Effects of spacing and cutting cycle on the yield of poplar grown as an energy crop

An experiment was set up at three sites in the UK representing a range of s oil types and annual rainfall. Three poplar clones, Populus trichocarpa x P . deltoides "Beaupre", Populus trichocarpa x P. deltoides "Boelare" and Pop ulus trichocarpa "Trichobel", were used to examine the effects of spacing a nd cutting cycle on yield production. Two spacings 1.0 x 1.0 m and 2.0 x 2. 0 m were examined factorially with two and four year cutting cycles. The highest yield of 13.6 oven dry tonnes per hectare per year was achieved by the clone Populus trichocarpa x P. deltoides ''Boelare" at the wettest site with the best soil moisture retention on a four year cutting cycle at the 1.0 x 1.0 m spacing. The 1.0 x 1.0 m spacing produced higher yields tha n the 2.0 x 2.0 m spacing. At the most productive site the annual yield fro m a four year cutting cycle was significantly greater than that from the tw o year cutting cycle. This finding was not repeated at the other two sites. However when the combined yield from the two two-year cutting cycles was c ompared with the four year yield, the four year yield was higher on all occ asions. This was significant for all clones at two sites but not significan t for two clones at the third site. This finding has strong economic implic ations for the grower as longer cutting cycles will increase yield and redu ce harvesting costs. Crown Copyright (C) 1999 Published by Elsevier Science Ltd. All rights reserved.