RESPONSE OF YOUNG DOUGLAS-FIR TO UREA FERTILIZER APPLIED ON AND OFF SNOW

The effects of 200 kg N ha-1 applied as urea fertilizer on 50 cm of sn ow or on bare ground were studied in an 11-year-old Douglas-fir (Pseud otsuga menziesii (Mirb.) Franco) plantation on Vancouver Island. Analy sis was done on all trees per plot and on 20 selected dominant trees p er plot. Up to 2 years after fertilization, urea significantly increas ed absolute DBH increments over controls in all trees and the 20 selec ted trees per plot; response to fertilization on snow was equal to tha t on bare ground. Between the 3rd and 9th year following fertilization , mean DBH increments were not significantly different for any treatme nt. Four-year absolute volume increments were 63 and 87% greater than the controls for bare-ground and on-snow applications, respectively. A positive and quantitatively similar response is expected in wetter co astal Douglas-fir stands whether urea is applied on snow or under bett er conditions during other seasons.