Science

Digestate as an Alternative to Chemical Fertilisers

SAC Consulting, part of Scotland’s Rural College (SRUC), has been involved in a six-month project gathering practical guidance and real-life examples to share with land managers on the benefits of using digestate on the farm.

Fiona Salter, of SAC Consulting, explained:

“Digestate, when used appropriately, can be a great source of nutrients for the farm and through the work we have been doing, we hope to make land managers aware of the risks involved, how to mitigate them and the benefits that are to be had.

“We know that many farmers are struggling right now with the rising costs of fertilisers, and we hope that we can provide insight into the nutrient benefit of using digestate appropriately and how to calculate the fertiliser replacement value.”

Digestate is a nutrient-rich substance produced by anaerobic digestion that can be used as a fertiliser. It consists of left over indigestible material and dead micro-organisms – the volume of digestate will be around 90-95% of what was fed into the digester. Digestate is not compost, although it has some similar characteristics. Compost is produced by aerobic micro-organisms, meaning they require oxygen from the air.

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A document has been created for land managers sharing guidance on digestate use on Scottish farms and details of the regulations and requirements involved. There are also two podcasts now available on Farming and Water Scotland’s website, one of which hears first-hand from William Rose of Mid Coul Farms, who is reaping the benefits of spreading digestate on his farm in Dalcross, Inverness.

Commenting, William said:

“Using digestate has really transformed our ability to grow bigger yields and more consistent crops, so it has been a big boon and if we can achieve our objective of using no bought-in fertiliser at all, even on relatively small areas, particularly in the current climate, then we would feel very satisfied.”

He added that using digestate has added organic matter into the ground and improved the structure of his soils, but advised farmers to read the guidance and use the products in the right way. 

“Spreading digestate well is challenging,” he continued.

“You must have accurate spreading equipment and must at least have a dribble bar or some form of injection. Being able to spread accurately and only where it is needed, is essential.”

For those who would like to listen back to the podcasts and download the guidance document on digestate use on Scottish farms, please visit https://www.farmingandwaterscotland.org/soil-nutrients/anaerobic-digestion-digestate/digestate-use-on-scottish-farms/

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