155
Different nitrogen sources for fertilizing western hemlock in western Washington
M. A.
RADWAN AND
D. S. DEBELL
Forestry Sciences Laboratory, Pacific Northwest Forest and Range Experiment Station, United States Department
of Agriculture, Forest Service, Olympia, WA, U.S.A. 98502
S.
R.
WEBSTER
Technology Center, Weyerhaeuser Company, Tacoma, WA, U.S.A. 98477
AND
S. P. GESSEL
College of Forest Resources, University of Washington, Seattle, WA, U.S.A. 98195
Received July 7,1983'
Accepted November 29,1983
M. A. , D. S. DEBELL, S. R. WEBSTER, and S. P. GESSEL. 1984. Different nitrogen sources for fertilizing western
hemlock in western Washington. Can. J. For. Res. 14: 155-162.
Effects of different sources of fertilizer N on selected chemical characteristics of soils and foliage, and on growth of western
hemlock (Tsuga heterophylla (Raf.) Sarg. ) were compared at three different sites in western Washington. Treatments were the
following: untreated control (0), ammonium nitrate (AN), ammonium sulfate (AS), calcium nitrate (CN), urea (U), and urea
- ammonium sulfate (US). Fertilizers were applied in the spring (April-May) at 224 kg N/ha. Forest floor and mineral soil,
to a depth of 5 cm, and foliage were sampled periodically for 2 years. Height and diameter of selected trees were measured
periodically for 4 years. Results are reported mostly for two sites, one in the Cascade Range and one in the coastal zone in
western Washington. The pH of forest floor and mineral soil varied by treatment, and the two urea fertilizers caused substantial
initial rise. Effects on soil and foliar nutrients varied by fertilizer, sampling date, and location. In general, all fertilizers
increased NH4 N, N03 N, and total N in the forest floor and mineral soil, and total N in the foliage. Also, with some exceptions,
especially with foliar P in the Cascade site, fertilization reduced foliar content of important nutrients. At the Cascade site,
4-year growth responses in height, basal area, and volume averaged over all fertilizers were 30, 34,and 32%,respectively.
AN, AS, CN, and urea resulted in height growth significantly (P < 0. 20) higher than that of the control. Significant basal
area growth and volume-growth responses were produced by AN, CN, and US. No significant height-growth response to any
fertilizer occurred in the coastal stand; basal area growth and volume-growth responses averaged 27 and 21%,respectively,
and best response occurred with urea. These results suggest that the low and inconsistent response of hemlock to N fertilization
cannot be improved by applying some N fertilizer other than urea. Factors limiting response to N fertilization may be associated
with availability of native N and other nutrients or other characteristics of hemlock sites and stands.
RADWAN,
M. A. , D. S. DEBELL, S.:.R..\.VEBSTER et
P GES S L 1984. :Different nitrogen sources for fertilizing western
hemlock in western Washingt?n,C:an .[J: For. Res J.4: 155-162.
RADWAN,
,·.
;.
, ·
Les auteurs ont etudie les effets de diverses sources d'azote d'engrais sur un ensemble de caracteristiques des sols et du
feuillage et sur la croissance de la pruche de I'ouest (Tsuga heterophylla (Raf. ) Sarg. ) dans trois stations de la partie ouest de
l'etat de Washington. Les traitements etaient les suivants: temoin (0), nitrate d'ammonium (AN), sulfate d'ammonium (AS),
nitrate de calcium (CN), uree (U) et uree sulfate d'ammonium (US). Les engrais furent appliques en avril- mai, au taux de
224 kg N/ha. Durant 2 ans, on a fait un echantillonnage periodique de la couverture morte et du sol mineral it une profondeur
de 5 cm, ainsi que du feuillage. La hauteur et Ie diametre d'arbres choisis furent mesures periodiquement pendant quatre ans.
Les resultats rapportes ici sont principalement pour deux stations du Cascade Range et une station de la zone cotiere de l'ouest
de l'etat de Washington. Selon les traitements, on a enregistre des changements de pH de la couverture morte et du sol mineral;
dans les cas des deux traitements it l'uree, l'augmentation fut importante. Les effets sur la teneur en elements du sol et du
feuillage ont varie selon la source d'azote, la date d'echantillonnage et Ie lieu. En general, tous les engrais ont provo que une
augmentation de N NH4, N N03 et N total de la couverture morte et du sol mineral, ainsi qu'une augmentation de N foliaire.
A peu d'exceptions pres, notamment pour P foliaire dans la station des Cascades, la fertilisation a occasionne une reduction
des concentrations foliaires d'elements. Dans la station des Cascades, les reponses en hauteur, en surface terriere et en volume
apres 4 ans s'elevaient en moyenne, pour tous les engrais, it 30,34 et 32%,respectivement. L'application de AN, AS, CN
et U s'est traduite par une augmentation en hauteur significative (P < 0. 20) par rapport au temoin. Les traitements AN, CN
et US ont augmente significativement la surface terriere et Ie volume. Dans les peuplements de la zone cotiere, les traitements
n'ont eu aucune reponse significative de croissance en hauteur; les reponses de croissance en surface terriere et en volume
s'elevaient en moyenne it 27 et 21%,la meilleure reponse etant obtenue avec l'uree. Ces resultats suggerent que, parmi les
engrais azotes utilises, seule l'uree peut ameliorer la croissance de la pruche. Les facteurs qui limitent la reponse it la
fertilisation azotee peuvent etre lies it la disponibilite de I'azote et d' autres elements endogenes, ou it d'autres caracteristiques
des stations et peuplements de pruche.
[Traduit par Ie journal]
Introduction
Western hemlock (Tsuga heterophylla (Raf. ) Sarg. ) is an
important timber species in the Pacific Northwest. Numerous
fertilization trials have been established to assess opportunities
'Revised manuscript received November 22,1983.
for increasing hemlock wood production. So far, however, the
species has not responded well to application of nitrogen (N)
fertilizer. Urea has been the most used fertilizer, and success
has been generally less in the coastal hemlock forests than in
stands on the lowlands west of Puget Sound and on the west
slopes of the Cascade Mountains (Webster et al. 1976; Olson
156
CAN. J. FOR. RES. VOL. 14, 1984
TABLE
Location in western
Washington
Elevation (m)
Tree dbh (em)
Tree height (m)
Tree age (years)
Site index (m)
Soil parent material
Soil series
I. Details of hemlock sites selected for fertilization
Coast I
Coast 2
Cascade
Northwest coast
325
13. 4
12,9
19
35
Sandstone
Snahopish
Southwest coast
270
12. 6
11.0
17
35
Sandstone
Vesta
Western Cascades
800
16. 8
15. 8
28
28
Pumice over andesite
Pitcher
NOTE: Tree dbh, height, and age were determined before treatment. Height and dbh are averages of 120 trees
per site. Age is total tree age estimated from measured breast-height age. Site index is based on height at 50
years (Wiley 1978).
et al. 1980).
Presently, the exact causes of the erratic response of hemlock
to N fertilizers are unknown. Results of recent investigations
suggest that response of hemlock to N fertilizer may be affected
more by native N levels and (or) by limiting supplies of one or
more of the essential mineral nutrients than by the source of N
in the fertilizer (Heilman and Ekuan 1980; Radwan and DeBell
1980a, 1980b; Gill 1981; Anderson et at. 1982; Radwan and
Shumway 1983). N-source results (Radwan and DeBell
1980b ), however, are based upon greenhouse experiments
with seedlings and may not be directly applicable to field con­
ditions. The present study, therefore, is a follow up to the
previous greenhouse investigation. It was conducted to elabo­
rate on the effect of the source of fertilizer N on the soils and
trees of western hemlock growing in natural stands located both
in the coastal hemlock zone and in the Cascades.
Methods and materials
The sites
Three forest sites occupied by 17- to 28-year-old, fully stocked,
natural stands of western hemlock were selected. Two sites were in the
coastal hemlock zone and the third site was in the western Cascade
Range. Canopies were closed at all sites, and understory vegetation
was negligible. Other pertinent information about each site is as given
in Table 1.
Plot installation and sample tree selection
Twelve plots, arranged in two blocks of six treatments each, were
installed at each site in fall 1976. Blocks were reasonably uniform in
stocking, site index, topography, and soil conditions. Treatment plots
were about 0.04 ha in size and plot edges were separated by buffers
of at least 7 m in width. Measurement plots, about 0.01 ha in size,
were established within the treatment plots. In each of these plots, 10
well -formed and healthy dominant or codominant trees were selected.
All 10 trees were used for height and diameter measurements, and 6
of the trees, chosen at random, were used to collect the foliage for
chemical analysis.
Fertilization treatments
There were five fertilization treatments and an unfertilized control.
Treatments were assigned at random to the plots within each block.
The fertilizers used were ammonium nitrate (34% N), ammonium
sulfate (20% N), calcium nitrate (16% N), urea (46% N), and Ufea
ammonium sulfate (41% N). All fertilizers were commercial agricul­
tural grade, in granular or prill form. Fertilizers were uniformly ap­
plied to the treatment plots by hand. Fertilization was made at the
coast I site on March 6 and at the Cascade site on April 12, 1978, at
a rate equivalent to 224 kg N/ha.
Sampling and chemical analysis of forest floor and mineral soil
Forest floor and mineral soil were sampled approximately 1. 5
(April - May 1978), 4. 5 (August 1978), 8.5 (December 1978), and
20.5 (December 1979) months after application of fertilizer. Each
collection consisted of material obtained from randomly selected spots
at distances of 0.5 to 2. 0 m from the measurement trees. There were
30 samples per plot in each collection, with 3 samples taken from the
vicinity of each measurement tree. Forest floors were obtained using
a 127-cm 2 template and a cutting knife, and the underlying soils were
sampled to a depth of about 5 cm. Stumps and logs were avoided, and
twigs and other material >6 mm in diameter were discarded. Samples
of forest floors and soils were composited separately for each plot.
Forest-floor samples included both litter and humus. About 0.02 m3
of soil was collected per plot, and volume of forest-floor collections
varied with its thickness. All samples were transported to the l abora­
tory for processing the same day they were collected.
In the l aboratory, individual samples were thoroughly mixed after
roots and rocks were removed. Forest-floor material was cut into small
pieces and weighed. Soils were passed through a 2-mm sieve. Fresh
subsamples were taken for determination of pH, ammonium N, and
nitrate N. Remaining material of each sample was dried to constant
weight in a forced-air oven at 65°C. Dried material was ground to 40
mesh and stored in closed containers at - 15°C until analyzed for total
N.
The pH was determined on I : I mixtures with water by glass elec­
trode. Ammonium and nitrate N were extracted with 2 N KCI, and
determinations were made by steam distill ation and the MgO-Devarda
alloy methods described by Bremner (I965b). Total N (including
nitrate) was determined on the 65°C dried soil by the standard
semimicro-Kjeldahl procedure (Bremner 1965a). Subsamples of the
mineral soil were dried to constant weight at 105°C, and total N results
were adjusted for moisture in the 65°C dried soil.
Sampling alld chemical analysis of foliage
CUlTent-year's foliage was collected approximately 4 (July 1978),
8. 5 (December 1978), and 20.5 (December 1979) months after treat­
ment. Collections were made from 6 of the 10 measurement trees, and
the same trees were used in all sampling dates. Samples were obtained
by climbing the trees and cutting one vigorous branch from the upper
third of the crown. Tips of secondary laterals, approximately 5 cm
long, were cut from the branches at random, and tips were composited
by plot. Samples were collected in precooled jars and transported to
the laboratory in a portable cooler.
In the laboratory, needles were separated from stems and buds.
Needles were dried to constant weight in a forced-air oven at 65°C.
The ovendry tissue was ground to 40 mesh and stored in sealed
containers at - 15°C until analyzed.
Foliar analyses were calTied out as foll ows: total N (including
nitrate) by the micro-Kjeldahl procedure (Bremner 1965a), P by the
molybdenum blue technique (Chapman and Pratt 1961), S and S04 S
(extracted with 0. 6 N HCI) by the turbidimetric method of Butters and
Chenery (1959), and K, Ca, Mg, Fe, Mn, Zn, and eu by standard
atomic absorption techniques (Anonymous 1976).
Growth measurements
Heights and diameters at breast height (dbh) were measured before
RADWAN ET AL.
6.00
COASTAL SITE
6.00
5.50
::c
a.
::c
a.
CASCADE SITE
u
5.50
;;
;;
o
;: 5.00
•
"
..
"
5.00
A
;;
u.
;;
u.
157
4.50
4.50
S
N
4.00
AprJ97a
AUG:1978
DEC.1978
4.00
,
OEC.1979
6.00
,
MAY 197a AUG.1978 OE6.1978
OEC.1979
6.00
5.50
5.5
::c
D.
::c
D.
'0
'0
iO •
Ii
IV
:i
:i
" 5 00
5.00
Q;
c
c
4.50
40
. 1PR.'1978 AUG:1978
OEC'.1978
Collection date
OEC.1979
4
y 1978
AUG.197a
DEC.197a
COllection date
DEC. 1979
FIG. I. Effect of fertilizer- fertilizer source on pH of forest floor and mineral soil of western hemlock. Treatments: 0, untreated control; AN,
ammonium nitrate; AS, ammonium sulfate; eN, calcium nitrate; U, urea; US, urea - ammonium sulfate.
fertilizers were applied and then annually until the end of the study in
1982. Height, basal-area, and volume growth increments and percent
growth response over the unfertilized controls were calculated. All
computations were based upon averages of the 10 measurement trees
of each plot.
Statistical analysis
Standard error of the mean was calculated for data resulting from
chemical analysis of the forest floor, mineral soil, and foliage. Means
for height, basal-area, and volume growth were calculated for each
plot. Treatment differences in height growth at each site were assessed
by analyses of variance, followed by single degree of freedom linear
contrasts. Differences were considered significant at P os; 0.20. We
chose a probability value higher than the conventional P os; 0.05
because inherent variation within the hemlock stands was high, num­
ber of replications was small , and we wanted to decrease the chances
of making a type II error (i.e. , concluding that fertilizers had no effect
on growth when in fact they did). Basal-area and volume growth were
evaluated as with height growth, except that covariance analyses were
used because these variables were strongly affected by pretreatment
size.
Results and discussion
Plots of the coast 2 site were inadvertently thinned by the
owner before final growth measurements were made. Results
from that site, therefore, are not presented. Reference to some
data collected before thinning, however, will be made occa­
sionally as needed. Also, for convenience, coast 1 site will be
referred to mostly as the coast or coastal site.
Effects on pH of the forest floor and mineral soil
The pH appeared to differ between the two sites (Fig. 1). In
general, forest-floor and mineral-soil values were somewhat
higher in the Cascade site than on the coast. This was true for
all treatments including the unfertilized controls. Ranges of pH
values were as follows: coastal forest floor, 4. 15-5. 78; coastal
soil, 4. 25-5. 20; Cascade forest floor, 4. 25-6. 02; Cascade
soil, 4. 55-5. 50.
At both sites, the fertilizers appeared to affect the pH of the
forest floor and mineral soil. Effects were greater in the forest
floor, where many hemlock "feeder" roots occur (Ross 1932),
than in the mineral soil. As expected, urea and urea - ammo­
nium sulfate (US) produced the greatest changes. In each case,
there was an initial large increase in pH resulting from urea
hydrolysis and production of ammonium carbonate. This was
followed by a steep decline during the next 9 months, and a
general leveling off during the following year. By the end of
two growing seasons (December 1979), pH values of the forest
floors and soils in the urea and US plots were about the same
as those of the controls. In contrast, the other three fertilizers,
ammonium nitrate (AN), ammonium sulfate (AS), and calcium
nitrate (CN), produced small changes in pH. By the end of the
second growing season, pH values were mostly lower than
those in the unfertilized plots. This was probably due to the
anions contained in the fertilizers and to nitrification of the
added ammonium.
Effects of the fertilizers on pH are generally in agreement
with available literature (e. g. , Radwan and DeBell 1980b). In
addition the large rise in pH caused by the urea fertilizers may
have adverse effects, however temporary, on hemlock's roots
and the associated beneficial mycorrhizae present, especially in
the forest floor (Gill 1981).
Efef cts on nitrogen in the forest floor and mineral soil
Some ammonium N was detected in nearly all the samples
collected (Fig. 2). Ammonium N concentrations, however,
158
14, 1984
CAN. J. FOR. RES. VOL.
COASTAL SITE
2
1000
CASCADE SITE
..
0
..
•
•
•
•
75
=
= 500
E
E
...
...
Z
z
.. 25
"
r.
z
r.
Z
o
O'�====�==��"""""--�
APR,1978
AUG,1978
DEC. 1978
o
DEC. 1979
'0
.. 300
iii
A
c
c
E 30
=
I
E
= 200
E
200
...
Z
"
r.
z
DEC. 1979
400
u
u
;;
:;
MAY 1978 AUG.1978 DEC.1978
Z
...
r.
Z
10 o
CN
0r==
APR.1978
AUG.1978
DEC.1978
DEC. 1979
Collection date
100
MAY 1978 AUG.1978
DEC.1978
D EC.1979
Collection date
FIG. 2. Levels of ammonium N in the forest floor and mineral soil of western hemlock at different times after applications of different sources
of fertilizer nitrogen (treatments as in Fig. 1).
varied by treatment, collection date, site, and between forest
floors and mineral soils. Concentrations ranged from 0 to 2200
ppm, and native NH4 N averaged about 8 ppm over all samples
from the untreated plots. There was much variability in NH4 N
between replicates, as evidenced by the high standard errors
calculated. Similar variability in NH4 N following urea applica­
tion has been reported by Johnson (1979).
Ammonium N increased soon after application of most fertil­
izers. The high initial levels, however, decreased rapidly with
time. By the end of the second growing season, NH4 N concen­
trations in the fertilized plots approached those found in the
unfertilized forest floors and mineral soils at both sites.
With few exceptions, the urea and AS fertilizers produced
the highest NH4 N levels, followed by AN. In the CN treat­
ments, on the other hand, NH4 N in most samples was only a
little higher than the controls.
Ammonium N concentrations were higher in most samples
of control and fertilized plots of the coastal site than in those
from the Cascade stand. In addition, regardless of the fertil­
ization treatment, NH4 N levels were mostly higher in the forest
floor than in mineral soil at both sites.
At both sites, native nitrate was low, if detected at all; it
averaged about 2 ppm in samples of forest floor and mineral
soil. Nitrate-containing fertilizers added directly to the nitrate
pool, while other fertilizers contributed to the N03 N present
through nitrification of the NH4 N added, With few exceptions,
levels of nitrate in the forest floor and mineral soil were much
lower than those of ammonium (average, 17 versus (vs,) 156
ppm), regardless of treatment. Forest soils, in general, do not
usually contain much nitrate because of low nitrification rates,
uptake by plants, and leaching,
As with NH4 N, N03 N varied considerably between repli­
cations at each site, Nitrate, ranging from 0 to 186 ppm, also
varied greatly by fertilizer, collection date, site, and between
forest floors and mineral soils, With very few exceptions, there
was more nitrate resulting from urea or urea - ammonium
sulfate than from any of the other fertilizers in both the forest
floor and mineral soil at both sites (average, 37 vs, 15 ppm),
Nitrate N peaked earlier in forest floor than in soil (April-May
1978 vs, August 1978), By the end of the first growing season,
levels were generally low (average, 6 ppm) and became even
lower during the following year (average, 2 ppm).
As with NH4 N, nitrate concentrations were generally lower
in the Cascade stand than on the coast (15 vs. 18 ppm), and
forest floors contained higher levels of nitrate than soils at both
locations (25 vs, 9 ppm),
Our values for N03 and NH4 N are higher than some of those
reported by others (e. g" Johnson 1979; Heilman et aI, 1982),
This is probably due to differences between sites, and because
we sampled the forest floor separately from mineral soil, and
sampled the latter to a depth of only 5 cm. More important, our
data, like those previously reported by others, show clearly that
all N fertilizers added much available N (NH4 and N03 N) to
the soil system.
As expected, levels of total N in the control plots were higher
in the forest floor than in mineral soil (Fig. 3). Native N was
also 40 -100% higher on the coast than in the Cascades. Aver­
ages for forest floor and mineral soil were 0. 76 and 0. 46%,
respectively, for the coastal site, and 0.64 and 0.23%, re­
spectively, in the Cascades.
With few exceptions, fertilization increased total N in both
the forest floor and mineral soil at both sites. Contribution to
RADWAN ET AL.
COASTAL SITE
1.40
1.20
0.90
US
..
1.00
"
.E
Z
0.80
CASCADE SITE
1.00
0
0;
159
CN
?
=
=
;:::
-....., ====
:::=--- ===
$
;
•
e
0.80
0.70
.E
z
!0 0.8
l-
0.6
DEC. 1979
I
MAY 1978
I
i
AUG.1978
DEC. 1978
i
DEC.197!i
i
DEC . 1 9 79
0.80
0.80
- =
= := ==2::::==
-
US,----_
_
'0
0.80
II)
"
c
'ill
.!:
---=-
-=
- ===:'
: =-=- --=
::::==== =
-=-=-=
==---=
=
C ==
0---__
____
(;•
_
f..
c
'ill
.E
0.40
Z
Z
iii
'0
!0
I-
0.60
0.40
I-
0.2
PR . 1978
AUG.I'978
DEd978
I
DEC. 1979
Collection date
0.2
AS
�;:S:;
:-
MAY 1978
I
AUG.1978 DEC.1978
I
Collection date
FIG. 3. Total percent N in forest floor and mineral soil of western hemlock at different times after application of different N fertilizers
(treatments as in Fig. 1).
the total N pool, however, appeared to differ by fertilizer.
Also, as with NH4 and NO) N, increases in total N were
considerable initially and then declined with time. Still, de­
tectable increases in total N persisted throughout the first 2
years. This finding is contrary to the general view that fertilizer
contribution to soil total N is not commonly detectable because
of the very small amount of added N relative to the very large
pool of native N in soil system.
Effects on foliar nutrients
Concentrations of all the macronutrients determined were
within the ranges reported in the literature (Beaton, Brown et
aZ. 1965; Beaton, Moss et aZ. 1965; Radwan and DeBell
1980a, 1980b). Only concentrations of nutrients contained in
the fertilizers used (i.e., N, Ca, S, and S04 S) are presented in
Table 2. Data of the other macro- (P, K, and Mg) and micro­
nutrients (Mn, Fe, Cu, and Zn) determined are not presented in
Table 2 to save space. These data are discussed briefly in the
text below.
Over all sampling dates, N concentrations in foliage of the
control trees averaged 1.15 and 1.12% for the coast and Cas­
cade sites, respectively. Levels of total N in needles of fertil­
ized trees always exceeded those of the controls. At both sites,
concentrations peaked in foliage collected the first dormant
season after fertilizer application. At that time, average peak
values over all fertilizers were 1.56% on the coast and 1.51%
in the Cascades. Concentrations dropped 1 year later, probably
because of dilution by growth.
Within sampling dates, foliar N levels varied among the
different fertilizers. Except for the July- August 1978 sam­
pling at the coastal site, however, differences between fertil­
izers were small «0.2%). The various fertilizers, therefore,
were not much different in supplying the trees with N. This is
in agreement with earlier studies with hemlock seedlings in
which foliar N did not vary significantly among 12 different N
fertilizer treatments (Radwan and DeBell 1980b).
Without fertilization, average P concentration in the foliage
was 0.17% on the coast and 0.19% in the Cascades. With few
exceptions fertilizers appeared to reduce P levels at both sites;
trends did not vary much by fertilizer. With fertilization, P
levels also seemed to decrease somewhat over time on the
coast, but to increase in the Cascades. This may be an im­
portant difference between the two sites, and is probably a
reflection of differences in soil available P. Average values for
extractable P in the mineral soils of the control plots
by bicarbonate extraction (Olsen and Dean 1965) were 6, 3,
and 10 ppm for the coast 1, coast 2, and Cascade sites,
respectively.
Potassium averaged higher in the foliage of the control trees
from the Cascade site than in needles of the unfertilized trees
on the coast (0.69 vs. 0.63%). At both sites, some fertilizers
seemed to increase percent K initially, probably resulting from
enhanced mineralization or availability owing to fertilization.
Later on, however, K levels of the fertilized trees dropped to
approximately the same concentrations of the controls or
lower, especially on the coast. As with N and P, decreases in
K concentrations were probably due to dilution by growth.
Average Ca concentration for the unfertilized trees varied
from 0.20% on the coast to 0.23% in the Cascades. At both
sites, fertilizers varied in their effect on foliar Ca levels, but
concentrations were mostly lower with fertilizer than without,
especially with US. The general drop in Ca concentration was
CAN. J. FOR. RES. VOL. 14, 1984
160
TABLE 2. Concentrations of selected nutrients in foliage of western hemlock collected at different times after application of different N fertilizers"
Cascade site
Coastal site
Treatment
July-Aug. 1978
Dec. 1978
Dec, 1979
July-Aug, 1978
Dec. 1978
Dec. 1979
N (0/0)
Control
Ammonium nitrate
Ammonium sulfate
Calcium nitrate
Urea
Urea - ammonium sulfate
1. 04±0,13
1,S4±0.03
I, SO±0.04
1. 30±0, 01
1. 2S±0.04
I. SI±0, 16
1. 22±0.20
1. 64±0, 04
1. 52±0. 14
I. SO±O.OS
I, S8±0, 06
1,S8±0. 04
1. 18±0,11
1. 36±0,II
1. 36±0,03
1, 36±0,00
1. 28±0,02
1. 34±0,00
1. 07±0. 1O
1. 37±0. 07
1.49±0,16
1. 32±0,01
1. 38±0. 03
1. 37±0. 01
1. 21±0,07
1.4S±0,04
I. S2±0,OS
1. 44±0,02
1, 60±0,00
I. S4±0,06
1.07±0,01
1,24±0, 04
1. 41±0, 13
1. 31±0. 04
1,32±0,06
1, 28±0. 00
Ca (0/0)
Control
Ammonium nitrate
Ammonium sulfate
Calcium nitrate
Urea
ammonium sulfate
Urea
0. 18±0. 06
0. 20±0.03
0. 16±0.01
0. 17±0, 03
0. 16±0, 04
0. 13±0,00
0,22±0. 06
0,19±0.01
0. 16±0, 03
0, 18±0. 03
0. 16±0, 01
0, 12±0, 03
0. 20±0,07
0. 18±0. OS
0, 18±0, 02
0,16±{J. 03
0,17±0. 01
O,IS±O. OO
0, 20±0,04
0,22±0,01
0,20±0,01
0,22±0,01
0,21±0,04
0,17±0, 03
0. 26±0,06
0. 22±0. 04
0, 20±0. 02
0.23±0.01
0, 22±0. 01
0. 18±0. OS
0. 23±0, 01
0,21±0,01
0,20±0,01
0, 2S±0, 04
0,22±0,OS
0, 21±0, 03
S (0/0)
Control
Ammonium nitrate
Ammonium sulfate
Calcium nitrate
Urea
Urea - ammonium sulfate
0. 09±0,00
0,08±0,00
0,1O±0,01
0,09±0,00
0, 08±0,00
0, 09±0.01
0. 12±0,00
0. 1O±0,01
0. 1O±0,02
0. 1O±0,01
O. IO±O.OO
0, 1O±0, 01
0,11±0. 01
0, 1O±0. 01
0,12±0. 01
0. 1O±0, 01
0. 1O±0,00
0, 1O±0,01
0,12±0, 01
0,1O±0, 01
0,13±0. 01
0. 11±0. 00
0.12±0. 01
O. II±O.OO
0,14±0. 01
O, I I±O.OO
0,12±0, 01
0. 12±0. 00
0,12±0. 01
0. 12±0. 01
0, 14±0, 01
0,12±0,01
0, 13±0,01
0,14±0, 01
0. 12±0. 01
0, 14±0. 01
S04 S (ppm)
Control
Ammonium nitrate
Ammonium sulfate
Calcium nitrate
Urea
Urea - ammonium sulfate
24±8
O±O
O±O
O±O
O±O
O±O
197±137
O±O
O±O
O±O
O±O
O±O
131±163
16±0
O±O
O±O
O±O
40±33
268±63
O±O
30±0
IS±21
22±32
O±O
437±17
O±O
200±0
88±18
37±S2
7S±106
26S±24
142±S9
132±48
133±47
IIS±24
172±IOS
"Values are averages of two composite samples each (±SEM),
also observed on the coast with calcium nitrate fertilizer.
Apparently, the unfertilized soils were sufficient in Ca.
Average levels of Mg were 0. 13 and 0. 15%, and those of S
were 0. 1 1 and 0. 13% for the coast and Cascade plots, re­
spectively. Again, there was a tendency for fertilization to
reduce concentration of these elements in the foliage. Also,
concentrations did not change much with time, and no fertilizer
N source effects were evident. Even the S-containing fertil­
izers, AS and US, failed to materially affect S content of the
fertilized trees more than the other fertilizers.
Ratios of S: N ranged from 0.06 to 0. 13, and trends were
similar to those of S. These ratios indicate that there was
sufficient S to balance the N present in the formation of foliar
protein (Turner et al. 1977), with some excess S present
especially in the untreated controls and in the Cascade site.
Unlike S, S04 S showed much change with fertilization and
time, and appeared to be a good indicator of S availability.
Concentrations averaged 1 17 and 323 ppm for the unfertilized
trees of the coastal and Cascade sites, respectively. Higher
sulfate concentrations in the Cascades is in agreement with
earlier results from another study (Radwan and DeBell 1980a ).
All values, however, are lower than the 400 ppm foliar S04 S
found to be required to obtain growth response of Douglas-fir
to 220 kg N/ha (Turner et al. 1979). Fertilization decreased
foliar S04 S levels considerably; similar results have been re­
ported earlier with N-fertilized Douglas-fir (Turner and Lam­
bert 1978). Concentrations were depleted to a much greater
extent on the coast than in the Cascades. Presumably, foliar
S04 S in combination with N was used in the formation of
S-containing amino acids and proteins. On the coast, more than
in the Cascades, sulfate rapidly became depressed probably
because of low supplies from the soil and much leaching.
Leaching may also explain low levels of S04 S in the foliage
of coastal hemlock even when the S-containing fertilizers, AS
and US, were used.
Results of analyses of the micronutrients, Mn, Fe, Cu, and
Zn, show some differences in foliar concentration owing to
some fertilizers and over time, All values were within levels
reported in the literature, and results did not appear useful
to understanding of hemlock's nutrition or its response to N
fertilization.
Effects on tree growth
Four-year height growth of the unfertilized trees at the Cas­
cade site averaged 2.0 m (Table 3). Height-growth response to
the various fertilizers ranged from 16 to 37% over the controls.
Trees fertilized with four of five fertilizers (AN, AS, CN, and
U) had significantly (P < 0,06) more height growth than the
unfertilized trees, At the more productive coastal site (coast 1),
height growth of the control trees averaged 3.4 m, and was not
significantly (P < 0.20) affected by fertilization. Accidental
thinning at coast 2 site precluded collection of 4-year data.
Height data at 2 years for this coastal stand indicated that height
growth was not stimulated by fertilization, and was signifi­
cantly depressed by AS. Response of trees at this site to three
other fertilizers (U, US, and AN) was also negative but growth
did not differ significantly from that of unfertilized trees.
Basal-area growth responses to added N at the Cascade site
RADWAN ET AL. TABLE
3, Growth response of western hemlock to application of different N fertilizersO
Height growth Increment
per tree
(m)
P
Coastal site
Control
Ammonium nitrate
Ammonium sulfate
Calcium nitrate
Urea
Urea - ammonium sulfate
Average 3. 4
3. 4
3,6
3,1
3. 4
3,1
0,89
0,59
0,31
0,89
0,34
Cascade site
Control
Ammonium nitrate
Ammonium sulfate
Calcium nitrate
Urea
Urea - ammonium sulfate
Average 2, 0
2,8
2, 6
2,8
2,7
2. 4
0,03
0,06
0,03
0,04
0,24
Treatment
161
Basal-area growth
Response
(%)
°
4
-8
°
-8
-2
37
29
37
33
16
30
Increment
per tree
(mZ
x
10-4)
p
Volume growth
Response
(%)
40
47
54
46
72
38
0,67
0. 42
0, 69
0,10
0, 89
16
33
15
78
-5
27
37
50
48
50
47
54
0, 13
0,31
0,13
0,31
0.D7
35
28
35
27
44
34
Increment
per tree
(ina
x
10-3)
P
Response
(%)
52
61
70
56
78
47
0. 46
0,15
0,74
0,07
0,70
19
36 8
50
-8
21
55
72
70
73
72
73
0, 20
0,37
0,18
0, 25
0,17
33
27
34
33
34
32
aFour years after fertilization, Response is calculated as percent of the different fertilization treatments over the unfertilized control. P is the probability that response to fertilizer
is different from that of the control, and differences were considered significant at P :5 0.20,
ranged from 27 to 44%, and averaged 34%, Three of the five
fertilizers (AN, CN, and US) led to growth significantly (P <
0. 13) higher than that of unfertilized trees; none of the fertil­
izers differed significantly from one another in their effect on
basal-area growth, Average response in basal area on the coast
was 27%. Only urea led to a basal-area response (78%) signifi­
cantly (P
0. 10) better than the controls, At the other coastal
site (coast 2), 3-year data show that none of the fertilizers
produced significant increase in basal-area growth over the
controls,
Four-year volume-growth responses at the Cascade and
coastal sites are very similar to those described for basal-area
growth, averaging 32 and 21%, respectively. At the Cascade
site volume-growth responses ranged from 27 to 34%, with
three of the five fertilizers (AN, CN, and US) significantly (P
::; 0. 20) increasing growth over unfertilized trees, At the coast­
al site, on the other hand, both urea and AS led to significant
(P ::; 0, 15) responses. In addition, 2-year data show no signifi­
cant responses to any fertilizer at the other coastal site (coast 2).
These results support earlier reports indicating more success
in fertilizing hemlock in the Cascades than on the coast (Web­
ster et aI, 1976; Olson et al. 1980), More importantly, results
indicate that it is unlikely that the response of hemlock to N
fertilization could be improved by using one of the N fertilizers
tested other than urea, the most commonly used N fertilizer in
northwestern forests. Regardless of urea's temporary effects on
pH, urea gave better basal area growth and volume-growth
responses than all other fertilizers tested on the coast 1 site,
None of the fertilizers tested, including urea, were effective at
the coast 2 site. Urea produced significant height-growth and
better than average volume-growth responses in the Cascade
stand, Furthermore, no particular fertilizer appeared con­
sistently superior to the other fertilizers tested on all sites,
Fertilizers containing sulfur, AS and US, did not increase
growth more than the other fertilizers, This is surprising since
S04 S in the untreated controls was apparently low (Turner et
al. 1979) and since S04 S concentrations decreased very rap­
idly with fertilization, especially on the coast. We must point
=
out, however, that adequate levels of S04 S, with and without
added fertilizer N, have not been defined for hemlock,
Likely factors other than the source of fertilizer N influ­
encing response of hemlock include site and stand factors (Ol­
son et al. 1980), and levels of native N (Radwan and Shumway
1983; this study), Aside from these factors, we believe that
other essential mineral nutrients are important for improved
growth of hemlock in presence of added N. This study and an
earlier investigation (Radwan and DeBeU1980a) show higher
foliar concentrations of important nutrients other than N (i. e. ,
P, K, Ca, S, B, and Mn) in the Cascade forests (where response
to N fertilizer is generally higher) than in coastal forests. So
far, however, field studies have failed to show response of
hemlock to fertilizers containing S (this study) or P (R, F,
Strand, private communication), Still, we believe that addi­
tional field studies with fertilizers containing elements other
than N, applied singly and in combination, are required before
a consistently effective fertilization treatment is developed for
hemlock.
ANDERSON, S"
R, ], ZASOSKI, and S, p, GESSEL. 1982, Phosphorus
and lime response of Sitka spruce, western hemlock seedlings, and
romaine lettuce on two coastal Washington soils, Can, ], For, Res,
12: 985-99\.
ANONYMOUS, 1976, Analytical methods of atomic absorption spec­
trophotometry, Perkin-Elmer Corp" Norwalk, CT.
BEATON, ], D" G, BROWN, R, C, SPEER, 1. MACRAE, W, p, T.
MCGHEE, A. Mos s , and R, KOSICK, 1965, Concentration of micro­
nutrients in foliage of three coniferous tree species in British Col­
umbia, Soil Sci. Soc, Am, Proc, 29: 299- 302,
BEATON, ], D" A, Mo ss , 1. MACRAE , ], W, KONKIN, W, p, T,
MCGHEE, and R, KOSICK, 1965, Observations on foliage nutrient
content of several coniferous tree species in British Columbia, For.
Chron, 41: 222- 236,
BREMNER,], M. 1965a, Total nitrogen, III Methods of soil analysis,
Part 2. Agronomy, 9: 1149- 1178,
--- 1965b, Inorganic forms of nitrogen, III Methods of soil anal­
ysis, Part 2, Agronomy, 9: 1179- 1237,
BUTTERS, B" and E, M, CHENERY, 1959, A rapid method for the
162
CAN.
J.
FOR. RES. VOL. 14. 1984
determination of total sulphur in soils and plants. Analyst, 84:
239- 245.
CHAPMAN, H. D. , and P. F. PRATI. 1961. Methods of analysis for
soils, plants, and waters. Division of Agricultural Science, Univer­
sity of California, Berkeley, CA.
GILL, R. S. 1981. Factors affecting nitrogen nutrition of western
hemlock. Ph.D. thesis, Oregon State University, Corvallis, OR.
HEILMAN, P. E. , T. DAO, H. H. CHENG, S. R. WEBSTER, and
S. S. HARPER. 1982. Comparison of fall and spring applications of
'5N-Iabeled urea to Douglas-fir. 1. Growth response and nitrogen
levels in foliage and soil. Soil Sci. Soc. Am. J. 46: 1293- 1299.
HEILMAN, P. E. , and G. EKUAN. 1980. Phosphorus response of west­
ern hemlock seedlings on Pacific coastal soils from Washington.
Soil Sci. Soc. Am. J. 44: 392- 395.
JOHNSON, D. W. 1979. Some nitrogen fractions in two forest soils and
their changes in response to urea fertilization. Northwest Sci. 53:
22- 32.
OLSEN, S. R. , and L. A. DEAN. 1965. Phosphorus. III Methods of soil
analysis. Part 2. Agronomy, 9: 1035- 1049.
OLSON, J. , W. ATKINSON, and M. RINEHART. 1980. Radial increment
response of western hemlock to nitrogen fertilization and thinning.
Regional Forest Nutritional Research Project Technical Report,
College of Forest Resources, University of Washington, Seattle,
WA.
RADWAN, M. A. , and D. S. DEBELL. 1980a. Site index, growth, and
foliar chemical composition relationships in western hemlock. For.
Sci. 26: 283- 290.
1980b. Effects of different sources of fertilizer nitrogen on
growth and nutrition of western hemlock. U.S. For. Servo Res. Pap.
PNW-267.
RADWAN, M. A. , and J. S. SHUMWAY. 1983. Soil nitrogen, sulfur,
and phosphorus in relation to growth response of western hemlock
to nitrogen fertilization. For. Sci. 29: 469- 477.
Ross, C. R. 1932. Root development of western conifers. M.S.
thesis. University of Washington, Seattle, WA.
TURNER, J. , and M. LAMBERT. 1978. Sulfur nutrition of conifers in
relation to response to fertilizer nitrogen, to fungal infections, and
to soil parent materials. III Forest soils and land use. Proc. North
Am. For. Soils Conf. 5th. Colorado State University, Fort Collins,
CO. pp. 546- 564.
TURNER, J., M. J. LAMBERT, and S. P. GESSEL. 1977. Use of foliage
sulphate concentrations to predict response to urea application by
Douglas-fir. Can. J. For. Res. 7: 476- 480.
1979. Sulfur requirements of nitrogen fertilized Douglas-fir.
For. Sci. 25: 461- 467.
WEBSTER, S. R. , D. S. DEBELL, K. N. WILEY, and W. A. ATKINSON.
1976. Fertilization of western hemlock. III Western Hemlock
Management Conference, Proceedings. Edited by W. A. Atkinson
and R. J. Zasoski. College of Forest Resources, University of
Washington, Seattle, WA. pp. 247- 252.
WILEY, K. N. 1978. Site index tables for western hemlock in the
Pacific Northwest. Weyerhaeuser For. Pap. No. 17.
---
---
A N ADA C
N
I
D
E
T
N
l
R
P