No. 93 New Series March, 1940
I Malnutrition Symptoms of Citrus
with Practical Methods
O. C. BRYAN .
STATE OF FLORIDA
Department of Agriculture 4/
HNathan Mayo, Commissioner
I ^ H
jf 4 S
. a a
The demand for better and higher quality fruit is
constantly before the grower, and it is felt that by
suggesting scientific methods of treating the soil and
plant nutrition problems, the grower would be better
able to produce high quality fruit more efficiently.
With this in mind The Florida Citrus Growers,
Incorporated, has sponsored this bulletin with the
hope of assisting the individual grower in recognizing
and treating malnutrition symptoms of citrus, and
thereby simplifying his production problems.
The Florida Citrus Growers are deeply indebted to
the State Department of Agriculture for providing
ways and means of publishing this bulletin and mak-
ing the information available.
INTRODUCTION ........................................... 7
SYNOPSIS OF MALNUTRITION SYMPTOMS OF CITRUS, SOIL
RELATIONS, TREATMENTS, EXCESSES, HISTORICAL USE
OF THE FOLLOWING NUTRIENTS:
Nitrogen ............... ............. ............ 8
Phosphorus ........................................... 9
Potassium ............................................. 10
Magnesium ................................. ....... 12
Copper ................................................ 15
Zinc ................................................. 17
Manganese ............................................. 20
Iron .................................................. 24
Calcium ...................................... ....... 30
Boron ................................................. 32
oUNIDENTIFIED LEAF SYMPTOMS ......................... 37
DEFICIENCY PROBLEMS AND FERTILIZER PRACTICES..... 37
FERTILIZER EFFICIENCY ................................. 38
LEACHING LOSSES ....................................... 43
ACCUMULATION OF SOIL NUTRIENTS ...................... 44
,TIME OF APPLICATION ............... .............. 46
NUTRIENT RATIOS AND RATES OF APPLICATION.......... 46
NUTRIENT EXCESSES AND TREATMENTS................. 47
PRINCIPLES OF SOIL FERTILITY ......................... 49
SUMMARY .................... .................. .... 50
ACKNOWLEDGMENT ....................................... 50
LITERATURE CITED ............. .. .................. 51
1. Deficiency Symptoms of Nitrogen in Orange Leaves ...... 21
2. Deficiency Symptoms of Magnesium in Grapefruit Leaves.. 23
3. Deficiency Symptoms of Copper in Pineapple Oranges.... 25
4. Deficiency Symptoms of Zinc in Orange Leaves .......... 27
5. Deficiency Symptoms of Manganese in Grapefruit Leaves.. 29
6. Deficiency Symptoms of Iron in Orange Leaves .......... 31
1. Deficiency Symptoms of Potassium in Grapefruit Leaves
and Trees ........................................... 11
2. Deficiency Symptoms of Magnesium in Grapefruit Leaves
and T ree ............................................ 14
3. Deficiency Symptoms of Copper in Pineapple Orange.... 16
4. Advanced Case of Zinc Deficiency in Orange Tree........ 19
5. Deficiency Symptoms of Manganese in Grapefruit Leaves.. 22
6. Advanced Case of Iron Deficiency in Tangerine Tree ..... 28
7. Deficiency Symptoms of Calcium in Grapefruit .......... 30
8. Deficiency Symptoms of Boron in Citrus Leaves and Fruit 35
9. Symptoms of Boron Toxicity in Grapefruit Leaves....... 36
10 & 11. Unidentified Leaf Symptoms ................... 36, 37
1. The Movement of Nitrate Nitrogen in a Citrus Soil as
Related to Rainfall and Nitrogen Application ........... 42
1. Plant Nutrients Removed From Soil in 100 Boxes Citrus
Fruit ........................................... . 39
2. Composition of the Principal Fertilizer Materials ........ 40
3. The Efficiency of Different Sources of Nitrogen on the
Production of Pineapple Oranges with and without
Copper ............................................ 41
4. Total Amount of Drainage During the Year (1924) and '
the Plant Food Leached ............................... 43
5. The Relation Between Total, Available, and Water-Sol-
uble Phosphorus in Citrus Grove Soils .................. 44
6. Pounds of Available Plant Nutrients in Some Typical
Florida Citrus Soils.......... ............ ........... 45
MALNUTRITION SYMPTOMS OF CITRUS WITH PRACTICAL
METHODS OF TREATMENT
O. C. BRYAN1
Economic conditions demand that wasteful practices in production
as well as marketing of citrus be reduced to a minimum, in order that
the grower may "live." To reduce the cost of production or selling
without affecting quality means money to the grower. This can be done
through the use of systematic and scientific methods of handling grove
problems. There was a time when the grower had a wider margin, with
less acute conditions.
Of the numerous production factors under the control of the grower,
that of commercial plant food is the most expensive. Unfortunately,
the growers know less about their plant food needs, losses and require-
ments than about many other factors. And unless they are able to
understand these problems sufficiently well to eliminate the wasteful
practices, many of them will be forced out of business.
If the known information regarding plant food needs is interpreted
to the growers, many of their problems will be solved.
The purpose of this paper is to bring before the grower, in a practical
manner, the known information regarding the mulnutrition problems
of citrus, pointing out the deficiency symptoms of the various nutrients,
as well as symptoms of excesses. By so doing and suggesting economical
treatments, it is hoped that the grower may understand his production
problem sufficiently well to eliminate wasteful practices and increase the
efficiency of production; and indirectly his marketing problems by
reducing production cbst and raising the quality of his product. Because
of the limited space available, no attempt is made to cite all the literature
dealing with this subject. Only those of direct concern will be men-
In order to discuss this subject without too many technical terms, it
will be necessary for the grower to accept the generally established facts:
that many chemical elements, including the primary as well as the
secondary nutrients, are required in the growth and production of all
crops, and that when these are lacking in the soil they must be supplied
through artificial means. The exact role played by the different nutri-
ents in the growth of plants is not definitely known, but the external
effects, deficiency symptoms, have been sufficiently correlated in most
instances so that the grower may understand and use them intelligently.
Science has shown that each of the required elements has a specific
function to perform in the plant, and that no one element can substitute
entirely for another. Therefore, when an element is present in insuffi-
cient amounts to perform its specific function, a very definite abnormal-
1Technical Director and General Manager, Soil Science Cooperative, Lakeland, Florida.
8 Department of Agriculture
ity develops, usually in the leaves and growing parts. Since the leaf
is the seat of almost all synthesis and growth, naturally that is the one
place where a deficiency symptom develops first. Because of this con-
dition, a good portion of this bulletin will deal with deficiency leaf
symptoms in actual colors as well as black and white half tones.
The reader is urged to study these illustrations in detail, because
they contain pattern differences that are difficult to describe in words.
In each case, typical and representative illustrations have been chosen,
and along with each illustration the important differentiating charac-
teristics and treatments are included.
Plates 1 to 6, inclusive, illustrate the deficiency patterns in color for
citrus leaves of the following nutrients: nitrogen, magnesium, copper,
zinc, iron and manganese. And Figures 1, 7 and 8 illustrate the deficiency
symptoms of potassium, calcium and boron, respectively. With addi-
tional information deficiency symptom patterns for other nutrients will
no doubt be described, and our views, regarding those herein presented,
modified. Two deficiencies sometimes 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 distinguishing characteristics
of each pattern. By so doing, the combination patterns usually can
The range of deficiency patterns of the different elements is more
completely illustrated in black and white half tones in Figures 1 to 8,
inclusive. If the reader will carefully study the plates and figures to-
gether with the legends, he will have little difficulty in understanding
the known deficiency patterns; thereby enabling him to recognize them
reasonably well in the field. A more complete description of the defi-
ciency symptom patterns is given as follows:
SYNOPSIS OF MALNUTRITION SYMPTOMS OF CITRUS,
Deficiency Symptoms: Since nitrogen has a marked influence on'
plant growth in general, its symptoms of deficiency are easily recognized
by most growers. The deficiency is first characterized by a uniform
loss of chlorophyll over the entire leaf, with occasional discoloration
of veins in early stages, resulting in a pale yellowish-green in early stages,
to old ivory color in the advanced stages. This uniform loss of chlo-
rophyll will serve to distinguish nitrogen from magnesium deficiency.'
The leaves are thinner than normal, but there is little abnormality of
the veins, and irregular colors so common with the deficiency symptoms
of most other nutrients. The colors of young and old leaves, are given
in Plate 1 on page 21. The deficiency extends over the entire plant, with
the greatest severity on fruiting branches, the leaves on which Imay show
a slight mottling effect due to acute deficiency of nitrogen during the
development of fruit. Severely affected trees show stunted condition.
Malnutrition Symptoms of Citrus 9
sparse foliage, dead wood, as well as a reduction in size and amount of
fruit. Other than size and amount, the quality of fruit is not adversely
Nitrogen deficiency should not be confused by a condition known as
vein chlorosis and yellowing of leaves brought about by girdling, disease,
root pruning, or any condition which interferes with the normal flow
of the sap of the tree.
Soil Relations: Deficiency symptoms of nitrogen may occur on any
mineral soil, but as a rule, they are most commonly found on the thinner
types, and in neglected groves' According to some growers, the level
of available nitrogen in the soil should be low during the summer and
fall, thereby avoiding too vegetative condition and coarse fruit. This,
to a large extent, seems to depend on the size of crop. With a heavy
load of fruit it is hardly possible to over-feed with nitrogen, provided
the other nutrients are present. If the soil reaction is favorable (about
pH 6.0 for most soils), the efficiency of the soil nitrogen will be higher.
This reaction will stimulate cover crops thereby maintaining favorable
soil condition for desirable bacteria and legumes.
Treatment: The treatment for nitrogen deficiency is too well known
to warrant a discussion here. Severe deficiencies should receive soluble
nitrogen, which gives quicker results than the insoluble forms. The
Comparative value of different sources of nitrogen and rates of appli-
cation will be discussed later in this bulletin. If moisture 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 long, succulent and angular. This condition is
likely to produce coarse fruit of low quality.) The vigorous growth
resulting from excess nitrogen utilizes other elements rapidly, and often
Shows the characteristic dieback and ammoniationn" symptoms, unless
copper is present. The copper deficiency will be discussed later in this
bulletin. An over-dose of any soluble salt, including nitrates, will cause
a premature dropping of foliage, and even burning of the leaves.
Historical Use: Nitrogen has been used in one form or another 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.
SDeficiency Symptoms: The importance of phosphorus for growth
and production of all crops is well recognized. However, there are no
recognized deficiency symptoms of the leaves under field conditions
which will serve to identify a shortage of this element in citrus. A
slow growth and lack of maturity appear to be the dominant effects
produced by a deficiency of this element on most plants, including citrus.
However, under controlled condition, Haas(26), of California, re-
ported that a deficiency of phosphorus in citrus was characterized
Department of Agriculture
by small, lusterless, brownish green leaves, wlich in advanced cases
showed irregular burning effects. Moreover, i phosphorous; shortage
produced a marked,absence of shoots or new branches.
Soil Relations: The phosphate problem on sands is not as serious.
as it is on clay soils, because the iron and aluminum compounds in the
clay render the phosphates unavailable. This is especially true in humid
regions where the soils are acid and have a low reserve of calciumn.
It is generally known that phosphates do not leach in appreciable
aliounts even on the sandy lands so common in Florida. For that reason
continuous applications over and above that of crop removals will result,
in an accumulation of this nutrient, and where the soils are relatively
low in fixing agents, such as iron and aluminum, the accumulated phos-
phates are available. Therefore, this nutrient is more efficient on sandy
soils with less extreme relationships than is the case with other nutrients.'
Treatment: Although there are a number of sources of phosphates
used in fertilizer practices, most of them center around acidulated or,
treated phosphate rock. (This is considered the standard phosphate
fertilizer and where this nutrient is deficient, the acidulated and soluble
forms are the most effective materials available. But where available
phosphates tend to accumulate, other sources may be used satisfactorily.
Phosphorus Excess: Due to the high fixing power of clay and loam
soils for phosphates, it is almost impossible to get an excess of this|
nutrient on such soils. But on sandy soils, large applications of soluble
phosphates build up a reserve, which may become so concentrated as
to interfere with the availability of zinc, copper and other elements.
West(48), of Australia, showed that "frenching" (zinc deficiency) of
citrus was induced by high phosphates. /Observations in Florida indi-
cate that the high phosphates aggravate "frenching" and dierback of
Historical Use: The use of phosphates began in the early days of thel
industry in Florida, first as bone meal, later as manufactured and acidu-
lated phosphates which are the major sources at present. Phosphates
are not used in citrus production in California and other countries as'
extensively as they are in Florida.
Deficiency Symptoms: For many cultivated crops, distinctideficiency
symptoms of potassium have been worked out for practical iuse under
field conditions, but a recognized leaf pattern for citrus has not been
A shortage of potassium under field conditions appears to stimulate
growth at first. This may result in an unbalanced tree condition. Later
growth and vigor are retarded with a reduction in foliage and sizeof crop.
Under controlled conditions, a deficiency of potassium in citrus is
characterized in early stages by deep-green leaves, which are often
puckered along the midribs, and in advanced cases the chlorophyll fades
Malnutrition Symptoms of Citrus 11
Figure 1. Deficiency Symptoms of Potassium in Grapefruit Leaves and Trees.
Upper: Left, normal leaf with progressive stages from left center to right. Note breakdown of
leaf tissue in advanced cases.
Lower: Left, early symptoms of potash deficiency showing vigorous growth and lack of rigidity in
branches. Right, advanced case showing defoliation and dying back of branches.
in small irregular spots in the leaves. These irregular yellow areas
develop small pustular-like spots which turn brown, rust-like and dis-
integrate or become necrotic. This necrosis or breaking down of tissue,
as illustrated in Figure 1 (upper), is a general symptom of potassium
deficiency with most crops. In severe cases the branches show a distinct
lack of rigidity and exhibit a drooping effect frequently dying back at
the tips with gum formation, as illustrated in Figure 1 (lower). Under
these conditions no fruit is set.
Soil Relations: Potassium is an active soil base, and has an affinity
for the soil complex colloidd). This results in the accumulation of
applied potassium salts somewhat in proportion to the amounts of soil
colloids (clay) present. Because of this affinity of the soil for potassium,
this'nutrient is not leached as readily as nitrates,' but since a large portion
of the citrus soils of Florida are sandy (low in absorbing agents) there
12 Department of Agriculture
is little tendency for it to accumulate. Especially is this true in acid
soils. The most practical method of increasing the ability of the soil to
retain potassium is through the addition of humus and finely divided
material, and by adjusting the soil reaction to a pH of about .0. How.
ever, if the soil is made alkaline, the availability of this nutrient seems
to be lowered. On the other hand, soil acids tend to dissolve the potash
and make it more leachable.
Treatment: Like phosphates, there are a number of sources of
commercial potassium for agricultural purposes, but the sulphates and
chlorides constitute the greater part of these sources. Both of these
salts are readily available and can be used for all potassium deficiency
Potassium Excess: 1The first effect of excesses of potassium is a re-
tardation 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 any soluble salt. This occurs only in rare instances.
However, a ratio of three to four times as much potassium as nitrogen
on sandy soils tends to lower the soil bases, reduce yield and retard tree
growth. According to Ruprecht (41) this was caused by the retarding
effect of the high potash on the intake of nitrogen.
Historical Use: Potassium has been used for citrus in Florida almost
as long as the industry has existed. The early sources consisted of hard-
wood ashes, kainit and natural materials. Other citrus growing areas
do not use as much potassium as does Florida due to differences in soils.
Bryan(4), of Florida, and Haas(23), of California, have recently pointed
out the leaf and fruit symptoms of potassium deficiency in citrus under
controlled conditions. But under field conditions, the symptoms are
more or less indefinite.
Deficiency Symptoms: Magnesium deficiency in citrus is character-
ized by 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 midrib. Later these areas enlarge often at an
angle to the midrib and usually coalese to form a yellow zone pgrround-
ing 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 intermediate 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
Malnutrition Symptoms of Citrus 13
Magnesium deficiency is closely associated with seediness of fruit
ancsize of crop. In a large measure this deficiency is responsible for
the alternate bearing habits of the common seedy grapefruit and pine-
apple oranges. Affected leaves appear to drop earlier from the orange
than the grapefruit trees, producing a somewhat sparse foliage during
the fall and winter, but in severe cases all varieties drop their affected
leaves freely, often leaving completely defoliated twigs, many of which
die and become diseased. Figure 2 (upper) shows a grapefruit tree
severely defoliated as a result of magnesium deficiency, and the range
of deficiency in the leaves.
There appears to be no direct fruit symptoms of this\ deficiency
excep5i reduced crop yields and alternate bearing qualities. The dead
wood 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 combination 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
liberal treatments of sulphates and chlorides tend to deplete the soils of
magnesium. The actual leaching losses of magnesium are very high in
comparison with those of phosphates and potash. The leaching loss,
together with continuous cropping without magnesium in the fertilizer,
has depleted many Florida soils of this element.
Treatment: Severe cases of magnesium deficiency should have sol-
uble magnesium at the rate of 100 to 300 pounds per acre, depending
upon tree size. However, in most cases, as well as for maintenance
supplies, dolomite in sufficient amounts to hold the soil reaction to about
pH 6.0 will supply the needed magnesium. It may be necessary to use
soluble forms on marls, but even here the magnesium in dolomite can
Magnesium Excess: Due to the marked tendency for soluble mag-
nesium salts to leach and the slow availability of carbonates and phos-
phates, it is doubtful that a rational practice would ever cause crop
injury. Excessive applications of dolomite rarely produce a reaction in
the soil of pH 7.0 or above, and no ill effects have been reported even
where excessive rates of dolomite and soluble magnesium have been
Historical Use: Although Averna-Saci(a) reported the value of
magnesium in correcting certain chlorosis of citrus on ferruginous soils
in 1912, the leaf symptoms of magnesium deficiency were first described
by Reed and Haas(37) in California in 1924. Later Bryan and De-
Busk (5) showed that the widespread trouble in Florida known as Citrus
Bronze was due to magnesium deficiency, and Tait(47) further demon-
strated the value of different sources of magnesium. Bahrt(1, 2) and
co-workers reported that lime, manganese, magnesium and potash salts
(a) Bol. Agr. (Sao Paulo) 13, Ser. 1912 (2) : 129-150. 1912.
Department of Agriculture
Figure 2. Deficiency Symptoms of Magnesium in Grapefruit Leaves and Tree.
Upper: Severe case of magnesium deficiency in grapefruit tree.
Lower: Range of magnesium deficiency symptoms in grapefruit leaves, showing ea ly stages on
left and progressive stages on right. i
Malnutrition Symptoms of Citrus 15
were beneficial on bronze groves as early as 1934, but failed to asso-
ciate the bronze with magnesium deficiency until 1937. In the latter year
workers in Australia (b) reported the beneficial effects of dolomitic
limestone (started in 1932) in correcting a leaf chlorosis of citrus, which
proved to be a magnesium deficiency. Several investigators (2, 5, 21, 34)
have shown that chlorotic and bronze leaves of citrus contain less mag-
nesium than healthy leaves. In recent years the problem of maintaining
the proper magnesium level in citrus soils has become a major activity
in Florida agriculture.
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 nitrogen 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, ridged
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 acutemultiple buds frequently develop
in the axis of the leaves. In aggravateid-ases 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 and Figure 3.
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 characterized by dark
brown, gum-soaked eruptions, varying from numerous, minute, scattered
specks to spots one-eighth inch in diameter. These eruptions may occur
as irregular blotches, frequently covering large areas of the fruit and
turning black as the fruit matures. Fruit blemished as a result of "die-
Sback" or exanthema are termedt'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.
SSince 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 the
effects of the 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
(b) Agr. Gaz. N. S. Wales 48(9) 501-504. 1937.
16 Department of Agriculture
Figure 3. Deficiency Symptoms of Copper in Pineapple Orange. Characterized by deep green.
oversized leaves with distorted and often curved shaped branches as "A" in thq illustration;
Multiple bud "B", "Ammoniated fruit" as "C", reddish brown eruptions "Red tust" as "D"
and gum pockets as "E" are associated with the deficiency.
copper deficiency. With acute deficiency of one or more elements, the
less pronounced deficiencies may not be apparent until the acate case is
Copper deficiency is quite common with young trees, possibly because
of the greater proportion of nitrogen in the fertilizer and the less need
for Bordeaux (copper) sprays. A low level of copper may result in a
deficiency when liberal applications of nitrogen are used. Hence the
general association of ammoniationn" (copper deficiency) witI nitrogen
fertilizers. This delicate balance of nitrogen and copper indicates a
possible need for more caution with other nutrient balances.
Soil Relations: Although copper deficiency is known to occur on
most any soil type, it is more prevalent on acid soils with clean cultural
practices than on neutral soils and types with plenty of cover crop. Any
soil condition that will induce rapid growth of trees may brig about a
copper deficiency. The rapid growth produced by nitrogen necessitates
proportional amounts of copper to avoid a deficiency.
Acid soils and clean cultural practices induce rapid leaching losses of
all bases including copper. A pH value of about 6.0 appears to be the
most suitable soil reaction ror the availability of copper. Since the
phosphates of copper are insoluble, it would be reasonable to assume
that a high level of phosphates in the soil would intensify copper defi-
ciency. This assumption is substantiated by field observations under
Malnutrition Symptoms of Citrus
Florida conditions, and has been experimentally confirmed for Zinc by
West (48) in Australia.
Treatment: Copper sulphate, either in the form of Bordeaux spray
or soil application is the specific treatment for this deficiency. The
spray produces much more rapid corrective results, but is often objec-
tionable because of the possible scale infestation following its usage,
thus necessitating oil sprays. Soil treatments at the rate of 1/8 to 1/
pound of copper sulphate per tree are sufficient for preventative measures,
but more will be needed for corrective measures. If the soil conditions
Share favorable, the treatments need not be repeated more than once a
year if that often. The possible need of copper in a maintenance pro-
gram may be determined by ascertaining the soil reaction (pH) and
content of active phosphates. (See soil relation.)
Copper Excess: The fact that copper sulphate is the most commonly
used fungicide indicates its poisonous properties, yet like all nutrients,
There is an optimum range for growth. Only small amounts of copper
are necessary for tree and fruit needs, and excessive rates (5 to 10 pounds
per tree I may cause injury resulting in the splitting of bark, gumming,
defoliation and possible death of tree. Injury from excess copper is
more likely to occur on acid and sandy soils low in buffer materials.
Active calcium (lime) and phosphates will reduce injurious effects from
Historical Use: The symptoms of citrus diebackk" or exanthema
were first described in 1875 by Fowler(16) from Florida, where the
trouble was known to have occurred as early as 1864(39). It was first
investigated in 1896 by Swingle and Webber(46) who concluded that
it was a malnutritional disease, and subsequently by Floyd and others.
Records (39) show that Bordeaux spray successfully controlled diebackk"
as early as 1897, but little attention was given to this treatment.
Floyd(18, 19) reported similar results in 1908 and 1913, as have other
workers in this and varied countries (14, 17). The use of copper, either
in Bordeaux or soil treatments, has been universally used for diebackk"
or exanthema for four decades, and it has been observed for some years
that Bordeaux frequently exerted a stimulating effect on the tree; but
only within recent years after correlating the analyses of fruit and vege-
tative parts of citrus trees with copper treatments has it been possible
to show that copper functions in a nutritional way. While some still
classify diebackk" or exanthema as a physiological disease (which is
nutritional in nature) it may be very well classed as a deficiency disease
of which copper is the specific treatment. Like many other agriculture
problems, the practice in the use of copper to correct this disease long
preceded the theory regarding its function.
Deficiency Symptoms: Like magnesium, zinc deficiency symptoms /
are characterized by specific leaf discolorations commonly known in
18 Department of Agriculture
Florida as "Frenching," and in California as "Foliocellosis."' 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 mixture of vivid green and white to yellow colors. These
colors and range of leaf patterns are illustrated in Plate 4. These
patterns will serve to identify the zinc deficiency more correctly than
In the early stages of the deficiency, the characteristic leaf pattern
may occur on apparently normal sized leaves, but as the deficiency
becomes more acute, the new leaves are small, narrow and pointed, with
a greater loss of chlorophyll as illustrated in Plate 4. The small, pointed
leaves are distinctive zinc deficiency symptoms in citrus.
LAssociated with the deficiency symptoms, there are marked tendencies
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 deficiency in the acute stages,
(Figure 4, right).
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 oranges. The
deficiency is commonly associated with copper and magnesium defi-
ciencies 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, off-size and
of poor quality. In severe cases, it is very small with woody palp 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 over-liped and
strongly acid soils. The excess lime tends to retard the avail4ility of
the zinc ion as a result of insoluble zinc compounds and calcium inter-
ference. On the acid side, the zinc is more likely to leach from the
soil or become fixed by the soluble phosphates. A pH of about 6.0
appears to be the optimum reaction for the availability of zinc under the
soil conditions in Florida. The necessity for a well-balanced soil reaction
is more important on sandy soils of a low buffer capacity than on
According to West (48), excess phosphates induce citrus frenching in
Australia. This has been partially confirmed under Florida conditions,
and apparently explains the persistent cases of frenching on some soils.
The fact that zinc deficiency in Tung trees is. more severe on phosphatic
soils seems to confirm these findings by West. The insolubility of zinc
phosphate would partially explain these observations.
Malnutrition Symptoms of Citrus 19
Figure 4. An advanced case of Zinc deficiency (Frenching) in a seedling orange tree resulting
from excess lime.
Treatment: Zinc sprays (using the sulphate) is the common treat-
ment for this def-ciency in Florida, while the spray and dust are satis-
factorily used in California. The humid condition in Florida may
inhibit the general use of the oxide as dust._The zinc sulphate spray
give quicker results and should be used in acute cases. But the cost
item and possible need for follow-up oil spray for scale control as.com-
pared to the permanency of the soil treatments warrants further inves-
tigation. If the soil reaction and phosphate balance are regulated,
soil treatinnts of zinc sulphate at the rate of 1/ to 1 pound per tree
can be satisfactorily used.l
\The sprays are used-t the rate of two to four pounds of the zinc
sulphate per one hundred gallons of lime sulphur or bordeaux spray.
These rates are for corrective measures. One-half these amounts will
suffice for a maintenance treatment. The treatments are usually most
effective when applied just prior to new growth. The spray treatments
20 Department of Agriculture
may be required once or twice a year for control, but the need for soil
treatments are much less frequent.
Zinc Excess: Excess zinc in the spray may aggravate the scale prob-
lemI and evergreen the fruit, especially if applied late in season' Due
to the tendency for insoluble zinc compounds in the soil, an excess of
zinc would not likely occur, except with large amounts on rather light
soils. Zinc is not as poisonous as copper, but excess rates would likely
cause a burning and loss of leaves, and possible splitting of bark.
Historical Use: The use of zinc as a corrective for frenching in citrus
developed first in California about 1932 (29). Its specific usage on citrus
resulted from a series of studies dealing with the influence of secondary
elements on little leaf of deciduous fruits (12). Within recent years, inves-
tigators in many citrus growing areas (3, 7, 10, 12, 29, 35, 36, 48) have
shown the specific needs of zinc for citrus as well as other crops. It is now
almost as widely used as fertilizer and accepted as a regular part of
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 colors 1,1 the deficiency pattern,
and the limited areas showing this deficiency. Nevertheless, the man-
ganese pattern is specific and reasonably well defined, and can be easily
recognized once it is understood.
(The symptoms occur on both young and mature leaves, without
a ting leaf size, whereas zinc deficiency has a market reduction on
size of leaves, and magnesium affects only mature leaves. With young
leaves, the manganese deficiency pattern is characterized/by green veins
on a light green background. 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 and Figure 5 show the range of the manganese
deficiency in grapefruit leaves. The light green area extends to the leaf
margin in severe cases; and the advanced cases are somewhat similar to
the early stages of zinc deficiency, although the color contrasts are never
as great. These symptoms are not entirely in agreement with those re-
ported for manganese under controlled conditions by Haas(25). 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 the twigs may die, associated with a marked reduction
in growth; but the twigs do not die so severely as with zinc deficiency,
nor do the trees show the rosette or bushy appearance. Manganese
deficiency was for a long time confused with frenching or zinc deficiency.
22 Department of Agriculture
Figure 5. Deficiency Symptoms of Manganese in Grapefruit leaves. Note the pattel
But with systematic studies of zinc and manganese treatment
terns have been clarified (7, 11).
A shortage of manganese has an unfavorable. effect on the
oranges and tangerines, according to Skinner and Bahrt(45).
Contrasted with copper and zinc, manganese deficiency does
oranges and grapefruit as readily as it does tangerines, temples
Soil Relations: Manganese deficiency is more common on
over-limedjjils than on the neutral and acid soils. This is d
insolubility of manganese in alkaline media. The reaction of
over-limed soils is generally pH_0.P or above, which renders
ganese unavailable. In some cases acid soils show manganese
as a result of soil depletion and fixation. Where crop ren
heavy, the soils may become depleted of available manganei
most cases the deficiency is a result of unbalanced soil con
much as to an a ctal shortage.
Treatment: (Manganese sulphate is the common corrective
ganese deficiency, using it at the rate of 1/2 to 5 pounds per tr<
treatments, depending on the size of the tree, severity of case
of soil; or in spray similar to the use of copper sulphate in
e to the
24 Department of Agriculture
or in conjunction with bordeaux and lime sulphur sprays. li the
copper and zinc spray, the manganese may increase the scale i zard,
thus necessitating an oil spray to follow. Unless the deficiency ii vere,
it is advisable to use soil treatments, except on marls which may uire
excessive amounts. In such cases, mulching with cover cro using
acid fertilizers and soil treatments of manganese will usually ifice.
The spray treatment gives quicker results, though it is less pe anent.
Manganese Excess: No known symptoms of manganese exc have
been reported in Florida, though the rates of application have b a high
in places. Manganese has not been used extensively in other citr areas.
Historical Use: Manganese has not been of general use in ag ture
until comparatively recent years. Its use on citrus in Florida t sug-
gested by its stimulating effects produced to truck crops gro rg on
marly soil, first reported by Schriener and Dawson(44), and pecht
(42). Following these results, Florida citrus growers used m nese
with success on marly soils. Skinner (45) and his co-workers ( later
reported that manganese on acid soils had a marked improvement n the
quality of fruit, while Camp and Peech(ll) correlated m mese
deficiency in citrus with soil analysis. Manganese is now bein widely
used in Florida on citrus and other crops. It is also producing rked
responses with citrus in California, and will probably become a widely
used on calcareous soils as fertilizers.
Deficiency Symptoms: Iron deficiency in citrus is comm l y re-
ferred to as iron or marl chlorosis. The latter term, however, gen-
eral one applied with equal frequency to manganese deficiency ]so of
widespread occurrence on marl soils. f Iron deficiency is char prized
by a general chlorotic condition of the leaves, particularly the ngest
ones, with the midrib and smaller veins retaining their chl phyll
longer than the leaf tissue, resulting in green network on a y ish-
green or light green background. The range of these colors a rena-
tions are illustrated in Plate 6. \ In severe cases, the young le e are
small and yellowish to old ivory in color and may be almost te of
venation. \ Such leaves usually shed early, leaving a defoliated at, as
illustrated in Plate 6. In light cases of iron deficiency, the le 1 issue
may become green as the leaves mature and the netted vein e f dis-
appears entirely. Mild forms of iron deficiency may occur on lig iandy
soils,lbut severe and chronic cases invariably are associated wit nearly
or over-limed soils.
In acute cases, the twigs die back severely in the tree t e and
extremes of the branches, with the trees becoming greatly reduce I size,
Figure 6. Such trees produce little or no crop; but other tl size
of crop, no characteristic fruit symptoms have been associated l iron
deficiency. Although all varieties of citrus are susceptible to n de-
ficiency, oranges seem to be the most severely affected.
26 Department of Agriculture
It is quite common to find other deficiencies associated vI iron
deficiency in citrus. This is particularly true with'magnesium t zinc.
Under such conditions there are certain blends of both patted s; but
careful examination shows that the specific patterns persist an can be
recognized in the presence of others.
Soil Relations: Marly and alkaline soils usually induce ijn defi-
ciency. Here again the soil reaction has a positive and control g effect
on the availability of a nutrient. An alkaline reaction reduces t solu-
bility and hence the availability of iron, thereby producing i iron
chlorosis. An excess of most carbonates produces an alkaline action.
This principle accounts for most of the iron chlorosis in all crop includ-
ing citrus, and is greatly aggravated in soils with a low c tent of
Light and bleached acid to neutral sands often show sy ms of
iron deficiency in citrus. This is a case of soil depletion or ciency
rather than unavailability resulting from an unfavorable soil action.
Treatment: No very satisfactory treatment for iron deficit y has
been worked out for citrus on alkaline soil. The most practice ethod
of treating this deficiency on such soils consists of the use heavy
mulching with organic matter and acid fertilizers. The acidulat ; effect
produced from both the fertilizer and organic matter will bring Enough
iron in solution to alleviate the trouble in the majority of cas, unless
the marl extends very close to the surface.
On alkaline soils soluble iron salts are precipitated so raI f y that
they are not available. Furthermore, spraying for iron defic ny has
not been as satisfactory with citrus as it has with pineapples A other
crops. Solution-of iron salts readily hydrolyze in water and i lowed
to come in contact with fruit and foliage wilj burn unless ne alized.
In a numberof Western states injections with soluble iron sal uch as
iron citrate or tartrate have given beneficial results in some ca How-
ever, the treatment usually has to be repeated at intervals, and s objec-
tionable owing to the damage to wood.
On the thin, sandy soils of acid and neutral reaction, irona phate
applied at the rate of 1 to 5 pounds per tree has given benef result
in some cases. Even here the use of mulches and acid ferti rs will
prove helpful. In many cases, applications of manganese, c er and
zinc along with the iron will be beneficial, because they lik se are
Usually rendered unavailable along with the iron.
Iron Excess: The soluble iron salts such as sulphates and rides
are acidic in character, and will burn foliage and fruit if a > ed to
contact them. But all iron salts become insoluble soon at being
incorporated in the normal soil. Because of this tendency of Rn salts
to form insoluble compounds with other nutrients, excess iron reduce
the availability of phosphates as discussed on page 9. But i practice
it is rather doubtful that a grower will experience difficulties wb excess
28 Department of Agriculture
iron except under rather acid conditions. And here correcting Ie soil
acid will render the iron insoluble.
Historical Use: Iron deficiency in citrus as well as other c bps has
been a serious problem in some regions for many decades. This partic-
ularly true on alkaline soils (28, 33). Many investigators (8, 12, I 15, 22,
28, 30) have studied this problem and in recent years have p orted
encouraging results(2, 15, 30, 40). Bahrt and his co-workers ported
favorable results from the use of iron sulphates on Florida so The
deficiency has not been as extensive as that of other elements ir orida
except on marls. But like many of the other nutrients, it may come
a limiting factor without developing the characteristic deficit leaf
Figure 6. An advanced case of iron deficiency in a Tangerine tree on Marl
30 Department of Agriculture
Figure 7. Deficiency Symptoms of Calcium in Grapefruit Leaves and Trees. (Controlled
Upper: Leaves showing loss of chlorophyll in tips and edges of leaves.
Lower: Normal tree on right contrasted with calcium deficient tree on left.
Deficiency Symptoms: One of the chief functions of calcium
soil appears to be that of regulating soil conditions and other ni
This associated with the stimulating effects on the absorption of 11
and other nutrients seem to be fully as important as the nut
value. Because of these indirect effects, distinctive deficiency sy)
on the foliage are slow to develop in citrus, as well as other crops
in rare cases has a deficiency symptom of calcium been reported
field conditions of any crop, and none for citrus.
Under controlled conditions, however, deficiency symptom
.$' bedn reported for citrus by Reed and Haas(37), and Bryan(6).
Symptoms are characterized by a marked stunted and hard condi
p. the trees. The flushes of growth are short, with a tendency for tho
nal branches to die back. In severe cases the leaves develop a yello
at the margins and tips which progresses toward the leaf ceni
base (Figure 7). In some ways this deficiency resembles a mi
32 Department of Agriculture
of boron toxicity. The tips of leaves are often somewhat bli and
sometimes incompletely developed.
Soil Relations: Of all the soil nutrients, calcium seems to r the
greatest controlling or balancing effect. It constitutes over 50 D' the
active bases in productive soils, being held largely in a replace orm
by the soil colloids (clays and humus). This in a measure re cents
the available calcium present. Soil acids tend to dissolve the ium
as well as magnesium, thereby increasing the intensity of leachin sses,
with a resultant lowering of fertility. In humid regions the um
losses from leaching alone are larger than any other nutrient, ying
from 200 to 1000 pounds or more per acre annually. So it i ghly
desirable to maintain the needed calcium to destroy acids as w s to
serve as a balancing agent for biological processes. This centers und
the age old problem of liming, which fell into disrepute in Flori out
two decades ago(20). Yet, a rational use of lime is the secret I soil
fertility in most areas, including Florida.
Treatment: Only under peculiar conditions does the soil l uire
calcium for nutritional purposes to a greater degree than li for
neutralizing soil acids. This means that where a soil reaction i ain-
tained at about pH 6.0 with the use of lime, preferably dolom i the
necessary amounts of calcium will be taken care of.
Calcium Excess: An excess of calcium in the soil solution rely
occurs, except in the form of chlorides or nitrates, because th hos-
phates and sulphates have a low solubility in soil water. But a cess
of lime carbonate or hydrate on sands produces high pH valueE ich
in turn reduces the availability of the secondary elements such an-
ganese, zinc and iron. /Many of the unproductive groves in Flo a are
traceable to excessive amounts of hydrated and carbonated li (20).
Fortunately, an excess of dolomite does not produce unfavorae pH
values and consequently does not produce the locking effect on sec-
Historical Use: Calcium in the form of lime, shells, ashes, bo ceal
and as a carrier of phosphates in the fertilizer, has been used fo any
decades. But the use of lime on Florida soils came into ill-reput out
1918 following excessive applications to groves. The case of hi cal-
cium lime is still a doubtful practice among many Florida grow but
where the secondary elements are applied, its ill effects are not as ere.
Since 1933 dolomitic limestone has been used on Florida 'soi ith
marked success (5). Its greatest value lies in the magnesium cont stand
non-injurious effect on the soil reaction.
Deficiency Symptoms: A number of leaf and fruit symptoms o virus
have been observed in Florida which agree with the boron de nc
symptoms reported by workers in other states and countries. H er,
Malnutrition Symptoms of Citrus 33
it has not been definitely established that the observed symptoms in
Florida actually result from a boron deficiency.
According to Haas(24), and Haas and Klotz(27), the leaf symptoms
of boron deficiency in water cultures are characterized by a pronounced
enlargement or vericose effect of the lateral veins, and occasionally
midribs. The veins often become conspicuously corky and raised on
the upper surface, followed by ruptures and longitudinal splitting of
veins, as illustrated in Figure 8. The older leaves become distinctly
thickened, somewhat leathery, but brittle, and in advanced cases may
become brownish-green to golden yellow or bronze, somewhat resem-
bling magnesium deficiency. They often manifest a distinctly puckered
or crinkled condition, and are sometimes malformed. Young leaves
often exhibit a marked curling effect as illustrated in Figure 8, which
may be confused with aphid injury.
According to Morris (31, 32), of Southern Rhodesia, boron deficient
fruit is characterized by one to several hard lumpy places with an
unusually thick rind. Such fruit exhibit a cheesy consistency on being
cut. These hard places frequently contain brown, gummy discolora-
tions. The fruit is often small and a portion, or all, of the pulp may
be hard, dry and lacking in juice. (Affected fruit sheds early and that
remaining on trees is often misshap n. Gum may be found anywhere
in the fruit, which often shows dark spots, dark seed coats and unde-
veloped seed. The trees have a tendency to wilt and die back with
small leaves sowing diminutive indentations on the ventral surface and
the young leaves often have small water-soaked spots which became
translucent in older leaves, but the corky nature and enlargement of
the leaf veins were not necessarily associated with the deficiency.
Soil Relations: Although boron deficiency has not been definitely
correlated with soil properties, it seems to be more prevalent on basic
and limed soils. This is in agreement with reports dealing with boron
deficiency in other crops, and would be expected because of the low
solubility of calcium borate. (However, acid sands in humid regions
may show a boron shortage, because of severe leaching. It appears that
the availability of boron is dependent on the soil reaction as well as
the amounts of other nutrients present,
Treatment: Borax has usually been the specific treatment for this
deficiency with most annual crops, using ten to fifty pounds per acre,
depending on crop and soil type. The lighter soils (sands) would not
require as much as the heavier clay types. The treatments for boron
deficiency in Florida is still in the experimental stage, though fairly
definite recommendations are made for citrus in Southern Rhodesia by
Morris(32). Five to ten pounds of borax per acre would supply needs
on sandy soils, and two to three times these amounts may be required
on heavy and marly soils.
Boron Excess: Like copper, boron is poisonous and quickly shows
evidence of excess. Yet, there is an optimum range for its usage.
34 Department of Agriculture
Because of the extremely sensitive nature of citrus to excess boron,
growers have heard more about toxicity resulting from excess than about
boron deficiencies. This would be expected because of the relatively
small amount of boron needed for the delicate nutrient balance required.
Boron toxicity is usually a result of excess boron in irrigation water
(in California and alkali regions). This has been an important problem
in the Western states, but in Florida only limited cases of boron toxicity
have been reported. These have usually been associated with borax
treated wash water from packing houses or to leachings from borax
treated crates left in the groves. In some instances in Florida and Cali-
fornia, evidence of excess boron in the fertilizer 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 frequently blend,
showing a somewhat mottled effect. Figure 9 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, followed by new flushes of
growth which may also show evidence of toxicity. Several successive
flushes may result, depending on the severity of the toxicity. In severe
cases the successive flushes are almost white and the twigs frequently
die. The under surface of the chlorotic areas show a rough, resenous
excrescence in the form of tiny brown to yellow pustules, which serves
to help identify the symptoms. These excrescences turn black with age.
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 boron is rather soluble in water, its injurious effect is usually
alleviated by flooding and rain. Calcium renders boron insoluble and
this can be utilized to overcome the excess in many instances by work-
ing 400 to 800 pounds hydrated lime per acre into the soil and watering
down. This, of course, applies to the sandier types where the toxicity
is most commonly found. Larger amounts would be required on heavier
Historical Use: Haas(22, 24) and Haas and Klotz(27) of California
pointed out the symptoms of boron deficiency in the vegetative parts
of citrus grown in water cultures (1927, 1930). Later Morris(81, 32)
of Rhodesia reported symptoms of boron deficiency in fruit. Certain
observations(6, 9, 10) in Florida indicate that the leaf symptoms re-
ported by Haas, and the fruit symptoms reported by Morris occur in
Florida. But experimental evidence demonstrating that these symp-
toms in Florida are due to boron deficiency has not been reported(10).
Whether or not the "lumpy rind" known in Florida for at least 2 dec-
ades(39) will prove to be boron deficiency as is "hard fruit" in Rhodesia
is yet to be demonstrated.
Malnutrition Symptoms of Citrus
Figure 8. Corking of veins and curling of terminal leaves of Grapefruit "A", puckering of leaves
with corking and splitting of veins "B" and "C", accompanied by leathery and brittle condi-
tions with bronze colorations are symptoms of Boron deficiency as reported by Haas.
Lower: Dry discolorations, abortive seed on left, and hard "rind" with gum formations, right, are
Boron deficiency symptoms of fruit as reported by Morris.
36 Department of Agriculture
Figure 9. A mild case of Boron Toxicity in Grapefruit leaves, showing yellowing of leaves at tips
Figure 10. Unidentified Leaf Symptoms. Leaf discolorations thought to be a result of excess
Boron in fertilizers. But this assumption has no experimental proof.
Malnutrition Symptoms of Citrus 37
Figure 11. Unidentified Leaf Symptoms. Yellow spot of citrus leaves observed in Florida for
many years. It is more marked on grapefruit and sour rootstock than on lemon. Cause unknown.
UNIDENTIFIED LEAF SYMPTOMS eo
Certain abnormalities of citrus which appear to be physiological in
nature, have been observed in Florida for many years. But little is
known regarding their cause. The leaf condition shown in Figure 10
is somewhat similar to the symptoms of boron toxicity, and it is thought
to be associated with excess boron in certain fertilizer. This, however,
has not been proven.
The cause of leaf condition in Figure 11 described by Floyd in 1908
as yellow spot is still unknown. It seems to be more closely associated
with grapefruit and sour rootstock than to rough lemon.
With additional information about the nutrition of citrus, it is very
reasonable to assume that these unidentified symptoms, and well defined
deficiency patterns for other elements, such as sulphur, chlorine, cobalt,
etc., will be explained.
DEFICIENCY PROBLEMS AND FERTILIZER PRACTICES
Although the grower may be able to recognize and diagnose deficiency
symptoms, it is more economical to learn how to avoid deficiencies than
to cure them. To work with practical and concrete phases of soil and
crop requirements rather than with abstract terms will do more to inform
the grower than any other procedure.
A cross-section of the problem of citrus nutrition in Florida, so far
as information is available, is given in the following tables. The data
are representative and will serve as a basis for determining the nutrient
needs, and thereby avoid unbalanced conditions and deficiencies. Table
38 Department of Agriculture
1 contains the average chemical analysis of citrus fruits, and should be
of material help in calculating the nutrient ratios, needs and amounts.
From the data in Table 1 it may be seen that citrus fruit contains
about three times as much nitrogen as phosphoric acid, and one and one-
half times as much potash as nitrogen. This is basic information
regarding the nutrient ratios needed. 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. In a
measure, this explains the general need for magnesium in Florida citrus
soils. The content of sulphur is also high. But thus far this nutrient
has been supplied as a carrier of other nutrients, and no need for extra
Additions have arisen. Calcium is also a carrier of other nutrients and
Sis rarely needed as a nutrient, yet often needed as a soil correctant.
Naturally the fruit does not absorb all of the nutrients required to
produce the crop. The tree, cover crops, and soil itself absorb consid-
erable 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
for other causes. Herein lies the secret of good soil management and
efficient production. The success of any science depends on the efficient
utilization of the factors involved, and the production of citrus is no
In order that a grower may better understand how efficiently his
fertilizer additions are utilized in practice, the data in Table 1
are calculated to give the nutrient requirements for different efficiency
/levels; namely, 10 per cent, 20 per cent, and 33 1/3 per cent. Here it
may be seen that as the efficiency increases, the need for plant food
decreases. Some groves in Florida have an efficiency of less than 10
per cent of the nutrients, and others have an efficiency of over 50 per
cent. As a rule the higher the efficiency the higher the net profit to the
Groves of low efficiency levels usually mean unprofitable returhs and
are indicative of one or more vital factors limiting utilization, e. g.,
Moisture, acidity, alkalinity, deficiency, diseases, etc. Within recent
years the deficiencies of the secondary elements have been a major factor
limiting citrus production. Where copper is deficient, though the
requirements are very small, the entire crop may be, and often is worth-
less. The same may be true of zinc, magnesium and even iron. If the
soil condition is favorable and the secondary elements applied in proper
amounts the efficiency of the major nutrients is increased, sometimes as
much as three to four hundred per cent.
The equivalent amounts of representative fertilizer materials for 100
boxes of fruit are also listed in Table 1. From these data a grower may
Malnutrition Symptoms of Citrus 39
calculate the required nutrients for different size crops. For example,
100 boxes of fruit remove from the soil onan 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 a 25 per cent efficiency,
100 boxes of fruit would require 40 pounds of nitrogen, 14 pounds of
phosphoric acid, 60 pounds of potash and 10 pounds of magnesium.
These are equivalent respectively to 250 pounds nitrate of soda, 90
pounds superphosphate, 120 pounds muriate of potash and 75 pounds
of dolomite. Conservative estimates indicate that bearing trees require
about one-half as much plant food as the fruit consumes.
/It is interesting to point out that the average efficiency in the state
is about 16 per cent. If the growers could increase this to 30 per cent
by improved practices they would reduce their fertilizer costs about
50 per cent, thereby lowering the most expensive item involved in citrus
production. If the efficiency of fertilizer is low (less than 25%), it is
Sadvisable to ascertain the cause and make corrections.
Table 2 gives the composition of the commonly used commercial
plant foods. A working knowledge of these materials will be of great
PLANT NUTRIENTS REMOVED FROM SOIL IN 100 BOXES CITRUS FRUIT (Average Analysis)
(Data compiled from available reports) (x)
in Fruit in
Amount of Nutrients
of Materials for
20% and 10% Effi-
ciency Levels (1)
Calcium (a) .56
Magnesium (a) .12
r (Sodium) ..04
Lbs. Lbs. 10%
12.7 15.0 K20 150
9.9 10.0 N 100
5.6 7.8CaO 78
1.5 3.4 P205 34.5
1.5 3.7S03 37.5
1.2 2.0MgO 20.5
.7 .7 CI 7.0
.4 .5 Na20 5.0
.05 .141 Fe293 1.41
.008 .010 MnO .1
.015 .019 ZnO .19
.018 .022 CuO .2
.005 .016 B203 .16
33) % Pounds of Materials
Lbs. or the Equivalents
45.1 150 Muriate of Potash
30.0 320 Nitrate of Soda
23.4 150 Lime (pH 6.0)
10.2 215 Superphosphate
11.1 Supplied with Phosphate
6.2 125 Dolomite
2.1 Supplied with Potash
1.5 Supplied with Nitrogen
.47 5.5 Iron Sulphate
.033 1.0 Manganese Sul.(LowGr.)
.063 1.0 Zinc Sulphate
.07 1.2 Bluestone (Copper Sul.)
.05 0 5 Borax
(1) Materials calculated on basis of 20 per cent efficiency for nitrogen and potash, 10 per cent
for calcium, phosphorus, magnesium and boron, and 5 per cent for copper, iron, manganese
and zinc. Efficiency is defined as the per cent of nutrients removed in crop.
Small amounts of other nutrients are present in fruit, such as iodine, cobalt, molybdenum, etc.
But thus far no positive beneficial effects have been associated with them.
(a) As a rule, calcium and magnesium can be supplied by maintaining the soil reaction at about
pH 6.0, using Dolomite where a deficiency of magnesium exists.
(x) Ind. & Eng. Chem., 29, 574: Hilgardia (U. of Cali.) 9, 192: Farming S. Africa, 13, 349-352.
Fla. Agr. Exp. Sta. Bulls. U.S.D.A. Univ. of Florida and Univ. of Ky.
40 Department of Agriculture
value to one trying to understand his plant food problem. Unless a
grower is familiar with these fertilizer ingredients, it will be difficult
for him to understand his nutrition problem.
- In Table 3 will be found the most authentic information available
regarding the efficiency of different sources of nitrogen used in pro-
ducing citrus under Florida conditions. Although these results were
secured on one soil type (Norfolk Sand) they are representative and
compare favorably with observations and data from other areas in the
state, and are confirmed by grower experience. When the residual
effects of the sources of nitrogen and the content of secondary nutrients
are considered, the data may appear inconsistent, yet it merits careful
study and analysis.
Theoretically the odds are in favor of the organic sources of nitrogen,
such as dried blood, over the inorganic on sandy soils because of the
Following reasons: (a) less leachable, (b) contain more secondary
COMPOSITION OF THE PRINCIPAL FERTILIZER MATERIALS
(Primary plant nutrients)
NITROGEN CARRIERS Nitrogen Acid Potash
Percent Percent Percent
N P205 K2)
Nitrate of soda.... .............. . ... .. 16
Nitrate of soda-potash .................. ... ...... 14 .... 14
Nitrate of lime (Calcium nitrate).. ....... ..... 15
Nitrate of potassium .................. 13 .. 44
Cal-Nitro.. .......... ........................ 16-20.5
SSulphate of ammonia ........... .... 20.5
"Ammophos" (Ammonium phosphate) ....... 11-16 20-48
U rea .. ................... ..... ............. . 46
Uramon........................................ 42 .
C alurea ............. ..... ... ... ......... 34
Cyanamide.......... ............ ........ 22
Nitrogen solutions.... .. ...... .............. 37-44
Dried ground fish...... .... .................. 6-10 4-6
Anim al tankage... ............. ... ....... 8.2 8
Cottonseed meal.... .. ... ...... .. ......... 6-8 2-3 1-2
G uano ................ . ............ .. .. 7-9 6-8 .5-1
Castor m eal.............. ...... ....... 5.8 1 1
Tobacco stem s............ ............ . .. 1.2-3.3 4-9
Linseed m eal(1) ........ ..... ........ ..... 5.5 1.7
Bonemeal ...... .. . ... ... ...... ... 2-5 24
Sewage sludge ................... ............ 4-6 2-3
Superphosphate (Acid phosphate). ........... ..... 16
Superphosphate (Acid phosphate) ........ ....... 20
Double and triple superphosphates.............. .32-40
Basic slag ................ ......................... 8-16
Ground phosphate rock (2) ...................... . .. 4
Calcine phosphate ............. ... .. .......... .34
M uriate of potash ................. ..... ... . 50-60
Sulphate of potash ................... .......... .. ... 48-50
Sulphate of potash-magnesia. ... ..... ........ ..... 25
M anure salts................................... ... .... 20-30
Kainit.. ....... ... ....................... .... .. 14-20
Hardwood ashes. ................ .................. .... 2-8
Cottonseed hull ash, etc .................. .. .... ... ... 20-34
(1) Many organic ammoniates are on the market such as milorganite, compost, humus and so
(2) Soft and "Colloidal Phosphates" are also considered as raw phosphates carrying from 15 to
32 per cent total P205.
Malnutrition Symptoms of Citrus 41
elements, (c) carry more calcium and magnesium, and (d) have more
humus producing materials. However, the yield and quality of fruit
appear to be better with the inorganic than the organic sources. It is
interesting to note that Plot 10 received all its nitrogen from stable
manure for some years and became so poor and unsightly that it was
discontinued. Several varieties of citrus were included in the study
but in no case was the organic nitrogen consistently ahead of the inor-
ganic. It appears that the organic ammoniates do not furnish enough
available nitrogen in the winter and spring months to take care of needs.
Then during summer, with more favorable temperature and moisture
and less tree needs, the organic sources become available and are leached.
The relative merits of inorganic sources of nitrogen over the organic
have been confirmed by workers with annual crops in many sections of
the country. Proper recognition and use of these facts for citrus will
save the growers money.
THE EFFICIENCY OF DIFFERENT SOURCES OF NITROGEN ON THE PRODUCTION OF
PINEAPPLE ORANGES WITH AND WITHOUT COPPER*
The Results Are Expressed in Pounds of Fruit Per Tree.
of Soda and
Nitrate of Soda
1549 2456 1555
*Drops not included in averages.
**All plots received steamed bonemeal and sulphate of potash.
***Copper sulphate applied in two applications Feb. 1934 and Nov. 1935. Underlined figures are
crops affected by applications.
NOTE: Copper had a marked influence on total yield as well as the alternate bearing nature
of this variety.
Data from Lake Alfred Experiment Station, mimeograph report, 1938. (a) Plot 10 received
all its nitrogen from stable manure until 1930.
Department of Agriculture
GRAPH I.-THE MOVEMENT OF NITRATE NITROGEN IN A CITRUS SOIL-NORFOLK
SAND-AS RELATED TO RAINFALL AND NITROGEN APPLICATION(I).
r* (tzsi) (rs199
't t tt 9 t' t
Sp tinber October November Decemer J nuary Febr.a.vy March
I 1 I 1 1 I
NITRATE NITROGEN- FPATS PER MILLION IN SoIL AT DATES INDICATED (4)
o.lI a. 4.s 56 #a 9.7 27 3S
4.4 0J.30. 0-
fZJ Il( JOY e
( 19o )
Tt R t t T t
TaurIty Ftbraury MarchI April May Jne July A g
NITRATE NITROGEN PARTS PER MIILLIONr IN SOIL AT DATES INDICATED (I)
o3 1 1, s Al'sm i e< 4C.01 m*
04 2.7 I, C */ 0'0 1.80 44.0/ 4.0.*/ (e.e/
I.' o.J o.fle _o0 4 i ./
S < Less than4 .
< Less than
(1) Graph taken from Citrus Industry, March, 1934.
Arrows indicate dates of nitrate determinations. Solid bars represent the rainfall in inches,
with the nitrate nitrogen in parts per million. To convert parts per million to acre twelve
inches of soil multiply by 4.
Malnutrition Symptoms of Citrus 43
TOTAL AMOUNT OF DRAINAGE DURING THE YEAR (1924) AND THE PLANT FOOD
Figures are in Pounds Per Acre, Except Drainage as Noted (a).
Tank No. No. 1 No. 2 No. 3 No. 4
Complete Fertilizer with Sulphate Nitrate
Different Sources of of Manure Blood of
Nitrogen Ammonia Soda
Total drainage in acre inches ............. 19.7 16.6 12.9 14.1
Total solids..................... ......... 16,317.00 6,365.00 8,735.00 1,243.20
Fixed solids............................... 11,777.00 5,572.00 7,353.00 10,954 00
Am m onla..... ............... .. ...... 151.35 1.08 2.55 1.59
Nitrites.................. . ........... 2.48 .13 .15 .40
'Nitrates (b) .. .. ... ......... ..... 1,321.00 76.81 476.75 1,628.00
Phosphate acid....... 7.30 3.36 3.68 3.25
Sulphates.. .. .... .... 6,815.00 2,775.00 3,868.00 4,724.00
Chlorine.......... ..... ... 115.77 145.24 111.12 269.50
Calcium oxile... ......... ............. 3,130.00 1,076.70 1,948.00 2,134.00
Sodium oxide.............. .. ..... .. 375.75 338.55 382.95 1,820.50
Potassium oxide ......... .............. 960.15 782.55 643.80 836.00
Iron oxide ................ ............... 3.77 .99 1.08 1.04
Magnesium oxide ........ .... . ........ 266.40 170.94 123.92
Tank No. No. 5 No. 6 No. 7 No. 8
Complete Fertilizer with Nitrate Sulphate
Different Sources of of Soda of Ammonia Blood Manure
Nitrogen Bone Bone Bone Bone
Total drainage in acre inches ........ 11.60 19.20 10.20 15.0
Total solids .. ... 4,570.50 7,524.00 4,801.50 3,987.50
Fixed solids . 3,206 50 5,329.50 3,437.50 3,135.00
Ammonia .. .... ... 2.02 121.00 9.63 2.79
Nitrites... 69 8.19 .68 .46
Nitrates (b)....... ...................... 1,265.00 1,155 00 675.00 555.00
Phosphate acid ... .... 1.65 3.91 1 .87 2.94
Sulphates.. ....... ........ 968.00 2,458.00 1,204.50 1,342.00
Chlorine.. ............... 96.80 148.50 154.00 154.00
Calcium oxide....... . ..... .. 177.00 687.50 594.00 250.00
Sodium oxide.. .. ... .. .. ... 1,122.00 319.00 473.00 329.45
Potassium oxide ......... .. 517.00 803.00 608.85 841.50
Iron oxide ........ ... .. ... .. .54 1.38 .44 .63
Magnesium oxide ...................... 66.55 144.10 150.70 195.80
(a) From Florida Agricultural Experiment Station Report, 1925. (Calculated).
(b) To convert nitrates into nitrogen divide by 4.4. For example, the 1,321.00 pounds of nitrates in
No. 1 would equal (1321-4.4)=300 pounds nitrogen.
The leaching data in the above table represent the relative plant food losses from a Norfolk
sand receiving different sources of nitrogen fertilizers with and without bonemeal. Although the
plant food losses from these heavily fertilized tanks are much larger than field records, the losses
from the ammonium sulphate treatment exceed that of the other treatments. This is largely due
to the acidulating and solution effect of the sulphate radical. The conditioning effects of the
manure and bonemeal had a pronounced effect in retarding leaching losses.
Table 4 gives the most complete information published regarding
the leaching losses of plant nutrients on sandy soils in Florida. They
are comparable with leaching data obtained by other workers and
should be reliable. Here it may be seen that nitrate nitrogen leaches
from the soil rapidly, while phosphates do not, with potash taking an
intermediate place. This is true regardless of the source of nitrogen
used. Moreover, calcium and magnesium leach rapidly. This means
that leaching losses must be restored, otherwise crop production is hin-
dered. Moreover, if one nutrient leaches more rapidly than another,
it would be reasonable to assume that the one subject to the greatest
44 Department of Agriculture
THE RELATION BETWEEN TOTAL, AVAILABLE, AND WATER-SOLUBLE PHOSPHORUS
IN CITRUS GROVE SOILS.
Blanton F. Sand........
Blanton F. Sand........
Norfolk F. Sand........
Norfolk F. Sand......
Norfolk F. Sand....... .
Orlando F. Sand..... .
Orlando F. Sand ......
Gainesville F. Sand... .
Norfolk Sand . .
Average of old seed
Norfolk F. Sand........
Norfolk F. Sand.......
Norfolk F. Sand... .
Norfolk F. Sand ..
St. Lucie Sand......
Average of budded
Norfolk Sand... ....
Norfolk F. Sand.........
Norfolk Sand...... .....
Norfolk Sand ........
Norfolk Sand...... ...
Blanton F. Sand ....
Average of young
Age of Grove
18 years ..
8 years. .
10 years ..
8 years ...
272 8 26
440 0 tr
Data taken from Jour. Soil Science Vol. 36, p. 246.
(1) To secure pounds per acre, multiply p.p.m by two, and to convert P205, phosphoric acid, into
phosphorus, divide by 2.28. For example, the Blanton F. Sand (first soil) has 440 p.p.m. of
available P2O0,. This multiplied by 2 (440X2) equals 880 pounds P205 per acre six inches. To
convert this into phosphorus divide by 2.28 (880 2.28--386 pounds of phosphorus per acre six
inches of soil). This figure is well within the range of phosphorus in the surface soils reported
in Table 6.
leaching should be used in proportionately large amounts. To ignore
this principle means a loss to the grower in several ways.
The rate and extent of leaching of nitrates under grove conditions
are shown in Graph 1. Here it may be seen that the greatest leaching
losses occur during the rainy season. Naturally the losses with less
soluble sources would be less rapid, but observations indicate that they
disappear during the season. A study of this graph will give the grower
the amount and distribution of rainfall conducive for rapid leaching
The data in Table 5 show that phosphates accumulate in proportion
to amounts applied. Because of the low fixing power of sandy soils the
accumulated phosphates are highly available according to chemical and
plant tests. A citrus grower in Florida can profit by investigating the
P20z 1-5 Extractl
Malnutrition Symptoms of Citrus
POUNDS OF AVAILABLE PLANT NUTRIENTS IN SOME TYPICAL FLORIDA CITRUS SOILS
(Data from page 55, Florida State Hort. Society Proceedings 1938)
Norfolk F. S..
Norfolk F. S.
Norfolk F. S.. .
Norfolk F. S.. ..
Norfolk F. S .
Norfolk F. S..
Norfolk F. S...
rNorfolk F. S..
Norfolk F. S.
Norfolk F. S...
Norfolk F. S. ...
Norfolk F. S.
Bladen F. S. Loam..
Bladen F. S. Loam..
Blunton F. S. ..
Blanton F. S. .
Eustis F. S. ....
Eustis F. S. ..
Gainesville F. S.
Gainesville F. S.
Parkwood S. Loam...
Parkwood Loam .
Portsmouth F. S......
Portsmouth F. S....
POUNDS PER ACRE SIX INCHES SOIL tion
cium Magnesium Potassium Phosphorus
1) (1) (1) Acid Water pH
568 87 175 272 20 5 5.16
420 32 110 368 13.4 5.50
56 1 23 48 1.9 5.30
300 14 41 176 9.4 5 39
32 4 18 32 2.2 5.09
194 5 55 234 14.2 5.44
30 5 19 55 8.4 5.01
500 21 78 390 15.9 5.14
149 16 48 35 4.5 5.20
240 24 150 326 10 3 6 35
065 27 130 140 24.4 5.45
560 72 59 240 9 6 6.24
28 2 20 48 7.7 4.85
215 73 250 1240 36 0 5.45
700 795 855 3160 92 0 5 .0
820 43 97 675 18 0 5 90
144 13 31 112 16.5 5 39
)49 54 56 40O 11 7 6.20
353 19 38 146 11.3 5.50
340 125 300 231 3.7 6.00
218 39 72 59 0 5.49
300 227 196 129 8.7 5.46
170 284 210 13 0.0 8 31
)10 133 140 26 13.1 5.26
152 16 19 10 2 7 5.06
(1) Replaceable in Neutral Ammonium Acetate.
(2) Soluble in dilute sulphuric acid (.002NI. Considered available.
availability of his reserve phosphate, because the fixing agents are low
and his applications have usually been high, with a result that his re-
serves are proportionately higher than nitrogen and potash.
The data in Table 6 show how Florida citrus soils retain calcium, mag-
nesiuin, potassium and phosphorus. It appears that the soil retension
cf magnesium and potassium is in proportion to the amount of organic
matter or clay present. However, the retention of calcium appears to
be related to the phosphates. This would indicate that potassium and
magnesium should be applied to sandy soils more often than calcium.
The availability of phosphates in sandy soils is again confirmed by the
data in Table 6. The grower will profit by studying the data in these
Too much emphasis can hardly be placed on the influence of soil
reaction on the leaching losses and efficiency utilization of nutrients.
Strongly acid conditions mean dissolving and loss of bases, while alkaline
conditions mean a locking effect of certain nutrients. A reaction of pH
6.0 is considered to be about optimum for citrus on sandy soils. More-
over, excessive amounts of any soluble salt, such as sulphate and chlo-
rides or even nitrates, will tend to deplete the soil of calcium, potassium,
magnesium, and other nutrients, largely because of the tendencies for
acidity and solubility. This is illustrated in Table 3, in which the
46 Department of Agriculture
relative losses of fertilizer nutrients under different nitrogen treatments
are given. The increased losses of calcium and other bases with am-
monium sulphate nitrogen were due to the acidulating effects of this
material. Citrus growers will profit by carefully studying the data in
In a measure, growing citrus on many Florida soils is similar to
working with sand cultures in which the nutrients are added in propor-
tions to that required (absorbed) by the crop. This principle is scien-
tifically sound and has been confirmed by workers with different crops
in many sections of the country. Due allowance should be made for
leaching and fixation losses, even on sands. Where this has been done,
grove records during the past ten years have shown that this method
can profitably be practiced in Florida.
TIME OF APPLICATION
Since most of the vegetative growth in citrus, as well as bloom and
setting of fruit, occur from February to July, it would be scientifically
and practically sound to apply most, if not all, of the plant food a few
months prior to, and during this period. In order for the tree to effec-
tively absorb and efficiently utilize the nutrients in setting and main-
taining a crop it is necessary to have them present in available and a
reasonably well-balanced form. Adding one at a time assumes that
the soil will adjust the balance. However, with sands of low buffer
capacity (low clay and organic matter) this assumption is often wrong.
Furthermore, to use from 2 to 3 times as much potash as nitrogen has
no experimental proof(41). And using one nutrient in excess and off-
setting its effects with another is neither sound nor economical. If the
trees have access to a reasonable supply of available nutrients and
moisture from December to March they will absorb enough in most
cases to produce a crop, thereby necessitating only maintenance sup-
plies if any in summer. This practice will insure early foliage and
avoid the need for much fertilizer during the summer and fall, thereby
making for better quality and early maturity. Slowly available nitrogen
and high potash in June and July may retard maturity.
NUTRIENT RATIOS AND RATES OF APPLICATION
Since nitrogen has such a profound influence on tree conditions and
response, a grower may use it as a guide regarding the amounts of other
nutrients to apply-assuming minimum leaching losses. By taking the
yield record data as guides for crop removal on sandy soils, a grower
can calculate the total nutrient needs for the crop, using the ratios and
efficiency levels in Table 1. Since the ratio of nutrient removal in citrus
is about 6-2-9-11/2 nitrogen, phosphoric acid, potash and magnesium,
respectively, and the ratio of leaching losses 4-.06-1-2 for unfertilized
Malnutrition Symptoms of Citrus 47
Florida soils, it would be reasonable to assume that a ratio of 6-10%
nitrogen, 2-5% phosphoric acid, 8-10% potash, and 2-5% magnesium
would be satisfactory for sandy soil low in fixing agents. These ratios,
or the equivalent have been successfully used by several Florida growers
for a number of years. Moreover, the accumulated phosphates indi-
rcated in Tables 5 and 6 confirm the soundness of these records. The'
rates of application will depend largely on the crop removal. As a
rule, applying 3 to 5 times the crop removal (see Table 1) for the
year will be sufficient, making adjustments for local conditions, soil
,types, variety, etc. Young and non-bearing trees should be fertilized
at the rate of 1 lb. of 4% nitrogen fertilizer per foot tree spread or the
"equivalent as needed. If more than these rates are required, the soil
is out of balance, and wasteful practices followed. Heavy soils, (sandy
loams and clays) need more phosphates and less potash. Calcium and
sulphur are added as carriers of other nutrients. No mention will be
made here for their maintenance.
In regard to boron, copper, iron, manganese and zinc, the amounts
"suggested in Table 1, or the equivalents, as a maintenance program
should suffice. Where a deficiency exists, more would be needed, and
in severe cases of copper, manganese and zinc deficiencies the trees should
NUTRIENT EXCESSES AND TREATMENTS
Under Florida conditions the grower is confronted more with prob-
lems of deficiencies than excesses. Nevertheless the significance of
nutrient excesses is greater than commonly believed, because of the
actual waste, besides the harm to crops.
Since the availability of many nutrients depend almost directly on
the amount of other nutrients present, the problem of deficiencies and
excesses is closely interrelated. This means that an excess of one
*nutrient often causes a deficiency of another. For example, an excess
of lime and phosphates lowers the availability of iron, manganese,
copper and zinc. Where the active calcium and phosphates are high
on sandy soils, more secondary nutrients will be needed. Naturally,
this is more expensive for the grower. The principle has been borne
out in practice, and has scientific confirmation by workers in different
It is generally known that clay and loam soils lower the availability
of phosphates by simple combination or chemical precipitation. The
red soils of Georgia and the Carolinas have a high content of iron and
aluminum. This is also true of the red and yellow loams and clay
soils in West Florida. There the iron and aluminum render the phos-
,cphates so low in availability that the native forage crops are very defi-
cient in this nutrient. These soil types will lock up millions of tons of
phosphate and render them unavailable soon after applying the phos-
phates to the soil. The reverse of this condition exists in many citrus
48 Department of Agriculture
grove soils where the content of iron and aluminum is very low, and the
added phosphates, because of low fixing agents, have accumulated to
the extent that the secondary elements are rendered less available than
they would be normally. It is interesting to point out that West(48)
in Australia, showed that excess phosphates rendered the zinc unavail-
able, thereby resulting in zinc deficiency or frenching. Certain obser?-
vations indicate that this is partially true in Florida. Moreover, records
show a greater need for copper to avoid dieback or exanthma on highly
phosphated soils than on low phosphated soils. It would be reasonable
to assume that where the available and water soluble phosphorus were
several hundred times that of the iron, zinc, copper and manganese they
would be out of balance and less available than where the active phos-
phates were lower.
An excess of potash appears to lower the efficiency of nitrogen,
resulting in a higher cost of production, because one nutrient tends to
offset the effect of the other.
This principle is sound and the grower can profitably use the pro-
portions of nutrients suggested in Table 1. Some modifications will be
necessary because of seasonal and soil differences, but when these are
accounted for the data in the table are better than mere guesses. A
grower can easily guard against using one nutrient in excess and
having to offset its effects by adding other nutrients.
The effects of nutrient excesses may be classed under several general
heads, namely, (1) over stimulation of growth, as with nitrogen; (2)'
reducing the availability and solubility of other nutrients, such as iron
precipitating phosphates or vice versa; (3) toxic or poisonous effect,
such as copper and boron. Other examples could be given.
As a rule the soil will go a long ways towards 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 any material,-
such as nitrates and chlorides, 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.
If a nutrient has poisonous properties, as in the case of boron and
copper, flooding is a very 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.
Unless the soil nutrients are reasonably well balanced, avoiding
excesses as well as deficiencies, it is not possible to have a highly efficient
grove. A balanced nutrient program for citrus is a somewhat debated
question today. But if one will use the known facts involved he will
avoid a great deal of waste and erroneous practices. The previously-
discussed tables will serve as guides to help the grower maintain a prac-
tical and economical approach to his problems. They have both scien-
tific and practical confirmation.
Malnutrition Symptoms of Citrus 49
PRINCIPLES OF SOIL FERTILITY
The principles of soil fertility are very simple and practical. They
center around the following factors: (A) Proper soil reaction (pH
values) about pH 6.0 for citrus to provide active calcium, destroy soil
toxins and conserve other nutrients, (B) adequate moisture, (C) humus
ror organic complexes to hold nutrients in available form and provide
food for bacteria, (D) proper aeration to provide for oxidation, (E)
nutrients in proportion to crop needs, making due allowance for leaching
and fixation losses.
Many citrus growers recognize these principles in one way or another
and are practicing them with success in several areas. Adjusting the
'soil reaction is not a difficult matter on sandy soils, which comprise most
of Florida's citrus. Several materials are available for this purpose,
such as hardwood ashes, bone meal, lime, slag, dolomite, etc. However,
under most conditions dolomite is to be preferred on sandy soils because
,it is economical and supplies a needed nutrient-magnesium. Further-
more, it does not produce dangerously high pH values as do some other
Many Florida citrus groves have access to some source of water for
irrigation, which often proves very valuable when properly used. This
principle has been demonstrated many times in Florida during the past
decade, and needs no further comment here.
The value of cover crops is well recognized by leading growers. This
'is often the life of the soil. The source and kind of cover crop is not as
important as amounts. Because of the value of the organic matter and
the virtues therein, many growers are hauling in large amounts of litter,
leaves, straw, etc., and mulching the trees. Such practice greatly im-
proves the grove conditions and supplies nutrients and other valuable
qualities. There is a very urgent need for adding humus or cover crops
to the soil regularly, because the warm humid climate induces rapid
,decomposition and losses.
Too much can not be said about the proper ratios and amounts of
nutrients for sandy soils to avoid unbalanced conditions and low avail-
abilities. But if the grower will use the data in the previously discussed
tables regarding crop removal, leaching losses, accumulation, etc., he
'will find that a ratio of about 6-10% nitrogen, 2-5% phosphoric acid,
,8-10% potash and 2-5% magnesium will supply the needs of most citrus
soils in Florida, using a range of 3 to 5 times the amounts of nutrients
removed in the crop. 1 Modifications of these ratios can be made depend-
ing on soil reserves. These amounts will provide for tree and cover
crop needs, as well as leaching and fixation losses. If more is required,
the grower should investigate his soil condition, reserves, etc., in order
to avoid waste and inefficient practices.
The question of aeration depends on the soil properties. Heavy soils
require more stirring or plowing than light types. Where there is a
tendency to pack or become hard following rains, some type of har-
Department of Agriculture
rowing or plowing will be helpful. Tight sods may exclude oxygen,
thereby necessitating some plowing to permit proper oxidation and
aeration. Since most citrus soils in Florida are rather sandy, disking
or shallow plowing in fall to work cover crop into soil and prevent fire
hazard has given satisfactory results. Then a harrow or disk to provide
uniform incorporation of fertilizer is ample. There is little to be gained
by stirring a loose dry sand. Too much plowing or stirring will speed
up the oxidation processes, and result in too rapid loss of organic matter.
The management of Florida citrus soils will be the title of a separate
Characteristic citrus deficiency symptoms of the following nutrients
have been described and illustrated: nitrogen, phosphorus, potassium,
calcium, magnesium, iron, copper, manganese, zinc and boron. These
have been presented in non-technical form understandable by the aver-
age 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.
Research data dealing with fruit composition, soil relations and
practical phases of managing lorida soils have been discussed with the
assumption that after a proper and accurate diagnosis of deficiencies
and the limiting factors, the most practical method of 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 soil 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 practices and most of his mal-
The author wishes to take this opportunity to express his sincere
appreciation to Messrs. E. F. DeBusk, C. R. Hiatt and A. S. Rhoads for
assistance in selecting suitable illustrations for this bulletin 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; and to-
numerous members of the Florida Citrus Growers, Incorporated, for
valuable counsel and suggestions regarding the growers' problems and
Malnutrition Symptoms of Citrus 51
1. BAHRT, G. M. Progress report of soil fertility and fertilizer experiments on
bronzing of citrus. Proc. Fla. State Hort. Soc. 47(1934) : 18-20.
2. BAHRT, G. M., and HUGHES, A. E. Soil fertility and experiments on bronzing of
citrus. Proc. Fla. State Hort. Soc. 50(1937) : 23-38.
3. BENTON, R. J. Mottle leaf of citrus trees. Control by zinc sulphate sprays dem-
onstrated. Agr. Gaz. N. S. Wales 48:571-572, 580. 1937.
4. BRYAN, O. C. Potash deficiency in grapefruit. Florida Grower 43(1): 14-16.
5. BRYAN, O. C., and DEBUSK, E. F. Citrus bronzing-a magnesium deficiency.
Florida Grower 45(2) : 6, 24. February, 1936.
6. BRYAN, O. C. Deficiency symptom patterns in citrus. Citrus Industry 19(3):
11-15. March, 1938.
7. CAMP, A. F. Studies on the effect of zinc and other unusual mineral supplements
on the growth of horticultural crops. Florida Agr. Exp. Sta. Ann. Rept. 67-69.
8. CAMP, A. F., and REUTHER, W. The yellowing of citrus leaves. Proc. Florida
State Hort. Soc. 49(1936) : 19-22. Also in Citrus Industry 17(5) : 8-9, 22. May,
9. CAMP, A. F. Boron in citrus nutrition in Florida. Citrus Industry 20(2) : 6, 7,
18. February, 1939.
10. CAMP, A. F.. and FUDGE, B. R. Some symptoms of citrus malnutrition in Florida.
Fla. Agr. Exp. Sta. Bull. 335, 55pp. 1939.
11. CAMP, A. F., and FEECH, MICHEAL. Manganese deficiency in citrus in Florida.
Proc. Amer. Soc. Hort. Sci. 36: 81-85. 199.
12. CHANDLER, W. H., HOAGLAND, D. R., and HIBBARD, P. L. Little-leaf or rosette of
fruit trees, II: Effect of zinc and other treatments. Proc. Amer. Soc. Hort. Sci.
29(1932) : 255-263. 1933.
13. CHAPMAN, G. W. The relation of iron and manganese to chlorosis in plants.
New Phyto. 30:266-283. 1931.
14. CHEEMA, G. S., and BHAT, S. S. The dieback disease of citrus trees and its
relation to the soils of Western India. Part I. Bombay Dept. Agr. Bull. 155:
15. FINCH, A. H.. ALBERT, D. W., and KINNISON, A. F. A chlorotic condition of
plants in Arizona related to iron deficiency. Proc. Amer. Soc. Hort. Sci. 30-
(1933) : 431-434. 1934.
16. FOWLER, J. H. On the dieback in orange trees. Proc. Florida Fruit Growers
Association 1875: 62-67.
17. FAWCETT, H. S. Citrus diseases and their control. Second edition. New York:
McGraw-Hill Book Co. 1936.
18. FLOYD, B. F. Treatment of citrus dieback. Fla. Agr. Exp. Sta. Press. Bull.
93: 2pp. 1908.
19. FLOYD, B. F. Bordeaux mixture for the control of dieback. Fla. Agr. Exp. Sta.
Ann. Rept. 1913: 27-30.
19a. FLOYD, B. F. Dieback, or exanthema of citrus trees. Fla. Agr. Exp. Sta. Bull.
20. FLOYD, B. F. Some cases of injury to citrus trees apparently induced by ground
limestone. Fla. Exp. Sta. Bull. 137:161-179. 1917.
21. FUDGE, B. R. Relation of magnesium deficiency in grapefruit leaves to yield and
chemical composition of fruit. .Fla. Agr. Exp. Sta. Bull. 331: 36pp. 1939.
22. HAAS. A. R. C., and REED, H. S. Significance of traces of elements not ordinarily
added to culture solutions for growth of young orange trees. Bot. Gaz. 83(1):
23. HAAS, A. R. C. The growth of citrus in relation to potassium. California Citro-
graph 22(1) : 6, 17,(2) 54, 62. 1936.
52 Department of Agriculture
24. HAAS, A. R. C. Boron as an essential element for the healthy growth of citrus.
SBot. Gaz. 89(4) : 410-413. 1930.
25. HAAS, A. R. C. Injurious effects of manganese and iron deficiencies on the
growth of citrus. Hilgardia 7(4): 181-206. 1932.
26. HAAS, A. R. C. Phosphorous deficiency in citrus. Soil Sci. 4212) : 93-116. 1936.
27. HAAS, A. R. C., and KLOTZ, L. J. Some anatomical and physiological changes in
citrus produced by boron deficiency. Hilgardia 5(8) : 175-196. 1931.
28. JENSEN, J. H. Chlorosis of citrus in Puerto Rico. Phytopath 2746) : 731. 1937.
29. JOHNSTON, J. C. Zinc sulphate promising new treatment for mottle leaf. A
preliminary report. California Citrograph 18(4): 107, 116-118. 1933.
30. MOORE, E. C. Treatment of citrus and windbreak trees affected with iron chlo-
rosis. California Citrograph 24(3) : 89, 129. 1939.
31. MORRIS, A. A. Progress report, 1935. Hard Fruit. British S. Africa Co., Mazoe,
Citrus Exp. Sta. (S. Rhodesia) Ann. Rept. pp. 60-61. 1936.
32. MORRIS, A. A. Some observations on the effects of boron treatment in the
control of "hard fruit" in citrus. Jour. Pomol. and Hort. Sci. 16(2) : 167-181.
33. McGEORGE, W. T. Some aspects of citrus tree decline as revealed by soil and
plant studies. Arizona Agr. Exp. Sta. Tech. Bull. 60:329-370. 1936.
34. PARBERRY, N. H. Mineral constituents in relation to chlorosis of orange leaves.
Soil Sci. 39(1) :35-45. 1935.
35. PARKER, E. R. Effect of certain zinc sulphate sprays for mottle leaf of citrus.
California Citrograph 19(8) : 204. 1934.
36. PARKER, E. R. Experiments on the treatment of mottle leaf of citrus trees. Proc.
Amer. Soc. Hort. Sci. 31(1933): 98-107. 1934.
37. REED, H. S., and HAAS, A. R. C. Nutrient and toxic effects of certain ions on
citrus and walnut trees with special reference to the concentration and pH of
the medium. California Agr. Exp. Sta. Tech. Paper 17: 75pp. 1924.
38. REED, H. S., and HAAS, A. R. C. Some relations between the growth and com-
position of young orange trees and the concentration of the nutrient solution
employed. Jour. Agr. Res. 28(3) : 277-284. 1924.
39. RHOADS, A. S., and DEBUSK, E. F. Diseases of citrus in Florida. Florida Agr.
Exp. Sta. Bull. 229: 213pp. 1931.
40. ROACH, W. A. Injection for the diagnosis and cure of physiological disorders of
fruit trees. Ann. of Appl. Biol. 21(2): 333-343. 1934.
41. RUPRECHT, R. W. The determination of the effect of varying amounts of potash
on the composition, yield and quality of the crop. Florida Agr. Exp. Sta. Ann.
Rept. 1933-34: 47.
42. RUPRECHT, R. W. Nutrition studies. Florida Agr. Exp. Sta. Ann. Rept. 1925-26:
43. Roy, W. R. The effect of soil applications of manganese on the mineral com-
position of foliage and maturity of fruit in citrus. Proc. Fla. State Hort. Soc.
50(1937) : 29-37.
44. SCHREINER, 0., and DAWSON, P. R. Manganese deficiency in soils and fertilizers.
Ind. & Eng. Chem. 19(3) : 400-404. 1927.
45. SKINNER, J. J., BAHRT, G. M., and HUGHES, A. E. Influence of fertilizers and
soil amendments on citrus trees, fruit production and quality of fruit. Proc.
Fla. State Hort. Soc. 47(1934) : 9-17.
46. SWINGLE, W. T., and WEBBER, H. J. The principal diseases of citrus fruits in
Florida. U. S. Dept. Agr., Div. Veg. Phys. and Path. Bull. 8, 42pp. 1896.
47. TAIT, W. L. Some field tests with magnesium sources. Proc. Florida State Hort.
Soc. 49 (1936): 9-14. Also in Citrus Industry 17 (8-9) : 11-14. Aug.-Sept., 1936.
48. WEST, E. S. Zinc-cured mottle leaf in citrus induced by excess phosphate. Jour.
Coun. Sci. & Industrial Res. Australia. 11(2) : 182-184. 1938.