This video is Mary’s first in the series focussing on the potential to use digestates from anaerobic digestion (biogas) in horticulture. This video could be useful for farmers, advisors, agronomists, agriculture and horticulture students, AD site operators and policy makers in understanding how digestates are made, and how they can be used, and potential uses in horticulture.
This video covers 4 main points:
1. How is digestate made?
2. What are the main types of digestate?
3. How is digestate used already?
4. A summary of situations where digestates show potential for use in horticulture
Mary summarises how digestate is produced via anaerobic digestion, and describes the different types of digestates: Whole, separated liquor (liquid) and separated fibre (solid) digestates.
In the UK and other countries there are regulatory controls in place for the production and use of digestates including those derived from food wastes and other animal by-products to ensure their safety. In some cases this limits what the digestates can be used for. A separate video about digestate regulations is in the pipeline.
In the UK, most of the whole and liquor digestate is applied to land, including to crops and grassland as a valuable source of available nitrogen and other plant nutrients. The solid digestate fibre is also applied to farm land, to add organic matter and nutrients to improve the soil. In some countries the separated fibre is dried and used as cattle bedding. However, this is not permitted for fibre produced from specific input materials in some countries.
Another developing opportunity for digestate fibre is as a renewable engineered construction material. Some research is being done looking at Medium-density fibreboard and wood/plastic composites.
We already know that digestates are used successfully to feed agricultural crops and improve soils. As an extension of this, could digestates be used in horticulture as fertiliser, soil mulch, soil conditioner, growing media ingredient? Over the last decade there has been a lot of research to address this question, with Mary summarising the main potential uses in this video.
Could digestate fibre be used as a growing media ingredient to replace peat? Traditionally, peat has been used as the basis for growing media including multi-purpose compost. Peat is very light, inert, consistent and has excellent moisture- retaining qualities. Unfortunately, peat is not a renewable resource, and destroying peat bogs has a negative impact on the environment, including wildlife, carbon emissions and water quality.
There are national targets to reduce peat usage in horticulture and to replace it with sustainably sourced alternatives. Research work has shown that digestate fibre has real potential to be a part of the solution for peat replacement. Trials have diluted the digestate with other growing medium ingredients, including wood chip, bark, coir or peat. This helps in regulating the right water holding capacity, bulk density, structural properties, electrical conductivity and nutrient balance. Results from trials are promising in terms of plant growth and quality. Where experimental mixes are made that do not match the profile of standard products, the plant growth and quality tends to be less good, which results in lower yields. Achieving the right mix for sale as a commercial product can be a fine art.
Research results do show that digestates can be used to grow edible horticultural crops such as tomatoes, strawberries and lettuce and ornamental plants, at the trial scale. These trials go to some lengths to ensure that commercial growing parameters are matched. Particularly tricky methods are hydroponics, as the balance of nutrients, pH and conductivity needs to be adjusted for each particular crop. Similarly, creating well balanced, well structured peat free growing media based on digestate fibre is a challenge. Easy wins are the use of digestates as soil improver and mulch, with products produced from crop-based digestates already for sale in the UK.
The scientific evidence shows that digestates can in theory be used as a biofertiliser and as a soil improver to produce high-quality food with reduced chemical fertilizer inputs. This is good news as reducing emissions to produce food more sustainably is what Mary’s channel is all about!
