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Group Title: Circular Florida Cooperative Extension Service
Title: Fertilization of slash pine plantations
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Permanent Link: http://ufdc.ufl.edu/UF00014513/00001
 Material Information
Title: Fertilization of slash pine plantations
Series Title: Circular Florida Cooperative Extension Service
Physical Description: 5 p. : ill. ; 28 cm.
Language: English
Creator: Kidder, Gerald, 1940-
Comerford, Nicholas B., Dd 1952-
Mollitor, Alfred V
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1987
Subject: Slash pine -- Fertilizers   ( lcsh )
Slash pine -- Soils   ( lcsh )
Pine -- Fertilizers   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Bibliography: p. 5.
Statement of Responsibility: Gerald Kidder, Nicholas B. Comerford and Alfred V. Mollitor.
General Note: Cover title.
General Note: "June 1987."
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Bibliographic ID: UF00014513
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA6953
ltuf - AEQ5374
oclc - 16848749
alephbibnum - 000943664
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Table of Contents
    Front Cover
        Front Cover 1
        Front Cover 2
        Page 1
        Page 2
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        Page 5
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Full Text

June 1987

Fertilization of

Slash Pine


Gerald Kidder
Nicholas B. Comerford
Alfred : Mollitor

A r .6t

tf'I::: I Al 1

Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean

Circular 735


Gerald Kidder is Associate Professor, Extension Soil Test Interpretation Specialist. Nicholas B. Comerford is Associate Professor, Forest
Soils Fertility Specialist, Soil Science Department. Alfred V. Mollitor is former Assistant in Forest Soils, Department of Forestry IFAS
University of Florida, Gainesville.


Slash pine is widely planted in the southeastern
U.S. On some soils increased wood production can
be realized by fertilization, but the long time (5 to
30 years) between fertilization and harvest makes
fertilization a long-term investment which requires
careful consideration.
The size and longevity of tree growth response
to fertilization can range from over 14 m3/ha/yr
(200 ft3 acre/yr)* for 20 years to less than 1.4
m3/ha/yr (20 ft3/acre/yr) for only a few years.
Forest fertilization initially became an accepted
forest management tool because on selected soils
one small application of phosphorus (P) changed un-
productive forests to very productive ones. While
not all growth responses to fertilization are this
dramatic, soils of the southeastern U.S. are gener-
ally infertile and pine plantations will show good
fertilizer response on many sites.
The purpose of this publication is to summarize

current interpretations of research findings and to
present pine fertilization recommendations that have
a good probability of increasing wood production.
The recommendations are based on research conduc-
ted by the Cooperative Research in Forest Fertili-
zation (CRIFF) program. CRIFF is a cooperative
venture between the University of Florida Soil
Science Department, the University of Florida De-
partment of Forestry, and thirteen private corpora-
tions. Throughout this report, an experimental
"fertilizer response" is one where the pine growth
response is at least 1.2 m3/ha/yr (18 ft3/acre/yr).
To provide economical benefit, a fertilizer response
may need to be higher depending on the conditions
of each situation.
Slash pine response to fertilization is soil-spe-
cific. For this reason, soils of the Florida-Georgia
Coastal Plain have been organized by the CRIFF
program into eight major soil groups (Table 1). The
groups are useful in that they contain soils of
similar physical properties and provide a common

Table 1. CRIFF soil-group definitions.
Soil Major Land
Group Area Drainage Important Features
A Savannas Very poorly to Sand to loamy sand surface layer less than 20 inches thick, with
somewhat poorly a finer-textured soil horizon below.
B Savannas Very poorly to Sand to loamy sand surface layer greater than 20 inches thick,
somewhat poorly with a finer-textured soil horizon below.
C Flatwoods Poorly to Spodic horizon below the surface layer; sandy loam or finer-
somewhat poorly textured soil horizon below the spodic.
D Flatwoods Poorly to Spodic horizon below the surface layer; sand to loamy sand soil
somewhat poorly horizon below the spodic.
E Uplands Moderately-well Sand to loamy sand surface layer less than 20 inches thick
to well drained with a finer-textured soil horizon below.
F Uplands Moderately-well Sand to loamy sand surface layer greater than 20 inches thick,
to well drained with a finer-textured soil horizon below.
G Sandhills Excessively Sand to loamy sand surface layer at least 100 inches thick.
H Depressions Very poorly High in decomposing plant residues. An organic soil.
(Adapted from Munson, 1984)
* Which units should we use? This question is not easily answered when we consider the many audiences for this
publication. English units are familiar to U.S. users but involve unwieldy factors. Metric units are easier to work
with, but some audiences lack familiarity with the system. Expression of phosphorus and potassium fertilizer rates can
also be confusing because fertilizer laws, written in the days of gravimetric analyses, require phosphorus content of
fertilizers to be expressed as P205 and potassium content as K2O. In this publication when we write P or K, we mean
the elemental equivalents, and when we write P20O or K20 we mean the oxide equivalents of the elements. Through-
out this publication phosphorus and potassium rates will be expressed as elemental in conjunction with metric units and
as P205 and K0O in conjunction with U.S. English units. The existence of multiple systems of measurement is incon-
venient but at present is a fact of life.

ground for the discussion of forest management
There are two common times in forest stand
development for fertilization in the South: in young
stands (up to 5 to 8 years old), and in mid- to
late-rotation stands. Forest fertilization recom-
mendations will be discussed within the framework
of these opportunities.

Fertilization of Young Plantations

Fertilization during the first five years of the
rotation must produce an economic response 18 to
30 years later when the wood is harvested. CRIFF
research has focused on several questions in deter-
mining the conditions where yield responses to
fertilization are likely. These questions are ad-
dressed below and the recommendations are summar-
ized in Table 2.

1. What sites should be fertilized?
The best way to identify potential long-term
response sites on the Coastal Plain is to use CRIFF
soil groups and soil fertility analyses. Knowledge of
one or the other is less helpful than both. Pines on
soils of Groups A and B have responded to P fer-
tilization in almost all cases tested, and P fertiliza-
tion at planting is generally recommended. An
exception is made when subsoil pH is near neutral
or higher. Under those conditions, the potential for
long-term response is questionable, and P fertiliza-
tion at planting is not recommended without further
knowledge of soil P status from soil analyses.
Trees on soil Groups D, E, F, and G have
responded to P fertilization so infrequently that no
P is recommended on those soils at present.
On Group C soils, slash pines have responded to
P fertilization at individual sites, but the soil group
alone has not been sufficient to predict respon-

siveness. In these cases, soil fertility testing pro-
vides information useful in identifying potentially
responsive sites. The soil must be sampled at three
depths -- 0 to 20, 20 to 40, and 40 to 60 cm -- to
provide the needed information. If Mehlich-1
extractable P is less than 6 to 8 ppm in the surface
20 cm of soil and less than 2 ppm in both the 20 to
40 and the 40 to 60 cm layers, the plantation
should respond to P fertilization. The IFAS Exten-
sion Soil Testing Laboratory provides the necessary
soil test. Information and forms are available
through county Extension offices.
Slash pines are unlikely to respond to P
fertilization on any soils which have been planted
to row crops in the past. Residual P is usually
sufficient for pines so P fertilization is not needed.
Results of long-term experiments are presented
graphically in Figure 1. The figure shows that pine
response to phosphorus is well related to the CRIFF
soil groups.

2. Which nutrients give responses?
Phosphorus provides the growth response most
often recorded in recently planted pines. In very
P-deficient areas, P fertilization is essential in
order to obtain a commercial stand. When nitrogen
(N) and P are used together, N sometimes produces
an additional growth response. In newly planted
stands, N and P together are not recommended
because the N may stimulate competing vegetation
growth to the detriment of the pine. After age
one, N and P in combination occasionally show good
growth response, but we currently cannot identify
accurately those sites where such responses may
occur. Nitrogen alone is not usually beneficial in
young slash pine plantations.
Responses to other elements have been recorded
across a range of Coastal Plain soils, but those

Table 2. Summary of recommendations for fertilizing young pine plantations ( <5 to 8 years old).


Sites to fertilize

Nutrients to apply

Amounts of nutrients

Sources of nutrients
Fertilizer placement

1. CRIFF soil groups A and B, except sites where subsoil pH is near neutral or higher.
2. CRIFF soil group C only where top 20 cm of soil tests less than 6 to 8 ppm Mehlich-1 P
and both subsurface layers (20 to 40 and 40 to 60 cm) test less than 2 ppm Mehlich-1 P.
3. Do not fertilize CRIFF soil groups, D, E, F, or G.

P alone, or P plus N.

60 kg P/ha; or 60 kg P/ha plus 45 to 55 kg N/ha; (120 Ib P205lacre; or 120 Ib P20s plus 50
Ib N/acre).
Any sources acceptable. Base choice on cost of fertilizer plus application.
Broadcast, band, or spot.


--r -

75 ft3/acre/yr
5 6 m /hectare/yr

Wood Volume Increase Over Control

Figure 1. This graph presents the results of long-term slash pine
fertilization experiments which were fertilized with 90 kg P/ha
(180 Ib P205/acre) at the time of planting. Eight years after
planting, the wood yield of the fertilized and unfertilized plots
were compared on each of the soil groups. The vertical line is
the average for each soil group, the box shows the standard error,
and the horizontal line shows the range of responses measured
at the various sites where the experiment was conducted. For
example, on Group B soils, fertilized pines produced an average
of 1.7 m3/ha/yr (24 cu ft/acre) of wood more than the unfertil-
ized trees. However, the response ranged from practically zero
increase at one location to 4.7 m3/ha/yr (68 cu ft/acre/yr) at
another location. The standard error is used as a statistical
estimate of the probability of response. In this example, 2/3 of
Group B soils would be expected to give a response of 1.2 to
2.3 m3 of wood/ha/yr (17 to 33 cu ft/acre/yr) to P fertilization
(data from Kushla and Fisher, 1980).



Volume 3000-

1500- -100

ft3/acre m3/ha





0 20 80

Pounds P205


per acre

Fertilization Rate

Figure 2. This graph shows the effect of phosphorus fertilization on soils of Groups A, B, and D. Different rates of phosphorus were applied
at planting and the wood yields were measured 17 to 20 years later. It may be appreciated that pines on Group A soils responded much
more dramatically to P fertilization than did pines grown on Group D soils (data from Pritchett and Comerford, 1982).



responses have been too inconsistent to support
recommendations at this time.

3. What fertilizer rates and sources should be used?
The recommended rate of P is 50 to 60 kg P/ha
(100 to 120 lb P2zO/acre). However, on highly
deficient Group A and some Group B soils, as little
as 20 to 30 kg P/ha (40 to 60 lb P205/acre)
produces a large growth response that lasts for the
entire 20- to 25-year rotation. Figure 2 illustrates
the wood volume responses to P fertilization for a
range of soils.
The long-term response of pines to phosphorus is
not dependent on the phosphorus source. Ground
rock phosphate is equal in effectiveness to soluble
sources such as super phosphate or ammonium
phosphate. Thus, the choice of P source is gen-
erally based on cost and application considerations.
(To obtain a 50 kg P/ha rate apply 220 pounds of
0-46-0, 220 pounds of 18-46-0, or 320 pounds rock
phosphate per acre.)
The recommended rate of N is 45 to 55 kg N/ha
(40 to 50 lb N/acre). The recommendation is based
on the observation that young plantations do not
have the ability to utilize a large quantity of N.
Diammonium phosphate (18-46-0) is the most fre-
quently used N source in young stands because it
is a convenient form in which to apply the recom-
mended rates of both N and P (i.e., 220 lb 18-46-
0/acre gives 40 Ib N and 100 lb P205/acre).

-25 0 25 50
-2 -1 0 2 3 4
-2 -1 0 1 2 3 4


r r

Surface soil
< 6 to 8 ppm P
neither subsurface
soil layer
> 2 ppm P

Figure 3. Decision scheme for fertilizing young slash pine plantations.

4. Where should fertilizers be placed?
It appears that spot placement, banding, or
broadcasting of fertilizers have approximately the
same effect on yield at the end of a rotation. This
has been the result both for P and for P plus N
Figure 3 is a decision key for young pine fertil-
ization. Table 2 contains other summary informa-

Mid- to Late-Rotation Fertilization

The second period in stand development in which
to fertilize pine plantations is after the stand has
become established and dominates the site. This
typically occurs in southern pines between 8 and 15
years of age. An obvious advantage of this later

fertilization is the reduced time between the pur-
chase and application of the fertilizer and the
harvest. The CRIFF recommendations for fertiliza-
tion of established stands are discussed below and
summarized in Table 3.

1. What sites should be fertilized?
Slash pines respond to mid-rotation fertilization
on all except Group G soils. Water is the limiting
factor in Group G soils, and fertilization of pines
growing on them is never recommended. On the
other soils, the probability of a large volume re-
sponse to fertilization is high on soils of Groups A,
B, C, and D and moderate on soils of Groups E and
F (Figure 4).
Phosphorus alone is the recommended treatment
on soil Group A when the trees have not been
fertilized with P earlier in the rotation. Nitrogen
should not be used alone under these circumstances.
Nitrogen should be included when re-fertilizing A
Group soils previously treated with P.


-25 0 25 50 75 100 125 ft3/acre/yr
-2 -1 0 1 2 3 4 5 6 7 8 9 10 m3/hectare/yr
Wood Volume Increase Over Control

Figure 4. This graph presents the responses of slash pine to fertiliza-
tion at mid-rotation with 225 kg N and 55 kg P/ha (200 Ib N
and 110 Ib P205/acre). The graph is set up like Figure 1. Please
read that caption for an explanation of the symbols (data from
Kushla and Fisher, 1980).

Table 3. Summary of recommendations for fertilizing mid-rotation pine plantations (older than 5 to 8 years).


Sites to fertilize
and nutrients to use

Amounts of nutrients

Sources of nutrients

1. Do not fertilize excessively drained sands (soil Group G).
2. Fertilize soil Group A with P. Do not fertilize with N alone. (If these soils were
fertilized at planting with P, then fertilize with N and P.)
3. Fertilize soil Group B with N and P. Do not use N alone.
4. If foliar N:P ratio is >14.5:1, fertilize soil Groups C, D, E, and F with N plus P. Do not
fertilize with N alone.
5. If foliar N:P ratio is <14.5:1, fertilize soil Groups C, D, E, and F with N alone or with
N plus P.

170 to 225 kg N/ha; or 170 to 225 kg N/ha plus 50 to 60 kg P/ha. (150 to 200 Ib N/acre; or 150
to 200 Ib N plus 100 to 120 Ib P20s/acre).

Any source acceptable. Base choice on cost of applied nutrient/ha.

Near neutral pH lower
or higher, than about
e.g., > 6.5 6.5

Surface soil
> 6 to 8 ppm P
at least one
layer > 2 ppm P




CRIFF kg P/ha (100 to 120 lb P205/acre) is optimum.
Soil Group? A summary of CRIFF mid-rotation fertilization
recommendations is provided in Table 3. The
S. Cr i decision scheme is presented graphically in Figure 5.
Group Group Groups Group
A B C, D, E, &F G
FERTILIZE DO NOT ratio in Fisher, R.F. and W.L.Pritchett. 1982. Slash pine growth
WITH N FERTILIZE foliage? response to different nitrogen fertilizers. Soil Sci. Soc. Am.
ALONE. WITH N J. 46:133-136.
i I Kushla, J.D. and R.F. Fisher. 1980. Predicting slash pine
> N' P 1 N response to nitrogen and phosphorus fertilization. Soil Sci.
> 14-.5: 1 <45 1 Soc. Am. J. 44:1301-1306.
WITH N PLUS WITH N Munson, K.R. 1984. Forest soils of Florida: Useful groupings for
P. DO NOT ALONE OR forestry purposes. Ext. Fact Sheet FRC-33, IFAS, Univ. of
ALONE. Pritchett, W.L. and N.B. Comerford. 1982. Long-term response to
Figure 5. Decision scheme for fertilizing slash pine at mid- to late- phosphorus fertilization onselected southeastern Coastal
rotation.Plain soils. Soil Sci. Sc. Am. 46:640-644

Pines growing on Group B soils respond best to
N plus P. Group B soils should not be fertilized
with N alone.
Nitrogen and phosphorus fertilization is recom-
mended for slash pines on Groups C, D, E, and F
because of the magnitude and longevity of tree
volume response. However, a portion of these sites
can show significant responses to N alone, allowing
for savings in P fertilizer cost. Foliar analysis of
the trees prior to mid-rotation fertilization is used
to distinguish the sites where N alone gives a
volume response greater than 1.2 m3/ha/yr (18
ft3/acre/yr). An N:P ratio greater than 14.5:1
signals the need for both N and P fertilization,
while a ratio less than 14.5:1 indicates that the
pines will respond to N fertilization alone. Where
N alone can be used, the volume growth will gener-
ally be smaller and shorter-lived. Figure 5 repre-
sents the decision scheme for fertilization of slash
pines at mid-rotation.

2. What fertilizer rates and sources should be used?
Two sets of long-term N rate tests have been
conducted by CRIFF. Interpretation of the data
resulted in a fertilization recommendation of 170 to
225 kg N/ha (150 to 200 lb N/acre). Fisher and
Pritchett (1982) found that there was no difference
in N sources. Thus, cost of material and applica-
tion are the concerns in choosing N sources.
The phosphorus rate to use in established stands
has been inferred from the previously discussed re-

search on young pine and from examination of four
mid-rotation studies employing multiple P rates.
That work suggested that an application of 50 to 60

This publication was produced at a cost of $548.99, or 42.0 cents per copy, to make available to the public current
IFAS fertilization recommendations for slash pine. 7-1.3M-87

director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and
June 30, 1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institu-
tions that-function without regard to race, color, sex or national origin. Single copies of Extension publications (excluding 4-H and Youth publica- RTYOF FLORIDA
tions) are available free to Florida residents from County Extension Offices. Information on bulk rates or copies for out-of-state purchasers is 1
available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing this publication,
editors should contact this address to determine availability.


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