1. Dr Mary Dimambro – Cambridge Eco
Dr Russ Sharp and Sam Brown – Moulton
2. Agenda
10:00 Welcome. Dr Russ Sharp, Moulton College
10:05
Introduction to anaerobic digestion and current research on the use of
digestates in horticulture. Jacks Guinness, WRAP
10:25
Introduction to the project on the use of digestates in novel growing
media for ornamentals. Dr Mary Dimambro, Cambridge Eco
10:35
Trial system design, growing media and results to date for black pine,
cyclamen and fern. Sam Brown – Moulton College
10:45 Potential application to industry. Dr Russ Sharp, Moulton College
11:00 Discussion
11:20 Viewing the glasshouse trials
11:45 Discussion, tea and coffee, networking
12:00 Close
3. About Moulton College
Moulton is the only land-based college to
teach from ‘special needs’ through to
‘doctoral studies’.
Graded by OFSTED as Outstanding!
Campuses/academies in Moulton, Higham
Ferrers, Silverstone, Daventry and
Peterborough
4. About Moulton College
Horticultural research currently funded on a
diverse range of subjects:
LED lighting
Growing media
Soil compaction (PhD)
Soil-borne diseases (PhD)
Plant propagation (PhD)
Urban cooling (PhD)
Alternative crops
Garden History
5. About Cambridge Eco
Advising Defra, WRAP, industry, growers
Experts in the use of
composts
digestates
6. Use of digestates as a liquid fertiliser for
commercial strawberry production
6 digestates
Grow bags with trickle irrigation
Digestate Control Digestate Control
8. Why bark and digestate?
Bark = Low bulk density, nitrogen content, and pH
+ an absorbent matrix
Digestate = High bulk density, nitrogen content, and pH
+ liquid digestate able to be absorbed onto matrix
Ornamentals chosen = non-food crop with high
tolerance to salinity and ammonium.
9. Use of digestates in novel
growing media for ornamentals
Project phases:
October-December: Desk study
January-February: Designing the admixtures
March-May: Glasshouse trial
June-August: Report
11. Design Considerations -
Admixtures
Key parameters:
Particle size, air filled porosity and drainage
Electrical conductivity important
Ferns and cyclamen: up to 200µS/cm with low levels of
nutrients
Pines: 600µS/cm (pollution and salt tolerant) with base
fertiliser and long term controlled release fertiliser
14. Can digestates replace
additives?
Dolodust (magnesium limestone): Raise the pH level &
adds traces of magnesium
Digestates pH balances the low pH of the bark, and
contain sufficient magnesium
Nitrochalk (ammonium nitrate & calcium carbonate)
Digestates have adequate or high levels of ammonia
and calcium
Fertilisers (base and controlled release)
Digestates contain sufficient nutrients
15. Trial design
Controls (industry standards)
Peat-based control (PC)
Peat-free control (bark and wood fibre based, BC)
4 digestates – each with 5 admixtures
5 replicates = 110 plants per trial
16. Trial design
Randomised plot design. Rearranged at fortnightly
intervals to minimise edge effects
Both labels and pot markings used to identify plants
in each treatment.
Extra plants bought in to allow grading of plants
before allocating treatments.
17. Trial Design
Plants irrigated to just below drip point to ensure that
digestate did not leak out and move between treated
plants.
Saucers not used to ensure no stagnant water was
present around the roots.
Plants monitored for signs of pests and diseases.
None currently found so far.
Electric heaters in use in early part of the trial and
then vents opened to ensure a cool growing
environment typical of an HONS nursery.
18. Subject species
Why Black pines? HONS plant highly tolerant to both
salt and heavy metal pollution.
Why Ferns? A HONS plant that thrives in organic
growing media rich in ammonium.
Why Cyclamen? A HONS plant that thrives in
organic growing media for which we can obtain
flowering data.
19. Making the admixtures
The main selection criteria were EC, structure and
consistency (not too wet or too dry)
Standard ingredients trialled
The final admixtures:
60% bark, 30% wood fibre, 10% top soil + digestate
23. Monitoring
Fortnightly assessment
Pines: Plant height and number of branches.
Ferns: Number of fully extended fronds and length of
longest frond
Cyclamen: Number of leaves and flowers
Monthly assessment
Foliage quality:
SPAD chlorophyll meter (ferns and cyclamen)
Visual assessment (all)
24. Results to date
Trials will finish over the next few weeks
All data collected so far show no significant
difference in the response of all three species to the
different growing media for all parameters tested.
Analysed via ANOVA and Kruskal Wallace tests.
Full results in final report, including changes over
time and final harvest measurements.
33. Digestate Requirement
1m3 digestate enough for
~ 5 m3 - 50 m3 growing medium
One lorry load digestate
~ 25 t digestate
~ 5 – 50 lorry loads of growing media
34. Digestate Storage
Volume Type Cost
/m3/year
over 10
years
1 m3 White 1000 Litre IBC container £ 7
1 m3 New IBC, timber pallet £ 10
10 m3 CT2200JA Tank £ 12
19 m3 V19000 £ 13
36 m3 Elliptical Concrete Tank £ 15
72 m3 Small AD storage unit £ 24
4500 m3 Steel / concrete above ground £ 3.5
4500 m3 Earth bank lagoon £ 2
35. Transport
Transport cost depends on
Distance
Volume
Frequency of deliveries
Typical digestate transport costs per 26t lorry:
£4 /m3 if using infrastructure of digestate producer
£6 /m3 if 4 lorry loads per day are delivered
£23 /m3 if 1 lorry load per day is delivered
36. Ingredients
Cost of peat has increased
Due to adverse weather conditions during harvest
World shortage of peat in 2013
Lacking peat content is replaced with bark and
woodchip and other materials
Now less than 80% peat in some peat based growing
media
Cost of growing media ingredients is volatile
Currently the cost of some peat free growing media is
artificially lowered to encourage uptake
Cost of raw ingredients is only a snapshot / estimate
37. Growing Media Cost
Peat Free
Nursery
Stock
Peat Based
Nursery
Stock
Digestate / Bark
Admixtures
£60 - £78 /m3 £60 - £177 /m3 Bark fine 60% £ 38.50
Wood fibre 30% £ 18.50
Top soil 10% £ 9.30
Digestate storage £ 1
Digestate
transport
£ 4
Total £71 - £78 /m3 £71 - £177 /m3 £ 71.30 /m3
*Delivery costs included
38. Potential application to industry
New growing media
Potential for use as liquid fertiliser (diluted)
Potential for closer links with plants for disposal of waste
material, especially infected material that should not be
composted.
Unlike other peat-alternatives, peat and digestates are
produced on in massive volumes, thus able to satisfy a
large proportion of current demand.
Challenges: the grade of bark to use and optimising
nutritional content of media for different species.