Short rotation biomass trials were undertaken on two reclaimed coal tips (Bryn Pica and Fforchwen) in the Cynon Valley of South Wales. Three species - Populus interamericana 'Beaupre', Alnus glutinosa and Salix cinerea – were grown with five experimental treatments, these being control, NPK, broom intercrop, sewage cake and sewage slurry Each treatment/species was repeated three times in blocks, on each site using six metre square plots with trees planted at metre centres, giving a total of 36 trees per plot. Edge trees were discounted at the end of the trials, the yield calculations therefore being based upon 16 trees. Site preparation and management (based upon best practice at the time) included weed control, soil ripping to 500mm and stock proof fencing. After an initial one year establishment period a 'maiden cut’ was undertaken to initiate coppicing. The stools were allowed to grow a further two seasons before harvesting. All interior trees were cut down and their wet weight measured. Samples of each species from both sites were oven dried and a wet dry weight ratio was determined. Analysis of variance undertaken on the raw data showed that there were significant differences between species and treatments, and within blocks of the same species, on the Bryn Pica site. However on the Fforchwen site there were indications of site homogeneity. There was also more inter tree variability on Bryn Pica. Significant improvement in growth performance had been achieved by some of the experimental treatments. Survival rates of all three species were very high. Poplar with the right conditions, namely no compaction and nutrient availability, performed very well, alder performed consistently well regardless of treatment; and willow least well. On one of the sites the poplar grown on sewage cake achieved yields calculated in dry tonnes per hectare per annum almost comparable to poplar grown on lowland agricultural sites (10-12 dry tonnes per hectare at Long Ashton). Results indicated a clear potential, given the expanding knowledge of the subject and the demand for sustainable, renewable energy sources for this type of short rotation biomass production to be used as an economic end use for reclaimed or derelict land in the UK. Secondary social and environmental benefits may also result from this type of biomass planting, not least the ability to produce a fuel where there is virtually no carbon dioxide gain to the atmosphere from the combustion of an energy fuel.
|Date of Award||1996|