The Beyond N Study

Fertilizer influence on SNC disease severity across a gradient of disease:  The Beyond N Study

  • The Beyond N study was initiated in Winter 2006/2007 to help address questions about the impacts of fertilization on SNC disease severity and tree growth in the Oregon Coast Range.
  • Objectives:
    • To test whether specific nutritional amendments might diminish or offset the effects of SNC on tree growth & foliage retention.
    • To test the growth response of individual trees to fertilizations across a range of SNC disease severity.
    • To evaluate foliar nutrient dynamics of SNC infected DF following fertilization.
    • To determine if specific fertilization treatments worsen or ameliorate SNC disease severity, as measured by pseudothecia density on DF needles from individual treated trees.
  • Methods: 16 study sites were established across a gradient of SNC from Coos Bay, OR to Mineral, WA in winter 2006/2007.
    • Target stands were 15-25 yrs old with 200-400 TPA and no past fertilization.
    • At each site, 10 replications of 5-8 treatments were randomly assigned; some sites excluded one or more of the site-specific fertilization treatments (below).
    • Circular .025-ac treatment plots (5.7 m radius) were centered on an undamaged plot tree.
    • Measurements on plot center trees included DBH, ht, ht to crown, sapwood width, diameter at 18ft and foliage retention.
    • Foliage was sampled to assess foliar nutrient levels and SNC disease severity, and 2 soil cores per plot were sampled to assess soil nutrients before and after treatment.
    • 7 Treatments:
      • Control
      • N urea (200 lbs N/ac)
      • Lime (calcium carbonate; 1000 lbs Ca/ac)
      • Calcium (calcium chloride; 100 lbs Ca/ac)
      • Phosphorus (mono-sodium; 500 lbs P/ac)
      • Kinsey (site-specific; fertilized over 2 yrs to avoid over application)
      • Fenn (site-specific)
  • Products:  Analyses will account for stand variables and look for the effect of fertilization on various response variables, including:
    • Change in foliage retention
    • Change in volume growth
    • Change in form quotient
    • Change in sapwood area at crown base
    • Pseudothecia density (infection index) on the needles of treated trees (determined from foliage collected in Spring 2010)
  • Preliminary Results:
    • N fertilization (urea) is only beneficial to tree growth on sites with low site indices (<160), relatively higher % Ca: % N, and relatively higher soil pH (i.e. significant positive volume responses varied by site).
    • Nitrogen, phosphorous and Kinsey treatments significantly changed soil pH on treatment plots during the course of the study.
    • After adjusting for site and tree covariates (DBH, ht, crown ratio, and plot-level basal area), increases in volume production were marginally greater with nitrogen and lime treatments only (~3.4% increase).
    • Average foliage retention decreased on all but 2 sites (including controls) over the three years of the study; overall, fertilizer treatments do not appear to have dramatically impacted needle retention; pseudothecia counts are currently underway to determine if there are fertilization impacts on disease severity.