Willow crop production - the basic story

By Roger McDermott, FTMTA

31 December 05 : As part of Budget 2006, the grant aid and tax exemptions for the production of Biofuels received a twenty fold expansion, and as a result of this you can be sure that bioenergy will gain more and more interest. Expansion in the Biofuel industry could provide farmers with a valuable alternative use for their land, in the form of energy crops. And with rising fossil fuel prices, renewable energy policies and carbon taxes, these energy crops providing a clean, sustainable, carbon neutral energy may well be a preferable commercial option. This article takes a look at the growing of one such energy crop, Short rotation coppice Willow, as a commercial energy crop.

Production of short rotation coppice willow

Ireland has the fastest wood-growing climate in Europe, yet we rely on fossil fuel imports for 90% of our total energy requirements. Short rotation coppice (SRC) willow is suitable for growing in Irish climatic conditions is considered to have the greatest potential as it can coppice well and has a high productivity.

Willow grows rapidly in the temperate Irish climate with best results on good agricultural soils; however it can also be grown successfully on soils that are marginal for traditional crops.

Generally, better quality soil will produce greater yields earlier in the rotation. Sustainable yields of 10 to 12 tonnes dry matter per hectare per year can be achieved in Ireland on suitable sites.

These plantations not only produce large quantities of renewable wood fuel, but can also be used as controlled, environmentally sound treatment zones for problem slurries and waste water. This fertilizes the crop to increase yield while at the same time providing a sustainable solution for the waste producer.

Growing the crop

The crop is grown from cuttings which are mechanically planted. Effective weed control is absolutely essential when establishing a new plantation; however inputs of fertilizer and chemicals are lower than for most agricultural crops. Depending on ground conditions the Willows will reach a height of 2 - 3 metres in the first season. They are then cut back; this is known as coppicing and encourages the growth of multiple shoots.

Preparing the land to plant willows is similar to preparing a cereal seedbed, but it needs to be cultivated more deeply. This usually involves ploughing to a depth of 20 - 25 cm in autumn, followed by power harrowing shortly before planting.

A good test is to ensure that a person can push a 20 cm long cutting into the ground by hand, if not, machine planting will be difficult.

Weed control

Newly-planted willow cannot compete strongly against most weeds, and timing of weed control is critical. Most plantation failures are due to weed competition.

Prior to planting, weeds are encouraged to germinate and then killed by cultivation or the application of herbicide. Common practice is to apply a translocated herbicide in autumn, with a follow-up application shortly before planting in spring.

After planting it is usual to apply residual herbicide before the weeds emerge. After harvesting, weeds will initially develop faster than willow shoots, but well-rooted willow can often overtake the weeds and close the canopy after mid summer.

Planting machinery and time

Cut-and-plant machines have been used successfully for large areas of willow coppice. Long willow sticks, fed by hand into the mechanism, are pressed vertically into the soil to a depth of 200 mm and automatically cut just above ground level. Four-row machines planting 20,000 cuttings/ha can achieve work rates of 6 - 8 ha/day.

The planting material needs careful selection for these machines as the sticks must be reasonably straight in order to feed through the mechanism. Transplanters, similar to those used for vegetable seedlings, can be adapted to plant willow cuttings, but the operation is labour intensive.

Usually the soil is then immediately rolled after planting, firming the soil around the cutting. The soil should be firm enough to prevent a person pulling cuttings out of the ground using finger and thumb. Willow is generally planted in spring; though planting from December through to June is possible.

Early planting leads to more problems with weed control. Crops planted later need less herbicide, but are more susceptible to drought.

Fertilizing and liming

Fertiliser is generally not used in the crop's first year, as they tend to increase weed growth. Liquid bio-solids can be applied in the second and subsequent years by a hose reel irrigator and dribble bar. This offers a very useful waste management system for producers of waste. Lime, where needed, is applied before planting or immediately after harvest.

Harvesting the Crop

The first harvest is usually taken off four years after the willows have been planted i.e. three years after coppicing the willow. Harvesting is carried out in the winter months when there are no leaves and when the moisture content in the stems is at its lowest.

A Forage Harvester, with a modified maize header specifically adapted for use with willow can be used successfully for harvesting. The willows are chipped whilst going through the harvester, blown into a silage trailer and taken back to the yard where they are tipped onto a grain drying floor for drying. At time of harvesting, willows have a typical moisture content of 50%. Normally a harvester can cut up to six hectares per day dependant upon ground conditions and accessibility.

Plantation removal

The economic life of a willow plantation is expected to be up to 25 years, some farmers may want to re-plant earlier if improved varieties become available, or if the economics of production change. Studies indicate that land growing willow coppice can be returned to agricultural production without major difficulties.

The coppice stools have to be killed using herbicide after the final harvest. Ploughing, followed by use of a heavy disc harrow or rotary cultivator, will then break down the stools. In practice this usually involves at least one "fallow'' year before the land returns to agriculture. The overall cost of producing willow is approximately €2,500 to €3,000 per hectare, which is quite high.

However, a planting grant would make the growing of willow a much more attractive option and with an economic life of up to 25 years, the future of willow plantations in Ireland could be bright.

Processed wood pellets achieve a price of approximately €150 per tonne, and after growing the main expenses will be harvesting, drying and processing the willow into pellets.

Willow, like other energy crops has potential for providing farmers with an alternative and fresh option for the use of land, and with more government money being allocated to the development of the biofuel industry, growing these crops may become an attractive option sooner rather than later.

Key Points

• Willows

• Good land needed.

• Weed control essential.

• 4 years to first harvest

• Lasts up to 25 years.

• Costs €2,500-€3,000/ha to establish.

• Wood pellets €150/t.

• Yield 10-12 t/ha.

• Future prospects - yes but city sludge fees are a huge help for real commercial viability.