Estimating Response of Douglas-fir to Urea in Western Oregon

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Estimating Response of Douglas-fir to Urea in
Western Oregon Washington
By Eric Sucre M.S. Thesis Defense
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Outline

• Fertilization History and Background
• Research Objectives
• Locations of Study Sites
• Site Descriptives
• Brief Description of Experimental Design
  Sampling Methodology
• Soil Site Properties Examined
• Statistical Model for Calculating Response
• Significant Chemical And Physical Soil Property
  Differences
• Regression Models
• Conclusions

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Background

• Regional Forest Nutrition Research Project-RFNRP
• Lake Shawnigan Study in British Columbia
• Stand Management Cooperative (SMC)
• gt55 hectares of forests fertilized annually
• Fertilizers Typically Used
• 1) Urea (NH2 2CO)
• 2) Ammonium Nitrate (NH4NO3)
• 3) Biosolids

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Background cont

• Nitrogen Pools in Pacific Northwest Soils
• Total Nitrogen vs. Available Nitrogen
• Mineralization Rates
• Potential Negative Effects of N Fertilization
• Response Time for Douglas-fir Varies
• Predictors for Douglas-fir Response to N
  Fertilization
• 1) CN ratio Total N
• 2) Foliar SO4-S
• 3) Genotypes
• 4) Site Index

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An Example in the PNW

• 2000-4000 kg ha-1 of Total N
• 1-2 Mineralization Rate
• 20 to 80 kg ha-1 of Available N per year
• Fertilizer Rate of 224 to 448 kg ha-1
• Approximately 25 of total goes to Biomass
  Increment
• Typically 10 to 20 of Added Fertilizer Enters
  Trees
• Where does the remaining fertilizer go?

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Forest Nitrogen Cycling Process Representing
Major Fates and Effects of N Fertilization
(Nason and Myrold, 1992)
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Factors Influencing Timing of Fertilization
1) Time of Year 2) Temperature 3) Wind Speeds 4)
Precipitation Patterns
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Project Objectives

1. Assess Relative Response for Total Volume and
   4-year PAI
2. Test for differences between site, stand and soil
   variables
3. Examine relationships between Response and site,
   stand and soil variables

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Locations of SMC Type I Fertilized Research
Installations
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Site Descriptives
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Experimental Design

• Six 0.4 hectare Douglas-fir plots per
  installation were examined for this study.
• 3 pairs of fertilized and non-fertilized plots
  with different initial stocking levels were
  compared to each other.
• 1) ISPHA Fertilized vs. ISPHA Non-fertilized
• 2) ISPHA/2 Fertilized vs. ISPHA/2
  Non-fertilized
• 3) ISPHA/4 Fertilized vs. ISPHA/4
  Non-fertilized

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ISPHA
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ISPHA/2
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ISPHA/4
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Pretreatment Conditions
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Density Management Regimes for Plots Examined
within Each Installation
ISPHA, Repeated thinning RD55-gtRD35, RD55-gtRD40,
subsequent RD60-gtRD40 ISPHA, Repeated thinning
RD55-gtRD35, RD55-gtRD40, subsequent RD60-gtRD40,
fertilized with 224 kg N ha-1 as urea every 4
years ISPHA/2, Minimal thinning RD55-gtRD35, no
further thinning ISPHA/2, Minimal thinning
RD55-gtRD35, no further thinning, fertilized with
224 kg N ha-1 as urea every 4 years ISPHA/4, No
further thinning ISPHA/4, No further thinning,
fertilized 224 kg N ha-1 as urea every 4 years



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Sampling points for soil and forest floor in SMC
Type 1 plots.
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Soil Site Properties Used in Stepwise
Regression Analysis

• Mean Annual Precipitation
• Elevation
• Slope
• Relative Density (RD)
• Quadratic Mean Diameter (QMD)
• bulk density (Db)
• pH
• Total C N
• C N
• CN ratio
• cation exchange capacity (CEC)
• Inorganic nitrogen (NO3- and NH4)
• Mineral Soil only

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Statistical Model

• yijk µ ai ?j a?ij ß1x1ijk ß2x2ijk
  ß3x3ijk ?ijk
• yijk is total volume 4-yr PAI for the
  fertilization level i, thinning j
• µ is overall average of D.F. volume
• ai is the fixed effect of the i-th fertilizer
  regime
• ?j is the fixed effect of j-th thinning regime
• a?ij is the interaction effect of the i-th
  fertilizer j-th thinning regime
• ß is the slope of volume vs. various
  covariates
• x1ijk is Site Index for given plot/installation
• x2ijk is ISPHA before treatment
• x3ijk is Breast Height Age of plot before
  treatment

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Total Volume 4-yr PAI relative response for
each Density Management Regime 4-yrs following
the 1st Treatment
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Total Volume 4-yr PAI relative response for
each Density Management Regime 4-yrs following
the 2nd Treatment
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Total Volume 4-yr PAI relative response for
each Density Management Regime 4-yrs following
the 3rd Treatment
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ANCOVA by Treatment Intervals
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H.L. Allen, 2002
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Significant Chemical And Physical Soil Property
Differences
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Adj. R2 .622 Y -57.066 .001(NH4 (30-50cm)) p
lt .001
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Adj. R2 .712 Y -238.22 41.24RD p lt.001
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Conclusions

• Thinning effects were significant across all
  treatment intervals.
• 4-yr PAI was significant during the first 2
  treatment intervals, but insignificant during the
  latest interval
• Longer Fertilization Periods (8 years)
• RD most influential variable
• Significant contribution of soil variables to
  regression equations

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Acknowledgements

• Committee Members
• SMC Cooperative Members for Funding
• Fellow Soil Grad Students
• Dongsen Xue
• SMC Staff

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• Questions/Comments
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