Journal Article Outline
Title: Estimating Response of Douglas-fir to Urea in Western Oregon and Washington:
Site vs Soil Properties
Authors: E.B. Sucre, R.B. Harrison, E.C. Turnblom, and D.G. Briggs
Abstract: Estimating the amount of response of Douglas-fir [ Psudotsuga menziesii
(Mirb.)] stands from N fertilization is extremely difficult due to the high variability that
exists between sites. Our objective was to determine how various site (site index, age,
relative density and total precipitation) and soil variables (total N, soil cation exchange
capacity, available N, bulk density, pH, and C/N ratio) influence stand response to
multiple applications of 224 kg N ha-1 as urea. Composite samples of the forest floor and
3 depths of mineral soil (0-15cm, 15-30cm, and 30-50cm) for 6 fertilized Stand
Management Cooperative (SMC) Douglas-fir stands located in western Washington and
Oregon were used to quantify soil variables. The response variable (relative difference in
volume growth between fertilized and control plots) was regressed against site and soil
variables. The data were stratified by 3 different stocking levels [ISPA (initial stems per
acre), ISPA/2, and ISPA/4) and geographic location.
- Discuss results such as strongest and weakest related variables in estimating
volume response to fertilization
- Justify which variables and why either site or soil properties or both help
scientists and land managers make decisions on fertilization.
Introduction:
A) Talk about the relevance of this research
1) reduce uncertainty of fertilization as a tool to improve stand quality
2) better estimate which stands, based on site and/or soil properties, are
most suitable for a gain in volume as a result of urea fertilization.
B) Pertinent Lit Review of past research on topic to include in intro & other sec.
1) Miller et al., 1989 (Predicting Douglas-fir growth & response to N
fertilization in Western Oregon)
2) Edmond & Hsiang, 1987 (Forest Floor & Soil Influence on Response of
Douglas-fir to Urea)
3) Peterson et al., 1984 (Response of Northwest Douglas-fir Stands to Urea:
Correlations with Forest Soil Properties)
4) Prietzel et al., 2004 ( Long-term effects of repeated urea fertilization in
Douglas-fir stands on forest floor nitrogen pools & nitrogen mineralization)
5) Hopmans & Chappell 1994 (Growth response of young, thinned Douglasfir stands to nitrogen fertilizer in relation to soil properties and tree nutrition)
6) Chappell et al., 1999 (Long-term effects of nitrogen fertilization on
nitrogen availability on coastal Douglas-fir forest floors
7) Cole, 1995 (Soil nutrient supply in natural and managed forests)
8) Binkley and Reid,1985 (Long-term increase of nitrogen availability from
fertilization of Douglas-fir
9) Dangerfield & Brix, 1979 (Comparative effects of ammonium nitrate and
urea fertilizers on tree growth and soil processes
10) Homann et al., 2001 (Douglas-fir soil C and N properties a decade after
termination of urea fertilization
11) Mitchell et al., 1996 (Biomass and nutrient element dynamics in Douglasfir: effects of thinning and nitrogen fertilization over 18 years
12) Nason & Myrold, 1992 (Nitrogen fertilizers: Fates and environmental
effects in forests)
13) Strader & Binkley, 1989 (Mineralization and immobilization of soil
nitrogen in two Douglas-fir stands 15 and 22 years after nitrogen fertilization)
14) Turner et al., 1977 (Use of foliage sulphate concentrations to predict
response to urea application by Douglas-fir)
*15) Radwan & Shumway, 1984 ( Site Index and selected soil properties in
relation to response of Douglas-fir and western hemlock to N fertilization
16) Shumway, 1984 ( Total N, mineralizable nitrogen & site index as guides to
fertilization of Douglas-fir)
17) Shumway & Atkinson, 1978 (Predicting nitrogen fertilization response in
unthinned stands of Douglas-fir)
18) Stegemoeller & Chappell, 1990 (Growth response of unthinned & thinned
Douglas-fir stands to single and multiple applications of nitrogen)
19) Stegemoeller & Chappell, 1991 (Effects of fertilization & thinning on 8year growth response of second growth Douglas-fir stands)
C) Objectives of study
1) whether predictions from site variables can be improved by using soil
variables
2) explain differences in response to fertilization between Washington &
Oregon
3) is there enough evidence from analysis of soil properties to justify costs?
4) compare results to other published data involving N fertilization in
Washington & Oregon
Methods:
A) Study Sites
1) Detailed Description
2) Figure showing the location of sites
3) Table showing detailed description of each installation such as, township,
range, elevation, soil type, aerial photos, aspect, slope, state, county, longitude
and latitude and establishment year.
4) Table explaining abbreviated variable definitions
B) Soil Sampling and Chemical Analysis Methodologies
1) SMC protocol for sampling plots with references to experimental design,
equipment used, etc.
2) Description of equipment used with appropriate references to common
methodologies
a) Site Index (King 1966)
b) Relative Density (Curtis, 1982)
c) Total C & N- LECO Combustion method? (Nelson & Sommers, 1982)
d) pH (Glass electrode in 1:1 soil:water)
e) CEC (1.0 M NH4Cl method)
f) Available NH4+ & NO3- (KCL extraction using filter)
C) Statistical Analyses
1) One-way ANOVA to determine if attributes are significantly different
between fert and non fert for each stocking level and between WA & OR
2) Multiple Linear Regression models, experimenting with various
transformations of data to find strongest relationships
Results & Discussion:
A) Multiple Regression
1) Growth of unfertilized plots (tables w/ mean, SD, max, min)
2) Volume response to N fertilization (tables w/ mean, SD, max, min)
3) Graphs showing best and worst R2 values for site and soil variables
B) Site vs. soil property relationships and equations
C) Relate/Compare finding when appropriate to results from previous studies
specifically: (Edmonds & Hsiang, 1987, Miller et al., 1999, Peterson et al., 1984
& Hopmans and Chappell, 1994)