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 soil types and annual rainfall. Three poplar clones, Populus trichocarpa×P. deltoides “Beaupré”, Populus trichocarpa×P. deltoides “Boelare” and Populus trichocarpa “Trichobel”, were used to examine the effects of spacing and cutting cycle on yield production. Two spacings 1.0×1.0 m and 2.0×2.0 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×P. deltoides “Boelare” at the wettest site with the best soil moisture retention on a four year cutting cycle at the 1.0×1.0 m spacing. The 1.0×1.0 m spacing produced higher yields than the 2.0×2.0 m spacing. At the most productive site the annual yield from a four year cutting cycle was significantly greater than that from the two 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 compared with the four year yield, the four year yield was higher on all occasions. This was significant for all clones at two sites but not significant for two clones at the third site. This finding has strong economic implications for the grower as longer cutting cycles will increase yield and reduce harvesting costs.