challenge: A reduction of at least 55 per cent in greenhouse gas emissions in 2030 compared with 1990

Wageningen University & Research groups involved: Wageningen Livestock Research European countries involved: Denmark, Germany, the Netherlands and Sweden

Duration: 2020 – 2022

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