Agri-Tech East farmers optimising use of Anaerobic Digestate

Agri-Tech East farmers optimising use of Anaerobic Digestate
Farmers, NIAB & Cranfield University to improve Nutrient Use Efficiency
“We want to get back to the soils of 20 years ago,” says Patrick Allpress, Farm Director at Allpress Farms Ltd in Chatteris, Cambridge. As part of a consortium of six farmers led by Agri-Tech East, Patrick is undertaking field trials to optimise the use of liquid and fibre ‘digestate’ (organic fertiliser) produced as a by-product from Anaerobic Digestion (AD). 
Supported by the Soil Association’s Innovative Farmers’ network, Agri-Tech East has set up a field lab, using high 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. It is a controlled microbial process where organic materials are broken down into organic compounds in the absence of oxygen. Digestate is the material remaining after AD, alongside biogas. Digestate 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 invested in a 500kW AD plant in 2014, feeding it 50% onion waste and 50% leek waste. The plant is fed 12,000 tonnes of this feedstock into the plant, producing around 11,500 tonnes of digestate. In one year, the plant can produce a potential 4.4 million kilowatt hours, which is roughly enough to supply electricity to 900 houses.
“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 [Allpress Farms] hope to use digestate like a regular fertiliser; an alternative to inorganic fertilisers.”
The project originated from discussions at the Royal Norfolk Show, as many farmers with Anaerobic Digestion (AD) plants wish to maximise its value.
“The farmers in this field lab want to find ways to ensure that the maximum proportion of nitrogen is available to crops,” says 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.”
Nitrogen, in the form of nitrates can be lost through the soil profile or through volatilisation (as ammonia) and lead to diffuse pollution if preventative measures are not employed. Cranfield University will be evaluating laboratory scale trials through various acidification options that can be used to mitigate pH levels and control loss of nitrogen.
Dr Ruben Sakrabani, Senior Lecturer in Soil Chemistry at Cranfield University says: “Optimisation of digestate NUE (nutrient use efficiency) in crops will not only provide a solution for soil health but also food production and minimise environmental pollution.”
Andrew Blenkiron, Estate Director at Euston Estate in Suffolk is also taking part in the trial.  He is set to speak at Agri-Tech East’s annual REAP conference this November. He says: “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 the longer-term benefit on the soil health.”

In addition to cutting-edge scientific input from Cranfield University, NIAB are also lending their expertise.
“Farmers in the East of England are among some of the most innovative in the country and NIAB is working with a group to maximise use of digestate on farm,” says Dr Lydia Smith, Head of NIAB Innovation Farm. “In this field lab, NIAB aims to help them take this a step further and to use this resource in combination with other strategies to improve soil quality and hence function. We will draw on the results of several long term studies at NIAB including use of cover crops and interactions within the vital soil microbial community.”

Cover crops are of great interest to the group, as they help reduce soil erosion, improve structure and composition, retain key nutrients and water in the soil and hopefully improve the efficacy of the digestate. The farmers have agreed to use vetch, black oat, fodder radish and a low level of Buckwheat as the cover crop.

Dr Belinda Clarke, Director of Agri-Tech East comments: “By bringing together farmers and researchers for these on-farm trials, we hope to improve the efficacy of digestate and understand the costs. Our annual REAP conference in November will also focus on sustainable farming, with a keynote on the benefit of ‘no-till’ for soil health.”

For further information on the Soil Association’s ‘Innovative Farmers’, please click here.
The farms involved in the project are: Holkham Estate (Norfolk), Upton Suffolk Farms (Suffolk), Boxford Suffolk Farms (Suffolk), Allpress Farms (Cambridgeshire), Euston Estate (Suffolk) and JF Temple (Norfolk).

Agri-Tech East is the UK’s first and largest membership organisation for agri-tech, bringing together businesses and academia across different disciplines to help improve the productivity, efficiency and sustainability of UK agriculture and horticulture. Agri-Tech East has become an internationally recognised catalyst for open innovation and entrepreneurship, helping to bring new ideas and thinking to the industry to become a commercial reality