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, Betsy Vance, and Rob HarrisonUniversity of Washington, School of Environmental and Forest Science

Background:• 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

Figure 1: Differences in the efficiency of Nitrogen fertilizer uptake between pot/greenhouse studies and actual field experiments1 2.

Pot Studies

12-43%85-95%

?Missing57-88%

Field Studies

Study Area: Methods:• 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)

% of Applied Nitrogen retained by target trees

100 km20112012

Installation Sites

Figure 2: 10 sites along the Western Douglas-fir region of Oregon and Washington

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.

100m2 plot boundary-224 kg N ha-1

Target tree

Litter and Soil Sample

Treatment Plot(Aerial view)

Fertilizer Description Mechanism

Urea Industry standardVolatilization loss

controlled via timing of application

ESN (Agrium)

Polymer coated urea

Delays hydrolysis of urea for 60-90 days;

release of urea is temp. and moisture

dependent

Urea+NBPT

(Agrotain)

Coated with N-(n-butyl)

thiophosphoric triamide

Slows hydrolysis by blocking active site on urease for 7-21

days

Urea+CuF (Arborite)

Coated with phosphate

Granular urea pellets coated with boron

solution- acts as both an inhibitor and a

binder for additional nutrient layer (PO4)

UnfertilizedControl

No fertilizer added within the 100m2 boundary

N/A

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)

Results:

_x0006_0_x000d_2011

_x0001_4 _x0002_10 _x0002_16 _x0002_22 _x0002_282011 Total

-20

0

20

40

60

80

100

120

Weeks after fertilization

δ 15N

Urea + CUF

Urea

Urea + NBPT

ESN

Control

Figure 4: Concentrations of the fertilizer label in the 2011 foliage from 0-34 weeks after treatment. 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.

Foliage

Figure 5: Concentrations of 15N with mineral soil depth one year after fertilization. This is preliminary data as it represents the concentrations from only one of our study sites.

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.

4 6 8 10 12 14 160

10

20

30

40

50

60

δ 15N

Soil

Dept

h (c

m) Urea + CUF

Urea

Urea + NBPT

ESN

Control

Mineral Soil (1 Year)