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Tracing the Fate of Applied 15 N Fertilizers in Douglas-fir Plantations Stephani Michelsen-Correa, Rob Harrison, and Betsy Vance University of Washington, School of Environmental and Forest Science. Study Area:. Background: - PowerPoint PPT Presentation


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Projected Deliverables:

Estimates of N losses due to leaching, volatilization, and uptake by competing understory vegetation

Determine the relative efficiency of the four fertilizer treatments

Produce data that can be incorporated into a model useful for land managers wanting to predict stand response to fertilizer applications in the PNW

Tracing the Fate of Applied 15N Fertilizers in Douglas-fir PlantationsStephani Michelsen-Correa, Rob Harrison, and Betsy Vance University of Washington, School of Environmental and Forest ScienceBackground:Nitrogen (N) is known to be a limiting nutrient in Pacific Northwest forests. Fertilization is commonly used to maintain the quantity of N needed to support high growth rates in Douglas-fir plantations. Research on the growth response to fertilization has produced variable results. One explanation for the poor response is that of the applied fertilizer, only 12-43% is actually being taken up by the trees1 2. The fate of the remaining 57-88% is currently unknown.

Objectives:Use 15N labeled urea fertilizers to trace the fate of nitrogen in the ecosystem following application.Compare the uptake efficiency and losses of four commonly used fertilizers

Study Area:


10 sites (Figure 2) were installed over a 2 year period (2011 and 2012) -Sampled for baseline 15N values

Each installation consists of a randomized block design with five treatment plots (Figure 3)

The four fertilizers used have all been enhanced with 15N, a stable isotope of N that is of relatively low abundance in the environment compared to 14N (Table 1)

Ecosystem components were sampled again one year after fertilization and analyzed for 15N recovery (Figure 3)

100 km20112012Installation Sites10 sites along the Western Douglas-fir region of Oregon and Washington

Includes the range of parent material and latitudes typically seen in Douglas-fir plantations forests of the Pacific Northwest

Figure 3: Treatment plot showing ecosystem components sampled for 15N recovery. Each of the 10 sites contains five of these plots, one for each treatment.

Table 1: Five treatment types used at each of the 10 installations. The fertilizers were enhanced with 15N (0.5 AP, ~370 0/00 15N)


Figure 4: Changes in 15N values in the 2011 foliage from 0-34 weeks after treatment. Figure 5: Changes in 15N with mineral soil depth one year after fertilization. Figure 1: Differences in the efficiency of Nitrogen fertilizer uptake between pot/greenhouse studies and actual field experiments1 2.


85-95%?Missing57-88%Field Studies% of Applied Nitrogen retained by target treesPot Studies100m2 plot boundary224 kg N ha-1Target treeLitter and Soil Sample

Treatment PlotAerial view

Urea, NBPT, and CUF follow a similar trajectory through week 10. However, by week 16 urea had the highest concentrations followed by NBPT and CUF respectively.

Preliminary results suggest greater uptake efficiency for the standard urea fertilizerAll four treatments show leaching of the applied fertilizers as indicated by the increasing 15N value with depth

Urea + NBPT was substantially higher at the surface and showed the least amount of leaching

References: 1. Amponsah, I., Lieffers, J., Comeau, P., Landhausser, S. (2004). Nitrogen-15 uptake by Pinus contorta seedlings in relation to phonological stage and season. Scandinavian Journal of Forest Resources. 19:329-338. 2. Salifu, K. and Trimmer, V. 2003. Nutrient retranslocation response of Picea mariana seedlings to nitrogen-15 supply. Soil Science Society of America Journal 67:905-913.Progress to-date:

All sampling for this project has been completed (Table 2)

Preliminary results are available for volatile losses, foliage uptake, forest floor, and mineral soil retention for 2011

Processing of the remaining 2012 data continues as we wait to receive our 2011 15N analysis back from Virginia Tech.

Table 2: Summary of progress. Items marked with X indicate completion and denotes work in progress.