• TABLE OF CONTENTS
HIDE
 Front Cover
 Title Page
 Table of Contents
 Introduction
 The coastal plain region
 Coastal plain soil groups for purposes...
 Differences in fertilizer needs...
 Diagnostic techniques
 Nutrients, sources, methods, and...
 Additional considerations for established...
 Fertilizer recommendations
 Some economic aspects of forest...
 Fertilizers for forest soils
 Back Cover
 Historic note






Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; 774
Title: Fertilizer recommendations for pines in the southeastern Coastal Plain of the United States
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027424/00001
 Material Information
Title: Fertilizer recommendations for pines in the southeastern Coastal Plain of the United States
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 23 p. : ill. ; 23 cm.
Language: English
Creator: Pritchett, William L
Gooding, J. W
Publisher: Agricultural Experiment Stations, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1975
 Subjects
Subject: Pine -- Fertilizers -- Southern States   ( lcsh )
Pine -- Soils -- Southern States   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: W.L. Pritchett and J.W. Gooding.
General Note: Cover title.
 Record Information
Bibliographic ID: UF00027424
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 001596998
oclc - 02692269
notis - AHM1128

Table of Contents
    Front Cover
        Page i
        Page ii
    Title Page
        Page iii
    Table of Contents
        Page iv
    Introduction
        Page 1
    The coastal plain region
        Page 2
    Coastal plain soil groups for purposes of forest fertilization
        Page 3
        Page 4
        Page 5
    Differences in fertilizer needs due to stand age
        Page 6
        Page 7
    Diagnostic techniques
        Page 8
    Nutrients, sources, methods, and timing of applications
        Page 8
        Page 9
        Page 10
    Additional considerations for established stands
        Page 11
    Fertilizer recommendations
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
    Some economic aspects of forest fertilization
        Page 19
        Page 20
    Fertilizers for forest soils
        Page 21
        Page 22
        Page 23
    Back Cover
        Page 24
    Historic note
        Page 25
Full Text
Bulletin 774


Fertilizer Recommendations for Pines

in the Southeastern Coastal Plain

of the United States

W. L. PRITCHETT AND J. W. GOODING


Agricultural Experiment Stations, Institute of Food and Agricultural Sciences
University of Florida, Gainesville, J.W. Sites, Dean for Research
MIMI EmllElh MelbMMI I% -A


June 1975























































Cover: Representative soils of three drainage classes: (la) Bladen and
(1b) Plummer soils are poorly to very poorly drained; (2a) Mas-
cotte and (2b) Albany represent somewhat poorly drained soils
of the flatwoods; and (3a) Red Bay and (3b) Bonifay are well-
drained soils. Soils designated (a) have fine textured materials
near the surface, and soils marked (b) have fine textured ma-
terials at considerable depths in the profile.










FERTILIZER RECOMMENDATIONS FOR PINES
IN THE SOUTHEASTERN COASTAL PLAIN
OF THE UNITED STATES

W. L. PRITCHETT AND J. W. GOODING
Dr. Pritchett is a Professor of Forest Soils in the Soil Science
Department and Mr. Gooding is an Assistant in Forest Soils School
of Forest Resources and Conservation, University of Florida.


This public document was promulgated at an annual cost
of $1,115.63, or a cost of 55 per copy to give fertilizer
recommendations for pine forests in the southeast.







CONTENTS


Introduction ..-..... ..-..........-...------------------ 1


The Coastal Plain Region .----.........-.........---- ...------------- 2

Coastal Plain Soil Groups for Purposes of Forest Fertilization 3

Very Poorly to Poorly Drained Soils (Bays and Savannas) 4

Poorly to Somewhat Poorly Drained Soils (Flatwoods) .... 4
Moderately Well to Well Drained Soils (Sands to loamy
sand-clay hills) ..---.......-..........------------------- 5
Excessively Drained Sands (Sandhills) .-...............------.-----. 6

Differences in Fertilizer Needs Due to Stand Age .---......-......- 6


Diagnostic Techniques ....--................-------------------- 8

Nutrients, Sources, Methods, and Timing of Applications -..... 8
Phosphorus -....----..--..-.------------------------..... 8
Nitrogen ........-------------.......-------------10
Potassium and Other Essential Elements .--.................--..-10


Additional Considerations for Established Stands .....---......... 11

Fertilizer Recommendations .....................-----------------12
Very Poorly to Poorly Drained Soils ..................-------.---..-.12
Poorly to Somewhat Poorly Drained Soils ..............--------.. 16
Moderately Well to Well Drained Soils ......................--------17

Some Economic Aspects of Forest Fertilization .........--....---- 19


Appendix ------....... -------- ---------..----- 21







INTRODUCTION


In the last 20 years there has been a major trend toward grow-
ing southern pines, particularly slash (Pinus elliottii var. elliottii
Engelm.) and loblolly (Pinus taeda L.) in even-aged planted
stands. Advances in forest management technology in the Coastal
Plain of the southeastern United States have made successful re-
forestation much more certain through a sequence of practices
which include clearcutting existing timber; preparing and bed-
ding the site with heavy equipment; planting genetically im-
proved seedlings; and fertilizing to increase tree growth rates.
This trend was triggered by the need to shorten the turn-
around time between harvest and stand reestablishment and to
take advantage of the availability of genetically improved plant-
ing stock to increase forest productivity on land which is be-
coming increasingly expensive to own and manage. Rapidly
increasing demands for southern pine as raw material for the
manufacture of pulp, paper, construction lumber, and plywood
have been a parallel factor in stimulating the adoption of these
high-production systems.
Southeastern Coastal Plain conditions are almost ideal for
intensive forest management. The flat, sandy terrain and large-
block ownerships made it feasible to mechanize forest operations.
Long growing seasons and high' levels of biological activity result
in rapid growth rates and relatively short pine crop rotations.
Short rotations, in turn, make for short payout periods on capi-
tal invested in management practices.
The operational use of fertilizers in forests as a production
factor is a recent development. In many instances, soils used for
forestry are not capable of supplying sufficient nutrients to sus-
tain rapid tree growth since the generally sandy soils of the
region are inherently infertile. This has been demonstrated by
research results from more than 225 field experiments1 which
indicate that significant growth gains from fertilizer applications
can be expected on approximately two-thirds of the locations
tested. These research results have also stimulated the operational


1 Experiments were conducted in the Cooperative Research in Forest Fer-
tilization (CRIFF) program. The cooperation, both financial and materi-
al, from the following forest industries is gratefully acknowledged: Bruns-
wick Pulpland Company; The Buckeye Cellulose Corporation; Container
Corporation of America; Continental Can Company, Inc.; Georgia-Pacific
Corporation; Hudson Pulp & Paper Corporation; International Paper Com-
pany; ITT Rayonier Inc.; Owens-Illinois; Scott Paper Company; St. Joe
Paper Company; St. Regis Paper Company; and the Union Camp Cor-
poration.







fertilization of some 300,000 acres of forest land in the Coastal
Plain prior to 1974.
Operationally, fertilizers have been applied primarily to young
planted stands less than 4 years old. However, about 100,000
acres of 12- to 18-year-old established stands, with slowed or stag-
nant growth rate, were also fertilized. A wide variety of rates
and materials have been used, but nitrogen (N) and phosphorus
(P) were the two fertilizer nutrients most frequently applied.
This publication lists fertilizer recommendations, based on re-
sults of field experiments and operational experience, for im-
proving,growth rate of southern pines in the Coastal Plain of the
southeastern United States. Soil drainage condition, P-retention
capacity, and stand age are the three major factors which can
be used to prescribe the kind and amount of fertilizer needed for
optimum tree growth. The fertilizer recommendations reported
herein are derived primarily from research with slash pine, but
they probably have application for other Southern species. Pine
species is not considered as important as soil condition and stand
age in determining the most effective source and rate of fertilizer
to use in forests. The various species of Southern pine undoubted-
ly differ in their nutrient requirements just as they differ in their
site requirements, but it is likely that these differences are not
large when each species is grown on a site to which it is well
adapted. Many edaphic, climatic, and biotic factors as well as
stand age and stocking will condition the magnitude of response
obtained from applications of fertilizers.

THE COASTAL PLAIN REGION
The Southeastern Coastal Plain forms a belt about 150 miles
wide on the Atlantic seaboard and up to 400 miles wide along the
Gulf coast, and extends from Virginia to Texas. It is a relatively
flat to undulating area, varying from sea level to a few hundred
feet in elevation. There are many inland plateaus and extensive
areas of broad swampy flats near the sea. Of the approximately
161 million acres in the Southeastern Atlantic and Gulf Coastal
Plain, about 63% are in the rolling to strongly hilly topography
of the upper Coastal Plain, while the remaining 37% (60 million
acres) occupies the coastal lowlands or lower Coastal Plain -
sometimes called the coastal flatwoods.
The upper Coastal Plain is nearly all in farms, with one-half
to three-fourths in woodlands, mostly small holdings. Elevation
increases gradually from 50 to 100 feet in the lower Coastal Plain
to 300 to 400 feet in the Georgia-Carolina sand hills and lower
Piedmont. The region is underlain by unconsolidated sands, silts,






and clays. Upper stream valleys are narrow but they develop into
broad, shallow valleys with widely meandering streams in the
nearly level lower Coastal Plain.
The lower Coastal Plain is characterized by flat to undulating
topography, high water table, and generally sandy soil. Much of
the lower Coastal Plain is in large public and industrial holdings
with 70% to 90% in forest. The influence of the sea on tempera-
ture and humidity results in a fairly uniform climate throughout
the area. As a consequence, soil factors play the dominant rdle in
determining forest productivity. For example, small differences in
elevation and depths to a fine-textured (argillic) layer or water
table have considerable effects on soil moisture conditions. Al-
though the soils are generally low in nutrient reserves, soil mois-
ture or drainage conditions probably have a greater influence on
productivity than any other site factor. In fact, most forest site-
quality classification schemes are based on some expression of soil
or site drainage characteristics, depth to a subsoil horizon, or
other factors influencing effective rooting depth of trees. The
height to which the water table rises and the length of time that
it remains at that level largely determine the volume of soil
available for tree root exploitation. The presence of fine-textured
material near the surface increases not only the water-holding
capacity of sandy soils, but also their capacity to retain phos-
phate fertilizers. These soil properties appear to affect not only
tree growth rate, but also the increase in growth obtained from
fertilizer applications.



COASTAL PLAIN SOIL GROUPS FOR PURPOSES
OF FOREST FERTILIZATION

Grouping of soil series according to properties that in-
fluence the kinds and amounts of fertilizers usually needed for
forestry purposes appears highly desirable. Soil drainage is one
factor that can be determined in the field after minimal experi-
ence and appears to be a useful tool for stratifying forest land
for fertilization purposes. Stratification can also be based on soil
P-retention capacity. Although P-retention capacity cannot be
accurately estimated in the field, it can be determined on soil
samples in the laboratory, permitting soils to be grouped by P-
retention capacity within drainage classes. The following discus-
sion of drainage classes, along with a listing of typical soil series
found in each of the groups, should aid in delineation of land
areas with similar drainage and P-retention characteristics.







VERY POORLY TO POORLY DRAINED SOILS (Bays and savannas)
These soils are found mostly in coastal flat lands in nearly level
depressions and stream terraces. Wiregrass (Aristida stricta),
pitcher plants (Sarracenia minor), some hardwoods, and a fair
to poor growth of pine occur natively on these poorly to very
poorly drained soils of the coastal flats, sometimes called wet
savannas. In most instances, pine growth is slowed by excessive
moisture and lack of soil available P. Most of these soils are
flooded from 5 to 30 days, one or more times during the growing
season, with the water table ranging from 6 to 20 inches below
the soil surface much of the remaining time. Because they were
formed under impeded drainage,'these soils often contain 10%
or more organic matter in the surface horizon and most are ex-
tremely acid and low in nutrient reserves. These very poorly-to
poorly-drained soils vary greatly in their profile characteristics.
They can be grouped for purposes of fertilizer recommendations
on the basis of depth to and nature of subsoil horizons which also
reflect their P-retention characteristics.
(1) High P-retention-Soils such as those represented by the
Amy, Bayboro, Bladen, Coxville, Elkton, Leaf, Lumbee, Myatt,
Ogeechee, Pansy, Pantego, Pooler, Rains, and Wahee series have
a dark gray to black fine sandy loam surface, with dark brown to
grayish finer-textured material within 20 inches of the surface
and varying degrees of gray mottles reflecting wetness. These wet
soils with clay near the surface generally have a very high capaci-
ty to fix P in a form only slowly available to trees. The use of
ground rock phosphate (GRP) or band placement of soluble
phosphates, such as concentrated superphosphate (CSP), is
recommended for increased fertilizer effectiveness. (See photo
la, back cover.)

(2) Moderate P-retention-A second group of very poorly-
drained soils contain fine-textured horizons deeper than the sur-
face 20 inches, but because of their relatively high organic matter
content, they have a moderate capacity to retain P. Either ordi-
nary or slowly-soluble phosphates can be used successfully on
these soils. Typical series are Ellabelle, Pelham, Plummer, Ports-
mouth, Rutledge, Surrency, and Torhunta. (See photo Ib, back
cover.)

POORLY TO SOMEWHAT POORLY DRAINED SOILS (Flatwoods)
The flatwoods comprise one of the most extensive groups of
forest soils in the Coastal Plain. These acid sands to loamy sands







are low in fertility and support such native cover as saw palmetto
(Serenoa repens), gallberry (Ilex glabra), runner oak (Quercus
falcata), and wiregrass (Aristida stricta), as well as slash, lob-
lolly, and longleaf pines (Pinus palustris Mill.). Slash pine is
particularly adapted to most flatwood sites, but good growth may
not result without improving the nutrient status of the soils. Flat-
wood soils occupy nearly level to gently sloping flat areas where
the water table rises to within 5 to 20 inches of the soil surface
for from 1 to 4 days, one or more times each growing season.
Their generally sandy surface horizons range in color from gray
to dark gray and often overlay a bed of leached grayish to white
sand. The flatwood soils can be conveniently grouped into soils
with and without organic pans.

(1) Low P-retention capacity (Spodosols) -Characteristically,
many flatwood soils contain a weakly cemented organic hardpan
that is dark brown to black and occurs from 12 to 40 inches be-
low the surface. This "spodic" horizon may become rather hard
when dry, but apparently does not greatly impede tree root de-
velopment. Typical series of the organic hardpan soils include
Immokalee, Leon, Lynn Haven, Mascotte, Ona, Olustee, and
Ridgeland. Flatwood soils with organic hardpans deeper than 16
inches have little capacity to retain P in the soil surface due to
their low aluminum (Al) and iron (Fe) content (<40 ppm ex-
tractable Al and Fe). For this reason, the use of GRP is recom-
mended for long-term effectiveness. (See photo 2a, back cover.)

(2) Moderate P-retention capacity-Other poorly to somewhat
poorly drained soils often classed as flatwoods, but without a
"spodic" horizon, include the Albany, Ardilla, Dunbar, Leefield,
Lenior, Lynchburg, Ocilla, Scranton, and Tetotum series. Most
of the soils have fine-textured horizons within 20 to 80 inches
of the surface. Unlike the flatwood-hardpan soils, these soils have
moderate capacity to retain P. Either ordinary or slowly-soluble
phosphate sources can be successfully used on these soils. (See
photo 2b, front cover.)

MODERATELY WELL TO WELL DRAINED SOILS (Sands to loamy
sand-clay hills)
These soils range from relatively deep, moderately well-drained
sands to the well-drained loamy sands and sand-clay hills. Typi-
cally, the former sands occupy nearly level to rolling regions of
the lower Coastal Plains. They have gray to brown surface layers
overlaying 30 inches or more of grayish- to yellowish-brown







sands. These sands, which include the Blanton, Bonifay, Chipley,
Troup, and Wagram series, have a low capacity to retain water,
but they have reasonable good moisture relations because of their
topographic position, and they are generally considered good for-
est soils. (See photo 3b, front cover.) Often they are used for
pastures, field crops, and vegetables even though they are in-
herently low in nutrients and fertilizers must be used to obtain
good yields of those crops.
Moderately well- and well-drained sand-clay hill sites normally
contain red to yellow fine-textured subsoils within 30 inches of
the surface, such as found in the Angie, Cahaba, Carnegie, Claren-
don, Dothan, Faceville, Fuquay, Gilead, Goldsboro, Kalmia, Ke-
nansville, Lucy, Marlboro, McLaurin, Norfolk, Orangeburg, Rus-
ton, Stilson, and Tifton series. (See photo 3a, front cover.) Sur-
face horizons are generally loamy sands to sandy loams; because
of their relatively high content of clay material, they have a good
capacity to retain moisture and nutrients and are excellent lob-
lolly pine sites. They are also good agricultural soils, and most
existing stands in the area are on abandoned farm land, much of
which had been severely eroded.

EXCESSIVELY DRAINED SANDS (Sandhills)
Rather extensive areas of these deep sands are in pines in
north Florida, Georgia, and the Carolina sandhills. Longleaf pine,
turkey (Quercus laevis) and bluejack (Q. incana) oaks, and wire-
grass are dominant native species. Extensive areas of slash pine
have been planted in the sandhills, but sand pine (Pinus clausa
Chapm.) and longleaf pine are recommended for use in reforesta-
tion. Soils such as those of the Alaga, Alpin, Eustis, Kershaw,
Lakeland, and Paola series are deep, coarse-textured, low in nu-
trients, and drought. Water deficits generally limit responses
to fertilizers even on the most nutrient-deficient sites. Fertilizers
are not generally recommended for pine plantations in the sand-
hills due to site moisture limitations. However, 150-200 Ib DAP/
acre (banded) may be successfully used on young sand pine,
while urea is sometimes recommended for older stands of sand
pine on excessively drained sands.

DIFFERENCES IN FERTILIZER NEEDS DUE
TO STAND AGE
Nutrient requirements differ between young (1- to 3-year-old)
trees and older (12- to 16-year-old) established stands because
there are changes in nutrient requirements as well as soil nutrient







reserves as the forest stand develops. Many of the infertile sands
of the Coastal Plain cannot supply the relatively small amounts
of nutrients required for good sustained tree growth. This condi-
tion may have been aggravated by recent management innovations,
such as intensive site preparation and use of faster-growing trees,
which places greater demands upon the nutrient supply of the
soil. This may be particularly true of the lower Coastal Plain
where most young plantings are on intensively prepared sites.

Mixing of the soil during site preparation speeds up decomposi-
tion of debris and soil organic matter and the release of nutrients
they contain. Bedding operations further concentrate these or-
ganic materials in ridges and increase the accessibility of released
nutrients to the young trees. The accelerated release of nutrients
from such operations may improve tree growth for several years
on sites containing large amounts of litter and soil organic mat-
ter. However, on sandy soils, some of the released nutrients may
be lost by leaching before the native vegetation and seedlings
develop sufficient roots for effective nutrient absorption. Such
losses may increase the need for fertilizers during the latter part
of the rotation period.

It is often more difficult to predict the need for fertilizers in
older stands of Southern pine than in young plantations. Older
trees have deeper root systems than most annual plants. Given
time, deep penetration may allow roots to absorb nutrients from
subsoil horizons even though surface horizons are low in available
nutrients. Surface layers of organic debris developed under es-
tablished stands serve as a nutrient reservoir, releasing nutrients
as the material slowly decomposes. For example, an acre of trees
may absorb almost as much nutrients annually as an agricultural
crop. Only a small percentage, usually only 1 to 10 pounds of
each nutrient per acre, is retained for stem wood and bark pro-
duction. The remainder of the nutrients are recycled in leaf and
litter fall. A protected forest approaches an equilibrium with the
input of nutrients from the atmosphere, weathering of soil min-
erals, and biological-N fixation almost equaling the amount of
nutrients lost from the system by leaching, fires, and harvest.
The amount of nutrients removed in a 40-cord per acre pulpwood
harvest of slash pine is about 150, 12, and 65 pounds per acre
of N, P, and K, respectively. However, the nutrient release rate
from biomass decomposition may be inadequate for a stand's
needs. Accumulation of N in the forest floor is thought to be the
primary cause of N deficiencies often found in established stand
-particularly in cool climates.







DIAGNOSTIC TECHNIQUES
In severely deficient areas, poor sites (site quality less than
50) where moisture is not limiting such as the wet savannas and
flatwoods, fertilizers will need to be used to obtain merchantable
stands with short rotations (20 to 25 years). On better sites (site
quality 50 to 80) soil and tissue analyses are of considerable
value in locating deficient areas and determining what nutrients
are needed. Table 1 contains the currently accepted macronutri-
ent "critical levels" for slash pine in the Coastal Plain.
While soil and foliage chemical tests can be useful tools for
determining current nutrient status, they are not infallible and
should be used along with other site information from newly
planted or established stands for deciding where fertilizers can
best be used. Soil maps giving soil profile and drainage charac-
teristics are also helpful in delineating areas where fertilizer
response is likely. When one or more of these guides indicate
that fertilization will likely result in an economic response, the
fertilizer source, rate, and application method should be pre-
scribed according to soil drainage conditions, P-retention charac-
teristics, and profile properties.

Table 1. Approximate critical' soil and foliar nutrient ranges for slash
pine in the Coastal Plain.
Element Soil2 Foliage3
NHOAc(pH 4.8) HCI+HSO,

N 0.8 -1.0%
P 1.5 2.0 ppm 4.0 6.0 ppm 0.08 0.09%
K <10 ppm <10 ppm 0.25-0.30%


1. Nutrient determinations found to be lower than the ranges provided would
indicate that trees are growing at less than 90 percent of their maximum
potential.
2. Soil samples consist of a composite of 12 to 15 surface (0- to 8-inch)
samples.
3. Foliage samples consist of a composite collected from at least 10 domi-
nant or codominant trees.

NUTRIENTS, SOURCES, METHODS, AND
TIMING OF APPLICATIONS

PHOSPHORUS

Phosphorus is the nutrient most frequently deficient in coastal
plain soils, particularly in young stands. Phosphorous applica-







DIAGNOSTIC TECHNIQUES
In severely deficient areas, poor sites (site quality less than
50) where moisture is not limiting such as the wet savannas and
flatwoods, fertilizers will need to be used to obtain merchantable
stands with short rotations (20 to 25 years). On better sites (site
quality 50 to 80) soil and tissue analyses are of considerable
value in locating deficient areas and determining what nutrients
are needed. Table 1 contains the currently accepted macronutri-
ent "critical levels" for slash pine in the Coastal Plain.
While soil and foliage chemical tests can be useful tools for
determining current nutrient status, they are not infallible and
should be used along with other site information from newly
planted or established stands for deciding where fertilizers can
best be used. Soil maps giving soil profile and drainage charac-
teristics are also helpful in delineating areas where fertilizer
response is likely. When one or more of these guides indicate
that fertilization will likely result in an economic response, the
fertilizer source, rate, and application method should be pre-
scribed according to soil drainage conditions, P-retention charac-
teristics, and profile properties.

Table 1. Approximate critical' soil and foliar nutrient ranges for slash
pine in the Coastal Plain.
Element Soil2 Foliage3
NHOAc(pH 4.8) HCI+HSO,

N 0.8 -1.0%
P 1.5 2.0 ppm 4.0 6.0 ppm 0.08 0.09%
K <10 ppm <10 ppm 0.25-0.30%


1. Nutrient determinations found to be lower than the ranges provided would
indicate that trees are growing at less than 90 percent of their maximum
potential.
2. Soil samples consist of a composite of 12 to 15 surface (0- to 8-inch)
samples.
3. Foliage samples consist of a composite collected from at least 10 domi-
nant or codominant trees.

NUTRIENTS, SOURCES, METHODS, AND
TIMING OF APPLICATIONS

PHOSPHORUS

Phosphorus is the nutrient most frequently deficient in coastal
plain soils, particularly in young stands. Phosphorous applica-






tions are generally recommended near time of planting on defici-
ent sites because an adequate supply of this element is essential
for the development of vigorous root systems in young trees.
Furthermore, the effect of a P application may last for an entire
forest rotation. Although most Coastal Plain sands are low in P,
significant increases in tree growth have resulted from applica-
tions on only about two-thirds of the sites included in fertilizer
trials. Responses to phosphate fertilizers are influenced by such
factors as intensity of site preparation, available soil moisture,
level of native soil P, soil P-retention capacity, and the amount
and solubility of applied phosphate fertilizer.
The effect of soluble phosphate fertilizers is long lasting in
most soils; however, there are two broad groups of soils in the
Coastal Plain where this may not be true. One group is the ex-
tensive coastal areas of flat, wet savanna soils with fairly high
clay content near the surface. The active aluminum and iron in
these soils have a capacity to fix large amounts of P. For these
soils, slowly-soluble forms of P, such as GRP, or basic slag are
generally recommended. Minimizing soil contact by localized
placement of the fertilizer will increase availability to plants.
This is particularly important if soluble forms of P, such as CSP
or diammonium phosphate (DAP), are used. The other group of
soils where the effect of phosphates may be short-lived is the acid


(.)1 YI.


Figure 1. Severely phosphorus deficient slash pine on a wet savanna
soil. (Age 12 years.)







flatwood Spodosols. These constitute one of the most extensive
soil areas of the lower Coastal Plain, and many soils contain too
little Al and Fe to effectively retain P in the surface layers.
Ground rock phosphate is generally recommended for soils with
very low P-fixing capacity, as well as for soils with very high
fixing capacity. Soluble phosphates are normally recommended
for other deficient soils, such as well-drained sands and soils
containing a moderate level of Al and Fe. A soil chemical test
which indicates Al and Fe concentrations in the soil is especially
helpful in choosing the most effective P source and method of
application.



NITROGEN

Deficiencies of N most frequently occur in older stands, espe-
cially on flatwood soils and old agricultural lands. A gradual re-
duction in available N apparently results from its immobilization
in the forest biomass.
In young stands, additions of N with the P fertilizer often
results in additional growth increment. Where both N and P are
needed early in the rotation, they may be applied together to re-
duce spreading cost. However, if separate operations are re-
quired, it is best to delay the N application for 2 to 3 years,
thereby reducing possible leaching losses and discouraging ex-
cessive weed competition. Since most N fertilizers are highly
soluble, they may reduce survival when applied to young stands,
particularly on sandy soils and during dry periods. Excessive
weed growth resulting from N applications also may be detri-
mental to the survival and growth of pine seedlings. Urea is the
source of N generally recommended as most effective, but any
ammoniacal source should prove satisfactory. Nitrate sources are
not generally recommended for forest ecosystems.



POTASSIUM AND OTHER ESSENTIAL ELEMENTS

Levels of potassium (K) and micronutrients are generally low
in Coastal Plain soils, but growth responses are seldom obtained
from the application of these nutrients to pine plantations. If a
deficiency of K is suspected, on the basis of soil or foliar tests,
an application of 50 to 100 lb K/acre can be supplied separately
as KC1 or in a mixed fertilizer such as 20-20-20.







ADDITIONAL CONSIDERATIONS FOR
ESTABLISHED STANDS

Although growth in many stands declines as trees approach
middle age, it is not always possible to revive normal growth
rates with fertilizers. Growth stagnation may result from over-
stocking and adverse site conditions other than insufficient nu-
trients; for example, lack of available soil moisture, poor drain-
age, or some other factor limiting the depth of rooting.
Because many biological factors may influence the effectiveness
of fertilizers in older stands, the following should be considered
in developing an established stand fertilization program:
(1) Age-Stand age appears to influence the degree of growth
response obtained. Planted pine in the 12- to 16-year-old bracket
often respond to fertilizers with greater relative growth and
actual volume increase than younger trees. Normally N should
be applied no later in the rotation than five years before cutting,
in order to obtain a reasonable benefit from the fertilizer.
(2) Site-Preliminary indications are that yield increases from
fertilization in stands having a site-ratio (average dominant tree
height/stand age) greater than 3.0 will be less than 0.2 cords/
acre per year.
(3) Stocking-Stand density should be adequate to utilize ef-
fectively the added nutrients. A density of 60 to 90 square feet
of basal area per acre for a 12- to 16-year-old stand is probably
needed to obtain a good return from the fertilizer investment. At
this time, it does not appear advisable to fertilize over-stocked
(more than 120 sq ft per acre) stands of slash pine.
(4) Stand-fertilizer interactions-On sites with adequate mois-
ture, response can often be obtained from an application of N and
sometimes P alone. However, with many stand conditions, re-
sponse magnitude is often greatest if the two materials are ap-
plied in combination. Indications are that applications of N to
poor stands-stands with many stems per acre but small in
diameter-will result in the largest fertilizer response magnitude
provided the poor stand condition was not due to acute P de-
ficiency. In poor stands with the number of stems exceeding 500
per acre more than 50 pounds P/acre may be necessary to assure
maximum response from application of fertilizer containing both
N and P.
(5) Fusiform rust-The effect of fertilization on rust incidence
is not yet clear. However, it is questionable whether a stand with






more than 25-30% stem rust (Cronartium fusiforme) infection
should be fertilized due to the danger of excessive stem breakage
from the added crown weight resulting from treatment.
(6) Fire-Forest stands with a vigorous understory should be
controlled burned prior to fertilization in order to reduce nu-
trient immobilization in the litter and by understory vegetation.
Following fertilization, fire should probably be excluded for at
least a year, unless excessive competition appears to be limiting
tree response to fertilization.
(7) Timing-Although applications of fertilizers to established
forest stands in the Coastal Plain can be made at any convenient
time of the year, they are probably somewhat more effective
when applied in early to late spring.
(8) Application methods-While one generally has a choice of
using either ground or aerial equipment in fertilizing young
stands, this choice is not always available in fertilizing older es-
tablished stands, and other areas not easily accessible from the
ground. A more uniform spread may be obtained from helicopter
than from fixed-wing aircraft, but much depends on pilot experi-
ence. Consequently, the choice between helicopters and fixed-
wing aircraft generally depends on the availability of a landing
strip, total application costs, and personal preference.


FERTILIZER RECOMMENDATIONS
There are vast areas of Coastal Plain soils that do not contain
sufficient nutrients for optimum tree growth under intensive
plantation management. Research results indicate that fertilizers
can significantly increase tree growth in many of these areas. All
indications are that the use of fertilizers will increase greatly in
intensively managed forests of the Coastal Plain in the next
decade. The recommendations contained in this publication should
help the forest manager avoid some of the possible pitfalls in-
volved in the widespread use of fertilizers in forests. Recommen-
dations are summarized by soil drainage classes and stand age
in Table 2 and discussed in the following sections.

VERY POORLY TO POORLY DRAINED SOILS (Bays and savannas)
These wet soils natively have a low site index for pine, but
they may be highly productive if properly managed. Young pines
have responded to fertilizers on more than 90% of the wet sites
tested. Responses were primarily to P and then to N after cor-






reacting the P deficiency. Because of extended periods of flooding,
tree roots are able to exploit only a shallow layer of soil. Bedding
results in marked growth responses, probably because it concen-
trates soil organic matter in the ridges and increases nutrient
availability in the rooting zone and elevates the seedling roots
above the water during rainy periods. Fertilizers, however, can
largely replace the need for this management practice by provid-
ing nutrients normally deficient under high water table conditions,
thereby accelerating tree growth, which will lower the water
table through increased transpiration.
Pine growth generally stagnates at an early age on P-deficient
savannas and frequently on other wet soils. The primary symp-
tom of P-deficiency is very slow growth, often resulting in trees
no more than 40 to 45 feet in height after 25 years. Visual symp-
toms include few branches, short needles, and early abscission of
needles, all resulting in very sparse crowns, as seen in Figure 1.
Soil or tissue tests are usually not needed to identify these de-
ficient areas because plant symptoms are easily recognized. How-
ever, soil tests are useful in determining what P source, rate, and
application method will likely result in the greatest long-term
growth response. For example, soils with low P contents and
high P-fixing capacities (ie., 180 ppm or more of exchangeable
Al and Fe) should be fertilized with slowly-soluble sources of P.
If a soluble P source such as CSP is used on these savanna soils,
it should be applied in bands and incorporated into the bed, if
feasible. Furthermore, soluble P may have to be applied at a
high rate (or in more than one application) for continued growth
response. Trees growing in the wet savannas with the above
symptoms are also often N deficient. However, N fertilizers
should not be applied unless the P deficiency is first corrected.
Fertilizing these soils gives greater return on the investment
than on any other soils in the Coastal Plains. They almost in-
variably respond to P, or P and N, and the following fertilizer
practices are recommended.

Young Stands
1. For wet savanna soils where fine-textured horizons occur
within 20 inches of surface, broadcast 400 to 800 pounds GRP/
acre (56-112 pounds P/acre) prior to bedding. Rock phosphates,
or other slowly soluble phosphates, are generally recommended
because of their resistance to fixation by Al and Fe, which occur
in most of these soils. Pelletized GRP is easier to apply than the
powdered form and should be used when available. Broadcast or









Table 2. Summary of fertilizer recommendations.


Soil drainage
condition


Representative
soil series


Pounds per acre of fertilizer materials1
Young stands2 Established stands3


Very poorly to (1) Bladen, Coxville, 400-800 GRP or cogranular 300-400 GRP+100
poorly drained Rains GRP-urea (at same P rate) -150 urea
(Bays and wet
savannas) (2) Pelham, Plum- 300-400 CSP or DAP 250-300 DAP
mer, Rutlege (banded)


Poorly to some-
what poorly drain-
ed (Flatwoods)


(1) Leon, Mascotte,
Ridgeland
(2) Leefield,
Lynchburg,
Scranton


100-150 urea or
300-400 GRP+100 urea4

100-150 urea or
200-250 DAP4


150-250 urea or
300-400 of 20-20-04


(same as above)


Moderately well Blanton, Bonifay, 150-200 urea or 200-250 urea or
to well drained Norfolk, Stilson 200-300 DAP (banded)4 300-500 of 20-20-04
(Sands to loamy
sand-clay hills)

Excessively Kershaw, 150-200 DAP 200-250 urea
drained (Sand- Lakeland (for sand pine only) (for sand pine only)
hills)
1 See Appendix for description of fertilizer materials, including ground rock phosphate (GRP); diammonium phosphate (DAP); and con-
centrated superphosphate (CSP).
2 Young stands are fertilized near time of planting, or within 2 to 3 years after planting when N is applied alone.
3 Established stands are well stocked, 12- to 16-year-old stands, without excessive stem rust.
4 To be used in stands where P is tested as deficient. Potassium should also be applied (50-100 Ib K/acre) when tested deficient.







banded (4-foot band down the row of trees) applications after
planting are also effective, but because of the slow solubility of
GRP, full response to surface applications are usually not realized
until after 1 or 2 years.
Concentrated superphosphate, or other soluble forms of P, can
be used if GRP is unavailable. In fact, early response has gener-
ally been better to readily-soluble phosphates than to equivalent
rates of slowly-soluble forms. However, the slowly-soluble forms
(GRP) will result in superior growth after 6 to 8 years, due to
less P fixation. Concentrated superphosphates should be applied
at rates of 300 to 400 pounds CSP/acre (60-80 pounds P/acre)
near time of planting. Band or spot placement reduces soil con-
tact and is recommended as a method of reducing fixation of P.
Nevertheless, a subsequent application will probably be needed
to assure continued good growth beyond 10 to 15 years on fine-
textured wet savanna soils, if soluble phosphates are used.
2. On wet soils with relatively thick sandy surface layers (fine-
texture horizons not within 20 inches of surface), P is only mod-
erately fixed, and either form of phosphate can be used.
3. Nitrogen applied alone to young pine on these soils results
in no increased growth and can result in growth suppression. How-
ever, with adequate P, an additional growth response of 10-15%
can be expected from added N. Diammonium phosphate can be
substituted pound for pound for CSP as a source of both N and
P. If N is to be applied separately from the GRP or CSP, it may
be applied as urea at the rate of 150-180 lb/acre, 2 to 3 years
after planting.

Established stands
1. Ground rock phosphate is also an effective source of P for
older stands on soils with a high capacity to fix this element, but
CSP can also be used effectively for established stands on all wet
sites. Whether GRP or CSP is used, it should be pelletized, es-
pecially if it is to be applied from the air, and it should be applied
with some N. Rates of 300-400 pounds of CSP or GRP plus 100-
150 pounds urea/acre are recommended.
Probably a more practical method is to broadcast 250-300
pounds DAP/acre to stagnant trees during early to late spring.
Trees as old as 18 to 20 years of age will respond to fertilizers
under these conditions. Aerial applications may be required, even
though the trees are small, because the soil is often too wet for
ground equipment.







POORLY TO SOMEWHAT POORLY DRAINED SOILS (Flatwoods)
Probably the second highest priority, after the wet savannas,
should be given to fertilizing the flatwoods. Response to fertilizer
were obtained in about 80% of the young slash pine plantations
under test on flatwood sites. Nitrogen alone generally results in
increased tree growth in the flatwoods. Phosphorus is also de-
ficient in a high percentage of these soils, but should be applied
only if a soil or tissue test indicates a deficiency. Responses to P
can normally be expected when the soil test value is between
1.5 to 2.0 ppm P, using the ammonium acetate extractant, or
4 to 6 ppm P extracted by the double-acid method (Table 1),
unless some other factor, such as potassium deficiency, is limit-
ing growth.

Young Stands
1. Young pine plantations on most flatwood sites respond to
N at rates of 45 to 70 pounds element/acre. Where P is adequate,
this N can be supplied by 100 to 150 pounds urea/acre. A delay
of 2 or 3 years in the N application may prevent excessive com-
petition from weedy vegetation or loss from leaching.
2. Diammonium phosphate broadcast at 200 to 250 pounds
DAP/acre has given excellent growth response on P-deficient
sites. However, since most flatwood soils with organic hardpans
have a very low capacity to retain P in the surface horizon (<40
ppm Al), long-term responses on these soils can probably be ex-
pected only from the less soluble P-sources (such as 300-400 lb
GRP/acre). After 10 to 15 years, soluble phosphates may need
to be reapplied for continued good growth on acid flatwood
Spodosols. Most of the P lost from the surface horizons is re-
tained in the spodic horizon, but it is not known how much of
this P can be used by deep-rooted trees. Retention of P in those
soils with fine-textured materials within 20-40 inches of the
surface is not a problem and either soluble or slowly- soluble
phosphates may be used effectively.

Established stands
Older stands in the flatwoods are often.deficient in N and less
frequently deficient in P. When practical, a foliage and/or soil
test should be used as a diagnostic tool.
1. Broadcast 125 to 200 pounds of urea or 250 to 350 pounds
ammonium sulfate/acre on 12- to 16-year-old stands not sus-
pected of a P deficiency.







2. On P deficient stands, broadcast a fertilizer containing an
N:P205 ratio of about 1:1. A mixed fertilizer, such as 20-20-0, or
urea-ammonium phosphates (28-28-0) should be applied at the
same rate of N as shown in Table 2.
3. Potassium, calcium (Ca), magnesium (Mg), and micro-
nutrients are seldom limiting to tree growth in the flatwoods. A
tissue test should be used to confirm suspected deficiencies
of these elements. Where K is deficient, it should be included
in the fertilizer program at 50 to 100 pounds K/acre.


MODERATELY WELL TO WELL DRAINED SOILS (Sands to loamy
sand-clay hills)
Many soils in this category are desirable agricultural lands
because of their favorable moisture relations and, as a conse-
quence, forests are often found in old abandoned fields where
years of cultivating and erosion have resulted in the loss of
much of the original organic matter. Nitrogen is more likely to
be deficient than P on these soils. However, a foliage and/or
soil test is needed to pinpoint deficient areas. Even where a test
indicates a P deficient area, best results are usually obtained
from a combination of N and P fertilizer.

Young stands
1. For young stands, apply 200 to 300 pounds DAP/acre, pre-
ferably banded. As an alternate program, an equivalent amount
of CSP may be applied at planting time followed in 2 to 3 years
by a broadcast application of N, as urea or ammonium sulfate,
at 45 to 90 pounds N/acre. Rock phosphate is the preferred
source for acid soils of the sand-clay hills with high P-fixing
capacities (ie. extractable Al > 180 ppm).
2. In old-field plantations, and other areas where a test indi-
cates adequate soil P, urea or ammonium sulfate may be broad-
cast to 2- or 3-year-old trees at 45 to 90 pounds N/acre.

Established stands
Foliage or soil tests are especially needed as guides in deli-
neating deficient areas among older stands on the moderately
well to well drained soils. Where a deficiency is indicated, the
following fertilizers are recommended.
1. Broadcast 200 to 250 pounds urea/acre, or equivalent rates of





Table 3. Economics of fertilizing a young and an established stand of slash pine.

Soil Expected yield Average final
drainage Site Average increase from Rate of yield with
conditions quality1 yield2 Material Cost3 fertilization return4 fertilization

feet cords/acre Ib/acre S/acre cords/acre % cords/acre
A. Fertilized at Planting Time and Harvested at Age 20
Very poorly to poorly (Range 40-60) 400 GRP+
(Bays and wet savannas) avg. 50 16 100 urea $28.50 10-36 17-25 39
Poorly to somewhat (Range 45-65) 400 GRP+
poorly (Flatwoods) avg. 55 22 100 urea $28.50 6-10 14-17 30
Moderately well to (Range 50-80)
well (Sands to loamy avg. 65 33 300 DAP $30.00 4-6 11-14 38
sand clay hills)

B. Fertilized at Age 15 and Harvested at Age 25
Very poorly to poorly (Range 40-60) 400 GRP+
(Bays and wet savannas) avg. 50 21 100 urea $28.50 5-13 23-35 29
Poorly to somewhat (Range 45-65) 400
poorly (Flatwoods) avg. 55 27 20-20-0 $31.50 3-5 16-22 31
Moderately well to (Range 50-80) 500
well (Sands to loamy avg. 65 41 20-20-0 $39.00 2-4 9-16 44
sand clay hills)


1 Average height of dominant and codominant trees in unfertilized stands at 25 years of age.
2 From Barnes, R. L. 1955. Univ. of Fla., School of Forestry, Res. Rept. 3. Yield is at age 20 for stands fertilized at planting and at age
25 for stands fertilized at age 15 years, at planting density of 700 stems per acre.
3 GRP at $40.00/ton, CSP @ $120.00/ton, Urea $225.00/ton, DAP @ $165.00/ton, 20-20-0 @ $120.00/ton; application at $0.0175
per pound; hauling cost at $1.50 per ton; management cost of $0.05 per acre. (Estimated costs as of February, 1974)
4 Rate of return: i =100 ( nJiY/FC -1), where: n=number of years investment carried.
AY=value of increased stumpage (based on a current stumpage price of
$25.00/cord with annual increases in value of 8%, or $45/cord after
10 years and $65/cord after 20 years).
FC fertilization costs.







N from ammonium sulfate, on well-stocked, 12- to 16-year old
stands.
2. If a P deficiency is identified, apply 300 to 500 pounds of a
mixed fertilizer, such as 20-20-0 or 28-28-0.



SOME ECONOMIC ASPECTS OF
FOREST FERTILIZATION

Forest fertilization recommendations previously discussed are
based primarily on biological considerations. Since the probabili-
ty and magnitude of a growth response resulting from a fertilizer
application varies with different site conditions, forest lands
are stratified for purposes of fertilizer recommendation accord-
ing to soil drainage conditions. However, before forest managers
can justify the use of fertilizers on an operational basis, responses
must not only be statistically significant, but also be economically
attractive. Due to the long period over which investments must
be carried, economics of any forest management practice are
difficult to assess. This results from the uncertainty of future
wood prices and possible changes in management objectives, as
well as the difficulty in predicting the magnitude of growth re-
sponse to treatment.
In spite of these difficulties, some estimates of economic re-
turns from the use of fertilizers (a) at the time of planting and
(b) in 15-year-old established stands are made for the three
principal soil drainage conditions for which recommendations are
developed. The responses used in these estimates are based on
early results from some 225 field trials, and results obtained 10
to 15 years after fertilization in 12 experiments. For stands fer-
tilized near planting time, Barnes' plantation yield and survival
equations were used to project early growth response due to
fertilization to increased yield at rotation age. There is an un-
derlying assumption that increases in tree height resulting from
fertilization are commensurate in all respects to increase in site
quality. Whether fertilization will alter normal plantation sur-
vival trends, height to diameter relationships (stem form), or
stand diameter distribution is not known for all conditions.
An example of the techniques used in Table 3 for calculating
returns from fertilizing young stands is as follows: A nutrient-
deficient Leon soil that received an application of 45 pounds N plus
40 pounds P/acre at planting time resulted in a 4-foot increase






in height for fertilized trees over unfertilized trees by age 10.
With a base site quality of 65, site quality for the fertilized stand
was raised to 71. Yield at age 20 from 700 planted stems/acre,
site quality 65 (unfertilized), is 33 cords/acre; site quality 71
(fertilized), 41 cords/acre. Therefore, by these calculations,
fertilization will result in a yield increase of 8 cords/acre at
harvest time (20 years).
Calculations of returns from fertilizing established stands
are largely based on 3-year basal area response data from 32
field experiments. Net basal area/acre increase and basal area
to volume ratios were used to calculate increased merchantable
volume for a 5-year interval. Average periodic annual increment
across all stand conditions in field experiments where responses
to fertilizers were obtained was 0.3 cord/acre/year. Calculated
5-year increases in volume were 1.0, 1.5, and 2.0 cords/acre
for the three soil drainage conditions, very poorly drained to
well drained, respectively. The average values presented in the
table for the three soil drainage conditions do not appear to be
out of line. In the few tests where fertilizers have been applied
to established stands for 5 years or more, there are indications
that the increase in volume associated with fertilization may
become greater after the first year or two. This lag in response
is due to the time required for foliar expansion in crowns of
nutrient-deficient trees. Furthermore, the assumption is made
that fertilizers will be applied to deficient sites only. It is ex-
pected that forest managers will take advantage of soil and
foliar tests, and soil-site maps as well as the recommendations
contained in this publication, in developing an economically
feasible fertilizer program.







APPENDIX


FERTILIZERS FOR FOREST SOILS

Forest trees require at least 16 nutrient elements for their
survival and growth. With the exception of carbon, hydrogen,
and oxygen, which are derived from air and water, the tree
obtains these essential elements from the soil. Three of them-
N, P, and K-are of primary concern in most fertilizer pro-
grams because they are used in relatively large amounts by
plants and are the elements most often deficient in soils. The
concentrations of these three nutrients are listed on most fer-
tilizer bags, as percentage of N-P.O,-K.O, such as 20-20-20, in
the material. Three other elements-calcium (Ca), magnesium
(Mg), and sulfur (S)-are also required in fairly large amounts,
but these elements and the micronutrients-boron (B), chlorine
(Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum
(Mo), and zinc (Zn)-while essential to plant growth, are not
often deficient in forest soils.


Nitrogen

Nitrogen makes up some 78% of the atmosphere, but this
gaseous N is not readily available to higher plants. On the con-
trary, N is the most widely deficient of the essential elements in
soil. It is largely associated with the organic matter in soils, and
much of it would be lost from the ecosystem during normal
processes of organic matter decomposition, if it were not for the
rather efficient uptake and recycling by forest vegetation. Never-
theless, additions of fertilizer N are often needed for continued
good tree growth under present intensive management systems,
because relatively large quantities of N are removed from the
soil and immobilized in non-cycling components of the forest
biomass. Properties of some N materials used for forest fertili-
zation are listed below.
a) Urea is a white, crystalline, synthetic organic material con-
taining 45%o N in a water soluble form. It is manufactured in
regular and extra large pellets for efficient aerial applications
in forests. Once dissolved, urea moves readily in soils; but
fortunately it soon converts to ammonium and is retained as
such by the soil colloids. It is reported that 10% or less of
the total N contained in urea is lost as ammonia gas from
average applications in coastal plain forests. As a conse-






quence, high-analyses urea is a desirable source of N for
forestry. The solubility of urea granules may be reduced by
coating them with S or other materials.
b) Ammonium sulfate, a white or grayish crystalline salt, is an
excellent fertilizer for forestry purposes, but because of its
relatively low N concentration (21%), it is more expensive
to apply per unit of N than most sources.
c) Ammonium nitrate is a water-soluble, pelletized material
with good physical properties and a N content of 33.5%.
Because one-half of the N in this material is in the form of
nitrate, which is subject to leaching in sandy soils, it is not
as desirable as urea for supplying N to forested coastal plain
soils.
Note: Other nitrate sources are not generally recommended
for forestry due to the mobility of the NOs ion and
because trees generally use ammonical sources more
effectively.
d) Ureaformaldehyde is a synthetic organic material con-
taining 38% N that is slowly available and will supply N
for longer periods of time than the more soluble sources. Be-
cause of its low salt index (non-burning) properties, it has
been used successfully in nurseries and in young plantations,
but it is not in great demand due to its high cost per unit of N.

Phosphorus
Phosphorus fertilizers vary greatly in their solubility rates.
Ammonium phosphates and superphosphates are largely water-
soluble and plant-available, while basic slag and GRP are water-
insoluble and slowly available. Phosphorus does not leach from
soils, except in acid, white or gray sands ( low in Fe and Al con-
tent) such as many flatwood soils. When applied early to stimu-
late young tree growth, the effects of the P may last throughout
the rotation period. Phosphorus concentration in the bag is guar-
anteed as "available phosphoric acid (POs)," and this value can
be converted to percent phosphorus (P) by multiplying the P20s
concentration by the factor of 0.44. Some properties of the more
common P sources useful in Coastal Plain forestry are listed
below.
a) Concentrated Superphosphate (CSP) contains 46% P20,
(20% P) in readily available form. Ordinary superphosphate,
which contains 20% P205 (9% P), is also readily available
but is not as popular in forest operations as CSP due to its






lower P content (greater bulk). These materials are made by
mixing ground rock phosphate with sulfuric acid to increase
their solubility.
b) Ground Rock Phosphate (GRP) is a slowly soluble powdered
material of varying P content. The material generally avail-
able in the U.S. Southeast contains from 30-33% PO, (13-
14% P). While it is difficult to spread in the powdered form,
granulation is feasible. Processes have been developed for
partial acidulation-granulation and for granulating with
other fertilizer salts, such as urea. A cogranular urea-GRP
material (18-18-0), developed by TVA, appears promising
under field study as an N-P fertilizer having slow P-release
characteristics.
c) Ammonium phosphates are high-analyses, water-soluble ma-
terials that contain N as well as P. Diammonium phosphate
(DAP), containing 18% N and 46% P,05 (20% P); monam-
monium phosphate (MAP) containing 11% N and 54% P205
(24% P); and ammonium polyphosphate (APP) analyzing
about 15-60-0, are excellent fertilizers for young plantations
in many P-deficient areas. Urea can be granulated with am-
monium phosphates to produce such water-soluble materials
as a 28-28-0 fertilizer.

Potassium
Potassium fertilizer is not generally used in Southeastern for-
estry, but where a soil or foliar test indicates a deficiency of this
element, it is normally applied in a mixed fertilizer containing
N and P, such as 20-20-20 fertilizer. Most K fertilizers are water
soluble, but only minimal leaching occurs under stable forest
conditions. Potassium is expressed as percent K0O on the fer-
tilizer bag and can be converted to the element by multiplying
by a factor of 0.83. Potassium chloride (KC1) is the compound
most often used to supply K in mixed fertilizers.









HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
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(EDIS)

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Cooperative Extension Service.






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