1. 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 15 N Fertilizers in Douglas-fir Plantations Stephani Michelsen-Correa, Betsy Vance, and Rob Harrison University 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 trees 1 2. The fate of the remaining 57-88% is currently unknown. Objectives: Use 15 N 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 experiments 1 2. Pot Studies 12-43% 85-95% ? Missing 57-88% Field Studies Study Area:Methods: 10 sites (Figure 2) were installed over a 2 year period (2011 and 2012) -Sampled for baseline 15 N values Each installation consists of a randomized block design with five treatment plots (Figure 3) The four fertilizers used have all been enhanced with 15 N, a stable isotope of N that is of relatively low abundance in the environment compared to 14 N (Table 1) Ecosystem components were sampled again one year after fertilization and analyzed for 15 N recovery (Figure 3) % of Applied Nitrogen retained by target trees 100 km 20112012 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 15 N recovery. Each of the 10 sites contains five of these plots, one for each treatment. 100m 2 plot boundary -224 kg N ha -1 Target tree Litter and Soil Sample Treatment Plot (Aerial view) FertilizerDescriptionMechanism UreaIndustry standard Volatilization 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 (PO 4 ) Unfertilized Control No fertilizer added within the 100m 2 boundary N/A Table 1: Five treatment types used at each of the 10 installations. The fertilizers were enhanced with 15 N (0.5 AP, ~370 0 / 00 15 N) Results: 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 15 N 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. Mineral Soil (1 Year)