Wednesday, November 15, 2006

Effect of Urea Fertilization on Nitrogen Leaching Fluxes in Douglas Fir Plantations in the Hood Canal Watershed, WA.

Cindy Flint1, Rob Harrison1, AB Adams1, and Randall Greggs2. (1) Univ of Washington, CFR, Box 352100, Seattle, WA 98195, (2) Green Diamond Resource Company, Shelton, WA 98584

Anthropogenic nitrogen (N) additions to the Hood Canal, WA may be the cause of hypoxia in the canal in recent years.  One potential contributor to this N loading is forest fertilization.  This study explores the leaching fluxes of N out of the rooting zone in Douglas fir forests of the Hood Canal watershed following fertilization.  Six study sites were chosen, each containing 0.081 ha control and treatment plots with tension lysimeters installed at depths of 20cm and 100cm.  The study sites are all located on the Shelton soil series (Typic haploxerand), for which the parent material is glacial till with root restricting basal till at approximately 100cm.  Once N leaches past 100cm, it is considered out of the rooting zone and can then travel to the streams or groundwater.  Treatment plots were fertilized with 224 kg/ha urea-N in March, 2006.  Solutions were collected on a weekly basis for 6 weeks following fertilization and then monthly.  Lysimeter solutions were analyzed for total N, NO­3-N, NH4-N, and total C.  Fluxes were calculated with measured precipitation data and estimated evapotranspiration rates.  Results to date have shown a significant increase in the NO­3-N concentration at the 20cm depth the month following fertilization (p = .094) and a significant increase in the NH4-N concentration at the 20cm depth two months following fertilization (p = .08).  There were no statistically significant differences in concentration at the 100cm depth or differences in leaching fluxes at either depth.  Data will continue to be collected through March, 2007.