East Anglian farmers look at how best to use AD plant digestate in soil - without it escaping as gas

Stephen Temple’s AD plant (JF Temple).

Stephen Temples AD plant (JF Temple). - Credit: Agri-Tech East

East Anglian farmers are taking part in a field trial looking at how to get the best out of a nitrogen-rich organic fertiliser which is a by-product of anaerobic digestion (AD) process.

The study, investigating the liquid and fibre digestate produced by AC plants, is being led by Agri-Tech East involves six farms, including three in Suffolk.

Upton Suffolk Farms at Herringswell, Bury Saint Edmunds, Boxford Suffolk Farms near Sudbury and the Euston Estate near Thetford are part of the project, along with the Holkham Estate and JF Temple in Norfolk, and Allpress Farms in Cambridgeshire.

The Soil Association, NIAB and Cranfield University are also involved.

With funding and support from the Innovative Farmers’ network, Agri-Tech East has set up a field lab, using hi-tech tools to measure the impact of digestate.

The farmers will be investigating how to ensure the maximum amount of nitrogen is available to the crop and the best way to prevent it escaping as ammonia gas.

AD has become an attractive technology for many farmers to generate energy from waste products and involves organic materials being broken down into organic compounds in the absence of oxygen, producing biogas and digestate.

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Digestate has three forms: whole, which is similar to livestock slurry, liquor, which is the whole digestate with most or all solid matter separated and fibre, which is similar to compost as the separated solid material.

Allpress Farms invested in a 500kW AD plant in 2014, feeding it 50% onion waste and 50% leek waste. It produces around 11,500 tonnes of digestate.

“The farmers in this field lab want to find ways to ensure that the maximum proportion of nitrogen is available to crops,” said Liz Bowles, head of farming at the Soil Association.

“The desired outcome is to find techniques which allow this to happen – for example, acidification might be helpful in reducing the pH of the digestate.”

Andrew Blenkiron, estate director at the Euston Estate, said: “It is a big challenge to work out the economic benefits of spreading 30,000 tonnes of organic material from the anaerobic digester, compared to the cost of artificial applications - but I know that the organic material will have a longer-term benefit on soil health.”