Admixtures Final Report

Final project report
Bark admixtures:
Formulation and testing of novel organic
growing media using quality digestates for
the production of containerised plants
Options for the use of quality digestates in horticulture
and other new markets
Project code: OMK006-009
Research dates: October 2012-July 2013 Date: July 2015

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Document reference: WRAP, 2015, Bark admixtures: Formulation and testing of
novel organic growing media using quality digestates for the production of
containerised plants
Written by: Dr Mary Dimambro and Dr Joachim Steiner
(Cambridge Eco)
Dr Russ Sharp and Sam Brown (Moulton College)
Front cover photography: Pine, cyclamen and fern grown in a range of admixtures, a bark control and peat control
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Bark admixtures: Formulation and testing of novel organic growing media
using quality digestates for the production of containerised plants 3
Executive summary
The Defra/DECC Anaerobic Digestion Strategy and Action Plan identified the need to develop
appropriate markets for quality digestates, and one of WRAP’s aims is to identify whether
there is a potential market opportunity for digestate use in the horticultural industry.
One area in which the use of digestate could be considered is its use in ornamental plant
horticulture. The successful introduction of digestates in this sector would provide
confidence in their beneficial properties, not only in the horticultural sector, but potentially in
agriculture and field horticulture.
One of the approaches taken in this feasibility study was to target a sizeable section of the
market for potted plants produced for indoor and garden use in the UK. One of the largest
species within this sector is cyclamen with a market share of 16.8% in 2007 (Defra 2008).
This feasibility study had the aim of establishing whether a variety of digestates produced in
the UK, combined with bark and other peat-free ingredients, could be used as a growing
media ingredient in horticulture. For this trial, the following four digestate feedstock/
digestate type combinations were used:
Digestate feedstock Digestate type
Food waste Separated liquor
Food waste Whole
Potato waste Whole
Maize Separated liquor
Digestate/bark admixtures with suitable structure for ornamental horticulture were produced.
It was found that a suitable base mix for subsequent addition of digestate and the creation
of admixtures with an open structure was: 60% bark, 30% wood fibre and 10% topsoil by
volume. This was combined in a ratio of 5l base mix to five different volumes of digestate
(0.1l, 0.25l, 0.5l, 0.75l and 1l) to create the final experimental admixtures. In addition to the
four digestates, each added at five rates, two industry standards were used as controls –
one peat based and the other peat free. Odours quickly dissipated when digestates were
mixed with the bark / wood fibre / topsoil base mix. Water holding capacity of the
digestate/bark admixtures was not significantly different to peat based growing media.
Admixture densities for 0.5, 0.25 and 0.1l digestate in 5l bark/wood fibre were generally
similar to or below the density of the peat and peat free growing media. Admixtures with
0.75l or 1l digestate contents were 21% to 43% higher in density. The resulting density of
the growing medium may ultimately impact on transport cost, and under these
considerations up to 0.5l digestate/bark admixtures appear to be most suited for large scale
production and transportation in the ornamental horticulture sector.
The plant species investigated were wavy cyclamen (Cyclamen repandum), fern (Asplenium
scolopendrium) and black pine (Pinus nigra). The bark-loving cyclamen was chosen as it was
considered likely to tolerate the very high C:N ratio of bark and wood. To extend the scope
beyond flowering plants, two other plant species were included. Ferns were chosen to
represent foliage plants and pine was chosen as a representative for responses of a tree
species, especially the range of conifers produced in the UK. Pines thrive in organic growing
media with a slight acidity.
The three plant species were purchased as healthy specimens before potting them on into
the admixtures and assessed regularly for at least 90 days. For all species, plant quality and

growth parameters were determined during the growing season, and plant weight
determined via the destructive harvest at the end of the trial.
For black pines there was no significant difference in any growth parameter compared to the
controls. Growth parameters measured were number of stems, plant height and plant
quality. A growth vs time analysis showed pines of all treatments grew at comparable rates.
Destructive harvest analysis to determine the mean dry weight of the whole plant, of stems
and of roots as well as dry matter content and mean root-to-shoot ratio did not generally
show statistically significant differences between the various treatments and the controls.
For ferns there was mostly no significant difference in any growth parameter compared to
the controls. Growth parameters measured were number of fronds, frond length, chlorophyll
content and foliage quality. A growth vs time analysis showed ferns of nearly all treatments
growing at comparable rates. Destructive harvest analysis to determine the mean dry weight
of the whole plant, of stems and of roots as well as dry matter content and root-to-shoot
ratio do not generally show statistically significant differences between the various
treatments and the control. Admixtures with high doses of 1l food waste digestate were the
exception to the above findings. A significant reduction in fern chlorophyll content and leaf
quality was observed, which was attributed to comparatively high sodium content originating
from the food waste digestates.
For cyclamen, there was no significant difference in any growth parameter measured
compared to the controls. Growth parameters measured were number of leaves, number of
flowers, chlorophyll content and foliage quality. A growth vs. time analysis showed cyclamen
of all treatments senescing at similar times. It was found that variability between the number
of flowers per plant within each treatment was very high, rendering this parameter
unsuitable for comparison between treatments. Destructive harvest analysis was carried out
on the cyclamen corms, as all plants had senesced at the point of harvest. The mean dry
weight of the corm and dry matter content did not generally show statistically significant
differences between the various treatments and the control.
Liverwort growth was suppressed when using digestate admixtures, which is likely to
positively impact on overall plant quality in a commercial setting. There were also no signs of
shore flies or sciarid flies on any of the plants.
No fertiliser supplementation was required during the trial, indicating that the range of
digestates investigated was able to provide an appropriate level of nutrients for the three
species under test. All four digestates contained essential plant macro- and micronutrients.
Analysis of the digestates also showed that the majority of the available nitrogen was in the
form of ammonium, with some nitrates also present. The concentration of potentially toxic
elements (heavy metals) was extremely low compared to the maximum permitted in the UK
specification for digestate quality (BSI PAS 110).
The outcome of the experiments showed that using digestate/bark admixtures as a growing
medium for all three plant species generally did not significantly affect plant quality.
From reviewing the cost factors such as the cost of source materials, fertiliser, digestate
storage, adapting machinery to handle digestate as well as transport, it is clear that there is
a large variability within each component. Hence it depends on the particular circumstance of
each producer whether digestate/bark admixtures as growing media can be sourced cost-
competitively compared to traditional growing media. However, in general terms, the cost
benefit analysis showed there is potential for digestates/bark admixtures to fit into a
competitive cost model, and are currently most likely to compete favourably within the
market segment where products contain peat imported from overseas.

Contents
1.0 Introduction ................................................................................................. 8
1.1 Digestates in the UK...................................................................................8
1.2 Using digestates in protected horticulture.....................................................9
1.3 Bark and wood chippings..........................................................................10
1.4 Project aims ............................................................................................10
2.0 Methodology............................................................................................... 11
2.1 Digestates used .......................................................................................11
2.2 Creating the admixtures ...........................................................................12
2.2.1 Analysis of the growing media.........................................................14
2.3 Trial establishment...................................................................................14
2.4 Monitoring...............................................................................................15
2.5 Final harvest............................................................................................16
2.6 Statistical analysis ....................................................................................16
3.0 Admixture properties.................................................................................. 17
4.0 Trial results and discussion ........................................................................ 19
4.1 Growth measurements during the trial.......................................................19
4.1.1 Cyclamen growth measurements.....................................................19
4.1.2 Fern growth measurements ............................................................22
4.1.3 Pine growth measurements.............................................................25
4.2 Growth/time series analysis ......................................................................28
4.2.1 Cyclamen growth/time series analysis..............................................28
4.2.2 Fern growth/time series analysis .....................................................29
4.2.3 Pine growth/time series analysis......................................................29
4.3 Occurrence of liverworts on fern growing media .........................................31
4.4 Destructive analysis..................................................................................32
4.4.1 Destructive analysis - cyclamen.......................................................32
4.4.2 Destructive analysis - fern...............................................................33
4.4.3 Destructive analysis - pine ..............................................................35
4.5 Fern transpiration rates ............................................................................38
5.0 Cost benefit analysis .................................................................................. 39
5.1 Cost of source materials ...........................................................................39
5.2 Cost of digestate storage..........................................................................40
5.3 Cost of adapting machinery to handle digestate..........................................42
5.4 Cost of transport......................................................................................42
5.5 Potential quantity of admixtures that could be used for ornamentals in the UK
44
6.0 Considerations for future work................................................................... 45
6.1.1 Further work using the admixtures ..................................................45
6.1.2 Refining the admixtures..................................................................45
6.1.3 Can the admixtures be created using commercial mixing equipment? .46
6.1.4 Can the moisture content of the admixtures be reduced? ..................46
6.1.5 Can the admixtures be used in a commercial nursery setting using
standard potting methods? .......................................................................46
6.1.6 Do the admixtures compare to standard growing media for plant shelf
life? 46
6.1.7 Digestate as a liquid fertiliser on nurseries .......................................46
7.0 Conclusion .................................................................................................. 47
7.1 Can digestate be used as a growing media ingredient in protected horticulture?
47
7.2 Are there any constraints, and can these be overcome? ..............................47

7.3 Are there business benefits? .....................................................................48
7.4 Should the ADQP be changed to include using digestates in growing media as
a permitted use? ................................................................................................48
8.0 References.................................................................................................. 49
9.0 Appendices ................................................................................................. 51
9.1 Appendix 1. Characteristics of eight UK digestates ......................................51
9.2 Appendix 2. Admixture analysis results ......................................................52
9.3 Appendix 3. Fern, pine and cyclamen photos at the end of the trial .............58
9.4 Appendix 6. Fresh weight of fern and pine at the end of the trial .................59
10.0 Appendix 7. Analysis techniques ................................................................ 61
10.1 Digestate analysis ....................................................................................61
10.2 Growing media analysis ............................................................................61
Acknowledgements
Our thanks go to:
 WRAP for funding the trials;
 Dr Francis Rayns of Garden Organic for his assistance with the literature searches;
 Dr Katherine Keeling at the University of Warwick Crop Centre for technical support
with the digestates;
 The anaerobic digestion sites for providing their digestates;
 The members of the growing media supply chain who gave an industry perspective
throughout the planning and execution of the trial; and
 The students of Moulton College for their voluntary assistance with the trial set up
and destructive harvesting of the plants.

Glossary
AD Anaerobic digestion
Admixture The substance that results from mixing all the ingredients in a growing
media ‘recipe’; more generally a mixture which results when two
different materials are combined without occurrence of chemical
reactions
ADQP Anaerobic Digestate Quality Protocol – End of waste criteria for the
production and use of quality outputs from anaerobic digestion of
source segregated wastes.
Biofertiliser Biofertiliser is the name adopted for quality digestates that meet the
ADQP and PAS110 specification
Biogas Mixture of gases produced by anaerobic digestion
Biomass Any living or recently dead plant or animal material
DECC The Department of Energy & Climate Change
Digestate fibre Fibrous fraction of material derived by separating the coarse fibres
from the whole digestate
Digestate liquor Liquid fraction of material remaining after separating coarse fibres from
whole digestate
EC Electrical conductivity
HONS ‘Hardy Ornamental Nursery Stock’. Plants grown on nurseries for use in
gardens and managed landscapes. Hardy refers to them being able to
survive the winter without significant damage from frosts.
MBT Mechanical Biological Treatment – combination of mechanical and
biological treatments for extracting recyclables from mixed household
waste
PAS110 The publicly-available specification (PAS) BSI PAS 110 is an industry
specification against which producers can verify that their digestate is
of consistent quality and fit for purpose. PAS110 specifies:
 Controls on input materials and the management system for the
process of anaerobic digestion and associated technologies
 Minimum quality of whole digestate, separated fibre and separated
liquor
 Information that is required to be supplied to the digestate recipient
PTEs Potentially toxic elements (heavy metals)
Whole digestate Material resulting from an anaerobic digestion process that has not
undergone post-digestion separation
WRAP Waste and Resources Action Programme

1.0 Introduction
The UK government is actively seeking to phase out the use of peat in commercial
horticulture by 2030 (Defra 2011). In 2009 the UK market for growing media and soil
improvers was 7 million m3
, of which 3 million m3
was peat. Of this, 99% of the peat used
was in growing media and only 1% was used in soil improver products (Defra 2010).
There are a range of growing media ingredients which are gradually becoming more
widespread in the UK, including wood fibre, bark, green compost and coir (Defra 2010). For
example, in 2012 in UK growing media and horticultural products market, the proportion of
green waste compost was 9%, coir 8%, bark 8% and wood-based products 14% (Waller
and Denny, 2013).
The potential to use digestates from anaerobic digestion (AD) as a growing media ingredient
is currently the focus of a research programme funded by WRAP. This project is one of a
number of WRAP and Defra funded projects ascertaining the potential for using a range of
digestate types in horticultural applications. Crops included in these trials cover a variety of
ornamentals, plus the edible crops of tomatoes, cucumber, lettuce and strawberries.
A number of key factors in the production of sustainable growing media have been
highlighted by growing media manufacturers and the Sustainable Growing Media Task Force
(2012):
 All growing media must be fit for purpose;
 Sustainable growing media must be economically viable; and
 All growing media should be made from raw materials that are environmentally and
socially responsibly sourced and manufactured.
1.1 Digestates in the UK
Renewable energy production via the process of anaerobic digestion (AD) is on the increase
in the UK, with over 100 working AD plants and many more in the planning stage. The AD
Strategy and Action Plan (DECC and Defra 2011) has demonstrated a commitment to
increasing energy from waste through AD.
Figure 1 Example of an AD plant producing energy and digestate (biofertiliser). (Source:
DECC and Defra 2011)

The AD process involves the production of biogas from organic wastes and/or purpose
grown crops. The biogas is used to generate renewable energy or can be upgraded and
injected into the gas grid (see Figure 1). The AD process also produces digestate which is a
nutrient-rich biofertiliser. The digestate can be used whole, or separated to produce liquor
and fibre. The characteristics of the digestate depend on the feedstock used and whether the
digestate has been separated. Some examples are illustrated in Appendix 1.
In 2008/09, over 105,000 tonnes of digestate was produced through AD in the UK, with 76%
of this being used as fertiliser in agriculture and the remainder as soil conditioner (AfOR
2010). As the number of AD plants in the UK increases, so will the production of the nutrient
rich digestate, with recent estimates suggesting a total figure of 1.44 million tonnes of
digestate with 678,465 tonnes from waste-fed sites (WRAP, 2013). By 2016 markets may be
needed for nearly 2m tonnes of digestate. WRAP is working to develop markets for
digestates in various sectors including agriculture, landscaping and land regeneration,
horticulture and forestry.
One area in which the use of digestate could be considered is its use in ornamental
horticulture. The successful introduction of digestates in this sector would provide
confidence in their beneficial properties, not only in the horticultural sector, but potentially in
agriculture and field horticulture.
Furthermore, if the digestate adds to the quality of the growing media, this could infer a
higher market value for the digestate than when used in agriculture. Thus digestate-
containing growing media represent a potential revenue stream for a product that AD plants
may currently provide to users free of charge or pay to dispose of.
Confidence in the use of digestates in the UK has been improved by the existence of PAS110
and the Anaerobic Digestate Quality Protocol (ADQP). These ensure that there are minimum
standards for the production and quality of digestates, and enable the reclassification of
waste-derived digestates into products. In England (as well as Wales and Northern Ireland)
if an operator complies with both and is independently certified to both, then the biofertiliser
is no longer a waste and can be used as a product. The approach is slightly different in
Scotland.
Currently ADQP digestates of specific types can be used for agriculture, soil/field-grown
horticulture, forestry and land restoration. Currently, using ADQP digestates in growing
media is not a permitted use, and as such an Environmental Permit or Exemption from
environmental permitting would be needed prior to use. However, by demonstrating that
BCS approved digestates can be used safely and beneficially in protected horticulture, and
that they are fit for purpose, these rules could be reviewed.
The main research questions of this project are:
 Can digestate be used as a growing media ingredient in the production of hardy nursery
stock?
 Are there any constraints, and can these be overcome?
 Are there business benefits?
 Should the ADQP be changed to include using digestates in this way as a permitted use?
1.2 Using digestates in protected horticulture
A number of academic studies outside the UK have been published, demonstrating that
whole, solid and liquid digestates from a range of feedstocks can be used in protected
horticulture. Trials have shown that digestate can be used as a biofertiliser and/or mixed
with other growing media ingredients, ranging from a straight mix with peat through to
mixes with coir, perlite and soil.

For example, digestates from pig slurry were found to be an effective inorganic fertiliser
replacement for containerised tomato production (Poustková et al 2009; Kouřimská et al,
1999 and 2009). Kohlrabi and peppers have been shown to grow in mixes of soil with pig
slurry digestates just as well as when conventional fertilisers are used (Lošák et al 2011,
Zhang et al 2010).
Digestate from the anaerobic digestion of municipal waste performed as well as conventional
fertilisers for the fertigation of three ornamentals (silverleaf dogwood (Cornus alba),
common ninebark (Physocarpus opulifolius) and Spiraea spp.) grown in a bark mix (Chong et
al 2008).
Solid (also known as fibre) digestates mixed with other growing media ingredients were
found to be comparable to conventional mixes for a range of potted plants including Petunia
(Rakers et al 2010), ryegrass (Do and Scherer 2012), lettuce (Crippa et al 2011) and roses
(Wrede 2012).
Thus there is evidence of the potential for creating suitable growing media that incorporate
whole, liquid and solid digestates derived from a variety of organic wastes for the
containerised production of a range of plant species.
1.3 Bark and wood chippings
Bark and wood chippings are by-products of forestry and arboriculture practices. The main
current markets for virgin wood waste (which will include bark and wood chippings), are
animal bedding, horticultural mulches and the panelboard sector, in addition to use as wood
fuel (Defra, 2012).
Bark and wood chippings are currently not used widely as a growing medium for plants as
the wood contains a very high C:N ratio (400:1) and have a very low nutrient content, low
water content and are too acidic. As such, of the 1.9 million m3
of bark used in horticulture
in 2009, the vast majority was used in landscaping as a surface mulch over soil (Defra
2010).
Chippings and bark can provide a good organic matrix, which is a well-aerated and free-
draining medium. Bark is a good medium for the growth of roots if extra nutrients are
supplied, and as such bark is now being incorporated into the mixes of growing media for a
number of amenity plants, including ferns, cyclamen and some conifers. 100% bark is only
used for the cultivation of epiphytes (plants that naturally grow in the canopy of trees) such
as tropical orchid house plants. Wood fibre, another by-product of forestry is also being used
now as an ingredient in growing media to reduce peat usage in the UK.
1.4 Project aims
The aims of the experimental part of this study were:
1) To produce a range of bark admixtures, consisting of bark mixed with a range of
anaerobic digestates as well as other sustainable growing media ingredients to create
novel growing media with suitable pH and nutrient profiles to support the growth of
plants.
2) To identify the proportions at which whole and liquor digestates can be incorporated
into the growing medium without reducing plant performance when compared with
conventional nutrient amendments added to growing media.

2.0 Methodology
In order to identify the appropriate range of digestate additions to growing media, the
project was divided into several distinct phases.
In phase one, digestates were obtained from four UK based anaerobic digestion plants. The
selection of digestates was designed to balance the range of feedstocks and digestate types
available with the logistical practicalities of an initial feasibility study. The two food waste
derived digestates chosen were certified to PAS110 standard.
In phase two, the appropriate mixing ratios of digestate, bark and wood fibre were
determined. The main selection criteria were electrical conductivity (EC) and structure. The
EC limits used in this study were obtained by speaking to a number of growers and
considering ranges used in standard growing media. The highest digestate addition
represented the very top limit for EC and moisture, with the lowest being below standard EC
levels for growing media, but still within the recommended limits. Also in phase two, the
mixtures produced were analysed for their nutrient content.
In phase three, the growth trial was undertaken, which included an assessment of crop
quality and biomass production.
2.1 Digestates used
Four digestates were obtained for the trial in December 2012. The digestates were analysed
for a range of characteristics, as shown in the tables below. The analysis methods are listed
in Appendix 7. All four digestates contain essential plant macro- and micronutrients, as
shown in Table 3 and Table 4. The majority of the available nitrogen is in the form of
ammonium, with some nitrates also present (Table 2). The concentration of potentially toxic
elements (heavy metals) was extremely low, as compared to the maximum permitted levels
for PAS110 (Table 5).
Table 1 Details of the digestate types used
Code Digestate Digestate
feedstock Type
FS Food waste Separated liquor
FW Food waste Whole
PW Potato waste Whole
MS Maize Separated liquor
Table 2 Digestate analysis results. Available nitrate and ammonium, pH, conductivity, dry
matter and organic matter
NO3-
N
NH4-
N Conductivity
% dry
matter % organic matter
Digestate mg/l mg/l pH (dS/m-1
) w/w dry mass
FS 4.16
2543.
0 8.06 20.1 2.9 89.3
FW 1.90
3736.
0 8.36 30.5 2.5 88.0
MS 4.93
1601.
5 7.73 16.6 5.3 94.2
PW 1.09
1932.
0 7.86 19.6 2.2 86.4

Table 3 Total nutrients in the digestates (nd = not detectable)
N Na P S Zn Mo
Digestate mg/l mg/l mg/l mg/l mg/l mg/l
FS 4257.3 986.7 349.5 189.5 5.30 nd
FW 5876.4 1472.6 338.8 164.2 4.87 nd
MS 3801.0 130.1 418.0 254.4 6.44 0.25
PW 2913.5 35.9 220.2 101.8 2.99 nd
Table 4 Total nutrients in the digestates
B Ca Cu Fe K Mg Mn
Digestate mg/l mg/l mg/l mg/l mg/l mg/l mg/l
FS 0.84 869.5 0.99 56.38 1329.1 110.96 4.10
FW 0.82 420.2 0.94 36.51 2361.1 12.36 1.69
MS 1.46 898.4 1.82 57.22 3271.6 201.72 6.58
PW 1.23 131.0 0.88 68.17 4775.3 55.03 1.44
(nd=not detected)
Table 5 Potentially toxic elements in the digestates and the PAS110 limit
Total
Copper
(Cu)
Total
Zinc
(Zn)
Total
Lead
(Pb)
Total
Cadmium
(Cd)
Total
Mercury
(Hg)
Total
Nickel
(Ni)
Total
Chromium
(Cr)
Digestate mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg
FS 1.493 4.180 0.588 <0.01 <0.05 0.428 0.223
FW 1.573 4.093 0.139 0.019 0.000 0.368 0.287
MS 2.290 5.030 0.107 0.016 0.037 0.634 0.195
PW 4.550 7.180 0.366 0.061 0.000 3.520 0.540
PAS110
limit
200 400 200 1.500 1.000 50 100
2.2 Creating the admixtures
The range of nutrients contained within the digestates was deemed sufficient (by
comparison with standards for growing media) for plant growth for the duration of the study
and so no extra nutrients were added to the admixtures.
Initial tests involved mixing digestates with a range of standard growing media ingredients
for pines, cyclamen and ferns, including bark, composted green waste, wood fibre and top
soil. The addition of wood fibre was found to be particularly useful, as any digestate not
absorbed by the bark was easily taken up by the wood fibre.
Electrical conductivity (EC) was used as a proxy measure of salt levels in the admixtures
during the initial test phase. EC is a commonly used test for growing media, as high EC can
be detrimental to plant growth. It was found that the admixtures had comparable EC to the
control standard growing media. It was decided to include one admixture with an EC higher
than the controls to ascertain whether this higher level would influence plant growth and
quality.

The optimum recipe for enabling the soaking up of the digestate and the creation of
admixtures with an open structure was found to be 60% bark, 30% wood fibre and 10% top
soil by volume, and this was used as the base mix. A standard volume of 5 litres of the base
mix was used, with a range of digestate volumes added to this.
Box 1. Details of the growing media used for the trial
Peat control: Standard Sinclair nursery product for professional HONS production
 80% Peat: 0-10mm 25%, 3-15mm 27.5%, 15-25mm 27.5%
 15% bark: 6-15mm
 5% grit
 N 120, P 140, K 240
Peat-free control: Standard professional mix for HONS from Petersfield Growing Mediums
 60% composted Fine Bark / Bark Fines
 30% woodfibre
 10% sterilised soil
 Base fertiliser, 1kg/m³ PG Mix 14:16:18 (N:P:K)
 Trace elements (undefined quantity)
 Controlled release nitrogen supplement (woodfibre / bark)
 Wetting agent
Bark: Standard professional product from Sinclair via LBS Horticulture
 Nursery grade (8-16mm)
Top soil: Sterilised loam from Petersfield Growing Mediums
Wood fibre: Standard professional product from Petersfield Growing Mediums
It was found that adding between 100 and 750ml of digestate to 5 litres of the base mix
resulted in admixtures which were of a similar nature to standard growing media, with the
digestate being well absorbed. These admixtures were similar in weight to standard controls.
Admixtures with up to 1000ml digestate in 5 litres of growing media were possible, but this
resulted in a slightly sludgy mix which did still retain the moisture with no release of liquid
when the admixture was squeezed. This dilution was felt to be the maximum in terms of
moisture and EC. A range of dilutions up to 1000ml in 5 litres was then created. The same
mixtures were created for each of the four digestates.
The admixtures for the trial were combined in a cement mixer to ensure thorough mixing.
Firstly the digestate was gradually poured onto the bark whilst mixing for several minutes
until thoroughly combined. The wood fibre was then added and mixed. Finally the soil was
added and mixed again until the admixture was even and the digestate was completely
absorbed. The admixtures were then bagged and used to establish the trials.
Table 6 Admixtures for the trial
Digestate Digestate Volume of digestate in 5 litres of admixture
(60% bark, 30% wood fibre, 10% top soil)
feedstock Type 100ml 250ml 500ml 750ml 1000ml
Food waste Separated liquor FS1 FS2 FS3 FS4 FS5
Food waste Whole FW1 FW2 FW3 FW4 FW5
Potato waste Whole PW1 PW2 PW3 PW4 PW5
Maize Separated liquor MS1 MS2 MS3 MS4 MS5

In addition to the five treatments for each of the four digestates, there were also two
industry standards used as controls; one peat based control (PC) and one peat free control,
which was bark and wood fibre based (BC). The trials included five replicates of each
treatment.
Summary of the 22 treatments
Peat control  1 rate
Peat-free control  1 rate
Food waste digestate Separated liquor  Dilution 1-5
Food waste digestate Whole  Dilution 1-5
Potato waste digestate Whole  Dilution 1-5
Maize digestate Separated liquor  Dilution 1-5
2.2.1 Analysis of the growing media
Once the admixtures had been created they and the controls were analysed for a range of
parameters, including nutrients, EC and pH, with the results shown in Appendix 2. Admixture
analysis results Both available nitrogen in the form of NO3 and NH4, and total nitrogen were
analysed. This ensured that a direct comparison could be made between the admixtures and
the controls as to their concentrations of readily available nitrogen. The total nitrogen
includes the nitrogen locked up in the growing media (such as in the bark), which is not
readily available, but may be released slowly over time.
2.3 Trial establishment
The trial was carried out in a heated Keder growth house (insulated polyethylene) at Moulton
College, Higham Ferrers Campus in early 2013.
The plant species used for the trials were black pine (Pinus nigra), fern (Asplenium
scolopendrium) (both from James Coles and Sons) and wavy cyclamen (Cyclamen
repandum) (from Jacques Amand). The bark-loving cyclamen was chosen as it is likely to
tolerate the very high C:N ratio of bark and wood. To extend the scope beyond flowering
plants, ferns were chosen to represent foliage plants and pine was chosen as a
representative for responses of a tree species. Pines thrive in organic growing media with a
slight acidity, and are moderately salt tolerant.
All three species are classed as hardy ornamental nursery stock (HONS), with cyclamen and
ferns produced for both the indoor and outdoor market, and pine for the outdoor market in
the UK. Initial cultivation of all three species generally occurs in glasshouses or polytunnels,
often until retail with cyclamen and ferns.
Pine. Photo taken on 20th
February five days
after potting up
The three species were all potted up in the
admixtures using standard procedures as
used in a commercial nursery.
For both the fern and pine, the plants
were removed from the pots and the
excess growing media removed as much
as possible, avoiding any damage to the
root.

Ferns. Photo taken on 20th
February just after
potting up
The pine trees (Pinus nigra) were supplied
in 2l pots in a standard organic growing
medium with an age of approximately two
years. The plants were well rooted into the
growing medium. These were planted into
3l pots on 15th
February.
The ferns (Asplenium scolopendrium) were
supplied in P9 pots (0.5l) in standard
organic growing media with an age of
approximately two years. The plants were
fairly well rooted into the growing medium.
These were planted into 2l pots on 20th
February.
The Cyclamen repandum were provided in P9 pots
(0.5l) in standard organic growing media. These plants
were not well rooted out. These were planted into 1L
pots on 1st
March. Great care was taken to avoid
damage to the corm or roots, with approximately 2cm
of growing medium removed from the base.
After each plant had been potted using the treatments
described, initial base measurements were undertaken
and arranged in randomised plot design.
Due to the trial commencing in late February no
supplementary lighting was used, as would be the case
in a commercial nursery. Pests and diseases were
controlled using industry standard techniques
(integrated pest management).
Cyclamen. Photo taken just after
potting up on 1st
March
2.4 Monitoring
Growth measurements were taken at the start of the trial and every two weeks, as follows:
 Pines: Plant height and number of branches.
 Ferns: Number of fully extended fronds and length of longest frond
 Cyclamen: Number of leaves and flowers
Foliage quality was assessed every four weeks using a SPAD chlorophyll meter (for the ferns
and cyclamen) and visual assessment undertaken when differences were perceivable with
the naked eye.

Cyclamen and fern foliage visual assessment scoring system
0 Dead Dead or severely defoliated/deformed (>70%)
1 Poor growth Stunted with yellowed foliage >50%
2 Adequate growth Some yellowing, but generally acceptable
3 Good
Strong growth with leaves mostly mid green with very little or no
yellowing
4 Very good Fully green, strong growth
5 Excellent Deep green, lush, strong growth with large / long leaves
Pine foliage visual assessment scoring system
0 Dead All foliage orange in colour and / or with many (>50%) deformed needles
1 Very poor All foliage yellow, with many (>50%) deformed needles
2 Poor All foliage yellow, with some (<50%) deformed needles
3 Adequate
Foliage mostly mid green, but showing some yellowing (<50%), with some
(<50%) deformed needles
4 Good
Foliage mid green, with some yellowing (<10%), and with few (<10%)
deformed needles
5
Very
good
Foliage mid green, with no yellowing and no deformed needles
6 Excellent
Foliage deep green, with no yellowing and no deformed needles. Needles
uniformly long
2.5 Final harvest
At the end of the trial the growth measurements were repeated, and for the pines and ferns
an assessment of plant quality was carried out. The cyclamen and fern were harvested after
growing in the admixtures for 90 days (13 weeks), and the pine after 105 days (15 weeks).
Each plant was then carefully removed from the pot and the soil removed as much as
possible. For the cyclamen this was sufficient to obtain the corm and any remaining plant
material, and to record the fresh weight. For the fern and pine the roots were washed and
separated from the stem and leaves. The fresh weight of the roots and stems were recorded
separately. All plant material was dried in an oven for 48h at 60°C.
2.6 Statistical analysis
Analysis of variance statistical tests were used to examine whether there were any significant
differences between all of the parameters measured.

3.0 Admixture properties
The detailed chemical analysis results for the admixtures and the two controls are shown in
Appendix 2. The bulk densities of the admixtures with up to 500ml of digestate in 5 litres of
base mix (treatment 3) was the same as or lower than the peat-free control, with the
exception of FS3 (Figure 2).
The electrical conductivity of the admixtures increased as the quantity of digestate in the mix
was increased (Figure 3). As the food waste-derived digestates had higher electrical
conductivity than the maize and potato-derived digestates, due to their one order of
magnitude higher Na content (Table 3), higher conductivities for the admixtures would be
anticipated. Indeed, the majority of ECs were below or within the range of the two controls,
with the exception of FS5, FW4 and FW5 which had higher EC levels.
Figure 2 Bulk density of the two controls and the 20 admixtures. The two red lines indicate
the bulk density of the two controls
0
100
200
300
400
500
600
700
BC
PC
MS1
MS2
MS3
MS4
MS5
FS1
FS2
FS3
FS4
FS5
PW1
PW2
PW3
PW4
PW5
FW1
FW2
FW3
FW4
FW5
Densitymg/m3

Figure 3 Electrical conductivity of the two controls and the 20 admixtures. The two red lines
indicate the electrical conductivity of the two controls
Figure 4 Admixtures at the start of the trial
0
100
200
300
400
500
600
700
800
900
1000
BC
PC
MS1
MS2
MS3
MS4
MS5
FS1
FS2
FS3
FS4
FS5
PW1
PW2
PW3
PW4
PW5
FW1
FW2
FW3
FW4
FW5
ElectricalconductivityuS/cm

While some of the undiluted digestates had a pungent smell, when mixed with the other
ingredients, this odour quickly dissipated. This lack of odour in the final admixtures and
during the trial is extremely beneficial, as any odours would have otherwise restricted which
ornamentals the admixtures could be used for (e.g. indoor plants).
An excess of the admixtures was created at the start of the trial and placed in opaque plastic
bags in a shed at the Moulton College campus. At the end of the trial these were assessed
and were observed to have not changed in any way. There was no mould or fungus growing
on any of the admixtures and the volume had not noticeably reduced.
4.0 Trial results and discussion
This section presents the results for plant growth during the trial, followed by the destructive
harvest at the end of the trial. For the vast majority of variables measured on all species at
all times there were few significant differences between the digestate/bark admixture
treatments and both control treatments. This demonstrates that these admixtures show
potential for use on hardy nursery stock without significantly impeding growth or plant
quality.
4.1 Growth measurements during the trial
Figure 6 - Figure 13 illustrate the data on growth from the final measurement dates for
each of the three plant species, with the exception of cyclamen where the flowers and leaves
naturally senesced towards the end of the experiment.
4.1.1 Cyclamen growth measurements
Figure 5 Cyclamen on 27/3/2013
The cyclamen plants were extremely variable at the start of the trial, with the number of
leaves ranging from 1-11. Thus the plants were sorted and plants were selected with a range
of leaves for all of the treatments.
For cyclamen, the mean number of leaves shows significant variation, with FW1 showing a
significant reduction below the control values (Figure 6 A). For flower numbers, the data
shows great variability even within each treatment. This is due to the small number of
flowers per plant and some plants producing no flowers at all. In this experiment the flower
number shows too large a variation to allow interpretation.

Figure 6 Growth responses of wavy cyclamen (Cyclamen repandum) to differing growing
media. A) mean number of leaves, B) mean number of flowers. Error bars represent ±1
standard deviation. Data taken from the week with the most flowers in all treatments on
12th April 2013.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5 PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meannumberofleaves
Treatment
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meannumberofflowers
Treatment
B)
A)

Figure 7 A and B show that for most of the digestate admixtures there was no significant
effect on cyclamen foliage quality. The exception is FS3 which had both a lower chlorophyll
content and was judged to be of inferior quality. This was due to one FS3 plant having one
leaf at the start of the trial, which then died off, so skewing the results. However, the higher
digestate inclusion rates for the FS mixes produced plants with significantly greater
chlorophyll contents compared to the standard control media mixes.
Figure 7 Responses of wavy cyclamen (Cyclamen repandum) to differing growing media –
foliage quality. A) mean chlorophyll content and B) mean foliage quality score. Error bars
represent ±1 standard deviation. Data taken from the week with the most flowers in all
treatments = 12th
April 2013.
0
10
20
30
40
50
60
70
BC
PC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meanchlorophyllcontent/SPAD
Treatment
0
1
2
3
4
5
6
7
8
BC
PC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meanfoliagequalityscore
Treatment
B)
A)

4.1.2 Fern growth measurements
Figure 8 Fern on 27/3/2013
At the start of the trial the fern plants had 6-22 fronds, and as with the cyclamen, were
graded and a range of plants were allocated to each treatment. During the course of the trial
the ferns growing in all treatments produced a large number of fronds.
The number of fern fronds and frond length were not significantly affected by the media mix
used (Figure 9 A and B).

Figure 9 Growth responses of fern (Asplenium scolopendrium) to differing growing media.
A) mean number of fronds, B) mean frond length. Error bars represent ±1 standard
deviation. Data taken on 22nd May 2013 (day 90)
0
5
10
15
20
25
30
35
40
45
50
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meannumberoffronds
Treatment
0
20
40
60
80
100
120
140
160
180
200
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meanfrondlength/mm
Treatment
B)
A)

Figure 10 Responses of fern (Asplenium scolopendrium) to differing growing media –
foliage quality. A) mean chlorophyll content and B) mean foliage quality score. Error bars
represent ±1 standard deviation. Data taken on 22nd May 2013 (day 90)
The data for fern chlorophyll content and foliage quality shows that the highest dose rates of
the two food waste digestate admixtures (FS5 and FW5) had a large impact on foliage
quality (Figure 10 B) with a significantly reduced mean quality score given to those plants,
as compared to the two controls (BC and PC). Photos of these plants can be observed in the
appendix. The observed reduced mean quality score is likely to have an impact on the
saleability of the plants. This was not observed with the MS and PW digestates, and may be
related to the significantly higher sodium content of the FW and FS admixtures.
0
10
20
30
40
50
60
70
80
BC
PC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meanchlorophyllcontent/SPAD
Treatment
0
1
2
3
4
5
6
BC
PC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Treatment
A)
B)

4.1.3 Pine growth measurements
Figure 11: Pine on 27/3/2013
For the pines, there was no significant difference in any growth parameter measured in the
final week compared to the controls (Figure 12 and Figure 13). This backs up the
commonly held belief that black pines are very tolerant to changes/sub-optimal growing
media (Kew Gardens, 2013; USDA, 2013).
In addition to no significant differences between treatments, there were no obvious
digestate dose responses for any of the variables tested for the pine.

Figure 12 Growth responses of black pine (Pinus nigra) to differing growing media.
A) mean number of stems, B) mean plant height. Error bars represent ±1 standard
deviation. Data taken on 6th June 2013 (day 105)
0
5
10
15
20
25
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meannumberofstems
Treatment
0
100
200
300
400
500
600
700
800
900
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meanplantheight/mm
Treatment
A)
B)

Figure 13 Responses of black pine (Pinus nigra) to differing growing media.
A) mean increase in plant height over the duration of the experiment and B) mean foliage
quality score data taken on 6th
June 2013. Error bars represent ±1 standard deviation.
0
50
100
150
200
250
300
350
400
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
MeanIncreaseinheight/mm
Treatment
0
1
2
3
4
5
6
7
BC
PC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Treatment
A)
B)

4.2 Growth/time series analysis
The growth of the three trial species was assessed by plotting the main growth
measurements as a time series. Growth patterns were similar between dosage rates within
each treatment. Within each treatment, dose rate 4 gave the most consistent growth pattern
time series, and only this time series is shown here – plotted along with the two controls.
4.2.1 Cyclamen growth/time series analysis
For the cyclamen the leaf number remained quasi constant until senescing commenced in
early May (Figure 14 A). A peak in flowering was observed in mid-April (Figure 14 B).
This is as expected because the cyclamen is a herbaceous perennial and quickly produces
leaves and flowers in the spring, which then senesce as fruit are set.
All treatments showed the same pattern of growth over the time series, but with the
different treatments showing difference in the degree of change in the lines of best fit (not
shown). The apparent bell curve of flower production was most pronounced for the control
and MS4 treatments and shallowest in the FW4 and FS4 treatments.
Figure 14 Changes in growth variables of the wavy cyclamen (Cyclamen repandum) over
time in six differing growing media. A) mean number of leaves and B) mean number of
flowers.
0
0.5
1
1.5
2
2.5
3
3.5
4
15/02/2013 07/03/2013 27/03/2013 16/04/2013 06/05/2013 26/05/2013 15/06/2013
Meannumberofleaves
Date
BC
PC
FS4
FW4
MS4
PW4
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
15/02/2013 07/03/2013 27/03/2013 16/04/2013 06/05/2013 26/05/2013 15/06/2013
Meannumberofflowers
Date
BC
PC
FS4
FW4
MS4
PW4
B)
A)

4.2.2 Fern growth/time series analysis
Figure 15 shows a steady increase in growth over time for the ferns, which slowed down
towards the end of the trial. This is as expected for fern production.
Figure 15 Changes in growth variables of the fern Asplenium scolopendrium over time in six
differing growing media. A) mean number of fronds, B) mean length of the longest from per
plant. Error bars represent ±1 Standard error.
4.2.3 Pine growth/time series analysis
Figure 16 shows that the pines produced a typical growth curve during the experiment for
both stem elongation and stem production. These findings confirm that the plants were
actively growing at the same pace during the trial. While slight differences between the
treatments in plant height and branch production became accentuated as the experiment
continued, no statistically significant difference between treatments was observed. The
plateauing of the growth curve towards the end of the experiment also shows that no great
change would be expected for the rest of the growing season, as the flushes of growth
would have ceased for the year.
0
5
10
15
20
25
30
15/02/2013 07/03/2013 27/03/2013 16/04/2013 06/05/2013 26/05/2013 15/06/2013
Meannumberoffronds
Date
BC
PC
FS4
FW4
MS4
PW4
0
20
40
60
80
100
120
140
160
15/02/2013 07/03/2013 27/03/2013 16/04/2013 06/05/2013 26/05/2013 15/06/2013
Meanlengthoflongestfrond/
mm
Date
BC
PC
FS4
FW4
MS4
PW4
A)
B)

Figure 16 Changes in growth variables of black pine (Pinus nigra) over time in six differing
growing media. A) mean number of stems >5cm diameter, B) mean number of stems (total)
and C) mean plant height. Error bars represent ±1 standard deviation.
0
5
10
15
20
26/01/2013 15/02/2013 07/03/2013 27/03/2013 16/04/2013 06/05/2013 26/05/2013 15/06/2013
Meannumberofstems>5cm
Date
BC
PC
FS4
FW4
MS4
PW4
0
5
10
15
20
25
26/01/2013 15/02/2013 07/03/2013 27/03/2013 16/04/2013 06/05/2013 26/05/2013 15/06/2013
Meannumberofstems
BC
PC
FS4
FW4
MS4
PW4
0
100
200
300
400
500
600
700
26/01/2013 15/02/2013 07/03/2013 27/03/2013 16/04/2013 06/05/2013 26/05/2013 15/06/2013
Meanplantheight/mm
Date
BC
PC
FS4
FW4
MS4
PW4
A)
B)
C)

4.3 Occurrence of liverworts on fern growing media
During the course of the trial we became aware that there were large differences in the
incidence of liverwort on top of the growing media used for ferns. Liverworts are the chief
weed problem on hardy ornamental nurseries and considerable labour (weeding) and
herbicides are used to control them. At the end of the trial we scored each plant on the
extent of liverwort cover (0-4 with 0=no liverwort, 4= most of growing media surface
covered) and the results are illustrated in Figure 17. It is clear that all the digestate
treatments were superior to the peat-based media in having lower levels of liverworts on
their surface This was significant for some treatments (FS2 compared to both controls, and
FS2, FS3, FS5, MS1, MS2 and PW4 compared to the peat control). There was no apparent
dose response, which indicates that it was the lack of peat, rather than the presence of the
digestate that was causing this beneficial effect. This is further supported by the finding that
the bark control also had lower liverwort colonization.
Figure 17 Responses of the fern Asplenium scolopendrium to differing growing media -
Mean liverwort score rs represent ±1 standard deviation.
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meanliverwortscore
Treatment

4.4 Destructive analysis
Following on from the results of non-destructive monitoring, this section focuses on the
findings of final destructive measurements. Figure 18 - Figure 22 illustrate the data on
destructive analysis for the three species, including dry weights. As the fresh weight data
show the same pattern as the dry weight data, these graphs are not included in the main
text, but are presented in Appendix 6.
4.4.1 Destructive analysis - cyclamen
At the end of the trial the cyclamen had senesced and so it was only the corms that
remained for the destructive harvest. Figure 18 shows that there was no statistically
significant difference in the final measurements in the growth of the cyclamen corms in any
treatment during the experiment. There was also no dose response within each digestate
type.
Figure 18 Responses of wavy cyclamen (Cyclamen repandum) to differing growing media.
Final destructive measurements. A) Total fresh weight of corms, B) total dry weight of
corms, C) % dry matter. Error bars represent ±1 standard deviation.
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meandryweight/g
Growing media code
0
5
10
15
20
25
30
35
40
45
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
%drymatter
Growing media code
A)
B)

4.4.2 Destructive analysis - fern
Figure 19 A shows that the dry weight (biomass production) of the FS5 and FW5
treatments were significantly reduced compared with the two controls. This graph also
shows that ferns were also affected at the higher dosage rates of MS, with the MS4
treatment seemingly more affected than MS5. The dry weights of the fern plants in all other
treatments were not significantly different to the controls. The fresh weight results show the
same pattern with the FW5 admixture being over 40% lighter than the bark control. This
reduction in plant biomass can also be observed in the photographs in Appendix 3.
Figure 24 B and C illustrate that lower fresh weights of fern plants at the higher dose rates
of the FS and FW treatments (admixture rate 5) were found in both root and shoot growth,
but that the effect was greater for shoots (Figure 24 C) and statistically significant at
P=0.003.
Figure 20 A shows similar % dry matter levels for all treatments except for FS1. As this is
the lowest dose rate for the digestate it appears to be an anomaly, but is noted nonetheless.
Figure 20 B illustrates that there was no significant alteration in the root:shoot ratio in any
of the treatments. This is a parameter that can change according to the growing media
conditions. For example, plants growing in poor soils (eg. nutrient deficient, dry or polluted)
often have a higher root:shoot ratio as the plant puts more resources into securing nutrition
from the harsh conditions. Therefore, the finding that there was no change to this ratio in
any of the digestate treatment is further evidence that these media mixes show promise
commercially.

Figure 19 Responses of the fern Asplenium scolopendrium to differing growing media. Final
destructive measurements – dry weights. A) total dry weight B) dry weight of stems C) dry
weight of roots. Error bars represent ±1 standard deviation.
0
2
4
6
8
10
12
14 PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meandryweight/g
Growing media code
0
1
2
3
4
5
6
7
8
9
10
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meandryweightofstems/g
Growing media code
0
2
4
6
8
10
12
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meandryweightofroots/g
Growing media code
A)
C)
B)

Figure 20 Responses of the fern Asplenium scolopendrium to differing growing media. Final
destructive measurements. A) % dry matter B) root to shoot ratio. Error bars represent ±1
standard deviation.
4.4.3 Destructive analysis - pine
For pines the final fresh weight data (Figure 25) shows differences, but as with the
cyclamen results, few are significantly different from the control plants for all variables. No
digestate dose response trends are observed in the fresh weight data. While the biomass dry
weight data show some slight reductions for PW1 compared to the controls (Figure 21 A
and Figure 22 A), the differences are not significant and are not repeated at the higher
dose rates, and appears to be due to a reduction in stem mass. As was the case for the
ferns, the pine root:shoot ratio was unaltered in any of the treatments (Figure 22 B).
0
5
10
15
20
25
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
%drymatter
Growing media code
0
0.2
0.4
0.6
0.8
1
1.2
1.4
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meanroot:shootratio
Treatment
A)
B)

Figure 21 Responses of black pine (Pinus nigra) to differing growing media. Final
destructive measurements. A) total dry weight B) dry weight of stems C) dry weight of roots.
Error bars represent ±1 standard deviation.
0
20
40
60
80
100
120
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meandryweightofstems/g
Growing media code
0
10
20
30
40
50
60
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meandryweightofroots/g
Growing media code
0
20
40
60
80
100
120
140
160
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meandryweight/g
Growing media code
B)
C)
A)

Figure 22 Responses of black pine (Pinus nigra) to differing growing media. Final
destructive measurements - % dry matter and root:shoot ratio. A) % dry weight and B) root
to shoot ratio Error bars represent ±1 standard deviation.
Overall the results in Figure 18 - Figure 22 show that the pines and ferns did not change
the way they allocated resources, with the root to shoot ratio remaining very stable between
treatments. The % dry weight data also shows that plants did not change their water
content or water storage differently in the different treatments with only one treatment
showing a notable difference, with PW1 showed lower % dry matter than the controls. As
this treatment was the lowest level of digestate, it is unlikely to be due to the presence of
digestate and could represent an issue with one plant in the treatment being particularly
succulent
0
10
20
30
40
50
60
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
%drymatter
Growing media code
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
PC
BC
FS1
FS2
FS3
FS4
FS5
FW1
FW2
FW3
FW4
FW5
MS1
MS2
MS3
MS4
MS5
PW1
PW2
PW3
PW4
PW5
Meanroot:shootratio
Treatment
A)
B)

4.5 Fern transpiration rates
A student project was undertaken during the trial studying water use in the ferns in the
different whole food waste digestate admixtures and the peat free control. Using a
porometer, the transpiration rates in the ferns were measured four times during the trial.
The results in Figure 23show that there were no significant differences in the transpiration
rates between the plants growing in the different growing media at any of the sampling
points.
This is an important finding as it indicates that the digestate admixtures did not have inferior
hydraulic performance. One of the potential drawbacks of moving away from peat-based
growing media is the lack of water-holding capacity. Traditionally this has meant that non-
peat media need to be irrigated more frequently. If not, the plants suffer periodic water
deficits and the health problems that result from this; for example, retarded growth, poor
flowering, fruiting and blossom end rot. The findings suggest there is evidence that water
use is not affected by changing from the standard controls to the admixtures.
Figure 23 Mean stomatal conductance of the fern Asplenium scolopendrium over time in six
differing growing media. Error bars represent ±1 Standard error
70
90
110
130
150
170
190
Control 100 250 500 750 1000
StomatalConductance(gs)(mmolm2s-1)
Anaerobic digestate concentration whole food (ml/5l)
01/03/2013
15/03/2013
04/04/2013
26/04/2013

5.0 Cost benefit analysis
It has been shown in this feasibility study that bark/digestate admixtures have the potential
to be used as replacement for peat-based growing media. This section looks in more detail
at the costs required to manufacture digestate/bark admixtures compared to peat based
growing media. This will include the cost of source materials, storage costs, costs associated
with possible adaptions to blending processes, and transport costs.
5.1 Cost of source materials
The cost of source materials is often a deciding factor in deliberations on whether there is a
business case for introducing novel growing media. Growing media manufacturers
unanimously comment that the production costs of a novel growing medium must be such
that it is competitive in the market place.
In the growing media sector there are a variety of business models which have immediate
effect on the costing of source materials. One example is the cost of peat in 2013. Due to
unfavourable weather conditions the peat harvest was exceptionally poor in the UK in 2012.
Some growing media manufacturers were directly affected by this, being forced to import
peat from overseas, which in turn resulted in significantly increased transport cost and
higher overall material cost.
On the other hand, some growing media manufacturers with their own UK peat bogs had
sufficient amounts of peat stored from the previous year, and even the unfavourable
weather conditions did not significantly affect their peat availability, keeping material costs
low.
An attempt has been made to compare material costs for peat-based growing media and
bark/digestate admixtures. As mentioned above, material costs vary significantly between
manufacturers, and so it is suggested that growing media manufacturers might prefer to
insert their own costings into the model given here.
Material costings listed here were obtained through price enquiries in high volume, i.e. in
costs per lorry load, which is usually at volumes of around 70m3
-80m3
or more. Costs include
overland transport over medium distances, apart from overseas peat which includes only the
transport cost for shipping to Liverpool Harbour in the UK.
Costs of digestate transport were not included in Table 7, and the large variability of this
cost is discussed in Table 11

Table 7 Cost of materials ex VAT in lorry load quantities (typical values –actual costs can
vary substantially)
Growing
medium
Material
Material cost
per m3
for
lorry load
(quantities
>80m3
)
Volume
constituent
in 1m3
growing
medium
Cost as
part of the
1m3
mix
Peat based,
imported
Peat imported
(overseas)
£25 77% £19
Wood fibre £25 15% £4
Bark fines £25 8% £2
Fertiliser £5
Total cost (ex
VAT)
£30
UK peat based
UK Peat (from
own peat bog)
*cost is author's
estimate
£15 77% £12
Bark fines £25 8% £2
Fertiliser £5
Total cost (ex
VAT)
£22
Bark/
digestate
admixtures
Bark £25 60% £15
Sterilised top
soil
£50 10% £5
Total cost (ex
VAT)
£28
5.2 Cost of digestate storage
The cost of storage is looked at in more detail here, as storing digestate with less than 8%
dry matter will require additional liquid storage capacities which are not part of the current
equipment inventory of growing media manufacturers. Maintenance costs are not included in
this estimate.
In order to gauge the potential storage requirements for typical manufacturing sites, it was
assumed that 10% of all growing media produced will incorporate digestate. For a medium

sized UK growing media producer (Table 8) producing 100,000m3
per annum, 10,000m3
are
suggested to incorporate digestate. The storage requirement in this case would be between
200m3
and 2000m3
. The latter volume is that of a medium sized anaerobic digestate store
which is large enough to achieve a favourable cost per m3
(Table 9).
Smaller scale storage units (72m3
) are least cost effective, while single 1m3
storage
containers, caged, on timber pallets are the lowest cost solution for small digestate volumes.
As can be seen in Table 7 storage of digestate has a small influence of the cost of the
bark/digestates admixtures (between £0.25 and £1.80 per m3
admixture).
Table 8 Typical volumes produced on growing media manufacturing sites; digestate
volumes required assuming that 10% of all growing media incorporate digestate
Growing medium
manufacturing
scale
Volume /m3
of
growing
medium
produced per
year
Total digestate volume required in m3
,
assuming 10% of all growing media produced
would incorporate digestate
min (100ml
digestate /5l
growing medium)
max (1l digestate /5l
growing medium)
Large 250,000 500 5000
Medium 100,000 200 2000
Small 50,000 100 1000
Total digestate volume required in m3
Experimental small
scale trials
100 2 20
Table 9 Digestate storage: Volume vs. typical cost (ex VAT) per m3
over a period of 10
years
Volume Type Cost /m3
digestate /year
over 10 years
1 m3
IBC (Intermediate bulk container)
on timber pallet for effluent/waste
storage
£10
10 m3
Above ground water tank from UV
stabilised medium density moulded
polyethylene (MDPE)
£12
19 m3
single skin oil tank £13
36 m3
Elliptical concrete tank £15
72 m3
Small AD storage unit £24
1500 m3
Steel / concrete above ground £6
4500 m3
Steel / concrete above ground £3.50
4500 m3
Earth bank lagoon £2

5.3 Cost of adapting machinery to handle digestate
A common system for producing growing media mixes effectively in large quantities is to
drop the ingredients onto a conveyor belt. The hoppers that are used to hold and deposit the
dry growing media constituents such as peat and wood fibre can, with high probability, also
be used for the dry components of the bark/digestate admixtures.
Liquid growing media constituents are usually clear liquids, such as dissolved wetting agents
and nutrients. These liquids are sprayed or dripped onto the conveyor belt.
Digestates are generally significantly more viscous than traditional liquids used in the
growing media manufacturing process. The viscosity of the digestate depends significantly
on the original AD feedstock mix and the anaerobic digestion method. Hence it is important
to define the range of acceptable digestate physical properties and ensure digestate supplied
has a stable set of nutritional as well as physical properties.
While some of the existing systems may not need any adaption at all in order to dose
digestates, it is highly recommended to carry out initial trials to test whether existing
commercial equipment is suitable for digestates.
5.4 Cost of transport
As can be seen in Figure 2, the density of peat based growing media is roughly the same as
that of digestate/bark admixtures with 250ml digestate added to 5l of growing medium (e.g.
FS2). Addition of less digestate produces growing media that are even lighter than the peat
based control. Adding 500ml digestate to 5l growing medium produced admixtures that were
roughly 10% more dense than the peat based control, or the same density as the bark
control.
Addition of 750ml or even 1l of digestate produced admixtures that were between 20% and
45% more dense compared to the peat based control. Addition at these levels is likely to
increase transportation costs. However, addition of less digestate than that appears to be
more beneficial to plant quality. Moreover, should the admixtures be stored uncovered then
drying out could occur naturally, which would slightly reduce the density. Hence it is
assumed that at appropriate digestate/bark admixture ratios, transport costs remain the
same compared to peat based growing media.
Furthermore, transport cost is strongly influenced by factors such as distance from the
digestate supplier, typical delivery volumes and on-site digestate storage volume. Three
typical costs have been listed in Table 9. The table highlights that a suitable storage volume
is required to optimise costs.

Table 10 Density of digestate admixtures as compared to the peat based control growing
medium
Material Density / (g/l)
Density
relative to PC
Extra weight
compared to
PC
PC 420 100% 0%
BC 468 111% 11%
MS1 405 96% -4%
MS2 406 97% -3%
MS3 462 110% 10%
MS4 551 131% 31%
MS5 575 137% 37%
FS1 366 87% -13%
FS2 414 99% -1%
FS3 505 120% 20%
FS4 545 130% 30%
FS5 607 145% 45%
PW1 419 100% 0%
PW2 427 102% 2%
PW3 465 111% 11%
PW4 599 143% 43%
PW5 571 136% 36%
FW1 344 82% -18%
FW2 411 98% -2%
FW3 461 110% 10%
FW4 507 121% 21%
FW5 591 141% 41%
Table 11 Variability of transport cost of whole or liquid digestate with less than 8% dry
matter
Transport type
Cost /m3
digestate
Cost /m3
bark
admixture
Cost /m3
bark
admixture
min (100ml
digestate/5l bark
admixture)
max (1l
digestate/5l
bark admixture)
Using existing transport
infrastructure of digestate
supplier
£4 £0.08 £0.80
Subcontractor delivering 4
lorry loads of 26m3
digestate
per day
£6 £0.12 £1.20
Subcontractor delivering 1
lorry load of 26m3
digestate
per day
£23 £0.46 £4.60

5.5 Potential quantity of admixtures that could be used for ornamentals in the UK
This section considers the potential volumes of digestate admixtures that could be used in
the UK horticultural sector. Initially the UK growing medium requirements for cyclamen,
ferns and pines is estimated and put into the context of potential digestate volumes
required. This is followed by a more general look at the potential maximum volumes of liquid
digestates that could be used in UK growing media.
The latest national statistics for crops grown in glasshouses show that 6.9 million pots of
cyclamen were produced in 2007, compared to 3.5 million pots of chrysanthemums and 1.9
million poinsettias for indoor use (Defra and National Statistics 2008). This equates to the
market share for cyclamen to be 16.8% of potted plants produced for indoor use. Of the 3.7
million pots of foliage plants produced the same year, 0.2 million ferns were produced.
These Defra figures do not specify whether all of the plants produced will, once sold, require
protection (indoor end use) or are suitable for outdoors (HONS), and are generally
considered by the industry to provide a sufficient estimate of plant production for both
sectors. No figures are available for Pinus nigra production, although grower estimates are
that no more than 20 thousand pine plants of a range of species are grown and sold each
year. Table 12 provides an estimate of the total volume of growing media used per plant
and in total for each species trialled.
Table 12 Estimated number of plants and growing media volume used for cyclamen fern
and pines produced in the UK each year
Plant type
Estimated
number of
plants
(million)
Estimated
growing
media volume
/ plant (litres)
Estimated
total growing
media volume
(million litres)
Cyclamen 6.9* 0.4 2.76
Ferns 0.2* 1 0.2
Pine 0.02 10 0.2
*Figures taken from Defra and National Statistics 2008. Other figures are estimates from growers
The total volume of growing media used for cyclamen, fern and pine production in the UK is
potentially over 3 million litres (3000m3
) per year. If a third of this volume was an admixture
with a digestate content of 500ml in every 5 litres, this would equate to a digestate usage of
200,000 litres, or 200m3
. For comparison, in 2012, the average UK AD plant produced a
volume of approximately 1,650m3
of digestate per year, with 87 AD sites producing 1.44
million tonnes of digestate a year (WRAP, 2013).
For growing media (not including soil improvers), the largest market was the amateur
gardening sector with nearly 3 million m3
used in 2009. The second largest sector was
professional growers using 1.2 million m3
in the same year. Landscaping and local authority
followed on with relatively small use of growing media of about 0.059 million m3
and 0.008
million m3
, respectively (Defra 2010).
Assuming 500ml digestate in every 5 litres of growing media, hypothetically, the total volume
of digestate used to amend the complete UK growing medium volume of about 4 million m3
would be 400,000m3
of digestate. This is the equivalent to the yearly digestate production of
64 average UK AD plants.
Realistically, only a small percentage of growing media might be amended in the near future.
Optimistically, if 10% of all UK growing media were amended with digestate, this would
require the yearly digestate output of 6 average anaerobic digestion plants, or about 6% of

the UK digestate production in 2013. Moreover, for some AD sites where digestate use for
agriculture is less feasible, digestate for growing media could provide a suitable alternative
end use.
As this feasibility study has demonstrated, admixtures could be used on a variety of plant
types. Hence there is scope for much wider usage for admixtures to replace peat based
growing media in the UK.
6.0 Considerations for future work
This feasibility study has demonstrated that there is clearly potential for digestate/bark
admixtures to be used in ornamental protected horticulture. In order to further the
knowledge in this area a number of recommendations follow.
6.1.1 Further work using the admixtures
The results from this feasibility study demonstrate that over the 90 day period for the
cyclamen and fern, and 105 days for the pine, no additional fertiliser was necessary to
ensure adequate nutrient supply.
For woody perennials, such as pine, a trial duration of at least two years is recommended to
identify treatment effects.
For the cyclamen growth cycle, the trial ran for a sufficient length of time to complete one
growing season only. However, a trial running for two consecutive growing seasons would
highlight any treatment effects on the cyclamen corms and the resultant plant quality in the
second year.
Moreover, were the ferns and pines to be grown for a much longer period prior to retail,
liquid fertilisers would normally be applied in a standard nursery setting. In this instance it
would be interesting to study whether digestates could be used as a replacement for
inorganic fertilisers, with some work already undertaken in this area (WRAP 2014a and
WRAP 2014d).
The plants chosen for the trial represent a range of species. However it would be necessary
to trial the admixtures on a range of other plant species to test this application more widely
in the industry.
6.1.2 Refining the admixtures
There is scope to refine the admixtures in a range of ways as listed below:
 Try different bark types and sizes;
 Try chipped compost oversize ;
 Consider using smaller bark sizes, which could be necessary if the media is to be used in
the commercial potting machines currently in use by major nurseries; and
 Replace the soil component with alternative sustainable growing media ingredients.
The particle size, air filled porosity and drainage properties of growing media are particularly
important for crops grown outdoors where the grower cannot control the level of irrigation
received by the plants. Therefore the growing media must be relatively coarse in
consistency. Where crops are grown indoors or under cover, there is more control over
irrigation and therefore the growing medium can be a finer grade. Trialling a range of bark
sizes within the admixtures may broaden the range of plant species suitable for
digestate/admixtures growing media.

6.1.3 Can the admixtures be created using commercial mixing equipment?
A mixing trial is recommended in collaboration with a commercial growing media
manufacturer to ascertain whether standard mixing equipment can be used to create the
admixtures.
6.1.4 Can the moisture content of the admixtures be reduced?
Adding digestate to the base mix when adding the larger volumes of digestate (>500ml in 5
litres base mix), did create a denser growing medium than the standard controls. It would be
interesting to ascertain whether the excess heat produced during the AD process (the CHP
engine) could be used to dry out the admixtures to a desired extent to create a lighter
material which would be cheaper to transport, but still retains the required moisture content,
which would be comparable to the standard controls.
6.1.5 Can the admixtures be used in a commercial nursery setting using standard potting
methods?
A trial is recommended at a number of commercial nurseries with a range of equipment to
ascertain whether standard potting equipment can be used with the admixtures. This may
result in some changes in the admixture recipe for some sites. For example, some equipment
is not suitable for growing media containing coir whereas others are suitable. It is possible
that there may be similar considerations for the admixtures due to the bark size. In some
cases the media needs to be finer than for hand potting in order for the machine to fill the
pots to a consistent level.
6.1.6 Do the admixtures compare to standard growing media for plant shelf life?
It is recommended to investigate how well plants survive in the admixtures after the nursery
production phase is complete. A simple method would be to trial a situation where the plants
are not watered and note how long it takes for their quality to be compromised. This could
be compared to watering less or watering as normal. If a longer plant shelf life was
observed, this could add value to the admixtures.
6.1.7 Digestate as a liquid fertiliser on nurseries
In addition to using digestate at the growing media production site, there could also be
opportunities to incorporate whole and liquid digestate during the routine fertilisation of
nursery stock plants growing outdoors or under polytunnels. This could make use of a much
larger volume of digestate, but is untested in the UK. The literature search undertaken at the
start of this project did find some evidence for this application in other countries, with
dilution of the digestate to the required nutrient values being an important aspect. There are
some recent WRAP projects on the use of digestates as liquid fertilisers for edible crops both
in hydroponic and grow-bag scenarios (WRAP 2014 b and WRAP 2014 d), but not on
commercial nursery stock.
In addition to protected horticulture, using digestates for fertilising field-grown trees could
also be explored. Many nurseries grow trees and shrubs in fields and then sell them as root-
balled stock to landscapers and garden centres.

7.0 Conclusion
The project focussed on four main research questions, which are addressed below.
7.1 Can digestate be used as a growing media ingredient in protected horticulture?
The outcome of this feasibility study showed that an admixture of digestate with bark, wood
fibre and topsoil was generally a promising growing medium for wavy cyclamen (Cyclamen
repandum), fern (Asplenium scolopendrium) and black pine (Pinus nigra). There was no
immediate indication that digestate could not be used more widely in protected horticulture.
Two of the digestates investigated were derived from household food wastes, whilst the
other two were derived from potato waste and maize respectively. All admixtures provided
an appropriate level of nutrients and suitable pH levels for use in ornamental horticulture.
Odours quickly dissipated when digestates were mixed with the bark and wood fibre. Water
holding capacity of the digestate/bark admixtures was not significantly different to peat
based growing media.
Liverwort growth was suppressed when using the admixtures (compared with the peat-
based control), which is likely to positively impact on overall plant quality in a commercial
setting. There were also no signs of shore flies or sciarid flies in any of the treatments.
A suitable range for digestate admixture was found to be between 0.1l and 0.5l digestate per
5l bark/wood fibre. Densities of these growing media were the same as or below the density
of the control peat free growing medium. Within this range there was generally no significant
effect on plant quality.
7.2 Are there any constraints, and can these be overcome?
Specific constraints derived from the results of the feasibility study were observed with high
doses of food waste derived digestate. The fern particularly showed stress response in the
form of reduced growth and reduced foliage quality in digestate admixtures with EC levels of
>570 µS/cm, which is deemed high by growers. This response is attributed to the elevated
sodium content within food waste derived digestates. This constraint can be addressed by
monitoring digestate EC levels and especially sodium levels as a routine part of the growing
media production process, and taking remedial action (such as reducing the volume of
digestate used) to ensure relevant levels are not exceeded in the final growing medium.
More generally, the dominant use of bark and wood fibre adds constraints due to specific
properties of digestates bark/wood fibre admixtures. The time dependent interplay of pH-
stabilising digestate and any acidifying effect of decomposing bark was not investigated in
this feasibility study. Future work could include assessing the changes in pH and EC of the
admixtures over time with different irrigation regimes to assess whether any acidifying
effects due to do bark decomposition occur over time, or whether the admixture ingredients
provide a buffer to potential acidification. While the findings of this study were promising, it
is suggested that longer term trials are carried out with a wider range of plants species.
This feasibility study was specifically aimed at using bark and wood fibre as the main
growing media ingredients. A more diverse choice of sustainably sourced ingredients in
admixtures with digestate could enable the production of growing media that are more
tailored to the widely varying requirements of different ornamental plant species.
From a legislative perspective, the constraints imposed by the ADQP mean that digestates
cannot be used in growing media (except as a permitted waste management activity). Based
on the evidence gathered in this study, the ADQP constraints on use of liquid digestates in
growing media could be reconsidered.

7.3 Are there business benefits?
The cost benefit analysis showed there is potential for digestate/bark admixtures to be
competitive – particularly with growing media that include peat imported from overseas.
Whether or not digestate/bark admixtures can be cost competitive depends on a number of
factors:
 Costs of peat – particularly imported peat (domestic peat is likely to remain competitive
with the alternatives trialled in this project);
 Optimisation of digestate transport and storage;
 Future availability and hence cost of bark and wood fibre (since demand for these
materials may increase with more widespread biomass power generation);
 The capability of growing media mixing systems to allow dosing with liquid digestate
(which could require adaptions to be made).
7.4 Should the ADQP be changed to include using digestates in growing media as a
permitted use?
This feasibility study and other WRAP trials and research (WRAP, 2014 a-d) have
demonstrated that the use of food waste, maize waste and potato waste-derived digestates
in growing media can have beneficial effects on plant nutrition and within reasonable
boundaries did not generally show significant effects on plant health. Results from these
experiments suggest that digestate may feasibly be used in ornamental horticulture as an
admixture ingredient.
Further work is recommended to produce guidelines on the recommended quantities of
digestates to be combined with other ingredients. This could include maximum
recommended EC and ammonium levels for different plant species, to address potential
differences in the available range of quality PAS110 certified digestates.

8.0 References
AfOR, 2010, 'Survey of the UK organics recycling industry 2008/09', Association for Organics
Recycling
Anonymous. 2010. ‘Wood fibre availability and demand in Britain 2007 to 2025’. Edinburgh:
Confor, UKFPA and WPIF.
Chong, C., Purvisa, P. Lumisa, G., Holbeinb, B.E., Voroneyc R.P., Zhoud H., Liub H.-W.,
Alama M.Z., 2008, 'Using mushroom farm and anaerobic digestion wastewaters as
supplemental fertilizer sources for growing container nursery stock in a closed system',
Bioresource Technology, 89, 6, 2050-2060
Crippa, L., Zaccheo, P., Orfeo, D., 2011, 'Utilization of the solid fraction of digestate from
anaerobic digestion as container media substrate', ISHS International Symposium on
Growing Media, Composting and Substrate Analysis, Book of Abstracts, ed. Martínez Farré,
F.X., 142-143
DECC and Defra, 2011, 'Anaerobic Digestion Strategy and Action Plan', DECC and Defra,
56pp
Defra, 2011, 'Natural Environment White Paper ', Defra
Defra, 2013, 'Government Response to the Sustainable Growing Media Task Force', Defra,
21pp
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Biodiversity Action Plan target (SP08020)', Defra, 21pp
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'The Effect of Fertilisation with Fermented Pig Slurry on the Quantitative and
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9.0 Appendices
9.1 Appendix 1. Characteristics of eight UK digestates
Table 13 Characterisation of eight UK digestates . These digestates were analysed as part
of this study in late 2012
Food
waste
Food
waste
Food
waste
Food
waste
&
slurry
Potato
waste Slurry
Maize,
slurry &
milk
waste Maize
Separated Whole Whole Whole Whole Separated Separated Separated
N (mg/kg) 3700 4900 6000 5600 2400 3900 4200 4100
Mineral N (mg/kg) 2990 3784 5260 5590 2039 2945 2044 2175
(% NH4-N) 2990 3784 5260 5590 2039 2945 2044 2175
(% NO3-N) >0.1 >0.1 >0.1 >0.1 >0.1 >0.1 >0.1 >0.1
P (mg/kg) 202 315 456 257 128 351 514 246
K (mg/kg) 1330 1869 1109 2804 4752 3507 4661 3382
Ca (mg/kg) 797 2000 1974 942 126 1961 1862 889
Mg (mg/kg) 92.9 93.3 63 86.8 46 302 436 188
S (mg/kg) 134 236 342 188 78 242 303 171
Fe (mg/kg) 75 231 555 118 57 119 197 54
Mn (mg/kg) 3.4 8.4 5.0 8.3 1.3 23.0 15.9 6.4
Na (mg/kg) 1021 1146 2225 1501 46.4 531 439 121
Total solids (%) 2.9 3.7 4.5 3.8 2.2 3.8 7.1 5.1
C:N 4.0 3.5 3.3 3.3 3.3 5.6 7.3 6.1
pH 8.5 8.4 8.4 8.8 8.2 8.4 8.2 8.2
EC (1:6)
(dS m-1
)
4.4 5.4 7.0 7.3 4.2 4.8 4.5 3.8

9.2 Appendix 2. Admixture analysis results
Table 14 Admixture and controls total nutrients analysis results 1. All results are on a dry
weight basis
Total
Nitrogen
Dumas
Total
Sulphur
Total
Potassium
Total
Phosphorus
Total
Magnesium
Total
Copper
Admixture % w/w mg/kg mg/kg mg/kg mg/kg mg/kg
BC 0.72 2181 3850 1330 3306 31.6
PC 0.91 1806 2427 949 3145 18.3
MS1 0.31 407 1695 531 1410 14.5
MS2 0.36 351 1859 508 1262 13.2
MS3 0.43 332 2780 537 1140 11.4
MS4 0.51 542 3044 600 1207 12.6
MS5 0.6 498 3910 648 1168 12
FS1 0.39 391 1624 489 1297 13
FS2 0.38 332 1669 609 1391 14.3
FS3 0.45 368 1989 684 1589 42.3
FS4 0.47 411 2065 688 1476 15.3
FS5 0.63 506 2473 767 1440 14.5
PW1 0.36 407 1874 552 1574 16.5
PW2 0.4 410 2375 539 1608 16.1
PW3 0.43 421 3262 581 1423 14.7
PW4 0.44 383 4303 596 1305 13
PW5 0.47 381 4622 601 1255 13.5
FW1 0.42 363 1644 487 1261 11.3
FW2 0.41 366 1879 661 1528 16.1
FW3 0.52 407 2302 722 1411 15.9
FW4 0.61 475 2763 826 1413 15.7
FW5 0.69 610 2681 796 1296 14.4

Table 15 Admixture and controls total nutrients analysis results 2. All results are on a dry
weight basis
Total
Zinc
Total
Iron
Total
Calcium
Total
Boron
Total
Manganese
Total
Sodium
Admixture mg/kg mg/kg mg/kg mg/kg mg/kg mg/kg
BC 82.8 13328 11187 11.9 512 304
PC 22.1 6100 6948 5.8 221 272
MS1 50.8 15089 3441 3.1 331 106
MS2 44.9 12688 3397 2.4 345 116
MS3 40.8 11006 5141 2.3 235 151
MS4 44.1 12622 3430 0.9 258 150
MS5 41.8 12291 4171 1.5 272 183
FS1 46.2 11954 3637 0.5 295 205
FS2 56 17166 3692 0.7 387 322
FS3 55.6 17009 3999 0.2 381 520
FS4 50.8 16110 3669 <0.1 304 670
FS5 79.9 16836 4283 <0.1 415 1001
PW1 56.2 16662 3702 <0.1 363 105
PW2 51.8 15064 3494 <0.1 294 93.3
PW3 49.9 15109 3888 <0.1 324 95.6
PW4 45.8 13286 3598 <0.1 287 98.2
PW5 45.6 13024 3348 <0.1 277 99
FW1 43.4 11884 4005 <0.1 259 257
FW2 55.1 17014 4290 <0.1 388 407
FW3 54.5 14416 4248 <0.1 409 725
FW4 55.1 14852 4771 <0.1 359 1040
FW5 50.4 13549 4335 <0.1 296 1114

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