What is the impact of digestate on soil?


Allpress Farms Anaerobic DigeterDigestate, a by-product of anaerobic digestion, is increasingly of interest to farmers as it promises a rich source of nitrogen and an alternative to artificial fertilisers, but how to use it effectively to ensure the maximum amount of nitrogen is available to the crop and the best way to prevent it escaping as ammonia gas is still under debate.

Following discussions at the Innovation Hub last year, it was agreed to set up a field lab as part of the Innovative Farmers’ network to investigate.

Agri-Tech East is coordinating a consortium of six farmers with the support of Cranfield University, NIAB and the Soil Association. It is the farmers that design the trial and establish what was important to measure. In this case, yield data will be collected and used to determine Nutrient Use Efficiency (NUE).

Field lab to explore potential of digestate

AD has become an attractive technology as it allows farmers to generate energy in the form of biogas from waste products. It is a controlled microbial process where organic materials such as onion leaves are broken down into organic compounds in the absence of oxygen.

Digestate is the material remaining after biogas is removed, and has three forms: whole (similar to livestock slurry), liquor (the whole digestate with most or all solid matter separated) and fibre (similar to compost – the separated solid material).

Allpress Farms power and the glory

Patrick Allpress, Farm Director, Allpress FarmsPatrick Allpress, Farm Director at Allpress Farms Ltd in Chatteris, is participating in the trial. He invested in a 500kW AD plant in 2014, feeding it 50% onion waste and 50% leek waste. The plant produces around 11,500 tonnes of digestate and enough energy to power 900 homes.

“The first point is getting the value out of digestate – we know what it costs, but measuring the value of it as a farm input is difficult,” explains Allpress. “By doing the trials we hope to use digestate like a regular fertiliser, replacing the inorganic fertilisers.”

More information about the trial will be available shortly.


Images from www.allpressfarms.co.uk

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