Abstract
Hangs, R. D., Schoenau, J. J., Van Rees, K. C. J. and Knight, J. D. 2012. The effect of irrigation on nitrogen uptake and use efficiency of two willow ( Salix spp.) biomass energy varieties. Can. J. Plant Sci. 92: 563–575. Nitrogen (N) fertilizers historically have been applied to support increased productivity of purpose-grown willow (Salix spp.) biomass energy plantations. However, a frequently observed lack of willow growth response to added fertilizer N is often attributed to poor fertilizer use efficiency. The objective of this study was to determine the effect of irrigation on the recovery of broadcast15N-labelled fertilizer, applied during the final year of a 3-yr rotation, by two willow varieties. A split-split-plot experiment was established on a fertile heavy clay soil in Saskatoon, SK, Canada, which consisted of two willow varieties (Charlie and SV1), three irrigation treatments (no irrigation, 75%, and 100% field capacity), and two fertilization treatments (1× and 2× the recommended fertilizer rate of 100:30:80:20 N:P:K:S; kg ha−1). Irrigation increased fertilizer N uptake by Charlie, but had no effect on the amount taken up by SV1, which was attributed to greater N use efficiency of SV1 compared with Charlie when irrigated. Eighty-two percent of the applied fertilizer N was accounted for in the following sinks: 43% in the soil (0–60 cm), 31% in the willow tissues (i.e., stems, leaves, stump, and roots), 7% in the LFH layer, and <1% in the non-crop vegetation; the balance (approximately 18%) was presumed lost primarily through denitrification from the poorly drained soil, but possibly some may have leached below the root zone as well. Although the willow varieties accessed only a portion of the applied fertilizer N during the year of application, the majority of the residual fertilizer N was conserved within the production system and, therefore, remained available for willow uptake in subsequent years.
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