An experiment was established in central New York State in 1987 to determine the effect of spacing and fertilization on wood biomass production of one willow clone grown with intensive culture and harvested annually. Spacings were 0.15 x 0.15, 0.30 x 0.30 and 0.46 x 0.46 m. Half of the plots were fertilized annually with N, P and K at elemental rates of 336, 112 and 224 kg ha(-1). All plots were irrigated during their third, fourth and fifth growing seasons. Fertilizer increased the rate at which trees attained their maximum production, but their maximum estimated production level was reduced compared with non-fertilized trees. Trees responded positively to fertilizer during the first three growing seasons. Trees spaced at 0.46 x 0.46 and 0.30 x 0.30 m had significantly higher maximum estimated production levels than trees spaced at 0.15 x 0.15 m. During the fourth and fifth growing seasons, trees spaced at 0.46 x 0.46 m were most productive, but cumulative production after five successive annual harvests was highest by trees spaced at 0.30 x 0.30 m. Survival remained high (83% averaging spacing and fertilizer treatments) after five harvests and was not affected by spacing or fertilization. Copyright (C) 1996 Elsevier Science Ltd.