DISTRIBUTION AND RECOVERY OF N-15-UREA IN A TAMARACK BLACK SPRUCE MIXED STAND ON A DRAINED MINEROTROPHIC PEATLAND

The distribution and quantitative recovery of N-15-labelled urea fertilizer was studied in a tamarack/black spruce ecosystem on a drained minerotrophic peatland in central Alberta, Canada. The site was ditched in Fall 1987 and urea fertilizer at 53 kg ha(-1) was applied on 1 June 1989. Recovery of labelled N 3 and 15 months after fertilization was determined in tree and understory vegetation biomass, and in soil. Fertilizer N showed little mobility in soil and tended to accumulate within the 0-20 cm depth. Mean fertilizer N recovery in soil at 3 and 15 months after fertilization was about 54 and 47%, respectively, of the applied N. Corresponding recovery in above tree components was 5.7 and 9.2%, respectively. This increase in recovery of fertilizer N in aboveground tree components was attributable to black spruce since N-15 recovered in black spruce increased significantly during the second growing season. In both years a greater proportion of N was recovered in black spruce compared with tamarack. A substantial amount of N was recovered in understory vegetation suggesting that understory may be a significant sink for N.