Fast-growing tree species, such as willows, can benefit from sludge application. While sludges are good fertilizers, they may contain heavy metals which could reduce productivity and cause environment risks. The aims of the present research were to: i) determine the biomass production of Salix discolor Mtihl. and Salix viminalis L. when supplied with various amounts of dried and pelleted sludge and ii) assess the uptake and accumulation of heavy metals. Trials were carried out using unrooted cuttings that were planted in large plastic pots containing sandy soil and grown outdoors for a 20-week period. Five doses of sludge were applied: the equivalents of 0 (TO), 40 (T1), 80 (T2), 120 (T3), 160 (T4) and 200 (T5) kg "available" N ha -l . Trees which received the highest dosage of sludge showed the best growth. Stem biomass was significantly greater for S. viminalis which had received sludge treatments. The relationship between the total biomass yield Y (g) and the rate of fertilization X (equivalent to kg of "available" nitrogen provided per hectare) is linear. Regression equations of predicted biomass production were established as follows: S. discolor, Y = 28.36 + 0.56X and S. viminalis, Y = 39.95 + 0.64X. For both species, the greatest stem biomass per g of N applied was produced with treatments 4 and 5. Amounts of nitrogen per leaf area (N/LA) and per dry leaf mass (N/DL) were higher for S. viminalis. The metal transfer coefficient did not vary between the species but was significantly different for Cd and Zn. Plants were able to absorb Cd and Zn, but were less able to absorb Ni, Hg, Cu, and Pb. It was concluded that the dried and pelleted sludge is a good fertilizer. S. discolor and particularly S. viminalis can be used as filters for the purification of wastewater sludge as well as for biomass production purposes.

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Recycling wastewater sludge as fertilizer in short-rotation intensive culture of willows offers a viable opportunity to increase biomass productivity. Salix discolor Mühl. and Salix viminalis L. were planted at two densities (20 000 and 30 000 cuttings/ha), on two sites: a well and a poorly drained site. Three doses of dried and granulated sludge (100, 200, 300, and 0 kg/ha of "available" N) were applied in the spring of the first and the second seasons of growth. The aims of the experiment were to (i) investigate growth and nutritional plant response to fertilization and (ii) estimate the impact of sludge application on the soil. Over two seasons, aboveground biomass was similar for S. discolor and S. viminalis on both sites and for all sludge treatments. Every increment in the sludge dose applied induced an increase in willow productivity. Vector analysis of stem and branch nutrient concentration suggested that nitrogen was the most limiting nutrient. At the end of the second season, plots fertilized with the highest doses of sludge indicated soil enrichment in organic matter. However, nitrate concentration in the soil increased with increasing sludge doses. The accumulation of heavy metals from sludge was not hazardous to the environment according to provincial limits. A moderate dose of dried and pelleted sludge (100 kg/ha "available" N) may reduce nitrate leaching and appears to be a good fertilizer during the establishment of willows.Résumé : Le recyclage des boues usées comme fertilisant dans la culture intensive avec de courtes rotations du saule peut être envisagé comme un moyen pour accroître la productivité de cette essence. Des boutures de Salix discolor Mühl. et de Salix viminalis L. ont été plantées selon deux densités (20 000 et 30 000/ha) sur deux sites aux conditions de drainage différentes : un bien et l'autre mal drainé. Trois doses de boues sous forme de granules séchées (100, 200, 300 et 0 kg/ha N « disponible ») ont été appliquées au printemps de chacune de deux saisons. Les objectifs de cette étude étaient : (i) d'étudier la réponse des plants (productivité et état nutritionnel) à la fertilisation et (ii) d'estimer les changements dans le sol suite à l'application des boues. Au cours des deux saisons, la production aérienne de biomasse des deux espèces était équivalente sur les deux sites et pour tous les traitements de fertilisation. Chaque augmentation de la dose de boues s'est traduite par une augmentation de la productivité des saules. L'analyse vectorielle de l'état nutritionnel (concentration et contenu) des branches et de la tige suggérait que l'azote était l'élément qui limitait le plus la performance des plants. Après deux saisons, la teneur du sol en matière organique des parcelles fertilisées avec les plus fortes doses de boues a augmenté. Cependant, ces doses ont entraîné une augmentation des nitrates dans le sol. L'accumulation de métaux lourds contenus dans les boues ne présentait pas de risques pour l'environnement selon les normes du gouvernement provincial. Une dose modérée...