growing short rotation coppice

8/3/2019 Growing Short Rotation Coppice

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Best Practice GuidelinesFor Applicants to Defras Energy Crops Scheme

Growing ShortRotation Coppice


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Introduction 4

Why grow energy crops? 5What is SRC? 6

Where to grow SRC 7

Site selection 7

Plantation design 8

Land preparation 9

Planting material 10

Establishment 12

Planting 12Establishment year management 13

Cutback 14

Calendar of activity 16

General management 18Headlands and rides 18

Fertilisation 18

Nitrate Vulnerable Zones 19

Pests and diseases 19

Harvesting 22Rod harvesting 22

Direct-chip harvesting 22

Billet harvesting 23

Yield 24

Biodiversity 25

Removal of SRC 26Poplar SRC 27Site 27

Planting material 27

Planting 27

Management 28

Yields 28

Harvesting 28

Removal 28

References 29

Contacts 30

Contents

3


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This booklet has been produced by the Department of Environment, Food

and Rural Affairs (Defra) to introduce farmers to a new crop. It providesguidance on the choice of site, planting techniques, crop management

and harvesting methods required when growing short rotation willow or

poplar coppice as an energy crop. The booklet summarises current

agronomic techniques and, therefore, may need to be modified as further

experience is gained. Please check that you have the latest copy of the

booklet with the Defra office at Crewe.

This booklet should be read in association with the Energy CropsScheme booklet, Establishment grants for short rotation coppice and

miscanthus which outlines the requirements for claiming grant to

establish the crop.

There is further information on short rotation coppice in the Forestry

Commission Information Note The establishment and management of

short rotation coppice a practitioners guide (Tubby and Armstrong, 2002).

4

Introduction


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Energy crops are used as fuel in powerstations and heating systems. In substi-tution for fossil fuels, they have thepotential to reduce emissions of thegreenhouse gas carbon dioxide. Energycrops will need to contribute if the UKis to meet its:

obligation under the Kyoto Protocolto reduce greenhouse gas emissionsby 12.5 per cent below 1990 levels

by 2012; domestic goal to generate 10% of the

nations electricity from renewablesources by 2010.

This provides a significant opportunity forthe energy crop industry.

Currently the major energy crop grownin the UK is short rotation coppice (SRC),

primarily willow, although poplar hasbeen used occasionally and may be

planted more commonly in the futurefollowing the production of varietiesmore suited to coppicing. This bookletconcentrates on willow SRC, although asection relating specifically to poplar hasbeen included.

Defra provides grants to assist with theestablishment of SRC under the EnergyCrops Scheme (ECS), part of the EnglandRural Development Programme (ERDP).

Grants are also available for setting up SRCproducer groups to facilitate harvestingand supply to the energy market. Fulldetails can be found in the ECS bookletsEstablishment grants for short rotationcoppice and miscanthus and Grantsfor establishing producer groups.

For details of support available for energycrops, contact the Defra office at Crewe

or visit the ERDP website:www.defra.gov.uk/erdp/erdphome.htm

Why grow energy crops?

5Woodchip boiler for heat ARBRE power station fuelled by woodchip


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6

SRC (short rotation coppice) consists ofdensely planted, high-yielding varieties ofeither willow or poplar, harvested on a 2 5 year cycle, although commonly every3 years. The osier, a shrub willow, isparental stock to the majority of willowvarieties planted for use as an energycrop. SRC is a woody, perennial crop, therootstock or stools remaining in theground after harvest with new shootsemerging the following spring. Aplantation could be viable for up to 30years before re-planting becomesnecessary, although this depends on theproductivity of the stools.

Willow SRC is planted in the spring usingplanting material produced by specialistbreeders and equipment specificallydesigned for the purpose. The willow will

grow rapidly in the first year reaching upto 4m in height. During the winter afterplanting the stems are cut back toground level to encourage the growth ofmultiple stems i.e. coppiced. Generallythree years after cutback and againduring the winter, the crop is harvested.The equipment used for harvesting willhave been specifically developed for thepurpose and depends on the fuelspecification of the customer/end-user.Most operations other than planting orharvesting can be completed usingconventional farm machinery.

In the UK, yields from willow SRC at firstharvest are expected to be in the range 7 12 oven dry tonnes per hectare peryear (odt/ha/yr) depending on site andefficiency of establishment.

What is SRC?

Willow SRC 3 months after planting Mature willow SRC


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The key determinants of SRC yield arewater availability, weed control, light andtemperature.

Willow SRC will produce good growthwhere there is sufficient soil moistureavailable within 1 metre of the soil surface.It can withstand seasonal flooding butnot permanent waterlogging. Whereland is prone to flooding most years, thewillow will survive but consideration must

be given to operational requirements,particularly the need to harvest in winter.Annual rainfall of 600-1000mm is ideal.

SRC can be established on a wide rangeof soil types from heavy clay to sand

including land reclaimed from gravelextraction and colliery spoil. Clay or sandyloams that retain moisture but are wellaerated are ideal soils. Establishment maybe slow on heavy clays as they tend to becold in spring although, once established,SRC grown on these soils can be highlyproductive. Where compaction may proveto be a problem, sub-soiling to a depth

of 40cm will be necessary to ensuremaximum root development. Soil pHshould be in the range 5.5 7.

Site selection

A site must meet the requirements of theECS, these can be found in theEstablishment Grants booklet.

As a perennial crop, SRC is likely to be inthe ground for up to 30 years and canreach 7-8 metres in height prior to harvest.Its impact on the local landscape, ecolo-gy, archaeology and public access musttherefore be considered alongside the

operational parameters.Under the ECS, a proposed SRC site isassessed and consultation takes place toensure there will be no significantadverse impact on the environment. Thisconsultation takes up a significant part ofthe 3-month application process time. Tospeed the process potential growers maywish to contact organisations that may

be affected by the planting of the crop inadvance, e.g. local councils for bylawsrelating to public rights of way or thecounty archaeologist to check the recordsfor any important archaeological remains.Where a proposed site is adjacent to ariver or on a floodplain, the EnvironmentAgency should be consulted.

Another factor to consider is soil erosion.Compared to many crops, SRC has largeareas of open ground within the cropduring establishment. On light, sandysoils this can lead to wind erosion of thesoils and also some damage to the newlyemerged shoots due to abrasion. Onsloping sites, soils can be eroded followingheavy rain.

Willow roots, which are fibrous in nature,will penetrate down to field drains and itis recommended that SRC is planted at

Where to grow SRC

7

SRC in the landscape


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least 30 metres from any drains that areconsidered important. When choosing asite consider the life of the drainagesystem in relation to the expected life ofthe SRC plantation.

To be eligible for grant the proposed sitemust be at least 3ha in total, althoughthis can be made up of smaller plots.However, to ensure economies of scalefor all field operations larger plantations

are better. The most appropriate fieldshapes are those that minimise the needfor short row lengths or require nochanges in direction during fieldoperations. Choosing fields that can beharvested economically is of criticalimportance. For ease of operations theideal site would be flat or with a slopeof no more than 7%. It is strongly

recommended that the slope of the fieldshould not exceed 15%.

Appropriate access must be available forall machinery involved in establishing andharvesting the crop. Gate widths shouldbe at least 4.5m but it is recommendedthat if new gates have to be installedthey should be up to 7.2m in width.Bridge height or weight restrictionsshould also be considered wherenecessary. Ideally areas for transferringand storing the harvested crop should beadjacent to the coppice.

Plantation design

The plantation design should fit in withthe surrounding landscape and advicerelating to this can be obtained from

Forestry Commission Guideline Note 2(Bell & McIntosh, 2001). Operationalrequirements must also be taken into

account. Headlands of at least 8 metresin width are necessary at both ends ofthe rows to allow for vehicle turning.Where only one trailer will be available atharvest or the harvester has an integraltrailer, row lengths should be restrictedto a maximum of 200 metres to avoidthe need to reverse along the rows to off-load. Where two or more trailers will beavailable, row lengths can be longer.However, if liquid sludge is to be appliedusing an umbilical system, the maximumrow length should be 400 metres. Ridesof 4 metres should be left along theedges of the crop to allow machineryaccess for willow beetle control ifrequired. A maximum of 20% openground is allowed within a SRC plantationunder the ECS.

Where to grow SRC

Edge of SRC plantation8


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The importance of efficient landpreparation for SRC cannot be stressed

too highly. As SRC is a long-term,perennial crop, ensuring ideal conditionsat establishment will reap benefits at firstand all subsequent harvests.

Weed control is a critical part of coppiceestablishment. Complete eradication ofall invasive perennial weeds is essentialprior to planting. One or two applications

of a glyphosate-based herbicide, appliedat the appropriate rate, should be carriedout in the summer/autumn prior tospring planting. Ideally the first herbicideapplication should take place in mid-summer with a follow-up application inautumn to control any further flush ofweeds. An additional application justbefore planting in spring may be necessary

on some sites. Spring spraying alone isunlikely to be effective.

If required the site should be sub-soiled toa depth of 40cm to remove compaction.It should then be ploughed to a depth ofat least 25cm and left to over-winter. Onlighter land it may be more appropriateto spring plough. Power harrowing ofthe site should be carried out immediately

before planting.Sludge cake, well-rotted farmyardmanure or other bulky organic manurewith a low available nitrogen content canbe incorporated into the soils prior toploughing.This is particularly beneficialon light soils where it will increasemoisture retention and help to conditionthe soil. The Defra Code of Good

Agricultural Practice for the Protection ofWater (1998) must be adhered to whenapplying organic manures.

Rabbits, if present, must be kept out ofthe crop at least during the first twoyears and ideally up to first harvest, toallow the crop to mature beyond its vul-nerable stage. Rabbit fencing should beerected to British Standard, buried andturned out. Defra and the Department ofTrade and Industry (DTI) have produced aleaflet on rabbit management techniquesfor SRC (McKillop & Dendy, 2000).

Land preparation

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Defra and the British Horse Industry Confederation

Joint Research on the Horse Industry in Great Britain

10

Planting material

Access to the ECS is not restricted tospecified varieties of willow. However,several willow varieties, bred specificallyfor use as SRC energy crops, are listedin the Forestry Commission InformationNote Poplar and willow varieties forshort rotation coppice (Tabbush, Parfittand Tubby 2002). The recommendedvarieties have been through trials toensure high yields, erect growth habitand resistance to, or tolerance of, disease.The list is updated as information onnew varieties becomes available andprovides a useful source of informationwhen selecting planting material.

Melampsora rust is the most commonfungal disease of willows. Ideally, a mix ofwillow varieties with diverse rusttolerance characteristics, referred to as

mix types, should be used. Details ofthese varietal characteristics are availablein the Forestry Commission InformationNote referred to above or from materialproviders. Recent research has also shownthat mixed planting can lead to reductionin damage caused by willow beetles, themain pest species of willows.

European Plant Breeders Rights protectthe majority of varieties and cropharvested on the farm cannot be used asplanting material. Further information canbe obtained from the holders of Rights.

Planting material

Planting Cut and trimmed willow

rods stems, generally 1.5 3m long

Cuttings Cut fresh from rods andbetween 18 20cm in length

Planting rods


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11

Willows are planted either as cuttingsor rods. Only licensed producers should

conduct willow propagation. Rods orcuttings are taken from one-year-oldmaterial that is harvested betweenDecember and March when the plantsare dormant. They must be either plantedimmediately or stored at -2 to -4C,where cuttings will remain viable forseveral weeks and rods up to 3 months.They should only be taken from cold

store and delivered to the planting site onthe morning of planting. If rods/cuttingsare left in temperatures above 0C a

break in their dormancy will occur,adventitious roots will develop and the

buds may burst. This will lead to areduction in water and nutrient contentand consequently reduced viability.

Willow cuttings colour-coded by variety


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Planting

Willows are planted either as cuttings orrods, depending on the type of plantingmachinery used. Details of the latestmachinery available to buy or hire can beobtained from British BioGens EnergyCrops Network (see Contacts section).

At present, the most commonly usedmachines are step planters. Willowrods of 1.5-2.5 metres length are fed

into the planter by two or more opera-tives depending on the number of rowsbeing planted. The machine cuts therods into 18-20cm cuttings, inserts thecuttings vertically into the soil and firmsthe soil around each cutting. 15,000cuttings per hectare is the currentstandard commercial planting densityusing this method. Lower density

planting may lead to thicker stems andconsequently larger chip size. Therefore,planting densities down to 12,000cuttings/ha may be appropriate wherequality of chip is of more importancethan yield.

For small areas of planting, modifiedcabbage planters can be used for planting

cuttings directly. These machines are noteconomic for planting large areas however.

A lay-flat planter is being developedwhich lays whole rods horizontally intofurrows opened by discs at 2-8cm depth.The rods are laid end to end with a slightoverlap, the soil covers them and is con-solidated to minimise moisture loss.Distance between rows can be controlled

but as the shoots tend to grow randomlyalong the length of the rods there is noway to accurately control density.

Planting should ideally take place afterthe last frosts but as early as February ifsoil conditions allow. Planting can besuccessful as late as June but late plantingis best avoided as the longer the firstgrowing season the better in order totake the plants successfully into winterand cutback. Another factor is that lateplanting has to rely on planting materialfrom cold store, i.e. harvested earlier inthe year. This will restrict the materialavailable, especially as cuttings start tolose viability after a few weeks in storage.

Willows should be planted in twin rows0.75 metres apart and with 1.5 metresbetween each set of twin rows. Thisspacing allows standard agriculturalmachinery fitted with wide tyres to workacross the crop. A spacing of 0.59 metresalong the rows when planting cuttingswill give a planting density of 15,000/ha,the commercial standard (see diagram

opposite).The site should be rolled immediatelyafter planting to consolidate the soil

Establishment

12

A step planter


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13

for effective herbicide application.Pre-emergence residual herbicide shouldbe applied within 3-5 days of planting.

If the site was previously grassland orlong-term set-aside, leatherjacket controlshould be applied. For commercial reasonsit is better to apply the insecticide at thesame time as the pre-emergence residualherbicide but ensure that it is beforeroot or shoot development.

Establishment year management

From each cutting 1 3 shoots will ariseand reach up to 4 metres in height by theend of the first growing season, depend-ing on soil conditions. In the case of rods,shoots develop randomly along thelength of the rod but the stem heightswill be similar to those from cuttings.

No fertiliser should be applied during theestablishment year.

A lay-flat planter

Growth shortly after planting


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The coppice should be monitored care-fully for pests, weed growth and generalhealth during the establishment year. If

remedial weed control proves necessary,a hooded band sprayer, specificallydesigned for use on SRC, should be used.

Cutback

During the winter following planting thewillow is usually cut back to within10cm of ground level to encourage thedevelopment of the multi-stemmed

coppice. The work should be carried outas late as possible in the winter butbefore bud-break, generally late February.The most effective machines are modifiedmowers/reapers as these give a clean cutto the stems.

A contact herbicide should be appliedafter cutback to control those weeds thathave grown during the establishmentyear. It is important that the herbicide isapplied before coppice bud-break

Establishment

14

Recommended planting design

1.5m 0.75m

0.59m

0.75m

0.59m

0.59m0.59m

0.59m0.59m

1.5m1.5m 0.75m0.75m

Plantation prior to cutback


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otherwise the crop will be damaged.Generally the use of systemic/translocat-ed contact herbicides should be avoideddue to the risk of crop damage althoughsome, e.g. amitrole, have been shown tobe safe when applied before bud-break.

Another option is to use a mix ofamitrole and pendimethalin (residualherbicide) after cutback. The addition ofthe residual herbicide helps maintain

weed-free conditions until canopyclosure. Again, if used, this mix must beapplied before bud-break.

5 20 shoots will emerge from eachcutback stool depending on the variety.Within 3 months of cutback, canopyclosure will have occurred providingnatural weed control due to reducedlight at ground level.

15

SRC stool


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Ca

lendaro

factivi

ty

Thefo

llowingtableprovidesanindicationof

thetimingofmajoractivitiesduringth

efirsttwo

harvestcyclesofawillow

SRCplantationund

era3-yearrotation.

Yea

r

Period

Activ

ity

-1

Jan-Jun

Con

sidersiteselectionandliaisewithneighbours,locala

uthorities,archaeologists,etc.

Prep

areevidenceofmarketforSRC

Prep

areandsubmitDefraEstablishmentGrantapplication

Jun-Sep

1stapplicationofglyphosate-b

asedherbicide

Oct-Dec

1stor2ndapplicationofglyph

osate-basedherbicide

Inco

rporatesludgecakeifrequ

ired

Sub-soiling

Plou

ghing

Orderingcuttings

1

Jan-Mar

Erectrabbitfencingwhere

necessary

Mar-May

2nd

or3rdapplicationofagly

phosate-basedherbicide

Pow

erharrowingandplanting

Rollingandapplicationofpre-emergenceresidualherbicide(togetherwithleatherjackcontrol

ifnecessary)

Mo

nitorforpestsandcheckrabbitfencing

Jun-Dec

Mon

itorforpests,maintainrabbitfencingandcheckove

rallcrophealth

Rem

edialweedcontrolifrequired

Pre-planting Establishment


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g

p

p

y

Feb-Mar

App

licationofcontactherbicid

e

Apr-Jun

App

lyliquidsludge/fertiliseras

required

Monitorforpestsandcheckrabbitfencing

Jun-Dec

Monitorforpestsanddiseasesandmaintainrabbitfencing

3

Mar-Aug

App

lyliquidsludge/fertiliserif

requiredandpracticable

Monitorforpests,particularly

willow

beetle

4

Mar-Aug

App



Monitorforpestsanddiseases,treatasnecessary

Oct-Dec

Agr

eeharvestingdatesandde

liveryschedulewithenduser

Harvestinganddeliverytoen

duserasfreshmaterial

Har

vesting,storageanddrying

5

Jan-Feb

Har

vesting,storageanddrying

Feb-Mar

App

lycontactherbicideifnecessary

App

lyliquidsludge/fertiliseras

required

Storageanddryingofharvestedmaterial

Deliveryofchiptoenduser

Mar-Aug

Monitorforpests,particularly

willow

beetleandsprayas

necessary

Storageanddryingofharvestedmaterial

Deliveryofchiptoenduser

6

Mar-Aug

App




7

Mar-Aug

App




Oct-Dec

Harvesting


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Headlands and rides

Headlands and rides should be grassedand cut twice a year. This regime providessome support for vehicle movements atharvest whilst also encouraging theestablishment of beneficial flora.

Fertilisation

Digested, i.e. treated, sewage sludge canbe applied to SRC as a fertiliser if it is

considered feasible by the local WaterCompany under UK sludge regulationsand their own guidelines. Accuratenutrient requirements of the crop are stillunder research but where treatedsewage sludge has been applied thesubjective view of growers is that it isbeneficial. Under the Code of GoodAgricultural Practice for the Protection of

Water (COGAP 1998), no more than250kg organic nitrogen/ha/year can beapplied to agricultural land. Willow SRChas a low demand for nitrogen (N) andthe current UK recommendations forapplication are 40, 60 and 100kg N/ha/yrfor the 1st (i.e. after cutback), 2nd and3rd years of the harvest cycle respectively(Johnson P. 1999). Where the soil has

high residual N levels from previouscropping or a high soil organic matterlevel, these rates should be reduced.

No fertiliser should be applied during theestablishment year, i.e. from plantinguntil after the post-cutback herbicideapplication has had time to be effective.

Unfortunately, due to the growth form

of SRC and the equipment currentlyavailable, fertiliser application can bedifficult in year 2 of the harvest cycle

and impossible in year 3. Opportunitiesto work over the crop usually have to betaken in year 1 after cutback and, wherepossible, in year 2. However, treatedsewage sludge in liquid form can beapplied using a dribble bar fed by anumbilical system. This allows the sludge tobe applied directly to the ground surfacethrough a series of pipes fed from thedribble bar with no contamination to thecrop and it can be used on coppice up to2.5 metres in height. Application shouldbe at the rates given above.

General management

18

Liquid sludge application using dribble bar


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The use of composted sewage sludgeapplied using standard agriculturalspreaders is being investigated toassess the benefits of applying up to 3times the annual limit of total N, i.e.700-750kg N/ha, in 1 application.Currently sludge cake or compostedorganic wastes, which contain very littleplant available N, may be applied at ratesof 500kg N/ha in 1 application every 2years, in areas not sensitive to nitrateleaching (COGAP 1998). The potential ofcomposted sludge is that it could beapplied after cutback and again afterharvest when there are few practicaldifficulties with working over the crop,although the height of the stems mustbe less than 50cm. Only 5-10% of thenitrogen would be released per year,i.e. during the growing season whentemperatures rise the composted sludgewould provide up to 70kg N/ha/yr foreach year of the 3-year harvest cycle.The remaining nitrogen is held within theorganic component of the compost andis not leached out. Defra will issue moreguidance on this as results from theinvestigations become available.

Nitrate Vulnerable Zones

A mature SRC plantation, i.e. after estab-lishment, will have a dense, widespreadroot system and this, combined with along growing season, enables the cropto efficiently utilise nutrients. Research, inthe UK and areas of Scandinavia withsimilar growing conditions, has shown

that the uptake of available nitrogen bySRC is very effective and, consequently,nitrate leaching is much lower than thatfrom fertilised grassland or arable land.

Also with SRC there is no soil disturbanceto promote mineralisation.

Nitrate leaching has been recorded in thefollowing situations:

after green cover removal in the landpreparation phase,

during the establishment year wherenitrogen has been applied as fertiliser,and

after final removal of the crop.It is therefore important that no fertiliseris applied during the establishment year,i.e. after planting and before cutback.The root system will not have fullydeveloped and would not be able toutilise the additional nutrients.

Although from research to date SRC willprove to be a beneficial crop for plantingwithin Nitrate Vulnerable Zones, it isessential that all Defra regulationsrelating to these zones are complied with.

Pests and diseases

Rust is the most important disease ofSRC, caused by a number of fungicalled Melampsora. Rusts can infectboth the leaves and stems of willowand, as they can adapt rapidly tochanging circumstances, can successfullyinfect a whole crop if appropriatemeasures are not taken.

Monocultures of willow, i.e. block plantingof single varieties, are highly susceptible torust damage. The UK and European PlantBreeding Programmes, one of whose

aims is to identify varieties that areresistant to rust, recommend that at least5 different varieties be planted in a ran-dom mix at each site. The Forestry

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Commission Information Note byTabbush, Parfitt and Tubby (2002) givesdetails of appropriate mixes. The use offungicides is not recommended foreconomic, practical and environmental

reasons.Chrysomelids (willow beetles) are themost important insect pest of willowSRC. Their numbers can build up rapidlyin spring and, as both adults and larvaefeed on the leaves, they can causeconsiderable damage to the crop. Forexample, removal of 90% of the leavesin summer can reduce the yield by as

much as 40%. Adult willow beetles over-winter in rotting wood, under the barkof trees and in similar habitats short

distances from the coppice. As tempera-tures start to rise in the spring, the adultsmove into the edge of the coppice, startfeeding, mate and then gradually movefurther into the crop.

If beetle numbers reach 100 adults ormore shaken from the canopy per squaremetre of ground surface, then either alocal application of an appropriateinsecticide directed specifically to wherethe beetles are congregating or a sprayapplied from the edges of the coppice ifthe beetles are more dispersed, will savethe crop from further damage.

Overspraying a mature plantation wouldprove costly, not only financially but alsoecologically as the insecticides used are

General management

20

Melampsora rust on willow leaves


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not specific to their targets and wouldtherefore damage many non-target andbeneficial insects. Beetle populations dotend to fluctuate between years so alarge infestation one year does notnecessarily mean that it will occur again.Planting a mix of willow varieties can havea beneficial effect as the beetles tend tofeed preferentially on some varietiesbefore moving onto others and this slowstheir spread through the coppice.

Browsing animals such as rabbits anddeer can also cause damage to SRC butmainly during establishment.

The Game Conservancy Trust has pro-duced a booklet describing integrated

pest management techniques for SRC(Tucker & Sage, 1999) which includessections on willow beetles and rust.

21Willow beetle larvae

Adult willow beetles


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Harvesting generally takes place on a3-year cycle, the first harvest being 3years after cutback. The work is carriedout during the winter, after leaf fall andbefore bud-break, usually mid-October toearly March. SRC can be harvested asrods, chips and billets (see table below).

End-users will generally require the fuelin the form of wood chip, to a maximumsize. They may also need the wood chip

dried to a particular moisture content(MC). For example, willow is generally inthe range 45-60% MC at harvest butend-users may want a MC below 30%.

The type of harvesting machinery usedwill depend on the end-users require-ments. Details of the latest machineryavailable to buy or hire can be obtainedfrom British BioGens Energy Crops

Network (see Contacts section).

Rod harvesting

A number of machines are available forrod harvesting most of them producingloose rods which need to be off-loadedinto heaps on the headlands or on farm.There is some wastage with this methodas rods are left in the field and aftercollection from headlands. However,loose rods do dry by natural convectionand do not deteriorate with time.Bundler harvesters cut whole stems,

bind them and then cut them into bundles2.5 metres long. The bundles can bestacked on headlands or on farm andcan dry down to approximately 30% MCin 3-4 months.

Chipping of dried whole rods or bundlestends to result in shattering of thematerial rather than chipping; therefore,where chip size and quality are important,chipping fresh material is recommended

Direct-chip harvesting

Specifically designed SRC headers fordirect chipping of the crop have beenfitted to forage harvesters: the stemsare cut, chipped and then blown into anaccompanying trailer. Although direct-chipharvesting is currently more efficient thanrod harvesting, storage and drying of the

fresh wood chip does cause problems.Stored, fresh wood chip can heat up to60C within 24 hours and start todecompose. During decompositioncalorific value, i.e. the energy value ofthe fuel, is lost. Also the fungal andbacterial spores produced during decom-position constitute a health hazard.

As the fuel will be needed all year,storage, drying and prevention ofdecomposition must be considered. Theuse of grain driers, ventilated-floor-driersand low-rate aeration using ducts are all

Harvesting

22

Harvested material

Rods Harvested stems up to 8m in length

Billets Cut material, 5 15cm long

Chips Cut material, up to 5 x 5 x 5 cm in size


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being investigated, although it is currentlyconsidered uneconomic to dry woodchip by any method other than naturalair-drying. It is important to ensure thatthe energy used in producing wood chipfor fuel is kept to a minimum.

Billet harvesting

Intermediate between rod and directchip harvesting is billet harvesting. The

stems are cut whole, cut further intobillets and blown into an accompanyingtrailer. Due to the spaces between the

billets, natural ventilation occurs withinstorage piles preventing the difficultiesassociated with chip storage. However,depending on the fuel specification ofthe end-user, the billets may need to bechipped prior to use.

23Direct-chip harvesting


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SRC yields will vary according to thelocation of the site. Soil type, wateravailability, general husbandry, and pestand weed control will also affect yield.Yield following the first harvest of anumber of commercial sites was in therange 5-9 odt/ha/yr. However, plantingdensities at many of these sites were12,000 cuttings/ha rather than the currentstandard of 15,000 cuttings/ha. Yieldsshould also increase at second and thirdharvests. Average yields from experimental

plots growing new varieties, some ofwhich are now commercially available,have reached more than 18 odt/ha/yr.Breeding programmes continue toproduce varieties that out-performolder varieties.

Yield

24

Harvested woodchip


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Despite the fact that it is essential toeradicate weeds during the establishmentof SRC, once the crop is mature thegrowth of a ground flora is beneficial.Ground cover encourages the presenceof invertebrates, which in turn leads to anincrease in the number of small mammalsand birds found. At least three times thenumber of plant-eating species spend partof their life cycle in the canopy of willowSRC compared to conventionally grownbarley and wheat (Sage & Tucker, 1998).

High numbers of bird species are alsofound throughout the year and over the3-year harvest cycle. For example, skylark,lapwing, yellow wagtail and snipe areoften found in newly planted, cutbackand harvested SRC. Species of highconservation value such as bullfinch,

reed bunting and song thrush have beennoted to regularly hold territories in SRCduring the breeding season.

Headlands and rides provide furtherhabitat opportunities for a wide rangeof plants and animals, for example, 14species of butterfly have been recordedon SRC headlands.

Many of the species that use the habitatsassociated with SRC will predate pestspecies. For example, two of the birdscommonly associated with SRC, thegarden and willow warblers, are two ofthe most important consumers ofdefoliating invertebrates. Therefore, anymanagement practice that enhances theconservation potential of the crop is likelyto prove valuable for pest management.

Biodiversity

25

Headland flora


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After the final winter harvest, the stoolsshould be left and allowed to shoot thefollowing spring. When shoots of morethan 15cm in height have developed, theentire coppice should be over-sprayedwith a glyphosate-based contact herbicideto kill the willow. Running either asub-soiler or a large diameter disc alongthe rows close to the stools will severthe main structural roots, which runhorizontally from the stools. When theshoots have died back, the stoolsthemselves can be mulched by use of abush-hogger (heavy-duty grass-topperor pulveriser) into the top 5-10cm ofsoil. The field can then be grassed forthe first year following removal and (if

appropriate) used for standard arablecropping the following year. Using thismethod, final harvest to re-seeding, willtake 18-24 months.

To shorten the process, the final harvestcan be taken in late summer/earlyautumn and the stools again allowed toshoot. When the shoots are 15cm ormore in height, the herbicide should beapplied, the structural roots cut and,

following death of the shoots, the stoolsmulched. Depending on soil type, thestools can be ploughed in prior to winter.This will allow an early re-seeding thefollowing spring.

Removal of SRC

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Poplar has been used as a short rotationcoppice crop on a small scale to date,often planted adjacent to willow SRC toprovide visual diversity.

Site

Poplar grows best in deep fertile soils,although it will grow in most conditions.The main exceptions are shallow soilsand sites that remain waterlogged. Soil

pH should ideally fall in the range 5.5 -7.5, although research suggests thatthere are varieties tolerant to soil pHoutside this range.

Preparation of the site should be thesame as that for willow SRC, taking careto ensure eradication of all weeds. Thesoil should be well cultivated to a depthof at least 25cm. Where compaction is

present, sub-soiling should be carried outto a depth of 40cm.

Planting material

Most new poplar varieties have beenbred for high yield but as a single stemcrop. Also a number of varieties plantedin the mid-1990s succumbed to rust astheir resistance broke down. However,current breeding programmes aim toproduce high yielding varieties that willcoppice more readily and have longterm resistance to rust. The currentrecommended and approved poplarvarieties for SRC are listed in theForestry Commission Information Note,Poplar and willow varieties for shortrotation coppice (Tabbush, Parfitt andTubby 2002).

Poplar varieties are controlled under theForest Reproductive Material Regulations,

which are in place to improve the qualityof poplar varieties, increase productionand ensure that the most suitable varietiesare used. These Regulations also controlthe marketing of poplar varieties so thatreproductive material is only availablefrom registered sources.

Planting

Planting should take place as early aspossible in the spring but avoiding frost.The density of planting has generallybeen lower than that for willow at

10-12,000 cuttings/ha. The cuttings are20-25cm long and must have an apicalbud within 1cm of the top of the cutting.This means that poplar cannot be planted

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using step planters, as the cuttings haveto be manually processed to ensure thepresence of the apical bud. Consequently,modified cabbage planters have to beused but due to the ridged nature ofpoplar stems, the cuttings occasionallyblock the planter mechanisms. The lay-flatplanter is currently being tested forplanting poplar rods.

Management

Weed control is very important in theestablishment year, so after planting androlling a residual herbicide should beapplied within 3-5 days. Cutback takesplace late in the winter following planting.Due to its apical dominance, poplar willgenerally produce only 1-3 shoots aftercutback.

Melampsora rust is also the mostcommon disease of poplar, althoughdifferent species of rust affect poplarand willow. Different poplar varietieshave different susceptibilities to rust so itis important to read the latest version ofthe Forestry Commissions varietiesInformation Note referred to above. Aswith willow, it is recommended that a

mix of varieties be planted.

Willow beetles are also an importantpest of poplars and should be treatedeither by spraying localised colonies or,if the population reaches 100 or moreadult beetles per square metre ofcanopy, edge spraying the coppice inearly spring. Overspraying the entireplantation would be ecologically andfinancially inadvisable.

Yields

Research has shown that poplar canoften outperform willow in terms ofyield but this appears to be site specificand highlights the fact that choosingthe appropriate varieties for a site isessential. Unlike willow, poplar tends toproduce better yields when allowed togrow for four years or more from cutback.

HarvestingAs poplar produces fewer, heavierstems, careful consideration must begiven to the harvesting machinery used;it must be capable of dealing efficientlywith large diameter, rigid stems. Detailsof the latest machinery available to buyor hire can be obtained from BritishBiogens Energy Crops Network (see

Contacts section).

Removal

The removal of poplar SRC at the end ofits life is more problematic than willow.The rooting system of poplar includes alarge taproot that grows down into thesoil. Removal of the stools (following finalharvest and spraying off of the shoots)

will generally require a large excavator.

Poplar SRC

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Bell S, McIntosh E 2001. Short Rotation Coppice in the Landscape. ForestryCommission Guideline Note 2. Forestry Commission, Edinburgh

Defra 1998. Code of Good Agricultural Practice for the Protection of Water.Defra Publications, London

Defra 2000. Establishment grants for short rotation coppice and miscanthus.Defra Publications, London

Defra 2000. Grants for establishing producer groups. Defra Publications, London

Forest Reproductive Material Regulations 1977. HMSO

Forest Reproductive Material (Amendment) Regulations 1992. HMSO

Johnson P 1999. Fertiliser requirements for short rotation coppice. ETSU reportB/W2/00579/REP/1

McKillop I G, Dendy J A 2000. Advice on rabbit management for growers of shortrotation willow coppice. DTI/Defra, Central Science Laboratory, York

Sage R, Tucker K 1998. Integrated crop management of SRC plantations to maximisecrop value, wildlife benefits and other added value opportunities. ETSUB/W2/00400/REP

Sludge (Use in Agriculture) Regulations 1989. HMSO

Sludge (Use in Agriculture) (Amendment) Regulations 1990. HMSO

Tabbush P, Parfitt R, Tubby I 2002. Poplar and willow varieties for short rotationcoppice. Forestry Commission Information Note. Forestry Commission, Edinburgh

Tubby I, Armstrong A 2002. The establishment and management of short rotationcoppice a practitioners guide. Forestry Commission Practice Note. ForestryCommission, Edinburgh

Tucker K, Sage R 1999. Integrated pest management in short rotation coppice agrowers guide. Game Conservancy Limited, Fordingbridge, Hampshire

References

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Energy Crops SchemeOrganic and Energy Crops NationalImplementation TeamRural Development ServiceDefraElectra WayCrewe CW1 6GJ

Tel: 01270 754 000Fax: 01270 754 088

[email protected]

www.defra.gov.uk/erdp/erdphome.htm

Energy Crops NetworkBritish BioGen16 Belgrave SquareLondon SW1X 8PQ

Tel: 020 7235 8474

[email protected]

Forestry CommissionGreat Eastern HouseTenison RoadCambridge CB1 2DU

Tel: 0845 367 3787Fax: 0122 346 0699

[email protected]

www.forestry.gov.uk

Pesticide Safety DirectorateMallard HouseKings Pool3 Peasholme GreenYork YO1 7PX

Tel: 01904 455 775Fax: 01904 455 733

[email protected]

www.pesticides.gov.uk

Contacts


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PB 7135 (reprint) Crown copyright August 2004Printed on material containing 80% post-consumer wasteand 20% Elemental Chlorine Free pulp.

Contacting DefraIf you have a query and are unsure about who to talk to in Defra, you can call the Defra Helplinewho will be pleased to help you to find the right person.

Defra Helpline: 0845933 55 77 (local call rate)

www.defra.gov.uk

Defra PublicationsAdmail 6000, London SW1A 2XXTel: 08459 556000

growing short rotation coppice

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