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

WRAP’s vision is a world without waste, where resources are used sustainably. Our mission is to accelerate the move to a sustainable resource-efficient economy through re-inventing how we design, produce and sell products; re-thinking how we use and consume products; and re-defining what is possible through re-use and recycling. Find out more at www.wrap.org.uk 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

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Figure 4 Admixtures at the start of the trial

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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.

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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.

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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)

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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.

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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)

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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).

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tio

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

PW

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PW

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PW

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ry w

eig

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of

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/ g

Growing media code

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60

PC

BC

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FS2

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FS5

FW1

FW2

FW3

FW4

FW5

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MS2

MS3

MS4

MS5

PW

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PW

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PW

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PW

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PW

5

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eig

ht

of

roo

ts /

g

Growing media code

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120

140

160

PC

BC

FS1

FS2

FS3

FS4

FS5

FW1

FW2

FW3

FW4

FW5

MS1

MS2

MS3

MS4

MS5

PW

1

PW

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PW

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PW

5

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an d

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/ 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

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60P

C

BC

FS1

FS2

FS3

FS4

FS5

FW1

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FW3

FW4

FW5

MS1

MS2

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MS5

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ry m

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r

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BC

FS1

FS2

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FS4

FS5

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FW2

FW3

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FW5

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MS2

MS3

MS4

MS5

PW

1

PW

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PW

3

PW

4

PW

5

Me

an r

oo

t:sh

oo

t ra

tio

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

Sto

mat

al C

on

du

ctan

ce (

g s)

(mm

ol m

2 s

-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

Defra, 2010, 'Monitoring the horticultural use of peat and progress towards the UK Biodiversity Action Plan target (SP08020)', Defra, 21pp

Defra. 2012. ‘Wood waste: A short review of recent research’. London: Defra. 29 p.

Waller P, Denny D. 2013. ‘Annual report. Tracking peat usage in growing media production’. AHDB. 28 p.

Defra and National Statistics , 2008, 'Glasshouse Survey 2007, England'

Do, T.C.V., Scherer, H.W., 2012, 'Compost and biogas residues as basic materials for potting substrates', Plant Soil Environ., 58, 10, 459-464

Kouřimská, L., Babička, L., Václavíková, K., Miholová D., Pacáková Z., Koudela M., 1999, 'The Effect of Fertilisation with Fermented Pig Slurry on the Quantitative and Qualitative Parameters of Tomatoes (Solanum lycopersicum)', Soil & Water Res., 4, 3, 116-121

Lenka Kouřimská, L., Babička, L., Václavíková, K., Miholová, D., Pacáková, Z., Koudela, M., 2009, 'The effect of fertilisation with fermented pig slurry on the quantitative and qualitative parameters of tomatoes (solanum lycopersicum)', Soil & Water Res., 4, 3, 116-121

Lošák, T., Zatloukalová, A., Szostková, M., Hlušek, J., Fryč, J., Vítěz, T., 2011, 'Comparison of the effectiveness of digestate and mineral fertilisers on yields and quality of kohlrabi (brassica oleracea, L.)', Acta universitatis agriculturae et silviculturae mendelianae brunensis, LIX, 3, 117-121

Poustková, I., KourImská, L., Václavíková, K., Miholová, D., BabIcka, L, 2009, 'The Effect of Fertilization Method on Selected Elements Content in Tomatoes (Lycopersicon lycopersicum)', Special Issue Czech J. Food Sci., 27, S394-S396

Rakers L., Schlüter E., Dieckmann S., Dinklage S., Daum, D., 2010, 'Eignung von getrockneten pflanzlichen Gärresten als Zuschlagstoff in gärtnerischen Kultursubstraten', XXXIX. Osnabrücker Kontaktstudientage, 32

Sustainable Growing Media Task Force, 2012, 'Towards Sustainable Growing Media. Chairman’s Report and Roadmap', 29pp



WRAP, 2013, ‘A survey of the UK organics recycling industry in 2012’. 126pp. WRAP project RAK005-002.

WRAP. 2014a. ‘Literature review: Digestate use in protected horticulture’. Banbury: Written by: Dimambro, M., Steiner, J., Rayns, F. 57 p.

WRAP. 2014b. ‘Options for the use of quality digestate in horticulture and other new markets’. Banbury: Written by: West, H. M., Ramsden, S. J., Othman, M. 57 p.

WRAP. 2014c. ‘The potential of anaerobic digestate fibre for horticulture’. Banbury: Written by: Stainton, D., Cheffins, N. 44 p.

WRAP. 2014d. ‘Use of quality digestates as a liquid fertiliser in the commercial production of strawberries’. Banbury: Written by: Dimambro, M. E., Steiner, J., Lillywhite, R., Keeling, C. 40 p.

Wrede, A., 2012, 'Gärrest als Substratzuschlagstoff - bei Rosen kein Problem', Deutsche Baumschule , private communication, Dr. Andreas Wrede, Landwirtschaftskammer Schleswig-Holstein, Gartenbau, Thiensen 16

USDA, 1971, ‘Bark and its possible uses’, US Department of Agriculture, Madison. 56pp.

Zhang, Y.-f., Zhu, Y.-l.,Na, W., Liu, W. , 2010, 'The effect of digestate as organic fertilizer for green pepper seeding bed', China Biogas



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



Table 16 Admixture and controls analysis results. Results are on sample fresh weights pH Cond.

at 20

◦C

Density Ammonia-N

Nitrate-N

Dry Matter

Dry Density

Admixture uS/cm kg/m3 mg/l mg/l % kg/m3

BC 6.4 435 468 48.1 6.9 52.9 247.6

PC 5.39 311 420 30.3 131 39.1 164.2

MS1 6 96 405 38.3 18.8 62 251.1

MS2 6.3 150 406 63.2 21.9 62.9 255.4

MS3 7 213 462 97 17.4 53.3 246.2

MS4 7.41 317 551 146 19.1 50.5 278.3

MS5 7.63 431 575 225.8 6.1 44.2 254.1

FS1 5.97 102 366 40.1 17.6 62 226.9

FS2 6.59 161 414 79.9 20 61.3 253.8

FS3 7.3 238 505 128.3 22.3 53.8 271.7

FS4 7.72 411 545 246 2.3 49 267

FS5 7.67 536 607 299.5 8.4 43.2 262.2

PW1 5.92 106 419 46.7 19.9 62 259.8

PW2 6.3 122 427 51.6 18.2 59 251.9

PW3 7.22 155 465 75.1 15.3 54.9 255.3

PW4 7.63 315 599 172.1 10.7 46.5 278.5

PW5 7.7 397 571 200.9 42.2 50.3 287.2

FW1 6.2 174 344 66.2 60 58.4 200.9

FW2 7.16 424 411 127.1 20.6 61.8 254

FW3 7.77 409 461 224.9 19.2 52.1 240.2

FW4 7.91 579 507 327.8 17.6 50.2 254.5

FW5 7.9 898 591 441.9 20.2 47.1 278.4



Table 17 Admixture and controls available nutrients analysis results 1. Results are on sample fresh weights

Available nutrients

Total Soluble

N

Chloride Sulphate Phosphorus Boron Potassium Copper

Admixture mg/l mg/l mg/l mg/l mg/l mg/l mg/l

BC 55 77.7 927.8 27.3 0.17 460.5 0.08

PC 161.3 18.7 228.4 78.1 0.19 253.7 <0.06

MS1 57.1 43.7 20 5.4 0.18 88.9 0.07

MS2 85.1 81.4 43.8 10.5 0.16 130 0.13

MS3 114.4 134.4 32.1 26.7 0.2 210.5 0.21

MS4 165.1 181.2 40.5 36.3 0.15 290.6 0.21

MS5 231.9 215.4 41.5 54.3 0.17 410.4 0.31

FS1 57.7 53.3 28.6 6.1 0.16 80.9 0.1

FS2 99.9 119.9 38.1 10.5 0.19 90.4 0.11

FS3 150.6 207.5 41.5 16.5 0.14 108.5 0.12

FS4 248.3 337.1 45.6 24.2 0.15 174.5 0.16

FS5 307.9 424.9 43.7 29.7 0.15 221.9 0.17

PW1 66.6 46.7 32.4 4.5 0.16 97.6 0.09

PW2 69.8 62.5 34.6 4.7 0.15 110.1 0.07

PW3 90.4 85.6 32 13.6 0.14 164 0.11

PW4 182.8 132.9 60.6 30.5 0.22 361.9 0.21

PW5 243.1 147.7 59.1 29.8 0.19 467.7 0.19

FW1 126.2 82.1 23.1 9.5 0.16 78.5 0.06

FW2 147.7 469.3 <0.6 17 0.16 115.8 0.11

FW3 244.1 282.4 53.6 25.5 0.15 175.7 0.15

FW4 345.4 330 41.2 31 0.15 232.3 0.17

FW5 462.1 541 88.6 47.1 0.19 361.9 0.31



Table 18 Admixture and controls available nutrients analysis results 2. Results are on sample fresh weights Available nutrients

Magnesium Manganese Calcium Zinc Sodium Iron

Admixture mg/l mg/l mg/l mg/l mg/l mg/l

BC 58.3 0.43 75.9 1.11 51.1 10.15

PC 72.3 1.05 56.7 0.1 34 1.14

MS1 5.9 0.31 4.9 0.18 13.3 31.17

MS2 12.5 0.78 10.3 0.46 17 73.5

MS3 16.9 1.3 14.8 0.7 19.7 100.63

MS4 9.3 0.82 11.9 0.48 25.1 52.83

MS5 18.9 1.63 25.1 0.88 31.3 106.24

FS1 14 0.85 10.9 0.4 19.4 83.04

FS2 12.2 0.74 9.5 0.4 37.1 76.38

FS3 8.7 0.52 7.6 0.34 62.4 55.22

FS4 10.4 0.64 10.6 0.37 113.3 64.21

FS5 11.4 0.69 14.7 0.5 149.1 62.92

PW1 10.5 0.57 8.7 0.31 14.4 62.64

PW2 5.1 0.29 4.1 0.17 11.9 31.24

PW3 7.2 0.4 4.6 0.25 11.8 51.19

PW4 20.5 1.13 10.4 0.64 17.9 135.81

PW5 35.3 1.29 15.2 0.57 18.3 127.22

FW1 41.1 0.69 9.9 0.18 25.8 32.71

FW2 13.3 0.88 21.9 0.32 52.9 62.75

FW3 11.2 0.62 13.6 0.36 100.9 69.96

FW4 9.8 0.54 17.7 0.31 148.3 63.45

FW5 27.4 1.54 40 0.86 221.8 168.97



Table 19 Admixture and controls PTEs (mg/kg dry matter), showing PAS100 and PAS110 upper limits

Admixture Total

Copper

(Cu)

Total Zinc (Zn)

Total Lead

(Pb)

Total Cadmium

(Cd)

Total Mercury

(Hg)

Total Nickel

(Ni)

Total Chromium

(Cr)

BC 32.1 82.4 20.2 0.44 0.06 9.29 11.1

PC 17.3 20 4.57 0.11 <0.05 1.43 2.01

MS1 13.7 47.2 19.2 0.22 <0.05 8.87 10.2

MS2 13 44.8 17.7 0.21 <0.05 8.49 9.5

MS3 10.9 38.7 13.6 0.19 <0.05 7.31 8.09

MS4 12.8 44 16.8 0.19 <0.05 7.74 9.2

MS5 11.7 41.1 14.7 0.19 <0.05 6.57 7.24

FS1 12.9 44.8 17.3 0.27 <0.05 7.1 8.72

FS2 14.5 58.2 20.5 0.28 <0.05 8.93 12

FS3 38 51.1 19.2 0.22 0.05 8.81 10.5

FS4 12 40.2 16 0.17 <0.05 7.08 8.54

FS5 12.3 46.2 17.5 0.24 <0.05 7.49 8.52

FW1 11.6 43 15 0.25 <0.05 6.47 8.18

FW2 16 53.2 22.7 0.25 <0.05 9.77 13.6

FW3 15.1 52 19.4 0.24 <0.05 8.88 10.2

FW4 15.1 53.2 21.7 0.26 <0.05 9.48 11.5

FW5 14.9 49.6 19.6 0.22 <0.05 8.68 10.1

MS1 13.7 47.2 19.2 0.22 <0.05 8.87 10.2

MS2 13 44.8 17.7 0.21 <0.05 8.49 9.5

MS3 10.9 38.7 13.6 0.19 <0.05 7.31 8.09

MS4 12.8 44 16.8 0.19 <0.05 7.74 9.2

MS5 11.7 41.1 14.7 0.19 <0.05 6.57 7.24

PW1 15.3 50.4 20.7 0.26 <0.05 8.93 11

PW2 16.8 51.5 21 0.23 <0.05 9.04 10.9

PW3 15.1 50.1 19.6 0.24 <0.05 9.27 10.4

PW4 13.5 43.8 16.6 0.22 <0.05 7.69 9.29

PW5 13.4 43.4 18.4 0.21 <0.05 7.85 8.65

PAS100 &

PAS110 upper limit

200 400 200 1.5 1 50 100



9.3 Appendix 3. Fern, pine and cyclamen photos at the end of the trial

Appendix 3 - Fern photographs

Bark control (BC) and peat control (PC) on 24 May 2013

Ferns grown in admixtures FS1-5 on 24 May 2013

Ferns grown in admixtures MS1-5 on 24 May 2013

Ferns grown in admixtures PW1-5

Appendix - Pine photographs

Pine grown in bark control (BC) and peat control (PC)

Pine grown in admixtures FS1-5 Pine grown in admixtures FW1-5

nn

Pine grown in admixtures MS1-5 Pine grown in admixtures PW1-5

Appendix - Cyclamen corns 29 May 2013

Corms cut in half at different angles representative of those harvested (treatments MS2, PW1, PW3)

Cyclamen corms. Peat free control (BC) and peat control (PC), showing £2 coin for scale

Cyclamen corms. Treatments FS1-5, showing £2 coin for scale

Cyclamen corms. Treatments FW1-5, showing £2 coin for scale

Cyclamen corms. Treatments MS1-5, showing £2 coin for scale

Cyclamen corms. Treatments PW1-5, showing £2 coin for scale



9.4 Appendix 6. Fresh weight of fern and pine at the end of the trial

Figure 24 Responses of the fern Asplenium scolopendrium to differing growing media. Final destructive measurements – fresh weight. A) total fresh weight, B) fresh weight of stems, C) fresh weight of roots. Error bars represent ±1 standard deviation

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Figure 25 Responses of black pine (Pinus nigra) to differing growing media. Final destructive measurements – fresh weight. A) total fresh weight, B) fresh weight of stems, C) fresh weight of roots. Error bars represent ±1 standard deviation

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10.0 Appendix 7. Analysis techniques 10.1 Digestate analysis Total N was extracted using Kjeldahl and measured (as NH4) by FIA (Flow injection analysis - Foss FiaStar). Mineral N was measured by FIA after a 50 times dilution of the concentrate. Other available elements were measured by ICP-OES (Inductively coupled plasma - optical emission spectroscopy - Jobin Yvon Ultima 2) after 50 times dilution. Total C was measured by loss on combustion at 450oC (assuming 58% C). Total solids were determined by drying (80oC). pH and conductivity were measured in neat solution using a pH/conductivity meter with appropriate electrodes. 10.2 Growing media analysis Compacted bulk density method: BS EN 13040:2000 Dry bulk density: 13041:2000 Electrical conductivity method: 13038:2000 A test portion is extracted with water under controlled conditions in an extraction of 1+5 (v/v) to dissolve the electrolytes. The specific conductivity is measured using an EC meter and the result adjusted to a measurement temperature of 25oC. pH method: BS EN 13037:2000 A test portion is extracted with water under controlled conditions in an extraction of 1+5 (v/v) . The pH is measured potentiometrically under controlled conditions. Water soluble nutrients method: BS EN 13040:2000 Water soluble nutrients are extracted using a weight equivalent to 66.7ml of the sample volume determined by measuring the bulk density of the sample. This is then extracted in 400ml of Deionised water and shaken at 250rpm for 1 hour at 22oC ±3oC. The pH and conductivity are measured on the shaken suspension. All other nutrients are measured on a filtered extract.

Cl, SO4-S, NO3-N Fl - Determined by Ion Chromatography

NH4-N - Determined by Colorimetric Analysis

P, K, Mg, Ca, Na, B, Cu, Fe, Mn, Mo, Zn - ICP-OES - (Inductively Coupled Plasma - Optical

Emission Spectroscopy)

Total carbon and nitrogen method: AOAC Official Methods of Analysis (1990) Method 949.12 Samples are totally combusted in an oxygen enriched atmosphere in a reaction tube. Nitrogen and Carbon products are carried by a constant flow of carrier gas (helium) through an oxidation catalyst, and then through reduced copper wires, where excess oxygen is removed and nitrogen oxides are reduced to elemental nitrogen. The nitrogen and carbon products are separated through a chromatographic column. As the products are eluted from



this column they pass through a T.C.D detector, which generates an electrical signal proportional to the amount of nitrogen and carbon present. Total elements method: The Analysis of Agricultural Materials, MAFF Reference Book RB427, ISBN 0 11 242762 6 The sample is digested in concentrated aqua regia at high temperature and pressure by microwave digestion or temperature controlled digestion block. The formation of strong oxidising agents will destroy organic matter and break down the mineral matrix of the sample. Most elements are dissolved in the acid. Silicates present in the sample are not solubilised and are left as an insoluble residue in the digest. The total elements in solution are then determined by Inductively Coupled Plasma Emission Spectroscopy (ICPES). Elements determined by this method include; Phosphorus, Potassium, Magnesium, Aluminium, Calcium, Sodium, Sulphur, Manganese, Copper, Zinc and Iron. ICP-ES is also used to determine Nickel, Chromium, Lead, Arsenic, Cadmium, Molybdenum and Cobalt. Mercury and selenium The sample is digested in concentrated hydrochloric and nitric acids at elevated temperature and pressure using a commercial laboratory microwave digestion system or a temperature controlled digestion block. The resulting liquid extract is then analysed by Atomic Fluorescence Spectroscopy as follows; Selenium: The sample extract is then treated with hydrochloric acid to convert all Selenium present into Selenite (Se VI). Sodium Borohydride is continuously added to the treated sample to produce gaseous selenium hydride which is atomised using a hydrogen diffusion flame. Atomic fluorescence is the measured after excitation using a selenium boosted discharge hollow cathode lamp. The concentration of selenium present is then determined by comparison with a series of standards of known concentration. Results are expressed as mg Se/Kg of dry sample. Mercury: Mercury ions in the sample (usually an acid extract of the material of interest) are reduced to elemental mercury vapour by reduction and purging with a stream of argon. The mercury is then detected by its fluorescence following excitation by a boosted hollow cathode discharge lamp. Quantification is then performed by comparison of the fluorescence signal to those of a series of mercury standards of known concentration. Results are expressed as mg Hg/Kg of dry sample.

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