dti

ARBRE MONITORING - THE FUEL SUPPLY CHAIN

CONTRACT NUMBER: B/U1/00626/00/00

NUMBER: 05/1077 The DTI drives our ambition of 'prosperity for all' by working to create the best environment for business success in the UK. We help people and companies become more productive by promoting enterprise, innovation and creativity.

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ii ARBRE MONITORING - THE FUEL SUPPLY CHAIN

B/U1/00626/REP URN 05/1077

Contractors ADAS Consulting Limited Transport Research Laboratory (TRL)

Prepared by Barbara Hilton John Garstang Simon Groves John King Phil Metcalfe Tim Pepper Ian McCrae (TRL)

The work described in this report was carried out under contract as part of the DTI Technology Programme: New and Renewable Energy, which is managed by Future Energy Solutions. The views and judgements expressed in this report are those of the contractor and do not necessarily reflect those of the DTI or Future Energy Solutions.

First published 2005 © Crown copyright 2005

iii EXECUTIVE SUMMARY

Objectives

The objectives of this project were to monitor the entire fuel supply chain for the ARBRE power plant from crop husbandry and yield, through the performance of harvesting machinery, to all handling and transport elements of the fuel supply chain from source to store and store to power plant. In doing this emissions from harvesting, processing and transport machinery were monitored, along with dust and spore emissions from the wood fuel through the store-chipping-handling chain. In addition to the above, water use of short rotation coppice (SRC) was monitored along with site drainage characteristics.

The objective data resulting from the work were to be used to establish confidence in the fuel supply chain for the ARBRE plant and future similar operations by verifying the environmental balance, the technical efficiency and overall performance.

Introduction

The use of renewable biofuels to generate part of the UK's energy requirements is central to the Government's current objectives of reducing CO2 emissions by 12.5% by 2010 (DTI, 1999) thereby honouring its obligations under the Kyoto Treaty of 1997. A further domestic target of reducing CO2 levels in particular to 20% below 1990 levels has also been set. To achieve these targets the Government envisages that 10% of the UK's energy demand will be met from renewables by 2010 with an aspiration that this will increase to 20% by 2020 and that a significant proportion will be biomass generated. Currently, just 3% of UK electricity is generated from renewable sources as a whole. The Energy White Paper (DTI, 2003a) accepted the Royal Commission on Environmental Pollution's (RCEP, 2000) recommendation that the UK should also have a longer term goal of reducing CO2 emissions by 60% by about 2050 compared to today's levels, "with real progress by 2020". In order to achieve this 60% reduction, it is envisaged that at least 30% to 40% of the UK's electricity generation should come from renewable sources (DTI, 2003b) with biomass energy again a significant proportion.

In 2001 ARBRE Energy Ltd completed construction of what was due to be the first commercial state-of-the-art wood-fuelled electricity generating plant of its type in Europe. The plant was of the Biomass Integrated Gasification-Combined Cycle (BIG- CC) design based on circulating fluidised bed gasification technology the principal benefits including high plant efficiency and a reduction in emissions to atmosphere from the combustion process. Commissioning was underway when, in July 2002 and for a number of reasons, ARBRE went into liquidation. The power plant would have generated 10MWe with 8MWe being exported to the local grid, providing enough electricity for the domestic consumption of 33,500 people. The fuel, in the form of wood chips, was from two sources: forest residues and specifically grown SRC with a requirement of 43,500 oven dry tonnes (odt) per annum. The wood chips would arrive at the power plant at or below 30% moisture content with a nominal 30mm size (30 x 30 x 30mm). The chips would then have been dried to 10%

iv moisture content using waste heat from the generation process prior to being fed into the gasifier.

To ensure the long-term viability of currently proposed biomass energy projects it is essential that all aspects of the production chain be run at optimal efficiency. This in turn should ensure that the energy balance of the heat and/or electricity generated is optimally positive. Large scale cropping of SRC for fuel, as was proposed for ARBRE and as is now taking place for a number of heat and/or power projects, and the burning of large quantities of biomass require comprehensive environmental monitoring to ensure that both plant operators and the general public are not exposed to any unnecessary hazards.

Work summary

The work carried out was as follows:

• The fuel supply chain was described from crop establishment through management and harvesting to final storage of the harvested materials. Changes in production methods were noted. • Exhaust emissions and energy consumption from vehicles and equipment were either monitored in the field or obtained from Transport Research Laboratory's (TRL) Emissions Database. • Vehicle performance at crop establishment, harvesting and delivery were monitored including the verification of planter efficiency. Any design faults or inadequacies on the harvesters were noted including cutting height variability and field losses. • SRC water uptake was determined on sand and clay sites using the ADAS water use programme Irriguide. • Drainage water from sand sites, treated and untreated with sewage sludge as fertiliser, and a clay site was monitored working from baseline data obtained prior to planting. The quantity of nitrate-N leached was calculated using the Irriguide model. • Changes in soil nutrient status and carbon accumulation within both sand and clay soils were assessed. • Overall performance of a number of the plantations was monitored including machinery used, herbicide and pesticide applications, fertiliser inputs, pests and diseases identified to general level and scored for severity, mammalian grazing activity and weed burden assessments. Field estimates of yield were also made plus percentage dry matter content. • The quality of water draining from piles of stored harvested material was determined by BOD analysis and tannin levels. • The runoff from the storage piles was also quantified using an automated sampler. • The spores and dust produced during storage and handling of the harvested material were determined using personal dust monitors attached to operators plus passive spore traps within the storage piles and at 10 and 50m distances from the piles.

v Conclusions

• Increased SRC yield reduces the emissions per oven dry tonne harvested for planting and cutback operations but not for harvesting operations nor field and road transport. • Planting and cutback operations contribute the least emissions at 1% or less of the total emissions for SRC production. • Harvesting operations, field and on-farm transport were the predominant sources of emissions during SRC production. • The SRC energy ratio does not alter radically between harvesting methods or lifetime of the crop but the higher the yield the more positive the energy ratio becomes. • The energy ratio for SRC production ranged from 19.7 (16 year crop yielding 9odt ha" 1yr"1) to 28.2 (30 year crop yielding 12odt ha" 1yr"1). • There was no major increase in levels of bio-aerosols above the upwind background concentrations when the chip storage piles were moved. • Bio-aerosol emissions from the chips in store were very low. • Dust exposure to staff and release to the environment during movement of the chip storage piles were within exposure limits for similar dusts encountered in grain stores. • The levels of dust emission are low enough to suggest that there is low general risk to the environment from wood chip storage facilities. • There were no apparent differences in the runoff patterns observed from storage piles of either SRC or forest residue chips. • Biological oxygen demand values recorded for runoff from stored wood chips are unlikely to cause problems provided some dilution occurs before any discharge to a watercourse. • Nitrate-N concentrations in runoff water from the chip storage piles were consistently low during the entire monitoring period, within the range 0.5 to 5.6mg l-1 (EC limit for potable water = 11.6mg l-1), with the highest values recorded in low volumes of runoff. • As shown in previous work, water-use in willows proved higher than continuous cereals, grass or bare soil. • This work confirmed that winter drainage under SRC might be limited to <60mm per winter compared with c. 150-240mm for grass or wheat. • Drainage water from a clay site where no sewage sludge had been applied showed nitrate-N concentrations declining rapidly in the winter following SRC establishment and continuing to decline during the second and third years after planting. Levels were generally below 1mg l-118 months after planting, much lower than would be expected from arable land and similar to values measured in MAFF's Nitrate Sensitive Area scheme when land was converted to nil- fertilised grassland. These concentrations were also 30 times lower than that recorded at the start of the study and a factor of ten lower than the EC limit for potable water.

vi • On a sand site, where no sewage sludge had been applied, nitrate-N concentrations again declined rapidly in the first year following planting to around 1mg l-1 and remained below this level for the following two years. • In contrast, nitrate-N concentrations, where slurry had been applied to a sand site, increased through the first winter, peaking at over 80mg l-1, with the pattern repeated during the following two winters with peaks of 176mg l-1 and 248mg l-1 respectively. • Due to the limited number of sites and treatments monitored for water quality, it was not possible to provide a detailed analysis of the current UK recommendations for the application of nitrogen to commercial SRC (Defra, 2002). However, from the results it can be concluded that, under normal commercial SRC management, leaching losses tend to be small. • The exception to this was the site that received sludge applications. Here, nitrate concentrations were large and it may be that the nutrient requirements of the crop were exceeded by these applications. This stresses the need to match nitrogen inputs to crop requirements. • Soil carbon measurements suggest that the unfertilised sand site had mineralised at least 24t ha -1 carbon as CO2 over the 4.5 years from planting to harvest. • At the clay site the soil was already at a post-grass equilibrium having been in tillage for many years. Here, a greater input of leaf litter coupled with the reduced oxidation of soil organic matter once cultivation had ceased produced an immediate increase in soil carbon. • By the end of the SRC rotation, expected to be 25 years, both sites should have achieved equilibrium for both processes i.e. loss and sequestration.

vii Herbicide application x 2 362 Glyphosate x 2 2741

Land preparation Land preparation Sub-soiling 6158MJ ha 1 6158MJ ha' 1 Ploughing

Power-harrowing

Loading cuttings

Delivering cuttings to field97

Planting

Rolling Establishment Establishment

Herbicide application x 1181 281 6MJ ha 1 281 6MJ ha 1 Mixed herbicide x 1 617

Cutback

Austoft billet Direct chip Herbicide application x 1181 harvesting harvesting Mixed herbicide x 1 617 7532MJ ha 1 7840MJ ha 1 Sludge application

Chipping

561MJ ha

Energy input for Energy input for establishment and establishment and chip production chip production

17.067MJ ha 1 16.814MJ ha 1

Energy ratio Energy ratio

25 year crop at 12odt ha 1yr 25 year crop at 12odt ha 1yr

Energy inputs (MJ ha' 1) for SRC establishment and two harvesting systems 12

Assumes SRC to have a calorific value of 18.6GJ odt (www.dti.aov.uk/enerav/inform/table a1 a2.xls) 2 Data from Table 17 of the main report Recommendations

The success of SRC plantations depends very much on their long-term productivity and this can only be ensured if the sites chosen are fertile in the broadest sense. Although it is expected that carbon accumulation is likely to continue well after the end of the first harvest cycle, the results show the importance of planting SRC on good quality sites.

For future SRC planting, the practical lessons learned from the ARBRE sites include the following, much of which is commonly known but not necessarily acted upon:

• Efficient land preparation is of critical importance particularly the need to control invasive perennials such as couch grass, thistles, nettles, horsetail, etc. Applying an appropriate broad-spectrum herbicide prior to ploughing, if necessary 2 or 3 times in the year prior to planting to ensure full control, will pay dividends in terms of reduced herbicide costs during establishment and increased yields. • Sub-soiling clay sites and those sites where a plough pan or compaction may be present will allow free root development and improved establishment. • There is no longer a specified list of willow varieties for energy crop planting. The Forestry Commission does however provide a list of both willow and poplar varieties that have been bred specifically for energy crop use and it is recommended that this be consulted prior to selecting planting material (Tabbush et al, 2002). • Ensure that contractors plant effectively, not at too high a speed, which leads to cuttings being inserted into the soils incorrectly or entire rods being misfed or not fed at all into the planting mechanism. • Ensure that contractors plant to the correct row widths and planting densities. • Ensure that cutback machinery cuts the stems at or below 10cm from ground level and that the cut is clean.

The needs of harvesting MUST be considered at the plantation design stage:

• Headlands of at least 8m are required for vehicle turning. • Row spacings should be 0.75m between paired rows with 1.5m between each pair of rows to allow access for standard agricultural machinery fitted with flotation tyres. • Access rides across long fields need to be incorporated to allow off-loading of trailers or harvesters. • Areas for storage of rods, bales, bundles or off-loading trailers of wood chip and loading lorries must be identified as close as possible to the coppice.

iX The harvesting operations themselves should aim to achieve the following:

• Provide a clean, low cut to the stools, ideally below 10cm. • All stems should be cut. • No cut material should be left in the field - wastage means lost fuel for the end- user and lost payment for the grower.

With regard to chip storage, although the monitored levels of dust were within the exposure limits for dusts found in similar storage situations, there is a potential risk for some stores that maximum exposure levels of 8-hour time-weighted average limits of 10mg/m3 may be exceeded. Care must therefore be taken to ensure that the stores are well managed to avoid mould formation and that staff are exposed for relatively short periods.

x CONTENTS

EXECUTIVE SUMMARY iv Objectives iv Introduction iv Work summary v Conclusions vi Recommendations ix

CONTENTS xi Tables xiii Figures xv

1 INTRODUCTION 1

2 EMISSIONS TO ATMOSPHERE - VEHICLES AND PLANT 5 2.1 Introduction 5 2.2 Methods 6 2.2.1 Planting 6 2.2.2 Cutback 7 2.2.3 Harvesting and chipping 7 2.2.4 Emissions 8 2.3 Results 9 2.4 Discussion 17 2.5 Forest residue harvesting 18 2.6 Chippers 22

3 ENERGY AND CARBON REQUIREMENTS 24

4 EMISSIONS TO ATMOSPHERE - SPORES AND DUST 27 4.1 Introduction 27 4.2 Materials and methods 27 4.3 Results 28 4.3.1 Gleadthorpe 28 4.3.2 Great Heck 30 4.4 Discussion 31

5 MODELLED WATER USE OF SRC 33 5.1 Introduction 33 5.2 Methods 33 5.3 Results 36 5.3.1 Comparison of water-use in SRC with other vegetation patterns 47 5.4 Discussion 49

xi 6 WATER QUALITY MONITORING 50 6.1 Introduction 50 6.2 Materials and methods 51 6.3 Results 52 6.3.1 Retford 52 6.3.2 Barmby Moor and Gainsborough 55 6.4 Discussion 61

7 WATER QUALITY OF RUNOFF FROM WOOD STORES 64 7.1 Introduction 64 7.2 Materials and methods 64 7.3 Results 64 7.4 Discussion 69

8 SOIL CARBON AND FERTILITY CHANGES 70 8.1 Introduction 70 8.2 Materials and methods 70 8.2.1 Sites 70 8.2.2 Soil sampling 70 8.3 Results 71 8.4 Discussion 75 8.5 Conclusions 76

9 PERFORMANCE OF THE SRC PLANTATIONS 78 9.1 Introduction 78 9.2 Methods 79 9.3 Results 79 9.3.1 Site details 79 9.3.2 Land preparation 80 9.3.3 Establishment 81 9.3.4 Weeds and pests 85 9.3.5 Harvesting 86 9.3.6 Yields 98 9.4 Crop economics 99 9.5 Recommendations 102

10 REFERENCES 104

11 ACKNOWLEDGEMENTS 108

12 APPENDIX A 109

xii Tables

1 Principal machinery used at planting 9 2 Fuel and energy summary for planting 10 3 Field efficiency at planting 10 4 Fuel and energy summary for cutback 11 5 Field efficiency at harvesting 12 6 Harvest yield and losses 12 7 Stool cut height after harvesting 12 8 Billet length 13 9 Moisture content of harvested and stored material 13 10 Harvester fuel usage 14 11 Haulage machinery information 14 12 Field haulage cycle 14 13 Emissions per tonne dry matter harvested based on a measured yield of 15 9.59odt ha -1yr-1 14 Emissions per tonne dry matter harvested based on an assumed yield of 16 12odt ha -1yr-1 15 Percentage of total engine emissions coming from each operation 17 16 Energy use and greenhouse emissions from the ARBRE fuel types 24 17 Primary energy inputs and greenhouse gas outputs for the establishment 25 of ARBRE SRC plantations 18 Energy ratios for SRC production based on two harvesting systems 26 19 Location of and activity dates for chip storage 27 20 Emissions of bio-aerosols from forest residue chips in store, Gleadthorpe 29 21 Emissions of bio-aerosols from forest residue chips when emptying the 29 store, Gleadthorpe 22 Emissions of bio-aerosols when unloading SRC chips from storage, 30 Gleadthorpe 23 Dust exposure for staff at Gleadthorpe during unloading of wood store 30 24 Emissions of bio-aerosols from SRC and forest residue chips when emptyin 31 25 Dust exposure for staff at Great Heck during unloading of wood store 31 26 Soil parameters used in the Irriguide model 33 27 Crop parameters used in the Irriguide model 33 28 Water-use for three vegetation patterns as a percentage of SRC water-use 48 29 Mean NO3-N and NH4-N concentrations in drainage water, Retford 2000/01 53 30 Drainflow and nitrate loss at Retford during 2000/01 53 31 Mean NO3-N and NH4-N concentrations in drainage water, Retford 2002 54 32 Mean NO3-N and NH4-N concentrations in drainage water, Retford 2003 54 33 Mean nitrate-N concentrations, Barnby Moor, 2000 55 34 Mean NO3-N and NH4-N concentrations in drainage water, Barnby Moor 55 and Gainsborough, 2000/01 35 Mean NO3-N and NH4-N concentrations in drainage water at Barnby Moor 57 and Gainsborough, 2001/02 36 Mean NO3-N and NH4-N concentrations in drainage water at Barnby Moor 58 and Gainsborough, 2002/03

xiii 37 Mean NO3-N and NH4-N concentrations in drainage water at Barnby Moor 60 and Gainsborough, 2003/04 38 Runoff and mean nutrient concentrations from stored forest residues, 67 2000/0 39 Mean BOD and coloration of runoff from forestry residue store, 2000/01 68 40 Basic soil fertility analysed for soil carbon dynamics over five years under 71 new plantations of willow SRC 41 Basic soil fertility in topsoil analysed for soil carbon dynamics at planting 72 of SRC and at first harvest after 4.5 years 42 Soil total organic carbon and nitrogen concentrations (% g/g) at Barnby 72 Moor, April 2000 43 Soil total organic carbon and nitrogen concentrations (% g/g) at Retford, 73 April 2000 44 Soil total organic carbon and nitrogen concentrations (% g/g) at Barnby 73 Moor, November 2004 45 Soil total organic carbon and nitrogen concentrations (% g/g) at Retford, 73 November 2004 46 Change in soil related organic carbon pools under first willow SRC 76 harvest cycle of 4.5 years (t ha -1) 47 ARBRE Chronicle - Planting from 1996 to 2001 (representative sites) 94 48 Assessed yields over 3 or 4-year harvest cycles 99 49 Indication of full costs for (A) establishing and (B) harvesting 1 hectare of 100 willow SRC 50 Indication of costs for SRC production with good land preparation and no 102 fencing costs

Xiv Figures 1 Austoft billet harvest and accompanying trailer 11 2 Harvesting and chipping trials for ARBRE, North Yorkshire 19 3 Flow diagram of the Irriguide model 34 4 Modelled annual water-use by site and year 36 5 Crop height and transpiration values for the year 2002 37 6 Modelled evapotranspiration (mm/day) and drainage beyond the root 38 zone (mm/day) at Retford 7 Measured daily rainfall (mm/day) and modelled drainage beyond the root 39 zone (mm/day) at Retford 8 Modelled Soil Moisture Deficit (SMD) in the root zone (mm) at Retford 40 9 Modelled evapotranspiration (mm/day) and drainage beyond the root 41 zone (mm/day) at Barnby Moor 10 Measured daily rainfall (mm/day) and modelled drainage beyond the root 42 zone (mm/day) at Barnby Moor 11 Modelled Soil Moisture Deficit (SMD) in the root zone (mm) at Barnby 43 Moor 12 Modelled evapotranspiration (mm/day) and drainage beyond the root 44 zone (mm/day) at Gainsborough 13 Measured daily rainfall (mm/day) and modelled drainage beyond the root 45 zone (mm/day) at Gainsborough 14 Modelled Soil Moisture Deficit (SMD) in the root zone (mm) at 46 Gainsborough 15 Modelled water use for 4 vegetation scenarios at Retford 47 16 Modelled water use for 4 vegetation scenarios at Barnby Moor 47 17 Modelled water use for 4 vegetation scenarios at Gainsborough 48 18 Mean NO3-N and NH4-N concentrations (mg l-1) at Barnby Moor, 2000/01 56 19 Mean NO3-N and NH4-N concentrations (mg l-1) at Gainsborough, 2000/01 56 20 Mean NO3-N and NH4-N concentrations at Barnby Moor, 2001/02 57 21 Mean NO3-N and NH4-N concentrations at Gainsborough, 2001/02 58 22 Mean N03-N and NH4-N concentrations at Barnby Moor, 2002/03 59 23 Mean N03-N and NH4-N concentrations at Gainsborough, 2002/03 59 24 Mean N03-N and NH4-N concentrations at Barnby Moor, 2003/04 60 25 Mean N03-N and NH4-N concentrations at Gainsborough, 2003/04 61 26 Runoff and nutrient concentration from stored forest residues, 2000/1 66 27 Runoff and nutrient concentration from stored forest residues, 2001/02 67 28 Runoff and nutrient concentration from stored willow chips, 2002/03 68 29 Distribution of total organic carbon in the soil profile with depth down the 74 rooting zone 30 The Mantis whole rod harvester, 2002 - developed from the Hvidsted 87 harvester 31 The Salix Maskiner Bundler, December 1998 88 32 The CRL chipper-harvester, May 2000 90 33 Stool damage caused by the Austoft billet harvester 91 34 Billets 91 35 Wood chips 91

xv xvi 1 INTRODUCTION

The use of renewable biomass fuels to generate part of the UK's energy requirements is central to the Government's current objectives of reducing CO2 emissions by 12.5% by 2010 (DTI, 1999) thereby honouring its obligations under the Kyoto Treaty of 1997 which recently came into force. A further domestic target of reducing c O2 levels in particular to 20% below 1990 levels has also been set. To achieve these targets the Government envisages that 10% of the UK's energy demand will be met from renewables by 2010 with an aspiration that this will increase to 20% by 2020 and that a significant proportion will be biomass generated. Currently, just 3% of UK electricity is generated from renewable sources as a whole. The Energy White Paper (DTI, 2003a) accepted the Royal Commission on Environmental Pollution's (RCEP, 2000) recommendation that the UK should also have a longer term goal of reducing CO2 emissions by 60% by about 2050 compared to today's levels, "with real progress by 2020". In order to achieve this 60% reduction, it is envisaged that at least 30% to 40% of the UK's electricity generation should come from renewable sources (DTI, 2003b) with biomass energy again a significant proportion.

For a number of years the UK Government's means of stimulating the development of renewable technologies was through the Non Fossil Fuels Obligation (NFFO). This provided a guaranteed premium market arrangement for the supply of electricity from renewable sources of energy in England and Wales. Generators of renewable energy were paid a premium price for the electricity they produced. Woodfuel-related technologies were included for the first time in the third round of NFFO in 1993 and what was then called the ARBRE Project was successful in obtaining a 15-year NFFO contract that would have enabled the company to sell electricity into the local grid at a guaranteed price (Pitcher et al, 1997). The three companies involved with ARBRE were Yorkshire Water plc with 85% ownership, Termiska Processer AB of Sweden with 10% ownership, providers of the gasification technology and Royal Dutch Schelde with 5% ownership, the company that began the original construction work.

Also in 1993 two 2.5ha trial willow SRC plantations were established as R&D schemes on land at two of Yorkshire Water's wastewater treatment works in Harrogate and Leeds. The coppices were used to assess the early establishment techniques for growing the crop at a commercial scale, to assess the management requirements of the crop and also for trialing machinery. By 1996 ARBRE Energy Ltd had been formed as a subsidiary of Yorkshire Water plc and the development of the power plant was being actively planned. Commercial planting of SRC also began in 1996 with three farmland sites, each of approximately 10ha in size, being established. As farmer interest in the crop between 1995, when contact with farmers began, and 1997 was low, many of the sites planted in those early years were on Yorkshire Water's own land. The majority of these were small, of awkward shape, had poor access and were on unsuitable land. It was felt necessary however to utilise these poor sites as a means of showing potential growers the growing crop as well as demonstrating establishment techniques.

1 At the same time as SRC production was being developed, contracts were being discussed with Forest Enterprise and local forestry contractors for the supply of forest residues to cover the first 5 years of plant operation ie until the expected SRC supply would come into full production. The residues were to be supplied in the form of softwood thinnings, low-grade broadleaf thinnings, tops and clearfell residues and would have come from forests in the Kielder, North Yorkshire and Sherwood areas. ARBRE was to be responsible for collecting and chipping the material. Trials were carried out over 1999 with a number of contractors to assess both the logistics of the process and also appropriate machinery, particularly chippers.

In 1998 construction began of the ARBRE power plant at Eggborough, near Selby in North Yorkshire. It was due to be the first commercial state-of-the-art wood-fuelled electricity generating plant of its type in Europe. The plant was of the Biomass Integrated Gasification-Combined Cycle (BIG-CC) design based on circulating fluidised bed gasification technology the principal benefits including high plant efficiency and a reduction in emissions to atmosphere from the combustion process. By 1998 ARBRE Energy Ltd was part of First Renewables Ltd, a subsidiary of Kelda plc previously known as Yorkshire Water plc. The power plant was to have generated 10MWe with 8MWe being exported to the local grid, providing enough electricity for the domestic consumption of 33,500 people. The fuel, in the form of wood chips, was from two sources: forest residues and specifically grown short rotation coppice (SRC) with a requirement of 43,500 oven dry tonnes (odt) per annum. The wood chips would arrive at the power plant at or below 30% moisture content with a nominal 30mm size. The chips would then have been dried to 10% moisture content using waste heat from the generation process prior to being fed into the gasifier. Four days' supply of fuel was to be stored at the power plant with an additional stockpile of 10,000t stored locally at a disused airfield. 5,000t of chipped forest residues had been delivered to the local store in 1999 and this stockpile continued to increase over the following two years.

Farmer interest in growing SRC increased considerably from 1998 following the start of construction. Also in 1998 a Locational Supplement was added to the Woodland Grant specifically for the ARBRE catchment area taking the grant for crop establishment from £400 to £1000 per hectare. The start of plant construction and the additional grant combined with a downturn in "conventional" farming led to approximately 300ha of SRC being planted in 1999 and 675ha in 2000, all on farmland. By 2001 the total area of SRC growing was approximately 1,350ha. The original target of 3,500ha had, by this time, been reduced to 1,500ha due to overall costs despite significant reductions in establishment costs. The final planting of 150ha was completed in spring 2002.

Commissioning of the power plant was underway when, in July 2002 and for a number of reasons but primarily technical and financial difficulties, ARBRE Energy went into liquidation. The plant had generated electricity for a maximum of 8 uninterrupted days during the commissioning process.

2 Despite the demise of ARBRE, the so-called "flagship of the UK biomass industry", the use of biomass to generate renewable energy is a technically feasible method of reducing the production of CO2 and other gases from the combustion of fossil fuels. However the economic viability of such projects with the present fuel price structures still tends to rest on the support they receive from grants. To sustain the longer term viability of such projects, possibly over a period when the fuel price structure changes in their favour, the technical efficiency of all the production and utilisation processes needs to be proven in commercially operating power plants. The ARBRE project gave the first opportunity for this to be done in the UK on a significant scale using SRC as the main fuel. The fuel supply chain uses soil, water and nutrients to produce combustible carbohydrates. While the main energy input from the sun is taken to have no effect on any balances or deleterious effects of the supply chain, the other components may be affected and monitoring is required to show that the overheads of fuel production, harvesting, processing and transport do not outweigh the benefits.

In 1999 the DTI agreed to fund three projects through ETSU (now Future Energy Solutions - FES) to monitor major aspects of the ARBRE project. The overall objectives of the ARBRE Monitoring Programme were:

• To verify the environmental balance - mass and energy balance of the integrated project - overall greenhouse gas balance - emissions inventory - local environmental quality

• To verify technical performance - equipment availability and efficiency for both the fuel supply system and power plant

• To verify economic and financial performance

The information was required to establish confidence in this type of project concept. The UK Government, EU officials, developers, financiers, environmental groups and the general public all required evidence of successful operation if widespread replication of this type of power plant was to be accepted. The information would also ensure that development lessons were learnt and disseminated to increase the likelihood of success for future projects.

The three funded projects were: the ecology of the commercial SRC plantations compared to arable land (Cunningham et al, 2004), this project to monitor the fuel supply chain plus a project to monitor the actual operation of the power plant. The ecological monitoring ran from 2000 to 2004, this project began in 1999 and was also due to be completed in 2004 whilst the monitoring of plant operations did not take place due to delays in commissioning and the eventual liquidation of ARBRE.

3 The outbreak of Foot and Mouth Disease (FMD) early in 2001 led to interruptions in the monitoring of the SRC sites as all site visits were suspended for the duration of the epidemic in accordance with Government and ADAS policy. ADAS' involvement across the whole agricultural industry made it necessary for a cautious approach to be taken with regard to all staff and vehicle movements. As the situation escalated it was stated that ADAS staff "do need to ensure that they do not visit any farmers' premises irrespective of whether they have livestock or not". ARBRE field operations such as harvesting and planting were also suspended at some sites. In 2002 the liquidation also led to interruptions to the work programme due to uncertainties as to whether the monitoring programme would continue.

ARBRE Energy were expected to set up the "ARBRE chronicle", a computerised operational database containing all relevant information relating to the SRC plantations such as fertiliser and pesticide inputs, including type of product and application rates and dates, pest and disease incidence, yield estimates, harvesting dates, etc. It was expected that the stored data would have been transferable to programs used by ADAS for data manipulation. The report derived from the chronicle was to be a general record for the first two years of operations with comment on plantation management. This was to include the efficacy of input management, specifically sewage sludge and fertiliser use versus nutrient balance using data from the water quality study, weed control and its effects on the establishment of SRC and pest and disease incidence, their epidemiology and the need for control measures. Unfortunately, although a computer programme was investigated by ARBRE for the accumulation of data, the computerised database was never fully operational. At liquidation, access to the filed information relating to all of the SRC sites was no longer possible. Therefore, as much information as possible for the performance monitoring was gathered from a number of the growers along with field visits to a selection of sites for yield estimation.

4 2 EMISSIONS TO ATMOSPHERE - VEHICLES AND PLANT

2.1 Introduction

Many of the overheads and reductions in energy efficiency associated with biomass renewable energy will be caused by unnecessary transport fuel use in agricultural and road transport vehicle operations. Additionally power is used in the harvesting of the crop and in the transport and application of fertilisers as sewage sludge or other material.

This section of work aimed to verify the technical efficiency and performance of the machinery used in the establishment, harvesting and transportation of the fuel for the ARBRE power plant. The following main areas were monitored:

• Vehicle performance at establishment and from harvest to delivery of fuel to the power plant • Fuel, oil use, electricity and other inputs • SRC planter efficiency • SRC harvesters and associated machinery

The objectives of the monitoring were:

• To derive information on work rates • To assess fuel and energy inputs • To verify machinery performance • To verify information in the ARBRE chronicle

The field operations can be categorised into the following major components:

• Planting • Cutback • Harvest • Storage

Direct-chip harvesting was adopted after ARBRE realised that the whole-rod harvesters available at the time of the first commercial harvests were unsuitable for use with UK SRC whilst to develop a machine of their own would prove prohibitively expensive. Direct-chip harvesting also appeared to be a cheaper method than whole-rod harvesting.

Specialist SRC headers, generally fitted to modified forage harvesters, combine both harvesting and chipping in one operation. This is beneficial due to increased efficiency through less handling but does bulk up the material leading to increased transport costs over long distances. The material would also be preserved better in storage if chipped at a later date. Billet harvesting also combines harvesting and chopping the material in one operation but produces billets, generally 5-20cm long, compared to chips of up to 5cm in size.

5 2.2 Methods

The crop specific inputs of planting, cutback, and harvesting were monitored. The land preparation cultivations are well documented and were not assessed and neither were the equally well documented spraying operations.

Fuel supply equipment handling forest residues has been extensively studied and the energy use relates to engine sizes, operating loads and working hours. SRC harvesting, whilst initially considering operations based on whole-rod harvesting and bundling, settled on higher throughput using a self-propelled billet harvester.

Modern diesel engines working largely under a fixed throttle setting have emissions that are predictable and linked to fuel and lubricant use. This data were derived from operating conditions. The calculation of emissions and energy consumption from the road vehicles used TRL's Emissions Database for information on emissions from engines and vehicles.

Planting and cutback operations were measured in May 2000 and February 2001 respectively. The harvesting operation measurements were postponed in the initial response to FMD, taking place in December 2001. Weighing equipment was serviced and certificated prior to use.

2.2.1 Planting

Field measurements were carried out in May 2000 at a 19ha site of medium to heavy soil in Nottinghamshire. The operations consisted of:

• Delivery of the planting material (willow rods or stems) contained in boxes, from cold storage to farm, in a 7.5t truck. The harvested rods are bundled together at the willow nursery, each bundle comprising approximately 100 metres of planting material. The bundles are then packed in cardboard boxes containing up to 4,400m of material, the equivalent of 18,000 to 24,000 cuttings depending on variety. • The truck delivered the willow into the field where it was off loaded at the headland using a Sanderson Telescopic loader. • The willow was loaded onto a flat, agricultural trailer, hitched up to a small Case International tractor. This tractor was used purely to move the trailer along the length of the headland for ease of filling the planter. For the majority of the time the tractor was stationary. • Planting the material using a Salix Maskiner 4-row Step Planter. When the planter was empty, it was reversed up to the trailer and filled by hand. This occurred approximately every second return. • Consolidation of the soil with 12m rolls.

6 For delivery, the distance from the cold store to the site was used and information on load weights from the number of boxes of rods delivered. The contractors supplied fuel consumption data for all operations.

Time taken to unload the delivery vehicle and take the rods to the field was measured. The work rate was normalised on a 1ha basis from the quantity of rods taken. The planting operations were monitored with timing spot planting rates calculated from measured distances in work and the row spacing. Overall work rates were calculated from the total time spent on site and the area planted.

Individual components of work ie time taken at headlands, filling of the harvester, breakdowns, etc were measured and field efficiencies calculated.

2.2.2 Cutback

Cutback was monitored in February 2001. Timing spot rates were measured as for the planting and overall work rates were calculated.

2.2.3 Harvesting and chipping

The harvesting machinery and performance monitoring was postponed as a result of FMD which had followed unreliability of the original direct-chip harvesting machinery. The modified forage harvesters had been delivered late to ARBRE so harvesting only began in January 2001. At the first site several breakdowns associated with the hydraulic drive delayed the harvesting operations involving delays of over a week at a time when parts had to be imported. The wet weather also prevented operations. Selection of the site was important for representative measurement and future weather restricted the opportunity for monitoring.

In February 2001 it was planned that the monitoring of harvesting would take place at a new site, as this would have been a sufficiently large area for representative measurements. This farm had livestock however and as the full extent of the FMD epidemic was emerging ADAS issued a Management Instruction that visits to agricultural premises were to be suspended. It was then agreed that it would not be appropriate to continue with the monitoring until the disease had been contained. Harvest monitoring later in spring 2001 was not possible, as the regrowth of leaf material would have made the harvest untypical.

Harvesting operations were finally monitored in December 2001 and consisted of the following:

• Harvesting the SRC and loading the accompanying trailer • Delivery from the field to storage area

The work undertaken consisted of harvesting operations, yield monitoring, emission quantification and chip length monitoring.

7 Harvesting operations were intensively monitored over a continuous period of 7 hours with an additional 2.5 hours unloading and setting-up operations on site.

The monitoring involved:

• Field measurement of harvesting operations • Spot harvesting and overall harvesting rate measurement • Loss measurement • Weighing of 11 loads of harvested chips and timings for 13 loads • Measurement of areas harvested • Machinery power unit and dimension data collection

An Austoft sugar cane harvester, adapted for use with SRC to produce short billets, harvested, chopped and side-loaded the billets into a trailer as a continuous operation. Work rates were monitored continuously as real time elapsed. Turning time at the headlands, spot rates, overall rate with and without maintenance and blockages were all recorded so that field efficiencies could be calculated. The contractors supplied fuel consumption data. The time taken to unload the billets was also recorded and the trailers weighed.

The resultant losses from harvesting included woody material littered over the ground. This was collected and weighed in quadrants that were perpendicular to the direction of the rows, 1m wide and 3 rows in length. An average value was extrapolated over the whole area to estimate the losses. The stools heights were obtained by measuring the height of 10 cut stools within each row.

The median cut length of the harvested material was evaluated by passing 12 litres of mixed billets, taken from the tipped trailer, through sieves of 30, 40, 50, 70 and 80mm size. Material that could not pass through was also recorded. The median chop length was evaluated from cumulative frequency charts.

2.2.4 Emissions

The fuel consumption was converted using estimated g/kWh emission to g l-1 of fuel and g t-1 of SRC harvested from published figures (Andrias et al, 1994). It was assumed that all engines conformed to EU stage 1 limits for off-road diesel engines except the loader/tractor Perkins 1004 .4T engine which was assumed to conform to stage 2. For the off-road machines a red diesel specification was assumed and for the road haulage current low specification diesel was assumed. The necessary factors were calculated with the assistance of TRL environment specialists.

8 2.3 Results

Monitoring of planting took place at a 19ha heavy clay site at Retford in Nottinghamshire.

Willow rods, contained in cardboard boxes, were taken from cold storage and delivered to the planting site on a Ford flat-back truck. The willow used was a mixture of the following varieties:

• 5% Sa/ix viminalis Bowles hybrid • 20% S. viminalis x shwerinii Tora • 15% S. viminalis Orm • 18% S. viminalis Ulv • 20% S. viminalis Sow • 20% S. viminalis Jorunn Table 1 provides information on all machinery used during planting.

The rods were delivered into the field by truck where it was offloaded at the headland using a Sanderson Telescopic. The rods were loaded onto a flat, agricultural trailer hitched up to a small Case International tractor used purely to move the trailer along the length of the headland for ease of filling the planter. For the majority of the time this tractor was stationary. When the planter was empty, it was reversed up to the trailer and filled by hand. This occurred at approximately every second return.

The planted field was rolled to consolidate the soil around the cuttings.

Machinery Type Use Engine Type Fuel tank Fuel capacity (L) consumption Massey To operate the Perkins 1060T 6 225 12.84L ha 1 Ferguson tractor planting cylinder turbo 6190 machine charge Salix Maskiner Planting the 4-row Step cuttings Planter Sanderson 725 To load the Perkins 1004 ,4T 4 135 No data willow onto the cylinder turbo trailer charge Ford Truck 75 To deliver Iveco Ford,6 90 2.46I ha 1 E15 willow to the cylinder headland

Table 1: Principal machinery used at planting

9 Overall workrate at planting: Time spent monitoring: 286 minutes Area planted: 2.93ha Work rate: 0.01 ha per minute Work rate: 0.61 ha per hour

Spot workrate at planting: Area covered: 0.014ha Average time to cover area: 31.25 seconds Work rate: 0.026ha per minute Work rate: 1.57ha per hour

Machine Fuel (L ha 1) Direct fuel (Mj ha" 1) % contribution Planter 12.84 487.92 69.0% Loader 0.72 27.36 3.9% Delivery 2.56 97.28 13.7% Rolling 2.5 95 13.4% Total 18.62

Table 2: Fuel and energy summary for planting

Stoppage reason Time (minutes) Lunch break 29 Preparation for rod delivery, collection of rods and machinery 105.12 repair Stoppages due to rods slipping on 27.24 belts mid-planting Headland turnings 8.54

Total 169.54 % time spent in work (field efficiency) 41%

Table 3: Field efficiency at planting

The machinery used at cutback consisted of a Massey Ferguson 4255 tractor with a contractor-constructed finger bar cutter with an effective width of 4.5m. The field operations went smoothly, although weed material delayed some runs. This was considered a legitimate disruption to field performance due to the incidence and severity of weed infestation in some newly established SRC.

10 Overall workrate at cutback: Time spent monitoring: 226 minutes Area cutback: 42,917m 2 Work rate: 189m 2 per minute Work rate: 11.39ha per hour

Spot work rate (30m) at cutback: Effective width cleared: 4.5m Average time to cover area: 19.4 seconds 3 Work rate: 2.5ha per hour

Field efficiency was 87%.

Machine Fuel Fuel energy % contribution (L ha 1) (Mj ha 1)

Tractor 3.6 136.8 100

Table 4: Fuel and energy summary for cutback

Figure 1: Austoft billet harvest and accompanying trailer

Harvesting was monitored on a 1.77ha sandy clay site in December 2001.

3 Mean of five 30m runs with no blockages due to weeds

11 The harvesting system consisted of a self-propelled Austoft sugar cane harvester adapted for use with SRC set to a nominal billet chop length of 50mm. Field haulage was by two trailers pulled by 104 kW tractors. Filling of the trailers was by driving alongside the harvester. The harvested billets were tipped in a medium-term storage area at the farm.

Time Hours In work net of hold-ups 2:45 In work plus headlands and maintenance 3:38 In work net of hold-ups and turning (spt) 2:29 Total time for 11 loads 04:20 Workrates ha/hour Area harvested 0.85

Spot work rates 0.34 Overall workrate with maintenance 0.23 Workrate without blockages, etc 0.31

Spot work rate over 30m 0.33 Overall efficiency 91%

Table 5: Field efficiency at harvesting

Yields Losses 4 year crop 75.54t ha' 1 38.37odt ha 1 Mean loss 1.23 kg m1 Annualised 18.89t ha' 1 9.59 odt ha 1yr1 Total loss 4.65 tonnes Percentage 7.296

Table 6: Harvest yield and losses

Load A B C D E F G H I J Row mean Number (cm) 2 13.5 10.5 18 12.5 19 20 15.5 15.5 12.5 11.5 14.85 3 18.5 23 17 16 19.5 16 18 13.5 13 15 16.95 4 15 16 17 18.5 17 15.5 14.5 16.5 13 14.5 15.75 5 11.5 21 17.5 20.5 15.5 19.5 15.5 22 20 12 17.5 6 15 22 9 15.5 13.5 19.5 19.5 18 15.5 11.5 15.9 7 16.5 20 17.5 16 19 9.5 12 15 14.5 14 15.4 8 10 16 19 12.5 15 16 24 12 17 14.5 15.6 9 13 12 19.5 22 16 14.5 17 17.5 19 11 16.15 Tota mean 16.01

Table 7: Stool cut height after harvesting

12 The cut height of the stool at harvest was influenced by the terrain, the previous cutback height and stem thickness.

Sample 1 Sample 2 Size range Weight Cumulative proportion Weight Cumulative proportion (m) (g) % (g) % <30 1060 18.6 0 0 31-40 895 34.2 695 25.6 41-50 1044 52.5 535 45.2 51-70 1225 73.9 670 69.9 71-80 690 86.0 520 89.0 >80 800 100.0 300 100.0 Total 5714 2720 Median 44mm 47mm chop length

Table 8: Billet length

Load Fresh Dry MC % Harvested material 2 652.91 334.4 48.78 3 707.61 367.56 48.06 4 672.77 335.07 50.20 5 696.7 355.85 48.92 6 651.94 332.93 48.93 7 679.37 347.51 48.85 8 682.55 346.65 49.21 9 707.83 355.47 49.78 10 * * * 11 689.63 347.93 49.55 12 706.9 355.37 49.73 Mean 684.821 347.874 49.20 Stored material 1 62.3 2 66.3 Mean 64.3

Table 9: Moisture content of harvested and stored material

13 Time Fuel Land area covered Mass/vol. Drive load Engine Fuel usage Fuel usage covered added (ha) treated % speed (l/t) (l/t) (L) (t /m3) wet weight dry weight O 66 8 8 '

100% » - r 66 363.76 1.84 121.1 High 3.0 5.9 high

Table 10: Harvester fuel usage

Trailer Tare Load dimensions (m) T ractor Model Power Weight identifier weight (t) width length height make (t) 1 3.75 2.23 4.88 2.01 NH TM165 119 1.8 2 3.76 2.23 4.88 2.01 NH TM150 104 1.75 Trailer volume 21.87m3

Table 11: Haulage machinery information

Trailer Laden Average Average time Distance Average time Hold ups identifier weight row length field to store to store store to field (minutes) (t) (m) (minutes) (km) (minutes) 1 9.6 339.96 2.7 0.58 1.6 2 9.6 346.72 2.5 0.58 1.8 Overall 9.6 343.65 2.6 0.58 1.7 3

Table 12: Field haulage cycle

41 hour spent on maintenance and stoppages

14 O O Operation Machine/Engine Engine CO S02 N20 NOx PM10 voc Legislation etc. Planting Emissions g t'1 dry matter Perkins 1004.4 green engine Unloading 4 cylinder turbo 4 litres est. Stage 2 6 0.04 0.01 0.01 0.07 0.01 0.01 rods 73 kW Ford Iveco 75 E15, 6 cylinder Rod engine est. 110 kW (8060- Stage 1 20 0.14 0.02 0.01 0.26 0.02 0.04 transport 25 R) Planting Perkins 6 cylinder 1060T 6 Stage 1 103 0.74 0.12 0.05 1.36 0.10 0.19 tractor litres turbo 110 kW Rolling 634DS Valmet Sigma 190 6 Stage 1 20 0.15 0.02 0.01 0.27 0.02 0.04 field tractor cylinder 10 litres est. 183 kW Perkins 1004T 4 cylinder 69 Cutback Stage 1 29 0.26 0.03 0.01 0.37 0.04 0.05 kW Harvesting Komatsu engine turbo 180 Harvester Stage 1 13621 100.1 15.25 7.01 184.1 10.81 26.01 kW In-field New Holland TM 165 7.472 Stage 1 1911 13.71 2.14 0.96 25.23 1.92 3.57 haulage litre turbo 119 kW Field to New Holland TM 165 7.472 farm store Stage 1 631 4.53 0.71 0.32 8.33 0.63 1.18 litre turbo 119 kW haulage Road haulage 20km Volvo FH12 380 tractor unit, No Euro 2 1485 2.01 0.06 16.9 0.30 0.56 round trip 12.1 litre turbo 279 kW data 60km Volvo FH12 380 tractor unit, No Euro 2 4455 6.02 0.18 50.79 0.91 1.69 round trip 12.1 litre turbo 279 kW data 100km Volvo FH12 380 tractor unit, No Euro 2 7424 10.03 0.30 84.66 1.52 2.82 round trip 12.1 litre turbo 279 kW data Total 20km rt 17854 121.9 18.4 8.38 237.3 138 31.70 40km rt 20823 125.9 18.5 8.38 271.1 14 32.83 100km rt 23793 129.9 18.6 8.38 305.0 15.1 33.96

Table 13: Emissions per tonne dry matter harvested based on a measured yield of 9.59odt ha 1yr1

15 O O Operation Machine/Engine Engine CO S02 N20 NOx PM10 voc Legislation etc. Planting Emissions g t'1 dry matter Perkins 1004.4 green engine Unloading 4 cylinder turbo 4 litres est. Stage 2 4.6 0.0 0.01 0.002 0.05 0.01 0.01 rods 73 kW Ford Iveco 75 E15, 6 cylinder Rod engine est. 110 kW (8060- Stage 1 15.7 0.11 0.02 0.008 0.21 0.02 0.03 transport 25 R) Planting Perkins 6 cylinder 1060T 6 Stage 1 82.2 0.59 0.09 0.041 1.085 0.08 0.15 tractor litres turbo 110 kW Rolling 634DS Valmet Sigma 190 6 Stage 1 16.0 0.12 0.02 0.01 0.22 0.01 0.03 field tractor cylinder 10 litres est. 183 kW Perkins 1004T 4 cylinder 69 Cutback Stage 1 23.0 0.21 0.03 0.01 0.3 0.028 0.04 kW Harvesting Komatsu engine turbo 180 Harvester Stage 1 13621 100.1 15.25 7.01 184.1 10.81 26.01 kW In-field New Holland TM 165 7.472 Stage 1 1911 13.71 2.14 0.96 25.23 1.92 3.57 haulage litre turbo 119 kW Field to New Holland TM 165 7.472 farm store Stage 1 631 4.53 0.71 0.32 8.33 0.63 1.18 litre turbo 119 kW haulage Road haulage 20km Volvo FH12 380 tractor unit, No Euro 2 1485 2.01 0.06 16.93 0.30 0.56 round trip 12.1 litre turbo 279 kW data 60km Volvo FH12 380 tractor unit, No Euro 2 4455 6.02 0.18 50.79 0.91 1.69 round trip 12.1 litre turbo 279 kW data 100km Volvo FH12 380 tractor unit, No Euro 2 7424 10.03 0.31 84.66 1.52 2.82 round trip 12.1 litre turbo 279 kW data Total 20km rt 17812 121.6 18.3 8.36 236.7 13.8 31.62 40km rt 20782 125.6 18.5 8.36 270.6 14.4 32.75 100km rt 23752 129.6 18.6 8.36 304.5 15.05 33.88

Table 14: Emissions per tonne dry matter harvested based on an assumed yield of 12odt ha 1yr1

16 Operation as a percentage of activity % of total emissions at two yields 9.59 odt ha 1 yr1 12 odt ha 1 yr1 Planting & cutback Field operations 1.1 0.9

+20km transport 1.0 0.8

+60km transport 0.9 0.7

+100km transport 0.7 0.6

Harvesting, field & on-farm transport

Field operations 98.9 99.1

+20km transport 90.5 90.7

+60km transport 77.6 77.8

+100km transport 67.9 68.0

Road haulage (round trip)

+20km transport 8.3 8.3

+60km transport 21.4 21.4

+100km transport 31.2 31.3 Increase in emissions by increasing road haulage round trip from: 60km 17 17

100km 33 33

Table 15: Percentage of total engine emissions coming from each operation

2.4 Discussion

The emission values shown in Table 13 are based on the measured yield of 9.59odt ha 1yr1. Those shown in Table 14 are based on an assumed yield of 12odt ha 1yr1. An increased yield reduces the emissions per tonne of dry matter harvested for the planting and cutback operations but not for harvesting, field and road transport. Table 15 shows, as a percentage, the proportion of total emissions coming from each operation. Planting and cutback were the operations contributing least emissions at 1% or less of the total. The overall reduction in total emissions from the annualised yield increasing from 9.59 to 12odt ha 1yr1 was very small being about 0.2%. Harvesting, field and in-farm transport were the predominant sources of emissions accounting for 91, 78 and 68% respectively of the total for road haulage round trip distances of 20, 60 and 100km. The proportions of emissions from road haulage were 8, 21 and 31% respectively of the total for round trip distances of 20, 60 and 100km. Increasing the road haulage round trip distance from 20 to 60 or 100km increases total emissions by 17, 33 and 56% respectively.

17 2.5 Forest residue harvesting

Large quantities of forest residues are available in the UK, chiefly in areas where there is a substantial forestry industry. These residues can be harvested and used as fuel and therefore represent a valuable renewable energy resource although environmental constraints may restrict how much, if any, residues are taken from a particular site. The Forestry Commission for example has a policy to prohibit the removal of residues from sites where there is the potential for nutrient depletion to occur. Soil protection must also be considered as the presence of residues helps to avoid disturbance or damage to soils by harvesting machinery. This is generally dependent on soil type and also the time of harvesting, with wetter conditions during winter tending to need residues in place more so than during drier, summer harvesting. Some residues must always be left on site at the end of operations in order to protect microhabitats for invertebrates and the growth of fungi and also to maintain soil fertility. However, with current methods and machinery it may not be physically possible to collect and lift all residues and then transport them from a harvesting site (McKay etal, 2003).

The original fuel supply for the ARBRE power plant was to be based on 80% SRC and 20% forest residues. Initially 100% of the fuel was expected to come from residues whilst the SRC plantations were being established and coming to first harvest. Gradually over time the predominant fuel was to become SRC. However, due to the high overall costs of SRC the long-term balance of the fuel supply changed to an expected 60% from SRC and 40% from residues although in reality this expectation was virtually reversed.

As ARBRE was to be responsible for collecting and chipping a major proportion of the forestry material, trials were carried out in 1999 to assess the logistics of the process and also appropriate machinery, particularly chippers. One major trial was carried out in North Yorkshire where clearfell residues were windrowed, allowed to dry for a month and then extracted to roadside where they were chipped. The residues reached an acceptable moisture content but achieving the required chip size of 30mm proved problematic. The difficulties associated with harvesting and handling the residues led to the increased use (ie material in store prior to chipping) of small roundwood for the forestry proportion of the fuel supply.

18 Figure 2: Harvesting and chipping trials for ARBRE, North Yorkshire

No monitoring of forest residue harvesting was undertaken during the course of this work.

As mentioned, it is accepted that not all residues can be harvested from a site during energy harvesting operations. Generally, all non-saleable stems and tops are recovered along with a large volume of limbs but some scattered limbs and needles will remain on site. The quantity of residues available for harvest depends on the tree and stand characteristics as well as the machinery used.

Current UK forestry harvesting practice removes the stem wood only in the form of roundwood products, sawlogs and small roundwood for the pulp and panel product industries. Forest residues include biomass not harvested or removed from logging sites in commercial forests as well as material resulting from forest management operations such as pre-commercial thinnings and removal of dead and dying trees. The residues include branches, tops, small trees and low quality stems that are not used in the pulp and paper industry. Recovery or harvesting of these residues can occur either during thinning operations or at the final tree harvest. Forest residue recovery at the time of final tree harvest can create synergistic effects as most of the costs can be carried by the roundwood harvested (Lundmark, 2004). The sale of forest residues could therefore make forest and woodland management more economically viable unless the extraction and processing of the residues occurs at a second visit, after the removal of the roundwood, which could then jeopardise economic viability.

There are three commonly used methods of harvesting wood for fuel:

• Whole tree chipping usually employed where the whole trees being harvested are small and not viable for timber production.

19 • Second-pass residue harvesting where the main stem wood is first removed then a second-pass removes the residue material that can be utilised as fuel. The residues can either be chipped directly at stump or harvesting site or be removed from the ground relatively intact and chipped it at a later stage either at a landing, the roadside or at the end-user. Forwarder mounted chippers can be used to process residues at the harvest site, the chips then being extracted to landing or roadside. Residues extracted by forwarder to the roadside can be chipped using both forwarder mounted and trailer chippers.

A forwarder mounted chipper achieved 5.17gt/pmh 5 whilst chipping pine residues at the harvest site and 6.75gt/pmh when chipping spruce residues at roadside. A trailer chipper was able to process spruce residues at a rate of 9.64gt/pmh when situated at roadside (Mitchell & Hankin, 1997).

The Bruks CT1002 residue chipper is commonly used in residue harvesting and is carried on a shortwood forwarder chassis and blows chips into a self-unloading bin. It can therefore be used in stump-area chipping. The production varies greatly between applications eg when chipping at the stump productivity is relatively low, between 5 and 8gt/hour. This is due to the dispersed nature of the branches and tops which increases travelling time and therefore reduces chipping time. When it is used roadside the productivity increases dramatically eg when chipping white birch trees it achieved 24gt/hour (Zundel etai, 1996).

• Shortwood harvesting associated with tree felling in urban areas and therefore suitable for broadleaf species in particular. It can involve removal of either the whole tree or individual branches.

Residues from traditional harvesting are likely to be the most common source of wood for fuel although other smaller but more regular sources may come from arboricultural arisings or felled urban trees. Currently a significant proportion of urban forestry residue is sent to landfill.

The method of harvesting will be largely governed by the size of the woodland area, the site characteristics such as layout of the woodland, degree of slope, soil type, etc, the scale of the harvesting operations and also the end-use specification.

One other method of handling residues is to bundle the material for ease of transport; a method tried by ARBRE although chipping the bundles proved difficult. Using current bundling machines eg the Timberjack, residues are collected and fed into the bundler, which produces compact bundles generally over 3m in length and 60-80cm in diameter. Each bundle contains about 1 MWh of energy when combusted and a felling area of 1ha yields approximately 150 bundles.

The bundles are transported from the forest to the roadside with standard forwarders where they can be stored temporarily or be transported directly to the end-user. Bundling or baling residues increases their density and therefore reduces

5 Gt/pmh = green tonnes per machine hour

20 transport costs (DTI, 1998) and as the profitability of using wood fuel is, to a large extent, dependent on transportation distance (Lundmark, 2004), this becomes an important consideration. Bundles are also a clean and easy method of handling and storing residues as they do not decompose too rapidly and can be stored and dried in stacks either at the forest or at the end-user and can therefore be used as required throughout the year.

The integration of forest chip production for energy with the procurement of roundwood opens up possibilities for cost savings. It should be feasible to use the existing transportation equipment for forest residues whenever possible. However, special equipment may be needed due to differences in handling and the final destination of the product. Unfortunately little machine compatibility has been achieved to date in the procurement of forest chips (Lundmark, 2004). This lack of compatibility is due to logging conditions varying considerably from thinnings to final harvest and because the technology is still relatively new. Poor compatibility increases the commercial risk for contractors and users when they invest in new equipment and may result in under-employment and unnecessary shifts of harvesting machines from one site to another.

A forest fuel production system is built around the chipping component. The position of the chipper in the procurement chain largely determines the state of biomass during transportation and consequently whether subsequent machines are dependent on each other. The system predominately used today is the roadside or landing chipping. Roadside chippers do not operate off-road and can therefore be heavier, stronger and more efficient than terrain chippers. The system has so far kept its position as the basic solution of large-scale procurement of forest chips.

Small-scale chipping at the landing or roadside is carried out by farm tractor driven chippers and in large-scale operations primarily with heavy truck mounted chippers or crushers. The residues are hauled with forwarders to the landing or roadside and collected into piles up to 5m in height. This facilitates operations in difficult terrain and in winter conditions and allows longer off-road hauling distances. The forwarder operates independently of the chipper. The chips are blown directly into a 100 to 130m3 loose volume trailer truck, which delivers the chip to the end-user.

The following examples of new technology that have been developed recently illustrate the rapid progress that is being made in the field of wood fuel:

• Multi-tree handling for cost effective felling in small sized tree stands • New forwarder variants for heavier payloads • Chippers operating on the strip road • Bundling or baling of residues to cut transportation costs and to increase efficiency of chipping • Heavy-duty chippers to meet the need for efficient, large-scale chipping at the end-user

21 Only 1500ha of SRC were established in total for the ARBRE fuel supply with no more to be planted due to cost. Assuming a 3-year harvest cycle, approximately 500ha would have been harvested each year and also assuming an average yield of 10odt ha" 1yr"1, this would equate to an annual supply of 15,000odt of wood chip ie less than 35% of the total fuel needed. With ARbRe's requirement for 45,000odt of wood chips per year this would have meant 30,000odt of fuel needing to be supplied from forest residues.

As mentioned the ARBRE forest residue harvesting trials highlighted the problems involved with collecting and handling the residues and also in producing chips to the specified size hence the stockpiling of roundwood. This proved easier to source, handle and store and also proved cheaper than SRC at the time.

2.6 Chippers

Wood fuel needs some form of processing prior to storage and combustion, primarily size reduction and drying. Processing in the form of chipping takes place either directly at harvest for both SRC and forest residues or post-harvest at the road side or at the end-user. Chipping is a relatively inexpensive method of converting wood into a material suitable for burning whilst also having the ability to flow easily. Chippers are well proven nowadays, using sharp blades that cut the wood against a stationary anvil. They are intended primarily for use with fresh wood, as drier material tends to result in high rates of wear. The chips produced can be uneven in size. The main types of chipper used are categorised by the device used to produce the chips:

• Disc chippers - with rotating knives that tend to produce the best chip but are particularly suited to chipping fresh material. The power consumption is lower than a drum chipper but disc chippers are generally more difficult to maintain. • Drum chippers - with knives mounted around a drum require considerably more power than disc chippers and are generally only available for large outputs of material. They are more capable of dealing with drier wood but tend to produce larger chips than disc chippers. • Screw chippers, developed in Scandinavia, use a spinning conical screw with sharpened outer edges and tend to produce a large chip and are usually fitted to tractors.

The output (m3 per hour), costs and quality of the chips vary between the different types of chipper. The end-users' chip specification plus the volume of material to be chipped will determine the most appropriate type for use. For efficient chipping it is essential to have sharp knives, which will probably need sharpening every 25-30 hours assuming no contaminated material is put through the machine.

Hammer mills use fast-moving blocks of metal to shatter the wood and then break it further against a metal screen. The machines are easy to maintain and tolerate

22 contaminated material ie the presence of stones and soil, although they tend to produce a coarse, variably sized chip.

Shredders are low speed machines that shear the feedstock with rotors. Very variable size chips are produced unless a screen is fitted.

Tub grinders were developed in the USA to reduce the volume of construction site waste. Most use a heavy rotor with rigidly mounted hardened steel projections that grind the material against heavy variable size screens.

The two most important factors for the successful use of wood chips for energy, where they must be able to flow unattended through the boiler, are consistent chip size and moisture content. Only certain types of chippers will produce a suitable chip. Nearly all chippers without exception that cut wood at right angles to the knives will not produce a uniform chip. These are usually the types of machine used by tree surgeons, etc just to reduce wood residues for ease of handling. The type of machine needed is one that cuts the wood at, ideally, a 45° angle to the knives and produces a uniform chip that will flow through the boiler system. Forest Research (Hall & Jones, 2004) are currently carrying out a series of chipper trials aimed at:

• Identifying suitable and readily available chippers • Defining outputs and costs for the machines and methods trialled • Defining optimum equipment settings.

In Sweden large-scale production of chips from forestry relies on roadside chipping as the machinery is heavier, stronger and more efficient than terrain chippers (Lundmark, 2004). Chipping at the roadside is performed in smaller operations with farm tractor-driven chippers and in large-scale operations primarily with heavy truck-mounted chippers or crushers. Terrain chippers are used at the site of harvesting operations, the chipped material then being extracted to the roadside.

The Swedish experience shows that the cost of wood chips increases if the residues are left to season on-site to improve fuel quality and reduce nutrient loss from the forest soils.

23 3 ENERGY AND CARBON REQUIREMENTS

Bioenergy projects burning wood or energy crops are often described as carbon neutral as the C02 taken in by the crop over its life is released on burning. However this term does not allow for the C02 and other greenhouse gas inputs required to manage, harvest, transport and prepare the fuel for burning. Many studies have been carried out on generic theoretical systems (eg Bullard & Metcalfe, 2001; Elsayed et at, 2003; Matthews etal, 1994) but few have targeted individual projects.

Table 17 provides the primary energy inputs for the main operations involved in the establishment and harvesting of a number of the ARBRE coppices. Direct energy inputs equal the energy released when fuels such as oil and diesel are consumed in equipment used for any activity providing a product or service. Indirect energy inputs arise from the consumption of energy from other operations such as repairs, maintenance and delivery of machinery plus the energy used in production of the raw materials, machinery, etc.

For methane and nitrous oxide less data were available but as the levels were generally negligible just a total figure was determined. Data were converted to C02 equivalents, based on the global warming potentials used by the Intergovernmental Panel on Climate Change (IPCC). This allows all greenhouse gases to be expressed in terms of C02 equivalents. The approach taken is consistent with the IPCC of a one hundred year time horizon, which assumes on a weight for weight basis that methane is 21 times more powerful than C02 and nitrous oxide 310 times more powerful (World Bank, 1998).

Resource Energy use (MJ odt1) C02 equivalent emissions (Kg odt1) Chipped forest 572 33 residues Chipped SRC 756 35

Table 16: Energy use and greenhouse emissions from the ARBRE fuels

Table 16 shows the energy use and C02 equivalent emissions from fuel production for the two main fuel options for the ARBRE power plant. The figures include direct inputs, indirect inputs and resource-related inputs (RCEP, 2004). These have been converted from values per fresh tonne to values per odt.

24 Rate Direct MJ ha-1 Indirect MJ ha-1 Total MJ ha-1 Direct CO2 ha-1 Indirect CO2 ha-1 Total CO2 ha-1 Total CH4 ha-1 Total N2O ha-1 Refs

Land preparation Herbicide application X 2 (machinery) 226.0 136.0 362.0 16.7 10.1 26.8 0.004746 0.000022 A Glyphosate application x 2 5L ha -1 2741.0 49.2 0.001800 0.015100 A Sub-soiling 1040.1 262.0 1302.1 77.0 19.4 96.4 0.021841 0.000104 B Ploughing 1040.0 262.0 1302.0 77.0 19.4 96.4 0.021840 0.000104 B Power harrowing 272.0 179.0 451.0 20.1 13.3 33.4 0.005712 0.000027 B

Establishment Loading cuttings to trailer 27.4 Delivering cuttings to field 97.3 Planting 487.9 Rolling 146.0 98.0 244.0 10.8 7.3 18.1 0.003066 0.000015 B Herbicide application x 1 (machinery) 113.0 68.0 181.0 8.4 5.0 13.4 0.002373 0.000011 A Mixed herbicide application x 1 617.0 D Cutback 136.8 Herbicide application x 1 (machinery) 113.0 68.0 181.0 8.4 5.0 13.4 0.002373 0.000011 A Mixed herbicide application x 1 617.0 D Sludge application 152.0 75.4 227.4 11.2 5.6 16.8 0.003192 0.000015 E

Harvesting Austoft billet harvester 7532.2 Chipping 134.0 427.0 561.0 D Direct chip harvesting 7614.5 225.0 7839.5 55.0 12.0 67.0 0.159904 0.000761 D A - Mortimer (2003), pers. comm. to ADAS B - Bullard & Metcalfe (2001) and Elsayed et al (2003) D - Elsayed et al (2003) E - Metcalfe & Cormack (2001)

Table 17: Primary energy inputs and greenhouse gas outputs for the establishment of ARBRE SRC plantations

25 Direct chip harvesting Austoft billet harvesting Life of crop Yield Energy production Energy Energy production Energy in years odt h 1yr1 MJ ha" 1 ratio MJ ha 1 ratio 9 157,200 19.7 157,507 20.5 16 12 212,400 26.3 212,707 27.3 9 157,461 20.4 212,969 21.2 30 12 212,661 27.1 208,169 28.2

Table18: Energy ratios for SRC production based on two harvesting systems

Using the data in Table 17 allows calculations to be made of the energy ratio for SRC production ie the energy cost of production compared to the energy content of the biomass produced. Table 18 shows the energy ratio for SRC production including land preparation and establishment for the two main harvesting methods. The calorific value is assumed to be 18. 66 MJ odkg 1. Two yield examples are provided over a crop life of either 16 years, equating to the length of the ARBRE contracts, or 30 years, the current expected productive life of an SRC plantation. Energy ratios for other crops and willow (Bailey, 1999) have been recorded as:

• Miscanthus 32.5 • Poplar 37 • Willow 30 • Wheat 8.8 • OSR 3.8

Conventional arable crops such as wheat and OSR have high agrochemical inputs and consequently lower ratios than energy crops generally, the latter requiring minimal inputs.

From this work the SRC energy ratios do not alter radically between the harvesting methods or life of the crop but as expected and as found in previous work (Matthews et al, 1994), the higher the yield the more positive the energy ratio becomes.

6 http://www.dti.aov.uk/energy/inform/table a1 a2.xls

26 4 EMISSIONS TO ATMOSPHERE - SPORES AND DUST

4.1 Introduction

The storage and chipping of wood can give rise to dust and fungal spores that may constitute a health hazard, this hazard depending on whether the fuel is stored as rods or is chipped prior to storage and possibly also the duration of storage (Nellist, 1997). Most dust and spores will be released during breakdown of the storage piles

The objective of this work was to determine spore and dust production from storage, handling and chipping wood. Spores and dust were monitored from both SRC and forest residue chips.

4.2 Materials and methods

The monitoring of storage facilities was undertaken from April to July 2002 and on final clearing of long-term stored material in November 2004.

Date Locations Material 17.04.02 ADAS Forest residue chip In store Gleadthorpe 10.05.02 ADAS Forest residue chip Unload store Gleadthorpe 20.06.02 Great Heck SRC & Forest residue chip Unload store 30.11.04 ADAS SRC Chips Unload store Gleadthorpe

Table 19: Location of and activity dates for chip stores

The stored chip at ADAS Gleadthorpe was that used in the evaluation of drainage water quality from the stored material. The quantities of material were relatively small at about 20 tonnes. The central ARBRE fuel store at Great Heck consisted of large storage heaps of both forest residue and SRC chips. Several thousand tonnes of material were stored at this site.

The method employed for the measurement of bio-aerosols was in accordance with the Composting Association's Standardised Protocol for the Sampling and Enumeration of Airborne Micro-organisms at Composting Facilities. The following organisms were monitored:

• Moulds at 25°C • Moulds at 37°C • Aspergillus fumigatus (a benchmark micro-organism with pulmonary health impacts) • Thermophillic actinomycetes

27 Single-stage Andersen samplers were used with portable pumps. For the samples taken in 2002 a sampling rate of 16L per minute was employed. This increased to 28L per minute in 2004, as new equipment was available. Sampling times for the emissions in 2002 were 20 minutes but with the increase in flow rate from the new pumps the sampling period was reduced to 10 minutes in 2004. The sampling height of 1.5m was used for all samples. Weather conditions at the time of the monitoring were recorded including wind speed and direction, temperature, humidity and cloud cover.

Monitoring the handling of wood chips was carried out at Great Heck in June 2002. A front-end loader was used to turn the pile simulating the effect of unloading. In addition personal dust monitoring was also carried out to determine dust levels.

Due to lack of access to arable fields on either side of the storage facility, the sampling points were limited to 10m downwind of both the forest residue and SRC chip piles. The 50m upwind sampling point was also compromised by the proximity of further wood chip storage. Three on-site workers were fitted with personal dust monitors, SKC air check personal samplers with total dust heads and an air flow rate of 2L per minute.

4.3 Results

4.3.1 Gleadthorpe

The data are presented as the number of colony-forming units/m 3 (cfu/m3) of air. Each colony-forming unit represents one micro-organism in the original sample.

After the SRC and forest residue chips had been placed into store in the autumn of 2001 the emissions from the site were monitored in April 2002, the results given in Table 20. The average temperature at the time of sampling was 9.6 oC, relative humidity 68% and cloud cover 6/8 ths .

Table 21 gives the results obtained when the forest residue chip store was unloaded when emptying the store. At the time the average temperature was 10.41oC, relative humidity 89% and wind speed 3.07m per second.

The results in Table 22, from samples collected in November 2004 during removal of the SRC pile at Gleadthorpe, show that there was no increase in levels of bio ­ aerosols over the background level after 2 years storage.

28 Date Sample Position Flow rate Thermophillic Aspergillus Moulds at Moulds at time (L/minute) actinomycetes fumigatus 37°C 25°C (minutes) cfu/m3 cfu/m3 cfu/m3 cfu/m3 23.04.02 20 upwind 16 n/a 0 >3 0 20.04.02 20 upwind 16.5 42 n/a n/a n/a 20.04.02 20 upwind 16 34 n/a n/a n/a 25.04.02 20 upwind 0 n/a 0 0 >6 20.04.02 20 upwind 0 0 n/a n/a n/a 23.04.02 20 downwind 16 n/a 0 >3 0 20.04.02 20 downwind 16.5 >6 n/a n/a n/a 20.04.02 20 downwind 16 <13 n/a n/a n/a 23.04.02 20 downwind 0 n/a 0 >3 0 20.04.02 20 downwind 0 0 n/a n/a n/a 25.04.02 20 control 0 n/a 0 0 >3 20.04.02 20 control 0 0 n/a n/a n/a

Table 20: Emissions of bio-aerosols from forest residue chips in store, Gleadthorpe

Date Sample Position Flow rate Thermophillic Aspergillus Moulds at Moulds at time (L/minute) actinomycetes fumigatus 37°C 25°C (minutes) cfu/m3 cfu/m3 cfu/m3 cfu/m3 13.05.02 5 at heap 16 <13 n/a n/a n/a 13.05.02 5 at heap 16 25 n/a n/a n/a 20.05.02 5 at heap 16 n/a 0 0 >112 20.05.02 5 at heap 16 n/a 0 0 125 20.05.02 5 at heap 16 n/a 0 0 10 20.05.02 5 at heap 16 n/a <3 0 13 13.05.02 10 downwind 16 >6 n/a n/a n/a 13.05.02 10 downwind 16 <19 n/a n/a n/a 20.05.02 10 downwind 16 n/a >69 0 >238 20.05.02 10 downwind 16 n/a <67 0 >239 20.05.02 10 downwind 16 n/a 0 0 30 20.05.02 10 downwind 16 n/a 0 0 14 13.05.02 10 upwind 16 <13 n/a n/a n/a 13.05.02 10 upwind 16 >6 n/a n/a n/a 20.05.02 10 upwind 16 n/a 0 0 >113 20.05.02 10 upwind 16 n/a 0 0 >19 20.05.02 10 upwind 16 n/a 0 0 <44 20.05.02 10 upwind 16 n/a >7 0 >181 13.05.02 10 control 16 1 n/a n/a n/a 20.05.02 10 control 16 n/a 0 0 9 20.05.02 10 control 16 n/a 0 0 1

Table 21: Emissions of bio-aerosols from forest residue chips when emptying the store, Gleadthorpe

29 Date Sample Position Flow rate Thermophillic Moulds at Moulds at time (L/min) actinomycetes 37°C 25°C (minutes) cfu/m3 cfu/m3 cfu/m3 30.11.04 10 5m upwind SRC 28 0 0 61 30.11.04 10 5m upwind SRC 28 0 0 336 30.11.04 10 10m downwind SRC 28 0 0 93 30.11.04 10 10m downwind SRC 28 0 0 100 30.11.04 10 10m downwind control 28 0 0 168 30.11.04 10 5m upwind SRC 28 0 79 0 30.11.04 10 5m upwind SRC 28 0 86 0 30.11.04 10 10m downwind SRC 28 0 4 0 30.11.04 10 10m downwind SRC 28 0 100 0 30.11.04 10 10m downwind control 28 0 111 0 30.11.04 10 5m upwind SRC 28 179 0 0 30.11.04 10 5m upwind SRC 28 161 0 0 30.11.04 10 10m downwind control 28 0 0 0 30.11.04 10 10m downwind SRC 28 132 0 0 30.11.04 10 10m downwind SRC 28 186 0 0

Table 22: Emissions of bio-aerosols when unloading SRC chips from storage, Gleadthorpe

5m 10m downwind upwind (fixed position) Sample time (mins) 80 80 Flow rate (L/min) 2 2 Exposure level (mg/m3) 0 6.25

Table 23: Dust exposure for staff at Gleadthorpe during unloading of wood store

4.3.2 Great Heck

In addition to the trial storage at Gleadthorpe the emissions were also monitored when material at the main ARBRE wood chip store at Great Heck was moved. The work was carried out in June 2002 and the results given in Table 24. At the time the average temperature was 22°C, relative humidity 77% and cloud cover 4/8 ths .

30 Sample Distance to Activity Chip Flow Thermophillic Aspergillus Moulds Moulds time boundary or type rate actinomycetes fumigatus at 37°C at25°C (mins) process (m) (L/min) cfu/m3 cfu/m3 cfu/m3 cfu/m3 10 50 upwind none none 18 >194 n/a n/a n/a 10 50 upwind none none 18 0 0 <17 n/a 10 10 downwind pile forest 18 <106 n/a n/a n/a moved 10 10 downwind pile forest 18 <267 n/a n/a n/a moved 10 10 downwind none forest 18 n/a 0 n/a 0 10 10 downwind none forest 18 n/a <17 <17 n/a 10 10 downwind none contro 18 n/a 0 n/a 1 I 10 10 downwind none contro 18 n/a 0 1 n/a I 10 50 upwind none none 18 >194 n/a n/a n/a 10 50 upwind none none 18 0 0 <17 n/a 10 10 downwind pile SRC 18 >244 n/a n/a n/a moved 10 10 downwind pile SRC 18 <155 n/a n/a n/a moved 10 10 downwind none SRC 18 n/a 0 n/a >83 10 10 downwind none SRC 18 n/a <39 <39 n/a 10 10 downwind none SRC 18 n/a >11 n/a n/a 10 10 downwind none SRC 18 n/a 0 n/a n/a 10 10 downwind none SRC 18 n/a 50 n/a n/a 10 10 downwind none SRC 18 n/a <6 n/a n/a

Table 24: Emissions of bio-aerosols from SRC and forest residue chips when emptying the store, Great Heck

Operative 1 Operative 2 Operative 3 Fixed sampler Driver Sampler Monitor 15m Sample time (mins) 171 158 171 176 Flow rate (L/min) 2 2 2 2 Exposure level (mg/m3) 0 0.32 0 0.28 Exposure level * hour 0 0.32 0 n/a TWA (mg/m3)

Table 25: Dust exposure for staff at Great Heck during unloading of wood store

4.4 Discussion

Bacteria and fungi occur naturally in many different environments and are therefore commonly present in the air. Concentrations are highly variable, but background levels of thermophillic actinomycetes or moulds (which includes Aspergillus fumigatus) do not normally exceed 1,000cfu/m3 (colony forming units per cubic metre of air). In line with guidance from the Environment Agency (Wheeler et a/, 2001)), a threshold value or reference level of 1,000cfu/m3 has been used within this

31 report, along with the specific "background" value results, when assessing the concentrations of bio-aerosols.

The levels of bio-aerosols observed at Great Heck and Gleadthorpe for both SRC and forest residue wood chips being moved from one storage position to another indicate that the levels of micro-organisms remain within reference levels. There was no major increase in levels above the upwind background concentration that were measured around the site. Spore measurements in work carried out on large- scale storage trials by Garstang et al (2002) revealed that no change in spore levels occurred during pile disturbance created artificially at the end of the storage period to mimic chip handling operations. Levels recorded were well within the current Health and Safety guidelines and no evidence of a significant health risk arising from exposure to wood dust or fungal spores during routine operations was found.

The emissions of bio-aerosols from the material whilst in store were very low.

The level of dust exposure to staff and the release to the environment at Great Heck from heaps of SRC and forest residue wood chips was within exposure limits for similar dusts encountered in grain stores (10mg/m3 over an 8 hour time weighted average).

The low exposure of the driver (Operative 1) indicates that risk is reduced when the staff are enclosed within a cab on the materials handling loader. Under Environment Agency pollution protection (1996), control limits of 100mg/m3 are given for processes such as animal feed preparation involving similar organic materials. The dust emissions were very low in comparison with the highest exposure being recorded for Operative 2, the sampler, with levels of 0.32mg/m3.

There is a potential risk for some stores that maximum exposure levels of 8 hour time-weighted average limits for dust of 10mg/m3 (COSHH, 1999) may be exceeded therefore care must be taken to ensure that the store is well managed to avoid mould formation and that staff are exposed for relatively short periods.

The levels of dust emission are low enough to suggest that there is low general risk to the environment from wood chip storage facilities.

32 5 MODELLED WATER USE AT THREE SRC SITES

5.1 Introduction The objective of this work was to model the water use of SRC and relate the findings to the water drainage data from the water quality study.

5.2 Methods Three sites were monitored to assess water uptake by SRC:

• Retford, Nottinghamshire, OS SK 713 824, an 8ha clay site. • Barnby Moor, Nottinghamshire, OS SK 670 875, a 7.5ha sandy site. • Gainsborough, Lincolnshire, OS SK 823 942, a 12.9ha sandy site where sewage sludge was added as a fertiliser. Data were collected using the equipment and methodology reported in the section "Water quality monitoring ". The ADAS computer programme Irriguide was used to estimate water use. This model uses detailed meteorological information from the Met Office, local rainfall data and crop specific information to estimate rates of evapotranspiration. The model is based on a Penman-Monteith equation and has been shown to provide good estimates of water use for many arable crops (Bailey & Spackman, 1996; Bailey et a/, 1996). As the model had not previously been used for SRC, new crop parameters, drawn from experimental measurements and the literature, were included in the model database. The model was then run using these parameters together with the crop and site details shown in Tables 26 and 27. It should be noted that the accuracy of the model has not been specifically evaluated for SRC and therefore the data generated should be viewed in this context.

Retford Barnby Moor Gainsborough Depth of topsoil 0.3m 0.3m 0.3m Topsoil texture Clay loam Clay loam Clay loam Available water capacity of topsoil 18% 18% 18% Subsoil texture Sandy clay loam Medium sand Peaty loam Available water capacity of subsoil 15% 7% 27%

Table26: Soil parameters used in the Irriguide model

Maximum rooting depth Maximum crop height Maximum leaf area index (m) (m) Year 1 1 1.5 2.5 Year 2 1.5 3 4 Year 3 2 4 4 Year 4 2 5 4 Year 5 2 57 4 Table 27: Crop parameters used in the Irriguide model

7 A maximum height of 3m was used at Gainsborough following harvest at the end of year 4

33 Figure 3 is a schematic of the computing methodology.

W e a th e r

Crop growth

Crop re sista nce growth

Soil ch a ra cte ristic s

(A E c) Previous SMD

Figure 3: Flow diagram of the Irriguide model. Pathways marked * involve crop specific constants.

Potential evaporation (PE) of a "reference crop" is calculated using the Penman- Monteith equation.

The equation is: A(tfN-6) + p cp (e-e) [1 + b'ra /p cp ] / XE = ------A + y (1 + rs /ra) [1 + b'ra /p cp ] where: E = rate of water loss (kg m2 s1).

34 A = rate of change of saturation vapour pressure with temperature (mb °C1)- p = air density (1.2 kg m-3). Cp = specific heat of air at constant pressure (1005 J kg 1). es = saturation vapour pressure at screen temperature (mb). e = screen vapour pressure (mb). X = latent heat of vaporisation (^ 2465000 J kg 1). Y = psychrometric constant (= 0.66 mb °C1). b = 4sa(273.1 + 7"s)3, where s = emissivity of surface, a = Stefan's constant (5.67 x 10-8 W m-2 K4) and 7s = screen temperature (°C). ra = bulk aerodynamic resistance (s m1). This is a function of the windspeed and crop height. rs = bulk surface resistance (s m1). For a given crop this is a function of leaf area index and surface wetness. G = soil heat flux (W m-2). RN = net radiation (W m-2) where RN = Rs + R - Rf. RS = net shortwave radiation at the surface. This is calculated from the time of year, latitude, sunshine duration and albedo. Rp= incoming long-wave radiation. This is a function of vapour pressure and temperature. Rf= outgoing long-wave radiation. This is found from Stefan's law assuming an albedo of 0.95.

Figure 3 identifies where the Irriguide model requires crop specific constants in order to produce estimates of actual evapotranspiration (AE crop) or crop water use. These constants were measured for SRC and the model run for the three sites used for water quality monitoring to estimate water use and drainage figures starting at the date of crop establishment.

Site specific information was collected from all 3 sites including:

• Local rainfall • Planting dates • Soil texture information • Depth of top soil • Assessment of leaf cover development and autumn leaf senescence • Maximum crop rooting depth • Crop density • Crop height

35 5.3 Results

The water-use data for each site in each year are summarised in Figure 4, the data being a sum of daily evapotranspiration calculated by the Irriguide model. Water use at Retford and Gainsborough was similar with slightly lower water use at Barnby Moor due to the lower water holding capacity of the lighter textured soil at this site.

Figure 4:Modelled annual water-use by site and year

Figure 5 shows the development of crop height for the three sites and the calculated actual transpiration values for the whole season from mid-January to the end of December 2002. The earlier growth at the Gainsborough site produced an earlier full canopy and greater transpiration losses for the season. For the 2002 season canopy height maximum was assumed taken as 3m for all sites.

36 SRC Crop height - Barn by Moor, Gainsborough and Retford

Retford Actual transpiration 473mm

Gainsborough Darnby Moor Actual transpiration 515mm Actual transpiration 463mm

21/ 4/2 18 / 4/3 18 / 1/4 15/ 29 / 13/ 27/ 10/ 24/ #7 22/ 5/8 19 / 2/9 16/ 30/ 14/ 28 / 11/ 25/ 9/1 23/ 1/0 102 2/0 102 3/0 102 4/0 4/0 5/0 5/0 6/0 6/0 102 7/0 102 8/0 102 9/0 9/0 10/ 10/ 11/ 11/ 2/0 12/ 02 02 02 02 2

Figure 5: Crop height and transpiration values for the year 2002

Figures 6 to 14 show the distribution of modelled water-use, drainage and measured rainfall during the course of the study.

37 Figure

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41 Figure 10: Measured daily rainfall (mm/day) and modelled drainage beyond the root zone (mm/day) at Barnby Moor

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Figure 11: Modelled Soil Moisture Deficit (SMD) in the root zone (mm) at Barnby Moor

43

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Figure 14: Modelled Soil Moisture Deficit (SMD) in the root zone (mm) at Gainsborough

46 5.3.1 Comparison of water-use in SRC with other vegetation patterns

In addition to estimates of water-use for SRC at the three sites, model runs were also completed for winter wheat, grass and bare ground to provide comparisons. Standard default settings were used for these crops in accordance with Bailey & Spackman, 1996. These runs assumed permanent grass cover, continuous bare soil or continuous winter wheat cropping with harvest in mid-August and sowing in late September. Figures 15 to 17 present the data for each site.

_ 700 n id a> o o (mi

Ol o o ill

o o

w o o

Is) o o evapotranspiration

o o

Actual o 2001 2002 2003 2004

Figure 15:Modelled water use for 4 vegetation scenarios at Retford

700 i E E o 15 Q.

O Q. E

o < 2001 2002 2003 2004

Figure 16:Modelled water use for 4 vegetation scenarios at Barnby Moor

47 700 i 600

.2 50 2 | M £ 30 o. g 20 0) § 10 o <

2001 2002 2003 2004

Figure 17:Modelled water use for 4 vegetation scenarios at Gainsborough

The data suggest that water-use in SRC was higher than continuous cereals, grass or bare soil. Table 28 presents these data as a percentage of total water use by willows between 2001 and 2004. These results compare favourably with work published by Cranfield University (Stephens et al, 2001), in that the relative differences in evapotranspiration rates between species were similar. The mean evapotranspiration rates across sites and seasons suggest slightly higher values for grass and SRC in this study (grass 474mm yr"1; SRC 541mm yr1) compared to those from the Cranfield work (grass 453mm yr1; SRC 491mm yr1). These differences are likely to be a function of site and season effects rather than any systematic bias in the model used. Other published estimates of water-use (poplar SRC 600mm yr1) exceed the data presented here indicating that the results obtained are comparable with other work (Hall, 2003).

Retford Barnby Moor Gainsborough Bare ground 53 60 53 Grass 84 89 90 Winter 78 81 88 wheat

Table 28: Water-use for three vegetation patterns as a percentage of SRC water-use

48 5.4 Discussion

It was noticeable that after the winter of 2000/2001 there was no drainage below the root zone at either the Retford or Gainsborough sites and only limited drainage at Barnby Moor during the winter of 2002. Substantial SMDs have been estimated for the winters of 2001/2, 2002/3 and 2003/4 at both Retford and Gainsborough. These data are based on the assumption of SRC rooting depths of 1m in year 1, 1.5m in year 2, and 2m from year 3 onwards, thus allowing substantial root zone SMDs to develop during periods of low rainfall. The model estimated that at all three sites soil water depletion in the summer of 2003 was sufficient to cause some degree of drought stress in the crop. There was supporting evidence of high SMDs during these winters as the automated sampler installed at the Retford site, used to collect drainage water for nitrogen analysis, was rarely triggered during the last two winters of the study. Other published work has concluded that winter drainage under SRC may be limited to <60mm per winter compared with c. 150-240mm for grass or wheat (Stephens et at, 2003)

The model estimates are heavily influenced by soil texture and crop rooting depth. Soil texture was assessed at all three sites to 1m and assumptions were made concerning the texture of soil beneath this depth. It was not possible to monitor rooting depth development in the field therefore estimated rooting depths were used based on measurements taken in other studies.

Water-use in SRC willow exceeds that of grass, bare ground and winter wheat.

49 6 WATER QUALITY MONITORING

6.1 Introduction

The impact of SRC plantations on both water use and the quality of drainage water were monitored as well as the quality of run-off water from the wood stores. If SRC plantations are to become common across the countryside it is important any effects on the environment are investigated.

On typically poorly draining clay soils in the UK artificial underdrainage systems are installed to control the winter water table therefore preventing saturation of the soil profile and surface ponding.

For a given agricultural system, losses from sandy soils will generally be more rapid (ie less water is required to leach the nitrate from the profile) and, hence, at a greater concentration. However, the role of the soil's hydrology needs also to be considered. Whereas sandy soils and shallow soils overlying rock are considered to be at greatest risk of nitrate loss, drained clay soils may also present considerable risk, especially for loss of surface-applied N.

Much depends on whether the nitrate is held in the soil matrix and, therefore, protected to some extent from leaching, or whether the nitrate is able to quickly move down cracks, fissures or macropores within the soil, or to the drains. Thus, the connectivity between soil surface and the drains will be an important factor.

The mechanism for drainage through structureless soils is relatively straightforward: water drains downward through the soil with a uniform wetting front, carrying nitrate in the soil profile downwards and towards the groundwater. This process can be described as 'piston flow' - rainfall pushing water and nitrate further down the soil, resulting in generally smooth nitrate leaching curves. Such soils are suitable for sampling with porous cups (Webster et al, 1993).

However, the mechanism for nitrate movement to surface waters is less certain (Armstrong et a/, 1999). In heavier textured, structured soils (clays and loams), water generally moves laterally, either across the surface ('surface runoff') or through the soil surface layers through to cracks, channels (and, ultimately, drains, if installed) - 'soil water drainage'. Importantly, this movement through eg root/worm channels, soil cracks or large pores ('macropore flow') can result in rapid water flow through soils that would at first be considered impermeable. This rapid water flow can occur either when the soil is fully wetted up, but also when the bulk of the soil is dry - then known as 'bypass flow'. Thus, water (and nitrate) movement through clay soils can occur as:

• Rapid movement through cracks, macropores etc (bypass flow) • Slow movement through the bulk of the soil

50 The concentration of nitrate in the drainage water (ie how much N is leached) will depend on how much contact the water has with sources of nitrate. For example, if most of the soil nitrate is held within the bulk of the soil, water moving rapidly through cracks, so not mixing with the soil, will be low in N. However if, for example, heavy rain falls after a recent fertiliser or manure application, water can pick up N before transferring to cracks.

The importance of this mechanism cannot be overstated. Structured soils can be considered retentive of N when the nitrate is protected in the bulk of the soil and only moves downwards with slowly mobile water. However, if rapidly moving water (bypass flow) has access to substantial N (eg N at the soil surface), then losses will increase.

The contribution of surface run-off to N losses varies depending on the susceptibility of that soil to water loss across the surface, but is generally small compared with drainage losses.

The aim of this work was to measure the effects of SRC on water quantity and quality draining from the soils.

6.2 Materials and methods

Three sites were monitored to assess water quality, primarily nitrate concentrations, draining from SRC plantations during their first harvest cycle:

• Retford, Nottinghamshire, OS SK 713 824, an 8ha clay site. • Barnby Moor, Nottinghamshire, OS SK 670 875, a 7.5ha sandy site. • Gainsborough, Lincolnshire, OS SK 823 942, a 12.9ha sandy site where sewage sludge was added as a fertiliser.

The sampling instrumentation, 10 porous cup suction samplers (Webster et al, 1993), was installed at Barnby Moor in February 2000. Samples were taken on four occasions (all pre-planting) when it was estimated that drainage through the soil profile was occurring. Following planting the instrumentation was checked to ensure that samples were taken close to the root zone.

The installation of porous cup samplers at Gainsborough was delayed pending the finalising of contracts between the landowner and ARBRE. Due to these delays the samplers had to be installed in early July after the site had been planted so there was no opportunity to obtain pre-planting soil-water nitrate data. At each site samples were taken at approximately 3-week intervals once the soil profile had wetted up in the autumn.

Porous cup samplers were not suitable for use on the Retford clay soil. Therefore a suitable field drain was selected for monitoring, using a tipping bucket flowmeter linked to a newlog datalogger with water sampling via an EPIC sampler. Due to the proximity of two heavily used footpaths to the proposed monitoring site, a metal

51 chamber was constructed to protect the tipping bucket flowmeter. The flowmeter and chamber were installed in March 2000, at which time a sample was taken for nitrate analysis with further background samples taken manually through the spring prior to planting. Following planting in late May, a fully automatic water sampler was installed on a field drain to take samples in proportion to drain flow. The tipping bucket flowmeter was replaced by a canister type weir flowmeter in February 2001, which was more suited to the flow rates experienced at the site during the first winter.

6.3 Results

6.3.1 Retford

Drainflow in the very wet April of 2000 amounted to 121.3mm, representing 83% of average rainfall for the month and over 70% of the expected annual drainage for this agro-climatic area. Drainflow continued at lower levels through most of May, totalling 19.6mm, 30% of average monthly rainfall. Nitrate-N concentrations through this period were in the range 25.7 to 38.1mg l-1 (mean 34.0mg l-1), giving a nitrate-N loss for April of 39.5kg ha" 1, a product of the exceptionally large April drainage. Nitrate-N loss and for May was 6.7kg ha -1.

The drain continued to flow until early summer 2000 although volumes were small in relation to rainfall. Nitrate-N concentrations were in the range 10.0-31.2mg l-1, the EC limit for nitrate-N being 11.3mg l-1 in potable water, whilst ammonium-N levels were below 0.3mg l-1. There was no drainflow during August and early September, but the return to field capacity during the very wet autumn period caused drainflow to start again in late September. During autumn and early winter, drainflow represented up to 82% of rainfall. Nitrate-N concentration during this period declined from a peak of 25.0mg l-1 in October to 3.6mg l-1 in late December whilst ammonium-N remained below 1.0mg l-1. Total nitrate-N loss was greatest in October 2000, representing 61% of the total Sept 2000 to February 2001 losses of 24kg ha -1. Sample concentrations for the period are given in Table 29 and mean monthly concentrations and total losses for the period are given in Table 30.

The drain discharge rates seen at the site during winter 2000/01, with peak flows approaching 5L s-1, were higher than anticipated, in part due to the soil remaining close to field capacity for most of the time. At times the flow rates exceeded the capacity of the installed tipping bucket flowmeter, which led to failure of the instrument in December 2000 and the consequent loss of drainflow data, although water samples continued to be taken. The tipping bucket was replaced by a canister type weir flowmeter in early February 2001, which was more suited to the sustained high drainflows experienced during that winter.

With the advent of FMD in February 2001 all visits to the site were suspended in accordance with ADAS policy and no further monitoring was possible before the cessation of drainflow in spring 2001. When site visits resumed no drainflow was recorded until early February 2002, with only sporadic flow observed through to

52 early April, giving an estimated total drainflow of 30mm for the period. Nitrate-N values declined from a maximum of 3.1mg/L1 to 0.3mg/L1 during this period. Sample concentrations are given in Table 31. No flows were then recorded until November 2002.

Date sampled N03-N nh 4-n (mg I'1) (mg I'1) 07.06.2000 31.15 0.05 30.06.2000 21.40 0.33 18.07.2000 17.70 0.16 06.09.2000 9.75 0.45 19.09.2000 9.97 0.58 03.10.2000 24.85 0.73

12.10 0.12 20.10.2000 03.11.2000 5.03 * 09.11.2000 1.48 * 17.11.2000 5.97 * 29.11.2000 2.72 * 14.12.2000 3.12 0.22

0.10 21.12.2000 3.56

02.01.2001 3.88 0.24 26.01.2001 3.69 0.21 09.02.2001 3.59 0.08

20.02.2001 5.27 0.19

Table 29: Mean N03-N and NH4-N concentrations in drainage water, Retford 2000/01

Flow as Mean Mean Rain (% Drainflo Rainfall NO3-N nh 4-n % of N03-N nh 4-n long-term w (mm) (mm) (kg ha" 1) (kg ha' 1) rainfall (mg I"1) (mg I"1) mean) Jun 4.1 37.2 11 26.5 0.2 1.09 7.8 76 Jul 2.4 47.5 5 17.7 0.2 0.43 3.9 85 Aug 0 47.3 0 73 Sep 24.9 94.6 26 9.9 0.5 2.46 127.5 182 Oct 79.1 105.2 75 18.5 0.4 14.63 332.8 206 Nov 100.1 122.6 82 3.6 3.63 198

0.2 Dec 8 62.0 77.9 80 3.1 1.93 130.5 144

0.2 Jan 8 25.0 27.8 90 3.7 0.98 53.0 52

0.2 Feb 8 40.0 56.0 71 5.3 0.42 84.5 133

Table 30: Drainflow and nitrate loss at Retford during 2000/01

Estimated from Irriguide due to flowmeter failure

53 Date sampled N03-N nh 4-n (mg I"1) (mg I'1) 30.01.2002 0.91 0.09 08.02.2002 0.69 0.05

21.02.2002 1.33 0.23 11.03.2002 0.91 0.05 22.03.2002 0.38 0.05 25.03.2002 0.24 0.05 12.04.2002 0.43 0.35

Table 31: Mean N03-N and NH4-N concentrations in drainage water, Retford 2002

Following the onset of winter drainflow, automated samples were taken on 23 occasions between December 2002 and March 2003 when drainflow ceased. Analysis showed that concentrations of N03-N and NH4-N remained low at 0.1- 1.6mg/l (mean 0.37mg/l) and 0.1-1.9mg/l (mean 0.34mg/l) respectively (Table 32). There was no further recorded drainflow at Retford until sampling ceased in 2004.

Date sampled NO3-N nh 4-n (mg I'1) (mg I'1)

0.1 21.11.2002 0.17 03.12.2002 0.11 0.14 06.12.2002 0.13 0.13 18.12.2002 0.05 0.16 19.12.2002 0.21 0.23 23.12.2002 0.21 0.25 23.12.2002 0.1 0.05 24.12.2002 0.12 0.29 26.12.2002 1.18 1.43 07.01.2003 0.11 0.05 13.01.2003 1.62 0.05 16.01.2003 0.1 0.22 17.01.2003 0.65 0.54 18.01.2003 0.31 0.45 19.01.2003 0.14 0.31 20.01.2003 0.19 0.05 21.01.2003 0.59 1.98 29.01.2003 1.15 0.27 03.02.2003 0.05 0.49 05.02.2003 0.42 0.05 07.02.2003 0.55 0.05 08.02.2003 0.13 0.49 20.02.2003 0.05 0.05 04.03.2003 0.05 0.05 11.03.2003 0.05 0.05

Table 32: Mean N03-N and NH4-N concentrations in drainage water, Retford 2003

54 6.3.2 Barnbv Moor and Gainsborough Porous cup samplers were used at these two sites. They allow sampling of the soil drainage water, but do not provide an estimate of drainage amount (Lord & Shepherd, 1993): this has to be determined indirectly, commonly by using a water- balance model such as Irriguide (Bailey & Spackman, 1996). However, these models are unproven for SRC. For this reason, concentrations were not converted to loads of nitrate. Mean nitrate-N concentrations for the samples taken prior to planting at Barnby Moor are given in Table 33.______Sampling date Mean N03-N (mg I1) 24.02 2000 12.8 06.03.2000 21.8 06.04.2000 28.3 18.04.2000 23.3

Table 33: Mean nitrate-N concentrations, Barnby Moor 2000 The two sandy sites were sampled at approximately two-week intervals following the return to field capacity, estimated from Irriguide, from late September 2000. At Barnby Moor, where no sewage sludge was applied, Nitrate-N concentrations declined from 11.4mg I1 to 0.9mg I1 between September 2000 and January 2001 (Table 34 and Figure 18). In contrast, concentrations at Gainsborough were much higher although still comparable to those from arable sites, peaking at over 85mg 11 in late November 2000 (Table 34 and Figure 19). It was assumed that these high values were as a result of sewage sludge application to this site.

Barnby Moor Gainsborough Barnby Moor Gainsborough Mean N03-N Mean N03-N Mean NH4-N Mean NH4-N Date sampled (mg I"1) (mg I'1) (mg I"1) (mg I"1)

21.09.2000 11.4 31.96 1.9 40.26 03.10.2000 9.3 43.83 *

6.8 20.10.2000 48.08 1.5 26.9 03.11.2000 5.7 67.53 * * 17.11.2000 3.4 81.87 * * 29.11.2000 2.2 85.59 * * * * 12.12.2000 1.7 71.42

1.2 21.6 02.01.2001 0.9 76.55 26.01.2001 1.3 80.23 1.1 22.1 05.02.2001 1.1 75.46 0.5 22.7

1.6 0.8 22 02.2001 61.18 18.6

Table 34: Mean N03-N and NH4-N concentrations in drainage water, Barnby Moor and Gainsborough 2000/01

55 As at Retford, all monitoring was suspended during the FMD outbreak.

NH3-N NH4-N =■ 20.0

o 10.0

Jan-00 Mar-00 May-00 Jun-00 Aug-00 Oct-OO Nov-00 Jan-01 Feb-01 Apr-01

Figure 18: Mean N03-N and NH4-N concentrations (mg I"1) at Barnby Moor, 2000/01

N03-N NH4-N

=■ 60

« 50

o 30

Sep-00 Oct-OO Oct-OO Nov-00 Nov-00 Dec-00 Jan-01 Jan-01 Feb-01 Mar-01

Figure 19: Mean NOs-N and NFI4-N concentrations (mg I1) at Gainsborough, 2000/01

56 Samples were obtained from the two sites from October 2001, the results given in Table 35 and Figures 20 and 21.

Barnby Moor Gainsborough Barnby Moor Gainsborough Mean N03-N Mean NOa-N Mean NH4-N Mean NH4-N Date sampled (mg I"1) (mg I'1) (mg I"1) (mg I"1)

09.10.2001 0.36 33.47 1.48 56.7

22.10.2001 0.52 59.98 2.87 46.11 08.11.2001 0.15 58.69 28.11.2001 0.40 61.63 1.225 37.33

20.12.2001 0.17 125.24 0.454 27.04 07.01.2002 0.29 92.54 1.158 28.61 29.01.2002 0.37 147.96 19.02.2002 0.46 165.7 0.593 28.6 23.03.2002 0.3 175.61 0.291 24.85

Table 35: Mean N03-N and NH4-N concentrations in drainage water, Barnby Moor and Gainsborough, 2001/02

N03-N NH4-N

Sep-01 Nov-01 Dec-01 Feb-02 Apr-02

Figure 20: Mean NOs-N and NH4-N concentrations at Barnby Moor, 2001/02

57 200.0 ♦ N03-N NH4-N 150.0

100.0

Sep-01 Nov-01 Dec-01 Feb-02 Apr-02

Figure 21: Mean N03-N and NH4-N concentrations at Gainsborough, 2001/02

The soil suction samplers were re instated in October 2002 with samples collected on 8 occasions up to March 2003 at approximately three-week intervals, after which an increasing soil moisture deficit led to the suspension of sampling for the winter. Results are given in Table 35 and Figures 22 and 23.

Barnby Moor Gainsborough Barnby Moor Gainsborough Mean NG3-N Mean N03-N Mean NH4-N Mean NH4-N Date sampled (mg I"1) (mg I'1) (mg I"1) (mg I"1)

22.10.2002 0.99 76.9 3.59 74.9 07.11.2002 0.28 98.2 0.94 74.7

21.11.2002 0.37 152.2 0.52 49.7 06.12.2002 0.53 125.5 0.81 53.9 18.12.2002 0.60 247.9 0.81 41.1 13.01.2003 0.71 216.3 1.04 38.0 03.02.2003 0.73 187.7 1.69 31.3 11.03.2003 0.73 217.0 1.20 28.5

Table 36: Mean N03-N and NH4-N concentrations in drainage water at Barnby Moor and Gainsborough, 2002/03

58 4.0

N03-N NH4-N

Sep-02 Oct-02 Nov-02 Dec-02 Jan-03 Feb-03 Mar-03 Apr-03

Figure 22: Mean N03-N and NH4-N concentrations at Barnby Moor 2002/03

300.0

N03-N 250.0 NH4-N

200.0

150.0

100.0

Sep-02 Oct-02 Nov-02 Dec-02 Jan-03 Feb-03 Mar-03 Apr-03

Figure 23: Mean N03-N and NH4-N concentrations at Gainsborough, 2002/03

59 The samplers were re instated in November 2003 with samples from Barnby Moor collected on 8 occasions to March 2004 at approximately three-weekly intervals. Gainsborough samples were collected on 6 occasions, the 6th approximately 2 weeks after harvest. Samples were taken again at Gainsborough on the 8 th sampling occasions for comparison, however only 3 suction samplers could be sampled as slurry had recently been spread. An increasing soil moisture deficit led to the suspension of sampling for the winter. Results are given in Table 36 and Figures 7 and 8.

Barnby Moor Gainsborough Barnby Moor Gainsborough Mean NOa-N Mean N03-N Mean NH4-N Mean NH4-N Date sampled (mg I"1) (mg I'1) (mg I"1) (mg I"1)

17.11.2003 1.1 83.5 2.1 58.1 01.12.2003 11.5 81.4 2.7 57.8 15.12.2003 14.0 86.7 1.4 56.6 05.01.2004 27.4 105.4 0.8 52.6 02.02.2004 32.1 155.6 0.5 41.2 01.03.2004 26.3 145.9 0.7 40.1 15.03.2004 27.2 * 0.7 * 29.03.2004 25.2 192.7 0.8 34.0

Table 37: Mean N03-N and NH4-N concentrations from drainage water at Barnby Moor and Gainsborough, 2003/04

NOS -N NH4-N

Nov-03 Dec-03 Jan-04 Feb-04 Mar-04

Figure 24: Mean N03-N and NH4-N concentrations at Barnby Moor, 2003/04

60 250 r N03-N NH4-N

S 150

c 100

Nov-03 Dec-03 Jan-04 Feb-04 Mar-04

Figure 25: Mean N03-N and NH4-N concentrations at Gainsborough, 2003/04

6.4 Discussion

At the clay soil site, Retford, water quality monitoring commenced during the very wet spring of 2000 with drainflow extending into the summer months. During this period nitrate-N concentrations declined from an initial peak of 31 mg I1 to around 10mg 11 by the summer. Although these concentrations were generally in excess of the EC limit for potable water, 11.3mg I1, they were in the range that has been measured at other arable sites on similar soils across the UK (Goulding, 2000). However, nitrate-N concentrations continued to decline rapidly in the winter following establishment of the SRC, to around 4mg I1 by February 2001. During this period the recovery of winter rainfall via the drainage system was in the order of 80%, typical for clay soils and suggesting little overall effect in terms of water interception from the crop. No monitoring was possible during the FMD outbreak of 2001 (February to September 2001). When monitoring resumed during winter 2001/02 drainage volumes were much reduced compared to the first winter of monitoring, representing only a small percentage of the winter rainfall. This trend continued with a complete lack of drainflow during the final winter of monitoring (2003/04), suggesting the SRC was utilising a large proportion of the excess winter rainfall by this stage in the harvest cycle. However, the effect of any root penetration on the integrity of the drainage system is not known.

Nitrate-N concentrations in the drainage water during the second and third years after planting continued to decline, and were generally below 1mg 11 by winter 2002. This is much lower than would be expected from arable land and similar to values measured in MAFF's Nitrate Sensitive Area scheme when land was converted to nil- fertilised grassland (Lord et a!, 1999). These concentrations were also 30 times

61 lower than those recorded at the start of the study and a factor of ten lower than the EC limit for potable water.

Initial soil water nitrate-N concentrations at the two sandy sites, Barnby Moor and Gainsborough, were similar and in the range 20-30mg l-1. At Barnby Moor concentrations declined rapidly in the first year following planting to around 1mg l-1 by spring 2001, and remaining at <1mg l-1 throughout the following two winters. In contrast, nitrate-N concentrations in sampled soil water at Gainsborough, where slurry had been applied, increased through the first autumn peaking at over 80mg l-1 in November 2000. The pattern was repeated in the following two winters with peaks of 176mg l-1 and 248mg l-1 respectively, although by this stage in the cycle the SRC rooting depth may well have extended well below the depth of sampling. This may have resulted in the samples being obtained from a relatively wet soil horizon compared with conditions at depth.

A mature SRC plantation, ie after establishment, will have a dense, widespread root system and this, combined with a long growing season, enables the crop to efficiently utilise nutrients (Defra, 2002; Tubby & Armstrong, 1992).

Research, in the UK and areas of Scandinavia with similar growing conditions, has shown that the uptake of available nitrogen by SRC is very effective and, consequently, nitrate leaching is much lower than that from fertilised grassland or arable land (Defra, 2002). The data from this project generally confirms this.

However, nitrate leaching has been recorded in the following situations:

• After green cover removal in the land preparation phase • During the establishment year where nitrogen has been applied as fertiliser • After final removal of the crop.

Again, this project confirmed these results by demonstrating greater leaching losses in the establishment year.

Defra give the following guidelines re fertiliser applications:

Digested, i.e. treated, sewage sludge can be applied to SRC as a fertiliser if it is considered feasible by the local Water Company under UK sludge regulations and their own guidelines. Accurate nutrient requirements of the crop are still under research but where treated sewage sludge has been applied the subjective view of growers is that it is beneficial. Under the Code of Good Agricultural Practice for the Protection of Water (COGAP 1998), no more than 250kg organic nitrogen/ha/year can be applied to agricultural land. Willow SRC has a low demand for nitrogen (N) and the current UK recommendations for application are 40, 60 and 100kg N/ha/yr for the 1st (i.e. after cutback), 2nd and 3d years of the harvest cycle respectively (Johnson P. 1999). Where the soil has high residual N levels from previous cropping or a high soil organic matter level, these rates should be reduced. No fertiliser should be applied

62 during the establishment year, i.e. from planting until after the post-cutback herbicide application has had time to be effective.

The number of sites and treatments within this project was limited and it is, therefore, not possible to provide a detailed analysis of this rationale. However, we can conclude that under normal commercial management, leaching losses tend to be small. The one exception to this was the Gainsborough site that received sludge applications. Here, nitrate concentrations were large and it may be that the nutrient requirements of the crop were exceeded by these applications. This stresses the need to match N inputs to crop requirements.

63 7 WATER QUALITY OF RUNOFF FROM WOOD STORES

7.1 Introduction

ARBRE were originally expecting to harvest SRC in the form of whole rods or stems, which would have been bundled, stored for initial drying and then chipped prior to delivery to the power plant. After unsuccessful trials with an imported prototype whole-rod harvester/bundler, ARBRE decided to investigate the possibility of developing their own UK whole-rod harvester/bundler. Realisation that this would prove technically difficult as well as costly and that it might also not be the most efficient method of harvesting led to the decision to trial direct-chip harvesting. This proved relatively successful with the prototype SRC headers available at the time.

For this project it was initially expected that runoff would be monitored from stores of bundled whole rods but, due to the change in harvesting method, runoff was monitored from stored wood chips.

Runoff was monitored from both stored chipped SRC and stored forest residues to measure the volume, colour and composition of the drainage effluent (nitrate and biological oxygen demand only) in order to assess any direct environmental inputs from such stores.

7.2 Materials and methods

After inspection of various sites it was decided to carry out the runoff studies on material stored at ADAS Gleadthorpe, Nottinghamshire as the site provided security for the sampling equipment and also allowed construction of a purpose built concrete storage base.

The facility to monitor leaching from SRC stores was established at ADAS Gleadthorpe in December 1999. The installation consisted of a 35m2 concrete apron with a two-course breeze-block retaining wall around the perimeter. The concrete was graded to fall both towards the front wall of the apron and to a central gutter, outfalling to pipework leading to a monitoring chamber downslope of the installation. A tipping bucket flow recorder and newlog datalogger were installed within the monitoring chamber. A metal grid covered the gutter to prevent blockage.

20 tonnes of chipped forest residues were weighed in to the test facility in December 1999, representing the highest pile that could be established without breaching the retaining walls. In early January 2000 an EPIC automatic water sampler was installed to take flow-proportional samples of runoff.

7.3 Results

Heavy rainfall (35mm) during late December 1999 resulted in 15mm of runoff from the stored material and a manual sample was taken for nitrate analysis. The result of

64 the single sample analysis gave a nitrate-N concentration of 0.6mg l-1. This sample was moderately coloured (1=clear, 2=slight colour, 3=moderate colour, 4=strongly coloured).

The period to the end of March 2000 was relatively dry with no runoff recorded. April was much wetter with total rainfall for the month of 145mm, with over 50mm falling during the first three days of the month. This intense period of rainfall resulted in 28mm (980 litres) of runoff from the store. Concentrations of nitrate-N in the runoff from this event were in the range 0.72-1.45mg l-1 (the EC limit for potable water being 11.3mg l-1 nitrate-N), and ammonium-N 0.34-0.77mg l-1. Samples were observed to be slightly coloured. Analysis of the leachate for biochemical oxygen demand (BOD) gave a concentration of 16mg l-1.

In response to 13mm of rainfall in mid-April 2000, 5mm of runoff was recorded from the store. Nutrient concentrations were similar to the previous event although the water collected was observed to be moderately coloured. There was insufficient sample volume for submission for BOD analysis. Flow continued at a low level until the end of April giving a total runoff for the month of 63mm representing 44% of the monthly rainfall figure. As the store was located on a concrete pad this indicates significant water uptake by the chipped material. Concentrations of nitrate-N in samples taken towards the end of the month showed a decline to 0.28mg l-1 and ammonium-N to 0.18mg l-1. No further runoff was recorded although May continued relatively wet with individual rainfall events of up to 20mm.

No runoff was recorded from the forestry residue store over the summer in 2000. Outflow started again in September suggesting that the store wetted up quickly in response to the very wet autumn in which nearly double the long-term mean rainfall fell during the period September to November. The high proportion of rainfall recovered as runoff (up to 80% in November) indicated that the store remained close to saturation throughout this period with little capacity for water uptake by the stored material. Monthly rainfall was closer to the average value during late winter and spring 2001, allowing some drying of the store and resulting in runoff occurring in only the larger rainfall events during this period. The proportion of rainfall recovered as runoff declined to 30% in March and April 2001 and runoff had ceased completely by the end of May 2001.

Nitrate concentration in the runoff water from the store remained low throughout the year with a maximum of 5.57mg l-1 for nitrate-N and 2.67mg l-1 for ammonium-N. These values were much lower than the EC drinking water limit of 11.3mg l-1 for nitrate-N. Total nitrate loss amounted to 11.3g and 6.0g for N03-N and NH4-N respectively.

BOD levels peaked in October 2000 at 30mg l-1 and again in January 2001 at 20mg l-1 before decreasing to 11 mg l-1 in April 2001. The runoff water remained strongly coloured throughout the period suggesting considerable leaching of tannin.

65 Samples were taken during October 2001 totalling 31mm, in response to 93mm of rainfall for the month. Maximum Nitrate-N values were 4.18mg/L 1. Sample colour was 4 (highly coloured) in all cases. Much drier conditions between October and January 2002 resulted in very little runoff.

From late January 2002 to the cessation of outflow in mid-March 2002 total runoff was 77mm compared to a rainfall total of 132mm for the same period. Nitrate-N values declined from a maximum of 2.7mg/L1 in mid-February to 0.58mg/L 1 by the time runoff ceased in March. Sample colour remained at 3 throughout January to March. BOD results for samples obtained in February gave values between 4 and 7mg I"1.

~ 0 E

"ro K 40

Figure 26: Runoff and nutrient concentration from stored forest residues, 2000/01

66 Runoff Runoff Rainfall Runoff Mean Mean NO3-N NH4-N (litres) (mm) (mm) as N03-N NH4-N load g load g % rain (mg I'1) (mg I"1) Jun 00 0 0 37 0 Jul 00 0 0 49 0 Aug 00 0 0 47 0 Sep 00 800 9 235 95 24 0.53 1.09 0.42 0.87 Oct 00 2560 73 105 70 2.45 1.19 6.27 3.05 Nov 00 3435 98 123 80 0.66 0.46 2.27 1.58 Dec 00 1935 55 78 71 0.57 0.20 1.10 0.39 Jan 01 230 67 28 24 0.54 0.17 0.12 0.04 Feb 01 720 21 56 37 0.37 0.05 0.27 0.04 Mar 01 390 11 38 30 0.57 0 0.22 0 Apr 01 560 16 53 30 0.58 0 0.32 0 May 01 140 4 38 11 0.53 0 0.07 0 Jun 01 0 0 24 0 0

Table 38: Runoff and mean nutrient concentrations from stored forest residues, 2000/01

rr 3 ------mm

♦ N03-N 2.5 ■ NH4-N O) E

1.5 .2

c o0) c o 0.5 O

Oct-01 Nov-01 Jan-02 Mar-02 Apr-02 Jun-02 Aug-02

Figure 27: Runoff and nutrient concentration from stored forest residues, 2001/02

9 Part estimated from Irriguide due to data logger failure

67 Mean BOD Colour (mg I'1) index 10 Sept 00 11 5 Oct 00 30 4 Nov 00 16 5 Dec 00 13 5 Jan 01 20 4 Feb 01 13.5 4 Mar 01 3 3 Apr 01 11 5 May 01 No sample 4

Table 39: Mean BOD and coloration of runoff from forestry residue store, 2000/0

The store was emptied in May 2002 and the forest residues replaced with willow chips.

Following the change in stored material from forest residue to willow chips in May 2002, some runoff was recorded during heavy rainfall in late summer 2002 (Figure 27). N03-N and NH4-N concentrations reached a maximum of 0.6 and 0.3mg I1 respectively.

Figure 28: Runoff and nutrient concentration from stored willow chips, 2002/03

10 1 =clear; 2=slight colour (weak tea); 3=moderate colour; 4=hIghly coloured (strong tea); 5=very highly coloured.

68 More sustained runoff occurred from late October 2002 to the end of January 2003 with similar N03-N and NH4-N concentrations up to 2.6mg l-1 (mean 0.34mg l-1 NO3-N) and 0.7mg l-1 (mean 0.13mg l-1 NH4-N). BOD values were in the range 4-94mg l-1 (mean 34mg l-1) over the same period. During the dry spring very little runoff was recorded with the last samples taken in March 2003. Over the October 2002 to March 2003 period approximately 80% of rainfall (total 361mm) was recovered as runoff from the store. The colour of the leachate was variable ranging from 2 to 4 depending on the volume of runoff.

7.4 Discussion

Despite the relatively high colouration, the BOD values were low in comparison with agricultural effluent like manure slurry (10,000-30,000mg-1), raw domestic sewage (300-400mg-1) or treated domestic sewage (20-60mg-1). These values are unlikely to cause problems provided some dilution occurs before any discharge to a watercourse. It would however be necessary to obtain Discharge Consent from the Environment Agency if this disposal route was chosen and specific conditions would apply to individual stores.

During the monitoring period, runoff from the uncovered store occurred mainly during the winter months (October to March), when evaporation losses were expected to be low and rainfall volumes often exceeded the water holding capacity of the stored material. Recorded runoff over the winter months averaged 80% of rainfall and peak runoff often equalled peak rainfall. There were no apparent differences in the runoff patterns observed from the two types of stored material monitored. Nitrate-N concentrations in runoff water were consistently low during the entire monitoring period, within the range 0.5 to 5.6mg l-1 (EC limit for potable water = 11.6mg l-1), with the highest values recorded in low volumes of runoff, especially during the autumn when there had been dry conditions in preceding months. Again, no differences in Nitrate-N concentrations between the two types of stored material could be distinguished. The colour of the runoff from the store varied between virtually clear following extended runoff events, to strongly coloured in low to moderate runoff following dry periods. There was no analysis in this study to determine the chemical source of the colouration observed. BOD levels over the monitoring period were also relatively low, varying from 4 to 94mg l-1. The processes influencing this variation were not apparent from the parameters monitored.

From evaluation of this limited set of determinants it seems unlikely that effluent from wood stores on hard standing would make any significant contribution to environmental nutrient levels. Good practice should dictate that action is taken to prevent effluent directly entering surface waters (Defra, 1998) although it is likely that dilution effects would reduce any contaminants to below detection levels.

69 8 SOIL CARBON AND FERTILITY CHANGES

8.1 Introduction

Although biomass-fuelled power generation should be carbon neutral, recycling the CO2 fixed via photosynthesis as equivalent CO2 emissions from combustion there is scope for an accumulation of carbon in the soil through roots and undecayed organic matter. This was assessed through soil carbon measurements when SRC was established and after 4 years.

The objective of this work was to measure any detectable change in the soil organic carbon content of SRC sites from planting to harvesting 4 years later. Changes in the soil nutrient status (primarily soil organic nitrogen content) were also monitored.

Carbon is cycled through soil by mineralization and immobilisation processes controlling the soil organic matter pool (SOM). The presence of a new SRC crop on a previously derelict or fallow site will effect the size of this pool by increasing inputs via above and below ground litter deposits (leaves and roots) and possibly by enhancing the mineralization of the previous SOM pool seen as increased soil respiration.

It is unclear whether there was a net gain in sequestered soil organic carbon over the study period due to the SRC inputs or whether inputs and soil respiration were in equilibrium.

8.2 Materials and methods

8.2.1 Sites

Two sites were chosen for study, one a predominantly clay material site and the other a sandier material site. Neither site had sewage sludge or other form of fertiliser applied.

The sites chosen were:

• Retford, Nottinghamshire, OSR SK 713 824, an 8ha clay site. • Barnby Moor, Nottinghamshire, OSR SK 670 875, a 7.5ha sandy site.

Both sites were planted in May 2000 at a density of 15,000 18cm willow cuttings/ha.

8.2.2 Soil sampling

Sampling of the soil at each site was by means of cores taken at successive depths to 0.9m. Both sites were initially sampled in April 2000, prior to planting with the second sampling due in April 2004 after the site had been harvested. Harvesting was delayed however until December 2004 so sampling was actually carried out within the crop in November 2004.

70 Each site was divided into four approximately equal sized sectors and three soil cores were taken at random by auger from each sector, ie 12 cores from each site. Cores were taken at depths of 0-15, 15-30, 30-60 and 60-90cm. The cores from each depth were bulked together within each sector so four samples were obtained for each site. Samples were analysed for total organic carbon and nitrogen and the samples from 0-15cm depth were also analysed for pH, P, K and Mg concentrations on both occasions, though all depths were analysed at the start of the project in 2000.

Sub-samples of each core were taken and bulked within each sector for depths 0-30 and 30-60cm for particle size analysis. Bulk density measurements were also made on each site in the 0-15cm layer by the "soil replacement " method. The particle size distribution measurements were taken in 2000 whilst the bulk density in the surface layer was measured in both 2000 and 2004.

In November 2004, after the crop had developed a standing litter layer, this layer was also sampled to measure the semi permanent pool of carbon that it constitutes. At the twelve locations core-sampled, a quadrat of 0.528m 2 was laid on the ground surface and all the litter within the area sampled. The samples were weighed after being dried at 80°C to constant weight.

8.3 Results

Basic fertility was measured across the whole of each site for non-nitrogen and carbon nutrients, pH and texture. These are shown in Table 40 and demonstrate that both sites were originally neutral and reasonably fertile for divalent cations with a magnesium index of 6 throughout. Available potassium was low with an index of 1 for both sites in the topsoil and Retford in the subsoil but 0 for Barnby Moor subsoil. Both sites were deficient in phosphorus (P index = 0) at all depths.

Depth Site Texture PH P K Mg interval mg/L mg/L mg/L cm Wq) Wq) (fxq/q) Barnby Moor 0-15 CL 6.9 8 79 490 15-30 " 6.7 9 74 475 30-60 SL 7.1 2 46 394 60-90 SL 7.2 3 40 245 Retford 0-15 CL 6.7 10 71 323 15-30 " 6.5 8 95 319 30-60 CL 7.1 4 83 446 60-90 ZC 7.6 2 95 701

Table 40: Basic soil fertility analysed for soil carbon dynamics over five years under new plantations of willow SRC

71 Nominally Barnby Moor was a "sandy" site whilst Retford was "clayey". However, the textural classification was Clay loam for both topsoils although Barnby Moor was a Sandy loam in the sub-soil and Retford a Silty loam. The change in basic fertility over 4.5 years was measured in the surface 0-15cm at both sites and the change in chemical parameters is shown below in Table 41. At Barnby Moor there was no appreciable difference over 4.5 years, whilst at Retford there were marginal reductions in P and Mg recorded plus slight acidification.

Depth Sampling "

Site PH K Mg interval date =d i E

mg/L mg/L cm B Wg) Wg) Barnby Moor 0-15 Apr. 2000 6.9 8 79 490 0-15 Nov. 2004 7.0 8 90 402 Retford 0-15 Apr. 2000 6.7 10 71 323 0-15 Nov. 2004 6.4 5 89 271

Table 41: Basic soil fertility in topsoil analysed for soil carbon dynamics at planting of SRC and at first harvest after 4.5 years

The total organic carbon and nitrogen profiles of the sites in April 2000 are given below in Table 42 for Barnby Moor and Table 43 for Retford and similarly in Tables 44 and 45 for samples taken in November 2004. Each site was divided into four sectors for sampling purposes though little variation was found between them at each site. At Barnby Moor, there was no appreciable difference in organic nitrogen concentrations, though sectors 1 and 2 were marginally lower in organic carbon below 15cm depth. Similarly at Retford no differences between sectors could be detected for organic nitrogen, though sector 3 had marginally lower organic carbon in the topsoil than the rest of the field. After 4.5 years the samples from 2004 indicated little spatial variation between sectors for either total N or C although sector 3 at Barnby Moor had marginally higher values for both in the topsoil.

C:N Depth interval N c ratio cm %g/g %g/g 0-15 0.38 (0.042) 4.13 (0.569) 10.7 (0.22) 15-30 0.35 (0.047) 3.86 (0.592) 11.2 (0.22) 30-60 0.08 (0.018) 1.06 (0.313) 13.2 (2.97) 60-90 0.06 (0.007) 0.64 (0.165) 9.7 (1.38)

Table 42: Soil total organic carbon and nitrogen concentrations (% g/g) at Barnby Moor, April 2000 (SEs in parentheses, n=4)

72 C:N Depth interval N c ratio cm %q/q %q/q 0-15 0.21 (0.011) 2.22 (0.188) 10.2 (0.74) 15-30 0.21 (0.010) 2.12 (0.123) 10.2 (0.22) 30-60 0.07 (0.005) 0.68 (0.052) 9.5 (0.75) 60-90 | 0.05 (0.004) 0.38 (0.047) 7.7 (0.82)

Table 43: Soil total organic carbon and nitrogen concentrations (% g/g) at Retford, April 2000 (SEs in parentheses, n=4). The "sandy" site (Barnby Moor, Table 42) proved to have noticeably higher organic matter levels than the "clay" site (Retford, Table 43) which is counter-intuitive as clay tends to exert a protective and retentive effect on organic matter in soil. These values increased marginally in two of the sectors but declined slightly in a third, so that overall the concentration of carbon cannot be said to have changed much in the topsoil over 4.5 years (Table 44). However, the site's history as grassland, which was ploughed out in the season prior to the initial sampling in 2000, explains the high original concentrations. Retford on the other hand was an ex-arable site which carried winter wheat in the preceding season and here topsoil carbon concentrations hardly changed during the first harvest cycle (Tables 43 and 45). The C:N ratios of the two sites were originally similar and fairly low, suggesting that neither had large quantities of organic matter incorporated before sampling and that both should mineralise nitrogen rather than immobilise any that may be added as fertiliser. The C:N ratios measured in 2004 in the subsoil of Retford site (Table 45), are unusually low and caused by unexpectedly high total N concentrations.

C:N Depth interval N c ratio cm % g/g % g/g 0-15 0.44 (0.041) 4.46 (0.351) 10.2 (0.22) 15-30 0.39 (0.042) 4.09 (0.466) 10.5 (0.25) 30-60 0.12 (0.011) 1.27 (0.120) 10.5 (0.43) 60-90 0.08 (0.004) 0.63 (0.032) 8 (0.61)

Table 44: Soil total organic carbon and nitrogen concentrations (% g/g) at Barnby Moor, November 2004 (SEs in parentheses, n=4)

C:N Depth interval N c ratio cm %q/q %g/g 0-15 0.22 (0.033) 2.40 (0.140) 11.5 (1.30) 15-30 0.19 (0.035) 2.28 (0.121) 13.5 (2.02) 30-60 0.17 (0.031) 0.82 (0.124) 5.2 (0.74) 60-90 0.16 (0.024) 0.48 (0.056) 3.5 (0.56)

Table 45: Soil total organic carbon and nitrogen concentrations (% g/g) at Retford, November 2004 (SEs in parentheses, n=4)

73 The values in Tables 42 to 45 are however total carbon concentrations. To calculate the total amount of carbon in the soil these have to be multiplied by the dry bulk density of material in each layer. These were measured in the surface 0-15cm layer as being 1.080 and 0.800kg L1 at Barnby Moor in 2000 and 2004 respectively and 1.406 and 1.285kg L1 at Retford again in 2000 and 2004. These same dry bulk densities were also assumed for the 15-30cm layer whilst the subsoil layers were assumed to be 1.33kg L1 which is a commonly adopted standard value for British soils.

Using the above dry bulk density values the distribution of soil organic carbon down the two site profiles was calculated as that displayed in Figure 29. This shows the much larger amount of carbon in the topsoil in 2000 due to incorporated grass residues at the Barnby Moor site. The total amounts of carbon in the soil over a 1m depth interval in 2000 amounted to 139t ha 1 at Retford and 205t ha 1 at Barnby Moor, 47 % more carbon in the ploughed-out grassland compared with the ex-arable site with annual cultivation. In 2004 the total amount of carbon in the surface 1m of soil had risen to 149t ha 1 at Retford but had fallen to 187t ha 1 at Barnby Moor.

In addition to changes in the soil organic carbon at both sites, there was a standing litter layer of 1.58t ha 1 (+ SE 0.066) dry matter at Barnby Moor and 1.43t ha 1 (+ SE 0.096) dry matter at Retford.

Surface

0.2m Soil depth 0.4m

_ Retford 2000

■ Retford 2004 0.6m ' Barnby Moor 2000 ■ ■ Barnby Moor 2004

0.8m

1.0m

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Amount of carbon in each soil layer (g/cm2)

Figure 29: Distribution of total organic carbon in the soil profile with depth down the rooting zone

74 8.4 Discussion

From the point of view of carbon dynamics the two sites started from very different situations. The ex-arable site at Retford was a relatively impoverished site for organic matter although it probably had the potential to retain much more carbon due to its clayey nature. The ex-grassland site at Barnby Moor however contained large amounts of carbon in the topsoil from incorporated low C:N ratio residues and the absence of annual cultivation. It was expected that the soil organic carbon levels at this site would progressively decline over the first season or two as the residues in the topsoil mineralised and when coppice leaf and root turnover were insufficient to appear below the very surface layer. In the second and third seasons both sites would have started to accumulate organic matter in the surface 30cm of soil from leaf and fine root turnover. There is evidence for this in the decline of bulk densities in the surface soil at both sites of the order of 0.2kg L-1. At the Retford site, which had been in tillage for many years the result was very little change in the total amount of carbon in the surface layers though the reduction in density had actually caused this to register as a slight decline (Figure 29). At Barnby Moor the combination of reduced density and mineralisation of grassland residues had caused an appreciable drop in the total amount of carbon stored in the topsoil layers (Figure 29).

An accumulation of soil carbon in the sub-soil was expected after several years once root penetration with depth was sufficient and indeed both sites displayed an increase in the total amount of carbon in the 30-60cm layer and also below this at Barnby Moor (Figure 29). This cannot be directly attributed to root turnover however, as it will also be allied to the changes in bulk density higher in the profile. Material that was relatively high in carbon and sampled as above 30cm depth in 2000 will be below 30cm depth from the surface data in 2004 and so contribute to that layer's carbon total.

The change in surface soil bulk density and inevitable re-adjustment of the surface data relative to previous depths in the soil provides a problem when assessing the relative merits of soil and crop treatments on carbon sequestration to soil. In these cases it is no use comparing the same depth of soil but rather a comparison should be made of the same amount of soil mineral material. To do this an adjustment must be made to the depth of material used for comparison at the second sampling occasion and certain assumptions must be made about the soil bulk density at intermediate depths in the soil. In this study it has been assumed that the 15-30cm layer has the same bulk density as that above which has been measured and that at all lower depths a universal mean bulk density of 1.33kg L-1 has been adopted. In this case the total amount of soil material sampled to 1m depth in April 2000 was 13,550t ha -1 at Retford and 12,550t ha -1 at Barnby Moor. To sample these amounts in 2004 would have required sampling to an extra 2.7 and 6.3cm depth below 1m in 2004 at Retford and Barnby Moor respectively. Assuming the carbon concentrations measured in the 60-90cm layer of soil in 2004 applied to this extra soil depth, then the actual amounts of total organic carbon in 2004 for Retford and Barnby Moor

75 were calculated as 151 and 193t ha 1 respectively for the same amount of soil that contained 139 and 205t ha 1 in 2000. These values are a closer approximation than those quoted earlier but the change does not overcome the loss of carbon at Barnby Moor site.

If the standing litter is also taken into account then the final changes in soil carbon "sequestration" for each site are those given in Table 46. Retford has sequestered an extra 13t ha 1 of carbon since 2000 whereas Barnby Moor has lost lit ha 1 in the same period under the same crop. In Table 46 the carbon concentration in litter material has been taken as 45%.

Carbon pool Barnby Moor Retford (Clay loam over sandy loam) (Clay loam over clay loam) 2000 205 139 2004 193 151 Soil organic carbon -11.73 +12.59 Standing litter + 0.71 + 0.64 Total -11.02 +13.23

Table 46: Change in soil related organic carbon pools under first willow SRC harvest cycle of 4.5 years (t ha 1)

8.5 Conclusions

The results are very instructive about the potential value of SRC biomass sites for carbon sequestration on-site over and above their value in substituting the carbon emissions from fossil fuels. This depends more on the past history of the sites and the possible alternative land uses and is less influenced by soil type. Considerable carbon sequestration was achieved at Retford, which had come out of tillage and would otherwise, presumably have remained in arable production. Conversely Barnby Moor, which had come out of mature pasture, lost almost the same amount of carbon that was gained on the arable site. The litter produced on both sites was comparable and so it can be assumed that production was also comparable and therefore that the carbon flux from the crop must have been similar. Barnby Moor began as the more fertile site of the two due to its grassland history with almost twice the nitrogen reserves in the topsoil as Retford. This differential was maintained through the first harvest cycle indicating that both sites could supply the crop requirements without detriment to site fertility. Nor was there any significant change in non-nitrogen site fertility.

This means that Barnby Moor must have actually mineralised at least 24t ha 1 carbon as C02 over the 4.5 years to arrive at the differential measured in 2004. It was expected that the large amount of soil carbon from ploughed-out pasture would decline over many years before reaching a new equilibrium and this was observed at Barnby Moor outweighing the carbon influx due to the willow crop. At Retford the soil was already at a post-grass equilibrium having been in tillage for many years. Here, a greater input of leaf litter from willow as opposed to cereal stubble

76 returns, coupled with the reduced oxidation of soil organic matter once cultivation has ceased, produced an immediate increase in soil carbon. This would be expected to continue until a new equilibrium balance between inputs and oxidation is again reached. By the end of the rotation, expected to be 25 years, both sites should have achieved equilibrium for both processes ie loss and sequestration. It would be interesting to see whether the final carbon store at Barnby Moor once again achieves that found under grass, or indeed surpasses it.

The success of SRC plantations depends very much on their long-term productivity and this can only be ensured if the sites chosen are fertile in the broadest sense. Although the carbon accumulation is likely to continue well after the end of the first harvest cycle, the results show the importance of planting SRC on good quality sites.

77 9 PERFORMANCE OF THE SRC PLANTATIONS

9.1 Introduction

The first commercial planting of SRC for the ARBRE plant began in 1996 with three farmland sites of 10ha, 11ha and 12ha in size being planted in North Yorkshire and Nottinghamshire. Uptake of further farm sites was slow with the majority of the coppice planted in 1997 and 1998 being on land owned by Yorkshire Water (approximately 73ha in total). After 1998, when construction of the ARBRE plant began, wheat prices were falling rapidly and the Establishment Grant for SRC within the ARBRE catchment area was increased from £400 to £1,000/ha, farmers' interest in growing the crop increased significantly. From 1999 to 2002 approximately 1,300ha of SRC were planted, virtually all on farmland within a 45-mile area. Site size ranged from 2 to 50ha planted in any one year although a number of farms established between 70 and 120ha over a 2 to 3-year period. A minimum site size of 5ha was set in 1999, increasing to 10ha in 2000 due to economies of scale. As sites were offered for SRC ARBRE assessed each one individually for suitability of the soils, ease of access for planting and harvesting machinery and also how the crop would fit into the local landscape. It was important to ensure that the crop would blend into its surroundings and not prove too obtrusive and also whether there was potential to block views from neighbouring properties or from important local vantage points.

Under the ARBRE scheme the growers were responsible for carrying out full land preparation prior to planting. ARBRE then provided the willow cuttings and established the crop on behalf of the growers using contractors and appropriate machinery for planting and cutback. ARBRE carried out the post-planting and post ­ cutback herbicide applications. ARBRE contractors applied remedial weed control, often required during the establishment year, using specialist machinery if required, but at the growers' cost. Harvesting was due to be carried out by ARBRE and was on some of the earlier sites but, due to the company's liquidation, harvesting and all of the associated costs became the responsibility of the growers. On-going management of the crop is also now the responsibility of the growers and this includes pest control, primarily willow beetles, and also post-harvest weed control, if necessary.

The purpose of this section of work was to record agronomic and operational inputs into the SRC plantations supplying the ARBRE plant in order to assess the energetic and economic efficiency of the fuel production and supply operation. At the inception of this monitoring project it was anticipated that detailed field records would be taken by ARBRE and that these might be used to aid diagnosis of yield expectation and yield reality and that these records would constitute the ARBRE chronicle. Specifically, it was anticipated that the chronicle would allow comment on plantation management and the efficacy of input management such as sewage sludge and fertiliser use versus nutrient balance, weed control and effects on the establishment of SRC, pest and disease incidence, epidemiology of diseases and the

78 need for control. The ARBRE chronicle was expected to be monitored during the first two seasons.

In 2000 the chronicle was considered to be at an advanced stage of development and a PC-based version was demonstrated in March of that year. Apart from one or two areas of potential refinement it was felt that it would provide sufficient information for crop performance monitoring. Unfortunately significant problems were then encountered during the design and operation of the chronicle database system and the networked version proved elusive. It was anticipated at the outset of the project that ADAS would receive electronic information that could be easily interrogated using Excel or similar software but this was not achieved. The information that was supplied was of limited use due to it being in report or printout format. At the time of the company liquidation all work was still outstanding due to the failure of ARBRE to set up a usable crop production record log.

9.2 Methods

Over 50 farmers or landowners were contracted to grow SRC for ARBRE prior to the liquidation of the company. In order to gather information in place of the chronicle over half of these growers were contacted for this project to obtain information on land preparation, establishment and management of their crop and 24 were prepared to provide information. The majority of the growers were able to provide details on land preparation but few had full details of the herbicides applied including the rate of herbicide applied during land preparation (carried out by the growers themselves). ARBRE had collected full details of each of the sites and held records on herbicide application rates and dates but, due to the liquidation, this information has not been available for this work.

The term ’site', in the context of this work, represents a discrete block of SRC established in one year so one farm may have a number of sites. The 24 growers who responded to this project have 49 sites between them, planted from 1996 to 2001.

9.3 Results

The information collected, shown in Table 47, includes:

9.3.1 Site details

These include site size, number of fields, land grade, soil type and previous land use. From the details available, the majority of sites were Grade 3 with six of Grade 2 and two of Grade 1. Previous land use was primarily arable with a varied range of crops grown from wheat, linseed and oil seed rape to potatoes, carrots and sugarbeet. A number of sites had previously been grassland used for sheep grazing. Reclaimed sites included ex-colliery spoil, sand and gravel workings and ex-landfill. Soil type also varied considerably ranging from sand over pulverised fuel ash (PFA) through sandy and clay loams to heavy clay with the poorest sites being on black peat.

79 A number of the early sites, from 1996 to 1998, were particularly poor in terms of soil quality, size, shape and access and were not well suited to commercial SRC production. Many were owned by Yorkshire Water and were used to ensure SRC establishment was going ahead, to gain experience in establishment techniques, to encourage the development of machinery and to allow potential growers to see the crop. From 1999, when farmland sites became available, size and quality of the sites began to improve considerably.

As sites improved so did the machinery used and the experience gained all of which led to a significant reduction in the cost of establishment per hectare. Costs of £3,500 ha -1 were recorded for some of the earliest sites with the major costs being cuttings, fencing and the use of specialist contractors. Costs were down to approximately £1,500 ha -1 by 2001 due to ARBRE investing in their own planting machines, a reduced need for fencing, cuttings supply from two sources and the use of agricultural contractors.

9.3.2 Land preparation

Within Table 47 details are given of the herbicide applied during the land preparation phase including, where known, the application rate and date. In all but two cases glyphosate as Roundup was applied, the exceptions being the use of paraquat as Gramoxone and no herbicide application at all. At some sites weed control at land preparation was not effective and this led to significant problems during the establishment year and beyond despite remedial weed control being carried out after cutback.

Sludge incorporation, in the form of cake, prior to ploughing was recorded for 14 sites. Where records of application rates were held these were 205kg Nha -1 at 2 sites, 150t ha -1 at 2 sites, 300t ha -1at 2 reclaimed sand and gravel sites and 400t ha -1 at 1 reclaimed colliery spoil site. Vegetable and potato washings were applied in one case and food waste and paper pulp in another. Under the Waste Management (Licensing) Regulations 1994, organic wastes including sewage sludge, paper waste, dairy, food processing and abattoir wastes can be applied to agricultural land where there is a benefit in fertiliser input or soil conditioning and no risk of pollution to soil, air or water and provided the waste spread does not exceed 250t ha -1 in any 12 month period. Before these products can be applied to land however a risk assessment must ensure that the receiving land is suitable for application and the product is analysed for Potentially Toxic Elements (PTEs) to ensure no risk of contamination to soil, water or the food chain. Research carried out by SAC (Douglas, 2000) showed that the response of crops and soil to paper waste indicated that, although it provides a potentially beneficial increase in soil organic matter levels, paper waste is an inadequate supplier of nitrogen and also transforms available nitrogen in soils into unavailable forms. Paper wastes are composed mainly of poorly biodegradable cellulose and tend to have a low content of plant nutrients but also low PTEs and a low risk of pathogen contamination. Their use in

80 composting may be more beneficial when blended with organic materials containing a higher nitrogen content.

Details of the operations involved with land preparation such as sub-soiling, ploughing and power harrowing were recorded on Site Data Sheets (two examples provided in Appendix A). Virtually all of the sites were sprayed, ploughed and power-harrowed prior to planting. Six sites were sub-soiled and 4 of the reclaimed sand and gravel sites and the reclaimed colliery spoil site were deep-ripped either once or twice during land preparation. Establishment proved slow at a number of heavy clay sites, expected to some extent due to clay soils remaining cold for longer into the spring, but it was felt that compaction may also have led to some of the problem. From this experience, sub-soiling was recommended for all clay sites and for any sites where a plough pan may have been present.

All of the earlier sites were rabbit fenced in their entirety, at ARBRE's cost. As fencing costs proved to be one of the two highest components of the total establishment cost per hectare, the other being the cuttings, it was decided to assess each site for potential rabbit damage and fence accordingly. In most cases it was found that only certain sections of the SRC plantation boundary would require fencing eg where in close proximity to woodland, and this helped to reduce overall costs without detriment to the crop.

9.3.3 Establishment

The establishment section of Table 47 provides details of the date of planting followed by the post-planting herbicide applied. Planting always took place in spring and after initial planting trials in 1996, the standard method used was the Salix Maskiner 4-row Step Planter. Length of the cuttings was set at 20cm in 1996 but this was reduced to 18cm from 1998. Planting densities increased from 10,000 cuttings ha" 1 in 1996 to 12,000 in 1997 and 15,000 ha" 1 in 1998, staying at this rate for the remaining years of planting. The cuttings were planted in twin rows 0.75m apart with 1.5m between each pair of twinned rows and 0.59m between each cutting along the rows at the 15,000 ha -1 density. The sites were rolled immediately after planting to consolidate the soils.

Problems associated with planting were:

• Cuttings not being inserted where the soils were particularly stony or the planter mechanism being jammed with stones. • Contractors not following written instructions as to the required spacings between the rows. • Cuttings being pulled forwards virtually out of the soil, due to the speed of planting. It was expected that 8ha could be planted in a day where the ground was well prepared and when there were no machinery breakdowns. Planting of 10ha or more tended to indicate too high a speed and consequent poor cuttings insertion.

81 • Sections along rows with no cuttings where operatives had either not fed or misfed rods into the planter's mechanism.

Where poor planting was due to the latter two reasons, gapping up after cutback was to the contractor's cost.

The first sites in 1996 had up to 13 willow varieties planted, as the varieties were being trialed plus small areas of poplar, generally 0.5ha, to provide some visual diversity. Half of the poplar was treated as SRC and cutback during the first winter, the remainder was allowed to grow on as single stem crop. The cutback poplar tended to produce a maximum of only 3 stems and also appeared to revert to single stem over time. It proved highly unsuitable as an SRC crop. Other problems included the need to provide the planting material as cuttings rather than rods as each poplar cutting requires an apical bud. Modified cabbage planters were therefore needed for planting the poplar and, due to the ridged nature of the stems, the planting mechanisms frequently became blocked.

In 1997 6 willow varieties were planted in a random mix:

• Saiix viminalis Bowles hybrid • S. vim. Jorunn • S. vim. Jorr • S. vim. x schwerinii Bjorn • S. vim. Orm • S. vim. Ulv

In 1998 Bjorn was replaced by S. vim. x schweriniiTora. Although Bjorn produced relatively high yields, its tendency to produce bifurcated stems created problems for the willow nurseries trying to provide straight stems for planting therefore it was removed from production. Bowles hybrid, an old variety incorporated at low levels, usually at 5% or 10% of the mix, was no longer used from 2000. Bowles hybrid had been used due to its tendency to develop stem cankers which harbour a naturally occurring rust biocontrol agent, Sphaere/iopsis fiium (Morris et al, 1994). This fungus obtains nutrients from Melampsora spp. rusts and eventually kills them therefore it was advantageous to have Bowles hybrid within the planting mix. To a lesser extent, the varieties Jorr, Orm and Ulv are also prone to stem canker development so their presence in the mix made up for the removal of Bowles hybrid.

Tora remained the highest yielding variety for some years and made up 30% of the planting mix. S. vim. x burjatica Stott was introduced into the mix in 2001 although it gave cause for concern in the establishment year as it proved to be slow growing until year 2.

All bar one of the ARBRE plantations to 2001 were planted using a randomly mixed pattern, the exception being planted in single variety blocks. Although random planting was time consuming and therefore more expensive than block planting, as

82 the operatives had to mix the varieties prior to planting, it followed industry best practice in order to prevent pest and disease control (Royle, 1992; DTI, 1995; Pei et al, 1998; Tabbush et al, 2002). Intimately mixing the varieties at planting provides the basis for integrated control of rust and beetle damage within SRC by delaying the spread and development of both organisms (Peacock et al, 2001).

From 1999 ARBRE arranged cold storage of the cuttings prior to planting at a local agricultural cold store to reduce costs. Maintaining the temperature at -4oC proved difficult, probably due to the doors having to be opened regularly for the removal of other stored material, although it was usually held between -1 and -2oC. Dormancy was broken, shown by the development of roots at the base of the rods, for material that was held in store for some months prior to planting.

The standard combination of post-planting herbicides applied by ARBRE was 5L ha -1 pendimethalin (Stomp) with 2l ha -1 isoxaben (Flexidor), usually applied within 3-5 days of planting. Virtually all of the sites were sprayed with this herbicide mix. Five sites also had paraquat incorporated either at 2.5L or 3L ha -1 and one had chlorpyriphos (Dursban) added at 1.49L ha -1 to control leatherjackets. Three sites had mechanical weed control in the form of either dragging the site twice, on black peat or inter-row cultivation once each month for 3 months after planting on reclaimed sand and gravel.

Remedial weed control was quite often required during the establishment year and the herbicides used reflected the types of weed present. Records of the herbicides used were available for 23 of the sites:

• Gramoxone (paraquat) used at a rate of 4L ha -1 on 12 sites • Laser (cycloxydim) used at 4 sites either at 1L or 1.25L ha -1 • Kerb (propyzamide) used at 3 sites - no application rate available • Weedazol (amitrole) used at 1 site at a rate of 9L ha -1 • Aramo (tepraloxydim), Eagle (amidosulfuran), Shield (clorpyralid) and Falcon (propaquizafop - 1.5L ha -1) were all used at single sites - generally no application rates were available • Roundup (glyphosate) was spot-applied using a knapsack sprayer at 1 site at a rate of 4L ha -1

A hooded, inter-row sprayer was developed for the application of remedial herbicides that would otherwise cause significant damage to the growing willow. The only pesticide used at establishment was Dursban, generally applied with the post-planting herbicide on ex-grassland or long-term set-aside land for the control of leatherjackets.

No fertiliser was applied during the establishment year ie from planting to cutback.

Cutback was always carried out in the winter following planting, generally during January to March, ideally as near as possible to bud-break with the requirement that the cut was to be no higher than 10cm above ground level and that the stool should

83 be cleanly cut. After trialing a number of methods the most efficient machine for cutback was a modified grass reaper with reciprocating blades able to cut 2 rows at a time. Post-cutback weed control was a mix of amitrole (Weedazol) and simazine on the early sites. Due to Water Company concerns over the use of the simazine it was withdrawn from the ARBRE approved herbicide list in 1998 and Weedazol was used alone, generally at 10L ha -1 although reduced rates (6 and 7L ha -1) were applied at 3 sites. Application usually took place shortly before bud-break.

If any gapping-up was required due to missed cuttings, the cutback material was used. Each stem was cut to 1m lengths and these were pushed into the ground by hand where needed. The 1m length prevented the newly planted cutting from being out-competed by its stronger neighbours. The majority of the cutback stems were left on the ground and eventually rotted down.

Sewage sludge in the form of slurry was applied post-cutback to a number of sites within the Severn Trent Water Company catchment. A system for applying slurry to SRC was developed by one of the SRC growers and Severn Trent's contractors using an umbilical system and dribble bar designed to apply the slurry to the ground between the rows of growing willow. This prevented leaf scorch, which can happen if slurry contamination occurs. Slurry was usually applied during May and June so the crop could be up to 1m in height depending on the quality of both the soil and land preparation. Although slurry was applied to 13 sites, records of the application rates were only provided for 3, 123t ha -1 (185kg Nha -1) on two "standard" farmland sites and 500kg Nha -1 on a site previously used for sludge "disposal". Sludge pellets supplied by Anglian Water were applied at one site but no application rates were available.

Composted sludge cake (or TCSS - treated composted sewage sludge) was applied post-cutback to 8 sites within the Yorkshire Water Company catchment, a method which started in 2000. Standard agricultural spreaders with rear discharge and vertical beaters were used to give an even spread across approximately 10m. The use of this equipment meant that the sludge had to be applied over a crop of 50cm or less in height. The application rate was recorded as 616kg Nha -1. As sludge cake is 35-50% dry solids and the spread was evenly applied, no damage occurred to the crop.

Pesticides were generally applied to the more mature coppices where Chrysomelids or willow beetles had appeared. A variety of pesticides were used but Hallmark (lambda-cyhalothrin) was approved for use on SRC in August 2003, although with the restriction that it "must not be applied to willow later than the first year after harvest or planting". Edge spraying of the crop to control willow beetles, as recommended by the Game Conservancy Trust (Tucker & Sage, 1999), was the usual method of application, generally after the grower considered beetle numbers appeared to be reaching a critical level. On some sites however, spraying appears to have taken place as a "precautionary measure" and blanket spraying, which may be harmful to beneficial invertebrates and should be avoided, was carried out after harvesting at others.

84 Records of the pesticides used post-establishment were available for 22 of the sites:

• Hallmark applied at 0.1L ha -1 at 3 sites • Cypermethrin applied at 0.25L ha -1 at 8 sites • Dursban applied at 4 sites - no application rates available • Fury (zeta cypermethrin) applied at 5 sites - no application rates available • Decis (deltamethrin) applied at 2 sites - no application rates available

A number of the pesticides were applied on more than one occasion, either twice in the same season or annually over 2 or 3 years.

9.3.4 Weeds and pests

The growers were asked to provide a subjective assessment of the weed burden and pest damage within their SRC during both the establishment year and the first year of the harvest cycle ie the year after cutback. Scores were from 1 to 9 for both weeds and pests with 1 for bare soil or low pest levels to 9 for aggressive weed competition or severe pest damage. Rabbits and willow beetles were the specific pests scored and where other pests had occurred such as hares, deer, aphids, these were noted on the Site Data Sheets.

At the majority of sites where data have been supplied, the weed burden was scored at 5 or below for both the establishment and first year. Where the score was above this in the establishment year, the weed competition had usually been reduced by the first year after cutback due to remedial action with the exception of one or two sites where weeds remained a continuing problem. At two sites, where post ­ planting weed control was not carried out due to wet conditions, the grower tried mechanical weed control through the establishment year. Gramoxone was applied by the grower after cutback as a trial to reduce the cost of weed control but this proved ineffective as weeds in general and nettles in particular began to compete with the willow. Grazon was then used to overspray the sites but within 4 weeks the willow had been severely damaged to the extent that the sites had to be completely re-planted.

No mention was made by the growers of either the presence of rust or crop damage due to rust infestation on any of the willows. The small areas of poplar planted at some sites in 1996 and 1997, Populus trichocarpa x P. deltoides varieties Boelare and Beaupre proved highly susceptible to rust and are no longer recommended for inclusion in SRC plantations.

Rabbits did not prove too much of a problem at most sites. ARBRE policy initially was to rabbit fence the SRC sites in their entirety, the contractors being asked to use British Standard fencing and also to bury and turn out the fencing. Over time and due to cost, fencing requirements were assessed for each individual site so that fencing was erected only where necessary and this proved both satisfactory and cost effective. Two sites were scored at 7 and 9 for rabbit damage, both on sandy soils where burrowing under the fencing had proved easy and rabbit populations in the

85 vicinity were high. Hares and deer were recorded at a number of sites but no serious damage was mentioned, the latter actually proving beneficial at one black peat site where they were helping to control the high level of weed growth. Goose and sheep damage was recorded at two sites.

Willow beetles proved to be a significant pest at some sites whilst others suffered little or no damage with only low numbers of beetles being noted. From 2000 to 2004 the Game Conservancy Trust was carrying out extensive ecological monitoring of 12 of the ARBRE SRC plantations (Cunningham et al, 2004). The Blue willow beetle Phyllodecta vulgatissima formed a high proportion of the total number of invertebrates recorded during their work and was present at damaging levels, high enough "to result in economically significant yield losses" at half of the sites surveyed. The numbers of sites with damaging levels of willow beetles also increased over the four years.

Due to the life cycle and habits of willow beetles, the Game Conservancy Trust have recommended monitoring adult beetle numbers in early spring as they come out of hibernation and move into the edges of the coppices to feed. When numbers reach a level of 10 or more adult beetles shaken from the canopy onto 1m2 of ground, defoliation may prove damaging to crop production and this is the time that an appropriate pesticide should be applied (Sage & Tucker, 1998). The Game Conservancy Trust has estimated that 90% defoliation leads to approximately 40% reduction in yield. Edge spraying is the recommended technique, ideally killing the adults before they mate and move further into the crop. As previously mentioned a range of pesticides was used by the growers to attempt beetle control.

Aphids and leatherjackets were the other two invertebrate pests recorded although no significant damage was mentioned.

9.3.5 Harvesting

From the inception of the project the ARBRE SRCs were expected to be harvested as whole stems or rods, ideally collected into bundles or bales at harvest, then stored as bundles and chipped on farm prior to delivery to the power plant.

The first harvest trials were carried out in February 1997 on a 2.5ha Yorkshire Water sacrificial site 11 in Leeds, planted in 1993 with 5 old varieties of willow at a density of 16,000 cuttings ha -1and cutback in 1994. The machine used was the Danish tracked Hvidsted whole-rod harvester that produced loose rods which were off-loaded into heaps at the headlands. Unfortunately, due to narrow headlands of between 2 to 4m widths, it proved impossible to turn the harvester in places so many of the edge plants had to be cut manually using a chain saw. The growth habit of the old varieties ie few, thick, spreading stems, caused problems in two ways: the hydraulic pipes on the harvester became snagged and had to be repaired plus many of the lowest stems

11 Previously used by Water Companies for the disposal of treated sewage sludge normally destined for agriculture but which had been contaminated in some way and was therefore no longer suitable for application to farmland.

86 were left un-cut. The harvested rods were carried up an elevator and dropped onto the integral trailer where an operative attempted to catch the rods and stack them neatly, not easy as the work was carried out in force 6 winds. Once full, the harvester would travel to the headland and off-load the rods. Unfortunately, considerable amounts of wastage (not quantified) occurred as much material was left either un-cut or cut but left in the field having not passed up the elevator or fallen from the trailer. The Hvidsted did clean cut the stems generally at or below 10cm above ground level and created no ground damage. Further wastage occurred during collection of the stored rods.

Figure 30:The Mantis whole rod harvester, 2002 - developed from the Hvidsted harvester Approximately 3t of the harvested rods were round baled using the Bala Baler into 8 polo' bales of 1.2m diameter by 1.2m long with a hollow centre of 0.5m diameter due to poor bale construction. The remainder of the harvested rods were stacked in parallel layers in a heap measuring 3m wide by 13m long with a mean height of 1.5m. Monitoring of temperature, humidity, dry matter loss and moisture content began in March 1997and was carried out over the following 8 months using data loggers placed within the heap (Beale, 1998). The results showed that dry matter loss averaged 1.7% per month, similar to other reported work although moisture content, measured initially at 44% (4 weeks post-harvest), had only fallen to 41% at the end of the 8 month monitoring. Temperature readings within the heap and the bales remained similar to ambient temperatures with no heating recorded in any of the stored material. There were no visible signs of decomposition. The Hvidsted harvester was used to successfully cutback an 11 ha site in 1997. Due to the site being prone to severe flooding the grower was concerned that the cut stems left on the ground following normal cutback would be washed into the local river and possibly cause blockages further downstream. The stems were therefore collected by the Hvidsted harvester to prevent this from occurring. Also, as the

87 machine was tracked, no damage was done to the extremely wet soils during the work. The second harvest trials took place in December 1998 on a 2.5ha trial site planted in 1993 at a density of 8,000 cuttings ha 1 on Yorkshire Water sacrificial land near Harrogate. The site had been block planted with a number of old willow varieties and had been cutback early in 1994 so the harvest cycle prior to harvest was 5 years. The headlands, as at the Leeds site were again too narrow and, as the machine used was offset, it was necessary to cut a ride' through the coppice to allow the work to start. A number of plants had to be manually cut by chain saw due to the diameter of their stems. Virtually all of the variety Germany had to be left un-cut as the volume was too great for manual harvesting and it was felt that, due to the prostrate and spreading nature of its stems they would not be gathered by the Bundler's cutting head. The harvester was the Swedish Salix Maskiner Bundler, which worked by cutting the stems with a chain saw, feeding the rods up an elevator and onto a table where the rods were fed transversely into the bundling mechanism. Each bundle was wrapped, cut to length by a saw blade and dropped at the side of the machine. Harvesting was slow, as the machine had to stop each time a bundle needed to be cut and off-loaded. The bundles were 2m long by 0.6m diameter and wrapped in polypropylene mesh. Bundle weight was expected to be approximately 250kg but the average was 136kg with the highest weight being 248kg and the lowest 69kg. Occasionally, if the bundle was loosely formed and the wrapping insecure, the bundle would collapse during handling. The bundler produced a clean cut to the stools but could not consistently achieve a cut height below 10cm, as the cutting mechanism did not follow the ground contours. There was little or no ground damage within the plantation or on the headlands.

88 The bundles produced were used for storage trials over the twelve months following harvest. The trials were set up on open ground adjacent to the coppice; each bundle was weighed and placed in a triangular shaped stack, with six stacks in total and each stack consisting of 45 bundles. There was a gap of approximately 1m between each stack. Two stacks were placed on hardcore, one on terram and the remainder on grass, one of the latter being covered with a layer of bitumen coated paper. The trial aimed to assess loss of fresh weight and dry matter over time, changes in percentage dry matter over time, temperature within the bundles and any adverse effects of long ­ term storage. At two-monthly intervals, one of the stacks would be dismantled and readings, taken by dataloggers incorporated in the stacks, were recorded along with moisture content.

Average moisture content at the start of the trial was 54%, this reduced to 30% after five months and reached a low of 19% after seven months and remained constant to the end of the trial, a further five months. Dry matter content reduced by 9.3% over the 12-month storage period. No rapid rises in temperature were detected indicating that levels of microbial activity were low and there were few signs of decomposition of the bundles even after 12 months. No root or shoot formation occurred and there were no discernible benefits in storing on hard core or terram, nor in covering the bundles with bitumen coated paper (Beale & Morpeth, 2000).

Whole-rod harvesting proved extremely expensive as did the possibility of developing a UK whole-rod harvester and baler which ARBRE considered in 1999. Direct-chip harvesting was trialed in 2000, using a prototype tractor-mounted harvester and in 2001 a Claas Jaguar forage harvester fitted with a Claas header specifically designed for use on Swedish SRC. The machine chosen for the work in 2000 was the CRL chipper-harvester as ARBRE had had input into the header design in the form of the following requirements:

• The height of cut must be below 10cm • The stools must be cut cleanly and with no damage • All stems must be cut • No ground damage in the form of rutting or compaction within the plantation

The tractor-mounted CRL chipper-harvester, used to harvest an 11ha site in North Yorkshire, used two overlapping circular saws as the cutting device. Due to problems with flooding at the site and the wishes of the farmer the harvest took place very late, into May when the crop was in leaf. This created problems due to leaves blocking the harvester mechanisms. These operational difficulties experienced by the machinery due to late harvesting showed that considerably more power was required to deal with stems in leaf compared to those harvested in winter. The end- user may also experience potential difficulties with wood chips incorporating leaf material including higher moisture content, higher levels of fungal growth leading to more rapid deterioration and an increased percentage of fines. With gasification technology problems might be caused due to these fines being carried over into the process and larger quantities of ash being produced.

89 Figure 32:The CRL chipper-harvester, May 2000

As well as the presence of the leaves causing problems, the design of the plantation also created difficulties:

• Many of the headlands were too narrow for turning • Row spacings were non-standard and not consistent across the site • Old willow varieties had been planted in places as part of trials by the contractor

Following the 2000 trials CRL felt that the productivity of a tractor-based SRC harvester was too limited for industrial chip production and went onto develop an SRC header for use with forage harvesters. Despite the problems with the chipper- harvester, the cut produced was clean, generally at or below 10cm and there were no problems with compaction or rutting.

The Claas header achieved an average harvesting rate of 2.6ha per day. Unfortunately, as with the Bundler, the Claas header had been developed for Swedish SRC which is planted as pure stands of one variety and also does not grow as rapidly as UK coppice due to the shorter growing season. This produces an homogenous crop with thinner stems that is easy to harvest. The Claas header eventually proved unsuitable for commercial use on the ARBRE plantations and would have required modifications for further use. It is not currently used for harvesting UK coppice.

Both the CRL and the Claas harvesters blew the chips into an accompanying silage trailer towed by a tractor. Usually two tractors and trailers were used to collect and transport the chips to store.

90 In 2001 ARBRE bought a modified Austoft sugar cane harvester from Sweden - a tracked, self-propelled billet harvester modified to produce billets of 5 to 10cm length. The use of this machine is reported above (page 11). The Austoft tended to cut the stools too high, an average of 16.1cm being recorded for this work, and also to badly damage the stools if the blades were not well maintained (Figure 33). Billet storage was expected to be less problematic than chip storage due to the greater airflow through the stacks although the billets would have needed chipping when dry prior to use at the power plant. Chipping of the dry billets was in itself likely to be difficult, as dry wood tends to shatter rather than produce chips.

Figure 33: Stool damage caused by the Austoft billet harvester (winter 2003/04)

91 None of the harvesting methods trialed by ARBRE proved completely successful and each had problems that needed rectifying:

• Whole-rod harvesting - Considerable wastage both at harvesting and at collection of the rods from the headlands - Some stems remained uncut. - Loose rods proved difficult to handle. - The rods, although drying rapidly and efficiently, proved difficult to chip. • Bundling - No efficient means of either bundling or baling SRC rods was available. - The bundles produced were of variable weights and densities. - The netting used to bind the bundles often did not keep the bundles intact. - To develop a UK harvester bundler or baler was expected to be extremely expensive. - The bundles dried efficiently and rapidly but handling and chipping proved a problem. • Direct-chip harvesting - The headers available at the time were not robust enough to deal with the ARBRE coppices. - Some stems remained uncut. - Chip storage had to be handled with care to prevent overheating of the piles and consequent deterioration of the material. • Billet harvesting - Some stems remained uncut. - The stools were cut too high. - Considerable damage occurred to the stools when the blades were not maintained. - Billets stored more easily than chips but problems may have occurred at chipping due to the dry wood. - Billets do not flow as easily as chips.

Two machines are currently used for commercial SRC harvesting:

• An unmodified, tracked Case sugar cane harvester that produces billets of 15 to 20cm length. These can be stacked in the field and dried efficiently but do need further processing prior to use. Average harvesting rates are between 5 and 6ha per 8hr day (M. Belton of Renewable Energy Growers, pers. comm.) • Coppice Resources Ltd have developed a mechanically driven SRC header for use with a Claas forage harvester for the production of wood chips. The header has a simple design including a front gathering wheel and contra-rotating twin saw blades. Currently the harvesting rate is between 5.5ha per 8hr day for thicker stemmed coppice (4 or 5-year harvest cycle) to 7.5ha for average stems (2 or 3- year harvest cycle). Further modifications to the header may be carried out to increase the efficiency and speed of harvest (M Paulson CRL, pers. comm.).

92 Whatever form of harvester is used, the needs of harvesting MUST be considered at the plantation design stage:

• Headlands of at least 8m are required for vehicle turning • Row spacings should be 0.75m between paired rows with 1.5m between each pair of rows to allow access for standard agricultural machinery fitted with flotation tyres • Access rides across long fields need to be incorporated to allow off-loading of trailers or harvesters • Areas for storage of rods, bales, bundles or off-loading trailers of wood chip and loading lorries must be identified as close as possible to the coppice

The harvesting operations themselves should aim to achieve the following:

• Provide a clean, low cut to the stools, ideally below 10cm • All stems should be cut • No cut material should be left in the field - wastage means lost fuel for the end- user and lost payment for the grower

93 Site details Land preparation Establishment Weeds and pests Yields

Site Ha Soil Grade Previous Sprayed Sprayed Sludge Planted Sprayed Sprayed Sprayed Cutback Sprayed Sludge Sprayed Weeds Weeds Rabbits Beetles Other Est yld Yield L/ha L/ha L/ha L/ha L/ha L/ha L/ha Est yr 1st yr odt/ ha/yr odt/ ha/yr

1 11.00 Clay sand 3 Roundup 1996 1997 Slurry 9 9 3 2 loam 2.5L March

2 1.77 Clay sand 3 Permanent Roundup 1997 Stomp 5L 1998 Weedazol / 3 3 2 7 6.77 grassland Flexidor 2L Simazine (4 yr) 3 23.04 Sand loam 3 Cereals Roundup 1999 Stomp 5L Laser 2000 Weedazol Pellets 6 3 8 3 8 Flexidor 2L February 10L Mar 2000

4 8.99 Black peat 4 Permanent set- Roundup 5L 1999 Stomp 5L 2000 Weedazol 9 8 4 Roe deer 5 9 Aut 1999 April Flexidor 2L February 10L Gramoxone 3L Mar 2000 Apr 1999

5 5.00 Warp over 1 Wheat & OSR Roundup 4L 1999 Stomp 5L Roundup 2000 Weedazol Hallmarkx 2 2 2 2 4 Deer 9 Spr1999 April Flexidor 2L 4L March 10L 0.1L Apr 1999 (small %) Mar 2000 Apr & Jun knapsacked 2002 & 2003 May 2000 6 5.76 Black land 4 Cereals Gramoxone 1999 Dragged x 2 Gramoxone 2000 Weedazol Slurry 5 2 2 9 Inter-row February Sugarbeet April 10L 123t/ha 4L Mar 2000 Jun 2000 Aug 2000

7 4.07 Clay 3 Wheat Roundup 4L 1997 Stomp 5L 1998 Weedazol 3 3 3 8 6.8 Combinable Mar 1997 March Flexidor 2L March 10L Mar 1997 Mar 1998 6.50 Reclaimed 3 Wheat Roundup 4L 1997 Stomp 5L 1998 Weedazol 3 3 3 2 6.8 ('50s) Ash Combinable Mar 1997 March Flexidor 2L March 10L Mar 1997 Mar 1998

2.76 Reclaimed 3 Wheat Roundup 4L 1997 Stomp 5L 1998 Weedazol 3 3 3 2 6.8 ('50s) Ash Combinable Mar 1997 March Flexidor 2L March 10L Mar 1997 Mar 1998

8 13.61 Clay 3 Permanent set- Roundup Gramoxone 1999 Stomp 5L 2000 Weedazol Cake Cypermethrin 5 4 2 6 Deer 6.7 aside/ arable May Flexidor 2L February 616kg N/ha0.25L Aphids rotation Spring 2001

4.40 Clay 3 Permanent set- Roundup 1999 Stomp 5L 2000 Weedazol Cake Cypermethrin 8 8 2 6 Deer 6.7 May Flexidor 2L February 616kg N/ha0.25L Aphids Spring 2001 5.75 Clay 3 Permanent set- Roundup 1999 Stomp 5L 2000 Weedazol Cake Cypermethrin 4 4 2 6 Deer 6.7 May Flexidor 2L February 616kg N/ha0.25L Aphids Spring 2001 2.95 Clay 3 Permanent set- Roundup 1999 Stomp 5L 2000 Weedazol Cake Cypermethrin 2 2 2 6 Deer 6.7 May Flexidor 2L February 616kg N/ha0.25L Aphids Spring 2001 Table 47: ARBRE Chronicle - Planting from 1996 to 2001 (representative sites)

94 Site details Land preparation Establishment Weeds and pests Yields

Site Ha Soil Grade Previous Sprayed Sprayed Sludge Planted Sprayed Sprayed Sprayed Cutback Sprayed Sludge Sprayed Weeds Weeds Rabbits Beetles Other Est yld Yield L/ha L/ha L/ha L/ha L/ha L/ha L/ha Est yr 1st yr pests odt/ ha/yr odt/ ha/yr

19.67 Clay 3 Wheat Roundup 2000 Stomp 5L 2001 Weedazol Cypermethrin 3 2 2 7 Deer March Flexidor 2L January 0.25L Aphids 2002 + 2003

10.84 Clay 3 Wheat Roundup Cake 2001 Stomp 5L 2002 Weedazol Cake Cypermethrin 4 3 3 5 205kgN/ha April Flexidor 2L February 616kgN/ha 0.25L 2003 15.53 Clay 3 Grassland & Roundup Cake 2001 Stomp 5L 2002 Weedazol Cake Cypermethrin 2 2 3 5 arable 205kgN/ha April Flexidor 2L February 616kgN/ha 0.25L 2003 9 2.25 Clay loam 2 Arable, turnips Roundup 1997 Stomp 5L 1998 Weedazol 2 1 3 6 8.8 Flexidor 2L March 10L 10 25.43 Clay 3 Grassland & Roundup Aut Roundup 2000 Stomp 5L Gramoxone Laser 2001 Weedazol Dursban 2002 x 2 2 1 7.5 9.5 set-aside 1999 June 2000 Flexidor 2L 4L 1L January 6L 2 Jun 2000 Mar 2001 11 10.02 Blue clay- 1 Spring barley Roundup 2000 Stomp 4L 2000 Weedazol 3 5 2 3 warp land silt 6L 8 May Flexidor 1.78L December 9L 27 Oct 1999 Dursban 1.49L Codazine 1.75L Apr 2001 12 14.92 Sand & black 3 Grass on NSA Roundup 2000 Stomp 5L 2001 JanuaryWeedazol Fury 4 4 3 1 6 9 loam 4L Flexidor 2L 6L Spr 2000 Jun 2000 Mar 2001 13 11.23 Clay loam 1-2 Cereals Roundup 1996 May Various 1997 Various Slurry 4 4 3 8.7

14 9.71 4 Roundup 5L 1999 Stomp 5L Gramoxone 2000 Weedazol Slurry 7 4 1 Aphids 8 Oct 1998 5 May Flexidor 2L 4L February 10L 123t/ha Gramoxone 3L 24 Aug 1999 16 Mar 2000 Jun 2000 10 Apr 1999

9.88 Sandy warp 3 Cereals Roundup 5L 2000 Stomp 5L 2001 Weedazol 4 3 1 Aphids 6.8 linseed Oct 1999 April Flexidor 2L 10L Gramoxone 2.5L

1 May 2000

15 12.91 Sand & black 3 Sludge disposalRoundup 2000 Stomp 5L Inter-row 2001 Weedazol Slurry 4 4 2 4 7.5 peat & sheep April 2000 May Flexidor 2L Aug 2000 1.25L January 6L 500Kg 1.5L May 2000 Jun 2001 Mar 2001 N/ha Apr Jun 2001 2001

16 12.11 Clay 3 Arable, cereals Roundup 1999 Stomp 5L Dursban 2000 Fury 2002 4 2 2 9 Deer 7 & grass Aut 1998 March Flexidor 2L May 1999 February Decis 2003 From 2001 onwards

17 10.00 Clay loam 2 Wheat Roundup 2000 Stomp 5L 2001 Weedazol Cypermethrin 4 5 4 7 Flexidor 2L March May 2001 0.25L June 2000

Table 47: continued

95 Site details Land preparation Establishment Weeds and pests Yields

Site Ha Soil Grade Previous Sprayed Sprayed Sludge Planted Sprayed Sprayed Sprayed Cutback Sprayed Sludge Sprayed Weeds Weeds Rabbits Beetles Other Est yld Yield L/ha L/ha L/ha L/ha L/ha L/ha L/ha Est yr 1st yr pests odt/ ha/yr odt/ ha/yr

18 14.10 Sandy loam 2 Mixedarable, Roundup 4L Veg & 2001 Stomp 5L Falcon Weedazol 9L 2002 Weedazol Veg 7 4 1 2 Aphids 7 veg, set-aside Feb 2001 potato May Flexidor 2L 1.5L Dec 2001 March 5L washings washings Gramoxone 2.5L Jul 2001 Mar 2002

18.42 Restored 3 Grass & linseed 1999 Stomp 5l 2000 Weedazol 3 2 2 1 Deer 9 sand gravel April Flexidor 2L March 10L

38.54 Restored 3 Potatoes, Food waste 2000 Stomp 5l Gramoxone 2001 Weedazol Laser (part) 5 3 3 2 Deer 8 sand gravel carrots, OSR, & paper pulp April Flexidor 2L 4L February 10L beet Inter-row

20.00 Sand 3 Potatoes 2000 Stomp 5l Shield 2001 Weedazol 7 2 7 1 8 April Flexidor 2L February 10L 18.96 Restored 3 Grass & linseed Cake 2001 Stomp 5l Aramo Gramoxone 2002 Weedazol Cake 4 2 2 2 8 sand gravel April Flexidor 2L Eagle Inter-row March 10L 616kg N/ha 4L (Part)

20.54 Restored 3 Grass & linseed Cake 2002 Stomp 5l Aramo Shield 2003 Weedazol Cake Hallmark 3 3 3 2 8 sand gravel April Flexidor 2L April 10L 616kg N/ha0.1L (Part) 19 2.00 Reclaimed 4 Spoil Roundup Cake 1999 Stomp 5L 2000 Weedazol 6 4 1 colliery spoil 400t/ha Flexidor 2L Spr 1999

20 9.19 Reclaimed 3 Sheep Roundup Dursban Annually 1997 Stomp 5L Gramoxone 1998 Weedazol Slurry 4 3 2 1 L/jackets 6.8 sand & Mar 1997 Mar 1997 March Flexidor 2L 4L February 6L May 98 (11-2nd gravel Mar 1997 Mar 1998 June 99 harvest)

13.10 Sand 3 Silt separation Cake Stomp 5L 1998 Weedazol Slurry 3 7 9 1 3.5 Flexidor 2L February Simazine Jun 1998 (2 year Jun 1997 Mar 1998 Jun 1999 crop) 3.32 Sand over 3 Sheep Roundup Cake 1998 Stomp 5L Gramoxone 1999 Weedazol Slurry Dursban 5 8 1 Sheep 8 PFA Mar 1998 Apr 1998 April Flexidor 2L Inter-row February 6L Jun 1999 edge sprayed L/jackets Apr 1998 4L Mar 1999 Jun 2000 Spr 2002 x 2

16.00 Topsoil 3 Reclaimed Cake 1999 Stomp 5L Gramoxone 2000 Inter-row Slurry Dursban 3 5 7 5 quarry 300t/ha Flexidor 2L Inter-row Jan & Apr May 2000 Jun 2000 edge sprayed Jun 1999 Jun 1999 4L (Flooding) Spr 2002 x 2 Aug 1999

5.50 Sand over 3 Sheep Roundup Cake 1999 Inter-row Gramoxone 2000 Gramoxone Slurry Grazon 5 9 6 L/jackets 6 PFA Mar 1999 Apr 1999 April cultivated Inter-row 2000 May, Jun, Jul 4L 2002 1999 4.00 Sand over 3 Sheep Roundup Cake 1999 Inter-row 2000 Gramoxone Slurry Grazon 5 9 6 L/jackets 6 PFA Mar 1999 Apr 1999 April cultivated 2000 May, Jun, Jul 2002 1999 12.91 Sand & 3 Cereals Roundup Roundup 2000 Stomp 5L Inter-row 2001 Weedazol Slurry 3 3 2 1 gravel Aut 1999 Jun 2000 Flexidor 2L cultivated January 2001 Jun 2000 Sep 2000 2002 30.00 Topsoil over 3 Linseed Roundup Roundup Cake 2000 Stomp 3L Gramoxone 2001 Weedazol Slurry Dursban 6 4 5 1 7 PFA Aut 1999 Jun 2000 300t/ha April Flexidor 1L Inter-row January 7L 2001 edge sprayed May 2000 Apr 2000 4L 2002 Spr 2002 x 2 Aug 2000 Table 47: continued

96 Site details Land preparation Establishment Weeds and pests Yields

Site Ha Soil Grade Previous Sprayed Sprayed Sludge Planted Sprayed Sprayed Sprayed Cutback Sprayed Sludge Sprayed Weeds Weeds Rabbits Beetles Other Est yld Yield L/ha L/ha L/ha L/ha L/ha L/ha L/ha Est yr 1st yr pests odt/ ha/yr odt/ ha/yr

21 10.26 Sandy loam 3 Cereals Roundup Roundup Cake 2000 2001 Weedazol Laser 1.5L 2 6 1 1 8 over clay Set-aside 4L 4L 150t/ha Apr/may Mar/Apr 10L Mar 2002 Aut 1999 Aut 1999 Mar 2000 Apr 2001 10.96 Sandy loam 3 Cereals Roundup Cake 2000 2001 Weedazol Laser 1.5L 3 6 3 3 8 over clay Set-aside 4L 150t/ha Apr/may Mar/Apr 10L Mar 2002 Aut 1999 Mar 2000 Apr 2001

22 5.77 Clay 2 Wheat & OSR Roundup 1998 Stomp 5L Kerb 1999 Weedazol Sludge Fury 3 3 5 8 Hares 7 Aut 1997 April Flexidor 2L February 10L pellets Deer Apr 1998 Mar 1999 Apr 1999

23 22.33 Clay 2 Wheat & OSR Roundup 1999 Stomp 5L Kerb 2000 Weedazol Fury 8 7 3 8 Hares 8 Aut 1998 Flexidor 2L February 10L Deer 6 Apr 1999 Mar 2000 4 24 19.36 Clay loam 2 Wheat & OSR Roundup 2000 Stomp 5L Kerb 2001 Weedazol Sludge Fury 5 4 2 3 6 Aut 1999 May Flexidor 2L Feb 2001 March 10L Apr 2001 8 May 2000 Mar 2001 8.00 Clay loam 3 Potatoes & set- Roundup 1999 Stomp 5L 2000 Weedazol Decis 3 2 1 1 8 Aut 1998 April Flexidor 2l January Spr 2003 10.00 Clay loam 3 Wheat Roundup 2000 Stomp 5L Laser 2001 Weedazol 3 3 2 1 Hares 7 Aut 1999 May Flexidor 2L July 2000 January Spr 2003 Gramoxone 2.5L June 2000

11.80 Clay loam 3 Wheat Roundup 2001 Stomp 5L Gramoxone 2002 Weedazol 3 3 1 2 7 Aut 2000 May Flexidor 2L January Spr 2003

585.16

Table 47: continued

97 9.3.6 Yields

The site details in Table 47 have, where possible, been recorded by field rather than by site ie if a site comprises 3 fields, details for each field are shown separately.

A number of the growers were reluctant to provide an estimated yield for their crop as they had not had a first harvest taken so had no experience in gauging yields. Where first harvest had been taken, actual yields in odt ha" 1yr"1 have been provided.

Harvesting of a number of sites was due in winter 2002/03 but was not carried out due to ARBRE's liquidation. Most of these sites were harvested in 2003/04 along with many due for harvest that winter. The machine used was an unmodified Austoft (now Case) sugar cane harvester producing billets of approximately 15-20cm in length. The crop was not weighed at harvest as no market had been found for the harvested material at the time and this remains the case at the time of writing.

Destructive and non-destructive assessments of yield were taken at a number of the sites prior to harvest so that the results could be compared with the actual yields as they became available. The sampling method was as follows (Matthews etai, 2003):

Non-destructive yield assessment

• 10 randomly chosen stools were measured per site (or per 10ha). • Stools were chosen by walking 10m into the crop from the headland and then one sample taken. A distance of 25 stools was then walked along the row and a distance of 5 stools across the rows and a further sample taken. This method was continued until 10 samples had been taken. Where the fields or rows were short, the samplers turned and worked back across the site. No samples were taken from outside rows or from within 5m of a headland. • The number of stems per stool was counted. • The diameter at 10cm and 100cm was measured on 5 major stems. • The length of the same 5 stems was measured from 10cm above ground level. • If the random selection procedure ended up at a gap, this was counted as one sample.

Destructive yield assessment

• One of the measured 5 stems was taken from each sample. • A record was taken of the diameter and length measurements. • The stem was cut at 10cm above ground level. • Total stem fresh weight was measured. • The stem was cut into billets and a 1kg (or total stem if <1kg) fresh weight sub ­ sample was taken for drying. • An assessment of percentage moisture content of the sub-sample was made.

98 Site Mean Mean Mean MC Destructive Nondestructive Actual yield Growers' stem stem stem % yield yield at T estimated numbers dia height odt ha yr odt ha yr harvest yield (mm) (m) odt ha yr odt ha- yr A 3.9 21.5 4.2 53.1 4.8 6.5 B 3.6 20.5 3.8 53.7 3.3 3.2 9 C 5.8 23.7 4.6 56.6 4.5 4.6 6.8 D 3.8 19.9 3.5 54.9 3.0 2.6 6.7 E 3.7 22.5 4.5 52.5 5.3 4.7 8.8 F 2.8 25.2 4.1 53.5 4.4 4.7 G 2.6 23.5 4.1 53.9 4.0 4.8 H 3.7 24.5 4.4 53.2 3.5 3.7 / 2.7 20.5 3.5 54.5 2.3 3.8 7 J 3.1 17.9 3.1 55.3 4.4 4.4 8 K 5.0 19.8 3.6 51.8 6.0 6.4 9 L 3.9 26.8 5.0 54.3 5.4 5.8 M 3.3 17.8 3.2 55.0 4.4 4.0 8 N 3.6 25.5 4.7 53.5 5.4 7.1 6 a2 13.9 17.8 3.3 51.1 22.9 25.2 Sites B, H and I were harvested 4 years after cutback Table 48: Assessed yields over 3 or 4-year harvest cycles Table 2 shows the assessed yields for 15 of the sites prior to harvest in winter 2003/04 plus actual yields where the first harvest had already been taken 3 years previously and growers' estimated yields where they were prepared to provide these. Harvest took place 3 years after cutback at 12 of the 15 sites with the remaining 3 harvested 4 years after cutback. At all sites except O, only stems with a diameter greater than 10mm were recorded. At site O all stems were recorded. Although actual yields were not available for comparison, both assessment methods appear to be significantly underestimating yield as it was expected that actual yields should be at least 7odt ha 1 yr1 with one site achieving more than 12odt ha 1 yr1 (Pers. comm. ARBRE grower). Where all stems had been recorded, yields were significantly overestimated.

9.4 Crop economics The economics of biomass production depend on the price the end user is prepared to pay for the fuel plus the cost of producing and delivering the fuel. For energy crops, full growing costs must be incorporated into the final fuel cost making overall production costs high. Therefore in order for SRC to be seriously considered by a good proportion of farmers the price paid per odt would have to equate to the crops or practice which it is hoping to displace. The higher the price for SRC the easier it will be to displace current agricultural crops and practice e.g. non-cropping.

12 Total number of stems were counted at this site. At all other sites total number of stems >10mm diameter were counted.

99 A Cost Approximate costs in E/odt E/ha across 5 harvests ie a 16 Operation year crop with the following Comments yields at harvest: 21odt ha 1 30odt ha' 1 Total yield (odt ha' 1) for 5 harvests assuming no increase in yield over the life of the crop 105 150 Land preparation Sites will generally need 1 to 3 Weed control x 2 40 applications prior to planting Sub-soiling 38 Ploughing 42 Assumes full fencing - may only need Rabbit fencing 350 partial or possibly no fencing Power harrowing 28 Land oreoaration costs 498 4.7 3.3 Establishment Price for 15,000/ha - this will vary Cuttings 900 according to variety and total quantity Excludes haulage of planter to site, Planting 165 setting up and T&S costs for operators Rolling 10 Weed control 100 Remedial weed Most sites need some remedial weed 65 control control during the establishment year Cutback 40 Weed control 70 Establishment costs 1350 12.9 9.0 Gross costs 1848 17.6 12.3 One-off payment following successful Establishment grant WOO crop establishment Net costs 848 8.1 5.7

B E/ha E/odt Excludes haulage of machinery to site Chip harvesting 325 15.5 10.8 and T&S costs for operators Storage 1 1 Handling 2.5 2.5 Transport to end-user 17 17 Harvesting costs 36.0 31.3

Includes nett establishment costs and ~ total cost/odt 44.1 37.0 harvesting costs End-user payment 35 35 Assumes payment of £35/odt delivered

Profit/odt -9.1 -2.0 able 49: Indication of full costs for {A) establishing and (B) harvesting 1 hectare of willow SRC* * Payments include the one-off £1000/ha establishment grant and an end-user payment of £35/odt delivered but with no annual increase due to inflation. Neither Single Farm Payments nor Energy Aid Payments have been included.

100 Table 49 provides an indication of costs for the establishment and harvesting of 1ha of willow SRC and costs per odt at two yields: 7odt ha -1y-1 and 10odt ha -1y-1 over a 16- year crop ie one establishment year plus five 3-year harvest cycles over 15 years. The costs include the main operations involved in preparing the land, planting and cutting back the crop during the establishment year and the costs for harvesting assuming chip harvest and storage. An indication of transport costs from farm to end-user is also included. There are no costs included for pest control (eg leatherjackets, slugs) and for ongoing annual management of the crop that may involve headland maintenance and possible willow beetle control.

The costs given are based on current contract prices for the specialist operations such as planting, cutback, remedial weed control, etc. Costs for standard arable operations such as ploughing, sub-soiling, etc are midway between contract prices (Nix, 2004) and average farmer costs where the farmer undertakes his own work. There will be scope for reducing costs eg where the land is clean and relatively weed free, where there are few or no rabbits and where land preparation has been carried out efficiently leading to no requirement for remedial weed control or, possibly, cutback. The costs for specialist operations, most particularly for harvesting, tend to be high as there are few specialist machines currently in the UK and few contractors who are competent in SRC planting and harvesting techniques. With increased hectarage of SRC requiring harvesting, these costs should reduce significantly (as did establishment costs over the first five years of commercial SRC planting) as more machinery and contractors become available and competition forces prices down.

Table 50 includes current harvesting costs and delivery but reduced net establishment costs where the assumption is that only partial rabbit fencing is required and land preparation has been good enough to rule out the necessity for remedial weed control. Under these circumstances, the price per odt of delivered wood chip just comes into profit with an end-user payment of £35 odt-1. Efficient establishment and management techniques combined with reduced contract harvesting costs should help to reduce overall production costs of SRC.

It is important to note that the figures provided in tables 49 and 50 DO NOT INCLUDE the Single Farm payment or the Energy Aid payment.

101 £ ha ’1 £ odt 1 Comments

Establishment Weed control x 2 40 Sub-soiling 38 Ploughing 42 Power harrowing 28 Cuttings 900 Planting 165 Rolling 10 Weed control 100 Cutback 40 Weed control 70 Establishment costs 1433 Less rabbit fencing and remedial Less establishment grant WOO weed control Net establishment costs 433 2.9

Harvesting, storage & delivery Excludes haulage of machinery Chip harvesting 325 10.80 to site and T&S costs for operators Storage and handling 3.50 Transport to end-user 17.00 Harvesting costs 31.3 At 30odt ha 1 yield at harvest Total cost 34.2 End-user payment 35.0 Profit 0.8

Table 50: Indication of costs for SRC production with good land preparation and no fencing costs

9.5 Recommendations

For future SRC planting, the lessons learned from the ARBRE sites includes the following, much of which is known but not necessarily acted upon:

• Efficient land preparation is of critical importance particularly the need to control invasive perennials such as couch grass, thistles, nettles, horsetail, etc. Applying an appropriate broad-spectrum herbicide prior to ploughing, if necessary 2 or 3 times in the year prior to planting to ensure full control, will pay dividends in terms of reduced herbicide costs during establishment and increased yields. • Sub-soiling clay sites and those sites where a plough pan or compaction may be present will allow free root development. • There is no longer a list of specified varieties for energy crop planting. The Forestry Commission does however provide a list of both willow and poplar varieties that have been bred specifically for energy crop use and that grow well when exposed to UK pest, disease and climate conditions (Tabbush et al, 2002). The list is updated as information on new varieties becomes available and it is

102 recommended that the list be consulted prior to selecting planting material. Plant material for varieties covered by Plant Variety Rights legislation may not be reproduced for planting or sale without permission from the plant breeder. • Ensure that contractors plant effectively, not at too high a speed, which leads to cuttings being inserted into the soils incorrectly or entire rods being misfed or not fed at all into the planting mechanism. • Ensure that contractors plant to the correct row widths and planting densities. • Dedicated cold storage facilities, where the temperature can be maintained between -4 and -6oC should be available to ensure the planting material is kept under optimum conditions and not allowed to break dormancy prior to planting.

103 10 REFERENCES

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107 11 ACKNOWLEDGEMENTS

The authors would like to thank those ARBRE growers who allowed access to their land for this work to be carried out over a number of years and also the contractors who worked with us during the vehicle and machinery monitoring.

Barbara Hilton would also like to thank those growers who kindly responded to the request for background information relating to the establishment of their SRC; their positive and helpful comments were much appreciated. Particular thanks go to Martin Belton who also provided information on pesticide applications and harvesting schedules.

108 12 APPENDIX A ARBRE Chronicle - site data sheet

Name: Tel: Address: E-mail: Site name: Hectares: 5 Year planted: 1999 Fields: 1 Soil type: Warp over sand Density/ha: 15,000 Grade: 1 Varieties Bowles hybrid, Jorr, Jorunn, Tora, Previous Wheat & OSR planted: Orm, Ulv cropping:

Land preparation Sprayed, ploughed , power harrowed prior to planting

Herbicide: Sludge applied Roundup 4L/ha spring 1999 None date & rate: type & timing: Herbicide: date & rate: Herbicide: date & rate: Pesticide: date & rate:

Establishment Planted and rolled immediately after planting. JV.

Planting date: Mar/Apr 1999 Cutback date: March 2000 Herbicide: Stomp Flexidor 5L & 2L/ha Sludge applied None date & rate: April 1999 type & timing: Herbicide: Knapsacked Roundup 6 weeks post ­ Herbicide: Weed a zo I 10L/ha date & rate: planting on sandy area of field only date & rate: March 2000 Herbicide: Pesticide: Hallmark 0.1 L/ha date & rate: date & rate: Apr & June 2002 Pesticide: Pesticide: Hallmark 0.1 L/ha date & rate: date & rate: Apr & June 2003 Newly developed sprayer for insecticide - sprays over the top of the edge willows. Also sprayer for Machinery used: spraying into willow from edge at mid-height.

Management Weed burden during 2 establishment year: Weed burden after 2 cutback: Grazing pressure: 2 Beetle infestations: 4 Sprayed as a precautionary measure Other pests: Deer - not causing any damage.

Harvesting Machinery used: Yield t/ha: Due 2002/3 - delayed to 2003/4 due odt/ha/yr: to liquidation. No growth apparent in 4- year. Estimated yield 9 odt/ha/yr:

1 1 =bare soil, 9=aggressive weed competition 2 1 =no presence, 9=highest incidence

109 ARBRE Chronicle - site data sheet

Name: Tel: Address: E-mail: Site name: Hectares: 10.26 Year planted: 2000 Fields: 1 Soil type: Sandy loam over clay - poorly drained Density/ha: 15,000 Grade: 2-3 Varieties Previous Jorr, Jorunn, Orm, Ulv, Tora Set-aside -6 years, cereals before that planted: cropping:

Land preparation Sprayed, sub-soiled, ploughed & power harrowed prior to planting.

Herbicide: Roundup 4L/ha Sludge applied Sludge cake incorporated early date & rate: Autumn 1999 type & timing: March 2000. 150t/ha. Herbicide: Roundup 4L/ha date & rate: Autumn 1999 Herbicide: date & rate: Pesticide: date & rate:

F t hr h t Rolled after planting. sa is men Good site establishment. 1 m tall after 3 months growth. Planting date: April/may 2000 Cutback date: March/April 2001 (late) Herbicide: Stomp Flexidor 5L/ha & 2L/ha Sludge applied date & rate: May 2000 type & timing: Herbicide: Laser 1,5L/ha + 1,6L crop oil as wetter Herbicide: Weed a zo I date & rate: 22 August 2000 date & rate: Herbicide: Herbicide: Patch sprayed with Laser 1,5l/ha date & rate: date & rate: March 2002 Herbicide: Pesticide:

date & rate: date & rate:

Pesticide: Pesticide: date & rate: date & rate: Machinery used: JV for cutback Little or nothing done due to uncertainty over future. Will keep it in until 2006 (2- harvest) and grub Management up if

Most of field. Weed burden during 2 ~3ha - couch & grassweeds, small areas of establishment year: 5 thistle. Weed burden after 6 cutback: Grazing pressure: 1 Beetle infestations: 1 Other pests: Harvesting Due 2003/4 Machinery used: Yield t/ha: odt/ha/yr: Estimated yield 8 odt/ha/yr: 1 1 =bare soil, 9=aggressive weed competition 2 1 =no presence, 9=highest incidence

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