Short-rotation willow productivity and nutrient dynamics after three years of irrigation and fertilization

Non-Peer ReviewedPurpose-grown shrub willow (Salix spp.) represents a viable bioenergy feedstock; however, there needs to be sufficient biomass production to support the economic viability of these plantations. The objective of this three-year study was to determine the effect of irrigation and fertilization on willow biomass feedstock quantity. A split-split-plot experimental design was used on a Sutherland clay soil in Saskatoon, SK and consisted of two willow varieties (SV1 and Charlie), three irrigation treatments (no irrigation, 75%, and 100% field capacity), and three fertilization treatments (no fertilizer, 1x, and 2x recommended fertilizer rate). During the final growing season, 15N-labelled fertilizer was used to determine the fate of the applied fertilizer. For both willow varieties, after the three-year rotation there was a highly significant (P values 0.05) effects of fertilization or irrigation x fertilization. Sixty-seven percent of the applied fertilizer N was accounted for, with approximately 30% present within the willow tissues (e.g., stems, leaves, and roots). The positive willow growth response to irrigation is indicative of the importance of soil moisture within the semi-arid climate of Saskatchewan. The lack of fertilizer effect probably reflects the fertile soil at the site and the apparently low nutrient requirement of willow