AN ABSTRACT OF THE THESIS OF
Ranjit Singh Gill
FOREST SCIENCE
in
Title:
for the degree of
presented on
Doctor of Philosophy
April 17, 1981
FACTORS AFFECTING NITROGEN NUTRITION OF WESTERN HEMLOCK
Abstract Approved:
Signature redacted for privacy.
Preliminary fertilization trials with western hemlock have
yielded responses which vary significantly from stand to stand, especially in areas near the Pacific Coast.
Growth responses have varied
from positive to negative in an erratic manner.
Previous data did not
permit validation of such hypotheses as, "the application of fertilizer to a hemlock stand results in unfavorable changes in soil
chemistry," "application of fertilizer damages the feeder roots of
hemlock so that uptake of water and minerals is reduced' or "nitrogen
is not the only growth limiting element on many coastal hemlock
sites."
The main purpose of the series of experiments outlined in this
thesis is to assess the effects of the application of urea fertilizer
upon the rhizosphere and the consequent absorption capacity of hemlock
roots.
Prilled urea at the rate of 224 kg/hectare of elemental nitrogen
was applied to test plots in six natural hemlock stands.
Periodic
soil core samples were extracted to examine the impact of urea on soil
chemical properties and hemlock's primary roots.
Foliage samples were
collected and analyzed to determine the impact of urea on hemlock's
mineral-nutrient status.
Also, a litter-bag study was conducted to
examine the impact of various forms of nitrogen fertilizers (urea
included) on rates of litter decomposition in hemlock stands.
The results of this study demonstrate that application of urea
significantly alters the soil pH, increases the concentrations of
extractable NH14 and NO3
nitrogen decreases the amounts of Ca, Mg and
K and increases the rate of litter decomposition in the rhizosphere of
western hemlock.
The magnitude of these changes in soil chemical
properties is maximum in the litter layer and decreases with soiL
depth and time.
The pH and NHt1-N concentrations
jfl
the litter layer
reach levels which are toxic to hemlock.
Urea fertilization results in significant reduction in the total
numbers of mycorrhizal roots and in significant changes in the relative populations of the mycorrhizal types.
The nagnitude of these
changes varies among the hemlock stands and is most likely a function
of the vertical distribution of mycorrhizal roots and their composition.
The maximum reduction in number of mycorrhizal roots occurs
during the first six months and at 0-5 cm soil depth, which is also
the time span and the soil depth at which the magnitude of changes in
soil properties following urea application are maximum.
The balance of essential nutrients in the foliage of western
hemlock is also altered significantly after urea fertilization.
Foliar concentration of nitrogen is increased and the concentrations
of 1',
Ca, Mg, Mn, Fe and B are generally reduced.
Reduction in con-
centration of these elements following urea application is probably
due to reduced uptake.
The relative foliar concentrations of some
essential elements (especially P) following urea treatment fall in the
range considered limiting to hemlock's growth potential.
FOREST RESEARCH LABORATORY
U BcY
OREGON STATE UNIVERSUY
FACTORS AFFECTING NITROGEN NUTRITION
OF WESTERN HEMLOCK
by
Ranjit Singh Gill
A THESIS
submitted to
Oregon State University
in partial fulfillment of
the requirements for the
degree of
Doctor of Philosophy
June 1981
L
TABLE OF CONTENTS
Page
CHAPTER I.
CHANGES IN SOIL CHEMICAL PROPERTIES FOLLOWING
UREA APPLICATION ON WESTERN HEMLOCK STANDS
Introduction
Materials and Methods
Discussion and Implications
Conclusion
Bibliography
CHAPTER II.
UREA FERTILIZATION AND THE PRIMARY-ROOT SYSTEM
OF YOUNG-GROWTH WESTERN HEMLOCK [TSUGA
HETEROPHYLLA (RAP.) SARGI
Introduction
Materials and Methods
Results
Discussion
Conclusion
Bibliography
CHAPTER III.
UREA FERTILIZATION AND FOLIAR NUTRIENT
CONCENTRATION OF WESTERN HEMLOCK (TSUGA
HETEROPHYLLA (RAP.) SARG.]
Introduction
Materials and Methods
Sampling
Statistical Analysis
Results
Discussion and Implications
Conclusion
Bibliography
CHAPTER IV.
IMPACT OF NITROGEN FERTILIZERS ON RATES OF
LITTER DECOMPOSITION IN COASTAL HEMLOCK STANDS
Introduction
Materials and Methods
Statistical Analysis
Results
C:N Composition of Litter
Carbon Components of Litter
Discussion
Conclusion and Implications
Bibliography
BIBLIOGRAPHY
1
1
2
13
16
36
39
39
40
43
46
50
57
59
59
60
60
61
61
63
67
72
73
73
74
76
77
78
79
81
84
90
LIST OF FIGURES
Page
Figure
1
Plot Layout and Soil Core Processing.
19
2
Soil pH of 0-5 cm Samples as Influenced by
Urea Fertilization.
20
Soil p11 of 5-10 and 10-20 cm Samples as
Influenced by Urea Fertilization.
21
Soil Water Content of 0-5, 5-10 and 10-20 cm
Samples as Influenced by Urea Fertilization.
22
Extractable NH (ppm) Content of 0-5, 5-10
and 10-20 cm Soil Samples as Influenced by
Urea Fertilization.
23
Extractable NO3 (ppm) Content of 0-5, 5-lO
and 10-20 cm Soil Samples as Influenced by
Urea Fertilization.
24
Total N (%) Content of 0-5, 5-10 and 10-20 cm
Soil Samples as Influenced by Urea Fertilization.
25
Total C (%) Content of 0-5, 5-10 and 10-20 cm
Soil Samples as Influenced by Urea Fertilization.
26
C:N Ratio of 0-5, 5-10 and 10-20 cm Soil Samples
as Influenced by Urea Fertilization.
27
10
Carbon Components (7.) in Organic Matter Fraction
of 0-5 cut Soil Samples as Influenced by Urea
Fertilization.
28
11
Extractable K (mg/lOO gm) Content of 0-5, 5-10
and 10-20 cm Soil Samples as Influenced by Urea
Fertilization.
29
12
Extractable Ca (mg/lOO gui) Content of 0-5, 5-10
and 10-20 cm Soil Samples as Influenced by
Urea Fertilization.
30
13
Extractable Mg (mg/lO0 gin) Content of 0-5, 5-10
and 10-20 cm Soil Samples as Influenced by
Urea Fertilization.
31
Figure
Page
14
Total Ca (%) Content of 0-5, 5-10 and 10-20 cm
Soil Samples as Influenced by Urea Fertilization.
32
15
Total K (%) Content of 0-5, 5-10 and 10-20 cm
Soil Samples as Influenced by Urea Fertilization.
33
16
Total Mg (%) Content of 0-5, 5-10 and 10-20 cm
Soil Samples as Influenced by Urea Fertilization.
34
17
Impact of Soil pH on Growth of Hemlock Seedlings.
35
LIST OF TABLES
Page
General Characteristics of the Test Stands
(1977).
18
Vertical Distribution and the Impact of Urea
Fertilization on Hemlock's Primary Roots
(Number of Tips/lOO CC).
51
Il-ti
Vertical Distribution and the Effect of Urea
Fertilization on Hemlock's Primary Roots
(Number of Tips/lOO CC).
52
Il-Ill
Total Numbers and Impact of Urea Fertilization
on Hemlock's Primary Roots (Number of Tips/Core
(251 CC)).
53
lI-tV
Total Numbers and Impact of Urea Fertilization
on Hemlock's Primary Roots (Number of Tips!
Core (251 CC)).
54
tI-V
Vertical Distribution and the Impact of Urea
Fertilization of Hemlock's Mycorrhizal Roots.
55
It-Vt
Relative Growth of Mycorrhizal and Non-mycorrhizal
Hemlock Seedlings Grown from a Cascade and a
Coastal Seed Source.
56
Ill-I
Macroelemeat and Al Concentration in Foliage of
Western Hemlock.
68
Ill-Il
Microelement Concentration in Foliage of Western
Hemlock.
69
Ill-Ill
Nutrient Balance of Elements in Hemlock Foliage
After Urea Fertilization.
70
Ill-tv
Two Year Basal Area Growth Response of Hemlock to
Urea Fertilization
71
IV-I
Litter Decomposition (L. Bags).
86
IV-II
Coefficient of Correlation (R) and Slope of
Regression Lines of: Percent Weight
Remaining, C:N Ratio and Percent Lignin
AgaInst Time (Months) Elapsed (18 Month
Period).
87
Table
Page
IVIII
C:N Composition of Litter.
88
tVtV
Carbon Components of Litter.
89
FACTORS AFFECTING NITROGEN NUTRITION
OF WESTERN HEMLOCK
CHAPTER 1.
CHANGES IN SOIL CHEMICAL PROPERTIES FOLLOWING
UREA APPLICATION ON WESTERN HEMLOCK STANDS
INTRODUCTION
Empirical studies in western Oregon and Washington show that the
response of young-growth western hemlock [Tsuga heterophylla (Raf.)
Sarg.] stands to applications of nitrogenous fertilizer is much more
erratic than is response of similar stands of Douglas-fir (Anonymous
1977, Webster et al. 1976, DeBell et al. 1975).
Addition of nitrogen mainly in the form of prilled urea to the
hemlock stands has resulted in basal area growth response ranging from
growth depression (down to -20 percent) to growth acceleration (up to
50 percent).
In general, hemlock trees in the coastal zone have
either failed to respond or have shown negative response to nitrogenous fertilizer.
In order to determine the causes of response variability to urea
application and to develop guidelines for efficient fertilization of
hemlock stands, studies of fundamental aspects of the impact of fertilizer application upon hemlock's rhizosphere, nutrition and growth
are needed.
The following study examines the effects of urea application
upon the soil chemical properties in the rhizosphere of hemlock stands
in the coastal and Cascade hemlock zones.
Urea was the selected
fertilizer because it is most commonly used for forest fertilization
in the Pacific Northwest.
MATERIALS AND METHODS
Stand Selection
A total of six natural stands of young-growth western hemlock
were selected for investigation.
Three of the selected stands
(Coast-i, Coast-7, Coast-8) are located in the coastal hemlock zone
near Seaside, Oregon.
The other three stands (Cascade-i, Cascade-2,
Cascade-3) are situated in the Cascade range near Vail, washington.
The selected sites consist of almost pure western hemlock (> 90 percent hemlock) stands that, except for few experimental plots, had not
been fertilized or thinned in the past.
The general characteristics
of the selected stands as determined during September 1977 are given
in Table I.
During September, 1977, eight circular plots measuring 0.0203
hectare (1/20 acre) were established at random in each of the six
selected hemlock stands.
pancy were defined.
1ithin each plot, three triangles of occu-
These triangles consist of the area enciosed by
lines connecting three hemlock trees.
Twelve sampling points were
defined in each of the triangles of occupancy as detailed in Figure 1.
Two soil cores were collected at random from the twelve defined points
in each triangle of occupancy (a total of six cores from each plot)
with a core sampler especially designed for this purpose.
This
equipment permits extraction of intact soil cores up to 30 cm in
depth, which can be divided into sub-cores to represent different soil
depths.
Soil cores collected from each plot were divided into three
sections:
HOR-I, representing 0-5 cm depth; HOR-Il, representing
5-10 cm depth; and FIOR-IlI, representing 10-20 cm depth.
In the
laboratory these sub-cores were weighed, broken by hand into fine
aggregates and pooled.
One half of each sample was utilized for soil
analysis; the second for root population determinations.
Roots were extracted from the soil samples by the wet sieving
technique of Marks et al. (1968).
Quantity of fine roots (< 2 mm in
diameter) in soil depths HOR-I, HOR-Il, and HOR-Ill in each plot was
determined by dispersing extracted roots in a rimmed perspex and examined with a zoom binocular microscope.
Results of this preliminary
study indicated that 0-5 cm soil depth (HOR-I) contained the majority
of fine western hemlock roots in all except Cascade-1 stands.
Therefore, for the purpose of initial plot selection, only soil
samples representing HOR-I were analyzed for soil properties.
Soil representing HOR-I was screened through a 2-mm mesh screen
and sifted by hand to remove root material left behind.
A 15-gram
subsample was dried in an oven at 105°C for 24 hours to determine percentage moisture in the sample.
The pH value was determined with the
suspension of 15 grams of wet soil in 30 ml of distilled water using
glass electrode pH meter.
The remainder of the soil was dried at 70°C
to a constant weight for determination of total nitrogen (N),
extrac-
table ammonium (NHLf) and nitrate (NO3) nitrogen, total carbon (C),
extractable and total cations (Ca, Mg, and K).
Total N was
determined by the micro Kjeldahl method outlined by Bremner (1965).
Extractable NHt,-nitrogen was determined by KC1 extraction and steam
distillation (Bremner and Keeney 1965).
NO3-nitrogen was extracted
with deionized water and analyzed on the autoanalyzer (Standard
Methods 1975).
Total C was determined using titration method of
Walkley and Black (1934).
Extractable K, Ca, and Mg were determined
by atomic absorption on an ammonium acetate extract (Peech et al.
1947).
Total K, Ca, and Mg were analyzed by atomic absorption using
perchioric-nitric acid digest modification of Pratt's (1965)
perchioric-hydrofluoric acid digest.
Six of the initial eight plots within each stand that had the
least between plot variation in the following parameterstotal live
fine roots, total N, C, K, Ca, Mg, and extractable NH-N, NO3-N, K,
Ca, and Mg--were selected for the study.
Of these six, th.ree randomly
selected plots in each stand were fertilized with prilled urea at the
rate of 224 kg of elemental nitrogen/hectare (200 lbs N/acre).
other three plots served as controls.
The
The Cascade and coastal stands
were fertilized on November 29, 1977, and December 6, 1977, respectively.
On both occasions, fertilizer was broadcast by hand under
conditions of light rain and cool temperatures.
Following urea treatment, soil core samples were taken at
1.5-month intervals for the first two sampling dates and at two-month
intervals at the following three sampling dates.
An additional set of
soil cores was taken on the three coastal plots on May 5, 1979.
The
procedure for soil core extraction and analysis for the postfertilization period was similar to the procedure used during initial
plot selection.
In addition, organic matter in HOR-I samples
collected on March 1978, September 1978, and May 1979 was analyzed for
lignin, cellulose and non-cell wall carbon components by the method
described by Van Soest (1963)1.
Statistical Analysis
The six stands were treated as six separate blocks and the data
for each sampling date was statistically analyzed by randomized
complete block design.
Also, a simple t-test analysis was used to
test for significant differences between urea-treated and control
plots at each sampling date for individual stands.
Duncan's multiple
range test was used to rate individual stands according to the magnitude of parameter values at each sampling date.
Re suits
The following results compare average of control plots with
average of urea-trated plots for the six stands at each sampling date
for the three soil depths.
For simplicity, preurea-treatment sampling
date (September 1977) is referred to as sampling date -0, and sampling
dates January 1978, March 1978, May 1978, July 1978, September 1978,
May 1979, representing 1.5, 3,
5,
7,
9, and 18-month intervals
after urea treatment, are referred to as sampling dates 1,
2,
3,
4,
5,
1Not all samples for each horizon on each sampling date were analyzed
because of budget limitations.
6
and 6, respectively.
Also, the 5 percent probability level (P < 0.05)
to test statistical significance of difference between treatments
(control and urea-treated) is used.
Soil pH
11CR-I.
Changes in HOR-I soil p1-I after urea treatment are shown
in Figure 2.
Urea treatment significantly increased the soil pH by
the first sampling date.
During the following months, the pH on urea-
treated plots declined slowly, remaining significantly higher than
that of the control plots up to the fifth sampling date but reaching a
lower value than that of the control plots by the
I{OR-II, HOR-Ill.
and HOR-Ill depths.
sixth sampling
date.
Figure 3 shows the changes in soil pH at HOR-lI
By the first sampling date, pH on urea-treated
plots had become significantly higher than that of the control plots.
However, pH at 11CR-It and
11CR-Ill of
treated plots had become signifi-
cantly lower than the pH of the control plots by the fourth and third
sampling dates, respectively, and remained lower up to the sixth
sampling date.
Soil Water Content
bR-I.
of
By the first sampling date, percentage moisture in HOR-I
treated plots became significantly higher than that of the control
plots (Figure 4).
By the fourth sampling date, however, the water
content of urea-treated plots did not differ significantly from the
control.
7
bR-u, HOR-Ill.
Water content in HOR-It and HOR-Ili soil depths
of urea-treated plots did not differ significantly from the control at
any sampling date after urea application (Figure 4).
Extractable
HOR-I.
mmonium Nitrogen (NH-N)
The average NHL,-N value of urea-treated plots became ten-
fold higher than that on control by the first sampling date (Figure
5).
Increase in NHt-N ranged from 1,157 percent on Coast-i to 793
percent on Cascade-3 stand.
The NH-N content in HOR-I of treated
plots declined slowly during the following months to the point that
there was no significant difference between NH-N average on ureatreated and control plots by the sixth sampling date.
1-bR-h, HOR-hhl.
The average NHt,-N value on treated plots at
HOR-LI and 1-bR-hi soil depths was, respectively, 8.3 and 2.5 times
higher than on control by the first sampling date (Figure 5).
Increase in NHLf-N values for HOR-hl on urea-treated plots ranged from
2,200 percent on Coast-i to 314 percent on Cascade-3 stands.
For
HOR-hhI increase in NHLf-N values on treated plots ranged from 429 per-
cent on Coast-7 to 102 percent on Cascade-2 stands.
The NH-N content
in baR-lI and HOR-hhl of urea-treated plots declined gradually during
the following months to the point that control and urea-treated plots
did not differ significantly by the sixth sampling date.
Extractable Nitrate Nitrogen (NO3-N)
HOR-I.
Average NO3-N on urea-treated plots became significantly
higher than control by the first sampling date and remained signif i-
candy higher for the duration of the experiment (Figure 6).
The
magnitude of difference between NO3-N values of control and ureatreated plots, for each stand, was greatest on the fourth sampling
date, at which time, the average value for urea-treated plots was
1,693 percent higher than the average value of control plots.
HOR-Il,
HOR-Ill.
The average NO3-N values for HOR-Il and HOR-Ill
on urea-treated plots, became significantly higher than control by the
first sampling date and remained significantly higher during the
following months.
As with HOR-I, the magnitude of difference between
urea-treated and control values for both HOR-Il and HOR-Ill was
greatest on the fourth sampling date.
The average NO3-N values for
HOR-Il and HOR-Ill on the fourth sampling date were, respectively,
4,343 percent and 3,446 percent higher than on control plots.
Total Nitrogen
HOR--I.
The average total nitrogen value became significantly
higher (up 31 percent) on urea-treated than on control plots by the
first sampling date and remained significantly (P < 0.05) higher for
the duration of the experiment (Figure 7).
There was, however, a gra-
dual decreasein the magnitude of difference in total nitrogen content
between urea-treated and control plots after the first sampling data.
9
HOR-lI, HOR-Ill.
At HOR-It depth, the average total nitrogen
content also became significantly higher (up 12 percent) on ureatreated plots by the first sampling date (Figure 7).
The difference
between average total nitrogen values for control and urea-treated
plots increased gradually up to 19 percent by the fifth sampling date,
but had declined to 15 percent by the sixth sampling date.
Total
nitrogen content at HOR-ItI depth did not differ significantly between
control and urea-treated plots for the duration of the experiment.
Total Carbon
HOR-I.
Total carbon content on urea-treated plots became signi-
ficantly lower than control by the first sampling date and remained
significantly lower up to the fourth sampling date (Figure 8).
By the
sixth sampling date, however, there was no significant difference bet-
ween the total carbon content of control and urea-treated plots.
HOR-Il, HOR-Ill.
Total carbon content in HOR-Il and HOR-Ill
depths was determined for soil samples taken on the first sampling
date only and there was no significant difference between the total
carbon averages of control and urea-treated plots (Figure 8).
Total Carbon:Total Nitrogen (C/N Ratio)
HOR-I.
As mentioned above, since urea application had resulted
in a significant increase in total nitrogen and a significant decrease
in total carbon content in I-bR-I, C/N ratio of urea-treated plots
became significantly lower (-31 percent) by the first sampling date
10
and remained significantly lower (-17 percent) up to the sixth
sampling date than the C/N ratio on control plots (Figure 9).
HOR-Il, HOR-lIt.
There was no significant difference between the
C/N ratio means of control and urea-treated plots by the first
sampling date (Figure 9).
The C/N ratios for HOR-It and HOR-Ill
depths beyond the first sampling date are unknown because total carbon
on these samples was not determined.
However, because the difference
in total nitrogen content between urea-treated and control plots at
HOR-tI depth increased from 12 percent on first sampling date to 19
percent by the fifth sampling date, it is most likely that the C/N
ratio on urea-treated plots became significantly lower than the C/N
ratio on control plots at later dates.
On the other hand, since there
was no significant difference between the total nitrogen content of
urea-treated and control plots at HOR-Ill depths, it can be assumed
that urea treatment did not cause any significant change in the C/N
ratio at this depth.
Carbon Components
HOR-I.
Percentage of non-cell wall carbon (NCW)
ifl
organic mat-
ter on urea-treated plots became significantly less (-13 percent)
while percentage of lignin and cellulose became significantly higher
than control by the third sampling date (Figure 10).
The NCW compo-
nent of organic matter remained significantly lower and the lignin and
cellulose components remained significantly higher on the urea-treated
plots than on control plots for the duration of the experiment.
11
Extractable Cations (K, Ca, Mg)
HOR-I.
Extractable K, Ca, and Mg averages on urea-treated plots
became significantly lower than on control plots by the third sampling
date and remained significantly lower during the following sampling
periods (Figure 11, 12, 13).
At the third sampling date, differences
between control and urea-treated plot averages were greatest for
extractable K (-35 percent) followed by extractable Mg (-26 percent)
and least for extractable Ca (-22 percent).
The magnitude of dif-
ference between average values of extractable cations of control and
urea-treated plots became progressively smaller during the following
months becoming 16 percent for extractable K, 14 percent for extractable Mg, and 7 percent for extractable Ca by the sixth sampling date.
HOR-IT, HOR-Ill.
Extractable Mg average of urea-treated plots at
HOR-Il and HOR-lIl depths was significantly lower than that on control
by the first sampling date,
and became progressively lower in the
following months (Figure 13).
Extractable K average of urea-treated
plots became significantly lower than that on the control plots by the
fourth sampling date and remained significantly lower during the
remainder of the experiment (Figure 11).
At HOR-It depth, although
smaller on urea-treated plots, extractable Ca average did not differ
significantly from control at any sampling date after urea application
(Figure 12).
At HOR-III depth, however,
there was a progressive
decrease in the average extractable Ca value on urea-treated plots
following urea application so that by the fifth sampling date
12
extractable Ca average on urea-treated plots was significantly lower
(-37 percent) than control (Figure 13).
En general, at HOR-I soil depth, the difference in extractable
cation (K, Ca, Mg) averages between control and urea-treated plots had
reached a maximum value on or before the second sampling date after
urea application and the magnitude of difference became progressively
smaller in the following months.
In contrast, at HOR-lI and HORIII
soil depths, the maximum difference between control and urea-treated
plot averages for extractable cations was reached more gradually by
the fifth or even sixth sampling dates following urea treatment.
Total Cations
HOR-I.
Average values of total cations on urea-treated plots
were significantly lower up to the fifth sampling date for total Ca
and up to the sixth sampling date for total K and total Mg (Figures
14, 15, 16).
At the first sampling date, difference between control
and urea-treated plot averages was greatest for total K (-25 percent)
followed by total Mg (-21 percent) and least for total Ca (-12
percent).
The magnitude of difference between average values of total
cations remained fairly constant up to the fifth sampling date but had
decreased by the sixth sampling date.
13
Average total Ca and total K values at HOR-tI
HOR-II, HOR-Ill.
or HOR-III soil depths, although consistently smaller on urea-treated
plots, did not differ significantly from control at any sampling date
following urea application (Figures 14, 15),
However, average total
Mg values at HOR-Il soil depth on urea-treated plots were signif i-
cantly lower on fourth and fifth sampling dates (Figure 16).
Total Mg
values at HOR-Il soil depth, although consistently lower on ureatreated plots, did not differ significantly from control at any
sampling date.
DISCUSSION AND IMPLICATIONS
Application of nitrogen in the form of prilled urea to western
hemlock stands in the coastal and Cascade hemlock zone resulted in
significant changes in the soil pH, litter decomposition rates, and
soil nutrient contents.
Initial increase in soil pH is due to hydrolysis of urea and the
subsequent lowering of the pH values is most likely due to increased
nitrification on the treated plots.
The pH values on urea-treated
plots observed on the first sampling date are probably not the peak
values because hydrolysis of urea is rapid and the peak pH values are
reached within a few days after urea application (Johnson 1979, Crane
1972, Roberge and Knowles 1966).
The observed increase in soil pH was
greatest, and persisted for the longest duration in the top 5 ciii of
forest floor.
The magnitude of pH increase and the persistence of
this increase, following urea application, decreased with soil depth.
The increase in soil pH may affect nutrient uptake by the trees in the
14
following manner:
the availability of iron, boron, manganese, copper,
and zinc is reduced as pH increases, and the growth of mycorrhizae and
mycorrhiza-forming fungi may be adversely affected by increase in soil
pH (Ttreault et al. 1978, Slankis 1974, Mikola 1973, Park, 1971,
Theodorous and Bowen 1968, Marx and Zak 1965, Richards and Wilson
1963).
The adverse effect of increase in soil pH would be especially
drastic for hemlock because a vast majority of its nutrient absorbing
roots are mycorrhizal and are found near the surface of the forest
floor1, the zone in which the pH increase is most dramatic.
In a greenhouse experiment, we amended the field pH (4.15) with
0.1 N sulphuric acid to a pH value of 3.15 and with 0.1 N calcium
hydroxide to values of 6.15 and 7.15.
The soil was equi1brated for
five weeks and potted up with 3 kg of soil per pot.
Four hemlock
seedlings were grown in each pot and each treatment was replicated six
times.
Seedlings were harvested 18 months after planting.
The
results (Figure 17) demonstrate a dramatic reduction in root develop-
ment and shoot growth at pH 6.15 and 7.15 as compared with field pH
and pH 3.15.
Heilman and Ekuan (1973) have also demonstrated signif i-
cant reduction in western hemlock growth following liming.
1Gill, R. S., and D. P. Lavender.
1981.
Urea fertilization and the
primary root system of young-growth western hemlock [Tsua
heterophylla (Raf.) Sarg.].
Thesis, Chapter II.
15
Both NHt-N and NO3-N levels increased as a consequence of urea
fertilization.
The magnitude of increase of both forms of nitrogen
decreased with depth.
The increased capability of all six hemlock
stands tested to form NO3-
is most likely due to a large supply of
NHt,-N and the increase in soil pH that results from urea hydrolysis.
Similar increases in NO3-N levels following urea application have been
reported by Heilman (1974) and Bollen and Lu (1968).
Cole and Gessel
(1968) on the other hand found no significant increase in nitrate pro-
duction following urea application on their test site.
The increased levels of Nitf-N, especially in the litter layer,
exceeded the concentrations considered toxic for conIfers
ifl
general
(Ingestad 1979) and for hemlock in particular (220-485 ppti NRt-N) (Van
den Berg 1971).
The increase in NO3-N may affect nutrient uptake by the trees in
the following manner:
high levels of NO3-
will depress phosphate
uptake, promote loss through leaching of essential cations (Johnson
1980), and reduce growth of mycorrhizae and mycorrhizae-forming fungi
(Gill and Lavender 1980, Park 1971, Theodorou and Bowen 1968,
Richards 1961).
Decrease in amounts of extractable and total cations
(Ca, Mg, K) in the top 20 cm of the forest floor following urea application is most likely due to replacement of these cations from the
exchange complex by the mass action of
and the subsequent loss
via leaching, facilitated by the increased levels of NO3 anion and the
death of hyphae that normally would capture and recycle these ions.
This loss of the essential cations from the rooting zone of western
hemlock, could result in rendering one or more of these elements
16
limiting to hemlock's growth.
Also, the increase in nitrification
would result in loss via leaching of the added nitrogen thus
decreasing the efficiency of urea fertilization.
Relative increase in percentage of lignin and decrease in percentage of non-cell-wall carbon in the organic matter, and decrease in
total carbon in the litter layer suggests a significant increase in
the rates of litter decomposition following urea application.
Increased litter decomposition was confirmed by a litter bag study
conducted simultaneously on the three coastal stands1.
Increase in litter decomposition on the urea-treated plots is
most likely due to dissolution of organic matter (as demonstrated by
increase in water content in the litter layer in Figure 4) as a result
of increase in pH (Sagara 1975, Ogner 1972, Bengtson 1970), and due to
a decrease in C/N ratio.
Increase in litter decomposition could further add to the loss of
essential nutrients, via leaching, from the rooting zone of hemlock if
the nutrient absorbing roots of the tree were adversely affected
during this time and were unable to absorb this flux of released
nutrients.
CONCLUS ION
This experiment demonstrates that application of urea signif i-
cantly alters the soil pH, increases the NH-N and NO3-N, decreases
Impact of nitrogen fertili1Gill, R. S., and D. P. Lavender. 1981.
zers on the rates of litter decomposition on coastal hemlock stands.
Thesis Chapter IV.
17
the amounts of Ca, Mg, and K, and increases the rates of litter
decomposition.
Further, the magnitude of these changes decreases with
increase in soil depth and with time.
Any impact of urea treatment,
therefore, can be expected to be more dramatic on the roots that grow
closer to the forest floor.
Consequently, the impact of changes i
the soil chemical properties following urea application can be
expected to be more dramatic on trees that have a large proportion of
their nutrient absorbing roots near the surface of the forest floor.
Response variability in hemlock stands to urea application, therefore,
may be due to differences between stands, in the
distribution
of
nutrient absorbing roots, and/or the relative sensitivity of the
nutrient absorbing roots, to the changes in soil properties that result
from urea application.
On shallow rooted hemlock stands, use of slow-
release and/or pH balanced fertilizers might be more desirable than
application of fertilizers such as urea which produce
rapid
tic changes in soil chemical properties in the rhizosphere.
and drama-
TABLE I.
GENERAL CHARACTERISTICS OF THE TEST STANDS (1977).
Elevation
(m)
Coast-i
Coast-7
Coast-B
Cascade-i
Slope
Aspect
(%)
Tree age
breast height
(average
36 trees)
Site class
DBH
(cm)
Basal area
(m2/ha)
(average
36 trees)
Soil type
168
N
10-40
38.76 ± 0.20
II (Hi)
64.98
32.13 ± 0.65
Hembre and
Astoria
Silt loam
107
N
0-30
25.19 ± 0.07
II (Lo)
49.59
30.53 ± 0.36
Astoria and
Hembre
Slit loam
10-40
46.74 ± 0.34
II (Hi)
67.27
38.91 ± 0.78
Hembre and
Astoria
Silt loam
10-40
40.89-0.23
III
65.44
34.46 + 0.63
Boumgard
76
488
SE
N
(BD)
Cascade-2
Cascad-3
488
701
E
NE
0-10
35.12 ± 0.27
IV
54.19
24.88 ± 0.55
Halsilt loam
10-30
22.71 + 0.20
V
57.60
20.50 + 0.39
Halsilt loam
Figure 1.
Plot Layout and Soil Core Processing
COASTAL, IIEMLOCI< ZONE
CASCAI)L HEMLOCK ZONE
3 31ANOS Ar EACIL ZONE
00
00
00
00
00
00
SEAND TI
STAND m
1
SOIL
NOR
ANALYSIS
U
r
I
iWO CORES EXIRACIED
Al RANDOM FROM
EACH I AT EACH
SAMPLING DATE AND
DIVIDED INTO THREE
SECrI0NS RESPECTIVE
SCCIIOHS FROM TILE
SAME PLOT ARE
EACH SEcTION
DIVIDED IN
T
5cm
'L1
r1
PRIMARY
ROOT
EXTRACTION
PX)I El)
I-
11011
Ill
-
TWO SEGMENTS
bern
t
MFSH
IN FAA
HOOTS B
FLOOIS
PHI SERVED
C
SOILS a
WAT ER
OLD?
ME Sil
Figure 2.
Soil pH of 0-5 cm samples as influenced by urea fertilization.
7.0
F-I
6.0
F = Urea treatment
C = Control
I = 0-5 cm depth
5.0
4.0
1977
I
J FM AM J
Coast
I
N
Urea
application
I
J
1978
I
A
May
1979
Figure 3.
Soil pH of 5-10 and 10-20 cm samples as influenced by urea fertilization.
7.0
6.0
F = Urea treatment
C
II
F-Il
I
I-
= ± Standard error
-
I
N
1977
5-10 cm depth
III = 10-20 cm depth
5.0
4.0
Control
1'
3
F
I
M
1_________ J.____.__
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M
Coast
1 Urea
Cascade J application
I
3
I
I
3
A
1978
1_I
S
0
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N
May
1979
Figure 4.
Soil water content of 0-5, 5-10 and 10-20 cm samples as influenced by urea fertilization.
/0
F-I
70
F = Urea treatment
C
Control
I
0-5 cm depth
II
5-10 cm depth
/
/
\
III = 10-20 cm depth
/
/
//
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I= ± Standard error
/
40
1977
i4 j
Loaat
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J
A
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Urea
application
/
1978
D
May
1979
Figure 5.
Extractable NH
fertilization.
(ppm) content of 0-5, 5-10 and 10-20 cm soil samples as influenced by urea
/
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Figure 6.
Extractable NO3 (ppm) content of 0-5, 5-10 and 10-20 cm soil samples
as influenced by urea
fertilization.
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Figure
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Total N (%) content of 0-5, 5-10 and 10-20 cm soil samples as influenced by urea
fertilization.
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samples as influenced by urea
fertilization.
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35
36
BIBLIOGRAPHY
Biannual Report, 1974-1976, regional forest nutri1977.
don research project. Institute of Forest Products, College of
Forest Resources, University of Washington, Contribution No. 25.
Anonymous.
67 p.
Bengtson, G. W. 1970.
Forest soil improvement through chemical
ammendments. J. Forestry 68:343-347.
Nitrogen transformation in soil
Bollen, W. B., and K. C. Lu.
1968.
beneath red alder and conifers. In Symp. Proc. Biology of Alder.
U.S. Forest Service Pacific Northwest Forest and Range
Experiment Station, Portland, Oregon.
In Methods of Soil Analysis:
Bremner, J. M. 1965. Total nitrogen.
C. A. Biack, D. 0.
Chemical and Microbiological Properties.
Evans, J. L. White, L. E. Ensminger, and F. E. Clark (eds.).
Monogr. 9, Am. Soc. Agron., Madison, Wisconsin. pp. 1149-1178.
Bremner, J. H., and D. R. Keeney. 1966. Determination of isotoperatio analysis of different forms of nitrogen in soils:
3.
Soil Sci. Soc. Amer. Proc. 30:577-582.
Cole, 0. W., and S. P. Gessel.
Cedar River Research--a program
1968.
for studying the pathways, rates, and processes of elemental
cycling in a forest ecosystem.
Forest Resources Monogr. No. 4,
Univ. Washington, Seattle. 53 p.
Crane, W. J. B. 1972. Urea-nitrogen transformations, soil reactions,
and elemental movement via leaching and volatilization in a
Univ.
coniferous forest ecosystem following fertilization.
Washington, Seattle. Ph.D. Thesis.
285 p.
DeBell, D. S., E. H. Mallonee, J. Y. Lin, and R. F. Strand. 1975.
Fertilization of western hemlock: a summary of existing knowledge.
Crown Zellerbach Corporation Central Research Department
Forestry Research Note No. 5.
15 p.
Gill, R. S., and 0. P. Lavender. 1980. Nitrogen fertilization and
the ability of western hemlock roots to absorb and translocate
labeled (F32) phosphorus. Abstr. Northwest Science, 53rd
Annual Symposium.
Heilman, P., and G. Ekuan. 1973. Response of Douglas-fir and western
hemlock seedlings to lime. Forest Science l9(3):220-224.
Heilman, P.
1974.
Effect of urea fertilization on nitrification in
forest soils of the Pacific Northwest. Soil
Amer. Proc.
Sd.
38: 664-667.
37
Mineral nutrient requirements of Pinus silvestris
1979.
Ingestad, T.
and Picea abies seedlings. Physiol. Plant. 45:373-380.
Some nitrogen fractions in two forest soils and
Johnson, D. W.
1979.
their changes in response to urea fertilization. Northwest
Science 53(l):22-3l.
relevance to nutrient
Anion mobility in soils:
1980.
Johnson, D. W.
transport from forest ecosystems. Environ. International 3:7990.
Marks, G. C., N. Ditchburne, and R. C. Foster. 1968. Quantitative
estimation of mycorrhizae populations in radiata pine forests.
Australian Forestry 32:26-38.
Effect of pH on mycorrhizal formation
Marx, D. H., and B. Zak. 1965.
on slash pine aseptic culture. Forest Science li(l):66-74.
Application of mycorrhizal symbiosis in forestry
1973.
Mikola, P.
practice.
In Ectomycorrhizae: Their Ecology and ?hyslology.
Academic Press, New
G. C. Marks and T. T. Kozlowski (eds.).
York.
1972. The composition of forest raw humus after fertilizaOgner, G.
tion with urea.
Soil Sd. 133:440-447.
Some ecological factors affecting the formation
Park, J. Y.
1971.
Can.
of Cenococcum mycorrhizae on basswood in southern Ontario.
J. Bot. 49:95-97.
1947.
Peech, M. L., T. Alexander, L. A. Dean, and J. F. Reed.
Methods of soil analysis for soil fertility investigations.
USDA Circ. 757. 25 p.
Digestion with hydrofluoric and perchloric acids
Pratt, P. F.
1965.
In Methods of Soil Analysis,
for total calcium and sodium.
Monograph No. 9, Am. Soc. Agron.
Part LI.
C. A. Black (ed.),
Madison, Wisconsin.
pp. 1019-1021.
Richards, B. N. 1961.
Nature, Land.
Soil pH and mycorrhizae development In Pinus.
Richards, B. N., and G. L. Wilson. 1963. Nutrient supply and
mycorrhizal development on Carribbean pine forest. Forest
Science 9:405-412.
Roberge, M. R., and R. Knowles. 1966. Ureolysis, immobilization and
Soil
nitrification in black spruce (Picea mariana Mill.) humus.
Soc. Amer. Proc. 30:201-204.
Sd.
38
Sagara, N.
1975. Ammonia fungi--a chemoecological grouping of
terrestrial fungi.
Contrib. Biol. Jap. Kyoto Univ. 24:205-276.
Standard Methods for the Examination of Water and Waste Water.
14th ed.
APHA-AWWA-WPCE. AA II Manifold.
pp. 620-624.
1975.
Slankis, V.
1974.
Soil factors influencing formation of mycorrhizae.
Ann. Rev. Phytopatholo. 12:437-457.
Ttreault, J. P., B. Bernier, and J. A. Fortin. 1978. Nitrogen
fertilization and mycorrhizae of balsam fir seedlings in natural
stands.
Naturaliste Can. 105:466.
Theadorou, C., and G. D. Bowen. 1968. The influence of pH and
nitrate on mycorrhizal associations of Pinus radiata D. Don.
Aust. J. Bot. 17:59-67.
Van den Berg.
J.
1971.
Some experiments on the mineral nutrition
of forest tree seedlings. Internal Rapport Nr. 8, Forest
Research Station, "De Darschkamp," Wageningen, Netherlands.
append.
p. 67
Van Soest, P. J. 1963.
Use of detergents in the analysis of fibrous
feeds.
II.
A rapid method for the determination of fiber and
lignin.
J. Assoc. Official Agric. Chem. 46:829-835.
Walkley, A., and I. A. Black. 1934. An examination of the Degtjareff
method for determining soil organic matter and a proposed
modification of the chromic acid titration method. Soil Sci.
37:29-38.
Webster, S. R., D. S. DeBell, K. N. Wiley, and W. A. Atkinson. 1976.
Fertilization of western hemlock. In Western Hemlock Management
Conf. Proc.
W. A. Atkinson and R. J. Zasaski (eds.). Univ.
Washington, Seattle.
pp. 247-252.
39
CHAPTER II.
UREA FERTILIZATION AND THE PRIMARY-ROOT SYSTEM
OF YOUNG-GROWTH WESTERN HEMLOCK
[TSUGA HETEROPHYLLA (RAP.) SARG}
INTRODUCT ION
The ability of trees to take up nutrients from soil depends on
the health and vigor of the primary roots.
The primary roots of coni-
fers are intimately associated with mycorrhiza-formiag fungi which
greatly influence nutrient uptake and resistance to drought and
disease (Marks and Kozlowski 1973).
The symbiotic association between
feeder roots and the mycobionts is affected by the supply of carbohydrates from the phycobiont (Bjorkmafi 1949) and by a variety of
edaphic factors (Slankis 1974, Marks and Kozlowski 1973).
In the face of increasing demand for timber, fiber and biomass,
use of fertilizers is fast becoming an important management tool to
stimulate growth of forest trees.
Although numerous studies report
increased growth of coniferous stands (Windsor and Reiner 1973,
Wells, 1970, Brise and Ebell 1969), attempts to stimulate growth of
young western hemlock (Tsuga heterophylla (Raf. Sarg.) by nitrogen
fertilization has met with limited success (Anonymous 1977, Webster et
al. 1976, DeBell et al. 1975).
Preliminary fertilization trials with
western hemlock have yielded responses which vary erratically from
stand to stand and from positive to negative.
The available data do
not permit validation of hypothesis such as, "application of
40
fertilizer damages the feeder roots of hemlock so that uptake of
nutrients and water is reduced."
The immediate objectives of this study were to determine the spacial distribution and the morphological characteristics of primary
roots of hemlock stands in the coastal and Cascade hemlock zones and
to study the impact of urea fertilization on these roots.
The ulti-
mate objective was to obtain knowledge of the interaction of forest
fertilization and mycorrhizae to explain variations in responses of
hemlock stands to fertilization.
MATERIALS AND METHODS
Details of edaphic and biotic characteristics of the selected
stands, plot selection, treatment application and sampling procedure
are explained elsewhere1.
In this paper, therefore, only a brief
discussion of the experimental design is presented.
Six natural stands of young-growth western hemlock were selected
for investigation.
Three (Coast-i, Coast-7, Coast-8) are located in
the coastal hemlock zone, and the other three (Cascade-i, Cascade2,
Cascade-3) in the Cascade zone.
These sites consist of almost pure
western hemlock (> 90 percent hemlock) stands that except for few
experimental plots, had never been fertilized or thinned.
Within each
stand, six circular plots, each 0.0203 hectare (1/20 acre) were
established in autumn, 1977.
Three triangles of occupancy within each
Changes in soil chemical
1981.
1Gill, R. S., and D. P. Lavender.
properties following urea application on western hemlock stands.
Thesis, Chapter I.
41
plot and twelve sampling points within each triangle were defined.
Of
the six plots in each stand, three randomly selected plots were fertilized with prilled urea at the rate of 224 kg of elemental
nitrogen/hectare and the other three plots served as controls.
Following urea application, root samples were taken from each
plot in soil cores at 1.5-month intervals for the first two sampling
dates and at 2-month intervals for the following three sampling
dates.
An additional set of soil cores was taken on the three
coastal stands at eighteen months after urea treatment.
At each sampling date, two cylindrical cores 20 cm deep x 4 cm
diameter (251 cc) were collected at random from the twelve defined
points in each triangle (a total of six cores/plot) and subdivided
into three sections:
HOR-I representing 0-5 cm depth, HOR-Il repre-
senting 5-10 cm depth, and HOR-IlI representing 10-20 cm depth.
The sub cores were pooled by plot and transported to the labora-
tory in glass jars where they were divided for soil analysis and fine
root population determinations.
The fine roots (< 2 mm in diameter)
were extracted from the soil samples by the wet sieving technique of
Narks et al. (1968).
This technique consists of collecting the large
root fragments on a 0.047 mesh B.S.S.
from gravel bydecantation.
The large roots are separated
The fine roots which pass through are
collected in a pail of water, agitated, and poured over a 0.0197 mesh
sieve.
The fine roots extracted by the above method were stored in a
solution of formalin: acetic acid: alcohol (10:10:100 v/v) until
counted.
42
Characteristics of the fine root population were determined by
dispersing a sample of the previously stored roots in water in a
rimmed perspex divided into one hundred one inch squares.
fragment in ten random squares was disected.
Each root
The outer appearance,
condition of the cortical cell layer and the central stele were examined with a stereo-zoom binocular microscope and tallied as follows:
Active mycorrhizae.
Short, without root hairs, sausage like
appearance, non suberized succulent cortical cell layer and a
possibly visible mantle.
Stained thin sections to obser
the
presence of hartig net were spot-checked with a compound micro
scope to confirm validity of the observations.
Nycorrhizae were
further classified as to type according to gross characteristics
such as color, appearance, etc.
Active non-mycorrhizal roots.
suberized.
Primary cortex present and non-
Light colored, transluscent, with a red tipped
apical meristem.
Unlike Douglas-fir roots, no root hairs were
observed on non-mycorrhizal roots of western hemlock.
Inactive (alive but not growing) roots.
shriveled even when soaked in water.
collapsed and/or suberized.
functional parenchyma cells.
Roots dark colored and
Cortical cell layer
Central stele firm, white and with
Feulgen nuclear staining spot
checks confirmed presence of functional parenchyma cells in the
stele and nonfunctional parencyma cells in remenants of cortical
cells.
Dead-roots.
Easily fragmented roots without functional
parenchyma cells.
43
Live root classes were quantified by counting only segments with
For dead roots, however, each fragment was tallied,
intact root tips.
because the tips on these roots were usually destroyed during the
extraction process.
RESULTS
The data on hemlock roots were analyzed individually for the
three depths (HORI, HORtI, HORIll) and as a sum of the three
depths.
A simple ttest analysis was used to test for significant
differences between the two zones, and between ureatreated and
control plots at each sampling date for individual stands.
The
results reported in the tables, however, represent the combined means
of the first five sampling dates following urea treatment.
The mean
data were analyzed by randomized complete block design (Dates
Blocks).
Duncan's multiple range test was used to test for signifi-
cant differences between stands.
representing 1.5, 3,
5,
7,
For simplicity, the sampling dates
9, and 18month intervals following
urea application, are referred to as sampling dates 1,
6, respectively.
2,
3, 4,
5 and
Also, the 5 percent probability level (P < 0.05) to
test statistical significance of difference is used.
Total numbers and vertical distribution of primary roots.
Numbers of live primary (mycorrhizal + nonmycorrhizal
inactive)
roots varied significantly between the three soil depths (Table I)
and among the stands (Table IV).
Percentage of the total nutrient
absorbing (mycorrhizal + nonniycorrhizai) roots in HORI, HORII, and
NORIll, varied significantly among the stands but not among the two
44
geographic zones (Table V).
Except for Cascade'-1, the percentage of
total nutrient absorbing roots was highest in HOR-I and tended to
decrease with increase in soil depth.
The values in HOR-I ranged
from 76 percent of the total on Coast-8 to 13 percent of the total on
Cascade-i.
Composition of the primary roots.--The total numbers and the
relative populations of the four types of mycorrhizae and the nonmycorrhizal roots varied significantly between the three soil depths
(Table II) and among the soil stands (Table III).
Even though the
mean totals and relative populations of mycorrhiza types and nonmycorrhizal roots of coastal stands differed substantially from those
Cascade stands, yet, except for White-mycorrhizae, these differences
were not significant (Table III).
Impact of fertilization.--IJrea fertilization significantly
reduced the total numbers of mycorrhizae in all except the Cascade-1
stand (Table IV).
A significant reduction in the total number of
niycorrhizae was observed by the first sampling date and was evident up
to the fifth sampling date.
As compared with the initial four
sampling dates, however, the magnitude of difference between the
control and fertilized plots had diminished by the fifth sampling
date.
On the sixth sampling date, the numbers of total mycorrhizal
tips in plots fertilized with urea did not significantly differ from
those on control plots.
On the average during the nine month period
following treatment, urea application, resulted in 10-41 percent
reduction in total mycorrhizal tips (Table V).
Except for Cascade-i,
the percent reduction in mycorrhiza numbers following urea
45
application was greatest in HOR-I, and tended to decrease with
increase in soil depth (Table V). The average percent reduction on
urea treated plots during the first nine months following urea treat-
mentranged from 10-55 percent in HOR-I and from 0-5 percent in
HOR-tIt; Coast-B and Cascade-3 stands actually increased significantly
in total number of mycorrhizae in HOR-tIt.
Urea fertilization significantly increased total nonmycorrhizai
root tips (Table III).
On the average during the nine month interval
following urea treatment, the relative population of non-inycorrhizal
roots on urea treated plots was nearly double the relative population
of these roots on control plots, and remained substantIally higher up
to the sixth sampling date.
The relative populations of the four types of mycorrhizae
tallied in the hemlock stands were significantly altered by urea fertilization (Table III).
The magnitude and nature of this alteration
varied among the stands.
The increase or decrease in percentages of
mycorrhizal types observed during the first nine months after urea
application usually persisted up to the sixth sampling date on the
three coastal stands sampled.
The average numbers and the relative
populations of Ectendo-inycorrhizal tips on fertilized plots became
significantly higher than on the control plots of all except Cascade-i
stand.
The average numbers and relative populations of white-
niycorrhizal tips were significantly higher in the fertilized than in
the control plots of the three coastal stands and significantly lower
on Cascade-i and Cascade-2 stands.
The average numbers and the rela-
tive populations of Brown-mycorrhizai tips became significantly lower
46
in all except Cascade-i and Cascade-2 stands.
The average numbers of
Black-mycorrhizal (mostly formed with Cenococcum geophilum Fr.) tips
became significantly lower on all except Cascade-i and Cascade-3
stands.
The relative population of the Black-mycorrhizal tips,
however, was significantly altered only on Cascade-2 stand.
Urea fertilization also substantially increased the numbers of
dead-root fragments and the numbers of inactive root tips (Table IV).
The differences, however, were not always statistically significant.
The attrition ratio (number of inactive root tips/total number of
live primary root tips) became significantly higher for urea treated
plots than for control plots on all of the stands (Table IV).
DISCUSS ION
The importance of the favorable nature of mycorrhizae to the
higher plants is well documented.
Mycorrhizae benefit forest trees
by aiding in nutrient absorption, deterring root pathogens,
increasing host plant resistance to drought and extreme soil temperatures, and supplying trees with growth-regulating substances
(Hacskaylo 1979, Bowen and Theodorou 1976, Marks and Kozlowski 1973,
Mark and Bryan 1971, Zak 1971, Melin and Nillsori 1952).
For western
hemlock in particular,. the data in Table VI clearly demonstrate the
importance of mycorrhizae to the growth of western hemlock.
The
importance of mycorrhizae to western hemlock is further demonstrated
in that under field conditions more than 95 percent of the active
nutrient absorbing roots of hemlock are niycorrhizal (Table III, Table
IV).
Studies also show that certain species of mycorrhizal fungi are
47
more effective in stimulating growth of forest trees than others in
given circumstances (Marks and Kozlowski 1973; Theodorou and Bowen
1970, Hocskaylo and Vozzo 1967, Levisohn 1957, Young 1940).
Therefore, significant changes in total mycorrhizal numbers and in
relative populations of mycorrhizal types that followed urea application in this study can have a substantial impact on the nutrient sta-
tus and growth of western hemlock.
The decrease in number of mycorrhizal tips on urea treated
plots, although short lived, occurred during the period when nitrogen
supplied by the fertilizer1 and the nutrients released by litter
decomposition2 were most available.
This could explain the
ineffectiveness of urea fertilization for growth stimulation of
hemlock stands, especially on shallow rooted stands where the
reduction in number of mycorrhizal tips following urea treatment is
most dramatic.
Even though the reduction in total number of mycorrhizal tips
following urea application was short lived, the change in relative
populations of tnycorrhizal types seems to persist longer.
The impact
of urea fertilization on nutrient status and growth of western hemlock
can, therefore, be expected to last beyond the recovery from initial
reduction in total number of mycorrhizal tips.
Changes in soil chemical
1G111, R. S., and D. P. Lavender.
1981.
properties following urea application on western hemlock stands.
Thesis, Chapter I.
Impact of nitrogen fertili1981.
2Gjll, R. S., and D. P. Lavender.
zation on rates of litter decomposition on coastal hemlock stands.
Thesis, Chapter IV.
48
In previous studies, some researchers report a reduction (Menge
et al. 1977, Richards and Wilson 1963), while others report an
increase in numbers of mycorrhizae (Koberg 1966, Meyer 1965) after
nitrogen fertilization.
The results of this study demonstrate that
urea fertilization reduces the total numbers of certain types of
of mycorrhizae and increases the numbers of the other types.
Therefore, depending upon the predominant type or types of mycorrhizae and the nature of the impact of the form of fertilizer on these
types, the fertilizer can result in either decrease or increase in
the total number of uiycorrhizae.
In other words the nature of the
impact of fertilization on nutrient absorbing primary roots is a function of the mycorrhizal types and their relative
frequency.
Researchers who have reported a reduction in numbers of mycorrhizal tips following nitrogen fertilization have failed to report
whether this decrease was due to mortality of the existing mycorrhizal
roots or due to reduction in formation of new mycorrhizal tips.
In
this study, the observed increase in fine dead-root fragments, inactive root tips and the attrition-ratio, especially during the fIrst 6
months following urea application, demonstrates that fertilization
with urea at the rate of 246 kg N/hectare accelerates the rate of
mycorrhiza mortality.
Therefore, it appears that a substantial por-
tion of the decrease in mycorrhiza numbers following fertilization is
due to mortality of existing mycorrhizae.
The results of this study further demonstrate that the maximum
reduction in numbers of active mycorrhizae and the increase in numbers of dead and moribund tnycorrhizae occurs during the time (first 6
49
months following urea application) and at the soil depth (0-5 cm)
which changes most in soil chemical properties after urea treatment1.
Two important conclusions can be drawn.
First, stands with greater
percentages of active mycorrhizal roots in the litter layer (0-5 cm)
would be more adversely affected by fertilization than stands with a
relatively smaller percentage, provided that the frequency and the
types of mycorrhizae present are identical.
Second, forms of fer-
tilizers that produce less dramatic changes in soil chemIcal properties should have lesser impact on uiycorrhizal populations than those
that produce rapid and dramatic changes.
Therefore, in shallow rooted
stands and/or stands with a greater percentage of susceptible
mycorrhiza types, use of slow-release and/or pH balanced fertilizers,
and/or lower rates of fertilizer application would be more desirable
than high rates of readily soluble fertilizers such as urea.
The niycorrhizal types in this study were tallied according to
gross color and form.
Most likely, mycorrhizae of different fungal
species were tallied in the same catagories.
Increase in number of
"white" mycorrhizal tips on coastal stands and decrease on Cascade
stands following urea treatment suggests that, even though classified
as "white', different fungi were involved in the two locations.
The
response variability by hemlock to urea fertilization may be due to
differences between stands in the distribution of mycorrhizal types
Changes in soil chemical pro1Gill, R. S. and D. P. Lavender, 1981.
perties following urea application on western hemlock stands.
Thesis, Chapter 1.
50
and the relative sensitivity of the associated fungi to urea-induced
changes in soil chemical properties.
CONCLIJS ION
Urea fertilization of hemlock stands significantly reduced total
numbers of mycorrhizae and significantly changed relative populations
of the mycorrhizal types present.
The magnitude of these changes
varied among the hemlock stands and is most likely a function of the
vertical distribution of the mycorrhizae and their composition (types
of mycorrhizae and their relative populations).
Because the vertical
distribution of tnycorrhizae and their composition varied significantly
among the hemlock stands, the variation in growth response to nitrogen
fertilization among western hemlock stands could well be due to differences in hemlock's primary roots.
TABLE 1.
V%1T1CAL IMSTKIRUTION ANt) T1tI
UiIACT OF tlI(I1A FERTILLZATION ON IIELILOCK'S PRIMARY ROOTSt
(NLNfllOi OF TIPS/lot) CC).
Sot I depth
Stand
Coast-I
Coast-i
Coast-B
Cascade-i
cm
0-5
5-10
10-20
Cascade-3
I
11
III
C
F
318a
170b
94c
363
728a
5891*
1,1691'
3,470
3,663
1,303
142
124
4981'
271c
435
265
2,444a
1,153b
2,614
1,473
290a
403**
971'
j37*
361c
415
23c
35
806a
252b
82c
5,0405*
2,082
533a
INOh
75c
632*
1,541a
229a
193
3,232a
3,294a
0-5
5-10
10-20
I
4,0I2a
11
2,2591'
437c
0-S
I
0-S
111
111
11
Itt
I
5-10
10-20
II
0-5
5-10
I
10-20
544
t,lSOc
1,141
3,195
1,337
4,929a
2,702b
S,612**
3,235*
906a
3,7321'
549c
480
II
2,584a
2,921a
111
1,0551'
3,604
4,2S2
1,047
111
Total
Total
mycorrhlzae
F
1
II
Total i,,arttve
C
F
110K
0-5
5-10
10-20
5-10
10-20
Cas:ade-2
Total dead2
193
76
323b
74c
89a
250b
51'
7
25
31*
557**
Va
30
26
202*
26*
27
41**
38**
76
16b
6c
9
22
31*
6545*
37a
53
191'
21
6c
6
25
35
51
48
318
84
78
5a
101'
69
48
68
18*
6
55
62
59
41a
116*5
221'
124
tIc
24
13
42
48
41
61
54
40
2,079*5
46a
73*
655*
355*
53
67
57
63**
244
' li/ic
1,183a
2,03O
1,6lLa
l,102**
334b
102c
312
330b
130c
400c
423
736b
271c
234*
5355*
267
60**
14a
13a
6
4a
211'
191'
tValtiea are averages of the nIne mouth sami)1 tog period followIng fert ilizat ton.
N
15.
2Nu,nber of frageeuits/ 100 cc -
Values within each st/intl which are fol lowed by the same totter .leatguatioii are not st/it Istitat ty
algol leant.
Stg LI leant dli ference from control at P '- 0.05.
55stgntfteart dIfference from i-not to) at P - 0.01.
C
coot rot
F - fertIlized
F
37*
193a
2,875a
ratIo
C
31
24
189
166
3,682*
1,729
Attiratton
21
349*5
3,267a
1,498h
F
C
2)6a
94
non-mycorrhtzac
24
37
47
74*5
5)
TABLE It.
VERTiCAL Dt8'I'RIIWTIOU ANI) TUE EFFECT OF UREA FERTIlIZATION ON UEMI.00K'S FRI}IARY
ROOTS1 (NIIUBER OF TIPS/lOG CC).
Non-
Sot I dc1tli
Stand
cm
Coant-(
0-5
5-10
10-20
Const-7
0-5
5-10
10-20
Coast-8
5-0
5-10
10-20
Cascade-I
0-5
5-10
10-21)
Caacade-2
0-5
5-10
10-21)
Cascade-3
0-5
5-10
10-20
lION
aycorchlzae
C
F
Black
mycorrhtzoe
aycorrhizae
C
F
C
Brown
F
20**
158a
12Th
126
78**
439a
21
111
14a
13a
6b
7
5/c
42**
124c
1
2/a
lôh
30
25*
280a
170**
58**
415a
105b
Ac
9
24c
1
3/a
19b
53
21
415a
11
Ac
6
25c
So
6
18
6
1 to
Ii
Ito
12
9
1
ft
11
111
III
1
II
111
1
II
[II
1
IL
III
lOb
4a
41a
22b
tIc
46a
211,
191,
9/b
IO3Ii
8a
116**
75a
24
13
177b
49c
73*
5**
355*
2,133a
28/b
86c
[5*
183**
97**
34
3001,
39c
1,063a
175b
37c
51**
62**
18*
84a
27b
145**
196**
23a
45**
21b
6c
25
10*
312**
41a
158
33
32i
9c
78**
43
10
0
113
36**
Ga
Oa
Oa
0
0
239**
46a
81
38
454a
72b
37c
556*
49*
35
353a
80b
I,641**
5/la
256**
62**
21*5
1/la
112c:
17o
14a
6b
154**
109**
158**
84**
37*
217b
122
Oa
127c
87
49
39c
221b
hr
tValueo ore averages of the nine month sampling er1od lot lowing Ireotineur.
127**
186
19
N
12c
37
12
21a
81**
14h
ic
21
5S I go If tc
cit
dii fe reicie I torn coot co I at
**Slgnf I Leant dl fferi'nce from rent ml at
C
control
F
fettIiIi.ed
(1.05.
I'
I'
0.01.
8*
0
148**
Oh
0
3b
3
13a
[Ia
9a
15.
Vol ne a wi thin eoch stand loll owed by the same letter ,Ie of gna I I on ace no to lit I or I call y
signiftcnt.
F
113a
62b
82c
39c
161
C
288**
138**
96**
148b
214
F
C
68
64*
120**
ii3
91b
Ectendomycorrhtzae
White
mycorrhtaae
54**
13
8
TABLE [LI.
TOTAL NUMBERS AND IMPACT OF UREA FERTILIZATION ON HEMLOCK'S PRIMARY ROOTSL
(NUMBER OF TIPS/CORE (251 cc)).
Nonmycorrhizae
Stand
C
F
Black
mycorchizac
C
F
50**
250a
5*
22
Coast-I
Percent of total2
25a
Coaet-7
Petcent of total2
35b
Coast-8
Percent of total2
45b
3
6
Cascade-i
Percent of total2
iSa
25*
6*
Cascade-2
Percent of total2
55c
Cascade-3
Percent of total2
60c
Average Coast
Average percent of total
35a
50
6
290a
3
Average Cascade
Average percent of total
40a
85
2
4
3
4
3
3
Brown
mycorrhlzae
C
F
White
mycorrliizae
C
F
180**
18**
620a
390**
38**
210a
55
19
Ectendoycorrhizae
F
C
310**
30**
30a
6O**
9**
90b
90**
11*
25a
2
95**
9**
45
7**
270a
160**
27**
380b
47
220**
36**
4Db
33
55
360a
220**
28
830c
63
340**
46**
6Db
27
25b
25
155d
235**
58**
255a
120*
Dc
1
51
29
0
0
35d
1OO
9**
100**
9**
125**
6**
7
5
4
lj.
2
130*
21**
75**
9**
6
38
650c
44
200**
18**
380b
425
39**
320c
22
270**
27
l,500d
1,400
68**
570a
23
185**
1O**
295c
13
260
190*
23
610a
320
lOOa
150
19
45a
27
4
99
12
720a
530
220
19
50
67
3lOa
26
20a
50
7
61
56
39
280
25
9
290b
20
25
13
2
20a
1
1
45**
2**
4
for individual stands are averages of the nine month samnpl ing period following
fertilization. N - 15.
1Va1ue
2Percentage of total rnycorrhlzai + non-inycorrhizal root tips.
Values in the same vertical column which are followed by the same letter designation are not statistically significant.
*Slgnif[cant dtffereocea from control at P - 0.05.
**Signtftcmnt differences from control at P - 0.01.
C - control
F
fertilized
TABLE IV.
TOTAL NUMBERS AND IMPACT OF UREA FERTILIZATION ON HEMLOCK'S FRIMARY ROOTSt (NUMBER OF TIPS/CORE
(251 CC)).
Stand3
C
F
Total
mycorrhlzae
Total
inactive
Total dead2
C
F
C
F
Total
absorbers3
C
F
Total 1ive
C
F
Attrition
ratio5
C
F
I,IOOa
950**
1,lOOa
770c
570**
600
1,300ab
720**
530a
650
4304
380
450c
400
l,000b
1,000
55
62**
6 200**
i3O00c
1,600
1,400b
i3O00
1,400a
i,1O0
2,500c
2,700
43
58**
4,200c
5,700**
3,000d
3,710*
2,400e
1,900*
2,400d
2,000*
5,600c
5,700 .56
.64**
Average Coast
4,300a
4,800
420a
490
i,lOOa
760
1,lOOa
800
1,400a
1,300 .27a .38*
Average Cascade
4,700a
5,400
l,600a
2,000
l,400a
1,100
I,400a
1,100
3,000a
3,100 .5lb .64*
Coast-i
5,600a
6,100*
430a
470
Coast -7
2,70Db
3,000**
27Db
380**
Coast-8
4,SOOc
5,50O
45Oa
Cascade-i
4,400c
4,400
Caacade-2
5,SOOa
Caacade-3
l,600a
1,500 .27
.32**
800b
620** 1,00Db
1,000 .25
.38**
i,300a
770** 1,900a
1,400 .29
45**
l,O0O
tValues for individual stands are averages of the, nine month sampling period following fertilization.
N - 15.
2Number of fragments.
3Mycorrhlzal + non-mycorthizal root tips.
"Total absorbers + Inactive root tips.
5lnactive I total live.
Valuer, in the same vertical column which are followed by the ease letter designation are not statistically
significant.
*Slgniftcant difference from control at P
**Signiftcant difference from control at P
C
control
F
fertilized
0.05,
0.1)1.
TABLE V .
VERTICAL DISTRIBUT[UU MD 01E IMPACT OF UREA FEwr1LizATtOr
Coast-i
Percent Percent
Soil depth Distri- Reduccm
fOR bution
tion
Coast-7
Percent Percent
Distributton
Reduc-
tiori
Coast-8
Percent Percent
Dtstributton
Reduc-
tiori
ON IIEtILOCK'S tIYCORRIIIZAL ROOTS.
Cascade-i
Cascade-2
Percent Percent Percent Percent
Distributton
Reduc-
tion
Distributlon
Redue-
tion
Cascade-3
Percent Percent
Distribution
Reduc-
tion
0-5
1
41
15
65
29
76
55
13
10
72
27
75
26
5-10
Ii
28
11
21
(5
16
1
36
20
15
26
20
21
10-20
III
31
1
14
5
8
0
50
4
12
2
15
(+13)
0-20
(Total core)
10
23
41
Percent distribution - ( Total mycorrhlzal tips in the soil core ) x ioo1
Hycorrhizal tips in each fOR
Percent reduction - Mycorrhizal tips in fertilized fOR ) - 1 x 1O0
Uycorrhizai tipu In control fOR
Average value for the nine month sampling period following urea application.
0
( +2)
11
23
23
TABLE VI:
RELATIVE GROWTH OF MYCORRHIZAL AND NONMYCORRHIZAL HEMLOCK
SEEDLINGS GROWN FROM A CASCADE AND A COASTAL SEED SOURCE
(VALUES ARE AVERAGE OF 4 SEEDLING/POT; 12 REPLICATIONS).1
Cascade Seed Source
Coast Seed Source
Mycorrhizal NonMycorrhizal Mycorrhizal NonMycorrhizal
Root status
Root length
43.00
65.00
17.00**
57.00
5.50
0.O1**
4.00
0.08**
51.50
3.70**
47.00
6.50**
3.70
O.02**
3.70
0.08**
1.10
2.00*
0.90
1.00*
(cm)
Root dry weight
(gui)
Shoot length
(cm)
Shoot dry weight
(gui)
Shoot/root
1Seedlings were grown for 18 months in a growth chamber set at 16 hour
Nonmycorrhizal seedlings
photoperiod arid 12-18°C daily thermoperiod.
were grown in a steam steril±zed forest soil. The pots were irrigated
by automatic drip irrigation to avoid contamination of nonmycorrhizal
seedlings through splashing.
Statistically significant difference (P K 0.05) from the nonmycorrhizal seedlings grown from coastal seed source.
*P < 0.05; **
< 0.01.
57
BIBLIOGRAPHY
Biennual Report 1974-6, Regional Forest Nutrition
Anonymous.
1977.
Institute of Forest Products, College of
Research Project.
University
of Washington Contribution No. 25.
Forest Resources.
The ecological significance of the ectotrophic
1949.
Svensk. Bot. Tidskr.
mycorrhizal association in forest trees.
43:223-262.
Bjrkman, B.
studies on phosphate uptake
Bowen, G. D., and C. Theodorou. 1967.
by mycorrhizas. Proc. I.U.F.R.O. 14th Congress, Munich.
5:116-138.
Effects of nitrogen fertilization
1969.
Brix, H., and L. F. Ebell.
on growth, leaf area, and photosynthesis rate in Douglas-fir.
Forest Sci. 15:189-196.
1975.
DeBell, D. S., B. H. Mallonee, J. Y. Lin, and R. F. Strand.
Fertilization of Western Hemlock: A Summary ofExistlng
Crown Zellerbach Corporation Central Research
Knowledge.
Department Forestry Research Note. No. 5.
-
Inoculation of Pnus caribea
Hacskaylo, B., and J. A. Vozzo. 1967.
with pure cultures of mycorrhizal fungi in Puerto Rico. Proc.
I.U.F.R.O. 14th Congress. Munich. 5:139-148.
Mycorrhiza: the ultimate in reciprocal
Hacskaylo, B.
1972.
parasitism? Bioscience 22(10) :577-583.
Dtingung und Mykorrhiza. Em
Koberg, H.
1966.
Kiefern. Forstwiss Centralbi 85:371-379.
Gefàssversuch mit
1957. Differential effects of root infecting mycelia
Levisohu, I.
on young trees in different environments. Emp. For. Rev.
36: 281-286.
Ectomycorrhiza. Their
1973.
Marks, C. C., and T. T. Kozlowski.
ecology and physiology. Academic Press, New York and London.
Marks, G. C., N. Ditchburne, R. C. Foster. 1968. Quantitative
estimates of mycorrhiza populations in radiata pine forests.
Australian Forestry 32:26-38.
Influence of ectomycorrhizae on
Marx, D. H., and W. C. Bryan. 1971.
surivival and growth of aseptic seedlings of loblolly pine at
high temperatures. For. Sci. 17:37-41.
58
Transport of labelled nitrogen
1952.
Melin, E., and H. Nilsson.
from an ammonium source to pine seedlings through mycorrhizal
Svenska Botanisk Tidsksjft 49:282-285.
raycelium.
The effect of
1977.
Menge, J. A., L. F. Grand, and L. W. Maines.
numbers
in
11-year-old
fertilization on growth and niycorrhizae
For.
Sci.
23(l):3744.
loblolly pine plantations.
Die Mycorrhiza der Waldbume.
1965.
Meyer, F. H.
Dendrol. Ges. 62:54-58.
Mitt. Deut.
Nutrient supply and
1963.
Richards, B. N., and G. L. Wilson.
For. Sci. 16:172-176.
pine.
mycqrrhiza development in Caribbean
Soil factors influencing formation of rnycorrhizae.
1974.
Slankis, V.
Ann. Rev. Phytopathol 12:437-457.
Theodorou, C., and G. D. Bowen. 1970. Mycorrhizal responses of
radiata pine in experiments with different fungi. Australian
Forestry 34:183-191.
1976.
Webster, S. R., D. S. DeBell, K. N. Wiley, and W. A. Atkinson.
Management
Hemlock
In
Western
Fertilization of western hemlock.
Univ.
Conf. Proc. W. A. Atkinson and R. J. Zasarki (eds.).
Wash., Seattle. p. 247-252.
Wells, C. G. 1970. Nitrogen and potassium fertilization of loblolly
pine on a South Carolina Piedmont soil. For. Sci. 16:172176.
Windsor, C. L., and M. Reines.
pine after fertilization.
Diameter growth in loblolly
J. For. 71:659661.
1973.
Mycorrhizae and growth of Pinus and Araucaria.
1940.
Young, H. E.
J. Aust. Inst. Agric. Sci. 6:21-31.
Detoxification of autoclaved soil by a mycorrhizal
1971.
Zak, B.
U.S. Forest Service Pacific Northwest Forest and Range
fungus.
14 p.
Experiment Station Research Note No. 159.
59
CHAPTER III.
UREA FERTILIZATION AND FOLIAR NUTRIENT COMPOSITION
OF WESTERN HEMLOCK ETSUGA HETEROPHYLLA (RAF.) SARG.]
INTRODUCTION
Forest stands with western hemlock [Tsuga heterophylla (Raf.)
Sarg.] as the primary species cover nearly ten million acres of highly
productive land along the Pacific Coast of the United States.
Attempts to stimulate growth of these stands by nutrient amendments
have met with limited success (Anonymous 1977, Webster et al. 1976,
DeBell et al. 1975).
Growth responses of young growth hemlock stands
to application of nitrogenous fertilizers mainly in the form of
prilled urea have been extremely erratic, ranging from growth
depression (down to -20 percent) to growth acceleration (up to 50
percent).
In general, hemlock stands in the coastal zone have either
failed to respond or have shown negative response to nitrogenous fertilizer.
In order to determine the cause of response variability to urea
application and to develop guidelines for efficient fertilization of
hemlock stands, studies of fundamental aspects of impact of fertilizer
application upon hemlock's nutrition and growth are needed.
The following study relates the foliar mineral-nutrient composition of hemlock trees to urea application in coastal and Cascade
hemlock stands.
Urea was selected because it is most commonly used
for forest fertilization in the Pacific Northwest.
60
MATERIALS AND METHODS
Stand Selection
A total of six natural stands of young growth western hemlock
were selected for investigation.
Three of the selected stands
(Coast-i, Coast-7, Coast-8) are located in the coastal hemlock zone
near Seaside, Oregon.
The other three stands (Cascade-1, Cascade-2,
Cascade-3) are situated in the Cascade Range near Vail, Washington.
The selected sites consist of almost pure western hemlock
C> 90 per-
cent hemlock) that except for few experimental plots, had never been
fertilized or thinned.
Within each stand six cIrcular plots, each
measuring 0.0203 hectare (1/20 acre) were established.
Out of these
six, three randomly selected plots were fertilized with prilled area
at the rate of 224 kg of elemental nitrogen/hectare in the early
winter of 1977.
Details of edaphic and biotic characteristics of the
selected stands, plot selection and treatment application are
explained elsewhere.
SAMPL INC
In October, eleven months after urea application foliage was
sampled and analyzed for six dominant or codominant trees with no
noticeable cone crop in each plot (a total of 18
trees/treatment/stand).
Five to six vigorous branches from all sides
Changes in soil chemical
1Gill, R. S., and D. P. Lavender.
1981.
properties following urea application on western hemlock stands.
Thesis, Chapter I.
61
of the top four whorls of each tree were clipped, transported to the
laboratory, and stored in a cooler at 5°C.
In the laboratory, the
foliage was divided into current year's mature (fully developed
needles), current year's immature (terminal needles not fully
developed), and old (2-3 year old) classes.
Subsamples from each
category were dried at 70°C to a constant weight.
After drying,
needles were separated from stems and ground through a 40-mesh size
screen for chemical analysis.
Total N in the ground samples was determined by the standard
microkjeldahl procedure (Bremner 1965).
Analyses for the minerals Ca,
Mg, K, P, Al, Fe, Mn, Cu, Zn, B were performed by direct reading spark
emission spectroscopy (Chaplin et al. 1974).
STATISTICAL ANALYSIS
Data were subjected to analysis of variance with randomized
complete block design to test for significant differences in foliar
nutrient content for:
coast vs. Cascade stands, control vs. urea-
treated trees on the coast and in the Cascades, and current vs. irnina-
ture vs. old foliage of control trees in each zone.
Also, for indivi-
dual stands, a simple t-test analysis was used to test for significant
differences in follar nutrient values in each type of foliage between
control and urea-treated trees.
RES IJLTS
The results of foliar macroelements (N, F, K, Ca, Mg) and
microelements (Fe, Mn, Cu, Zn, and B) are given in Table I and
62
Table II, respectively.
The tabulated results for each element
represent:
Comparison of zonal average value of the element in old and
immature foliage of control trees with that in current
foliage.
Comparison of average value of the element, by foliage type,
of control trees in the Cascades with the control trees on
the coast.
Comparison of average value of the element, by zone and
foliage type, of control trees with that of ureatreated
trees.
Comparison Between Foliage Types
Concentrations of F, K, Ca, Mg, Al, Fe, Mn, Zn, and B in the
current foliage of western hemlock differed significantly from old or
immature, or old and immature foliage.
Comparison Between Zones
The foliar concentrations of N, P, K, Ca, Mg, Al, Mn, Fe, Cu, Zn,
and B varied significantly by stand and by zone.
The concentration of
these elements was significantly higher in the Cascades than on the
coastal stands.
Comparison Between Treatments
For each stand and zone, the N level in each type of foliage of
fertilized trees was significantly higher than in the corresponding
63
type of foliage of control trees.
The differences ranged from 58 per-
cent in current foliage on Coast-i to 10 percent for immature foliage
on Cascade-i stand.
As compared with control, the foliage (immature,
current, and old) on urea-treated plots had gained an average of 0.524
mg of N per gram of foliage on the coastal stands arid an average of
0.430 mg/g of foliage on the Cascade stands.
The average zonal con-
centrations of P, Ca, Mg, Mn, Fe, and B in immature, current, and old
foliage of fertilized trees were significantly lower than those in one
or more classes of corresponding foliage of control trees.
The magni-
tude of difference between control and fertilized values varied by
element, foliage type, stand, and zone.
DISCUSSION AND IMPLICATIONS
The results of this study demonstrate that with the exception of
N and Cu, the concentration of essential macroelements and microelements varies significantly between immature, current, and old foliage
of western hemlock.
Determination of the nutrient status of hemlock
trees either from only one type of foliage, or from acomposite sample
in which the various foliage classes are not represented in proportionate amounts, would, therefore, lead to incorrect estimation.
Also
by separating the foliage into immature, current, and old classes, we
increased the sensitivity of the experiment for detecting the impact
of urea fertilization on hemlock's nutrient status because nutrient
concentration differences between control and fertilized trees did not
always show up in each type of foliage.
For example, differences
64
between control and fertilized trees for foliar P levels would have
gone undetected if only the current foliage was sampled.
The markedly lower concentration of the essential nutrients in
the coastal stands than on the Cascade suggests that more than one of
these elements may be growth limiting in the coastal hemlock stands.
An effort to stimulate growth of these stands by nutrient amendments
might, therefore, require fertilization with elements such as F, K,
Fe, and B in conjunction with nitrogen.
Application of urea to the hemlock stands resulted in an increase
in the foliar concentration of nitrogen in all stands.
This
demonstrates that nitrogen applied as urea to the forest floor is
available for uptake to hemlock and does improve the nitrogen status
of the trees.
If N were the only limiting nutrient and the applica-
tion of urea did not adversely alter the availability of other
nutrients, then application of urea should indeed stimulate the growth
of hemlock trees.
Comparison of foliage nutrient content of control
trees with that of fertilized trees, however, demonstrates that application of urea results in significant decreases in foliar levels of F,
Ca, Mg, Mn, Fe, Al, and B.
Further, except for Ca, this decrease in
nutrient concentration is more consistent and of greater magnitude in
coastal than on Cascade stands.
The general failure of the coastal
stands to respond favorably to nitrogen fertilization, therefore,
might well relate to further reduction in already low foliar levels of
these elements following urea application.
This reduction in foliar
concentration of the essential nutrients, if it is due to reduced
uptake, rather than purely because of dilution as suggested by Radwan
65
and DeBell (1980), might account for negative growth response of
hemlock stands to urea fertilization.
The following observations suggest that reduction in foliar concentrations of P, Ca, Mg, Mn, Fe, B, and Al following urea application
i
most likely due to reduced uptake than purely a dilution effect.
First, the specific weight (needle wt/surface area) of immature,
current, and old needles of the fertilized trees did not differ significantly from the specific weights of corresponding types of foliage
of the control trees.
Second, the canopy size, as determined from
sapwood basal area measurements (Grier and Waring l97) of the fertilized trees did not differ significantly from that of the control
trees.
Third, the most reduction in foliar nutrient concentration
occurred on coastal stands that had shown the least response (growth)
to urea fertilization.
For example, the most decrease in F, Mn, Fe,
and B foliar levels following urea application occurred- on Coast-8,
the stand which had shown a negative growth response to an earlier
urea fertilization trail (DeBell et al. 1975).
And finally, in a
separate study, we demonstrated that short term uptake of P32 from the
soil by hemlock seedlings that had been prefertilized with urea was
significantly less than that by nonfertilized seedlings (Gill and
Lavender 1980).
Some dilution effect, however, cannot be totally ruled out on the
basis of the above observations, because the correlation of increase
in canopy size with the corresponding increase in sapwood basal area
in a one-year span is not known.
Our use of sapwood basal area to
measure an increase in canopy size, therefore, might not be adequate.
66
The decrease in nutrient uptake by hemlock trees is most likely
due to changes in soil pH and soil nutrient concentrations1, and
number and types of tnycorrhizae2 resulting from urea application.
Whatever the cause of alteration in nutrient levels, nutrient
balance rather than the absolute amount of any single element is critical for optimum growth of trees (Itngestad 1979, 1977, Lavender
1970), and a low but balanced level of nutrient supply is more efficient for plant growth than fluctuating and unbalanced levels in
nutrient availability such as that which result from urea fertilization.
The results of Table III show that, relatively, Cascade-i had the
most balanced foliar mineral nutrient composition.
Consequently it
was the only stand to respond favorably to urea fertilization (Table
IV).
The nutrient imbalance in hemlock foliage (Table III) that
resulted from urea fertilization on the remainder of the stands,
therefore, could account for their poor growth response to urea fertilization (Table IV).
Changes in soil properties
1981.
following urea application on western hemlock stands. Thesis,
Chapter 1.
1Gill, R. S.,. and D. P. Lavender.
Urea fertilization and the
S., and D. P. Lavender.
1981.
primary-root system of young-growth western hemlock ETsuga
heterophylla (Raf.) Sarg.].
Thesis, Chapter II.
R..
67
CONCLUSIOM
Several conclusions related to foliar nutrient status of western
hemlock in general and the impact of urea fertilization on this
nutrient status in particular result from this study.
First is the
need to sample, at least, the immature, current, and old foliage in
order to estimate hemlock's nutrient status.
Second, application of
nitrogen in the form of prilled urea, to the forest floor is available
for uptake to hemlock and does indeed improve the nitrogen status of
this tree.
Third, the general failure of coastal stands to respond
favorably to nitrogen fertilizers is likely due to significantly lower
concentrations of essential nutrients (in addition to nitrogen) in the
coastal stands than on the Cascade hemlock stands.
This indicates, a
need to fertilize with nutrients such as P, K, Fe, and B in addition
to nitrogen to stimulate growth of coastal hemlock stands.
Fourth,
application of urea results in significant decrease iii foliar levels
of P, Ca, Mg, Mn, Fe, and B, possibly because of reduced uptake of
these elements.
The negative growth response of certain hemlock
stands to urea fertilization, therefore, is most likely due to further
reduction in already low foliar levels of these essential elements.
TABLE I.
HACROELEtIENT ANt) Al CONCENTRATION IN FOLIAGE OF WESTERN IIEULOCK.
N
1
Zone
0
C
I
0
P
K
Ca
Mg
Al
1
1
2
2
2
0
C
C
C
I
0
Coast
(control)
1.34
1.33
1.25
0.13
0.12
0.16)'
058
Cascade
(control)
1.44
1.53
1.55
015X 0.19
0.22)'
0.69"
7. Diff. - C
7.
DiEt. - F
C
1
0
C
1
0.69
0.72
0.21"
0.14
0.13
0.08
0.08
o.12'
0.12" 0.09
0.09
0.92
0.90
0.28"
0.19
0.22
0.09
0.09
0.15Y
0.14
0.13
U.S.
U.S.
26**
17*
38**
45**
U.S.
N.S.
11*
28**
4l**
8*
l5*
24**
15**
58
38**
19**
33**
25**
33**
36**
69**
U.S.
U.S.
16*
51**
51**
37**
12**
28**
16**
47**
3Q**
54**
37**
0L2
Coast
(fertilized)
1.80
1.98
1.71
0.10
0.12
0.14
0.57
0.72
0.80
0.18
0.11
0.11
0.06
0.06
0.10
0.11
0.08
0.08
Cascade
1.84
2.10
1.98
0.15
0.17
0.19
0.64
0.92
0.92
0.27
0.15
0.18
0.08
0.06
-
0.13
0.10
0.11
(fertilized) -
0.12
Statistically significant different (P < 0.05) between current and old foliage values
Statistically significant difference (P < 0.05) between current and immature foliage values
Statistically significant difference (P ( 0.05; P < 0.01) between control and fertilized trees of each zone
7. DUE.- C: Percentage by which the Cascade value differs from the coastal value; *; P ( 0.05; **: P < 0.01
7. DiEt.- F: Percentage by which the Cascade value differs from the coastal value on fart LI led plots.
0: Old; C Current; 1: Immature
0'
CO
TABLE IL.
MICROELENENT CONCENTRATION IN FOLIAGE OF WESTERN IIEHLOCK.
Mn
Zn
Cu
Fe
a
ppm
0
Zone
C
I
0
C
I
0
C
1
0
C
I
0
Coast
(control)
764x
617
757y
86x
71
80y
3.0
3.3
3.7
15x
7
lOy
29
22
32
Cascade
(control)
1085x
885
1213y
114x
105
l25y
5.3
5.0
5.1
24x
13
l.7y
25
22
37
1 Diff. - C
42*
43*
60*
33**
43**
56**
77**
51**
35**
6O*
86**
7O
N.S. N.S.
16**
1 01ff. - F
98**
70**
75**
34**
48**
58**
91**
54**
39**
54**
59**
44**
N.S. N.S.
17**
586
78
62
69
2.5
3.2
4.0
15
9
12
23
20
-
1053
105
93
109
4.7
4.9
5.1
23
15
18
25
23
34
550
Coast
(fertilized) Cascade
(fertilized)
1087
434
736
-
29
X: Statistically significant difference (P < 0,05) between current and old foliage
y: Statistically significant difference (P < 0.05) betw'en current and immature foliage
__: Statistically significant difference (P < O.Q5; P < 0.01) between control and fertilized trees of each zone
1 Dlii. - C: Percentage by which the Caacade value differs from the coastal value; A: P (0.05; **; P < 0.01
1 Diii. - F: Percentage by which the Cascade value differs from the coastal value on fertilized plots.
70
TABLE III.
NUTRIENT BALANCE OF ELEMENTS IN HEMLOCK FOLIAGE AFTER
UREA FERTILIZATION.
N
P
K
CA
Mg
Mn
Cu
%2
72
72
72
72
Fe
72
Zn
%1
72
72
Ingestad3
100
16
70
8
5
0.4
0.7
0.03
0.03
0.2
Coast-1
100
8
36
8
4
3
0.4
0.06
0.02
0.13
Coast-7
100
6
36
6
4
3
0.3
0.06
0.02
0.12
Coast-8
100
5
43
9
5
3
0.4
0.09
0.02
0.14
Cascade-1'
100
10
52
II
5
5
0.6
0.12
0.04
0.18
Cascade-2'
100
8
41
11
6
5
0.6
0.09
0.03
0.13
Cascade-3
100
8
35
9
5
5
0.4
0.08
0.02
0.12
Source
B
1Based on ovendry weight of composite foliage.
2Based on relative weight of nitrogen in the foliage.
3Optimurn concentration of nutrients in foliage of hemlock seedlings
(Ingestad 1979).
Composite foliage of fertilized trees.
71
TABLE IV.
TWO YEAR BASAL AREA GROWTH RESPONSE OF HEMLOCK TO UREA
FERTILIZATION1.
Growth Response
Stand
Coast-i
N.S.
Coast-7
N.S.
Coast-B
N S.
Cascade-i
±24*
Cascade-2
N.S.
Cascade-3
N.S.
1Percentage of growth above or below the predicted value based on
4 bi-yeariy growth increments prior to fertilization.
N.S.:
*:
Mon significant difference.
Significant difference at P = 0.05.
72
BIBLIOGRAPHY
Anonymous.
1977.
Biannual Report 1974-1976, Regional forest
nutrition research project. Institute of Forest Products,
College of Forest Resources, University of Washington.
Contribution No. 25. Seattle.
67 p.
Bremner, J. N.
1965.
Total nitrogen.
In Methods of Soil Analysis.
Chemical and Microbiological Properties. Monograph No. 9. LAm.
Soc. Agron. Madison, Wis.
pp. 1149-1178.
Chaplin, N. H., and A. R. Dixon.
1974.
A method for analysis of
plant tissue by direct reading spark emission spectroscopy.
Applied Spectroscopy 28:5-8.
DeBell, D. S., E. H. Malbnee, J. Y. Lin, and R. F. Strand. 1975.
Fertilization of western hemlock: a summary of existing
knowledge.
Crown Zellerbach Corp. Central Research Department,
Forestry Research Note No. 5.
15 p.
Grier, C. C., and R. H. Waring.
to sapwood area.
For.
Sd.
Conifer foliage mass related
20:205-206.
1974.
Gill, R. S., and D. P. Lavender. 1980. Nitrogen fertilization and
the ability of western hemlock roots to absorb and translocate
labeled (p32) phosphorus.
Abstract, Northwest Science, 53rd
Annual Symposium.
Ingestad, T.
1979.
Mineral nutrient requirements of Pinus
sylvesteris and Picea abies seedlings.
Physiol. Plant. 45:373380.
Ingestad, T.
1977.
Nitrogen and plant growth: maximum efficiency
of nitrogen fertilizers.
Ambio 6(2-3):146-151.
Lavender, D. p.
1970.
Foliar analysis and how it is used. Research
Note 52, School of Forestry, Forest Research Laboratory, Oregon
State University, CorvallIs. 8 p.
Radwan, N. A., and D. S. DeBell.
1980.
Effects of different sources
of fertilizer nitrogen on growth and nutrition of western hemlock
seedlings.
U.S. Forest Service, Pacific Northwest Forest and
Range Experiment Station, Research Paper PNW-267.
Webster, S. R., D. S. DeBell, K. N. Wiley, and W. A. Atkinson. 1976.
Fertilization of western hemlock. In Western Hemlock Management
Conf. Proc., W. A. Atkinson and R. J. Zaroski (eds.).
Univ.
Wash., Seattle. pp. 247-252.
73
CHAPTER IV.
IMPACT OF NITROGEN FERTILIZERS ON RATES OF
LITTER DECOMPOSITION IN COASTAL HEMLOCK STANDS
INTRODUCTION
In forest ecosystems a vital set of energy flows and nutrient
transfers result from litterfall and the subsequent biodegradation of
litter brought about by the interaction of microorganisms and soil
animals (Cromack 1973, Witkamp 1971, Crossley 1970).
These micro-
organisms and soil animals are strongly influenced by factors such as
soil-litter pH, temperature, moisture, and substrate makeup (Edmonds
1979, Fogel and Cromack 1977, Sagara 1975, Witkamp 1956).
Without
perturbations or unfavorable environment, nutrients cycle in a relatively orderly fashion with uptake by root systems; nutrient accumulation in stand components; return of organic matter and nutrients to
the forest floor by litterfall, root sloughing and mortality, foliar
leaching, and stem flow; release and transfer of nutrients from organic matter by biodegradation; and then re-uptake, supplying a major
portion of the stand's nutrient requirement.
Management-caused per-
turbations such as stand harvest, thinning, and fertilization can,
however, alter the existing rates of nutrient cycling in the forest
stands (Kelley and Henderson 1978, Miller et al. 1976, Wells et al.
1974, Gessel et al. 1963).
In the face of increasing demand for timber, fiber and biomass,
use of fertilizers is fast becoming an important management tool to
stimulate forest growth.
Western hemlock {Tsuga heterophylla (Raf.)
Sargi covers nearly 10 million acres of highly productive forest land
74
along the Pacific Coast of the United States and Canada.
Efforts to
stimulate growth of these stands by fertilization, mainly with prilled
urea, has met with limited success (Anonymous 1977, Webster et al.
1976, DeBell et al. 1975).
To develop guidelines for efficient fertilization of hemlock
stands, studies of fundamental aspects of impact of various fertilizers upon hemlock's rhizosphere, nutrition and growth are needed.
Studies by the current authors1 show that most western hemlock
nutrient absorbing roots are found in the litter layer (0-5 cm depth).
Any impact of fertilizer application on the rates of litter decomposition and the subsequent rates of nutrient release can therefore be
expected to significantly affect the nutrition and growth of western
hemlock.
Since various fertilizers are subject to different transfor-
mations at different rates, they might have differential impact upon
rates of litter decomposition and the subsequent release of nutrients.
The following study determines the impact of nitrogen fertilizers
in the forms of urea, gypsum-coated urea and calcium nitrate on
existing rates of litter decomposition in coastal hemlock stands.
MATERIALS AND METHODS
Two natural stands of young growth western hemlock in the coastal
hemlock zone near Seaside, Oregon, were selected for the study.
One
of the selected stands (Coast-i) is located outside of the coastal
Urea fertilization and the
1R. S. Gill, and D. P. Lavender. 1981.
primary-root system of young-growth western hemlock. Thesis,
Chapter II.
75
fog-belt and the other (Coast-8) lies in the fog-belt zone.
and Coast-8 stands have the following characteristics:
Coast-i
Coast-i:
ele-
vation - 168 meters, aspect - north, slope - 10-40 percent, site class
- II (high), basal area/hectare - 14.92 square meters, dbh - 32.13 cm
(average of 36 trees), tree age - 38.76 years (average of 36 trees),
Coast 8:
soil type - Hembre and Astoria silt loam.
elevation - 76
meters, aspect - southeast, slope - 10-40 percent, site class - II
(high), basal area/hectare - 15.45 square meters, d'oh - 38.91 cm
(average of 36 trees), tree age - 40.89 years (average of 36 trees),
soil type - 1-lembre and Astoria silt loam.
During November, 1977, litter in the
horizon was collected
from 36 randomly located 0.5 meter squares in each of the two selected
stands.
The collected litter consisted mainly of western hemlock
needles.
The litter from the two stands was cotnposited.
From this litter
at field moisture content, samples equivalent to 10 grams of oven
dried (70°C) litter were placed in 20 x 20 cm nylon mesh bags and
stored at 5°C until field distribution.
Mesh size of the bags was 1
mm, large enough to allow aerobic microbial activity and free entry of
small soil animals and fungal mycelium, yet small enough to retain
hemlock litter (Crossley and Hoglund 1962).
Three blocks, each containing four rectangular plots measuring
4.05 square meters (7 ft x 6 ft) were established at random locations
within each of the two selected stands.
Plots within each block were
separated by one meter (3.5 ft) buffer strips.
On December 6th, 1977,
urea, gypsum-coated urea and calcium nitrate in the amounts to supply
76
equivalent of 336 kg/hectare (300 lbs/acre) of elemental nitrogen were
applied to the three randomly selected plots (fourth plot served as
The fertilizers
untreated control) within each block in each stand.
were broadcast by hand under conditions of cool temperature and light
rain.
One day after fertilizer application, nine litter bags were
placed in each of the established plots.
The nine litter bags were
uniformly spaced within each plot and the four corners of each bag
were firmly tacked to the forest floor with u-shaped. tacks.
Three bags were randomly collected from each piot at three
6-month intervals.
After collection, litter from each bag was care-
fully removed and dried at 70°C to a constant weight.
if any, in the litter was removed prior to drying..
Moss ingrowth,
The dried litter
was weighed and ground through a 40-mesh screen for chemical analysis.
Total nitrogen was determined by the micro-Kjeldahl technique (Bremrter
1965), total carbon by the method of Walkley and Black (1934).
Lignin, cellulose and non-cell wall carbon components were determined
by Van Soest's method (1963).
Triplicate total nitrogen, total carbon
and carbon components analyses were conducted on composite sample of
original litter.
STATISTICAL ANALYSIS
The data for each of the sampling dates were statistically analyzed by randomized complete block design.
Duncan's multiple range
test was used to test statistical significance of difference between
treatments.
Log transformation was used to conduct regression by date
on each of the following:
weight remaining, prcent lignin, percent
77
cellulose, percent non-cell wall carbon, total nitrogen, total carbon,
and carbon nitrogen ratio.
RES ULTS
Litter Weight Loss
An exponential decay model was used to determine the rate of
annual weight loss (Cromack 1973, Jenney et al. 1949).
For each
treatment, weights of litter remaining in litter bags for the three
6-month sampling intervals and the annual decay constant (K) values
are given in Table t.
By the first sampling date, the amount of
litter remaining in the litter bags on treatment plots for Coast-8 was
significantly (P < 0.01) higher than the corresponding treatments on
Coast-i stand and remained significantly higher up to the final
sampling date.
On all treatments, litter weight in bags decreased
exponentially with time and the variance in weight remaining increased
with time.
Slopes and coefficients of correlation (r) for linear
regression of in (weight of litter remaining) with time for each
treatment are given in Table II.
After 18 months, all correlations
were significant (1' < 0.01) and the slopes of regression lines for
urea and gypsum-coated urea treated-plots were significantly different
(P < 0.01) than the slopes for control and calcium nitrate treated
plots.
Average r values for Coast-i and Coast-8 stands were 0.969 and
0.959, respectively.
Weights of litter remaining were significantly different
(Duncan's range test) between all treatments for the 6-month and
78
one-year sampling dates.
By the 18-month sampling date, however, the
difference between urea and gypsum-coated urea plots was not statistically significant (Table 1).
The amount of litter remaining with time
was consistently lowest (most weight loss) on urea treated and highest
(least weight loss) on calcium nitrate treated plots.
By the 18-month
sampling period, values for litter remaining on gypsum-coated urea
plots became closer to the values on urea treated plots and the values
for litter remaining on calcium nitrate treated plots became closer to
the values on control plots.
Annual decomposition constants (k) for all treatments on Coast-8
stand were significantly (P < 0.01) higher than the k values for the
correspdnding treatments on Coast-i stand.
Within each stand, k
values differed significantly between all treatments, being highest on
urea treated and lowest on calcium nitrate treated plots.
C:N COMPOSITIO1 OF LITTER
For all treatments, percent nitrogen and percent carbon in litter
increased exponentially while C:N ratio decreased exponentially with
time.
After 18 months positive linear correlation existed between
percent nitrogen in litter and time for all treatments, the r values
ranged from 0.898 to 0.966 with an average of 0.945.
Positive corre-
lation also existed between percent carbon in litter and time for all
treatments and the r values ranged from 0.372 to 0.981 with an
overall average of 0.869.
11egative linear correlations existed be-
tween C:M ratio of litter and time for all treatments.
The r values
ranged from 0.873 to 0.972 with an overall average of 0.941.
79
Percent nitrogen, percent carbon and the C:N ratio values in
litter for the three 6-month intervals are given in Table III.
As
compared with control, percent nitrogen values in litter were signif 1-
cantly and consistently higher on urea and gypsum-coated urea treated
plots and lower on calcium nitrate treated plots.
For Coast-B stand,
percent carbon values in litter on urea and gypsum-coated urea treated
plots were significantly higher than
itt
litter on control and calcium
nitrate treated plots at the three sampling dates.
Similar trends
were observed for percent carbon values in litter on Coast-i stand but
the differences were not always statistically significant.
C:N ratio
values for litter on urea and gypsum-coated urea trated plots were
always significantly lower than for litter on control and calcium
nitrate treated plots.
Overall, the C:N ratio values for litter on
gypsum-coated urea had a tendency to be higher, and the total carbon
and nitrogen values to be lower than those on the urea-treated plots.
Differences, however, were not always statistically significant.
Similarly, the C:N ratio values for litter on calcium nitrate-treated
plots had a tendency to be higher and the total carbon and nitrogen
values to be lower than on the control plots even though the differences were not always statistically significant.
CARBON COMPONENTS OF LITTER
For all treatments, percent lignin in litter increased exponentially and percent NCW decreased exponentially with time.
After 18
months, highly significant (P < 0.01) positive linear correlation
existed between percent lignin and time; values of r ranged from 0.953
80
to 0.986, with the average of 0.968 for all treatments.
For NCW, r
ranged from 0.828 to 0.981 with an overall value of 0.948.
The per-
cent cellulose values showed a significant linear relationship with
time in litter on urea and gypsum-coated urea plots but not in litter
on calcium-nitrate or control plots.
As compared with percent cellu-
lose values in original litter the values in litter on control and
calcium nitrate-treated plots showed an increase during the first six
months and a significant decrease during the following year.
Percent NCW, lignin and cellulose values in litter for the three
6-month intervals are given in Table [V.
As compared with control and
calcium nitrate-treated plots, percent lignin in litter on plots
treated with urea and gypsum-coated urea were significantly and consistently higher and percent cellulose significantly arid consistently
lower.
Percent lignin on urea-treated plots was significantly higher
than on gypsum-coated urea plots on the 6 and 12-month sampling dates;
by the 18-month sampling date, however, there was no significant dif-
ference between the two treatments.
Percent lignin in litter on
control plots was consistently higher than on calcium nitrate-treated
plots; the differences, however, were not always statistically
significant.
Percent NCW values in litter on treatment plots in both stands
were consistently in the following sequence:
urea < control < calcium nitrate.
urea < gypsum-coated
The differences between treatment
means, however, were not always statistically significant.
81
DISCUSSION
This experiment was designed to determine the effects of three
different sources of nitrogen on the rates of litter decomposition in
the litter layer of coastal western hemlock stands; the layer where a
substantial number of hemlock's nutrient absorbing roots are located.
Urea was selected because it is the form of nitrogen ferti1zer most
frequently used in forest fertilization.
Gypsum-coated urea was
selected because gypsum reduces the magnitude of increase in soil
litter pH resulting from hydrolysis of urea.
Calcium nitrate
was used to enable a comparison of the impact of NO3 - ion and NHt
ion on the rates of litter decomposition.
The two stands were
selected because even though they are situated in the same locality,
yet Coast-i had shown a positive response and Coasc-8 a negative
(growth depression) response to urea application (DeBell et al. 1975).
The results of this study indicate that for all treatments,
litter weight decreased exponentially with time.
The annual rate of
litter decomposition on Coast-8 stand was 21 percent higher (P < 0.01)
than on Coast-l.
Since Coast--8 is located in the coastal-fog belt
zone at lower elevation, therefore, the higher rate of litter decomposition on this stand is likely due to higher moisture content
(Figure 2) and temperature (data not recorded) in the litter layer.
The annual decomposition constant (k) values in both stands were in
the following sequence:
nitrate.
urea > gypsum-coated urea > control > calcium
Both urea and gypsum-coated urea increased the existing
rates of litter decomposition in the two stands.
The relatively rapid
82
increase in litter decomposition brought about by urea application is
most likely due to rapid hydrolysis of urea (Gould et al.
1973, Crane
1972, Roberge and Knowles 1966) resulting in a large flux of reduced
nitrogen (NH) and elevation in soil-litter pH' which in turn stimulated organic matter breakdown (solubilization) and microbial activity
in the zone of application (Sagara 1975, Ogner 1972).
The more gra-
dual increase in litter decomposition with time on plots treated with
gypsum-coated urea is likely due to relatively slow but continuing
release of NHL
to the soil litter layer and a less dramatic change in
the soil litter pH.
Application of calcium nitrate, on the other
hand, somewhat retarded the existing decomposition rates during the
first 6-month period following its application.
During the following
12-month period, however, there was no significant difference between
the rates of litter decomposition on control and calcium nitrate
treated plots.
vation.
There seems to be no clear explanation for this obser-
Inhibitive impact of NO3-nitrogen on certain soil fungi has
been reported in the literature (Park 1971, Nelson 1970, Theodorou and
Bowen 1968); but the extent and nature of any toxic affect of
NO3-nitrogen on microorganisms that are instrumental in litter decomposition on coastal hemlock stands is not known.
We can only specu-
late that the sudden addition of NO3-nitrogen might adversely effect
the indigenous microorganisms which, because of insignificant amounts
of naturally occurring NO3-nitrogen (0.12 and 0.16 ppm NO3-N on
Coast-i and Coast-8, respectively) in the forest floor, most likely
Changes in. soil chemical
1G111, R. S., and D. P. Lavender. 1981.
properties following urea fertilization. Thesis, Chapter I.
83
lack nitrate reductase activity.
Once the NO3-ion moves out of the
forest floor, the microbial activity would tend to revert back to the
pre-treatment level.
The exponential increase with time in percent of nitrogen in
litter indicates iuimobilization of this element by the microorganisms.
The relatively large values of percent nitrogen in litter bags on urea
and gypsum-coated urea treated plots most likely represents greater
microfloral activity on these treatments; rather than the result of
direct nitrogen addition because the litter bags were placed 24 hours
after fertilization application.
The apparent stimulation of
microfloral activity following fertilization was further indicated by
the dense white fungal growth which surrounded some litter bags on
urea treated plots.
Exponential increase with time in the percent of carbon in litter
bags is due to a parallel increase in percent of lignin which is
directly correlated with carbon content (Van Soest 1963).
Even
though, both percent of nitrogen and carbon in litter increased exponentially with time, yet the C:N ratio decreased exponentially because
the average rate of increase in percent of nitrogen was eight times
greater than for percent carbon.
The values of percent of nitrogen, carbon and C:N ratio in litter
for the 18-month period following treatment application show that the
rates of litter decomposition on different treatment plots were in the
following sequence in both stands:
control > calcium nitrate.
urea > gypsum-coated urea >
The same trend is supported by data on
84
percent of lignin, NCW and cellulose in litter following treatment
application.
Percent lignin in litter increased exponentially with time
because as compared with NCW and cellulose, it is the organic component that is most resistant to microbial degradation (Fogel and
Cromack 1977).
The overall, highly significant correlation of percent
of lignin in litter with time renders it an important measure of
This qualitative measure of litter decomposition
decomposition rates.
could prove more advantageous than the conventional method of quantitative 'weight" measurements in litter bags because of loss of
litter fragments from litter bags during handling unless a very small
mesh size is used.
Use of too small a mesh size, however, restricts
the free entry of soil organisms into the bags, rendering the results
of decomposition rates inside the litter bags less representative of
the actual rates on the forest floor.
Use of percent of lignin to
determine rates of decomposition would render the loss of litter
fragments from the bags less crucial, enabling the use of litter bags
with larger mesh size.
CONCLUSION AND IMPLICATIOt'S
Several conclusions related to decomposition rates on coastal
hemlock stands and decomposition research in general result from this
study.
First, subtle differences in edaphic factors such as tem-
perature and moisture can result in marked differences in decomposition rates between stands in the same general locality.
Second,
addition of nitrogen in different forms has different effects on the
85
indigenous rates of litter decomposition.
Third, in studies utilizing
litter bags to determine decomposition rates, percent of lignin with
time in the littr can be used as an alternative index to conventional
weight measurement.
In a separate study (Gill and Lavender 1981) we demonstrate that
a large percentage of hemlock's nutrient absorbing roots are located
in the litter layer, and that the application of urea results in a
The
dramatic but relatively short lived decrease in their numbers.
rapid increase in the rate of litter decomposition, such as that which
occurs following urea application, could therefore, result in a net
loss of soluble nutrient from this zone.
The combined effect of loss
of nutrient absorbing roots and nutrients could in eart explain the
adverse effect of urea application on growth of western hemlock.
of slow release fertilizers, such as gypsym-coated urea,
which
a gradual increase in the rate of litter decomposition could,
Use
produce
there-
fore, prove to be more efficient for fertilization of hemlock stands,
because a greater percentage of nutrients released via litter decomposition will coincide with the recovery period of hemlock's nutrient
absorbing roots.
86
TABLEI.
LITTER DECOMPOSITION (L. BAGS).
10 grams of litter/bag on December 1977
Coast-8
Coast-i
Coast-i
weight
weight
k
remaining remaining
Treatment
Sampling date
June 1973
Ca(NO3)2
Control
Gypsum urea
Urea
8.34
7.64
7.39
6,77
a
b
c
d
**7.30
**6.92
**6.65
**6.20
January 1979
Ca(NO3)2
Control
Gypsum urea
Urea
6.39
6.09
5.40
5.03
a
b
c
d
**5.93 a
Ca(NO3)2
Control
Gypsum urea
Urea
5.87
5.52
5.10
4.83
a1
b
c
c
**5,24
**4.96
**4.52
**4.4l
June 1979
Coast-8
k
a
b
c
d
**55Q b
**5.03 c
**4.68 d
0.45 a
0.50 b
0.62 C
0.69 d
**0.52
**o,60
**o.69
**0.76
a
b
c
d
a
b
c
c
Within each sampling date, values in the vertical column followed by
same letter designation are not significantly different.
**Values in the same horizontal column (Coast-i compared with
Coast-B) are significantly different (P < 0.01).
k = annual decomposition constant.
TABLE II.
COEFFICIENT OF CORRELATION (i) AND SLOPE OF REGRESSION LINES OF:
PERCENT LIGNIN AGAINST TINE (MONTHS) ELAPSEI) (18 MOUTH PERIOD).
Weight remaining
r
Slope
Coast-i
C:N ratio
r
Slope
X lignin
r
Slope
PERCENT WEIGHT REMAINING, C:N RATIO AND
Weight remaining
Slope
r
Coast-B
C:N ratio
Slope
r
1
r
lignin
Slope
Urea
0.95 **
-0.25 a1
0.87 **
-0.20 a
0.96 **
0.17 a
0.94 **
-0.28 a
0.92 *A
-0.23 a
0.95 **
0.18 a
Gypsum urea
0.97 **
-0.25 a
0.94 **
-0.12 a
0.97 **
0.17 a
0.96 *k
-0.27 a
0.97 **
-0.25 a
0.97 **
0.18 ab
Control
0.98
*
-0.20 b
0.95 **
-0.18 a
0.96 **
0.08 b
0.97 **
-0.23 b
0.96
-0.21 a
0.97 **
0.16 bc
CaLcium nitrate
0.98 **
-0.19 b
0.97 **
-0.18 a
0.97 **
0.08 b
0.96 **
-0.21 b
0.95 **
-0.22 a
0.99 **
0.12
1Values In the vertical column followed by same letter designation are not significantly different.
**Slgnificant at 1% level.
C
TABLE III.
C:N COMPOSITION OF LITTER.
Coast-8
Coast-i
Sampling date
Treatment
December 1977
Original litter
0.69
June 1978
Urea
Gypsum urea
Control
Ca(NO3)2
1.13
1.06
0.82
0.79
a1
a
b
b
44.37
43.61
43.93
42.93
a
a
ab
b
39.20
41.31
53.34
54.11
a
a
b
b
1.26
1.12
0.88
0.81
a
b
c
d
46.60
47.63
43.96
44.97
a
a
b
b
37.11
42.48
49.83
56.03
a
b
c
d
January 1979
Urea
Gypsum urea
Control
1.36
1.32
1.18
1.11
a
a
b
b
45.49
45.38
45.27
44.14
a
a
a
a
33.42
34.51
38.47
39.78
a
a
b
c
1.47
1.50
1.29
1.29
a
a
b
b
48.60
48.54
46.08
45.77
a
a
b
b
33.06
32.44
35.90
36.11
a
a
b
b
1.39
1.42
1.21
1.16
a
a
b
b
46.18 a
33.26
32.13
37.94
38.12
a
a
b
b
1.67
1.66
1.38
1.37
a
a
b
b
49.52
49.58
47.09
46.40
a
a
b
b
29.67
29.83
34.29
33.94
a
a
b
b
Ca (NO3)2
June 1979
Urea
Gypsum urea
Control
Ca (NO3)2
%C
%N
42.25
4581 a
45.61 a
44.22 b
C/N
7.N
61.68
0.69
%C
C/N
61.68
42.25
1Values in the vertical column followed by same letter designation are not signif ieantly different (P < 0.05).
TABLE IV.
CARBON COMPONENTS OF LITTER.
Sampling date treatment
% NCW1
Coast-i
% Lignin % Cellulose
35.21
20.02
% NCW1
Coast-8
% Lignin % Cellulose
44.74
35.21
20.02
December 1977
Original litter
44.74
June 1978
Urea
Gypsum urea
Control
Ca(NO3)2
35.94
38.01
38.33
39 51
a
b
bc
c
45.51
43.29
39.88
37 59
a
b
c
d
18.54
18.70
21.75
22.56
a
a
b
b
34.63
35.73
37.13
38 10
a
ab
cb
c
47.89
45.59
41.91
39 84
a
b
c
d
17.48
18.69
20.94
22 06
a
b
c
d
January 1979
Urea
Gypsum urea
Control
Ca(NO3)2
28.63
29.33
35.43
36.44
a
a
b
b
55.31
53.42
43.27
42.17
a
b
c
c
16.06
17.24
21.29
21.39
a
a
b
b
27.26
27.81
28.67
30.79
a
b
b
b
57.03
55.05
52.27
47.45
a
b
c
d
15.70
17.12
19.05
21.70
a
a
b
c
June 1978
Urea
Gypsum urea
Control
Ca(NO3)2
26.93
27.11
34.86
36.84
a
a
b
b
58.32
57.26
44.59
44.25
a
a
b
b
14.58
15.80
18.77
20.56
a
a
b
b
25.70
25.78
26.00
29.34
a
a
a
b
60.25
59.21
54.90
49.31
a
a
b
c
14.09
15.10
19.10
21.37
a
a
b
c
1NCW = non cell wall carbon.
Within each sampling date, values in the vertical column followed by same letter designation are
not significantly different (P < 0.05).
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