An Experimental Assessment of Native and Naturalised Species of Plants as Renewable Sources of Energy in Great Britain

Summary

Some wild plants of Great Britain could be used for energy sources because they cover vast areas or are very productive. However, no information is available on the stability of yield under various harvesting strategies or weather conditions, and no attempt has been made to increase the yields of these “weeds” by adding fertilizers.

This report presents results from the first year of a three year experiment to study the effects of repeated harvesting, the date of harvesting and the addition of fertilizers on the yields of Pteridium aquilinum, Spartina anglica and Reynoutria japonica. It also describes parallel experiments on the independent effects of nitrogen, phosphorus and potassium, and 4 planting densities on the yields of these and other potential energy crops.

P. aquilinum, which covers 3,200 km² of Great Britain, could be harvested in summer to give ca. 9 t ha^-1 which would be digested anaerobically to give 27 m3 of biogas t^-1 day^-1. P. aquilinum harvested in Autumn, and S. anglica harvested in winter (with yields of ca. 14 t ha^-1 would enter a thermal conversion route. Yields of a recently established monoculture of R. japonica were low (0′.8 t ha^-1 due to a low planting density and abnormal weather conditions but survival was good and yields should improve. No early season responses to fertilizers were shown but re-growth after early harvests was correlated with fertilizer input.

Results from the next two years will be critical in relating the stability of yield to harvesting pressure and identifying ways of increasing yields.