Caslin, B., Finnan, J., Johnston, C., McCracken, A., Walsh, L., Williams, C., Lindegaard, K., Rickerby, J., Carter, M. & Macalpine, W. (2023). Envirocrops: Short Rotation Coppice Willow Best Practice Guidelines. [online] Envirocrops. Available at: https://envirocrops.com/.

DISCLAIMER Throughout this publication, reference is made to a number of pesticides (herbicides, fungicides and insecticides) which have been used either commercially or experimentally in short rotation willow crops. It should be emphasised that with any pesticide application the relevant legislation (Health and Safety at Work Act 1974; Poisonous Substances in Agriculture Regulations 1984; Food and Environment Protection Act 1985; Control of Pesticides Regulations 1986; Control of Pollution Act 1974; Plant Protection Products (Sustainable Use) Regulations 2012 etc.) and the Product Label Recommendations must be adhered to.

1. INTRODUCTION

1.1. SHORT ROTATION COPPICE WILLOW

Short rotation coppice (SRC) utilises fast growing tree species that can be cut to a stool during their dormant winter stage, which then go on to produce multiple new shoots/stems in the following growing season. This is called coppicing. Coppicing is an ancient practice in the UK and Europe, being dated back to neolithic (4500 BC) times. Evidence of sophisticated coppicing practices was identified through the remains of wattle trackways found in the Somerset Levels, England. Since then, coppicing has been a traditional method of woodland management utilised for charcoal, fencing and shipbuilding.

In the past 30 years woody biomass has been recognised as an important biomass source which can be used primarily for heat generation (combustion), although more recently technologies such as gasification are being used for electricity production. Sources of woody biomass include conventional forestry and purpose-grown energy crops including SRC.

Salix spp. (Willow) is the preferred genus for SRC in Ireland, UK and northern Europe for a number of reasons. Willow is native to northern temperate zones and is a riparian species growing naturally around bodies of water. Therefore, it thrives in the cool wet conditions and largely heavy soils. Willow is a pioneer and one of the first woody species to colonise disturbed ground. Pioneer species, among other properties, generally exhibit vigorous juvenile growth which is exploited in the short harvesting cycles used under the SRC system.

Willow can be coppiced regularly and repeatedly without losing vigour, establishing rapidly from unrooted cuttings. In favourable conditions, roots can be produced within ten days of planting, which is important in making the cuttings self-sustaining as quickly as possible. SRC willow as an energy crop exploits the vigorous juvenile growth associated with Salix spp. and its ability to coppice. The crop does not need to be replanted after being cut back. An SRC willow plantation is established from hard-wood cuttings prepared from 1 year old stems produced by specialist nurseries. Cuttings are fully inserted into the ground in the spring. Growth is rapid and can be as much as 4 m in the first year increasing to 6-8 m at harvest in year 3 (short rotation).

Willow can be coppiced 6 to 8 times giving the plantation a life of 19-25 years, allowing for the establishment year. Shorter (2 years) and longer (4 or 5 years) harvest cycles have been considered depending on the productivity of the sites and other end use factors.

Energy from woody biomass is ideal for heat generation. Furthermore, energy produced from woody biomass is regarded as being carbon neutral, in that any carbon dioxide (CO2) which is released during combustion has recently been captured through photosynthesis by the growing plant. CO2 amounts to around 75% of all GHGs emitted, which in turn are responsible for climate change and global warming. Energy generation using woody biomass has therefore a significant contribution to make in reducing GHGs by substituting fossil carbon stored underground with carbon drawn recently from the atmosphere by plants. Furthering this, willow has been recognised for its phytoceutical properties, sustainable building material, and phytoremediation properties along with a plethora of other uses.

2. PRE-PLANTING

Willow is not a demanding species in terms of its site requirements. It will flourish in a wide range of soil types and environmental conditions, and likewise with other crops, productivity will be determined by site fertility, temperature, and availability of water and light. Albeit it’s undemanding nature, SRC willow plants will be in the ground for around 25 years, therefore it is essential to make sure that favourable conditions are provided by careful site selection and preparation.

2.1 SITE SELECTION

2.1.1. SUITABLE SOILS

Most agricultural soils with pH in the range 5.5-7.5 will produce satisfactory willow growth. However, light sandy soils, particularly in drier areas, may not hold sufficient moisture and highly organic should be avoided as initial weed control, which is vital, can be extremely difficult. Medium to heavy clay-loams with good aeration and moisture retention are ideal, although they must allow a minimum cultivation depth of 200-250 mm to facilitate mechanical planting.

2.1.2. WATER AVAILABILITY

Willow coppice requires more water for its growth than other conventional agricultural crops and hence requires a good moisture retentive soil. Areas with an annual rainfall of 900-1100 mm are best or where the crop has access to groundwater. The crop can tolerate occasional flooding, but this may have implications for harvesting. Nonetheless, willow has been successfully incorporated into natural flood management plans and novel harvesting techniques may be able to overcome this.

2.1.3. TEMPERATURE AND ALTITUDE

Willow in its native environment is a northern temperate zone plant and thus well suited to the climate of northern Europe. However, elevated sites can result in exposure problems and a reduction in the number of growing days per year. Therefore, production sites should generally be below 100 m above sea level.

2.1.4. SITE ACCESS

Harvesting is carried out in winter in the period December to April and whilst the root system of the growing coppice will support the harvesting and extraction equipment on the coppice site, hard access is required onto the site. Slopes greater than 13% will be difficult for harvesting machinery, particularly in wet conditions, and should be avoided.

2.1.5. SUITABLE LAND AREA

For logistical reasons there is a recommended minimum sustainable planted area. In most situations at least 5.0 ha and this should be in at least 2.0 ha blocks to facilitate large harvesting machinery. Smaller and irregular shaped fields are also more difficult to manage, and where rabbit fencing is necessary, they will be more costly to fence on a unit area basis.

2.1.6. LOCATION IN THE LANDSCAPE

Willow has more similarities with arable cropping than conventional forestry – it has a regular harvest pattern, and its deciduous nature gives it a seasonal diversity of texture and colour:

• SRC willow at the end of a 3 year growing cycle will be up to 8m tall, and therefore creates a 3D mass in the landscape which arable crops do not. Poorly planned SRC plantations have the potential to adversely affect the rural landscape. However, well-designed and carefully sited plantations could bring small but important landscape improvements.
• Siting in the landscape may well be constrained by existing enclosure patterns. Where these are well developed with hedgerows and trees, the problem is limited because sight lines are short. In addition to the deciduous nature of the crop, diversity is created with varietal mixtures and harvesting patterns.
• Because of the small-scale production and use patterns of SRC, it is unlikely to be a dominant landscape feature in any particular area.
• If enclosure patterns are weak, sight lines long, or topography flat, plantings should provide interlocking blocks with organic rather than geometric shapes. Additionally, in a large landscape, SRC plantings should be in scale and link up if possible with existing woodland to give visual and environmental benefits.
• If the extent of planting in any particular landscape is greater than the field pattern, it should conform to the overlying landform rather than be in larger rectangular blocks.
• SRC development is likely to be sited in landscapes which are already in agricultural use, and should not impinge on landscapes of special interest or scarcity.
• Short rotation coppice should not be planted on or adjacent to sites of historical importance or where it would obscure natural landscape features. Power lines will require consultation with the Utility Company involved, remembering that mature coppice can reach up to 8m before harvest.
• Sites with specific designations such as Areas of ‘Outstanding Natural Beauty’ or Areas of ‘Special Scientific Interest’ will also require consultation with the regulatory bodies concerned.
• Overhead power lines may pose a risk to farmers, contractors or anyone in the vicinity of machinery involved in site preparation, planting or husbandry of Coppice Willow. The Health and Safety Authority has published a booklet, ‘Guidelines for safe working near overhead electricity lines in Agriculture - Health and Safety Authority’ to ensure safety when a farming activity is carried out in the vicinity of overhead power lines.
• Coppice Willow in the 2-3 years prior to harvesting will reach a height that is very close to overhead power line heights. This can (1) create a serious electrical risk to anyone in the vicinity of harvesting machinery, (2) interfere with the safe operation of the power line. Contact ESB Networks before planting for advice if planting directly under an overhead power line is planned.

2.2. SITE PREPARATION

Since SRC willow is expected to be in the ground for approximately 25 years, thorough site preparation is essential.

2.2.1. SUB-SOILING

Land which has been regularly shallow ploughed or intensively grazed can both suffer from soil compaction. This will require deep ploughing and/or sub-soiling to allow full root development. Normally this would be carried out in the autumn before the soil becomes too wet and the ground is then allowed to weather over winter, subject to compliance with local regulation.

2.2.2. PRE-PLANTING PEST CONTROL

It is important that this phase is carried out effectively, particularly on old pasture land where the presence of perennial weeds such as docks and nettles is more likely. Herbicide application is required when weeds are still actively growing using a translocated (systemic) herbicide (Glyphosate 360 g/l product at 4-5 l/ha) in early autumn before ploughing, where permitted. Where leaving a field fallow for the winter is not permitted, spraying can be carried out in late winter/early spring, at least 10 days before ploughing. If necessary, the translocated herbicide can be re-applied just prior to cultivating and creating the seedbed. For stubble/arable ground a translocated (systemic) herbicide (e.g. Glyphosate - 360 g/l product at 3 l/ha) should be applied in early spring.

On grassland or set-aside sites measurements the need for controlling leatherjackets should be considered. Previously, Chlorpyrifos was used as a chemical control, however this is now banned in the UK and EU. Biological control methods and land management tend to be employed to control leatherjackets. Recommendations include ploughing in July to August (main egg-laying period) and covering the old sward. Additionally, a non-grass cover crop could be used, such as oilseed rape, the season before SRC willow planting. What is more, ploughing in March before planting exposes the larvae and allows birds to feed on the larvae, hence, encouraging bird populations on the farm is also advised.

Where sites have excessive heavy vegetation present, consideration should be given to cutting and removal of the vegetation to allow for effective weed control. If this is necessary, sufficient time should be allowed for re-growth to allow for active herbicide uptake.

2.2.3. SOIL TESTING & MANAGEMENT

Soil testing should be undertaken before planting. The pH and Soil Nitrogen Supply (SNS), phosphorus (P), potassium (K) and magnesium (Mg) indices should be screened for and should be adjusted during the site preparation stage if needed. There are multiple soil testing companies which can offer services with in-depth soil analysis and reporting. Even field level analyses can be provided to help carry out targeted nutrient application.

Based upon the results of the soil tests, nutrient or lime application can be carried out to adjust the levels to the optimal conditions for willow. It should be noted, unnecessary fertiliser application may only encourage weed competition during establishment.

What is more, baseline soil analysis can be used for identifying soil carbon stores.

https://ahdb.org.uk/knowledge-library/soil-and-forage-testing-companies

2.2.4. PLOUGHING

The plant or crop in the field must be dead/browning before ploughing. A minimum of ten days after herbicide application is required before the site can be ploughed. A minimum plough depth of 20-25 cm will be required to allow for insertion of the cuttings.

On free working soils, the site can be ploughed, and power harrowed, and a stale seedbed prepared in mid-March, 6 weeks before planting. The germinated weeds can then be sprayed off prior to planting using Glyphosate (360 g/l product at 2.0 l/ha). On heavy clay soils, this approach is not practical, and the site should be power harrowed as close to planting as possible. It may be necessary to remove stones after power harrowing to avoid interference with mechanical planters.

It should be noted, with the incurred cost of using expensive pesticides and negative environmental impacts, other methods of weed control have been explored. Relative amounts of success have been achieved with mechanical removal using a row crop cultivator with torsion weeder. A long-term study of mechanical weed removal shows little difference in mean yields in the 1st and second rotations when weeds were mechanically or chemically removed.

2.2.5. EXCLUDING VERTEBRATE HERBIVORES

Rabbits, hares, and deer, where they are present in sufficient numbers, can be very destructive in new and establishing coppice plantations and must be excluded with appropriate fencing. This is an expensive operation and where necessary, will represent the single largest cost in site preparation. The fencing may be temporary in nature as an established coppice is less susceptible to economic damage. Netting is generally used with the lower portion buried or turned horizontally to deter rabbits from burrowing underneath. Machinery is now available to plough in wire netting, and this substantially reduces the cost. Electric mesh fencing has proved satisfactory, but it must be kept weed free to prevent shorting out. The cost of fencing to exclude deer is prohibitively expensive, hence, alternative methods can be utilised. Planting of deer deterrent energy grass species such as Arundo, miscanthus, or switch grass, bordering SRC willow can reduce browsing from deer.

2.3. VARIETY SELECTION

Willow as a coppice crop is relatively new and considerable advances in increasing productivity and disease resistance are being made through breeding programmes, of which there are three: the European Willow Breeding Programme (EWBP) based in Yorkshire, The UK National Willow Collection at Rothamsted Research and that of the Swedish University of Agricultural Sciences in Uppsala marketed by Salix Energi. These breeding groups have produced varieties with significantly increased yields.

Commercially available varieties in 2023:

• Salix Energi - Tora, Sven, Torhild, Tordis, Olof, Gudrun, and Inger
• EWBP - Resolution, Endeavour, Beagle, Terra Nova, Advance, Meteor, Endurance and Paramore.
• Rothamsted Research - Roth Chiltern, Roth Cotswold, Roth Cheviot, Roth Mourne & Roth Hambleton

2.4. PLANTING MATERIAL

2.4.1. PLANTING RODS

Successful establishment depends on cutting quality. Cutting material is generally harvested between January – February when buds are fully dormant. Cuttings should be prepared from 1 year old wood, each planting rod having a minimum top diameter of 8 mm. It is important that this dormant state is maintained using refrigerated storage from -4 to -2°C up to the point of planting. Ideally, cold storage should also be provided on-site. This is particularly significant where delayed planting in the May-June period is anticipated. Dehydration is the most likely problem to be encountered in storage, thus, the cuttings and rods should be protected by wrapping in ‘polythene’ film. Generally, rods of - 1.6 to 2.2 m will be supplied by the specialist producer.

Planting rods should be:

• vigorous to ensure adequate carbohydrate reserves to sustain the cutting before establishment,
• be sufficiently mature (lignified) to prevent deformation on insertion into the prepared ground,
• not show any discoloration or wrinkling of the surface, indicating dehydration.

2.4.2. PLANTING MIXTURES

Melampsora species, a foliar fungal pathogen, causes willow rust disease. This is the primary limiting factor to sustainable production of SRC willow in cooler maritime regions, favoured by the cool moist climate (See section 4.3 – DISEASE & PESTS). An extensive research and development programme has been carried out by the Science Service of Department of Agriculture and Rural Development Northern Ireland (now the Agri-Food and Biosciences Institute) over the last 25 years to develop a non-chemical control strategy. The use of varietal mixtures has been particularly effective in this context.

Therefore, it is recommended that all commercial SRC willow plantations should contain at least 6 to 8 varieties sourced from different breeding programmes, to ensure maximum genetic diversity, and they should be planted in as intimate and random a mixture as practically possible. This generally means, when using the Step Planter, that the mixture will be planted as short runs (10 –15 cuttings dictated by the length of the rod used in the planter) of individual varieties followed randomly by short runs of the other mixture constituents as the planting rods are randomly fed into the planter.

It is imperative that mixtures of willow varieties are used when establishing a new plantation. These mixtures should contain at least 6 to 8 varieties drawn from different breeding programmes and have as wide a genetic diversity as is practically possible.

2.4.3. PLANT BREEDERS’ RIGHTS

All improved commercial varieties are protected by EU and/or UK plant breeders’ rights. In practice, this means that it is illegal to produce propagation material for self-use or sale from protected varieties. There is a minor derogation, which allows the gapping up of establishing crops with the material produced at cutback. Generally, therefore, cuttings will be produced by specialist growers in nursery beds and supplied as 1 year old rods for mechanical planting.

2.4.4. PLANTING MACHINERY

Rods are used in the Salix Maskiner Step Planter which has become the industry standard for establishing coppice willow crops. The planter will prepare individual cuttings from each rod. Other specialist planters including the Edegal Energy Planter and adapted vegetable transplanters have been used, however, the Step Planter has given reliable results in northern temperate conditions over several years.

3. PLANTING

Planting season extends from early spring (February/March) when weather conditions allow soil preparation, to late May and even June using cold stored cuttings. Early planting will give a longer growing season for the establishing crop with a lower risk of water stress from a late spring dry period. Late planting, especially in drier regions could lead to crop failure.

Over the years much information has been collected on a range of planting densities. To facilitate mechanical harvesting and machinery access, the crop is now planted in double rows 0.75m apart, leaving 1.5m between each pair of rows. An in-row spacing of 0.6m gives an initial planting density of approximately 15,000 cuttings per hectare. Establishment in good conditions should be more than 90%. Allowing for natural loss of stools in the early rotations, this should produce a cropping density of 13,500 per hectare. Where possible rows should be planted parallel to the longest axis of the field to maximise machine efficiency. Avoid placing rows across steeper slopes, as this will make accurate planting difficult.

Unplanted headlands can be a problem at harvest in the soil and climatic conditions of northern temperate regions. Harvesting and extraction machines require the increased carrying capacity that the root system of the growing crop provides. Therefore, sacrificial planting of marginal rides and headlands should be considered, in all but the lighter soils, accepting the reduced yield in these areas that compaction and rutting caused by harvesting and extraction will produce. If open unplanted areas in the coppice are required for environmental reasons, they are more easily managed as internal rides.

Several types of mechanical planters have been used but the dedicated Step Planter designed in Sweden by Salix Maskiner has become the industry standard. This machine plants two double rows at a pass and automatically makes cuttings from rods inserted into the planting heads. In ideal conditions, it has a capability of 6-8ha per day. However, in the smaller field sizes, as found on small holdings, this could be reduced to 4-5 ha per day.

After planting the site should be rolled to consolidate the surface and provide the best possible conditions for the application of residual herbicides.

4. POST PLANTING ESTABLISHMENT

Management of the crop post-planting for the first year is crucially important, particularly in terms of weed control. This cannot be over emphasised as newly planted willow cannot effectively compete against most weeds. As a pioneer species, willow has a low competitive ability. Hence, it’s imperative that the new plantation is kept as weed-free as possible during the establishment phase. If adequate weed control is not achieved, then a successful coppice system will not be established.

4.1. CUTBACK

During the first growing season, the inserted cuttings will produce 1-3 shoots with a maximum height of 2-3 m. Cutback (coppicing) after the first year of growth has been the standard practice in willow biomass production systems. There is discussion as to the necessity of cutback and the decision should be based on a range of factors. Field conditions, plant size, number of stems per stool, degree of weed competition, stage of plant growth and weather conditions can all affect the plant’s response to coppicing. In northern temperate regions where weed growth can continue throughout the year, cutback gives a second opportunity for herbicide application. Research has shown that there is little difference in yield between coppiced and un-coppiced plots after 4 years (4 straight years of growth versus 1 year of growth, coppice, and 3 years of re-growth).

Cutback occurs during its first winter to within 10 cm of ground level using a reciprocating type mower, which should produce a clean cut. Other types of swathers or flail mowers can cause excessive damage. This cutback will encourage the established cutting to produce multiple shoots, often eight to ten depending on variety. Re-growth is rapid and vigorous with ground cover/canopy closure being achieved by midsummer in the year following planting. Following cutback, the coppice enters its cropping cycle of between 2 and 5 years with the current industry standard being 3 years. At harvest, the coppice will have attained a maximum height of 7-8m. Only the most vigorous of the shoots produced at cutback will survive to this point, the weaker ones having been shaded out.

4.2. GAPPING-UP

However rigorously procedures were followed during planting and establishment there will always be gaps where a cutting was missed or failed to establish. This can be assessed at the end of the first growing season. Cuttings that have not been established in the plantation can be replaced through gapping up. If you cut back (see section 4.1), a lot of material will be available for gapping up. Push 1 metre rods into the gaps, leaving at least 50 cm protruding. This will allow the gapped-up willow to compete with those already established around it.

4.3. WEED CONTROL

Weed control can be divided into four distinct phases. The first phase of weed control has been covered in section 2.2.2 PRE-PLANTING PEST CONTROL. Details for chemicals to be used are provided in the Crop Management Prescription.

4.3.1. POST-PLANTING

An application of a pre-emergent residual herbicide mix to keep the crop clean during the establishment phase is required. There are several residual herbicides which can be used but a mixture of pendimethalin (455 g/l product at 3.3 l/ha) and isoxaben (500 g/l product at 0.5 l/ha) has been found to be an effective mix on a range of sites. These residual herbicides should be applied within 14 days after planting, it is essential that this is done before any growth begins. High volume (500 l/ha) applications should be used to give good surface coverage of the herbicide. The new crops should be monitored weekly during the first 3 months, so if any weed issues arise action can be taken immediately and effectively.

4.3.2. DURING ESTABLISHMENT

If weeds become a problem, as can be the case particularly on ex-grassland sites where the seed bank in the soil is greater than on ex-arable sites, there is only a very limited range of contact herbicides available for over-spraying the established crop. Additionally, these are highly specific herbicides with a limited weed spectrum. Effectively, there is only clopyralid (400 g/l product at 0.5 l/ha) for thistle control and fluazifop-p-butyl (150 g/l product at 1.5 l/ha), cycloxydim (200 g/l product at 2.25 l/ha) or propaquizafop (100 g/l product at 1.4 l/ha) for grass control. Other herbicides can be applied as directed sprays using an inter-row guarded sprayer. However, this is a skilled operation and should only be undertaken with advice as willow is highly susceptible to the herbicides used. Spot treatment of small areas of troublesome perennial weed (docks and nettles) can be undertaken with appropriate herbicides using guarded knapsack sprayers or weed wipes.

4.3.3. FOLLOWING ESTABLISHMENT AND AFTER CUTBACK

A further herbicide application will be necessary to keep the crop weed free until it achieves canopy closure, which usually occurs in midsummer of the second growing season. The use of the contact herbicide amitrole (225 g/l product at 2.2 l/ha), together with an additional application of residual herbicide – pendimethalin (455 g/l product at 3.3 l/ha), will provide the necessary control and should be applied before significant flushing, but delayed sufficiently after cutback to allow for wound sealing. Willow coppice has shown tolerance to amitrole just pre-flushing and therefore this application is made late March to early April. If weed cover is significant, a later cutback of the established crop in mid-March will delay flushing and will ensure that the weeds are actively growing, when they will take up the amitrole more effectively. Alternatively, inter-row selective glyphosate spraying could be utilised.

Mechanical weed control using inter-row cultivators is also an option but less likely to be effective in the climatic conditions in northern temperate maritime climates where the moist growing conditions do not favour the dehydration of the disturbed weed cover. The use of herbicides should be avoided if the crop is under any stress, particularly moisture stress, as crop damage is likely. There will be an increased emphasis on mechanical weed control in terms of sustainability and the high cost of chemical herbicide weed control. Some companies have now developed their own inter row cultivators.

It is important to read product labels prior to use and to follow the manufacturer’s instructions. Many herbicides or actives are being continuously removed from the market making the weed control challenge even greater. Products should not be applied if they are not approved by the Department of Agriculture – Pesticide Control Service (PCS) or local pesticide governing body. The application of herbicides which have not received approval, or which may have been removed from the market will result in cross compliance penalties. Controlling weeds, pesticides and diseases using husbandry techniques and approved materials to control pests and diseases… move towards sustainable/organic practice?

4.4. NUTRITION & FERTILISATION

Many soils have excess levels of phosphorus (P index > 3). This causes a significant potential to create surface water quality problems. With the relatively low level of phosphorus removal in the harvested SRC willow, the P status of the soil may well be adequate in most circumstances. The risk of nitrogen leaching from SRC willow plantations is relatively low compared with normal arable situations given the long-term perennial nature of the crop and the absence of soil disturbance through cultivation. The production of mineral fertilisers is heavily dependent on the input of fossil fuels when these are used on SRC willow plantations the energy balance (energy in vs. energy out) is adversely affected and GHG emissions may be increased.

Potassium can be relatively stable in soils and thus challenging for plant uptake. There is the potential for balancing most of the potassium exported from the site at harvest through returning the ash to the plantation after combustion of the wood chip to release energy. Two other important observations have been made over numerous years of growing SRC willow. Firstly, after the onset of serious rust (Melampsora spp.) infections on plantations in 1986, it was obvious that those stools in least competition for nutrients and light were those which were least affected by rust. In particular, the problem of stool death caused by entry of secondary dieback organisms into the stem tips following defoliation by the rust infection were less obvious. Additionally, reiterating the importance of planting mixtures (see section 2.4.4), mixed plantations with increased genetic diversity are more resilient to onsetting rust infections. Secondly, it’s also evident that in plantations where vigour had declined through poor nutrition, it was difficult if not impossible to recover that vigour. Hence, raising the necessity of maintaining the nutrient capital of the soil by balancing off-takes.

As with any crop, fertiliser should only be applied as the result of formal soil analysis and the consideration of other inputs should be reviewed. In perennial crops internal recycling of nutrients in the leaf litter can be utilised. In the case of SRC willow, current available research and data suggest a level of nutrient off-take in the harvested crop and this should be used in calculating fertiliser requirement.

There is evidence that on moderate to fertile soils particularly in the early rotations there is not necessarily a positive response to fertiliser applications, however, sites with a naturally poorer nutrient capital may need these early applications to maintain productivity. Fertiliser application is not recommended on most sites in the first growing season because the nutrient capital is generally adequate for establishment and the crop will not have developed the necessary root system for effective uptake. Additionally, it is in the establishment year that weed control is likely to be most difficult and fertiliser application may well exacerbate the problem.

Table - Nutrient cycling from SRC willow leaf litter – leaves allowed to fall before harvesting

Table - Typical offtakes of nutrients in wood harvested from short rotation coppice willow after 3 years growth following the previous coppicing are shown:

4.4.1. Biofiltration and The UK Fertiliser Recommendations (DEFRA RB209)

Although The DEFRA Fertiliser Manual (RB209: 8th Edition) suggests what level of nutrients are required to provide the “best financial return for the farm business” (page 1). It should also be noted that the authors of the Manual acknowledge that the data presented in the table (N and P off-takes by willow) on page 175 of RB209 are based on limited published information.

Unlike other crops described in the Fertiliser Manual (RB209: 8th Edition), SRC willow is officially recognised on page 175 as a crop capable of performing environmentally sound functions associated with bioremediation and bio-filtration capabilities and this can warrant the nutrient application rates outside the guidelines in the manual. On page 176 it also recognises the need for willow to have nutrient in years 2 and 3 from a single application in year 1, due to the difficulty in physically accessing the crop.

Current Application Regulations as agreed by NIEA (Northern Ireland) The application of 180 kg N ha-1 year-1, based on off takes is currently agreeable.

If the N is applied in conjunction with phosphorus (unbalanced crop requirement ratio eg biosolids), this can result in an accumulation of P in the soil which needs to be monitored.

Solid organic fertiliser can be applied to soils to P index 2, soils without concern of P leaching or run-off. This should cease when soils reach P index 3

The rate of P application will depend on the source of organic waste and the regulatory instrument in falls under. 24 kg ha-1 year-1 is a current workable estimate.

When irrigating low nutrient waste waters to src willow, communication and in-depth discussion with the environmental regulator is essential to weigh up and mitigate environmental risks with environmental, community, practical and other associated benefits.

The ongoing analysis of soil, soil-water and groundwater would normally be considered unnecessary, however in exceptional circumstances more detailed monitoring may be undertaken.

The Northern Ireland Environmental Regulator has current published soil testing regimes for application of certain organic wastes and will review other environmental analysis requirements on a case by case basis. TABLE - Soil P index

• Nitrogen 100% availability
• Phosphorus 100% availability
• The regulator may agree Phosphorus over addition for different organic wastes and on the basis of building up soil P reserves.

Current Application Advice from Teagasc (Republic of Ireland) Nutrient recommendations differ slightly between countries, recommendations can be summarised as follows.

TABLE - Willow nutrient recommendations: Teagasc (ROI)

• Nitrogen 40% availability
• Phosphorus 100% availability
• Local authorities may agree differing Phosphorus availabilities for different organic wastes

4.5. DISEASE & PESTS

4.5.1. LEAF RUST

Leaf Rust (Melampsora spp.) is the most important fungal pathogen of SRC Willow and potentially the most limiting to sustainable cropping, particularly in cooler maritime type of climates, which favour the development of this disease. It is a heteroecious rust (has an alternate host) and is first seen on willow in late spring – early summer as small orange coloured rust pustules on the underside of the leaf. These initial infections classically develop from aeciospores which have been formed on the pathogen’s alternate host – European Larch (Larix decidua). Development on the host willow is through repeated asexual cycling of urediniospores. This cycle can be as short as 2 weeks and consequently can lead to serious levels of infection very quickly on susceptible genotypes. High levels of infection result in premature defoliation, reducing growth, and more seriously enabling the entry of secondary dieback pathogens through the unprotected leaf scars. These dieback organisms (Fusarium sambucinum and Glomerella miyabeana) can cause significant levels of damage to, and subsequent death of shoots and stools. Yield losses in excess of 50% have been recorded.

Significantly, in moist and relatively mild winters, it’s also believed that Melampsora spp. urediniospores can survive over-winter in the bud scales and leaf litter, without the need to go through the alternate host. This can lead to infection and serious disease levels early in the growing season.

In common with most fungal diseases, control could be achieved using fungicides. However, in the case of SRC willow, this is not considered a practical solution for a number of reasons:

• economics - SRC willow is a high volume, low value crop and the necessary repeated fungicide applications could not be sustained economically,
• SRC willow is seen as an environmentally acceptable crop and the intensive use of fungicides would not be compatible,
• and practically, after the early stages of re-growth following coppicing, it is increasingly difficult to achieve the necessary chemical coverage of the plant to effect adequate disease control.

As a result, an alternative non-chemical disease control strategy needed to be developed and this has been the subject of ongoing research since the late 1980’s.

Since the major contributing factor to the development of rust disease was the lack of genetic diversity in the single variety plantations used in the early years, it was argued that the introduction of diversity by planting mixed variety plantations would be effective in control. This has proved to be a successful approach, with mixtures delaying the onset of the disease and reducing its spread, so that at the end of the growing season, the disease, although still present, was not at levels where yield was affected. This is a more sustainable approach, and several statements about mixtures can be made:

• Evidence clearly indicates that where disease pressure is high, such as in cool temperate maritime regions, the planting of single variety plantations even where the variety is less susceptible or resistant to rust, is a short-term high-risk strategy and not to be recommended. There are examples where previously resistant varieties have become susceptible as the natural rust population has evolved, resulting in severe losses in single variety plantations.
• The yield of the improved varieties from the breeding programmes in Sweden and the UK, together with their superior rust resistance, means that only they should be used in commercial developments.
• Yield from diverse mixtures is greater than the equivalent yield of the mixtures’ components grown in monoculture, even in the absence of the disease.
• Where less diverse mixtures have been planted e.g. mixtures of exclusively Salix viminalis varieties, these yield increases have not been recorded and the disease suppression aspects, whilst present, are not as marked. This is an important consideration since many of the commercially available improved varieties are of S. viminalis origin.
• Furthermore, increasing diversity in mixtures can result in yield compensation, where individual components of the mixture become susceptible to the disease over time and make increasingly smaller contributions to yield. This yield compensation occurs because of the remaining varieties occupying the space left by those that have become disease susceptible.

Consequently, at least 6 to 8 varieties should be included in commercial plantations. With the step planting machinery used, short run random mixtures are achieved which are as effective as completely random mixtures. There are differences in how individual mixture components contribute to the overall yield of the mixture and provided that individual components do not have a significant negative effect, their inclusion is justified by the diversity they bring and the positive effect they have as a result on sustainability.

4.5.2. WILLOW BEETLES

Willow beetles are part of the greater leaf beetle family, Chrysomelidae: This group of beetles represent a major economic pest problem in SRC willow.

There are three species of willow beetle involved include;

• brassy or green (Phratora vitellinae),
• blue (Phratora vulgatissima),
• and brown (Galerucella lineola).

The blue and brown species are more prevalent. Overwintering adults emerge from hibernation in April and, after a short feeding period, begin to breed. Egg-laying takes place between early May and late June. Larval stages are found from mid-May into July and develop through 3 instars before pupating. The new generation of adult beetles appear in July/August and feed until hibernating in the autumn. There can be 2 generations per year – the first emerging from the eggs laid by overwintering adults in May and a second generation in August. Adults feed on the upper leaf surface whilst the larvae feed on the underside of the leaf which eventually is skeletonised and turns brown. Unlike rust infections, skeletonised leaves usually remain attached. Economic damage has been recorded in the UK. However, damage may visually appear severe but defoliation experiments have shown if <30% leaf surface is damaged the effect on yield will be minimal. However, the willow plant has been shown to have increased sensitivity to beetle attack during the initial stages of regrowth following harvest, with significant effects recorded on both root and shoot growth. Beetle populations vary considerably from year to year, and just because there may be a heavy infestation in a particular year, does not mean that the following year will be equally affected. The overwintering adults often hibernate off-site, and this provides the only economic opportunity for control. If population numbers are large, they can be reduced by target spraying the borders of the plantation with insecticide when the beetles are re-colonising the plantation from their overwintering sites in early spring. However, this is a one-off operation and routine spraying is NOT recommended for both economic and ecological reasons. Mixtures have also been found to be effective in limiting damage as there is a variation in feeding preference of the beetles between the different varieties. The modern improved varieties also have increased resistance to insect damage.

4.5.3. OTHER PESTS

There is a range of other potential pest species feeding on willow and the most obvious of these are the various aphid species. There are 2 large species which form extensive colonies on the stems in late summer/autumn - the giant willow aphid, Tuberolachnus salignus, and the black willow aphid, Pterocomma salicis. These aggressive aphid species can grow to 6mm long and can form large colonies on the woody stems of some willow varieties. Both have been shown to have significant negative effects on above ground biomass yield and root systems. However, as with other aphid species, control with insecticides is not desirable either environmentally or economically, and nor is it possible practically. There are also various midges (Dasyneura spp.) which can result in the death of the terminal bud or can cause rolling of the leaf margins. Their effect on yield is uncertain and control is not practical. Sawflies have also been identified as potential pests of willow. If insect pest damage is detrimentally affecting plant health and yield, localised spot treatment using an insecticide such as lambdacyhalothrin in a knapsack, adhering to suppliers’ safety precautions, would be advised as a last resort.

5. HARVESTING

Cutbacks are a form of harvest and take place after the first year of growth. This initial growth period is to allow roots to set. Cutbacks are not always necessary and are dependent on-site specifics, such as soil quality and climatic conditions etc. However, if deemed suitable, the cut back will take place after the first year of growth and the cropping cycles begin. Cropping cycles, also known as rotations, in SRC willow can be from 2-5 years. Research has suggested that 3-year rotations are the most favourable for yields. In a system where cutbacks may be deemed unnecessary, the first harvest will take place after 3 years of growth, allowing for the setting of the roots in year 1 and initial shoot growth in the establishment year, followed by 2 years of biomass building. This is then followed by 3-year rotations for the duration of the lifespan of the plantation. However, this will be dependent on the land use, e.g. if the purpose of plantation is for biofiltration of slurry and/or leachates, which can be high in nutrients, efficient growth may occur to be able to harvest every 2 years.

5.1. TIMINGS

The harvesting window for the SRC Willow is from leaf fall to bud burst/flushing in the spring. In normal conditions, this gives a 3 to 3.5 month period from December to mid-March. In wet northern temperate conditions, soil trafficability is at its worst in this period and hence the need for hard access to the cropping site. Where earlier bud burst can be expected because of favourable site conditions, harvesting time should take account of this. Bud burst results from the mobilisation of a significant proportion of the reserves stored in the roots and stems and their transport to the developing shoots. Their removal in harvested material could weaken the stool, delay flushing, and lead to increased weed competition. Consequently, harvesting should be carried out on dormant stools. There are several approaches to harvesting: direct chip harvesting, whole rod harvesting, billeting, and baling. Each method has its own advantages and disadvantages. Harvesting is seen as a co-operative or contractors’ operation because of the specialised nature of the machines and the justification of their cost on relatively small individual holdings. It is unlikely that any single option will be the correct choice across the board. The availability of drying and or storage facilities, the requirements of the supply chain, site conditions etc. will determine choice.

5.2. HARVESTING METHODS

5.2.1 DIRECT CHIP HARVESTING

Chip harvesting is by far the most practical and common harvesting technique for the production of SRC willow biomass. Other methods are listed in the sections below, which can be utilised for varying end uses.

In this system the crop is cut and chipped and the harvested material used immediately or artificially dried to prevent deterioration. Each double row is cut in a single pass, using specialised harvesting heads mounted on standard forage harvesters and the green chip is blown into high side silage trailers for transportation to storage or the end user.

This is the most efficient harvesting operation but will require dedicated drying facilities if the chip is not being directly supplied to the consumer or processor. Green chips containing ~50% water, if untreated, self-heat, through the activation of decomposition by thermophilic microorganisms. This can lead to deterioration in fuel quality, loss of energy and mould growth with health and safety implications.

Ventilated grain drying floors have been used successfully and are available after arable crops have been sold. Forage harvesters have a capacity of 5-6 ha/day, though, in small holding conditions where field sizes may be small actual rates are likely to be 3-4 ha/day.

5.2.2. WHOLE ROD HARVESTING

With this method the crop is harvested as individual rods, which are then collected loose and stored outdoors in drying stacks. To date, no successful bundling and tying machinery has been developed and moving loose 6-8m rods can be difficult. Once dried, the rods will be handled for a second time during chipping.

Harvested rods are stacked on a hard standing area and with adequate natural ventilation will dry without deterioration, avoiding the need for specialised drying facilities. In northern temperate conditions during the winter months limited drying occurs. However, during the 3 months of spring, moisture levels will drop to approximately 30% and can fall to 25% through the summer.

Woodchips produced from dried rods may have a wider range of particle sizes and an increased dust fraction than that produced from direct chip harvesting. There is also a higher power requirement for the chipping operation. However, in northern temperate conditions, where individual coppice plantations may be small isolated, and without access to on-floor drying facilities, this may be the harvesting method of choice, even if it is more expensive.

The ‘Stemster’ whole rod harvester is a well proven design and has been operating in Ireland for a number of years. It weighs 7.5 tonnes empty and can carry approximately 2.8 tonnes of 4 year old willow. with a work rate of approximately 2 ha/day.

5.2.3. BILLET HARVESTING

An intermediate system between direct chip and whole rod harvesting. Originally developed for sugar cane and producing billets 5-10 cm in length, which are blown into trailers for transportation.

Due to billet size which allows air circulation, natural drying can occur in the same way as with whole rods. Billets will need to be chipped prior to use to maximise combustion efficiency, but unlike whole rods, they can be handled mechanically. However, chip quality may be reduced because the wood is relatively dry at 30% MC.

5.2.4. BIOBALER

The Biobaler from the Anderson Group in Canada was developed to compress biomass from woody weeds in between plantation rows. It has also been used to harvest SRC willow.

In a single pass, with only one operator, the Biobaler cuts and compacts biomass into a dense round bale. Thus, allowing cost-effective transportation from field to processing facility using conventional equipment.

Bales can be delivered immediately to customers or stored close to the field. Bales of biomass are not expected to deteriorate during storage even if harvested in wet conditions as they dry out naturally and without risk of self-heating, unlike a pile of fresh woodchips.

Research has shown that the moisture content of bales falls rapidly in the months after harvest reaching below 20% MC by the following summer.

6. POST HARVEST

6.1. YIELD

The principle on which crop yield is based is the conversion of light energy through photosynthesis into chemically bound energy in the economically valuable part of the crop. In the case of SRC willow, the above ground woody stems. It has been estimated that these represent 60% of the total biological yield, with 10% allocated to the leaves, and 30% to the stool/root systems. The leaves and fine root systems are recycled on an annual basis contributing to the soil organic matter.

For SRC willow, yield is normally quoted as tonnes of dry matter (DM) per hectare per year (DM/ha/yr). DM weights (water content = 0%) are used because they standardise the figures where fresh weights, which include moisture, vary depending on water content.

To optimise economic yield, the crop canopy must be maximised as early as possible in the rotation and maintained for as long as possible throughout each growing season. This ensures efficient interception of solar energy, thereby maximising yield potential.

On suitable sites, canopy closure or complete site capture usually happens in the second year of the first cropping cycle. However, it is delayed to the third year on poorer sites with resultant loss of yield. This can be exacerbated with light penetration to the soil allowing weed development to compete with the coppice crop.

Harvesting is normally carried out on a 3 year cycle. However, due to other considerations including the use of sewage sludge for optimising yield on poorer sites, cycles of 2 years may also be considered. This is particularly the case when high yielding hybrids are grown in mixtures where individual stem size could cause problems with harvesting.

A wide range of yield data has been published derived from randomised and replicated small trial plots. Yields in excess of 30 tonnes DM/ha/yr have been obtained where crop nutrient and water requirements have been supplied artificially. However, this should be considered as the theoretical maximum for the species and not a commercial reality.

Using available improved varieties from the three breeding programmes and planting them as recommended in minimum 6 to 8 variety mixtures, sustainable yields of 10-12 tonnes DM/ha/yr can be achieved on better sites. Influencing factors such as soil, fertility, light, exposure, or water availability can determine the suitability of a site and expected yields. Further ongoing improvements in planting material in terms of both its productivity and disease resistance could soon lead to 12-14 tonnes DM/ha/yr yields. Yields from the first cropping cycle can be expected to be lower than subsequent cycles because complete site capture is not achieved until the middle of the second year of the first cycle. Thereafter, yields will reach a plateau with the normal seasonal variations, due to the prevailing weather conditions etc. A 1 ha block of a 7 way mixture grown on a light soil in Co. Carlow, Ireland, yielded 12 tonnes DM/ha/yr at the first harvest and 12.3 tonnes in the second harvest.

There is still uncertainty over the yields that can be expected from different soil types although, in general, better yields can be expected from better soils. Extended cropping cycles have shown that yields can be sustained over 8-10 cycles when improvement in the available planting material could, on its own, justify replanting.

6.2. DRYING & STORAGE

SRC willow is generally harvested at ~50% moisture content (MC). For safe long-term storage of wood without mould deterioration and associated health risks the biomass material should preferably be below 25% MC. Also, small to medium scale biomass boilers normally require a good quality processed chip at or around 25% MC. The lower the moisture content the higher the heat output.

Generally, it is only the direct harvested chip that requires immediate drying in dedicated facilities. Harvested whole rods and billets do not have the same self-heating potential and will dry naturally down to between 25% MC and 35% MC. At the higher end of this range, the wood chip will often continue to require some extended drying or will need blending with drier material to establish a stable MC of around 25%. With decreasing wood chip moisture:

• net heat output increases,
• boiler efficiency increases,
• gaseous emissions decrease,
• boilers require less servicing.

Efficiency of drying depends on the temperature and relative humidity of the air used. The warmer the air, the lower the relative humidity, the more efficient the drying process will be. Generally, whilst large-scale combustion facilities accept chipped material directly from harvest (~50% MC), smaller heating equipment will work more efficiently with drier material. Completely dry wood has an energy content of approximately 19 MJ/kg. However, in wood at 30% moisture, this is reduced to approximately 14MJ/kg of usable energy because of the need to use a portion of its stored energy to remove the water before combustion can take place.

6.2.1. DRYING FLOORS

Drying floors are common in grain producing/storing farms, they can be used for drying grain, oilseed rape and woodchip. Drying floors usually consist of concrete slabs with ducts/vent strips that allow for warm air to be blown through the floor. The heated air is blown by a fan system through tunnels under the floor which then dissipates throughout the whole drying floor via the vent strips. This allows for the even and efficient drying of large quantities of woodchip. What is more, if a biomass boiler is set up in the location of the drying floor, it can provide the source of heat.

Ventilated drying floors have been used successfully to dry wood chip from SRC willow. They can achieve the required moisture contents for storage relatively quickly (3-6 weeks). Heated air (6-10oC) above ambient, to increase its water holding capacity, is circulated. This drying operation for direct harvested chip must begin immediately after harvest, as self-heating begins very quickly.

However, drying floors are an expensive initial investment. Hence, will not be readily available to newcomers to the biomass crop production industry or small holders. Alternatively, centralised grain-drying type drying floor facilities could be provided on a co-operative basis linked to the contract harvesting of the crop.

6.2.2. SIMPLE ON-FARM DRYING

Although the potential for co-operative grain-type drying floor facilities, this is not always practical. E.g. The number of growers in a rural area could be very low, requiring the wood chip to be transported farther than is economically practical. Therefore, there is a need to develop simple low cost drying systems which can be deployed at small scale, for example, utilising perforated ducts and low-rate ventilation from small fans. The practicalities of using conventional on-farm facilities are currently being investigated.

A low-cost, simple approach for drying willow chips has been developed and successfully demonstrated. The system employs a single-phase fan which blows air through a perforated duct. A clamp is constructed around the ducting into which fresh chips are loaded and is covered once filled. An air flow rate of 150m3 /tonne of wet chips for twelve hours a day, over a period of 3 months, was used to dry chips from a moisture content of >50% to <20%. Industrial non-heated fans operate between 0.10 – 0.30 kWh. Calculations of cost can be made depending on fan used, cost = (kWh x time (hours)) x cost per 1 kWh.

Whichever drying system is used, it is vital to provide consistent, high-quality fuel to the end user, both to optimise boiler operation and to achieve a standardised dry matter on which to price the fuel. With more advanced systems e.g. gasification, a lower moisture content of 10% will be required.

6.2.3. WOODCHIP QUALITY REQUIREMENTS

Willow woodchips used for combustion in small to medium scale boilers should meet specific quality and moisture standards set by the equipment manufacturers. Typically, moisture content needs to be less than 30% to avoid inefficient combustion and increased emissions. Willow chip size should conform with either the P16 (80% of chips smaller than 16 mm) or P45 (80 % of chips smaller than 45 mm) quality standards depending on the size of the boiler. The presence of unscreened large pieces causes auger restrictions and dust build up, restricting or stopping fuel flow.

Dried woodchip may require initial screening to improve fuel quality by removing oversized and undersized pieces and dust. A secondary stage to meet the P16 and P45 quality standards might then be needed. Commercial screening equipment is available.

6.3. TRANSPORTATION

The conventional methods for transporting harvested SRC willow can vary depending on the location, distance to the processing site, as well as the scale of the operation. However, some of the most commonly used methods for transporting harvested SRC willow are:

• Road transport: Harvested SRC willow is often transported by road using large trailers. The transportation cost can vary depending on the distance, the size of the load, and the type of vehicle used.
• Rail transport: In some cases, harvested SRC willow can be transported by rail, especially for longer distances. This can be a cost-effective option for large-scale operations. This method is typical for large scale biomass power stations.

When transporting harvested willow material by road vehicles will be subject to restrictions on load dimensions and weight. Weights should not exceed a reasonable weight, having regard to the engine capacity, brakes, tyres, and general construction of the vehicle. Dimensional limits that apply to agricultural vehicles in the UK as of January 1, 2016:

Length = 12 m (or 18.75 m when combined – i.e. tractor and trailer or other interchangeable towed equipment). Height = 4.65 m. Trailers used to transport loads of baled agricultural produce such as hay or straw etc. are exempt from this height limitation. Widths =

• Agricultural tractors and trailers – 2.55 m;
• Large tractors – tractors with a laden weight exceeding 7.52 tonnes – 2.75 m;
• Tractors with flotation tyres or dual wheel systems – 3.5 m; and
• Fully mounted equipment and interchangeable towed equipment – 3.0 m.

When transporting willow in bulk chipped form it can be transported on a walking floor trailer in 96m3 loads. Most operators report minimum loads of 17-19 tonnes per load at 20% MC indicating a bulk density of about 187-200 kg/m3. Where the willow is to be transported at 50% MC there would be 28-32 tonnes on the load giving a bulk density of 300-330 kg/m3. It should be again noted, weights should not exceed a reasonable weight, having regard to the engine capacity, brakes, tyres, and general construction of the vehicle.

6.4. SITE RESTORATION

When a willow coppice has reached the end of its life, the site will need to be restored to either grass or arable production or replanted with new higher yielding varieties of willow. In many of the heavy wet sites considered suitable for coppice, the root system of the crop will have improved soil structure and its mechanical removal may well cause significant damage.

Methods used to restore the land are listed below:

• After the last harvest, allow stools to re-sprout until they are 60-90 cm tall.
• Willow is extremely susceptible to herbicide, so a single application of a translocated herbicide glyphosate (e.g. 5 l/ha Roundup) is sufficient to kill off the actively growing crop. The crop should be left until the leaves are desiccated and stem bases turn brown to allow full absorption and translocation of the herbicide.
• Using heavy disc harrows, a rotavator or forestry mulcher, the stools and surface layer of the soil are incorporated to form a shallow tilth layer into which the grass is sown. This leaves most of the root system in place without damaging the soil structure.
• The return to grass production will take a full season. Reverting to arable will require a longer grass break to allow roots to decay, otherwise a much more involved and costly mechanical removal and collection of the stools and roots will be required.

Alternative options - depending on variety, cattle will graze on the young shoots. Similarly to herbicide treatment, shoots can be allowed to grow to 60 – 90 cm. Instead of being treated with glyphosate, cattle can graze on the willow shoots. This will strip the shoots of their leaves and bark which in turn will reduce the growth and eventually lead to the death of the stools. Advantages of this would be less compaction and pesticide usage.

7. ADVANTAGES & DISADVANTAGES

7.1. ADVANTAGES

• High yield potential: SRC willow has a high yield potential and can produce large quantities of biomass in a relatively short period of time. This makes it a popular crop for bioenergy and biofuels production.
• Renewable energy source: SRC willow is a renewable energy source that can be used to generate heat, electricity, and other forms of energy. It is considered to be a more sustainable and environmentally friendly alternative to fossil fuels.
• Carbon sequestration: SRC willow can sequester carbon dioxide from the atmosphere, which helps to mitigate climate change.
• Soil improvement: SRC willow can improve soil quality and reduce soil erosion. It can also help to control nutrient runoff and reduce fertiliser requirements.
• Environmental improvement: SRC willow can act as a refuge for nesting birds and the catkins can provide an essential food for insects and birds. Biodiversity in SRC willow plantations are higher than would be typically observed in arable crops.

7.2. DISADVANTAGES

• Land use: Planting and growing SRC willow requires land, which can compete with other land uses such as food production, which can offer more profit per ha of land.
• Water use: SRC willow requires water to grow, which can be a concern in areas with limited water resources.
• Pest and disease management: SRC willow is susceptible to pests and diseases, which can require management practices such as pesticide use.
• Harvesting and processing: Harvesting and processing SRC willow for biomass production can be costly and require specialised equipment