Growing biomass in the form of Short Rotation Coppice (SRC) willow offers a viable and economic option.

Why willow? Willow (Salix spp.) is a native tree and many of its species / varieties are particularly well suited to growing in the cool, wet maritime climate typically found in Ireland. It is easy to establish and grows extremely rapidly. Willow can be coppiced, meaning that in the Winter it can be cut back to ground level and the 'stool' left in the ground will resprout the following Spring.

Growing cycle: Willow is planted as hardwood cuttings in the Spring. Planting can be done mechanically using a step planter. Planting density is between 15,000 and 18,000 plants per hectare. Previous to planting the ground needs to be well prepared. For good establishment
and early growth, weed control is essential and a number of herbicides are available. At the end of the first (establishment) year the shoots are cut back. This ensures a strong, well-developed stool. The willow is then allowed to grow for three years before harvest and is harvested on a three-year cycle. It is possible to harvest 8–10 times giving a willow plantation a life of approximately 30 years. Hence if you harvest every three years you get the equivalent of 30 - 36 tonnes (dry matter) or approximately 60 to 76 tonnes wood with 50% moisture content.

In order to reduce rust disease problems it is recommended that plantations contain a mixture of at least six Salix spp genotypes – three from the European breeding programme and three from the Swedish breeding programme. Using mixtures of modern willow varieties and with good management yields of 10 – 12 tonnes (dry matter) hectares per year are readily achievable. The willow can be harvested with a forage harvester to produce wood chip. This chip is about 50% moisture at the time of harvest and needs to be dried immediately to reduce moisture to less than 20% for storage and utilisation. It is also possible to harvest willow as billets or even whole rods. If left in the field these will dry naturally to approximately 30%. However, a second handling procedure will be needed to produce wood chip.

Site selection: While willow is a highly versatile crop, correct site selection is absolutely essential for commercial production. Sites should not be more than 100m above sea level, should have a slope not greater than 30 degrees and must have hard access for planting and harvesting activity. Willow will grow in most soil types although organic soils should be avoided, as weed control is often impossible in such soils. It is commercially impractical to plant less than 5ha.

End uses: Currently approximately one third of energy requirements in Ireland are for heat production, one third for electricity production and one third for transport. The primary focus for willow wood chip is for heat production and a number of highly efficient wood chip boilers are commercially available. As part of an INTERREG IIIA project, ‘RENEW’ (Renewable Energy Networks for Environmental Welfare) willow wood-chip boilers have been installed at the new College of Further Education in Omagh, Co. Tyrone and at Gartan Outdoor Centre in Co. Donegal. Before considering planting SRC willow it is essential to explore potential end use outlets.

Bio-remediation: Willow is a fast growing plant with the ability to use high levels of water and nutrients. Trials are currently being conducted by scientists at AFBI to determine the efficiency of SRC willow for the treatment of a range of effluent types ranging from primary treated sewage effluent, farm effluents and effluents from food processors. Early results have indicated that SRC willow can deal with effluents high in nitrogen and is also very effective in absorbing certain heavy metals. It is probably less efficient in dealing with high phosphate effluents. SRC willow has also been used for the treatment of sewage sludge, which can be applied at the time of harvest and at the end of the first year’s growth.

SRC willow in Ireland: SRC willow could be a major contributor to enable Ireland and the UK meet their targets for energy from renewable sources. It also offers huge opportunities for farmers and the agriculture industry. SRC Willow is a viable and economic crop for alternative land use. It is a major disadvantage that there are no financial returns until the fourth year after planting. However, planting support has been provided in Northern Ireland for the past three years and an announcement is imminent in the Republic of Ireland of significant grants for the establishment of SRC willow plantations. SRC willow wood chip is a high volume fuel and therefore transport costs can be significant. It is therefore ideal that the point of production is as close as possible to the point of use. While willow wood chip may be used in certain large power stations probably its best application is in small scale, local energy production. For example one local district council in N. Ireland plans to heat the town leisure centre using a wood burning boiler supplied by a small consortium of local farmers growing the willow within a few miles. Similarly rural housing associations see the potential to heat blocks of accommodation with a basic ‘district-heating’ system from a boiler supplied by locally produced willow wood-chip. There may even be the opportunity to further integrate the waste-disposal with the wood production.

Conclusions: It is predicted that in the next few years there will be very significant areas of willow will be planted in Ireland.
Currently, almost 1000 ha has been planted in N. Ireland. There are genuine business opportunities for farmers who, working alongside other local partners, can address the rising costs of energy and the problems of waste-disposal. While many of these schemes may be local and small scale they are also making an important contribution to address issues of climate change and global warming.

Mini Bio: Alistair McCracken is a research scientist with the Agri-Food and Biosciences Institute in Northern Ireland. He is a plant pathologist who helps develop cost effective and environmentally friendly ways of plant disease control. He enjoys reading, especially biographies, his most recent being Bill Clinton’s, all 950 pages.