Group Title: Circular
Title: Citrus fertilizer management on calcareous soils
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 Material Information
Title: Citrus fertilizer management on calcareous soils
Series Title: Circular
Physical Description: 9 p. : ; 28 cm.
Language: English
Creator: Obreza, Thomas A., 1956-
Alva, Ashok K
Calvert, David V., 1934-
Florida Cooperative Extension Service
Publisher: Cooperative Extension Service, University of Florida, Institute of Food and Agricultural Sciences
Place of Publication: Gainesville
Publication Date: 1993
 Subjects
Subject: Citrus -- Fertilizers   ( lcsh )
Calcareous soils -- Florida   ( lcsh )
Citrus -- Soils   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 8-9).
Statement of Responsibility: Thomas A. Obreza, Ashok K. Alva, and David V. Calvert.
General Note: Title from caption.
General Note: "December 1993."
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Bibliographic ID: UF00008565
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 - AAA6829
ltuf - AJX0004
oclc - 29859377
alephbibnum - 001894739

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UNIVERSITY OF

FLORIDA


Circular 1127
December 1993


Florida Cooperative Extension Service


'Citrus Fertilizer Management on Calcareous Soils1

Thomas A. Obreza, Ashok K. Alva, and David V. Calvert2


INTRODUCTION

Soils in the south Florida flatwoods are underlain
by calcium carbonate (CaCO3) that has accumulated
through marine deposition over thousands of years.
In most flatwoods, the CaCO3 lies below the profile
and the overlying surface soil is usually acidic.
However, CaCO3 also can occur at the surface, either
naturally or as a result of earth-moving operations
that have mixed the soil. The resultant soil is called
calcareous. Soils also can become calcareous through
long-term irrigation with water from the Floridan
aquifer. This water contains small amounts of
dissolved CaCO3 that can accumulate with time.

Florida calcareous soils are alkaline (have pH
values greater than 7) because of the presence of
calcium carbonate (CaCO3), which dominates their
chemistries. These soils can contain from about 3%
to more than 25% CaCO3 by weight, with pH values
in the range of 7.6 to 8.3. Usually, the pH is not in
excess of 8.3 regardless of CaCO3 concentration,
unless a significant quantity of sodium (Na) is present.

Many Florida flatwoods soils contain one or more
calcareous horizons, or layers (see Table 1). A typical
characteristic is an alkaline, loamy horizon less than
40 inches deep, which can be brought to the surface
during land preparation for citrus planting. These
soils are important for citrus production in the Indian


River area (east coast) and, to a lesser extent, in the
Gulf region (southwest Florida). Increased nutritional
management often is required to grow citrus
successfully on calcareous soils. Some sites (e.g.,
ditchbanks) are composed of soils with extremely high
levels of lime rock or shell. Planting these sites may
not be economically justifiable, considering the
management problems and costs involved.

Citrus fertilizer management on calcareous soils
differs from that on noncalcareous soils because of
the effect of soil pH on soil nutrient availability and
chemical reactions that affect the loss or fixation of
some nutrients. The presence of CaC03 directly or
indirectly affects the chemistry and availability of
nitrogen (N), phosphorus (P), magnesium (Mg),
potassium (K), manganese (Mn), zinc (Zn), and iron
(Fe). The availability of soil copper (Cu) also is
affected; however, since the citrus Cu requirement is
normally satisfied through foliar sprays of Cu
fungicides, it is not discussed in this fact sheet.

THE EFFECT OF CaCO3 ON NITROGEN
TRANSFORMATIONS

Soil pH affects the rates of several reactions
involving N and can influence the efficiency of N use
by plants. Nitrification, or the conversion of
ammonium (NH4+) to nitrate (N03) by soil bacteria,
is most rapid in soils with pH values between 7 and 8.


1. This document is Circular 1127, a series of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food
and Agricultural Sciences, University of Florida. Publication date: December 1993.
2. Thomas A. Obreza, assistant professor, Soil and Water Science Department, Southwest Florida Research and Education Center, Immokalee,
Florida; Ashok K. Alva, assistant professor, Soil and Water Science Department, Citrus Research and Education Center, Lake Alfred, Florida;
and David V. Calvert, professor, Soil and Water Science Department, Agricultural Research and Education Center, Ft. Pierce, Florida,
Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville FL 32611.
The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research,
educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap,
or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office.
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean

SOF's I FnLORIDA ir"--





F&3(/ c
Citrus Fertilizer Management on Calcareous Soils 1 --1-7


Page 2


SCIE.4C
Nitrification approaches zero below pH 5.L EaXtisfactory tree nutrition. In cases wnere soil-applied
Ammonium-N fertilizers applied to calcareous soils fertilizer is ineffective, the only means of increasing
are converted within a few days to nitrate, which leaf Mg or K concentration may be through foliar
moves freely with soil water. The acidity produced application of water-soluble fertilizers, such as
during nitrification is quickly neutralized in highly magnesium nitrate [Mg(N03)2 or potassium nitrate
calcareous soils but may lower the pH value in soils (KNO3).
containing low levels of CaCO3.
THE EFFECT OF CaCO3 ON PHOSPHORUS
Ammonia volatilization is the loss of N to the
atmosphere through conversion of the ammonium ion Phosphorus availability in calcareous soils is
to ammonia gas (NH3). Volatilization ofammoniacal- almost always limited. The P concentration in the soil
N fertilizer is significant only if the soil surface pH solution is the factor most closely related to P
value is greater than 7 where the fertilizer is applied, availability to plants. The sustainable concentration
This condition occurs in calcareous soils, or where the is related to the solid forms of P that dissolve to
breakdown of the N fertilizer produces alkaline replenish soil solution P following its depletion by
conditions (e.g., urea decomposition). Nitrogen loss crop uptake. Many different solid forms of
through ammonia volatilization on calcareous soils is phosphorus exist in combination with Ca in calcareous
a concern when ammoniacal N is applied to the grove soils. After P fertilizer is added to a calcareous soil,
floor and remains there without moving into the soil. it undergoes a series of chemical reactions with Ca
Following an application of dry fertilizer containing that decrease its solubility with time (a process
ammoniacal N, the fertilizer should be moved into the referred to as P fixation). Consequently, the long-
root zone through irrigation or mechanical term availability of P to plants is controlled by the
incorporation if rainfall is not imminent. Urea application rate of soluble P and the dissolution of
breakdown creates alkaline conditions near the fixed P. Applied P is available to replenish the soil
fertilizer particle; surface application of urea can solution for only a relatively short time before it
cause N loss if the urea is not incorporated or converts to less soluble forms of P.
irrigated into the soil, regardless of initial soil pH.
TESTING CALCAREOUS SOILS FOR P
THE EFFECT OF CaCO3 ON MAGNESIUM
AND POTASSIUM Accumulation and loss of soil P can be evaluated
through soil testing, but more information is required
Although low concentrations of Mg and K in to make a fertilizer recommendation based on this
citrus leaves are not uncommon in groves planted on method. The amount of extractable P must be related
calcareous soils, there is not necessarily a concurrent to crop yield or quality. An ideal P-extracting
reduction in fruit yield or quality. If a low solution should remove from soils only those forms of
concentration of leaf K or Mg is found in a grove that P that are available to plants. This is difficult to
produces satisfactory yield and quality, attempts to achieve with the extracting solutions that are currently
increase leaf levels with fertilizer are not necessary. used.
However, if a detrimental condition such as low yield,
small fruit, or creasing is observed, an attempt to The major extractants used by southeastern U. S.
raise the leaf K or Mg concentration with fertilizer is soil testing laboratories to measure soil P include
justified. Mehlich 1 (double acid), Bray P1 and P2, and sodium
bicarbonate. Mehlich 1 is not appropriate for use on
It is often difficult to increase leaf Mg and K calcareous soils because its extracting ability is
levels with fertilizer applied directly to calcareous weakened by exposure to CaCO3. While Bray and
soils, which contain tremendous quantities of both sodium bicarbonate have been consistently correlated
exchangeable and nonexchangeable Ca. Leaf Mg and to P uptake by plants growing on calcareous soils in
K concentrations are strongly influenced by soil other parts of the United States, these extractants
conditions that control leaf Ca concentration, have not been calibrated with citrus leaf P
including high soil Ca levels. High Ca levels suppress concentration or yield on Florida calcareous soils.
Mg and K uptake by citrus trees in part, presumably, Mehlich 3, a newer extractant with promising ability
through the competition of Ca2+, Mg2+, and K. for Florida conditions, is not yet widely used and also
Citrus growing on soils high in Ca often requires will require calibration. Currently, no suitable
above normal levels of Mg and K fertilizer for extractant for soil P has an established, calibrated







Citrus Fertilizer Management on Calcareous Soils

sufficiency level for use with citrus grown on Florida
calcareous soils.

THE EFFECT OF CaCO, ON ZINC AND
MANGANESE

Soil pH is the most important factor regulating
Zn and Mn supply in alkaline soils. At alkaline (high)
pH values, Zn and Mn form precipitous compounds
with low water solubility, markedly decreasing their
availability to plants. A soil pH value of less than 7
is preferred to ensure that Zn and Mn are available
to plants in sufficient amounts. The soil around a
plant root (the rhizosphere) tends to be acidic due to
root exudation of H' ions. Therefore, soils that are
slightly alkaline may not necessarily be deficient in Zn
or Mn. In addition, Zn and Mn can be chelated by
natural organic compounds in the soil, a process that
aids the movement of these nutrients to the plant
root. On highly alkaline soils, however, Zn and Mn
deficiencies are not uncommon. Soil applications of
Zn and Mn fertilizers are generally ineffective in
these situations, but deficiencies can be corrected
through the use of foliar sprays.

THE EFFECT OF CaCO3 ON IRON

Calcareous soils may contain high levels of total
Fe, but in forms unavailable to plants. Visible Fe
deficiency, or Fe chlorosis, is common in citrus. The
term chlorosis signifies a yellowing of plant foliage,
whereas Fe deficiency implies that leaf Fe
concentration is low. Owing to the nature and causes
of Fe chlorosis, however, Fe concentration is not
necessarily related to degree of chlorosis; in chlorotic
plants Fe concentrations can be higher than, equal to,
or lower than those in normal plants. Thus, this
disorder on calcareous soils is not always attributable
to Fe deficiency; it may be a condition known as lime-
induced Fe chlorosis.

Iron is considerably less soluble than Zn or Mn in
soils with a pH value of 8; thus, inorganic Fe
contributes relatively little to the Fe nutrition of
plants in calcareous soils. Most of the soluble Fe in
the soil is completed by natural organic compounds.
(Fe nutrition in plants has improved in response to
the application of sewage sludge, which contains
organically completed Fe.) The primary factor
associated with Fe chlorosis under calcareous
conditions appears to be the effect of the bicarbonate
ion (HC03-) on Fe uptake and/or translocation in the
plant. The result is Fe inactivation or immobilization
in plant tissue.


Page 3


Susceptibility to Fe chlorosis depends on a plant's
response to Fe deficiency stress, which is controlled
genetically. Citrus rootstocks vary widely in their
ability to overcome low Fe stress (see Table 2). The
easiest way to avoid lime-induced Fe chlorosis in
citrus trees to be planted on calcareous soils is to use
tolerant rootstocks. Existing Fe chlorosis can be
corrected by using organic chelates, a method
discussed in detail in a later section.

FERTILIZER MANAGEMENT ON
CALCAREOUS SOILS

Nitrogen. Regardless of the initial form applied,
essentially all N fertilizer ultimately exists as N03-
because nitrification proceeds uninhibited in
calcareous soils. Rather than attempt to slow this
process, citrus grove management practices should
emphasize irrigation and fertilizer application
scheduling strategies that decrease N leaching. These
include irrigating based on tensiometer readings or
evapotranspiration measurements and using split
applications of N fertilizer. Applying a portion of the
required N fertilizer with irrigation water (i.e.,
through fertigation) and scheduling irrigations to
maintain the N in the root zone is a sound method to
prevent large N leaching losses. Using controlled-
release N also can increase N fertilizer efficiency.

Management of N fertilizer also should involve
practices that minimize its loss through ammonia
volatilization. Following an application of
ammoniacal-N to the surface of a calcareous soil, the
fertilizer should be moved into the soil profile with
irrigation water if rainfall is not likely. Urea applied
to the surface of any soil, regardless of its pH value,
should be moved into the soil via rainfall or irrigation.
Fertigation using either of these N sources is a
suitable application method, provided that there is
ample time to flush the fertilizer out of the lines and
into the soil.

Phosphorus. To maintain P availability to citrus
on calcareous soils, water-soluble P fertilizer should
be applied on a regular, but not necessarily frequent,
basis. Since phosphorus accumulates in the soil, it is
at least partially available as it converts to less soluble
compounds with time. Phosphorus deficiency has
never been found in citrus grown on Florida
calcareous soils where P fertilizer has been applied
regularly.

Phosphorus fertilizer should be applied each year
in newly planted groves, at a rate based on the







Citrus Fertilizer Management on Calcareous Soils

recommended rate for young trees, until the groves
begin to bear fruit. As the trees approach maturity,
P applications can be limited to once every few years.
Diagnostic information from leaf and soil testing can
help determine whether P fertilization is necessary.
Citrus yields have not been correlated with the results
of soil tests measuring P levels in calcareous soils;
however, soil testing with Mehlich 3, sodium
bicarbonate, or another suitable extractant still can be
useful in estimating the magnitude of accumulated P.
An increased level of P measured by soil tests
following periodic fertilization would indicate an
increase in available P above the native soil level.

Leaf tissue testing can be used to determine
whether soil P is available to citrus trees. For best
results, the leaf P concentration of 4- to 6-month-old
spring flush leaves from mature trees should be
evaluated. The optimum range for leaf P in mature
citrus leaves is from 0.12% to 0.16% on a dry weight
basis. A decline in leaf P concentration from
optimum to low over several years indicates declining
soil P availability and justifies a P fertilizer
application.

Potassium. For citrus on noncalcareous soils,
nitrogen and potassium fertilizer applications with a
1:1 ratio of N to K20 are recommended. If leaf
testing on calcareous soils reveals that high levels of
soil Ca may be limiting K uptake, the K20 rate should
be increased by about 25%. This approach may not
work in all situations, however. Another way to
increase leaf K concentration is through foliar
application of KNO3. A solution of 20 lbs KNO3 per
100 gallons of water, sprayed to the point of foliar
runoff, has been shown to raise leaf K, especially if
applied several times during the year. Concentrations
greater than 20 lbs KNO3 per 100 gallons of water
should be avoided, since high salt levels promote leaf
bur. The availability of N applied through foliar
spray equals that of N applied in regular ground
fertilizer programs. Therefore, the amount of N
applied as KNO3 should be considered when
determining annual N fertilization plans for citrus
groves.

Zinc and manganese. The most common
inorganic Zn and Mn fertilizers are the sulfates
(ZnSO4, MnSO4) and the oxides (ZnO, MnO).
Broadcast application of these compounds to correct
Zn or Mn deficiencies in calcareous soils is not
recommended, since the alkaline pH renders the Zn
and Mn unavailable almost immediately. Zinc is also
available in chelated forms, including Zn-EDTA and


Page 4


Zn-HEDTA. A chelate is a large organic molecule
that "wraps around" a micronutrient ion such as
Zn2,2 sequestering it from soil reactions that make it
unavailable. Chelated Zn is sometimes, but not
always, superior to inorganic Zn sources. Soil
applications of chelated Zn are rarely economical,
however. Manganese chelates have limited
effectiveness in calcareous soils and are not normally
used.

The least expensive way to apply Zn and Mn to
citrus is through foliar sprays. In addition to the
forms listed above, a number of other Zn and Mn
formulations are available for foliar spraying,
including nitrates and organically chelated forms using
lignin sulfonate, glucoheptonate, or alpha-keto acids.
Preliminary research data indicate little difference in
magnitude of foliar uptake, regardless of the form of
carrier or chelate applied. Similarly, foliar
applications of low rates of Mn or Zn (e.g., 0.5 to 1.0
lb elemental per acre) are not adequate to correct
moderate to severe deficiencies often found in soils
with high pH values.

Iron. It is not easy to remedy iron chlorosis of
citrus trees on susceptible rootstocks planted on
calcareous soils. Iron fertilizer formulations are
available that can correct chlorosis; however, the
required application rate and frequency make the
treatment expensive. Inorganic sources of Fe such as
ferrous sulfate (FeSO4) or ferric sulfate [Fe2(SO04)3
are not effective unless applied at extremely high
rates; these sources should not be used on calcareous
soils. Iron chlorosis should be addressed through soil
application of Fe chelates. Chelates are superior
sources of Fe for plants because they supply sufficient
Fe at lower rates than are required with inorganic Fe
sources. The most popular synthetic organically
chelated forms of Fe include Fe-EDTA, Fe-HEDTA,
Fe-DTPA, and Fe-EDDHA. The effectiveness of
these fertilizers varies greatly, depending on soil pH
(see Table 3). Fe-DTPA may be used on mildly
alkaline soils (with pH values of 7.5 or less),
whereas Fe-EDDHA is the chelate of choice for use
on highly calcareous soils (with a pH value greater
than 7.5).

Natural, organically completed Fe exists in
organic waste products such as sewage sludge, but at
lower concentrations than in chelated Fe fertilizers.
On calcareous soils in the western United States,
sludge applied at 15 tons per treated acre was an
effective Fe source for field crops severely deficient in
Fe. The efficacy of sludge as an Fe fertilizer for







Citrus Fertilizer Management on Calcareous Soils

citrus grown on Florida calcareous soils has not been
investigated. Sludge is potentially useful, however,
since it contains readily soluble forms of Fe that may
remain in soil solution through organic complexation.

Foliar application of FeSO4 or Fe chelates has not
proven satisfactory on citrus trees because of poor
translocation within the leaf. The use of foliar sprays
also increases the possibility of fruit and/or leaf burn.
For these reasons, foliar application of Fe is not
recommended to correct Fe chlorosis of citrus.

SULFUR PRODUCTS USED AS SOIL
AMENDMENTS

Although little work has been done in Florida on
the use of sulfur (S) products (soil acidulents) for
citrus grown on calcareous soils, application of these
products may be beneficial under certain
circumstances. This section, drawn from the results
of research conducted in other regions of the United
States, discusses the potential benefits of sulfur
products.

Soil acidulents can improve nutrient availability in
calcareous soils by decreasing soil pH. The rates of
soil acidulents required to cause a plant response
depend on the amount of CaCO3 in the soil. Soils
with visible lime rock or shell in the root zone would
require repeated applications of a high rate of
acidulent, and a lengthy interval would be needed to
observe results. Because plant response to broadcast
application of an acidulent is unlikely in this instance,
such applications are not recommended. In contrast,
soils containing little CaCO3, or those that have
become alkaline from irrigation water with high levels
of bicarbonate, require less acidulation and respond
faster. It is feasible to acidify in this situation.

Wide variability in soil types precludes a standard
recommendation for acidification. If soil acidulents
are used, a comprehensive program of soil pH
measurement should be undertaken. Portable soil pH
meters that can be taken into the field are readily
available. Soil pH should be measured prior to, and
periodically after, application of an acidulent to
monitor its effect. Decisions regarding the rate and
frequency of subsequent applications of acidulent can
be based on desired changes in soil pH and visible
plant response.

Examples of S-containing acidulents include
elemental S, sulfuric acid (H2SO4), and ammonium
and potassium thiosulfate [(NH4)2S203, K2S203].


Page 5


These compounds act to neutralize CaC03 with acid
(see Table 4); this, in turn, may lead to a lowering of
soil pH. Ammonium sulfate [(NH4)2SO4] acidifies the
soil by converting NH4' to N03- during nitrification.
The sulfate ion (SO42-) alone possesses no acidifying
power.

Pound for pound, elemental S is the most
effective soil acidulent. Although not an acidic
material itself, finely ground elemental S is converted
quickly to sulfuric acid in the soil through microbial
action. This material can be difficult to work with
because it creates dust and fire hazards. Larger
particles or flakes are easier to apply but react more
slowly, owing to their smaller surface area. Sulfur has
been formulated into porous, irregular granules to
overcome this difficulty.

In theory, 6.4 tons per acre of elemental S -- the
equivalent of 2,720 gallons per acre of concentrated
(66 Baume) sulfuric acid -- is required to neutralize
each 1% of CaC03 in the soil to a depth of 12 inches.
Broadcast application of S over the entire root zone
is not practical because a large amount of S is
required for acidification. It has been demonstrated
in field crops, however, that only a small fraction of
the root system is needed to absorb adequate Fe.
Thus, it may be possible to improve Fe nutrition in
trees by increasing Fe solubility in a small volume of
root zone. A high rate of S, or sulfuric acid,
concentrated in a small volume of calcareous soil
creates an acidic zone and increases the availability of
phosphorus and micronutrients to roots growing in,
and adjacent to, the acidic zone. In one study, citrus
on calcareous soil in Florida completely recovered
from lime-induced chlorosis after 4.5 lbs (0.3 gallons)
of concentrated sulfuric acid was distributed equally
into 6 holes dug within a tree's root zone; however,
this occurred only if Fe-EDTA was concurrently
applied to the holes at a rate of 2 oz of Fe per tree.

Sulfuric acid reacts more quickly than any other
material, but it is hazardous to work with and can
damage plants if too much is applied at one time.
Dilute concentrations of sulfuric acid can be applied
safely with irrigation water and used to prevent Ca
and Mg precipitates from forming in microirrigation
lines (see Fla. Agr. Exp. Sta. Bull. 258). Levels of
CaC03 in the soil and of bicarbonate in the irrigation
water determine the proper rate and frequency for
injecting sulfuric acid (see Notes in Soil Science No.
18, February 1985). Repeated applications of sulfuric
acid with irrigation water will tend to lower soil pH
within the wetted pattern of the emitter.






Citrus Fertilizer Management on Calcareous Soils

Ammonium thiosulfate and potassium thiosulfate
are clear liquid fertilizers (12-0-0-26S and 0-0-25-17S)
containing sulfur in the S2032- form. They can be
blended with N, P, and K solutions to form a wide
variety of N-P-K-S formulations. Thiosulfates are
noncorrosive and nonhazardous to handle; they also
are well adapted to the methods used to apply
fertilizer solutions. When applied to the soil, half of
the S2032- converts to elemental S, the other half to
SO42-. The elemental S further converts to sulfuric
acid, which gives the thiosulfate its acidifying power.
The NH4+ in ammonium thiosulfate also contributes
to the acidification reaction.

Thiosulfate is also a good reducing agent. Iron is
normally found in well aerated soils in the oxidized
(Fe3+) form. Before iron can be taken up by plants,
however, it must be reduced to Fe2+ at the root
surface. Thus, thiosulfate possesses the power to
increase Fe availability in calcareous soils to a greater
degree than simple soil acidification. It has been
demonstrated that soil levels of extractable Fe
increase when ammonium thiosulfate is applied to
calcareous soils.

Thiosulfate fertilizers can be applied under the
tree canopy with a herbicide boom, but this method
probably does not concentrate the material in a small
enough zone to be effective. Injecting thiosulfates
into a microirrigation system, as with sulfuric acid,
would be easier and would allow more concentrated
application. For example, if microirrigation were
used to apply 100 lbs of N per acre, in the form of
ammonium thiosulfate, to a grove containing 150
trees per acre, each tree would receive the acidifying
power of 1.1 lbs of elemental S. If each tree were
irrigated with a single microsprinkler with a wetted
pattern diameter of 12 ft, the equivalent S application
rate would be 1.0 Ibs per 100 square ft, an amount
that might be sufficient to correct a mild alkalinity
problem. In the same example, if the wetted pattern
diameter were 3 ft, as with young tree emitters, the S
application rate would increase to 15.7 lbs per 100
square ft. Very likely, this rate of acidification would
damage or kill the tree. Therefore, it is important to
consider the amount of surface area wetted when
applying acidifying materials through an irrigation
system. The rate of S should be limited to 1.1 lbs per
100 square ft-in any single application.

The soil within the wetted pattern of a
microirrigation emitter often becomes alkaline when
the water contains bicarbonate, while the surrounding


Page 6


soil may be neutral or acidic. To lower the soil pH in
this situation, acid or acidifying fertilizer must be
applied to the wetted pattern only. Applying acid or
thiosulfate fertilizer through the irrigation system can
be effective in treating this problem.

SUMMARY

1. Calcareous soils are alkaline because they
contain CaCO3. They are commonly found in
south Florida citrus groves, especially in the
Indian River area.

2. The availability of N, P, K, Mg, Mn, Zn, and Fe
to citrus decreases when soil CaC03
concentration increases to more than about 3%
by weight. These soils generally have a pH
value in the range of 7.6 to 8.3.

3. To avoid ammonia volatilization, fertilizers
containing ammonium-N or urea should be
moved into the root zone with rainfall or
irrigation, or be incorporated into the soil.

4. Phosphorus fertilizer applied to calcareous soils
becomes fixed in sparingly soluble compounds
over time. To maintain continuous P
availability, P fertilizer should be applied on a
regular, but not necessarily frequent, basis.

5. Soil testing is useful in determining the
magnitude of extractable P. Differences in P
soil tests over time indicate accumulation or loss
of soil P availability.

6. Leaf testing can gauge the effectiveness of soil P
as a supply for citrus uptake and should be used
to assess the need for P fertilizer application.

7. Citrus planted on calcareous soils may require
above normal levels of Mg or K fertilizer for
satisfactory nutrition. Foliar sprays of MgNO3
or KNO3 may be effective where soil
applications are not.

8. The least expensive way to correct Zn and Mn
deficiencies of citrus in calcareous soils is
through foliar application of inorganic or
organically chelated forms.

9. The easiest way to avoid lime-induced Fe
chlorosis on calcareous soils is to plant trees
budded on tolerant rootstocks.







Citrus Fertilizer Management on Calcareous Soils

10. The most effective remedy for lime-induced Fe
chlorosis on nontolerant rootstocks involves the
use of organically chelated Fe.


Page 7


11. Sulfur products that act as soil acidulents can
potentially improve nutrient availability in
calcareous soils.


Table 1. Potential extent of calcareous soils in major south Florida citrus-producing counties.

Percentage of Land Area Acres of Land Area Used
Acres of That is for Citrus Production
County Land Area Potentially Calcareousa (Rank in Florida)

St. Lucie 367,089 42 105,117 (1)
Hendry 772,903 21 87,396 (3)
Indian River 318,146 26 65,446 (4)
DeSoto 406,867 11 58,058 (6)

Martin 346,158 32 46,335 (8)
Collier 686,581b 37 34,167 (9)


Table 2. Citrus rootstocks ranked according to susceptibility to Fe chlorosis.

Sour orange (C. aurantium)
Rough lemon (C. jambhiri)
Cleopatra mandarin (C. reticulata) lowest susceptibility

C. macrophylla
C. volkameriana


Sweet orange (C. sinensis)
moderate susceptibility
Carrizo citrange (C. sinesis x P. trifoliata) moderate susceptibility


Trifoliate orange (P. trifoliata)
Single citrumelo (C. paradise x P. trifoliata) highest susceptibility
Swingle citrumelo (C. paradisi x P. trifoliata)


a Includes these soil series: Pineda, Riviera, Winder, Boca, Hilolo, Pople, Tuscawilla, Pinellas, Bradenton, and Felda.
b Includes only the portion of Collier County mapped in the USDA-SCS soil survey.






Citrus Fertilizer Management on Calcareous Soils


Table 3. Effective pH range of various Fe chelates.

Fe Chelate Effective pH Range
Fe-EDTA, Fe-HEDTA 4 to 6.5
Fe-DTPA 4 to 7.5
Fe-EDDHA 4 to 9
Source: Norvell, 1991.


REFERENCES

Barber, S. A. 1984. Soil nutrient bioavailability.
John Wiley & Sons, Inc., New York.

Basiouny, F. M., C. D. Leonard, and R. H. Biggs.
1970. Comparison of different iron formulations
for effectiveness in correcting iron chlorosis in
citrus. Proc. Fla. State Hort. Soc. 83:1-6.

Calvert, D. V. 1969. Spray applications of potassium
nitrate for citrus on calcareous soils. Proc. First
Int. Citrus Symp. 3:1587-1597.

Calvert, D. V., and H. J. Reitz. 1966. Response of
citrus growing on calcareous soil to soil and foliar
applications of magnesium. Fla. State Hort. Soc.
Proc. 79:1-6.

Calvert, D. V., and R. C. Smith. 1972. Correction of
potassium deficiency of citrus with KNO3 sprays.
In Proc. of Symposium of Fertilizer-Pesticide
Combinations. Agri. and Food. Chem. Soc.
20:659-661.

Kidder, G., and E. A. Hanlon, Jr. 1985. Neutralizing
excess bicarbonates from irrigation water. Univ.
of Fla., Soil Sci. Dept. Notes in Soil Science No.
18. Feb. 1985.

Kissel, D. E., D. H. Sander, and R. Ellis, Jr. 1985.
Fertilizer-plant interactions in alkaline soils. p.
153-196. In 0. P. Engelstad (ed.) Fertilizer
technology and use, 3rd ed. Soil Science Society
of America, Inc., Madison, WI.

Knudtsen, K., and G. A. O'Connor. 1987.
Characterization of iron and zinc in Albuquerque
sewage sludge. J. Environ. Qual. 16:85-90.

Koo, R. C. J. (ed.). 1984. Recommended fertilizers
and nutritional sprays for citrus. Fla. Agr. Exp.
Sta. Bull. 536D.


Page 8


Table 4. CaCO3 neutralizing power of several S sources.

Amount Needed to
Sulfur Source Neutralize
1,000 Ibs CaCO3
Elemental S 320 Ibs
Concentrated sulfuric acid
(660 Baume) 68 gal
Ammonium thiosulfate
12-0-0-26S 1,600 Ibs
Potassium thiosulfate
0-0-25-17S 3,800 Ibs
Ammonium sulfate
21-0-0-24S 900 Ibs


Korcak, R. F. 1987. Iron deficiency chlorosis. Hort.
Rev. 9:133-186.

Leonard, C. D., and D. V. Calvert. 1971. Field tests
with new iron chelates on citrus growing on
calcareous soils. Proc. Fla. State Hort. Soc.
84:24-31.

Leonard, C. D., and I. Stewart. 1952. Correction of
iron chlorosis in citrus with chelated iron. Proc.
Fla. State Hort. Soc. 65:20-24.

Leonard, C. D., and I. Stewart. 1953. Chelated iron
as a corrective for lime-induced chlorosis in
citrus. Proc. Fla. State Hort. Soc. 66:49-54.

Leonard, C. D., and I. Stewart. 1959. Soil
application of manganese for citrus. Proc. Fla.
State Hort. Soc. 72:38-45.

Leonard, C. D., I. Stewart, and G. Edwards. 1956.
Effectiveness of different zinc fertilizers on citrus.
Proc. Fla. State Hort. Soc. 69:72-79.

McCaslin, B. D., J. G. Davis, L. Cihacek, and L. A.
Schluter. 1987. Sorghum yield and soil analysis
from sludge-amended calcareous iron-deficient
soil. Agron. J. 79:204-209.

Norvell, W. A. 1991. Reactions of metal chelates in
soils and nutrient solutions. p. 187-227. In J. J.
Mortvedt et al. (ed.) Micronutrients in
agriculture, 2nd ed. Soil Science Society of
America, Inc., Madison, WI.







Citrus Fertilizer Management on Calcareous Soils

Peech, M., and T. W. Young. 1948. Chemical
studies on soils from Florida citrus groves. Fla.
Agr. Exp. Sta. Bull. 448.

Pitts, D. J., D. Z. Haman, and A. G. Smajstrla. 1990.
Causes and prevention of emitter plugging in
micro irrigation systems. Fla. Agr. Exp. Sta. Bull.
258.


Page 9


Reitz, H. J., and W. T. Long. 1952. Mineral
composition of citrus leaves from the Indian
River area of Florida. Proc. Fla. State Hort. Soc.
65:32-38.

Tisdale, S. L., W. L. Nelson, and J. D. Beaton. 1985.
Soil fertility and fertilizers, 4th ed. Macmillan
Publishing Co., New York.


1. The information contained in this publication was compiled and synthesized from all available research data and the best professional
judgment of the authors. Research is underway to substantiate some of the recommendations presented herein.






















































































COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, John T.
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