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Could digestate save you £110 per hectare on fertiliser inputs?

Agri-TechE Article

Could cover crops be used to stabilise nutrients provided by digestate and improve its use as an alternative to chemical fertiliser for the following crop?
Digestate is a by-product from the anaerobic digestion (AD) process used on farms to generate biogas from waste. It provides a rich source of nutrients and organic matter. Estimates suggest it could save £110* per hectare on artificial fertiliser application.
An Innovative Farmers Field Lab led by Agri-Tech East, with NIAB taking the research lead suggests this estimate is achievable and the results are to be discussed at an open meeting on 12th September.

Nitrogen levels increased

soil pit digestate project
Farmers were supported with soil analysis

Lydia Smith at NIAB comments: “AD Digestate is a good source of nitrogen and other nutrients (phosphorus, potassium, sulphur) and repeated applications of digestate can improve nutrient levels in the soil, but must be managed to ensure they are used by crops rather than pollute water courses.”
“The field lab was set up to answer a number of questions and in particular the farmers were interested in the use of cover crops to stabilise the nutrients present in the digestate, so that crops benefit.”
“It is important to make nutrients available to crops and the Innovative Farmers project has shown that nitrogen levels are considerably increased in the trial plots, and could reduce the requirement for chemical fertilisers, and hence costs.”


The digestate field lab is a consortium of six farmers that all have AD plants within their farming businesses. The lab is coordinated by Agri-Tech East, research is led by NIAB and Cranfield University. It is facilitated by Innovative Farmers, the not-for-profit network that enables farmer-led research.
Liz Bowles from Innovative Farmers said: “It has been great to see the farmers and researchers working together to make this field lab both scientific and practical, and we look forward to hearing their observations at the meeting which will hopefully encourage other farmers to get involved with the next stages of the research.”

Different soil health measures 

With help from NIAB, the farmers designed the trial and chose analyses and measurements that would be taken.

  • Yield data was collected and used to determine Nutrient Use Efficiency (NUE)
  • worm count
  • VESS (Visual Estimates of Soil Structure)
  • GAI (Green Area Index) of cover crop and following crop.
  • Soil samples were analysed for selected nutrients (available N, P, K, Mg), pH and organic matter.

Reducing loss to watercourses?

Laura says the findings are interesting

One of the concerns about using digestate is that if soluble nitrates are not taken up by crops, they can leach through the soil into watercourses or lost to the atmosphere as ammonia – avoiding this was a key question the farmer-led group wanted to answer.
Laura Bouvet Knowledge and Innovation Facilitator for Agri-Tech East commented: “Farmers must comply with NVZ (Nitrate Vulnerable Zones) regulations: where a farm is within those zones there are restrictions on use, storage and spreading periods. The farmers wanted to gain a better understanding of how to use digestate effectively within these regulations.
“Some treatments used cover crops and these were found to reduce the available nitrogen in the soil. This suggests that digestate is best applied within a rotation to avoid loss into groundwater.”

Reducing volatile gas?

One of the farmers and speaker at the event, Stephen Temple, also experimented with applying sulphur as the digestate comes out of the AD plant. Acidification is thought to prevent ammonia volatilisation but care needs to be taken if it is spread to prevent foaming.

Role of microorganisms?

George Crane, NIAB
George Crane of NIAB is one of the researchers

The project benefited from a parallel funded project, which is looking at the populations of beneficial mycorrhizal fungi that form a synergistic relationship with the plant. They colonise the root zone and help to make key nutrients more available to the plant.
Studies by a NIAB PhD student have found that inoculation with these fungi resulted in a greater uptake of nitrogen by the crop, and that the amount and type of roots were affected if certain nutrients were in abundance.
This could indicate that over-supply of nutrients may make the crop plant less resilient to changing adverse environmental conditions if its root system development was depressed.

Next steps

The field lab is producing promising results and these will be discussed at the Agri-Tech East event. A decision on extending the project to look at dosage rates will be made shortly.
The farmer-led trial has also been a learning experience for all involved. Each of the plots was on a working farm and the soil preparation, planting and monitoring had to fit within other farming priorities.
One farmer noted: “As a group, we have also learnt about the importance of establishing protocols ahead of data collection, to make sure they are realistic and achievable for everybody. I am looking forward to a good discussion about next steps.”
The event: Ruminating on the role of digestate in managing healthy soils will be held at NIAB Park Farm, Cambs CB24 9NZ on 12 September 2019 from 15.00 – 19.30. Farmers and others with an interest in digestate are welcome to attend.
*Using the typical values for whole food-based digestate set out in the AHDB Nutrient Management Guide and applying 30cu m/ha to a winter wheat crop in spring on a sandy soil with a P index 2 and K index 2-, growers can save a significant £110/ha on artificial fertiliser application.

The war on waste

Agri-TechE Blog

Potatoes growing
Potato Yield Model reduces waste by enabling prediction of the size ratio of the yield before harvest

We are on the verge of war…..a war on “waste”, which we expect to see increases in productivity, profitability and sustainability across the agri-food chain, and in which technology will be a major catalyst for change.
Yet despite the troops rallying for this war, it’s been difficult to gather robust data around the scale of the problem, particularly in primary agriculture.
Food grade waste
But in a recent report published by WRAP, a review of the available data reveals some shocking statistics about how much of the huge effort by farmers to produce food-grade products actually ends up as waste.
An estimated 7.2% of all food harvested ends up as food surplus and waste. That’s a whopping 3.6 million tonnes which could have had a market value of £1.2 billion.
Potatoes, wheat and sugar beet collectively make up more than 55% of the total estimate of waste in primary production. Horticultural crops make up nearly 60% of the rest, with cereals nearly a third, livestock 4% and milk 6%.
So what counts as waste? If food products that were originally intended for human consumption are disposed of, composted, ploughed in or sent to an anaerobic digester they count as waste. If, however, they can be redistributed across other supply chains, fed to livestock or used as part of the so-called “circular economy” to produce bio-based materials, they are considered “surplus.”
There is no doubt that innovation is at the heart of winning this war on waste. And progress is being made.
Matching demand with supply 
There are companies in our membership, such as Agronomex and COGZ, with software platforms designed to match supply and demand for surplus food-grade product, bringing additional sales opportunities to the producers.
Predictive yield mapping tools have been developed for crops such as lettuces through the IceCam project with G’s  – and the Potato Yield Model, thanks to NIAB and Agrimetrics. These help reduce over-planting and enable better supply chain management through line-of-sight of expected timings and yields.
Living bio-converters 
The Eastern Agri-Tech Innovation Hub, hosted by NIAB, offers a resource for innovators to develop their ideas and was the first home to Entomics as they developed their black solder fly innovations to reduce food waste. That activity is now underway within Agri-Grub in partnership with AMT Fruit, feeding the fly larvae on fruit waste.
Part of the reason it has been so difficult to establish the scale of the problem in primary agriculture is the difficulty in extrapolating losses between seasons – environmental and weather conditions almost certainly vary and the absence of year-on-year data collection has made calculations around waste challenging.
The War on wasteAnd, unlike household waste, which still far outweighs the waste in any parts of the value chain, there are limited opportunities for farmers to influence the scale of the problem. At a pre-harvest level, pest and diseases and extreme or unhelpful weather events are beyond the control of most producers yet can contribute to loss of marketable yield.
Precision agriculture and smart water 
Here again, precision agriculture tools can help with reduction of waste of inputs, with precision irrigation specialist Wroot Water, and mapping tools such as Omnia, and data solutions from Pix4D, with imaging and sensing technologies from companies such as Crop Angel, DroneAG, fieldmargin and the Small Robot Company.
Consumer behaviours linked to buying decisions in the supply chain and retailers can also influence supply and demand, and shortcomings in post-harvest storage and failure to meet quality requirements are another major source of waste generation.
Yet again, storage solutions and monitors to reduce damage to the product are being used, such as the award winning ImpacTrack by Martin Lishman which can be made to mimic different food shapes, Roboscientific’s electronic “noses” to detect rots in potato stores and Consus Fresh with process innovation to help manage the transition from fields to packhouses to reduce waste.
The UK’s Innovative Farmers programme is piloting a farmer-led approach to gathering data on food waste in the apple, carrot, egg, tomato and wheat sectors in England. The work is supported by WRAP and funded by DEFRA, and the resulting data will be used to refine future waste estimates.
We’ll be talking about our Innovative Farmers project around the use of digestate, a by product of anaerobic digestion  to improve soils health at our Pollinator on the 12th September in Cambridge.