Biomass from short-rotation coppice willow on marginal land

Abstract

A study to determine the economic feasibility of production and utilisation of biomass from short-rotation coppice willow is described. An area of 196 000 ha of marginal agricultural land (surface water mineral gleys), potentially suitable for biomass production, has been identified in Co. Fermanagh and west Co. Tyrone, Northern Ireland. Annual yields of 12–15 t ha −1 year −1 dry matter (DM) have been achieved over a 9 year period (1977–1985) from Salix x ‘Aquatica Gigantea’ Korso (SAG), harvested triennially. In terms of utilised metabolisable energy (UME) from marginal land grass for conventional beef/milk production gives 40 GJ ha −1 compared with 136 GJ ha −1 for willow used as a combustion fuel. Biomass yields have been maintained by recycling the leaf litter which contributes 130 kg ha −1 year −1 nitrogen. A density of 20 000 plants ha −1 (0·7 × 0·7 m) is the optimum for rapid site capture and maximum early yield with SAG. Candidate species of Salix, from breeding programmes in New Zealand, Finland, Sweden and North America, and a range of Alnus, Populus and Fraxinus species are being evaluated. Willow biomass as chips has been used successfully as the energy source for the production of early tomatoes over a 3 year period (1983–1985), at one third the cost of 32 sec. fuel oil. Burned in small chip-fuelled installations, biomass offers potential as an energy source for the commercial generation of electricity for rural based industries, with surpluses fed into the national grid. Briquettes (energy value of 19·5 MJ kg −1) have been successfully manufactured from willow biomass and compare favourably as a market product with briquettes from other resources. The Iotech Process — steam explosion pretreatment of wood chips followed by enzymatic hydrolysis — developed by Techtrol Ltd, Canada, from the mid-1970s, offers new opportunities for biomass, including the economic production of ethanol for use as a high octane enhancer to replace lead in petrol, or the production of a valuable high-digestibility (65%) animal feed supplement.