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Malnutrition
Cit
Sympto f of
rus A
By 0 C BRYAN
Larly Stage
Advanced Stage
STATE OF FLORIDA
DEPARTMENT OP AGRICULTURE
DOYLE CONNER. Commiss1ionel
TALLAHASSEE
BULLETIN NO 93 R AUGUST, 1961
Malnutrition
Symptoms
Citrus
with Practical Methods
of Treatment
By 0 C BRYAN
STATE OF FLORIDA
DEPARTMENT OF AGRICULTURE
DOYLE CONNER, Commissioner
TALLAHASSEE
This bulletin was originally sponsored by
the Florida Cttrus Growers, Incorporated, and
its publication and free distribution were made
possible through the generosity of the State
Department of Agriculture at Tallahassee.
The supply of the third printing of this
bulletin has been exhausted, and the demand
justified another reprinting. The State Depart-
ment of Agriculture is glad to make available
to citrus growers a fourth printing of the bul-
letin which has been revised and brought up
to date.
COVER-Deficiency symptoms of nitrogen in orange leaves.
Early stage (A) indicated by pale green color. Advanced stage
(B) indicated by yellow color. (See page 8 for description.)
FOREWORD
Commercial plant food-fertilizers-is not only one of the es-
sentials for citrus production in Florida, but one of the most ex-
pensive factors. The wide range of inherent properties of plant
nutrients greatly complicates soil fertility problems. That some
nutrients are required only in trace amounts and some in large
amounts is a deep mystery to both practical and technical work-
ers. Variations in individual nutrient properties account for much
of the wide range in soil reaction (pH). Furthermore, some nu-
trients are attracted to the soil particles and others are not. Some
leach rather readily while others accumulate with fertilizer prac-
tices. Successful management of soil fertility problems necessitates
a working knowledge of the behavior of nutrients m the soil. When
a nutrient is deficient, crops are abnormal, diseased and unpro-
ductive.
The discovery that each nutrient performs individual functions
in a plant, a deficiency of which causes specific deficiency patterns,
was a milestone in the progress of agriculture. This has enabled
growers to pinpoint many nutrition problems and place their en-
deavors on a scientific basis. To recognize and identify deficiency
symptom patterns in citrus is a worthy accomplishment. Yet, it
is equally important for the grower to know the reasons for the
abnormality, whether they are due to actual shortage in the soil,
or to unbalanced nutrients caused by unscientific practices. For
that reason some representative data dealing with nutrient needs,
fertilizer materials, and reaction of nutrients with typical citrus
soils are presented for study along with the deficiency symptom
patterns.
To correct malnutrition problems involves either supplementing
the soil for actual shortage, or counteracting excesses and adjust-
ing unbalanced nutrients. These have been repeatedly demonstrat-
ed since the original printing of this bulletin m 1940, and again
in 1950. Several new discoveries have been made since the last
printing. For these reasons, the bulletin has been revised and
brought up to date, adding new data and illustrations as deemed
advisable.
CONTENTS
Page
Foreword 3
Introduction 7
Synopsis of Malnutrition Symptoms of Citrus, Soil Relations.
Treatments, Excesses. Historical Use of the following Nutrients.
Nitrogen 8
Phosphorus 10
Potassium I Potash, 12
Magnesium 16
Calcium 20
Boron 22
Coppe> 27
Manganese 31
Iron 34
Zinc 37
Molybdenum 40
LEAF CHLOROSIS AND TOXICITY OF CITRUS 41
DEFICIENCY PROBLEMS AND FERTILIZER PRACTICES 46
FERTILIZER EFFICIENCY 49
LEACHING LOSSES 52
SOIL ACCUMULATIONS AND SOIL REACTION 54
NUTRIENT EXCESSES AND TREATMENTS 57
TIME OF APPLICATION 58
NUTRIENT RATIOS AND RATES OF APPLICATION 60
SUMMARY 62
ACKNOWLEDGMENTS 62
LITERATURE CITED 63
CONTENTS (Continued)
ILLUSTRATIONS:
Plates: Page
1. Deficiency Symptoms of Nitrogen in Orange Leaves Cover
2. Deficiency Symptoms of Magnesium in Grapefruit Leaves 17
3. Deficiency Symptoms of Copper in Pineapple Oranges 29
4. Deficiency Symptoms of Manganese in Grapefruit Leaves 33
5. Deficiency Symptoms of Iron in Orange Leaves .. 35
6. Deficiency Symptoms of Zinc in Orange Leaves 39
Figures:
1 Phosphorus Deficiency Symptoms in the Leaves and Fruit
of Oranges .-- ... .. - 11
2. Symptoms of Zinc Deficiency (Foliage) and Copper (Fruit)
in Pineapple Oranges .. 13
3 Deficiency Symptoms of Potassium in Common Grapefruit 15
4. Deficiency Symptoms of Magnesium in Grapefruit 19
5. Deficiency Symptoms of Calcium in Grapefruit Leaves and Trees 21
6. Leaf Symptoms of Boron Deficiency .. 23
7. Symptoms of Boron Deficiency in Citrus Leaves and Fruit 25
8. Mild Case of Boron Toxicity in Grepefiuit Leaves 26
9. Molybdenum Deficiency in Orange Leaves 40
10. Perchlorate Chlorosis in Grapefruit Leaves 42
11. Biuret Chlorosis of Cttius 43
12. Arsemc Toxicity of Grapefruit Leaves 44
13. Fluorine Toxicity of Grapefruit Leaves 45
CONTENTS (Continued)
Tables: Page
1. Nutrient Content of Citrus as Related to Fertilizer Needs
on Sandy Soils .... ....... ---. ....... .... 47
2. Composition of the Principal Fertilizer Materials 48
3. The Efficiency of Different Sources of Nitrogen on the Produc-
tion of Pineapple Oranges With and Without Copper ... .. 50
4. Total Amount of Drainage During the Year (1924) and the
Plant Food Leached .......... .............................. ..... . ..... 53
5. Relative Leaching Losses of the Major Fertilizer Nutrients
from Some Typical Florida Soils ..... ..... .... 55
6. Available Plant Nutrients in the Soil as Affected by
Different Fertilizer Treatments .. -. .-..-. ...... 56
MALNUTRITION SYMPTOMS OF CITRUS AND
PRACTICAL METHODS OF TREATMENT
By 0. C, BRYAN'
INTRODUCTION
The purpose of this bulletin is to bring before the Florida
grower, in a brief practical and scientific manner, the known
information regarding the malnutrition problems of citrus, point-
ing out the deficiency symptoms of various nutrients, as well as
the symptoms of excesses. By so doing and suggesting economical
methods of treatment, it is hoped that the grower will under-
stand production problems sufficiently well to eliminate wasteful
practices and increase the efficiency of production. The increased
demand for fruit of high internal quality necessitates more atten-
tion to those production factors which favorably affect quality.
Of all the production factors confronting Florida growers, that
of commercial plant food is one of the most expensive, the most
confusing and the least understood. Unless the gro wer has de-
pendable scientific methods rather than guesswork, he will not be
able to avoid wasteful practices in dealing with malnutrition
problems.
No attempt is made to cite all the literature dealing with this
subject. Some of direct concern will be mentioned
In order to discuss this subject, using a minimum of technical
terms, it will be necessary for the grower to accept the generally
established facts: That many chemical elements, such as nitrogen,
phosphoric acid and potash as well as boron, copper, zinc, man-
ganese, magnesium and others, are required for growth and produc-
tion of all crops. When any one of these is lacking in the soil or
exists in unbalanced form, it must be supplied or adjustments
made to permit a good utilization of the other nutrients. The
exact role played by the different nutrients in the growth of plants
is not definitely known, but the external effects or deficiency
symptoms have been scientifically correlated for most nutrients,
enabling the grower to understand and use them intelligently.
Years of study have shown that each of the required nutri-
ent elements has a specific function to perform in the plant, and
that no one element can substitute entirely for another. There-
fore, when an element is present in insufficient amounts to per-
'Technical Director. Soil Science Foundation, Lakeland, Florida.
Department of Agriculture
form its "Specific Function" and, or has antagonistic influences
from other elements, a very definite abnormality develops in the
leaves, branches and fruit. Since the leaf is the seat of almost
all synthesis and growth it is the place where most deficiency
symptoms develop. Because of this condition, a good portion of
this bulletin will deal with deficiency leaf symptom patterns
shown in color as well as black and white half tones. Any character-
istics deficiency symptoms in other parts of the plant will also be
pointed out.
Frequently, two or more deficiency symptom patterns occur
on the same leaf, thus producing a combination pattern which
may confuse the casual observer. For that reason, it is necessary
to study the range of identification characteristics of each nutrient
pattern separately. By so doing, the combination patterns can
usually be recognized. A brief description of the deficiency symp-
tom patterns of the different nutrients is presented, together with
the soil relations, treatments, symptoms of excesses, and histori-
cal usage. In addition, some patterns of leaf chlorosis and toxicities
are presented to give the grower a more complete understanding
of the abnormal leaf discolorations observed in Florida.
The reader is urged to study the illustrations in detail along
with the description, because the plates and figures contain pat-
tern differences that are difficult to describe in words. In each case
typical representative illustrations have been chosen, and along
with each illustration the important differentiating characteristics
and treatments are included.
NITROGEN
Deficiency Symptoms: Since nitrogen has a marked influence on
plant growth in general, its deficiency symptoms are easily recog-
nized by most growers. A deficiency of nitrogen in citrus is first
characterized by a uniform loss of chlorophyll over the entire leaf,
with occasional vein chlorosis in early stages. The symptoms range
from a pale yellowish-green color in early stages, to old ivory color
in the advanced stages. The off-color "hungry" appearance is usual-
ly recognized by most growers, The colors of young and old
leaves are given on the cover. The deficiency extends over the
entire plant, with the greatest severity on fruiting branches, the
leaves of which may show a slight mottling effect in acute cases.
Mlaliutrition Symptoms of Citrus
Severely affected trees show stunted condition, sparse foliage,
dead wood, as well as reduction in size and amount of fruit. Other
than size and amount, the quality of fruit is not adversely affected
The yellowing of leaves and vein chlorosis brought about by
girdling, disease, root-pruning, excess water, or any condition which
interferes with the normal flow of sap in the tree should not be
confused with nitrogen deficiency. One of the symptoms of early
boron deficiency is characterized by bronzed off-colored leaves and
vein chlorosis. See Figure 6.
Soil Relations: Deficiency symptoms of nitrogen may occur on
any mineral soil, but as a rule they are most commonly found on
the thinner sandy types and in neglected groves. Nitrogen fluctu-
ates in the soil more than any other nutrient and shows the least
tendency to accumulate, regardless of the amounts applied. Rec-
ords indicate that liberal amounts of available nitrogen in soil
prior to and during the bloom period and spring growth, with
lesser amounts during summer and fall, favor production and ma-
turity of fruit. If the soil reaction is favorable, (approximately
pH 6.0) the efficiency of nitrogen is improved.
Treatment: The treatment for nitrogen deficiency is too well
known to warrant discussion here. Severe deficiencies should re-
ceive soluble nitrogen, preferably nitrate nitrogen because it pene-
trates more quickly into the root zone. The comparative value of
different sources of nitrogen will be discussed later. If soil mois-
ture is low, it will be difficult for the trees to absorb any form of
nitrogen.
Nitrogen Excess: An excess of nitrogen produces a rank over-
green succulent growth. The leaves are abnormally green, large
and coarse, and the branches are succulent and angular. Excess
nitrogen in late summer and fall may produce tender rind fruit,
and with favorable moisture and warm weather, such fruit tend to
crease and split. The vigorous growth resulting from excess nitro-
gen utilizes other nutrients rapidly, and often develops characteris-
tic dieback and ammoniationn" symptoms, unless ample copper is
present. An over-dose of any soluble salt, including nitrates and
sulphates, will cause a premature droppage of foliage, and even
burning of the leaves.
Historical Use: Nitrogen has been used in one form or an-
other as long as citrus growing in Florida has been an industry.
Its usage is so commonly known that a discussion here would not
be justified.
Departlinent of Agriculture
PHOSPHORUS
Deficiency Symptoms: The importance of phosphorus for all
crops is well recognized. However. no distinct phosphorus defici-
ency symptom pattern develops in citrus leaves under Florida con-
ditions such as the characteristic leaf patterns of magnesium, zinc
and iron deficiencies. A slow stunted growth with small, lusterless
leaves and reduction in crop appears to be the dominant effects
produced by a deficiency of phosphorus in citrus under Florida
conditions.
According to Young and Forsoee (45) of Florida, a phosphorus
deficiency of citrus on organic soils produces small, thick-rind
fruit which drops prematurely. Figure 1 (lower right). They report
no leaf burns due to phosphorus deficiency. Haas (19) of Cali-
fornia reports that a deficiency of phosphorus in citrus is charac-
terized by small, lusterless, brownish-green leaves, which in ad-
vanced cases show irregular burning effects, as illustrated in Figure
1, upper. Moreover, a phosphorus shortage produces a marked ab-
sence of shoots or new branches. These symptoms occur under
controlled as well as under field conditions.
Soil Relations: The problem of phosphates in sands is not as seri-
ous as it is in clay soils, because iron and aluminum compounds
in the clays render the phosphate unavailable. This is especially
true in humid regions where the soils are acid and the reserves
of calcium have been depleted.
It is generally known that phosphates do not leach even on
sandy lands as rapidly as nitrogen. See Tables 4 and 5. For that
reason, continuous application over and above that of crop removals
result in an accumulation of this nutrient. Where the soils are rela-
tively low m fixing agents as it is the case with many Florida
soils, a good portion of the accumulated phosphates appears avail-
able for plant use. Therefore, this nutrient is more efficient on sandy
lands void of extreme relationships than most other nutrients
Treatment: Although there are a number of sources of phos-
phates available as fertilizer, most of them center around acidu-
lated or treated phosphate rock. This is considered the standard
phosphate fertilizer. Where this nutrient appears to be deficient,
the treated and more soluble forms are the most effective materials
available. Where phosphates tend to accumulate, other sources may
be used satisfactorily.
Phosphorus Excess: Due to the high fixing power of clay and
Figure 1. Phosphorus Deficiency Symptoms in the Leoves and Fruit of Oronges.
UPPER: Choracteristic burned areas, according to HAAS (19).
LOWER: Thickened rind (right) with deficiency of phosphorus, YOUNG AND
FORSEE (45).
12 Department of Agriculture
loam soils for phosphates, it is practically impossible to get an
excess of this nutrient on such soils. On sandy soils, however,
large applications of soluble phosphate build up a reserve, which
may become so concentrated as to interfere with the availability
of zinc, copper and other elements West (44) of Australia, showed
that "frenching" (symptoms of zinc deficiency) of citrus was in-
duced by high phosphates. Experimental records (Soil Science
Foundation, Short Research Grove) show that the high phos-
phates aggravate "frenching" and "die-back" of citrus, as shown in
Figure 2. Reuther, et al., (a) reported that excess phosphates
reduce Vitamin C content of fruit juices.
Historical Use: The use of phosphates began in the early days
of the industry in Florida, first as bone meal, later as manufactured
and acidulated phosphates, which are the major sources at present.
Phosphates are not used as extensively in California and other citrus
producing areas as they are in Florida.
POTASSIUM (POTASH)
Deficiency Symptoms: Deficiency symptom patterns of potash
rarely develop in citrus foliage and branches under grove condi-
tions. This appears to be due (1) to the ability of citrus roots
to secure potash from the subsoil layers, and (2) to the relatively
small critical levels of potash in citrus. In the fruit, deficiency
symptoms develop within 2 to 3 years after potash has been omit-
ted from the fertilizer, on sandy soils. The deficiency of the fruit
is characterized by small, thin-rind, smooth fruit which tend
to be soft and drop early compared to the normal. The fruit symp-
toms occur considerably in advance of leaf symptoms. Records show
that the foliage may be normal for several years even on sandy
lands, with no potash in the fertilizer, while at the same time
fruit on such trees become small with smooth rind within 2 or 3
years after omitting the fertilizer.
Under controlled conditions a reduction of potash seems to
stimulate growth at first as evidenced by large sized leaves
which often show a puckered and stitched condition along the
mid-rib. Later the growth and vigor of the trees are retarded and
the foliage may shed prematurely. As the deficiency advances,
the branches show a lack of rigidity and a drooping effect, as illus-
trated in Figure 3, upper The tips of the branches may die with
4a) Proceedings of Fla. State Hort Society. 1948. pages 44 and 55.
Malnutrition Symptoms of Cnitrs
(Courtesy Soil Science Foundation-Short Research Grove )
Figure 2. Symptoms of Zinc Deficiency (Foliage) and Copper Deficiency (Fruit)
in Pineapple Oranges induced by high amounts (35 Ibs.) of superphosphate per
tree in 1942 when the trees were 3 years old. These deficiency symptoms were
induced by unbalanced soil nutrients, rather than by actual deficiencies. This
is a problem common to many groves. These symptoms were in evidence for 2
years following the first application of phosphate. Subsequent applications of
high routes of copper in 1947, and again in 1952 did not produce these defi-
ciencies, indicating that the /4 unit of copper in the fertilizer soon produced a
favorable copper-phosphate balance.
See footnote Table 6, page 56, for fertilizer mixture used. The phosphates were
applied once every 5 years where copper deficiency developed.
The Short Research Grove is located on Lakeland Fine Sand. It was set to Pine-
apple Oranges (Rough Lemon Rootstock) in the summer of 1939.
Department of Agriculture
gum formations in places, and with advanced cases chlorophyll
fades, creating irregular chlorotic areas which become brown, pus-
tular and rust-like in appearance. This rust-like appearance usu-
ally is necrotic, indicating a breakdown of the tissue, as illustrat-
ed in Figure 3, lower.
Soil Relations: For many years it was claimed by leading agri-
cultural authorities that high amounts of potash have a favorable
influence on fruit quality-smoothness of fruit including cold re-
sistance. But recent studies and observations by a number of work-
ers indicate that these claims have no scientific confirmation, and
that the reverse may be the real facts. Since the function of potash
is largely catalytical in nature, the total amount of this nutrient
for citrus is less than that for nitrogen. Furthermore, potash, be-
cause of its solubility, may leach from the plant itself and be re-
absorbed, thus reducing the total amount needed. Because of the
affinity of the soil for potash, it does not leach as completely as
formerly thought, even from sandy soils. See data in Table 6. It
has been known for many years that the affinity of clay soils for
potash is rather high, thus explaining the relatively high levels
of this nutrient in most clay soils. Records during recent years
show that many of the sandy citrus soils of Florida have a marked
affinity for potash in the subsoil layers. This seems to account for the
ability of citrus trees to grow normally when the potash is omitted
from the fertilizer for several years.
Treatment: Like phosphates, there are a number of sources
of commercial potash for agricultural purposes, but the sulphates,
chlorides and nitrates constitute the greater part of tonnage used.
These salts are readily available and can be used for all potash
deficiency symptoms. From 100 to 150 pounds of available potash
per acre will supply needed amounts for sands. Larger amounts
will be needed for heavier soils
Potash Excess: The first effect of excesses of potash is a retarda-
tion of growth. With a large excess there is a premature shedding
of leaves and even a burning or scorching effect, not unlike the
burn from an excess of soluble salts. The burning effect is not as
common as leaf drop. However, a ratio of three to four times
as much potash as nitrogen tends to deplete other soil bases and
retard tree growth. Furthermore, excess potash on sandy soils low
in calcium produces large, coarse fruit of low quality, besides hin-
dering the intake of nitrogen, zinc, magnesium and other nu-
trients. (31) High amounts of lime (excesses) counteract the un-
favorable effects of excess potash. Replaceable potash in the soil
should be approximately 1'l0th that of calcium to maintain
smooth fruit.
.Maolnutrtron Sqmptorn.s of Cairns
Ii;
4w7
Figure 3. DefNciency Synpltos of Pomaesium in Common Grapefruit.
UPPER: Drooping of branches, tshaing lck of rigidity.
LOWER: Advanced case deficiency in the leaves. Left, normal, center yellow
area; right loaf tissue dilintagratd necrosis.
Department of Agriculture
Historical Use: Potash has been used for citrus in Florida al-
most as long as the industry has existed. The early sources consisted
of hardwood ashes, kainit and natural materials. Other citrus
growing areas do not use as much potash as does Florida, largely
due to differences in soil. Before 1940, it was thought that potash
reduced fruit size. But Chapman and co-workers (8) in California,
and Reuther and Smith (31) in Florida, have shown experimental-
ly that high levels of potash increase fruit size and coarseness.
MAGNESIUM
Deficiency Symptoms: Magnesium deficiency in citrus is char-
acterized by a type of leaf chlorosis commonly known in Florida
as bronzing. This discoloration or loss of chlorophyll occurs only on
mature leaves, and is more prevalent on heavily fruiting trees and
branches, and is more noticeable in late summer and fall, but may
be seen any season where the nutrient is deficient.
Although there is a variety of leaf symptoms associated with
this deficiency, the typical cases develop yellow chlorotic areas in
the initial stage on each side of the mid-rib Later these areas en-
large often at an angle to the mid-rib and usually coalesce to form
a yellow zone surrounding a wedge-shaped green area at the leaf
base. As the deficiency advances, the entire leaf becomes yellow or
bronze-like, hence the name. This advanced condition might be
confused with an advanced case of nitrogen deficiency, but inter-
mediate stages can always be found to serve for differentiation
The range of these color patterns is illustrated in Plate 2. The
patterns are usually more pronounced in grapefruit than oranges.
Magnesium deficiency is closely associated with seediness of fruit
and size of crop. Ample magnesium enables citrus trees to marked-
ly tolerate cold. In a large measure magnesium deficiency is re-
sponsible for the alternate bearing habits of the common seedy
grapefruit and pineapple oranges. Affected leaves appear to drop
earlier from the orange than the grapefruit trees, producing a some-
what sparse foliage during the fall and winter, but in severe cases
all varieties drop their affected leaves freely, often leaving com-
pletely defoliated twigs, many of which die and become diseased.
Figure 4 (lower) shows a grapefruit tree severely defoliated as a
result of magnesium deficiency, and the range of the deficiency
in the individual leaves (upper)
-- 0
~
Plte 2. Deficiency symptoms of mognosium in grapefruit loves, showing early
(A) and advanced (B) stages. See page 16 for description.
Department of Agriculture
There appears to be no marked fruit symptoms with this
deficiency except reduced crop yields and alternate bearing quali-
ties. The deadwood and twigs resulting from the deficiency may
increase the disease hazard of the fruit. The deficiency is often
associated with copper and zinc deficiencies, in which case com-
bination symptoms result.
Soil Relations: Magnesium deficiency occurs more generally
on the thin, sandy types of soil. but may be found on heavier types
and even marls;: it rarely occurs on muck and peat soils. Soil acids
as well as excessive amounts of potash and other bases tend to
deplete the soil magnesium. This was markedly true in Florida back
in the late twenties and thirties The actual leaching losses of mag-
nesium are much greater than crop removal in comparison with
those of phosphates. This means that magnesium must be added in
some form to maintain soil needs.
Treatment: Severe cases of magnesium deficiency should have
soluble magnesium at the rate of 75 to 150 pounds per acre, depend-
ing upon tree size. However, in most cases, as well as for mainte-
nance supplies, dolomite in sufficient amounts to hold the soil reac-
tion to about pH 60 will supply the needed magnesium, provided
the other nutrients are not in excess. It may be necessary to use
soluble forms on marls, but even here the magnesium in dolomite
can be used.
Magnesium Excess: Due to the marked tendency for soluble
magnesium salts to leach and the slow availability of carbonates
and phosphates, it is doubtful that a rational practice would cause
crop injury. Excessive applications of dolomite rarely produce a
soil reaction of pH 7.0 or above, and no ill effects have been re-
ported even where excessive rates of dolomite have been made. But
excessive amounts of a magnesium sulphate will deplete the soil of
other bases and result in an unbalanced nutrient ratio. This may
delay normal fruit coloring
Historical Use: Although Averna-Saca (*) reported the value
of magnesium in correcting certain chlorosis of citrus on ferrugin-
ous soils in 1912, the leaf symptoms of magnesium deficiency were
first described by Reed and Haas (30) in California in 1924. La-
ter Bryan and DeBusk (4) reported that the widespread trouble
in Florida known as Citrus Bronze was due to magnesium de-
ficiency, and Tait (43) further demonstrated the value of differ-
ent sources of magnesium. Bahrt (1, 2) and co-worker reported
that, lime, manganese, magnesium and potash salts were beneficial
**' Bol. Agr. ,Sao Paulo. 13. Ser. 1912 '2 : 129-150. 1912.
Figure 4. Deficiency Symptoms of Magnesium in Grapefruit.
UPPER: Range of magnesium deficiency symptoms in grapefruit leaves, show-
ing early stages on left and progressive stages on right.
LOWER- Severe case of magnesium deficiency in grapefruit tree.
Department of Agriculture
on bronze groves as early as 1934, but failed to associate the bronze
with magnesium deficiency until 1937. In the later year, workers
in Australia (y) reported the beneficial effects of dolomitic lime-
stone (started in 1932) in correcting a leaf chlorosis of citrus,
which proved to be a magnesium deficiency Several investigators
have shown that chlorotic and bronze leaves of citrus contain
less magnesium than healthy leaves.
The records show that Florida citrus industry was suffering
severely under the strain of magnesium shortage in the early
thirties and that they were aggravated by high levels of potash
and phosphoric acid in the fertilizer. A rational use of magnesium
during the past 20 years has been of invaluable help to the in-
dustry Since citrus needs liberal calcium and favorable soil pH.
dolomite has served a three fold purpose.
CALCIUM
Deficiency Symptoms: Only in rare cases has a deficiency symp-
tom of calcium booeen reported under field conditions of any crop,
and none for citrus. Under controlled conditions, however, cal-
cium deficiency symptom patterns have been described for citrus
by Reed and Haas (30), and Bryan (5). These symptoms are charac-
terized by a marked stunted and hard condition of the tree, with
small leaves. The flushes of growth are short, with a tendency
for the terminal branches to die back. In severe eases the leaves
become chlorotic at the margins and tips. which progresses toward
the leaf center and base (Figure 5). In some ways this deficiency
resembles a mild case of boron toxicity. But close examination
reveals that the undersurface of the leaves with the boron pat-
torn has gum excretions. (See Figures 5 and 8.) The calcium defi-
ciency pattern may be confused with an advanced case of Biuret
toxicity. The differences consist of smaller leaves with calcium de-
ficiency, and the chlorosis following the leaf margins, whereas
the Biuret toxicity is somewhat patchy in early stages, beginning
in the tip of the leaf and spreading inward with severe cases
to include most, if not all, of the leaf. The tips of calcium deficient
leaves are often blunt and sometimes incompletely developed.
Soil Relations: Of all the nutrients, calcium seems to have
the gicatest controlling or balancing effect in the soil. It con-
stitutes over 50',% of the active bases in productive soils, being
Alaintttratton Sym iptoios of Citrus
Figure 5. Deficiency Symptoms of Calcium in Gropefruit Leaves and Trees.
(Controlled Cultures.1
UPPER: Leaves showing loss of chlorophyll in tips and edges of leaves,
LOWER: Normal tree on right contrasted with calcium deficient tree on left
held largely in a replaceable form by the soil colloids (clays and
humus). This in a measure represents the available calcium pres-
ent. Soil acids tend to dissolve the calcium, thereby increasing the
intensity of leaching losses, with a resultant lowered fertility.
In humid regions the calcium losses from leaching alone are great-
er than that of any other nutrient, varying from 200 to 600 pounds
or more per acre annually. It is highly desirable to maintain the
needed calcium to destroy acids as well as to serve as a balancing
agent for biological processes. A rational use of lime is the secret
of soil fertility in most areas, including Florida.
Treatment: Only under unusual conditions does the soil require
calcium for nutritional purposes to a greater degree than lime
Department of Agriculture
for neutralizing soil acids. Although a soil reaction of approximate-
ly pH 6.0 is to be desired, it should be distinctly understood that
pH alone is not enough, and dependence on it may lead to trouble.
Records show that rain water has a favorable pH, but no calcium
and magnesium. Ample calcium should be the objective, rather
than a pH of 6.0 or otherwise. Sands and sandy soils should
have as much as 700 to 1000 pounds of calcium per acre 12 inches
of soil. This may be supplied from lime, slag, oyster shells, or dolo-
mite. Heavy soils and soils high in organic matter should have 50
to 100 per cent more calcium than that required by sandy soils.
Dolomite has done more to improve groves, per unit cost, than
any other single commodity. It supplies both calcium and mag-
nesium without the risk of too high pH values.
Calcium Excess: An excess of calcium in the soil solution rarely
occurs, since the sulphate and phosphate of calcium have a low
solubility in soil water. But an excess of calcium carbonate or hy-
drate on sands produces high pH values which in turn reduce
the availability of manganese, zinc and iron. Many of the unpro-
ductive groves in Florida, in the twenties, were due to excessive
amounts of hydrated and carbonated lime (15). Fortunately an
excess of dolomite does not produce unfavorable pH values and con-
sequently does not produce the locking effect on the secondary nu-
trients.
Historical Use: Calcium in the form of lime, shells, ashes, bone-
meal, and as a carrier of phosphates in the fertilizer, has been
used for many decades. But the use of lime on Florida soils
came into ill-repute about 1910 following excessive applications
to groves. The use of high calcium lime is still a doubtful prac-
tice among some Florida growers, but where magnesium and
trace elements are applied, its ill effects can be corrected. It is
interesting to note that since 1933, dolomitic limestone has been
used on Florida soils with marked success. Its greatest value lies
in the magnesium content and non-injurious effect on the soil
reaction, regardless of amounts.
BORON
Deficiency Symptoms: Boron deficiency in citrus foliage is char-
acterized by a marked tendency of the leaves to wilt, curl and
pucker. They have a dull brownish-green color with the absence
of luster.
Figure 6. Leaf Symptoms of Boron Deficiency as described by Smith and Routher for Valencia Orange. Proc. Fla. State Hort. Soc. 62, 1949.
Left: Early symptoms of curling and yellowing along midrib and lateral veins.
Right: Later stage showing pronounced veinal chlorosis, enlarged veins and defoliation.
Depart ment c of Agriculture
Young leaves shed prematurely and the stems show gum for-
mations and often die in irregular areas, The midrih and lateral
veins of young leaves ale chlorotic and are usually enlarged with
some splitting The young branches may have multiple buds with a
rosette appearance somewhat like that of copper deficiency. The
old leaves are often thick, brittle with bronze color, somewhat
like magnesium deficiency, and may develop split veins (Figure 7,
center and upper).
Boron deficient fruit is characterized by small, misshapen.
hard fruit which frequently contain brown gummy discoloration
in the albedo layer of ihe rind (Figure 7, lower). The fruit is
often lopsided. Gum may be found anywhere in the fruit, which
often shows dark spots, dark seed coat, undeveloped seed and
marked dryness. Sour rootstock seems to be more sensitive to
shortage of boron than lemon root.
Soil Relation: Observations, indicate that acid soils in humnd
regions often show distinct boron shortage, frequently containing
less than one part per million of water soluble boron. Like other
nutrients, the availability of boron is dependent on the soil reaction
as well as other nutrients present. Boron deficiency symptoms tre
noore evident during prolonged periods of drought than during nor-
inal seasons and where excess lime is used on light soil But boron
deficiency may occur on any soil type.
Treatment: Soil application of borax has usually been the spe-
cific treatment for this deficiency with most annual crops. This
is also true for citrus. In addition, borax has been successfully ap-
plied to citrus in a spray, at the rate of 1 pound per 100 gallons.
Soil applications range from 10 to 15 pounds borax per acre on
light sands to as high as 50 pounds per acre on marls and heavy
soils. Equivalent amounts of boric acid, fertilizer borate or other
boron sources are being successfully used. A Fritltd Borate-gound
glass-like material-is comparatively recent in usage. Because of its
slow solubility there is less risk involved on acid soils than the
water soluble forms.
Boron Excess: Like copper, boron is poisonous and quickly
shows evidence of excess, especially on ac2d sands. Yet, there
is an optimum range for its usage. Soil applications of soluble
boron rarely produce toxicity on neutral and marl soils. Because of
the extremely sensitive nature of citrus to excess boron, growers
have heard more about toxicity resulting from excess than about
boron deficiencies.
Boron toxicity is usually a result of excess boron in irrigation
Figure 7. Corking of veins and curling of terminal leaves of Grapefruit "A",
puckering of leaves with corking and splitting of veins "B" and "C", accompa-
nied by leathery and brittle conditions with bronze colorations are symptoms
of Boron deficiency as reported by Hoas
LOWER: Dry discolorations, abortive seed on left and hard "rind" with gum
formations, right, are Boron deficiency symptoms of fruit as reported by Morris.
Department of Agriculture
water used in alkali regions In Florida only limited cases of boron
toxicity have been reported. These have been associated with borax
treated crates left in the grove. In some instances in Florida and
California, evidence of excess boron in the fertilizer and spray
has been reported.
The first evidence of boron toxicity is a marked yellowing of
leaf tips. This yellowing often extends down the edges or sides
of leaves nearest the tips, and the yellow and green portions fre-
quently blend showing a somewhat mottled effect. Figure 8 shows
a typical case of boron toxicity in grapefruit, which is more sensitive
than the orange. Affected leaves frequently show dead areas at
tips and leaf margins. In severe cases the leaves shed quickly,
depending on the severity of the toxicity. With severe cases the suc-
cessive flushes are almost white and the twigs frequently die. The
under surface of the chlorotic areas shows a rough, resinous ex-
crescence in the form of tiny brown to yellow pustules, which
serves to help identify the symptoms. These excrescences turn
Figure 8. A mild case of Boron Toxicity in Grapefruit leaves, showing yellowing
of leaves at tips and margins. Gum excretion on the undersurfoce of leaves
serves to identify boron toxicity.
Malnutntion Symptoms of Citrus
black with age. This resinous excrescence on the under side of
leaves differentiates boron toxicity from fluoride toxicity. In light
cases of toxicity, small whitish areas occur between the veins
and near the leaf margins. These areas are sometimes confused
with injury from the six-spotted mites.
Since many boron compounds are soluble in water, their in-
jurious effect in the soil is usually alleviated by flooding and rain.
Calcium renders boron insoluble and this can be utilized to over-
come the excess in most instances by working 400 to 800 pounds
hydrated line per acre into the soil and watering down. This, of
course, applies to the sandier types where the toxicity is most com-
monly found. Larger amounts would be required on heavier soils.
Historical Use: Haas (18) and co-workers in California point-
ed out the symptoms of boron deficiency in the vegetative parts
of citrus grown in water cultures (1927, 1930). Later Morris (24)
of Rhodesia reported symptoms of boron deficiency in fruit. Ob-
servations in recent years indicate that both leaf and fruit symp-
toms occur in Florida, and experimental records confirm these
observations (38). Boron is now used in either sprays or in fertili-
zers as a general practice for citrus in Florida.
COPPER
Deficiency Symptoms: A deficiency of copper in citrus is much
more frequently noted in the fruit than in the foliage and
twigs. The first foliage symptoms to develop are deep green, over-
sized coarse leaves accompanied by long, vigorous, pliant and
often "S" shaped shoots, giving the appearance of excessive ni-
trogen fertilization. For this reason the early workers concluded
that diebackk" or exanthema (now known to be copper deficiency)
was due to excessive nitrogen fertilization. In the early stages of the
deficiency, young twigs often develop small, blister-like gum pockets
between the bark and wood at or near the buds. With the progress
of the disease the terminal twigs usually develop brown staining and
dieback at the ends, and reddish-brown, rigid eruptions develop
from the bark on the older twigs, giving rise to the term "Red Rust",
frequently applied to this disease by the grower. As the deficiency
symptoms become acute, multiple buds frequently develop in the
axis of the leaves. In aggravated cases the production of new shoots
and dieback of older ones result in a bushy rosette type of growth
These symptoms are illustrated in Plate 3.
Department of Agriculture
The fruit usually develops symptoms of copper deficiency before
the branches are affected, and in mild cases of the deficiency, the
symptoms may be confined entirely to the fruit. These are character-
ized by dark brown, gum-soaked eruptions, varying from numer-
ous, minute, scattered specks to spots one-eighth inch in diameter.
These eruptions may occur as irregular blotches, frequently cover-
ing large areas of the fruit and turning black as the fruit matures.
Fruit blemished as a result of diebackk" or exanthema are termed
"ammoniated" by the growers and have no commercial value.
This deficiency may occur on various kinds of citrus but is more
prevalent on oranges than grapefruit and tangerines.
Since copper deficiency has a more marked effect on the
fruit and twigs of citrus, a deficiency of other elements may mask
these symptoms. This is particularly true with a deficiency of zinc
and magnesium, and even manganese at times. A shortage of these
elements retards appearance of copper deficiency. But as a rule,
the symptoms are specific and the differences are merely a matter
of degree and not of kind. In severe cases, fruit symptoms are the
most reliable guides for copper deficiency. With acute deficiency of
one or more elements, the less pronounced deficiencies may not be
apparent until the acute case is alleviated
Copper deficiency is common with young trees on new land.
This is due to the low copper content of virgin soils, and the
tendency of active organic matter to render copper unavailable.
Heavy fertilizer without copper usually causes ammomation or cop-
per deficiency in young trees.
Soil Relations: Although copper deficiency is known to occur
on most any soil type, it is more prevalent on new land and soils
with clean cultural practices. Soils having a high humus content
require more copper than soils having low humus. Any treatment
or practice which induces rapid growth of trees may bring about
a copper deficiency where no copper is added in the spray or fertili-
zer program. A rapid growth necessitates proportional amounts of
copper to avoid a deficiency of this nutrient. Experimental records
(45) by a number of workers show that high amounts of available
phosphates cause a copper deficiency. The records indicate that high
phosphates hinder the intake of copper by the plants Copper
compounds in the soil are less soluble than compounds of nitrogen
and potash. Because of this fact. repeated copper applications result
in copper cumulation in soil.
Plate 3. Deficiency symptoms of copper in Pineaople oranr^ O hnwi g. ,nrlv (A)
and advanced (B) stages. ISoo page 27 for doscription.1
30 Department of Agriculture
Treatment: Copper sulphate, either in the form of a spray or as
a soil application, has been the usual treatment for this defi-
ciency. The spray produces much more rapid corrective results, but
is often objectionable because of the possible scale infestation
following its usage. If the soil is free of other nutrients which
cause antagonistic effects, the amounts of copper required to supply
needs are relatively small. Possibly 1 '100 to 1 50 that of nitrogen
will suffice. Organic soils and soils with high reserves of phos-
phates will need more. Within recent years, copper oxide, hy-
droxide and even finely ground metallic copper have been used
satisfactorily as a soil or spray amendment
Copper Excess: Very small amounts of copper are necessary for
tree and fruit needs, and excessive rates (3 to 8 pounds per tree)
will cause injury, even on marls, resulting in the splitting of bark,
gumming, defoliation and possible death of tree. Many growers have
applied liberal amounts of copper in the fertilizer (sometimes as
much as Y4 that of nitrogen) in addition to copper spray for a num-
ber of years, especially during the 40's, Since copper does not leach
from the soil to any extent this has resulted in a marked accumu-
lation of copper in some soils amounting to 800 pounds or more of
copper oxide per acre. This has become a serious problem in many
groves, especially on acid sandy soils. The excess copper is toxic to
tree roots, causing unthrifty and markedly stunted trees. It is
antagonistic to iron and accounts for the widespread problem of
iron deficiency in many Florida groves. Liberal amounts of lime
and or soil amendments sufficient to raise the soil reaction to pH
6.0 or above will reduce the severity of the problem of excess
copper. Iron salts, including Chelated iron, may be needed to correct
the iron deficiencies. Liberal phosphates are known to retard cop-
per absorption.
Historical Use: The symptoms of citrus diebackk" or exanthe-
ma were first described in 1875 by Fowler (12) from Florida, where
the trouble was known to have occurred as early as 1864 (32).
It was first investigated in 1896 by Swingle and Webber (42) who
concluded that it was a malnutritional disease, and subsequently by
Floyd and others. Records by Frotcher (xx) show that Bordeaux
spray successfully controlled diebackk" as early as 1897, but little
attention was given to this treatment. Floyd (13, 14) reported simi-
lar results in 1908 and 1913, as have other workers in this and varied
lxxI Proc Fin State Hort. Soc. 1897.
Malnutrition Symptoms of Citrus
countries (10). Along with the use of copper, either in Bordeaux
spray or soil treatments for diebackk" or exanthema, it was ob-
served for some years that Bordeaux frequently exerted a stimulat-
ing effect on the tree. In the middle thirties, Fudge of the Florida
Citrus Experiment Station showed experimentally that copper reg-
ulated the absorption of nitrogen and served in a nutritional man-
ner for citrus. While some still classify diebackk" or exanthema of
citrus as a physiological disease, it is in reality a deficiency. Like
many other agricultural problems, the practice in the use of copper
to correct abnormalities preceded the theory regarding its function.
Furthermore, if small amounts produced good results, more were
often used, resulting in excesses.
MANGANESE
Deficiency Symptoms: The symptoms of manganese deficiency in
citrus are usually less distinct than those of magnesium and zinc
This is due to the small contrast of the leaf color in the deficiency
pattern, and the limited areas showing this deficiency. Nevertheless.
the manganese pattern is specific and well defined, and can be easily
recognized once it is understood.
The symptoms occur on both young and mature leaves, without
affecting leaf size, whereas zinc deficiency has a marked reduction on
size of leaves, and magnesium deficiency pattern is characterized by
green veins on a light green background, and may be confused with
iron deficiencies. (Compare Plates 4 and 5.) As the leaves become
more mature, the pattern develops bands of green along the main
and lateral veins with light green tissue. The color contrasts are less
vivid than in the case of zinc deficiency. Plate 5 shows the range of
the manganese deficiency in grapefruit leaves. The light green area
extends to the leaf margin in severe cases; and the advances cases
are somewhat similar to the early stages of zinc deficiency, al-
though the color contrasts are never as great. If the deficiency of
manganese is severe, the pattern persists with normal size leaves
and the light green colors may develop a gray to slight bronze effect,
which might be confused with magnesium deficiency. Manganese
deficiency is often found on marl soils, hence the term "Marl
Frenching."
The deficiency is seldom severe enough to cause twig symptoms.
With acute cases, however, the twigs may die, associated with a
marked reduction in growth. The symptoms of dying twigs are not as
severe as in the case of zinc deficiency, nor do the trees show the
Department of Agriculture
rosette or bushy appearance. Manganese deficiency was for a long
time confused with frenching or zinc deficiency. From systematic
studies of zinc and manganese treatments, the pattern differences
have been identified (6).
Manganese has a favorable effect on the quality of oranges and
tangerines, according to Skinner and Bahrt (37).
In contrast with copper and zinc, manganese deficiency does not
affect oranges and grapefruit as readily as it does tangerines, Tem-
ples and King oranges.
Soil Relations: Manganese deficiency appears more often on
marl and over-limed soils than on the neutral and acid soils. This is
largely due to the high pH values (pH 7 0 and above) of maryland
over-limed soils which render the manganese insoluble. In some
cases acid soils show manganese deficiency as a result of soil deple-
tion and fixation. Where crop yields are heavy, the soil may become
depleted of available manganese, but in most cases the deficiency
results from unbalanced soil conditions as much as from actual
shortage of the soil.
Treatment: Manganese sulphate and oxide are commonly used
as the corrective for manganese deficiency, applied in soil treatments
at the rate of 1, 2 to 2 pounds per tree, the amount depending on tree
size. severity of case and type of soil. Manganese sulphate may
be applied in spray form, using solution of about the same con-
centration as copper sulphate in Bordeaux, or in conjunction
with Bordeaux and lime sulphur sprays. Like copper and zinc
spray, the manganese may increase the scale hazaid, thus necessi-
tating an oily spray to follow later. Unless the deficiency is severe,
soil treatments are generally used, except on marl soils. The spray
treatment gives quicker results, but the effects are not as long
lasting. In soil treatment, mulching, or use of heavy cover crops with
applications of manganese, will usually suffice.
Manganese Excess: No known symptoms of manganese excess
have been reported in Florida, though the rates of application have
been high in places. As with other nutrients, excessive amounts of
manganese will hinder the utilization of other nutrients, and may
even be toxic.
Historical Use: Manganese has become of general use in agricul-
ture within recent years. Its use on citrus in Florida was suggested
by the stimulating effects produced in truck crops growing on marly
soil. first reported by Schriener and Dawson (36). Following these
results, Florida citrus growers used manganese with success on
Malnutrttion Symptoms of CUrtis 33
C
C
-D
0)
U C
C
t
C
C
~ 0)
E
C,
C
< Li]
Plate 4. Deficiency symptoms of manganese in grapefruit leaves, showing early
(A), intermediate (B) and advanced (C) stages. ISee page 31 for description.)
Department of Agriculture
marly soils. Skinner and his co-workers (37) later reported that
manganese on acid soils had a marked improvement on the quality
of fruit, while Camp and Peech (6) correlated manganese deficiency
in citrus with soil analysis. Manganese is widely used in Florida
and California on citrus and other crops, especially on alkaline soils
and soils low in available manganese.
IRON
Deficiency Symptoms: Iron deficiency in citrus has been com-
monly referred to as iron or marl chlorosis. The latter term, howev-
er, is a general one applied with equal frequency to manganese
deficiency, and is also of widespread occurrence on marl soils. Within
recent years, iron deficiency in citrus has markedly increased on
acid sandy soils due to the accumulation of copper.
Iron deficiency is characterized by a general chlorotic condition
of the leaves, particular the younger ones, with the midrib and
smaller veins retaining their chlorophyll longer than the leaf tissue,
resulting in a green network on a yellowish-green or light green
background. The range of these colors and veinations is illustrated in
Plate 5. In severe cases the young leaves are small and yellowish
to old ivory in color and may be almost free of veination. Such
leaves usually shed early, leaving a defoliated effect. In light cases,
the leaf tissue may become green as the leaves mature and the
netted effect disappears entirely. This is not unusual on sandy soils,
but severe and chronic cases are usually associated with marly or
over-limed soils.
In acute cases, the twigs die back severely in the tree tops and
extremes of the branches, showing a marked decrease in tree size
Such trees produce little or no fruit but other than size of crop no
characteristic fruit symptoms have been associated with iron de-
ficiency. Although no varieties of citrus are susceptible, oranges
seem to be the most severely affected.
It is quite common to find other deficiencies associated with iron
deficiency in citrus. This is particularly true with manganese and
zinc. Under such conditions there is definite blending of the indi-
vidual patterns. Careful examination, however, shows that the
specific patterns persist and can be recognized in the presence of
others.
<
Va
-v
Plate 5. Deficiency symptoms af iron in orange leaves, showing early (A) and
advanced (B) stages. (See page 34 for description.)
36 Department of Agriculture
Soil Relations: There are three soil conditions conducive to iron
deficiency in citrus, namely: (1) marl and alkaline soils, (2) sands
with white sandy subsoil and (3) sands which have a high amount
of cumulated copper. Marl and alkaline soils usually induce iron
deficiency. Here the soil reaction has a positive and controlling
effect on the avathability of a nutrient. An alkaline reaction re-
duces the availability of iron, thereby producing an iron chlorosis.
An excess of carbonates on sand produces an alkaline reaction and
accounts for much of the iron chlorosis in sandy annual crops as
well as citrus. This is greatly aggravated in soils with a low content
of organic matter.
Citrus trees growing on light sands with white subsoil often
show iron deficiency patterns, yet the total content of iron in such
soils appears relatively high. This is aggravated by unfavorable soil
reaction or excess of other nutrients, particularly copper and heavy
metals. Excesses of copper seriously aggravate iron deficiency on
acid soils and hinder production. Records by many growers indicate
that iron improves fruit color, especially on the light soils.
Treatment: No entirely satisfactory treatment for iron deficiency
has been developed for citrus on all alkaline soils. But some of the
new Chelated materials offer promise. The Chelate known as
"Verson-ol" is successful for some marl soils There is good reason
to feel that satisfactory chelates will be perfected for all alkaline
soils. A practical method of treating this deficiency on such soils
involves the use of heavy mulching with organic matter and acid
fertilizers. The acidulated effect resulting from the fertilizer and
organic matter will usually bring enough iron into solution to alle-
viate the trouble, except where the mall extends to the surface.
Iron sprays have not been as satisfactory with citrus as they
have with pineapple and other crops. In some of the Western states,
(33) injection of soluble iron salts, such as iron citrate or tartrate.
directly into the trees has been known to give beneficial results
This treatment usually has to be repeated at somewhat frequent
intervals, and is objectionable because of the damage to the wood.
On thin, sandy soils of acid or neutral reaction, iron sulphate
applied at the rate of 1 to 3 pounds per tree has given beneficial
results. Even here the use of mulches proves helpful. Chelated iron
is much faster and more desirable than the sulphate in severe cases.
But the amount of iron applied in the Chelates is very small and
the treatment has to be repeated almost each year Observations
Malnutrition Symptoms of Citrus
and limited experimental data indicate that iron in slags will alle-
viate iron deficiency if the soil pH is favorable. Where copper is
excessive, adjusting soil pH to 6 0 or above is necessary to avoid
severe toxicity.
Iron Excess: The soluble iron salts such as sulphates and chlo-
rides are acidic in nature, and will burn the moist foliage and fruit
if allowed to come into contact with them. All the common iron
salts become insoluble soon after being incorporated into the soil
due to the tendency of iron to form soluble compounds with other
soil constituents and nutrients. For this reason excess iron reduces
the availability of phosphates. In practice, it is doubtful that
difficulty will be experienced from excess iron except under rather
special and very acid conditions. The chelates are more acid than the
common salts, and will burn foliage and fruit if not used with
caution.
Historical Use: Iron deficiency in citrus as well as other crops
has been a serious problem in some regions for many decades. This
is particularly true in alkaline soils. (9), (11), (33). Many inves-
tigators have studied this problem with varied degrees of success.
The use of chelated iron was first studied in California. Leonard and
Stewart of Florida Citrus Experiment Station showed that it was a
ready and quick method of combatting iron deficiency of citrus in
Florida This has proven to be very valuable for severe cases of iron
deficiency.
ZINC
Deficiency Symptoms: Like magnesium, zinc deficiency symp-
toms are characterized by specific leaf discolorations commonly
known in Florida as "Frenching," and in California as "Foliocello-
sis" and "Mottle leaf." The initial stages of the deficiency appear as
irregular chlorotic areas in the leaf tissue, between the main and
lateral veins The tissue immediately adjoining the veins remains
green, while the chlorophyll disappears (or fails to develop in the
leaf tissue). This results in an irregular, mottled or variegated mix-
ture of vivid green and white to yellow colors These colors and
range of leaf patterns are illustrated in Plate 6. These patterns will
serve to identify the zinc deficiency more correctly than word de-
scriptions.
In the early stages of the deficiency, the characteristic leaf pat-
tern may occur on apparently normal sized leaves, but as the de-
ficiency becomes more acute, the new leaves are small, narrow and
Department of Agriculture
pointed, with a greater loss of chlorophyll as illustrated m Plate 4
(B). Small, pointed leaves are one of the distincitve zinc deficiency
symptoms in citrus.
Associated with the deficiency symptoms, there are marked ten-
dencies for twigs to be small, short and bushy. These twigs are
weak and die back rapidly, leaving an abundance of dead wood and
partly defoliated branches so commonly associated with zinc de-
ficiency in the acute stages. This advanced deficiency is often asso-
ciated with dense interior growth of water sprouts.
Although zinc deficiencies may occur on all varieties of citrus, it
is most severe on oranges and least severe on tangerines. Pineapples
and Valencias are more susceptible than the early varieties of or-
anges. The deficiency is commonly associated with copper and mag-
nesium deficiencies and may appear more severe in combinations
than when alone, because of the increased weakness of the trees.
But the individual leaf patterns remain almost unchanged.
Fruit produced on zinc deficient trees is usually small, offsize,
and of poor quality. In severe cases, it is very small with woody pulp
and insipid taste, except when borne on water sprouts (so common
with zinc deficiency). Here it is large, coarse and of poor quality.
Soil Relations: Although zinc deficiency in citrus may occur on
almost any soil type, it'is most commonly found on marls, over-
limited or strongly acid soils. Excesses of lime, nitrogen, phos-
phates, potash and other nutrients tend to retard the availability of
zinc. A pH of about 6.0 appears to be the optimum reaction for the
availability of zinc under the soil conditions in Florida. The neces-
sity for a well-balanced fertilizer is more important on sandy lands
than on heavier types. Zinc is more sensitive to unbalanced nutri-
ents and soil reaction than most other nutrients. Since zinc does not
leach, even from sandy soils, its use in sprays and fertilizer during
the past two decades has resulted in a build-up of zinc in many
grove soils. Consequently the zinc problems have been reduced.
Treatment: Zinc sulphate spray was the common treatment for
this deficiency in the early years of its usage. California growers
were the first to use zinc oxide as a successful treatment for this
deficiency Zinc oxide and carbonate are now being successfully used
in many cases But the scale problem is usually worse following
sprays. Within recent years many growers have successfully used
soil applications of zinc, where the soil reaction and phosphates can
be modified
The most widely used treatment for zinc deficiency consist of
two to four pounds of neutral zinc per one hundred gallons of spray
These rates are for corrective measures One-half these amounts will
suffice for maintenance. The zinc in zmeb sprays furnishes a
goodly portion of zinc needs in most groves. Soil applications at the
0
C
1),
ti
-v
Plate 6. Deficiency symptoms of since in orange laves, showing typical (A) and
advanced (B) stages. ISc page 37 for description.
40 Department of Agriculture
rate of 1 3 to 2 3 pound of the sulphate or the equivalent per tree
annually will furnish ample zinc for citrus, except in unbalanced
soils.
Zinc Excess: Excess zinc in the spray may aggravate the scale
problem and over-green the fruit, especially if applied as a spray late
in season. Due to the tendency for insoluble zinc compounds to form
in the soil, an excess of zinc would not likely occur, except with
large amounts on rather light soils. Zinc is not as toxic as copper, but
excess rates would likely cause a burning and loss of leaves.
Historical Use: The use of zinc as a corrective for frenching in
citrus developed first in California about 1932 (11, 26), (32), (33).
Its specific usage on citrus resulted from a series of studies dealing
with the influence of secondary elements on little leaf of deciduous
fruit (11). Within recent years, investigators in many citrus grow-
ing areas have shown the specific needs of zinc for citrus. It is now
widely used and accepted as a regular part of citrus production pro-
gram.
MOLYBDENUM
Deficiency Symtoms: The symptom of molybdenum deficiency
appears first as water soaked areas in the spring flush, later develop-
ing into interveinal circular chloritic areas. It is more noticeable
during the summer and early fall months. Figure 9 gives a typical
circular spot pattern. In this figure the green and yellow chlorotic
Figure 9. Molybdenum Deficiency in Orange leaves. This deficiency is charac-
terized by yellow circular chlorotic areas. (See text.) It was formerly known as
YELLOW SPOT.
Malnutrition Symiptoms of Cilrus
areas are contrasted in black and white. This yellow circular spot-
ting is a positive identification of molybdenum deficiency. With ad-
vanced cases the yellow tissue becomes necrotic and often disap-
pears, leaving holes in the leaves. Severely affected trees may
become defoliated and the fruit show marked breakdown of the
rind The deficiency has been reported in all kinds of fruit, but trees
on grapefruit lootstock appear to be the most susceptible.
Soil Relations: Molybdenum deficiency is found on acid sands far
more than on heavier and better types Low nitrogen fertilizer on
deep acid sands usually shows this deficiency more than on the
normal soils, and it is rarely if ever noted on marl soils. Acid fer-
tilizer aggravates the deficiency, whereas neutral fertilizers and lime
usually relieve it The availability of soil molybdenumn seems to
decrease with an increase in soil acidity It appears that extremely
low amounts of water soluble molybdenum are required, ranging
from 5 1000ths or less parts per million before the deficiency symp-
toms develop. The deficiency is somewhat seasonal and may disap-
pear without any special treatment. Only in rare cases does it
influence production. Liberal amounts of dolonmite often correct the
deficiency
Treatment The ai munt of molybdenum necessary for plant
growth, including citrus, is indeed very small, amounting to grams
rather (han pounds per tree. The actual amount to correct deficiency
ranges from 1 to 2 ounces of sodiuni mol1bdate per 100 gallons of
spray of equivalent amounts from other soluble sources. It can be
satisfactorily applied in ]mne sulphur spray Affected tiees are rather
responsive, and favorable results show up 2 to 4 weeks following the
application. Wherever a deficiency is suspected, the application
should be made in the spring.
Historical Use: Floyd (13) first described this patten as yellow
spot in 1908, reporting it as being present in many groves in Florida
at that time. Since then several attempts have been made to de-
termine its cause, all of which were unsuccessful until 1950, when
Stewart and Leonard (41) of the Florida Experiment Station
showed experimentally that yellow spot was due to a deficiency of
molybdenum
LEAF CHLOROSIS AND TOXICITIES OF CITRUS
Since deficiency symptoms of many nutrients involve a loss of
chlorophyll, it appears advisable to present the commonly observed
chlorosis and toxicity symptoms induced by certain chemicals in
order to avoid confusion and mistaken identity. The following leaf
abnormalities have been associated with certain chemicals, namely:
(1) Perchlorate Chlorosis induced by impurities in Chilean Nitrate
of Soda-Potash. (2) Biuret Chlorosis induced by impurities in Urea,
Department of Agriculture
(3) Arsenic toxicity chlorosiss) induced by excess arsenic in sprays,
(4) Fluorine toxicity induced by gaseous fluorine and fluorides
from triple super phosphate plants, (5) Boron toxicity resulting
from excess boron in either spray or fertilizer. (Fig. 8, page 26).
1. PERCHLORATE CHLOROSIS: The yellow tipping of citrus
leaves has been observed in Florida for many years and was once
thought to be associated with excess boron in certain fertilizers.
The symptoms first develop at the leaf tip and may be confused with
boron toxicity, but careful examination reveals that the yellow
tipping, that is, the chlorotic areas, do not blend with adjoining
green tissue. The transition from green to chlorotic areas is sharp
and abrupt, producing a patchy appearance; whereas the boron tox-
icity pattern shows a gradual change from green to chlorotic areas,
producing a blend of colors. Furthermore, the under surface of the
yellow tipped leaves is free from resinous excretions which are
common with boron toxicity. The difference in the patchy appear-
ance and blends is illustrated in black and white in Figure 10, and
can be easily recognized by the casual observer without confusion.
The yellow tipped pattern has been experimentally proven to be due
to perchlorate impurities in Chilean Nitrate of Soda-Potash (40).
The chlorosis is less common now than in former years and has little
or no influence on production. Reports from producers indicate that
these impurities are being removed from the commercial products.
Figure 10. Perchlorote Chlorosis in Grapefruit Leaves. The patchy-like chlorotic
areas, indicated by light color in above figure, are characteristic of Peichlorate
Chlorois..
Malnutrition Symptoms of Citrus 43
Figure 11. "Biuret" Chlorosis in citrus leaves following application of Uramon
containing Biuret impurity.
LEFT: Orange leaf showing slight Biuret pattern.
CENTER and RIGHT: Grapefruit leaves showing severe Biuret patterns. The
blends of chlorotic areas, light into green areas (black), differentiate the Biuret
Chlorosis from Perchlorate Chlorosis. The absence of gum on undersurface of
chlorotic areas differentiates the Biuret Chlorosis from Boron toxicity.
2. BIURET TOXICITY: A leaf chlorosis resulting from sprays
and soil applications of urea has caused considerable attention dur-
ing recent years. The chlorosis has been experimentally shown by
Oberbacker (26) to be due to Biuret impurities in commercial
grades of urea. The symptoms first develop at the leaf tips and
margins, and the early stages may be confused with the early stages
of Perchlorate Chlorosis; but with the Biuret, the green and chlorotic
areas blend, though some patchy appearance may be in evidence.
The color of Biuret chlorosis is yellow compared to an orange color
with the Perchlorate chlorosis. The advanced cases of Biuret chloro-
sis may show a burning effect which is more severe on immature
than mature leaves. The chlorosis may spread over the entire leaf
and cause severe drops. The yellow color of the Biuret chlorosis is
similar to that of boron toxicity, but the Biuret colors are somewhat
patchy and free from gumming on the under surface. Light and
severe stages of the Biuret toxicity are shown in black and white
(contrasting the yellow with green) m Figure 11, for comparative
study
3. ARSENIC TOXICITY: The chlorotic leaf patterns frequently
Department of Agriculture
Figure 12. Grapefruit leaves showing progressive stages of arsenic toxicity. This
pattern is sometimes confused with manganese deficiency. The chlorosis result-
ing from arsenic toxicity is identified by a bronze-like color which is irregular
and does not remain consistent with different shades of green so characteristic
with manganese deficiency.
observed following arsenic sprays is commonly known as arsenic
toxicity. The degree of chlorosis is usually In the order of the
amount of arsenic applied. Weak trees seem to be affected more than
healthy trees. The symptoms show a loss of chlorophyll without any
distinct patterns except that of chlorosis Arsenic toxicity may be
confused with the manganese deficiency patterns but close exami-
nation indicates that the chlorosis due to arsenic extends across the
veins whereas the chlorosis from the manganese deficiency is inter-
veined. Figure 12 (in black and white) contrasting the green with
chlorotic areas is a typical arsenic toxicity pattern. Note the dif-
ferences in leaf veins in Figure 12 compared to Plate 4.
4 FLUORINE TOXICITY: The chlorotic leaf patterns of citrus
and other plants in the proximity of phosphate plants in Polk and
Hillsborough Counties have been identified as fluorine toxicity re-
sulting from gaseous fumes of fluorine coming from the stacks of
triple super phosphate mines Although a number of gaseous ma-
terials come from the stacks it has been definitely shown that
fluorine and fluorides are the most injurious The early stages of the
toxicity are somewhat similar to boron toxicity but the under sur-
face of the leaves show no resinous excretion with the fluorine
1alnuitrlition Symptoms of Citrus
Figure. 13. Flourine toxicity on qrapefruit leaves showing the ranges of toxicity
from the early stages to the advanced tip burning stages.
toxicity whereas it is generally true for boron. The fluorine toxicity
shows considerable blends of different shades of green which may be
confused with manganese deficiency. The range of these different
shades ncliiding dead leaf tips im advanced eases is shown in
Figure 13.
Considerable work has been done by the phosphate industries
and public agencies to alleviate this problem and some progress
has been made; but it has not been solved because the foliage of
a number of groves in the vicinity of the plants still show toxt-
cities. especially those in the paths of prevailing winds from the
stacks Records indicate that the tender foliage and blossoms are
more sensitive to the gaseous materials than the older tissues, and
production records may be reduced where groves are located in the
paths of prevailing winds from the stacks. Dust and solid particles
coining from the stacks have an indirect effect in aggravating citrus
pest problems. The dust and solid materials which settle on forage
and pasture crops create a serious animal problem. Once the toxicity
develops their e a re no known methods of correcting it.
No flIoride problems have been reported where liberal amounts
of finely ground rock phosphate carrying high levels of fluorine have
been applied to the soil. This indicates that insoluble fluorides added
to the soil are not injurious. Since calcium fluoride is insoluble, it is
46 Department of Agriculture
logical to assume that liberal amounts of soil calcium would be
justified in districts having fluoride problems. Many records indi-
cate that toxicities developed from excesses of aluminum, boron,
copper and other elements are markedly reduced by the addition
of lime to properly condition the soil.
DEFICIENCY PROBLEMS AND FERTILIZER PRACTICES
Although the grower may be able to recognize and diagnose
deficiency symptoms, it is much better for him to know how to
avoid deficiencies than to correct them because citrus trees are
considerably impaired in health before visible deficiencies are in
evidence.
The successful production of citru. or any crop is the result of
several factors operating simultaneously: namely, (a) Adequate soil
moisture, (b) Favorable temperature, (c) Favorable reaction
(pH), (d) Favorable soil conditions to promote penetration of fer-
tilizer into the root zone, (e) Pest control, (f) Soil Aeration, (g)
Ample amounts of organic matter, and (h) Adequate amounts of
properly balanced plant nutrients. If any one of these factors is not
favorable, all of the others are impaired.
In order to be a successful operator, it is necessary to study and
evaluate each factor affecting production, including the kind and
amounts of fertilizers applied. This involves a working knowledge
of what the crops actually remove from the soil, what nutrients are
lost through leaching and what amounts are needed for tree and
cover crop growth. This also involves a knowledge of what nutrients
become insoluble and unavailable, and what benefits are derived
from cover crops, as well as a knowledge of seasonal absorption as
related to fertilizer applications.
The major problem confronting most Florida growers is that of
applying the needed fertilizer nutrients in a balanced form to avoid
antagonistic effects resulting in deficiencies. Other citrus areas do
not use the poundage of commercial plant food as do Florida
growers.
A rational use of soil amendments, irrigation, drainage, cultural
practices, cover crops, pest control, and fertilizers pay good divi-
dends.
Reliable records indicate that a large per cent of nutrient de-
ficiencies in Florida citrus is traceable to unbalanced and often blind
fertilizer practices. This is especially true for growers on sands and
sandy soils so common In Florida. Continued fertilizer application on
such soils without regard to accumulations and leaching losses, is a
blind and expensive operation. A cross section of data regarding
these problems is presented in the following tables as helpful guides.
The first of these is presented in Table 1 which shows the nutri-
ent content of citrus as related to fertilizer materials. The data in
this table represents averages, and individual cases could be ex-
N1 Titil.NT (i)\TINT OF ([FRI S III.IATI:I] TlO I'EIiTIIIZ.1t N':I)S ON .''AMN S.011.S
([)Jiil |{"pn.l(cil^ 1VIFlg A ililvlo'l y \VNtigi l)
AM .jiir I,'e I izl n
N nlllrii,'lH
N i rt'lit in C! i I
Traci r Ilem.,nt-
lf0iiLit ls I umilly
Added a- (''I'ill,
if O(thlr Nul riil1-
plaint.N11tant
Ciitriiir~ iii I
I 14~-t'
IPolitii N tdi rl P l th
I) f.tn I[i [ d 1
of I'lIti l "ritrli, el,
Nihogen'n
lPotmbh
[\;1[111 -lllU
1,IKII:*'IIII"
('.l ininr
(J ill''t
( 'ppepri h
I [ron
Mg ill.
7,iiit
hl]4 h ll l
('lorip
.^iiIiiii i
lilr,.i iit ilt, l',t nipi.. of
ill.,' lU 11lllr'l- llPiM iltril to
.Sisi4s N,*iltp "ii Niil-ri
211) Ills Niitail Sidili
75 1Is Su]ltstphPt( (20%)
550 Ib- I.ulpiinag
So lbs. DoulinilT
SO UI., [Dl)iil
2 1 lbs 1 h1ia\
2 3 II', ('o r Sulpthat
7 5 Hb, In stp iiIihatt
3 0 Il1 Mungnnse il ilihat.
3 lb,. Zin Siulphale
Not Uii tilly i'ninIt tl(( In ialkiitg
ulp fcIrlh/rr
(i) !it pulled it I,i.-tp of 10 1 tI ( < iP ec r, i Ip'sl, r I(J', (rfh lOta
Xri I ri I 'I ii I; t I r ) 11 111 1 1 U i t I II|| ILI, Iurui .B 1 i atlU ) 1 ir 111 i 1 .1 1. .I It. rt.i vtol oM mtlmI 't .lI I h. III t
lir.-ra ( frtilstr ana iiing 111-1 I1-1- I I p .'2 Xiihoroiin Plip]]hirii 1iiL, Pp.tadh 1(. i -iuinwn M ngan is.ti (o C it r t inme irpn rine Ltil, .rplitiki at the
raiteoli aIpfni atli 3 l nt L lin i" r bI" rut i ll w~ll I i i l di ntlir n fl, or Irniin riiut tak on 8amln a n ild. SmIr r't a id mI l t txiKtsltok uk i t. mue i <;
to iri thin ti in c o rliioi i|I i -inllliir a n ill. H itt r na aill } ,rk pli> rk i j w \ }ali uil Il ltid morn piliuilrtit lind lI-p tiitngti tind pot litii [pirltherlilnr( orgTnic
nll| s tii ad ilpk carriniM llibuitiutnl lI'dilliillioii u im r rTil. Ill rqi ri]nrr lime ii.s niln ge
( MI) i le ,Mo i liin II riiqiin'l ll bill li n'll m inl l l l... s 1t11 I I1T ll r 1r I ipsit i itill ppli] d l it I I i lt Fi i t l rtil. of Ip I unIr pe r 1 ) g' ll.io nsIR tp .
N I II 10 ;)1
aX ,:. :3 8 15,2
I.D 1I 50 15 30
\I O ;i1) 3 t)
Mg() :(0 3'
(i.O S0 I 8 21
T I .'l 2
COMPOSITION OF' TIl'; PRIINCIPAL IAI',11TTIlZIH MAT I-:HI1,S
( 'Pril:l'i Y r y l] l N. l ]('.li Il
V r tllize,. '[iern il
-rri'ltl :) ('urniHE.Rn
Nitraic of Soda
Nitrat o
Nitrate of Lime ((C'aliun Nilrate)
NiO lttl of Po[l!a ll]lun
Col-Nitom ,,
sIIjulphati of Anunriiinuli
"Ai]ni pihos" (Ammoiniirnlohi P)hoh|ll<)
mI'iunoun iand r -
( aldiitm Cyannlllde.
Nitrogen Soliition,
Drilod (;riund Fish iid u tli.,
Anl imil Tan kage I SliiJ le
C('lili,,-]d MWnl aoi (Cistlor AllAl
PIHOPHY \T H ('Mt]I-RL
Bonemanil .
Amuninoiited Sper pholisp.hate.
Siie ))r)osjhi tiic (Anid Ph'lmoph :tt,)
Do!ll, land i TripleS perlo]p)li p]hal,.
(Ilrotnd lIhojphiie Rocki
'orAMIi CIhRRIEII
Muriatle f oI'ILI.-
Sulphate of Ilota-hJ
SllphaILp of Potash--Magne,4ia ,
Manmie Slts ...
Nitiate of Soda.-PuIlI
1anld"ood As.he
,r i l' I, 1 <, ,i %.ni l' t,
N
I
1 1
I3
20 5
20 5
II Ii
12- Ii
22 I
37 --I
( -10
8.2
5-8
25
I I
urn "I Ph, o n[ rin O oe d Ion K ih
N IPr* IC o
21) IX
S
12 100
33-1 500
250
8:3
125
1() 125
125-250
.'on(
1 Miiny o ria. ir [ nn m imrnict ar. n the rn ark t. .e n. i.,r, .rel l, rInIIiII t, IhLnIIo anJ n. l forth
SS ft iLn, "'pit, nInl L'I, ,,lr., an, i- ,i.. Ile rd I. r" il,, ,i, , ut, i irr ,g frm I F t, 2 i, r n i,,tal I nd from 'i l . to I' .i.,il I0., 20
plil Ki l
125
143
131
154
DS
125 1-82
44 IS
200) 3;
24
113
00 lOCH)
1 1IN
Malnutrition Symptoms of Citrus
pected to vary as much as 10 to 20%. From these data, it may be seen
that citrus fruits contain about 3 times as much nitrogen as phos-
phoric acid, and about 1.5 tunes as much potash as nitrogen. This is
a basic starting point regarding the nutrient ratios utilized by citrus
The content of magnesium in the fruit is relatively high-almost
that of phosphorus and several times that of the combined amounts
of copper, manganese and zinc. This explains the general need of
magnesium for citrus. The content of sulphur is also high But thus
far this nutrient has been supplied as a earner of other nutrients and
no need for extra additions have arisen. Calcium is also a carrier of
other nutrients and is rarely needed as a nutrient, yet often needed
as a soil correctant. Citrus foliage contains remarkably high amounts
of calcium, compared to the other nutrients. It is of significant
interest to note that the citrus fruit contains more boric acid (a trace
element) than the combined amounts of copper, manganese and
zinc. It is of further interest to note that only grams and not
pounds of molybdenum are required
Naturally the fruit does not absorb all of the nutrients re-
quired to produce the crop. The tree, cover crops, and soil itself
absorb considerable amounts. Moreover, leaching takes its toll. Only
under very favorable conditions does the fruit absorb more plant
food than is applied in the fertilizer, because of leaching losses,
fixation and needs of cover crops. Herein lies the secret of good soil
management and efficient production. The success of any science
depends on the efficient management of the factors involved, and
the production of citrus is no exception. The assumed efficiency
levels given in the table are reasonably good working units.
FERTILIZER EFFICIENCY
In order that a grower may better understand the utilization
of his fertilizer nutrients, the data in Table 1 are calculated to give
the nutrient requirements for different efficiency levels; namely,
33 1/3% for nitrogen, 25% phosphoric acid, 50% potash, 10% for
boric acid, 1% each for copper, zinc, manganese and iron. Records
show that some groves have an efficiency of less than 10% of the
major nutrients and less than 1% of the minor nutrients, while
others have an efficiency of over 50% of the major nutrients and
5% of the minor nutrients. As a rule the higher the efficiency, the
higher the net profit to the grower.
Groves of low fertilizer efficiency usually mean unprofitable re-
turns and are indicative of one or more vital factors limiting utiliza-
tion, e.g., moisture, acidity, alkalinity, deficiency, diseases, etc. If
copper is deficient in the soil, or its utilization hindered by unbal-
anced nutrient conditions, the crop will be seriously impaired, even
though the actual pounds needed are very small The same may be
true of zinc, magnesium, and even iron. If the soil conditions are
50 Department of Agrtculture
TABLE 3
THE EFFICIENCY OF DIFFERENT SOURCES OF NITROGEN
ON THE PRODUCTION OF PINEAPPLE ORANGES
WITH AND WITHOUT COPPER
All plots received steamed bonemcal and su)phate of potash and equivalent
amounts of nitrogen from sources indicated The results are expiessed in pounds of
fruit per tiee *
PLOT 6
Nitrate of
Soda
with
1929-30 121 133
PLOT 7 PLOT 8 PLOT 9
Sulphate of
Ammonia
Dried Blood
Ifth'
Blood; Nitrate
of Soda and
Sulphate of
Ammonia
with
PLOT 10*
Nitrate of
Soda
Sulphate of
Ammonia
with
Data front Lake Alfred Experiment Station Mimeograph Report, 1938 Drops not included in
records.
F Plot 10 received all nitrogen from compost until 1930
*' Copper Sulphate applied in two appliations, February 1934 and Novembor 1935 Bold figures
are crops affected by application
The superzortyv of mnorgamc sources of mtragon over orint sources has been further confirmed
by tho Florida Experiment Station in 1940 Proceedings fonda State Hortloultural Soclety. The
above data show that dried blood as a source of nitrogen was not as efficican as nitrate of soda and
sulphate of ammonia without addition of copper for a period of 7 ears The addition of copper in
1944 markedly increased production, 1ith the inorganic sources of nitrogen in the lead See discuOsion
of this table on page 51.
Malnutrition Symptoms of Citrus 51
favorable and the secondary elements applied in proper amounts the
efficiency of the major nutrients is increased, sometimes as much as
two to three hundred per cent.
The amounts of fertilizer materials needed for 100 boxes of fruit
are also listed in Table 1. From these data a grower may calculate
the required nutrients for different size crops. For example, 100
boxes of fruit contain on an average, 10 pounds of nitrogen, 3.5
pounds of phosphoric acid, 15 pounds of potash and 2.5 pounds of
magnesium This means that with 33 1/3'; efficiency for nitrogen,
25% phosphoric acid, 50% potash, 339- magnesium, 100 boxes of
fruit will need 30 pounds of nitrogen, 15 pounds of phosphoric acid,
30 pounds of potash and 9 pounds of magnesium. These are equiva-
lent, respectively, to 200 pounds nitrate of soda, 75 pounds 20%'
superphosphate, 60 pounds, muriate of potash and 75 pounds of
dolomite, or 500 pounds of a 6-2-9-2 (nitrogen, phosphoric acid,
potash and magnesium). Conservative estimates indicate that bear-
ing trees require about one-half as much plant food as the fruit
consumes, due allowance should be made for cover crops and
leaching losses. If the fertilizer efficiency is less than 25% for the
major nutrients and less than 2'> for trace elements, the practice is
wasteful (see footnote Table 1). Those data are cited for grower's
comparison with his own records.
Table 2 gives the composition of the commonly used commercial
fertilizer materials with the pounds needed to give 1 unit or 20
pounds plant food A working knowledge of these materials will be
of great help to one trying to understand lus fertilizer problem.
They are used in making fertilizer mixtures, and unless a grower is
familiar with their composition and properties, it will be difficult for
him to intelligently understand fertilizer problems.
The data in Table 3 give the relative efficiency of different
sources of nitrogen used in producing citrus under Florida condi-
tions. Although these data were secured on one soil type (Lakeland
sand), they are representative and compare favorably with observa-
tions and data from other areas, and are confirmed by grower ex-
perience. These records cover a ten year period of continuous nitro-
gen comparison (nitrogen being the only variable), and the data
show that with the addition of copper the inorgame sources were
noticably superior to the organic sources This has been a debated
question for many years, but repeated trials by growers and
research workers ( ) reaffirm the records that when the needed
(*) Proc. Fla. State Hort. Soc. 1949.
Department of Agriculture
secondaries and other nutrients are furnished, inorganic nitrogen
is more efficient than organic for citrus in Florida.
From an overall viewpoint it would appear that the organic
sources of nitrogen would be superior to the inorganic on sandy
soils in a humid climate, because the organic sources are: (a) less
leachable, (b) contain more trace elements, (c) carry more calcium
and magnesium, and (d) have more humus producing materials.
However, repeated records by many workers show that pound for
pound the inorganic sources of nitrogen when supplemented with
needed secondaries and trace elements are superior to the organic
sources. This is of particular interest to practical growers because
the inorganic sources are usually less expensive and more control-
lable. The records indicate that the organic sources do not furnish
enough available nitrogen in the root zone during the critical winter
and spring months to take care of needs. Then during summer,
with more favorable temperature and moisture, the organic sources
become available and are apparently lost through leaching processes
or voltalization as gasses. Proper recognition and use of these facts
will be of great help to growers.
LEACHING LOSSES
Unless the leachability and relative losses of plant nutrients are
taken into consideration in formulating fertilizer grades on sandy
lands in humid regions, the grower cannot escape confusion. The
data in Table 4 show the total leachings for a typical twelve month
period (1924) from a representative grove soil, receiving different
sources of nitrogen.
These records show that insoluble organic nitrogen tends to
reduce the total leaching losses, and that calcium losses were greater
from superphosphate than from bone meal treatments, and that
nitrates, sulphates, magnesium, sodium and potassium leach to a
far greater degree than phosphates, iron and ammoniacal nitrogen,
regardless of whether the fertilizer was acid or neutral.
The data in Table 5 show that almost 100 per cent of nitrate
nitrogen is leached below the 24 inch soil level in typical soils, with
10 inches of water, whereas the same amount of water leached
about 2/3 of the potash. Only in exceptional cases will the leaching
losses be as great from loams and clay soils as from sands.
Growers can materially profit by carefully studying the data in
these tables when formulating fertilizer grades because they show
Malnutrtion Symptoms of Citrtus
TH.Be 4
TOTAL AMOUNT OF DRAINAGE Dt-RING TIrE YI,;AIt (191)24)
AND THE PLANT FOOD LEACHED
Figu r- !ire in Pound. per Afre, e\,tepl D)raiisge a. Noted (a)
TANK NUMBER No. I
Co mphleo Ferhliinr witlh
Differpnt Sources of HiuIphite of
Nitrogen Anmmioma
(P:Oa from Superphiwpha~it
Totl Drainage in A< r.
InOche" 19 7
Total Solids 16,317 00
Fi'\d Solids, 11,777 00
.Ammona. 151 35
Nitrite. 2 4S
Nttrate, (h) 1.321 00 ,
Plh nkhone Acid 7 30
Sulphhit
Calcium Ondie 3.130 00
Soiu0-\i Oide 375 75
Pot!L ..uno O(ud, 060-I.' 1
Iron Oxide 3.77 I
Magneiulll (0)\ld
No. J Xo 3 No. 4
Manuire Btlod Nitntt'of Soulti
14.1
1,243 20
10.954 00
1.59
.40
1,628.00
3 25
4,724.00
269 50
2,134.00
1.820.50
836.00
1.04
123 92
T\NK NI'. MLR No ,E No-.i N~ 7 No 8
Crnnlpir Ferftlizz r u[th
rhnrn'iit Smurces of NiblE;< rf M]!plenic of
Nitrolnl Smin Anim onna I1 rnl M1 -luro
('PsOr, from Hole Miel)
Tolal Dr.linale in \rre !
Inches II 60O 19.20 10 20 15 0
Total solid- 1 570 50 7.524 00 1 SO] 50 3,qS7.50
Fil\ed Slid-, 3,206i 50 5,329 50 3 437 50 3 135 00
Anmona 2 02 121.00 C )3 2.79
Nitrites. (1 8 1I1 S .4(6
Nitrate (h) 1,2i5 00 1, 15.3 00 675 00 555 00
Pho..phoncAl Ad 16 3 9l1 1 97 1 2.I
Sulphat(s 968S 00 2 45S800 1 204 50 1,342 00
Ch lorine i 6 80 148 .50 154 00 154 00
C.alrtum O\de 177.00 I M7 50 5!1; 00 250 00
aoiumn Ovde 1.122,00 31) 00 4.173 00 329 4,
P]',(,.siin O(id.e 17 00 803.00 l00 85 841 50
fro Oxide 54 1 38 I 44 .103
ianle..ium O.dcl fi6 55 144.10 l 15070 195 SO
(ul From Honnda~ 4crcultiinil l:ii rnseinn Saioin Rreinri, 1I3 ('>I~nIrulatal)
(1) To .onTer namie l ntrur'n
SNo 1 nul ntia 1321 I.1 -- 3M0 p0[nd ntrogcn,
Thu lL'uhlng d lat 11 the ab1ve tIle n xprriti the r0 lihH.. |.ll.t. fud Ilia-- frou [, Lakelan. I n-d
rrcl*Iiin O diffrfulit -, i fa OF IIItrF,. n fur .ililrr. .Ulll nd ,i th-l 'hni cl. A llhii h K t l imIit
fowld lhose from th.rs (ear lt ferntlmel tanh4 ar- much greater than heldh records, tle laI.se. fro. n th
anlimomum tulphlia( *.eud th h, ine of the nllher t treatment. Thi i largerv din tl (he ncidulartn v.ffecl
of thne snlhihart ra',ih-d Thl. enadndtionini; effrt of the mnrie arill botrnmehal ha, a pronounced in-
fluence in ta rdnirnm lacking ]i^-s"'
54 Department of Agriculture
extensive leaching of some nutrients, and relatively none with oth-
ers. The losses must be restored, otherwise crop production will be
hindered. If one nutrient leaches more rapidly than another, it
would be reasonable to assume that the one subject to the greatest
leaching should be used in proportionately larger amounts. To ig-
nore this principle means an unbalanced soil, and loss to the grower.
Furthermore, repeated applications of a nutrient which does not
leach will result in accumulation of such nutrient. This has been
confirmed by many workers. Accumulations and unbalanced nutri-
ents create more problems on sands than on heavy soils The records
indicate that it is far better for a grower to keep his soil nutrients
balanced, void of extremes, and supplement leaching losses, rather
than to use blanket applications year after year, and risk the danger
of guessing
SOIL ACCUMULATIONS AND SOIL REACTION
Records by many workers show that repeated application of high
rates of phosphates on sandy lands tends to build a reserve of phos-
phates in the soil. The data in Table 6 shows that in addition to
phosphate accumulation, copper and manganese tend to accumulate
with repeated applications To a certain extent calcium, magnesium
and potash accumulate in soils, but nothing like phosphates and cop-
per. If properly managed, the principle of building soil reserves on
sands is to be commended, but it is necessary to guard against ex-
cesses which result in toxicities and antagonistic effects.
Too much emphasis can hardly be placed on the influence of
soil reaction on the leaching losses. However, pH records are not
enough. The amounts of calcium and magnesium in the soil are more
important than pH alone. Rain water has an ideal pH, ranging from
5.5 to 6.5, yet it has no calcium.
Strongly acid soils mean dissolving and leaching loss of bases,
while alkaline soils mean a locking effect of certain nutrients. The
increased losses of calcium and other bases with ammonium sul-
phate nitrogen in Table 4 are due to the acidulating effects of this
material A reaction of pH 6.0 is considered to be about optunum for
citrus on sandy soils. A soil reaction of pH 7.0 or above tends to
lock such nutrients as manganese, iron and zinc. These data will
prove helpful in studying the problem of leaching losses.
Malnutritton Symptoms of Citrus 55
TnI.n 5
RELATIVE LEACHING LOSSES OF THE MAJOR
FERTILIZER NUTRIENTS FROM SOME
TYPICAL FLORIDA SOILS
The boils were placed in aluminum tubes 2 inches in diameter, 26 inches long, by
passing tube into soil without molesting soil column. The tubes were then placed in
iacks with app opriatc steves to hold soils in place, and dlistled water added at rate
of approximately 2 inches at a time The nutrienis were deti mined in the leachate
using standard procedures and technique
A 6 -6 fetilizer was applied at the rate of 2000 pounds per aiee to both the
Lakeland and Gainesville soils and 1000 pounds per acre to (he Leon soil, after 10
inches of wafer had been added The first two soils had been fer ilihzed prior to draw-
ing samples for study.
PARTS PER MILLION OF NuTTRIENTS IN
SUCCESSIVrE LEACITATES EACH REPRESENTING
2-ACRE-INCH ADDITIONS O1 WATER
SOIL TYPE ____ ______
NUTRIENTS |- -d
1st 2nd rd 4lh 5th 5th 7th 8th i9th 10th
LAKELAND
FIND SAND
(Grove Soil)
Nitrate Nitrogen. 84 49 14 6 6 46 34 10 4 3
Phosphoric Acid. 0 0 0 01 0 2 0 6 0 0 0 4 9 11
Potash 42 21 8 11 8 39 49 28 17 13
Calcium 52 32 Iq 10 7 47 41 17 6 2
Magnesium 34 20 10 2 2 26 23 4 3 1
LEON
FINE SAND
(Virgin Soil)
NitiatcNiirogen 6 4 3 3 2 19 IS 4 1 0 5
Phosphoric Acid 3 0 5 0 2 0 S 0.5 10 36 14 6 3
Potah .... 1 2 3 2 1 12 37 8 3 2
Calcium 6 4 4 5 6 9 15 7 3 3
Magnesium 5 3 1 1 0 6 29 18 1 3 0
GAINEBVILLE
SAXDY LOAM
(Grove Soil)
Nitrate NiTrogen 34 16 5 5 4 20 46 13 8 5
Phosphoric Acid 02 0 1 02 0.7 0 4 0.6 0.6 0 6 0 4 0
Potash 14 7 3 8 6 15 38 31 19 10
Calhium 32 17 15 12 9 33 73 57 24 8
Magnesium 16 7 4 2 1 10 34 23 8 2
Co mints N Sumerotus -reords indicate thnt these data represent lat happens to grove soils
when fertizers are applied The records clearly show the range of leachlnm losses with excess oater,
and that the losses are diretly related to the time of fertilizer applicition From these records it would
be logial to assini that 8 to 10 tnchei of raintail within a period of a week would depleot the soluble
nutrIntE froc tihos stands which are tyvpicl Florida sands. furthermore, phosplates are eachod in
apprectible amounts from the Leon .nd, sleht ,Lh outa from Lakelnd sand, but only trace alio lnt
from the G ines' lle sandy loam It is of marked interest to note that potash i retaincd by all the
soils longer than the mnitogon and rgnesimm
TAIIIR 6
AVAILABILITY o)1' PLANT NUTRIENTS AT DIFFEIIRE'NT MOIL DEPIITHS AS AFFECT-;IED BY RATES OF APPLICATION (,
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Il pH i
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innl;dard wnlhoul :tRinZ-1Usn I
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.Slittilard withlmi ('opper)
11 4 8-2- 5 0
Sltari Iad with 3 Iln.'. ('opC[.r
G 4 9-2- 5 75
M nIi i- Ihpisphri!c
. nimii Acid
247 123
It 3W,
s 13
1117 15l
22 10
I1 15
227 46
32 7
2(1 7
I.. 10I
10 27
11 8
12. 23
4 5
4 100
T 32
T 17
221 124
23 44
1:1 l1
227 110
21 25 I
S 13 10
I ut as' ita,~(t
*T t staundnr, firtlllir rornsted of A i- 4-S-2-5-.25-, 2-, (N-PI205-K1C-2-MiO-tnO-COiO-ZtO-B203, niierrtivey. Tfid. miture wa kpplird in thre
jplicatin.spery iira, muImael0lylO;' l -t annual w w'd.Ni inNo embr anar0' eh in elnrsry ondiJun. Tlh-in ,nrrdwtaw, rr ,nkred from.taard iilmtertal.
T1 rntt ure ontr7Jn ; riwtlublr tnta t-en *nd oim. ia.ncniahlfA (tfrom nntrl .a .nmonmm nmnrn VariatMr. ne int e mnlur .r noted. The
mfildl.,rr. Tr ty plmr.i rintmn'usAl> to* Far pn.lj trot 1.lti Iknnl 4 and imni t1939). fr(mc, |12; to 195. mmrind,,.. Thi ral.e.1 am .cordrna to ur|pl't' Imritn.,
inrwtu *imth uSof ltl Itr 'e Thr trs e a-rashd 6 boiM s f frIut Ia 19. Tir Lata takeL frum l95I are tyiial and wIre7int'tm"InI .in..wan the trat. 4f the derf
..t (cr1'linar nuxmrnt.. Ther records mnalientr tat 11 hitnenh .r pran t |EA rmrn.r,'ble am.u..nt., ven w le nnr. se bern *eiil.nl If. p*renM of 13 ret. Thu it,
t..II li mil iniificanrn bccsu.' the practical nwmrr wanst. In knuiw Low niate). o gam.iLand lor iigiti,,iIa 'ntduct'uit .i0l r11 tlnrmiaili aanrnl>- w it rft-nith 1" know tllimr
ruitrmi't iia.i9 W ill.ta it c.rTr. latasE kii, i.l innal ria da1a wtih crop rILp.ulri, Ih.1 a1 aIlyseM l-a.1 ri tivrly Ill VitLai,
hkilabl NjitraL. io Parads p. r A-r
Malnutrition Symptoms of Citrus
NUTRIENT EXCESSES AND TREATMENTS
In a measure, growing citrus on many Florida soils is similar to
working with sand cultures in which the nutrients are added in
proportion to those required (absorbed) by the crop. The sand
culture method of growing plants has been successfully used by
many workers. Due allowance should be made for leaching and
fixation losses, even on sands. Where this is done, records during
the past two decades have shown that the method is profitable.
Here again it should be pointed out that attempts to guess at the
extent of nutrient reserves and leaching losses, even on sands, are
misleading, resulting in unbalanced nutrients and wasteful prac-
tices. The excessive accumulation of phosphates and copper in Flor-
ida groves has been a result of blind guessing
Since the availability of many nutrients depends almost directly
on the amount of other nutrients present, the problem of deficiencies
and excesses are closely interrelated, especially on sands. This means
that an excess of one nutrient often causes a need for another. For
example, an excess of potash increases magnesium losses. Further-
more, an excess of calcium on sandy soils reduces the availability
of zinc, manganese and other bases. An excess of copper hin-
ders the availability of iron.
It is generally known that clay and loam soils lower the availa-
bility of phosphates by simple combination or chemical precipitation.
Heavy clay and loam soils will lock up millions of tons of phos-
phate by chemical combination and render them unavailable. The
reverse of this condition exists in many Florida groves where the
content of iron and aluminum is very low, and in some cases the
phosphates have accumulated to the extent of hindering the avail-
ability of secondary nutrients. It is interesting to point out that
West (44) in Australia first showed that excess phosphates ren-
dered the zinc unavailable. Later, Soil Science Foundation, Lakeland
(Figure 2), and others confirmed West's reports. Moreover, rec-
ords show a greater need for copper to avoid dieback or exanthema
on highly phosphated soils than on low phosphated soils. It would
be reasonable to assume that where the water soluble phosphorus
is high, as is the case in some groves on sandy soils, the available
iron, zinc, copper and manganese would be unfavorably affected.
Growers can profitably use these records in formulating their
fertilizer grades from year to year. Some modifications will be nec-
essary because of seasonal and soil differences, but when these are
accounted for they are better than mere guesses. The practice of us-
Department of Agriculture
ing one nutrient to excess and then offsetting its effects by adding
other nutrients is poor business
The effects of nutrient excesses may be classed under several
heads; namely, (1) over-stimulation of growth, as with nitrogen;
(2) excess of soluble salts producing a salt or burning effect on roots
and foliage; (3) one nutrient reducing the solubility of other nu-
trients, such as Iron precipitating phosphates or vice versa; (4) toxic
or poisonous effect, such as copper and boron; (5) one nutrient
being antagonistic to another, reducing absorption and utilization,
such as excess copper reducing iron absorption and excesses of
potash lowering magnesium absorption.
As a rule, the soil will go a long way toward offsetting the
ill-effects of excesses, especially where carbonates of calcium and
magnesium are present, both of which have a balancing effect on
other nutrients.
In the case of burning as a result of excess amounts of chlorides,
nitrates and sulphates, flooding with water is a practical remedy.
Mulching with litter, muck and even soil will be helpful. In most
cases the burning effects are temporary, being alleviated by rain.
Experimental records at the Short Research Grove show that high
levels (50% above normal) retard production without showing
any burning effects.
If a nutrient has poisonous properties, as in the case of boron,
flooding is a good remedy. Hydrated lime at the rate of 400 to 800
pounds per acre on sands will retard the ill effect if watered or
worked into the soil. In the case of excess copper, lime in sufficient
amounts to raise the soil reaction to pH 6.0 or above, should be
used.
Unless the soil nutrients are reasonably well balanced, it is not
possible to have a highly efficient grove. The optimum or proper
balance for all nutrients is not known. But any practice which
tends to losses is not only wasteful, but may cause injury resulting
in years of expense to correct.
TIME OF APPLICATION
Numerous analyses over a period of years indicate that available
nitrogen is leached from Florida soils-because of summer rains-to
a greater degree than any other nutrient. This is not true in areas
Malnutrition Symptoms of Citrus
of low rainfall. Furthermore, experimental records by Roy and Gard-
ner (35), show that citrus trees absorb proportionately more nitro-
gen during the fall and winter than any other nutrient. These
findings have a practical value.
Inasmuch as most of the vegetative growth, including bloom
and setting of citrus fruit, occurs from February to July, it would
appear advisable to apply the greater part, if not all the needed
plant food a few months prior to and during this period. This may be
done in two or more applications, but records indicate that from
one-half to two-thirds of the annual needs should be applied by
February 15th. Especially is this true for groves which cannot be
irrigated. Where moisture is limited, during the fall and winter
period, some time is needed for the fertilizer to penetrate into the
root zone. This should be taken into consideration in applying fall
and winter fertilizer. Furthermore, insoluble fertilizers are less effi-
cient than soluble forms, because the roots can absorb only soluble
forms. And with limited moisture, heavy litter and grass will retard
the penetration of fertilizer into the root zone. Under such con-
ditions, irrigating and/or incorporation of the fertilizer in the soil
will prove profitable.
If the records show that a nutrient is needed, it should be applied
30 or 40 days in advance of the growth period, preferably longer
in dry soils. If soil records show ample reserves of available nu-
trients, such as phosphates, magnesium, potash, copper and manga-
nese, there is nothing to be gained by applying them. Maintenance
amounts should be applied sufficiently in advance of the needs to
allow penetration and absorption.
Records show that fertilized trees hold fruit and withstand
drought and cold better than hungry trees. Furthermore, summer
applications of fertilizer are more subject to leaching and are not as
conducive for the high quality fruit as spring applications, which
promote better spring flush and foliage.
Young trees and trees with sparse and unhealthy foliage should
have summer fertilizer. Furthermore, heavily loaded trees and cover
crop may need summer fertilizer. But if 3/10 to 4/10 of a pound of
nitrogen per box has been applied prior to bloom and during spring
period, together with other needed nutrients, rarely will any sum-
mer fertilizer be needed for trees on lemon root. Sweet root, seed-
lings, Cleo and sour root usually require more than lemon root,
depending on the soil. The annual needs can be easily calculated
from records of tree capacity, using data in Tables 1 and 2
60 Department of Agriculture
NUTRIENT RATIOS AND RATES OF APPLICATION
Unbalanced fertilizer is not only wasteful but leads to deficiency
problems and inefficient practices. Records by different workers in-
dicate that a large part of the deficiency problems confronting Flor-
ida growers is due to unbalanced fertilizer practices. Nutrient ratios
of 1-2-2 and 1-2-3 (nitrogen, phosphoric acid and potash) can be
justified only on soils which have a high chemical fixing power for
phosphates and potash. Such is not true for the sands commonly
used for citrus in Florida.
The accumulated records during the past two decades show that
citrus fruit contain approximately three times as much nitrogen
as phosphoric acid, and approximately two-thirds as much nitrogen
as potash (Table 1). Moreover, repeated records in Florida (Tables 5
and 6) indicate that nitrogen leaches rapidly and phosphates only
sparingly, on sandy lands. If the soil has little or no absorbing power
for phosphates, the needs for this element should not be greater
than one-third to one-half that of nitrogen; and if soils contain
ample phosphate reserves, additional amounts can hardly be justi-
fied. This is true for all nutrients.
The data in Table 6 show that available potash is retained by
sands longer than magnesium and calcium This is partially con-
firmed by the fact that trees show no ill effects when potash is
omitted for twenty-four months or more. The overall interpretation
of these leaching data, together with the absorption data, indicates
that for the sandy soils under Florida conditions a grower would be
entirely safe in applying potash at approximately the same rate as
that of nitrogen. (See footnote Table 1.) This would furnish the
needed potash without causing the replacement of other elements.
To secure a proper phosphate ratio in the fertilizer necessitates
a knowledge of the soil reserves of phosphates, especially sands
which have been fertilized for a number of years. As a rule, the
initial phosphate application for loam and clay soils should be five
or more times that of nitrogen, decreasing the phosphate with
time To a lesser extent this is true for the sands according to the
records in the Short Research Grove. But as the phosphates ac-
cumulate with the years of treatment, some of this cumulative ma-
terial is available. So, it would be profitable for a grower to ascertain
the extent of soil reserves. The progressive grower will want to have
Malnutrition Symptoms of Citrus
specific information regarding his own soil. This can be had only
from the measurement of actual soil nutrients from time to time.
Especially is this true for phosphates, calcium, magnesium and the
trace elements Records over a period of years show that the cost of
such information is more than offset by increased improvement A
general guessing program cannot compete in efficiency with a scien-
tific program. Until more information is available, the suggested
nutrient ratio in Table 1 can be safely used in bearing groves on
sandy soils under Florida conditions.
The rate of fertilizer application will vary according to soil
type, variety and general management practices. As a rule, the
fertilizer rate is gauged by its nitrogen content. For many years
the rate of fertilizer was based on the age of the tree and extent of
tree spread, but records indicate that the age and tree spread
are not the best guides to follow in determining the needed fer-
tilizer. The box capacity of the tree offers a more direct method
of determining fertilizer needs than any known factor to date.
When this is done with due consideration to variety, rootstock and
grove response, efficient and profitable practices have been secured.
This can be boiled down to the principle of applying from .3 to .5
pound of nitrogen and other nutrients in proportion to needs, an-
nually, per box capacity of the trees for mineral soils; organic
soils will need less nitrogen Furthermore, soils receiving heavy
leguminous cover crops would need less nitrogen For the bearing
groves on typical sandy soils, approximately 35 of a pound of nitro-
gen per box fruit can be used as a guide for the annual application
on rough lemon root. Sour rootstock will need approximately .45 of
a pound per box These rates are equivalent to 6 and 8 pounds of a
fertilizer containing 5% nitrogen, or 3 and 4 pounds of a fertilizer
containing 10% nitrogen. These rates can be gauged up or down
according to tree condition. But it is very important that the tree
have approximately one-half of the yearly supply prior to and during
the bloom period. If the foliage is sparse or off-color, the rate should
be increased accordingly
Where growers use greater amounts than these suggested rates,
no material gain will be had except in abnormal cases. The problem
may be moisture, poor mechanical condition of the soil, disease, or
some other factor. Records indicate, however, that some growers
use as much as .9 pound of nitrogen, and other nutrients in propor-
tion, to produce a box of fruit.
Department of Agriculture
SUMMARY
Characteristic citrus deficiency symptoms of the following nu-
trients have been described and illustrated: nitrogen, phosphorus,
potash, calcium, magnesium, iron, copper, manganese, zinc, boron
and molybdenum. These have been presented in a non-technical
manner understandable by the average grower. In addition, the soil
relation, treatment and symptoms of excess have been pointed out
where known. Brief statements regarding the historical use of the
nutrients are also given.
Some typical leaf chlorosis and toxicities of citrus are also pre-
sented for study to avoid confusion with deficiency symptom pat-
terns. These are Perchlorate, Bluret and Fluorine Chlorosis, and
Arsenic Toxicity.
Research data dealing with fruit composition, soil relations and
practical phases of managing Florida soils have been discussed with
the assumption that after a proper and accurate diagnosis of de-
ficiencies and the limiting factors, the most practical method to
approach for the grower would be a simple and logical procedure
based on scientific data.
The available data indicate that if a grower will maintain a
soil reaction of approximately pH 6.0, and a nutrient ratio on sandy
soils, parallel to crop composition, using three to five times the
crop removal, avoiding deficiencies and excesses, he will be able to
secure efficient utilization of his fertilizer nutrients, other factors
being favorable, and thereby eliminate many of his wasteful prac-
tices and most of his malnutrition problems.
ACKNOWLEDGMENTS
The author wishes to take this opportunity to express his sin-
cere appreciation to Messrs. E. F. DeBusk, C. R. Hiatt and A. S.
Rhoads for assistance in selecting suitable illustrations for this bul-
letin and critically reading the manuscript. And to Dr. A. S. Rhoads
for making most of the photographs and critically reviewing the
literature.
The author also wishes to express his indebtedness to the Respess
Engraving Company for helpful suggestions in making the color
plates; to the varied technical publications dealing with the subject;
to numerous Florida citrus growers for suggestions regarding grower
problems and needs, and to the Board of Directors and members of
Soil Science Foundation for valuable counsel and assistance.
Malnutrition Symptoms of Citrus
LITERATURE CITED
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2 BAHRT. G. M.. and HUGHES, A E Soil Feitility and experimnnents on
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64 Department of Agriculture
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