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

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

Background Regional Forest Nutrition Research Project-RFNRP Lake Shawnigan Study in British Columbia Stand Management Cooperative (SMC) >55 hectares of forests fertilized annually Fertilizers Typically Used: 1) Urea ([NH 2 ] 2 CO) 2) Ammonium Nitrate (NH 4 NO 3 ) 3) Biosolids

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) C:N ratio & Total N 2) Foliar SO 4 -S 3) Genotypes 4) Site Index

An Example in the PNW 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?

Forest Nitrogen Cycling Process Representing Major Fates and Effects of N Fertilization (Nason and Myrold, 1992)

Factors Influencing Timing of Fertilization 1) Time of Year 2) Temperature 3) Wind Speeds 4) Precipitation Patterns

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

Locations of SMC Type I Fertilized Research Installations

Site Descriptives

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

ISPHA

ISPHA/2

ISPHA/4

Pretreatment Conditions

ISPHA, Repeated thinning: RD55->RD35, RD55->RD40, subsequent RD60->RD40 ISPHA, Repeated thinning: RD55->RD35, RD55->RD40, subsequent RD60->RD40, fertilized with 224 kg N ha -1 as urea every 4 years ISPHA/2, Minimal thinning: RD55->RD35, no further thinning ISPHA/2, Minimal thinning: RD55->RD35, 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 { { { Density Management Regimes for Plots Examined within Each Installation

Sampling points for soil and forest floor in SMC Type 1 plots.

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 C:N ratio cation exchange capacity (CEC)* Inorganic nitrogen (NO 3 - and NH 4 + )* *Mineral Soil only

Statistical Model y ijk = µ + α i + γ j + αγ ij + β1x1 ijk + β2x2 ijk + β3x3 ijk + є ijk y ijk = is total volume & 4-yr PAI for the fertilization level i, thinning j µ = is overall average of D.F. volume α i = is the fixed effect of the i-th fertilizer regime γ j = is the fixed effect of j-th thinning regime αγ ij = is the interaction effect of the i-th fertilizer & j-th thinning regime β = is the slope of volume vs. various covariates x1 ijk = is Site Index for given plot/installation x2 ijk = is ISPHA before treatment x3 ijk = is Breast Height Age of plot before treatment

Total Volume & 4-yr PAI relative response for each Density Management Regime 4-yrs following the 1 st Treatment

Total Volume & 4-yr PAI relative response for each Density Management Regime 4-yrs following the 2 nd Treatment

Total Volume & 4-yr PAI relative response for each Density Management Regime 4-yrs following the 3 rd Treatment

ANCOVA by Treatment Intervals

H.L. Allen, 2002

Significant Chemical And Physical Soil Property Differences

Adj. R 2 =.622 Y= (NH 4 + (30-50cm) ) p <.001

Adj. R 2 =.712 Y= RD p = <.001

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

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

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