Willow SRC is grown as a long-term woody perennial crop that is harvested in general every 3 years. The growing of Willow SRC is more comparable to agricultural cropping methods than it is to forestry. Stems are initially planted in densities of approx 15,000 per hectare within a range of 10,000 to 18,000/ha. The plants are cut back at the end of their first season to encourage branching and the formation of the multi-branched coppice plants.
There are thousands of species of willow, with several hundred varieties being readily available in Wales. Management of the crop will differ depending upon the fertility, pH and moisture content of the soil as well as the altitude of the site. The suitability of SRC as a biomass crop in Wales has been well researched. The crop is recognised as having potential on both lowland and upland sites, including land that has traditionally been used for sheep farming. It therefore represents one of the few opportunities for farmers in Wales to diversify.
The key objective of the £1.4 million Willow for Wales project is to demonstrate the potential of SRC willow as a biomass crop in Wales, in addition to engaging farmers as partners in establishing crop test sites and as potential commercial producers. The Wales Biomass Centre and Cardiff University have also looked at willow in some depth. Their report on “The silviculture, nutrition and economics of SRC Willow Coppice in the uplands of Mid Wales” can be accessed here.
Growing the crop
A brief technical leaflet on SRC as a crop can be accessed via the CALU website. For more detailed information on growing the crop, the Defra guidelines for growing SRC, produced in England contains a good source of information that is largely applicable to the growth of the crop in Wales. In addition the Forestry Commission are developing yield models for the crop that also includes South Wales. The environmental implications of growing the crop also need to be considered. An Environmental Statement obtainable from the Forestry Commission needs to be completed to determine whether a full Environmental Impact Assessment (EIA) is required. The NetRegs website gives further information on the environmental aspects of growing SRC.
How much energy could you produce?
The energy content of SRC and Miscanthus are broadly similar, and the energy calculator on the miscanthus page can be used to look at energy values for either crop. SRC is harvested on a 3 year cycle with the yield then annualised. Annual yield of an established crop is likely to be in the region of 8 to 12 odt/ha/year. Moisture content at harvest tends to be high at around 40 to 50%.