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SOIL SCIENCE
Vol. 140, No.6
t) I ver, some mistakes may
Printed in U.S.A.
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,I
EVALUATION OF DIFFERENT EXTRACTANTS FOR PHOSPHORUS IN WESTERN HEMLOCK SOILS M.
Phosphorus
(P)
A. RA.DWAN/ J.
M.
KRAFT/
has been shown to affect
AND J. S. SHUMWAy2
source of "available" P for hemlock nutri­
tion; and (2) the potential usefulness of P
tests to predict growth response of hem­
growth of western hemlock and its re­
sponse to N fertilizer. The objective of this
study was to assess different extractants
lock to N fertilization, especially when P
is low. The data also suggest that stronger
extractants, such as Bray and mixed acid,
may be more suitable than the weaker ace­
tates for evaluating the P status of hemlock
soils.
for determining the P status of hemlock
soils and the use of soil P to predict growth
response of hemlock to N fertilizer. Sam­
ples of forest floor and mineral soil to a
depth of 15 cm were collected from 16 sites
of western hemlock (Tsuga heterophyila).
The sites, located in both the coastal and
Cascade zones in western Wa.,hington,
were selected from among the fertilizer­
Economically, western hemlock (Tsuga het­
erophylla (Raf.) Sarg.) is second in importance
only to Douglas fir (Pseudotsuga menziesii
test installations of the University of
Washington Regional Forest Nutrition Re­
search Project. Using six techniques, we
(Mirb.) Franco) in forests of western Washing­
extracted and determined P in the col­
lected samples, and we determined reJa­
ton and Oregon. Yet information about the nu­
tionships among P amounts extracted by
the different methods and between the ex­
tracted P and growth response of hemlock
is still scant. In addition, attempts to increase
trition and nutritional requirements of hemlock
hemlock production by application of nitrogen
(N) fertilizer have shown much variability and
to nitrogen (N) fertilization. 'Vith both the
forest floor and mineral soil, P values dif­
fered by extractant (within zones) and be­
tween the two hemlock zones (within ex­
tractants).
Phosphorus
concentrations
were consistently higher in the forest floor
than in mineral soil. Concentrations aud
inconsistency in response, especially in the
coastal hemlock forests (Webster et a1. 1976).
Recent investigations into the nutritional re­
lationships of hemlock, through both foliar and
soil analyses, suggest phosphorus (P) as an im­
portant variable affecting the growth. of hemlock
amounts of P extracted from the forest.
floor and mineral soil were always higher
in the Cascades than on the coast. For both
the forest floor and mineral soil, amounts
of P extracted by most methods were sig­
nificantly related to each other, and the P
determined by some procedures was sig­
nificantly correlated with growth re­
sponse. The highest correlations with re­
"pons e , however, were with Bray-1-,
Bray-2-, and NaHCOa-P of the forest floor
and with mixed-acid- and Bray-l-P of the
miner::-'! soil. The study reaffirms previ­
ously reported results with resllect to: (1)
the i mp o rt ance of the forest floor as a
and its response to N fertilizer (Radwan and
DeBell 1980; Radwan and Shumway 1983a,b;
Radwan and Shumway 1984a). In these studies,
we extracted soil P with Bray-2 solution (Bray
and Kurtz
1945). However, researchers have
used numerous extractants to evaluate the P
status of soil, especially in agriculture (Bingham
1962; Olsen and Sommers 1982). Also, in the
southeastern United States, P extractant.s var­
ied widely in their effectiveness for predicting
response of southern pines to P fertilization
(Wells et a1. 1973; Ballard and Pritchett 1975).
This study is an extension of a previous in­
vestigation into the relationships of soil prop­
erties to growth response of hemlock to N fer­
1
Forestry Sciences Laboratory, USDA Forest Serv­
ice, Olympia, Wash. 98502.
2
For e s t Land !vTanagement Center, Wl\shingf.on
SLate Dept. of Natural Resources, Olympia, Wash.
98502.
Heceived for jJublication 13 November 19iH; revised
20 February 1985.
tilization (Radwan and Shumway 1983a, 1984a).
The work was undertaken:
(1) to compare
amounts of P extracted from hemlock soils and
forest floor materials with six different tech­
niques, and (2) to determine the relationRhips of
P by the various extraction methods to growth
response of hemlock to N fertilizer.
429
430
RADWAN, KRAFT, AND SHUMWAY
MATERIALS AND METHODS
Forest floor and soil sampling and processing
Sites were sampled for the forest floor and
underlying mineral soil to a depth of 15 cm.
The sites
Sixteen sites were selected from among the
Thirty samples, each 78.5 cmz in surface area,
were collected from the individual sites. Sam­
unthinned, fertilizer-test installations of the Re­
gional
Forest
Nutrition
Research
Project
pling was at 3-m intervals along each of three
(RFNRP) of the University of Washington.
30-m transects laid out in the untreated strips
between the RFNRP plots at each site. Sam­
There were 18 undamaged RFNRP installations
located in Washington. The study included all
eight coastal installations, which were within 40
km of the Pacific coast, and another eight in­
pling points were moved to avoid stumps and
logs, and twigs and other material >6 mm in
diameter were discarded. There were 10 samples
stallations, selected at random, located inland
per transect, and samples from each transect
on the west slopes of the Cascade Range. On
were composited and mixed thoroughly. Sam­
average, the coastal zone is considered to be
more productive than the Cascade zone, and N
ples were air-dried, and large pieces of roots,
sterns, and rocks were removed. Forest floor
fertilization is believed to be more successful in
samples were weighed and ground. Soil was
the Cascades (Webster et a!. 1976; Olson et a!.
1980). All stands were unthinned; they were 10
passed through a 2-mm sieve, and the resulting
fractions were weighed. All samples were stored'
to 40 yr old when the RFNRP established the
at -15°C until analyzed.
various installations in 1969.
Phosphorus extraction and determination
Site index
Six different procedures were selected for ex­
Indexes at 50 yr were calculated from tree
traction and determinati n of P. The procedures
heights and breast-height ages (determined by
were chosen because of their wider use in for­
RFNRP) and the use of Wiley's (1978) tables.
estry than other methods. All procedures were
Values were based on 36 trees at each site.
applied to all forest floor and soil samples in
same manner, and without modification from
Growth response
the original, published instructions with respect
Seven-year, radial increment response to ap­
to soil:solution ratio, shaking time, or method
plication of 224 kg N/ha was determined by
of P determination. A summary of the analytical
Olson (1979), using a tree-pairing method. Fer-
procedures follows
Procedure/extractant
Soil (g):
Solution {ml}
Shaking
time
Reference
1. Bray-1/0.03N NH4F in 0.025 N
HCl
1:7
2. Bray-2/0.03N NH4F in 0.1 N HCl
3. Olsen/0.5 N NaHCOa, pH 8.5
1:7
1:20
40 s
Bray and Kurtz (1945)
30 min
Olsen et a!. (1954)
4. Ammonium acetate/0.7 N 1:5
30 min
Page et a!. (1965), Bal­
1 min
NH40Ac in 0.5 N HOAc, pH 4.8
Bray and Kurtz (1945)
lard and Pritchett
(1975)
5. Sodium acetate/0.73 N NaOAc in
1:5
30 min
0.5 N HOAc pH 4.8
Peech and English
(1944), Greweling and
Peech (1965)
6. Mixed acid (North Carolina)/0.05 N HCl in 0.025 N H2SO4
1:4
5 min
Nelson et a!. (1953),
Page et a!. (1965)
tilized and unfertilized trees were paired accord­
Phosphorus in the extracts was determined
ing to similarity in size, competitive status, and
past diameter growth. Percentage of response
colorimetrically after color development with
molybdate reagent in procedures 1 through 5,
was based on 30 pairs of trees at each site.
and with molybdate-vanadate reagent in proce­
431
S
TS FOR HEMLOCK SOIL
PHOSPHORUS EXTRACTAN
at least in
dure 6. All determinations were run
duplicate.
Statistical analysis
Phosphorus in
the forest /1oor
Extracted P varied considerably among and
within sites and between zones (Table 2). Values
ranged from 0.1 kgfha «1 ppm) by the NH40Ac
procedures
Relationships among the different
response
th
grow
and
P
of
unts
amo
and between
calculating
by
d
mine
deter
were
izer
fertil
to N
cients (r) ac­
the appropriate correlation coeffi
analyses, re­
all
In
cording to Snedecor (1961).
p ::5 0.05.
at
t
fican
signi
sults were considered
method on some sites on the coast to 8.2 kgfha
RESULTS
ently higher in the Cascades than on the coast.
Examples of Cascade and coast values are: 3.0
The sites
kgjha versus 1.6 kgjha (63.1 ppm versus 40.2
ppm) by Bray-2; and 004 kgfha versus 0.1 kgfha
m in
The 16 sites ranged from 60 to 900
l, sed­
glacia
was
rial
mate
t
paren
Soil
elevation.
forest floor
imentary, or volcanic. Weight of the
43 tjha
ged
ranged from 22 to 82 tjha; it avera
nse to
respo
h
GroWt
over the 16 sites (Table 1).
(-20
sites
the
g
amon
ly
great
N fertilizer varied
was
6%,
t
abou
at
nse,
respo
age
Aver
to 38%).
occurred on
nse
respo
ive
posit
good
but
low,
the Cascade
some sites in both the coastal and
zones (Olson 1979).
(149 ppm) by Bray-2 for site 117 in the Cascades.
On the coast and in the Cascades, the average
extracted P varied greatly among the extrac­
tants in the order of: Bray-2 > Bray-I > Na­
HCOa > HCI + H2S04 > NaOAc > NH.OAc.
Within extractants, the averages were consist­
(7.2 ppm versus 2.7 ppm) by NI-LOAc.
There were significant correlations between
the amounts of P extracted by the different
procedures (Table 3). In addition, most P values
(kgjha) were significantly correlated with
growth response of hemlock to N fertilizer; the
strongest correlation was r = 0.76, P = 0.001 for
Bray-2, and the weakest was r = 0046, p = 0.076
for NH40Ac.
TABLE 1
and stand characteristics·
site
ock
heml
ted
Selec
Location and
site number
Coastal zone
100
84
15
80
9
4
3
42
Soil
series
Kydaka
Klone
Palix
Lyre
Willaby
Wishkah
Calawah
Germany
Average
Cascade zone
24
23
109
108
Revel
58
18
117
Tokul
III
Average
Elwell
Pilmore
Winston
Tokul
Mashel
Darnell
Growth response
Weight of
forest floor, t/ha
Site index
at 50 yr, m
40
28
49
48
38
29
22
74
41
34
37
38
30
34
37
34
36
35
1
7
17
10
3
3
-20
16
82
39
52
32
29
31
44
48
45
26
36
34
37
39
31
36
34
34
20
9
-12
-2
2
to N fertilizer, %
5
-12
5
38
6
Site index is based on heights and ages
RP fertilizer-test installations.
• Site number" are those of the RFN
t growth response to 224 kg N/ha
emen
l-incr
by RFNRP. Seven-year, radia
of 3G trees at each site measured
a tree-pairing method.
using
),
(1979
Olson
by
d
was determine
432
RADWAN, KRAFT, AND SHUMWAY
TABLE 2
Phosphorus, kg/ha, extracted from hemlocll forest floor with different extractants"
Location and site nu;r,ber Extractant
Bray·l
Bray·2
NaHC03
NH,OAc
NaOAc
HCI + H2SO,
0.5
1.0
3.1
2.3
0.7
1.5
0.4
1.2
1.3
0.7
1.1
3.8
2.6
0.9
1.8
0.5
1.8
1.6
0.3
0.6
1.7
1.5
0.3
0.9
0.2
0.3
0.7
0.1
0.1
0.2
0.3
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.2
0.3
0.1
0.1
0.1
0.1
0.1
0.1
0.1
0.7
0.4
0.2
0.3
0.2
0.4
0.3
5.1
1.3
1.5
2.0
1.3
1.9
1.0
5.5
2.4
5.1
1.4
1.6
2.3
1.6
2.4
1.3
8.2
3.0
3.0
0.7
0.8
1.0
0.6
0.9
0.6
3.4
1.4
1.7
0.2
0.2
0.2
0.1
0.2
0.1
0.6
0.4
1.7
0.3
0.2
0.2
0.1
0.2
0.3
0.7
0.5
2.8
0.5
0.6
0.4
0.3
0.5
0.5
1.4
0.9
Coastal zone
100
84
15
80
9
4
3
42
Average
Cascade zone
24
23
109
108
111
58
18
117
Average
• Site numbers are those of the RFNRP fertilizer-test installations. See text for composition of different
extractants.
TABLE 3
Correlation coefficients r of the linear regressions among the phosphorus extracted from the forest floor with
different extractants and between the extracted phosphorus and growth response of hemlack to N fertilizer·
Groy,th response
Extractant
to N
fertilizer/extractant
Bray·1
Growth response
0.72
(0.002)
Bray-1
Bray·2
NaHCO.
NH.OAc
NaOAc
0.76
(0.001)
0.97
(0.001)
0.72
(0.002)
0.99
(0.001)
0.96
(0.001)
0.46
(0.076)
0.78
(0.001)
0.63
(0.009)
0.77
(0.001)
0.50
(0.050)
0.79
(0.001)
0.65
(0.006)
0.79
(0.001)
0.99
(0.001)
Bray-2
NaHC03
NH.OAc
NaOAc
•
HCI + H.SO.
0.53
(0.035)
0.85
(0.001)
0.73
(0.001)
0.84
(0.001)
0.97
(0.001)
0.98
(0.001)
Probabilities p are shown in parentheses. Correlations are considered significant at p ;$ 0.05. See text for
composition of extractants and Table 1 for percentage of growth re ponse to N fertilizer.
Phosphorus in the mineral soil
For all extractants, mean concentrations of P
compared with those in the forest floor, were:
22.0 versus 51.6, Bray-2; 10.7 versus 42.6, Bray-
depth of 15 cm than in the forest floor. Over all
1; 9.7 versus 23.4, NaHC03; 8.2 versus 12.0, HCl
+ H S04; 1.0 versus 6.1, NaOAc; 1.4 versus 5.0,
NH.OAc. Amounts of extracted P (kg/ha), how­
16 sites, average P concentrations (ppm) in soil,
ever, were consistently higher in the mineral soil
were consistently lower in the mineral soil to a
433
PHOSPHORUS EXTRACTANTS FOR HEMLOCK SOILS
(Table 4) than in the forest floor (Table 2)
because of the much larger weight of the soils.
DISCUSSION AND CONCLUSIONS
The techniques tested in this study for the
As with the forest floor, there were large dif­
ferences in extracted P by extractant, within
extraction and determination of soil P varied
zones, and between the two hemlock zones,
tages over other methods; they require no char­
within extractants (Table 4). Overall, average
coal and the shortest extraction times, and they
extracted P values (kgjha), in descending order
were: 13.3, Bray-2; 6.5, Bray-I; 5.9, NaHC03;
give unmistakable, higher colorimeter readings.
greatly. The Bray tests had some notable advan­
Amounts of P varied considerably among the
1.9, HCI + H2S04; 0.8, NH40Ac; and 0.6,
NaOAc. Also, for most extractants, the averages
extracts tested. This was expected because the
solutions tested extracted different forms of P
seemed higher in the Cascades. Examples of
(Bray and Kurtz 1945; Nelson et aJ. 1953; Olsen
values (kgjha) obtained in the Cascades and on
and Sommers 1982). Phosphorus values were
the coast are: 8.5 versus 3.3 (13.8 ppm versus 5.6
highest with Bray-2 (followed by Bray-I), inter­
ppm) by NaHC03, and 2.4 versus 1.3 (4.3 ppm
mediate with mixed acid and bicarbonate, and
versus 2.2 ppm) by HCI + H2S04•
lowest with the acetates. This agrees with the
generally acknowledged differences between the
With two exceptions, amounts of P, by the
solutions tested (Wells et a1. 1973; Ballard and
different procedures tested, were significantly
related to each other (Table 5). Unlike the forest
floor, P by only two procedures was significantly
Pritchett 1975). Strict comparison of our results
with those from other studies in the literature is
correlated with growth response to N fertilizer;
not possible because of differ€llces in properties
of the soils used and modifications to the stand­
the strongest correlation with response (r = 0.71,
p = 0.002) was with P extracted with HCL +
H2S04, and the weakest relationship (r = 0.44,
P = 0.085) was with NaOAc-P.
ard methods adopted by different investigators.
Soil:solution ratios and shaking times are the
main modifications reported by others (Alban
TABLE 4 Phosplwrus, kg/ha, extracted from hemlock forest mineral soil with different extractants" Location and
site number
Extractant
HC!
+ H2SO,
Bray-l
Bray-2
NaHC03
NILOAc
NaOAc
0.5
5.2
10.5
2.6
0.5
6.7
0.8
5.3
4.0
1.9
4.5
30.0
6.6
1.7
9.4
3.3
12.6
8.8
0.5
3.9
12.1
2.8
0.5
3.6
0.5
2.3
3.3
0.2
1.0
2.6
1.0
0.4
0.2
0.1
0.5
0.8
0.1
1.4
1.8
0.4
0.1
0.4
0.1
0.6
0.6
0.6
1.7
2.5
0.9
1.1
1.3
0.8
1.5
1.3
10.2
21.1
0.5
10.9
1.8
6.4
0.9
'19.5
8.9
13.9
42.7
2.0
26.8
7.2
17.5
3.3
29.6
17.9
9.9
19.4
0.5
14.3
3.6
6.3
0.6
13.5
8.5
1.1
1.5
0.2
1.5
1.3
0.3
0.4
0.9
0.9
0.7
1.0
0.1
1.0
0.5
0.6
0.1
0.8
0.6
3.9
3.9
1.2
1.5
0.6
1.9
1.1
'5.5
2.4
Coastal zone
100
84
15
80
9
4
3
42
Average
Cascade zone
24
23
109
108
111
58
18
117
Average
a
Site numbers
extractants.
arc
those of the RFNRP fertilizer-test installations. See text for composition of different
434
RADWAN, KRAFT, AND SHUMWAY
TABLE 5
Correlation coefficients r of the linear regressions among the phosphorus extracted from the mineral soil with
different extractants and between the ex racted phosphorus and growth response of hemlock to N fertilizer·
Extractant
Growth response
to N
fertilizer/extractant
Growth response
Bray-1
Bray-l
Bray-2
0.60
(0.014)
0.45
(0.082)
0.93
(0.001)
NuHC03
NH,OAc
NaOAc
Hel + H2SO.
0.46
(0.070)
0.94
(0.001)
0.96
(0.001)
0.46
(0.076)
0.54
(0.032)
0.67
(0.005)
0.70
(0.002)
0.44
(0.085)
0.61
(0.012)
0.67
(0.005)
0.69
(0.003)
0.84
(0.001)
0.71
(0.002)
0.89
(0.001)
0.73
(0.001)
0.77
(0.001)
0.38
(0.149)
0.47
(0.069)
.
Bray-2
NaHC03
HN.OAc
NaOAc
• Probabilities p are shown in parentheses. Correlations are considered significant at p ::; 0.05. See text for
composition of extractants and Table 1 for percentage of growth response to N fertilizer.
1972; Wells et al. 1973; Cajuste and Kussow
eral soil. Prediction of growth response, there­
1974; Ballard and Pritchett 1975). Such changes
fore, may require different P extractants for the
may lead to values different from those obtained
different components of the soil system.
by the original, standard methods. For example,
This study reaffirms previously reported re­
increasing the shaking time with some solutions
sults (Heilman and Ekuan 1980; Radwan and
has lowered extracted P because of readsorption
(Russell and Prescott 1917; Cajuste and Kussow
importance of the forest floor as a source of
1974). We confirmed this phenomenon in
Shumway 1983a, 1984b) with respect to: (1) the
a
"available" P for hemlock nutrition, and (2) the
small test with several soils from this study; we
potential usefulness of P tests to predict re­
found an appreciable (>50%) and progressive
sponse of hemlock to N fertilization, especially
decrease in P extracted with Bray-2 as shaking
when P is low. Results also suggest that the
time was increased from 40 s to 30 min. Even
stronger extractants, such as Bray and mixed
without major modification in analytical meth­
acid, are probably more suitable than the weaker
ods, we would expect different results from dif­
acetates for evaluating the P status of hemlock
ferent laboratories depending on how the P test
soils in the Pacific Northwest.
is actually run. Again, because of readsorption,
lower results will be obtained with some extrac­
tants, such as Bray, when shaking time is un­
intentionally increased, or when extracts are not
immediately and speedily filtered after shaking.
All methods tested gave higher P concentra­
tions in the forest floor than in the mineral soil.
A similar result with hemlock soils was reported
earlier (Heilman and Ekuan 1980).
With only two exceptions, correlations be­
tween P extracted by the different methods were
significant; this suggests that the methods tested
probably extract some of the same kind of soil
P. More important, most P values were signifi­
cantly correlated with growth response. Highest
correlations, however, were with Bray-2-P in the
forest floor and with mixed-acid-P in the min­
ACKNOWLEDGMENTS
We thank the University of Washington Re­
gional Forest Nutrition Research Project for
providing the growth response data and the
measurements used in calculating the site index
and for making the study sites available for
collecting soil samples.
REFERENCES
Alban, D. H. 1972. The relationship of red pine site
index to soil phosphorus extracted by several
methods. Soil Sci. Soc. Am. Proc. 36:664-666.
Ballard, R, and W. L. Pritchett. 1975. Evaluation of
soil testing methods for predicting growth and
response of Pinus e/liottii to phosphorus fertiliz­
ation. Soil Sci. Soc. Am. Proc. 39:132-136.
Bingham, F. T. 1962. Chemical tests for available
phosphorus. Soil Sci. 94:87-95.
PHOSPHORUS EXTRACTANTS FOR HEMLOCK SOILS
Bray, R H., and L. T. Kurtz. 1945. Determination of
total, organic, and available forms of phosphorus
in soils. Soil Sci. 59:39-45.
Cajuste, L. J., and W. R Kussow. 1974. Use and
limitations of the North Carolina method to pre­
dict available phosphorus in some oxisols. Trop.
Agric. (Trinidad) 51:246--251.
Greweling, T., and M. Peech. 1965. Chemical soil tests.
Bull. 960, Agric. Exp. Stn., Cornell Univ., Ithaca,
N.Y.
Heilman, P. E., and G. Ekuan. 1980. Phosphorus
response of western hemlock seedlings on Pacific
coastal soils from Washington. Soil Sci. Soc. Am.
J.44:392-395.
Nelson, W. L., A. Mehlich, and E. Winters, 1953. The
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