Canadian Forest Service Publications
A bioassay of the availability of residual 15N eight years after application to a forest soil in interior British Columbia. 1994. Preston, C.M; Mead, D.J. Plant and Soil 160: 281-285.
Issued by: Pacific Forestry Centre
Catalog ID: 3436
Although a high proportion of fertilizer N maybe immobilized in organic forms in the soil, no studies have examined the long-term availability of residual fertilizer 15N in forestry situations. We investigated this by growing lodgepole pine (Pinus contorta) seedlings in surface (0-10 cm) soil sampled eight years after application of 15N-urea, 15NH4NO3 and NH415NO3 to lodgepole pine in interior British Columbia. After nine months of growth in the greenhouse, seedlings took up an average of 8.5% of the 15N and 4.6% of the native N per pot. Most of the mineral N in the pots without seedlings was in the form of nitrate, while pots with seedlings had very low levels of mineral N. In contrast to the greenhouse study, there was no significant uptake of 15N by trees in the field study after the first growing season, although half of the soil organic 15N was lost between one and eight years after fertilization. This indicates the need to understand the mechanisms which limit the uptake of mineral N by trees in the field, and the possible mismatch of tree demand and mineral N availability.