An experiment was established in central New York State in 1987 to determine the biomass production potential of Salix using ultrashort-rotation intensive culture with annual harvests. Half of the plots were fertilized annually with N, P, and K, and all plots were irrigated during their third, fourth, and fifth growing seasons. The most productive clone, willow clone SV1, yielded 16 o.d. t ha-1 yr-1 during the fifth growing season. Fertilization significantly increased the rate at which clones reached their annual maximum biomass production, but the annual maximum level ultimately achieved was the same with or without fertilization. Total five year biomass production was increased by fertilization for specific clones. Large clonal variation in biomass production potential and survival was observed, along with significant clone-by-fertilizer interaction.