BIOMASS PRODUCTIVITY AND WOOD ENERGY OF SALIX SPECIES AFTER 2 YEARS GROWTH IN SRIC FERTILIZED WITH WASTE-WATER SLUDGE

The energy equivalent of willows in short-rotation intensive culture ( SRIC) varies in terms of yield and woody biomass characteristics. Thre e willow species (Salix discolor Muhl., Salix petiolaris Smith and Sal ix viminalis L.) were planted on two sites, well-drained and poorly dr ained, in two different densities (20 000 and 30 000 plants per ha). F our doses of dried and granulated sludge were applied: the equivalents of 0, 100, 200 and 300 kg ''available'' N per ha. At the end of the s econd season, above-ground biomass was similar for S. discolor and S. viminalis, and greater than that of S. petiolaris on both sites and fo r all sludge treatments. On the well-drained site, each increment in t he sludge dose significantly increased the performance of the species, regardless of plant density. Fertilized with a sludge dose equivalent to 300 kg N per ha, S. viminalis and S. discolor yielded 30.17 and 24 .97 t/ha of dry matter respectively. On the poorly drained site, diffe rences in performance were also observed between fertilized and unfert ilized plots, but not among the various treatments. The calorific valu e of the wood of the three species being similar (19.21-19.59 kJ/g), t he energy equivalent of a hectare of willows is proportional to the yi eld of each species. Thus the energy equivalent of S. viminalis and S. discolor is two to three times that of S. petiolaris. S. viminalis ha d the highest woody biomass quality, with an FVI (fuelwood value index ) of 1030.58 (100%), followed by S. petiolaris with 954.25 (92.6%) and S. discolor with 849.08 (82.4%). (C) 1997 Published by Elsevier Scien ce Ltd.