Table of Contents
 List of Illustrations
 Unidentified leaf symptoms
 Deficiency problems and fertilizer...
 Fertilizer efficiency
 Leaching losses
 Soil accumulations and soil...
 Nutrient excesses and treatmen...
 Time of application
 Nutrient ratios and rates...
 Literature cited

Group Title: New series
Title: Malnutrition symptoms of citrus with practical methods of treatment
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00002899/00001
 Material Information
Title: Malnutrition symptoms of citrus with practical methods of treatment
Series Title: New series
Physical Description: 57 p. : ill. (some col.) ; 23 cm.
Language: English
Creator: Bryan, O. C ( Ollie Clifton ), b. 1894
Florida -- Dept. of Agriculture
Publisher: State of Florida, Dept. of Agriculture
Place of Publication: Tallahassee
Publication Date: <1950>
Subject: Citrus -- Nutrition   ( lcsh )
Citrus -- Diseases and pests -- Florida   ( lcsh )
Deficiency diseases in plants -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Includes bibliographical references (p. 55-57).
Statement of Responsibility: by O.C. Bryan.
General Note: "Sept. 1950."
General Note: Cover title.
 Record Information
Bibliographic ID: UF00002899
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 002567186
oclc - 44577425
notis - AMT3473
 Related Items
Other version: Alternate version (PALMM)
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Table of Contents
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    List of Illustrations
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    Unidentified leaf symptoms
        Page 37
    Deficiency problems and fertilizer practices
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    Fertilizer efficiency
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    Leaching losses
        Page 45
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    Soil accumulations and soil reaction
        Page 48
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    Nutrient excesses and treatments
        Page 50
    Time of application
        Page 51
    Nutrient ratios and rates of application
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    Literature cited
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Full Text
No. 93 New Series Sept. 1950
Malnutrition Symptoms of Citrus with Practical Methods of Treatment
O. C. Bryas
S T A T I'. () F F I. O i! I 1) A Department of Agriculture Nathan Mavo. Commissioner Tallahassee

This bulletin was originally sponsored hi/ the Florida Citrus Growers, Incorporated, and its publication and free distribution were made possible tlirotigli the generosity of the Stale Department of .Agriculture at Tallahassee.
The decade just past since the bulletin was first published has demonstrated its usefulness to citrus growers and technical workers. The supply of the original printing has been exhausted, and the current requests for if justified reprinting. Therefore, the State Depart men! of Agriculture is again glad to make available a second printing which has been revised and brought up to date.

The decade that has elapsed since this bulletin was published in 1940 has confirmed its practical usefulness to citrus growers, and further ratified the scientific soundness of its recommendations.
Although the bulletin was originally sponsored by Florida citrus growers, the State Department of Agriculture provided the ways and means of publishing it for free distribution.
Cumulated records of soil and fertilizer studies by many workers show that: (1) Nutritional problems in areas of intensified agriculture may be due to fertilizer practices as well as to soil deficiencies, and that they are profoundly affected by the ratio of nutrients applied in the fertilizer. This is particularly true for citrus on the sandy lands of Florida; (2) That a fertilizer program can be intelligently "balanced" only in relation to the needs of a particular soil or crop; and, (3) That high production of quality fruit and crops can best be attained by a systematic-use of scientific methods.
Representative data and records from field and laboratory have been summarized compactly and clearly so that the grower may intelligently understand the nutritional needs of his soils and crops, and thereby formulate efficient fertilizer practices.
Soil productivity in humid climates is greatly affected by the kind and amount of fertilizer used, and crops differ in their fertilizer requirements. Furthermore, the value of mineral elements in fertilizers is markedly influenced by the humus and active organic matter in the soil. Hence the need for abundant cover crops annually.

Introduction ........................................... 7
Synopsis of Malnutrition Symptoms of Citrus, Soil Relations, Treatments, Excesses, Historical Use of the following Nutrients:
Nitrogen .......................................... 8
Phosphorus ........................................ 10
Potassium (Potash) ................................ 14
Magnesium ....................................... 16
Copper ............................................ 20
Zinc .............................................. 23
Manganese ........................................ 26
Iron .............................................. 28
Calcium ........................................... 31
Boron .............................................. 33
UNIDENTIFIED LEAF SYMPTOMS ..................... 36
FERTILIZER EFFICIENCY............................. 41
LEACHING LOSSES ................................... 45
TIME OF APPLICATION ............................... 51
SUMMARY ............................................ 54
LITERATURE CITED .................................. 55

1. Deficiency Symptoms of Nitrogen in Orange Leaves 9
2. Deficiency Symptoms of Magnesium in Grapefruit Leaves ........................................ 17
3. Deficiency Symptoms of Copper in Pineapple Oranges 21
4. Deficiency Symptoms of Zinc in Orange Leaves 25
5. Deficiency Symptoms of Manganese in Grapefruit Leaves ......................................... 27
6. Deficiency Symptoms of Iron in Orange Leaves 29
1. Phosphorus Deficiency Symptom in the Leaves and Fruit of Oranges ................................ 11
2. Symptoms of Zinc Deficiency (Foliage) and Copper (Fruit) in Pineapple Oranges ................. 13
3. Deficiency Symptoms of Potassium in Common Grapefruit .......................................... 15
4. Deficiency Symptoms of Magnesium in Grapefruit 19
5. Deficiency Symptoms of Calcium in Grapefruit Leaves and Trees ....................................... 32
6. Leaf Symptoms of Boron Deficiency ... 34
7. Symptoms of Boron Deficiency in Citrus Leaves and Fruit ........................................... 35
8. Mild Case of Boron Toxicity in Grapefruit Leaves 36
9. & 10. Unidentified Leaf Symptoms ................. 39

6. Available Plant Nutrients in the Soil as Affected by Different Fertilizer Treatments ................... 49
1. Nutrient Content of Citrus as Related to Fertilizer Needs on Sandy Soils ............................ 42
2. Composition of the Principal Fertilizer Materials 43
3. The Efficiency of Different Sources of Nitrogen on the Production of Pineapple Oranges With and Without Copper ......................................... 44
4. Total Amount of Drainage During the Year (1924) and the Plant Food Leached........................... 46
5. Relative Leaching Losses of the Major Fertilizer Nutrients from Some Typical Florida Soils .............. 47

0. C. Bryan'
The purpose of this bulletin is to bring before the Florida grower, in a brief, practical and scientific manner, the known information regarding the malnutrition problems of citrus, pointing out the deficiency symptoms of the various nutrients, as well as the symptoms of excesses. By so doing and suggesting economical methods of treatment, it is hoped that he may understand production problems sufficiently well to eliminate wasteful practices and increase the efficiency of production. The increased demand for fruit of high internal quality necessitates more attention to those production factors which favorably affect quality.
Of all the production factors confronting Florida growers, that of commercial plant food is the most expensive, the least understood, and probably the most confusing. Unless the grower is able to follow dependable scientific methods rather than guesswork in coping with production problems, he may encounter difficulty in avoiding wasteful practices and malnutrition problems.
No attempt is made to cite all the literature dealing with this subject. Some of direct concern will be mentioned.
In order to discuss this subject, using a minimum of technical terms, it will be necessary for the grower to accept the generally established facts: That many chemical elements, such as nitrogen, phosphoric acid and potash as well as boron, copper, zinc, manganese, magnesium and others, are required for growth and production of all crops. When any one of these is lacking in the soil or exists in unbalanced form, it must be supplied or adjustments made to permit optimum utilization of the other nutrients. The exact role played by the different nutrients in the growth of plants is not definitely known, but the external effects or deficiency symptoms have been scientifically correlated for most nutrients, enabling the grower to understand and use them intelligently.
Years of study have shown that each of the required nutrient elements has a specific function to perform in the plant, and
'Technical Director, Soil Science Foundation. Lakeland, Florida.

that no one element can substitute entirely for another. Therefore, when an element is present in insufficient amounts to perform its "Specific Function" and or has antagonistic influences from other elements, a very definite abnormality develops in the leaves, branches and fruit. Since the leaf is the seat of almost all synthesis and growth, it is the place where most deficiency symptoms develop. Because of this condition, a good portion of this bulletin will deal with deficiency leaf symptoms shown in colors as well as black and white half tones. Any characteristic deficiency symptoms in other parts of the plant will also be pointed out.
The reader is urged to study the illustrations in detail along with the description, because the plates and figures contain pattern differences that are difficult to describe in words. In each case typical representative illustrations have been chosen, and along with each illustration the important differentiating characteristics and treatments are included.
Frequently, two or more deficiency symptoms occur on the same leaf, thus producing a combination pattern which may confuse the casual observer. For that reason, it is neccesary to study the distingishing characteristics of each nutrient. By so doing, the combination patterns can usually be recognized. A brief description of the deficiency symptom patterns of the different nutrients is given, together with the soil relation, treatment, effect of excesses, and historical usage. This plan should enable growers to correlate their malnutrition problems with practice.
Deficiency Symptoms: Since nitrogen has a marked influence on plant growth in general, its deficiency symptoms are easily recognized by most growers. A deficiency of nitrogen in citrus is first characterized byr a uniform loss of chlorophyll over the entire leaf, with occasional discoloration of veins in early stages, resulting in a pale yellowish-green color in early stages, to old ivory color in the advanced stages. The off-color, "hungry" appearance is usually recognized by most growers. The colors of young and old leaves are given in Plate 1. The deficiency extends over the entire plant, with the greatest severity on fruiting branches, the leaves of which may show a slight mottling effect in acute cases. Severely affected trees show stunted condition, 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 affected.

Nitrogen deficiency should not be confused with yellowing of leaves and vein chlorosis brought about by girdling, disease, root pruning, or any condition which interferes with the normal flow of sap in the tree. One of the symptoms of early boron deficiency is characterized by bronzed off-colored leaves and vein chlorosis. See Figure 6.
Soil Relations: Deficiency symptoms of nitrogen may occur on any mineral soil, but as a rule they are most commonly found on the thinner sandy types and in neglected groves. Nitrogen fluctuates in the soil more than any other nutrient and shows the least tendency to accumulate, regardless of the amounts applied. Records indicate that liberal amounts of available nitrogen in soil prior to and during bloom period and spring growth, with lesser amounts during summer and fall, favors production and maturity of fruit. With trees heavily loaded with fruit, it is hardly possible to overfeed with nitrogen, provided the other nutrients are present. If the soil reaction is favorable, showing a very slight acidity (about pH 6.0 for most soils), the efficiency of soil nitrogen is improved.
Treatment: The treatment for nitrogen deficiency is too well known to warrant discussion here. Severe deficiencies should receive soluble nitrogen, preferably nitrate nitrogen because it penerates more quickly into the root zone. The comparative value of different sources of nitrogen will be discussed later. If soil 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 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 die-back and "ammoniation" symptoms, unless copper is present. 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.
Deficiency Symptoms: The importance of phosphorus for all crops is well recognized, however no distinct phosphorus

show stunted condition, sparse foliage, dead wood, as well as reduction in size and amount of fruit. Other than size and amount, the quality of fruit is not adversely affected.
Nitrogen deficiency should not be confused with yellowing of leaves and vein chlorosis brought about by girdling, disease, root-pruning, or any condition which interferes with the normal flow of sap in the tree. One of the symptoms of early boron deficiency is characterized by bronzed off-colored leaves and vein chlorosis. See Figure 6.
Soil Relations: Deficiency symptoms of nitrogen may occur on any mineral soil, but as n rule they are most commonly found on the thinner sandy types and in neglected groves. Nitrogen fluctuates in the soil more than any other nutrient and shows the least tendency to accumulate, regardless of the amounts applied. Records indicate that liberal amounts of available nitrogen in soil prior to and during the bloom period and spring growth, with lesser amounts during summer and fall, favor production and maturity of fruit. If the soil reaction is favorable, (approximately pH 6.0) the efficiency of nitrogen is improved.
Treatment: The treat mi' lit for nitrogen deficiency is too well known to warrant discussion here. Severe deficiencies should receive soluble nitrogen, preferably nitrate nitrogen because it penetrates more quickly into the root zone. The comparative value of different sources of nitrogen will he discussed later. If soil moisture is low, it will be difficult for the trees to absorb any form of nitrogen.
Nitrogen Exccsj: An excess of nitrogen produces a tank overgreen SUCCUlent growth. The leaves are abnormally green,
large and coarse, and the branches are succulent and angular. Excess nitrogen in late summer and fall may produce tender rind fruit, and with favorable moisture and warm weather, such fruit tend to crease and >plit. The vigorous growth resulting from excess nitrogen utilizes other elements rapidly, and may show the characteristic diebark and "aminoniation" symptoms, unless copper is present. An over-dose of any soluble salt, including nitrates and sulphates, will cause a premature droppage of foliage, and even burning of the leaves.
Historical Use: Nitrogen has been used in one form or 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.

Dcjtartmcnt of Agriculture
Deficiency Symptoms: The importance of phosphorus for all crops is well recognized. However, no distinct phosphorus deficiency symptom pattern develops in citrus leaves under Florida conditions such as the characteristic leaf patterns of magnesium, zinc and iron deficiencies. A slow stunted growth with small, lusterless leaves and reduction in crop appear* to be the dominant effects produced by a deficiency of phosphorus in citrus under Florida conditions.
According to Voting and Forsec ('15) of Florida, a phosphorus deficiency of citrus on organic soils produces small, thick-rind fruit which drop prematurely. Figure 1. lower right). They report no leaf burns due to phosphorus deficiency. Haas (19) of California reports that a deficiency of phosphorus in citrus is characterized by small, lusterless. brownish-green leaves, which in advanced cases show irregular burning effects, as illustrated in Figure 1. upper. Moreover, a phosphorus shortage produces a marked absence of shoots or new branches. The.-e symptoms occur under controlled as well as under field conditions.
Soil Relations: The problem of phosphates in sands is not as serious as it is in clay soils, because iron and aluminum compounds in the clays render the phosphate unavailable. This is especially true in humid regions where the soils are acid and the reserves of calcium have been depleted.
It is generally known that phosphates do not leach even on sandy lands as rapidly as nitrogen. See Tables 4 and 5. For that reason, continuous application over and above that of crop removals result in an accumulation of this nutrient. Where the soils are relatively low in fixing agents as it is the case with many Florida soils, a good portion of the accumulated phosphates appears available for plant use. Therefore, this nutrient is more efficient on sandy lands void of extreme relationships than most other nutrients.
Treatment: Although there are a number of sources of phosphates available as fertilizer, most of them center around acidulated or treated phosphate rock. This is considered the standard phosphate fertilizer. Where this nutrient appears to be deficient, the treated and more soluble forms are the most effective materials available. Where phosphates lend to accumulate, other sources may be used satisfactorily.
Phosphorus Excess: Due to the high fixing power of clay and

Fig. 1. Phosphorus Deficiency Symptom in the leaves and fruit of oranges.
UPPER: Characteristic burned areas, according to HAAS (21).
LOWER: Thickened rind (right) with deficiency of phosphorus. YOUNG AND FORSEE (48).

deficiency symptom pattern develops in citrus leaves under Florida conditions such as the characteristic leaf patterns of magnesium, zinc and iron deficiencies. A slow stunted growth with small, lusterless leaves and reduction in crop appears to be the dominant effects produced by a deficiency of phosphorus in citrus in Florida.
According to Young and Forsee (48), of Florida, a phosphorus deficiency of citrus on organic soils produces small, thick-rind fruit which drop prematurely. (Figure 1, lower right). They report no leaf burns due to phosphorus deficiency. Haas (21,24) of California reports that a deficiency of phosphorus in citrus is characterized by small, lusterless, brownish-green leaves, which in advanced cases show irregular burning effects, as illustrated in Figure 1, upper. Moreover, a phosphorus shortage produces a marked absence of shoots or new branches. These symptoms occur under controlled as well as under field conditions.
Soil Relations: The phosphate problem on sands is not as serious as it is for clay soils, because iron and aluminum compounds in the clays render the phosphates unavailable. This is especially true in humid regions where the soils are acid and have a low reserve of calcium.
It is generally known that phosphates do not leach in appreciable amounts, even on sandy lands. For that reason, continuous application over and above that of crop removals results in an accumulation of this nutrient. Where the soils are relatively low in fixing agents, a good portion of the accumulated phosphates appear to be available for plant use. Therefore, this nutrient is more efficient on sandy lands void of extreme relationships than most other nutrients.
Treatment: Although there are a number of sources of phosphate available as fertilizer most of them center around acidulated or treated phosphate rock. This is considered the standard phosphate fertilizer. Where this nutrient appears to be deficient, the treated and more soluble forms are the most effective materials available. Where phosphates tend to accumulate, other sources may be used satisfactorily.
Phosphorus Excess: Due to the high fixing power of clay and loam soils for phosphates, it is practically impossible to get an excess of this nutrient on such soils. 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 (47), of Australia, showed that "frenching" (symptom of zinc deficiency) of citrus

(Courtesy Soil Science FoundationShort Research Grove.)
i.e. 2. Symptoms of Zinc Deficiency (Foliage) an;] Copper Deficiency (Fruit) in Pineapple Oranges induced by high amounts (35 lbs.) of superphosphate per tree. These deficiency symptoms were induced by unbalanced soil nutrients, rather than by actual deficiencies.
The Short Research Grove is located on Lakeland Fine Sand. It was set to Pineapple Oranges (Rough Lemon Rootstock) in the summer of 1939.

was induced by high phosphates. Experimental records (Soil Science Foundation, Short Research Grove) show that the high phosphates aggravate "frenching" and "dieback" of citrus, as shown in Figure 2.
Historical Use: The use of phosphates began in the early days of the industry in Florida, first as bone meal, later as manufactured and acidulated phosphates, which are the major sources at present. Phosphates are not used as extensively in California and other citrus producing areas as they are in Florida.
Deficiency Symptoms: Potassium has a regulating influence on plant growth. Reduction of this nutrient from the fertilizer stimulates growth at first, as evidenced by large leaves which often show a puckered and stitched-like condition along the midrib. Later, growth and vigor of the trees are retarded with a reduction in amount of foliage, which sheds prematurely. As the deficiency advances the branches show a general lack of rigidity and exhibit a drooping effect, as shown in Figure 3, upper. Frequently the branch tips die back with gum formation. In advanced cases the chlorophyll fades, creating irregular areas, which become brown, gummy, pustular, and rust-like in appearance, and finally become necrotic. This necrosis or breaking down of tissue, is illustrated in Figure 3, lower. Small size fruit, and low volume of fruit are associated with potash deficiency in citrus.
Soil Relations: Because of the affinity of the soil for potash, it does not leach out as readily as calcium and magnesium (see Table 6), yet there is little tendency for potash to accumulate in most of the sandy citrus soils in Florida. Especially is this true when the pH is below 5.5. But on clay soils, potash accumulates in measurable amounts. The most practical method of increasing the ability of the soil to retain potash is through the addition of humus and finely divided material, and by neutralizing soil acids. Potash serves to regulate the intake of nitrogen and other nutrients, and as a catalyst more than as a nutrient. It may even leach out of the plant and be re-absorbed. Since the plant does not utilize potash as a synthesized product, the total amount needed is not as great as formerly thought. This is confirmed by the fact that omitting potash from the fertilizer shows no deficiency symptom patterns for two or three years, even or. sanely foils.

Figure 3Deficiency symptoms of Potassium in Common Grapefruit.
UPPER: Drooping of branches, showing lack of rigidity. LOWER: Advanced case deficiency in the leaves. Left, normal, center yellow area; right leaf tissue disintegratednecrosis.

Treatment: Like phosphates, there are a number of sources of commercial potash for agricultural purposes, but the sulphates, chlorides and nitrates constitute the greater part of these sources. These salts are readily available and can be used for all potash deficiency symptoms. From 100 to 150 pounds of available potash per acre six inches of sands will supply needed amounts.
Potash Excess: The first effect of excesses of potash is a retardation of growth. With a large excess there is a premature shedding of leaves and even a burning or scorching effect, not unlike the burn from an excess of soluble salts. The burning effect is not common. However, a ratio of three to four times as much potash as nitrogen tends to deplete other soil bases, reduce yield and retard tree growth. Furthermore, excess potash produces large, coarse fruit of low quality, besides hindering the intake of nitrogen, zinc, magnesium, and other nutrients. (12)
Historical Use: Potash has been used for citrus in Florida almost as long as the industry has existed. The early sources consisted of hardwood ashes, kainit and natural materials. Other citrus growing areas do not use as much potash as does Florida, largely due to differences in soils. Before 1940, it was thought that potash reduced fruit size. But Chapman and coworkers (12) in California, and Neller and others (x) in Florida, have shown experimentally that high levels of potash increase fruit size, with a tendency for coarse fruit.
Deficiency Symptoms: Magnesium deficiency in citrus is characterized by a type of leaf chlorosis commonly known in Florida as bronzing. This discoloration or loss of chlorophyll occurs only on mature leaves, and is more prevalent on heavily fruiting trees and branches, and is more noticeable in late summer and fall, but may be seen any season where the nutrient is deficient.
Although there is a variety of leaf symptoms associated with this deficiency, the typical cases develop yellow chlorotic areas in the initial stage on each side of the midrib. Later these areas enlarge often at an angle to the midrib and usually coalesce to form a yellow zone surrounding a wedge-shaped green area at the leaf base. As the deficiency advances, the entire leaf becomes yellow or bronze-like, hence the name. This advance! 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 oranges.
Magnesium deficiency is closely associated with seediness of fruit and size of crop. Cold injury of citrus is amplified by a deficiency of magnesium more than any other nutrient. In a
(x) Proc. Fla. State Hot. Soe. 1944.

Piute 2. Deficiency symptoms of magnesium in grapefruit leaves, showing early (A) and advanced (B) stages. (See pae 16 fir description.)

large measure magnesium deficiency is responsible for the alternate bearing habits of the common seedy grapefruit and pineapple oranges. Affected leaves appear to drop earlier from the orange than the grapefruit trees, producing a 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 4 (lower) shows a grapefruit tree severely defoliated as a result of magnesium deficiency, and the range of the deficiency in the individual leaves (upper).
There appears to be no marked fruit symptoms of this deficiency except reduced crop yields and alternate bearing qualities. The deadwood and twigs resulting from the deficiency may increase the disease hazard of the fruit. The deficiency is often associated with copper and zinc deficiencies, in which case 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 excessive amounts of potash and other bases tend to deplete the soils of magnesium. The actual leaching losses of magnesium are very high in comparison with those of phosphate and potash. The leaching losses of magnesium are greater than crop removal, and must be added to soil to maintain plant needs.
Treatment: Severe cases of magnesium deficiency should have soluble magnesium at the rate of 75 to 150 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, providing the other nutrients are not in excess. It may be necessary to use soluble forms on marls, but even here the magnesium in dolomite can be used.
Magnesium Excess: Due to the marked tendency for soluble magnesium salts to leach and the slow availability of carbonates and phosphates, it is doubtful that a rational practice would cause crop injury. Excessive applications of dolomite rarely produce a soil reaction of pH 7.0 or above, and no ill effects have been reported even where excessive rates of dolomite and soluble magnesium have been made. Excessive amounts of magnesium sulphate will deplete the soil of other bases.
Historical Use: Although Averna-Saca (=::) 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 (34) in California in 1924. Later Bryan and DeBusk (5) reported that the widespread trouble in Florida known as Citrus Bronze was due to magnesium deficiency, and Tait (46) further demonstrated the value of different sources of magnesium. Bahrt (1,2) and
(*) Bol. Agr. (Sao Paulo) 13, Ser. 1912 (2); 129-150. 1912.

Figure 4.Deficiency Symptoms of Magnesium in Grapefruit.
UPPER: Range of magnesium deficiency symptoms in grapefruit leaves, showing early stages on left and progressive stages on right.
LOWER: Severe case of magnesium deficiency in grapefruit tree.

co-worker reported that lime, manganese, magnesium and potash salts were beneficial on bronze groves as early as 1934, but failed to associate the bronze with magnesium deficiency until 1937. In the later year, workers in Australia (y) reported the beneficial effects of dolomitic limestone (started in 1932) in correcting a leaf chlorosis of citrus, which proved to be a magnesium deficiency. Several investigators have shown that chlorotic and bronze leaves of citrus contain less magnesium than healthy leaves. 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 "dieback" 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 acute, multiple buds frequently develop in the axis of the leaves. In aggravated cases the production of new shoots and dieback of older ones result in a bushy rosette type of growth. These symptoms are illustrated in Plate 3.
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 "dieback" or exanthema are termed "ammoniated" by the growers and have no commercial value. This deficiency may occur on various kinds of citrus but is more prevalent on oranges than grapefruit and tangerines.
Since copper deficiency has a more marked effect on the fruit and twigs of citrus, a deficiency of other elements may mask these symptoms. This is particularly true with a deficiency of zinc and magnesium, and even manganese at times. A shortage of these elements retards appearance of copper defi-
(y) Agr. Gaz. N. S. Wales 48 (9) 501-504. 1937.

Plate 3. Deficiency symptoms of copper in Pineapple oranges, showing early (A> and advanced (B> stanes. (See page 20 for description.)

ciency. But as a rule, the symptoms are specific and the differences are merely a matter of degree and not of kind. In severe cases, fruit symptoms are the most reliable guides for copper deficiency. With acute deficiency of one or more elements, the less pronounced deficiencies may not be apparent until the acute case is alleviated.
Copper deficiency is common with young trees on new land. This is due to the low copper content of virgin soils, and the tendency of active organic matter to render copper unavailable. Heavy fertilizer without copper usually- causes ammoniation or copper deficiency in young trees.
Soil Relations: Although copper deficiency is known to occur on most any soil type, it is more pi-evalent on new land and soils with clean cultural practices. Any treatment or practice which induces rapid growth of trees may bring about a copper deficiency where no copper is added in the spray or fertilizer program. The rapid growth necessitates proportional amounts of copper to avoid a deficiency of this nutrient. Experimental records (36) by a number of workers show that high amounts of available phosphates cause a copper deficiency'. The records indicate that high phosphates hinder the intake of copper by the plants. Copper compounds in the soil are less soluble than compounds of nitrogen and potash. Because of this fact, repeated copper applications x*esult in copper cumulation in soil.
Treatment: Copper sulphate, either in the form of a spray or as a soil application, has been the usual treatment for this deficiency'. The spray produces much more rapid corrective results, but is often objectionable because of the possible scale infestation following its usage. Soil treatments at the rate of y.\. to 1 pound of coarsely ground copper sulphate per tree are sufficient for preventative measures, but more will be needed in severe cases. If the soil is free of excesses of other nutrients which cause antagonistic effects, the amounts of copper required to supply needs are relatively small. Possibly 1/100 that of nitrogen will suffice. Within recent years, copper oxide, hydroxide and even finely ground metallic copper have been used satisfactorily as a soil amendment.
Copper Excess: The fact that copper sulphate is the most commonly used fungicide indicates its poisonous properties, for 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) 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 sancty soils low in buffer materials. Active calcium (lime) and phosphates will reduce injurious effects from excess copper.
Historical Use: The symptoms of citrus "dieback" or exanthema were first described in 1895 by Fowler (16) from Florida, where the trouble was known to have occured as early as 1864

(37). It was first investigated in 1896 by Swingle and Webber (45) who concluded that it was a malnutritional disease, and subsequently by Floyd and others. Records by Frotcher (xx) show that Bordeaux spray successfully controlled "dieback" as early as 1897, but little attention was given to this treatment. Floyd (17, 18) reported similar results in 1908 and 1913, as have other workers in this and varied countries (14). The use of copper, either in Bordeaux or soil treatments, has been universally used for "dieback" 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 vegetative parts of citrus trees with copper treatments has it been possible to show that copper functions in a nutritional way. While some still classify "dieback" or exanthema as a physiological disease (which is nutritional in nature) it may very well be classed as a deficiency disease for 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 Symptom: Like magnesium, zinc deficiency symptoms are characterized by specific leaf discolorations commonly known in Florida as "Frenching," and in California as "Foliocellosis" and "Mottle leaf." The initial stages of the deficiency appear as irregular chlorotic areas in the leaf tissue, between the main and lateral veins. The tissue immediately adjoining the veins remains green, while the chlorophyll disappears (or fails to develop in the leaf tissue). This results in an irregular, mottled or variegated 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 word descriptions.
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 (B). Small, pointed leaves are one of the distinctive zinc deficiency symptoms in citrus.
Associated 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. This advanced defi-cienc\r is often associated with dense interior growth of water-sprouts.
(xx) Proc. Fla. State Hort. Soc. 1897.

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 deficiencies and may appear more severe in combinations than when alone, because of the increased weakness of the trees. But the individual leaf patterns remain almost unchanged.
Fruit produced on zinc deficient trees is usually small, off-size, and of poor quality. In severe cases, it is very small with woody pulp and insipid taste, except when borne on water sprouts (so common with zinc deficiency). Here it is large, coarse and of poor quality.
Soil Relations: Although zinc deficiency in citrus may occur on almost any soil type, it is most commonly found on marls, over-limed or strongly acid soils. The excess lime tends to retard the availability of the zinc ion as a result of insoluble zinc compounds and calcium interference. A pH of about 6.0 appears to be the optimum reaction for the availability of zinc under the soil conditions in Florida. Field observations indicate that an excess of potash, nitrogen and phosphates may cause a zinc deficiency in citrus. The necessity for a well-balanced fertilizer is more important on sandy lands than on heavier types.
Treatment: Zinc sulphate spray was the common treatment for this deficiency in the early years of its usage. California growers were the first to use zinc oxide as a successful treatment for this deficiency'. Zinc oxide and carbonate are now being successfully used in many citrus growing areas. The spray treatments give quicker results and should be used in acute cases. But the scale problem is usually worse following sprays. Within recent years many growers have successfully used soil applications of zinc, where the soil reaction and phosphates can be modified.
The sprays arc used at 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 may be required once or twice a year for control, but the need for soil treatments are much less frequent. Soil applications at the rate of i/{ to -/; pound of the sulphate or the equivalent per tree annually will furnish ample zinc for citrus, except in peculiar soil conditions.
Zinc Excess: Excess zinc in the spray may aggravate the scale problem and overgreen the fruit, especially if applied as a spray late in season. Due to the tendency for insoluble zinc compounds to form in the soil, an excess of zinc would not likely occur, except with large amounts on rather light soils. Zinc is not as toxic as copper, but excess rates would likely cause a burning and loss of leaves, and possible splitting of bark.

Piute i. Deficiency symptoms of zinc in orange leaves, showing typical (A) and advanced (B) stages. (See page 23 for description.)

Historical I'se: The use of zinc as a corrective for frenching in citrus developed first in California about 19:52 (11,26). Its specific usage on citrus resulted from a series of studies dealing with the influence of secondary elements on little leaf of deciduous fruits (11). Within recent years, investigators in many citrus growing areas have shown the specific needs of zinc for citrus as well as other crops. It is now widely used and accepted as a regular part of citrus production program.
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 in the deficiency pattern, and the limited areas showing this deficiency. Nevertheless, the manganese pattern is specific and well defined, and can be easily recognized once it is understood.
The symptoms occur on both young and mature leaves, without affecting leaf size, whereas zinc deficiency has a marked reduction on size of leaves, and magnesium affects only mature leaves. With young leaves, the manganese deficiency pattern is characterized by green veins on a light green background, and may be confused with iron deficiencies. (Compare plates 5 and 6). As the leaves become more mature, the pattern develops bands of green along the main and lateral veins with light green tissue. The color contrasts are less vivid than in the case of zinc deficiency'. Plate 5 shows the range of the manganese deficiency in grapefruit leaves. The light green area extends to the leaf margin in severe cases: and the advanced cases are somewhat similar to the early stages of zinc deficiency, although the color contrasts are never as great. If the deficiency of manganese is severe, the pattern persists with normal size leaves and. the light green colors may develop a gray to slight bronze effect, which might be confused with magnesium deficiency. Manganese deficiency is often found on marl soils, hence the term "Marl Frenching."
The deficiency is seldom severe enough to cause twig symptoms. With acute cases, however, the twigs may die, associated with a marked reduction in growth. The symptom of dying twigs is not as severe as in the case of 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. From systematic studies of zinc and manganese treatments, the pattern differences have been identified (10).
Manganese has a favorable effect on the quality of oranges and tangerines, according to Skinner and Bahrt (43).
In contrast with copper and zinc, manganese deficiency does not affect oranges and grapefruit as readily as it does tangerines, temples and king oranges.

Plate 5. Deficiency symptom? of manganese in grapefruit leaves, showing early (A), intermediate and advanced (C) stacos.

Soil Relations: Manganese deficiency appears more often on marl and over-limed soils than on the neutral and acid soils. This is due to the insolubility of manganese in alkaline media. Marl and over-limed soils are generally slightly alkaline with a pH of 7.0 or above, which renders the manganese unavailable. In some cases acid soils show manganese deficiency as a result of soil depletion and fixation. Where crop yields are heavy, the soil may become depleted of available manganese, but in most cases the deficiency results from unbalanced soil conditions as much as from actual shortage in the soil.
Treatment: Manganese sulphate is commonly used as the corrective for manganese deficiency, applied in soil treatments at the rate of '/o to 4 pounds per tree, the amount depending on tree size, severity of case and type of soil. Manganese sulphate may be supplied in spray form, using solution of about the same concentration as copper sulphate in Bordeaux, or in conjunction with Bordeaux and lime sulphur sprays. Like copper and zinc spray, the manganese may increase the scale hazard, thus necessitating an oil spray to follow later. Unless the deficiency is severe, soil treatments are generally used, except on marl soils. The spray treatment gives quicker results, but the effects are not as long lasting. In soil treatment, mulching, or use of heavy-cover crops, with applications of manganese will usually suffice.
Manganese Excess: No known symptoms of manganese excess have been reported in Florida, though the rates of application have been high in places. As with other nutrients, excessive amounts of manganese will hinder the utilization of other nutrients, and may even be toxic.
Historical Use: Manganese has become of general use in agriculture within recent years. Its use on citrus in Florida was suggested by the stimulating effects produced in truck crops growing on marly soil, first reported by Schriener and Dawson (42). Following these results, Florida citrus growers used manganese with success on marly soils. Skinner and his co-workers (43) later reported that manganese on acid soils had a marked improvement on the quality of fruit, while Camp and Peech (10) correlated manganese deficiency in citrus with soil analysis. Manganese is widely used in Florida and California on citrus and other crops, especially on alkaline soils and soils low in available manganese.
Deficiency Symptoms: Iron deficiency in citrus is commonly referred to as iron or marl chlorosis. The latter term, however, is a general one applied with equal frequency to manganese deficiency, also of widespread occurrence on marl soils. Iron deficiency is characterized by a general chlorotic condition of the leaves, particularly the younger ones, with the midrib and smaller veins retaining their chlorophyll longer than the leaf

Plate fl. Deficiency symptoms of iron in orange leaves, showing early tA) and advanced (lit stages. (See pajre 2S for description.)

tissue, resulting in a green network on a yellowish-green or light green background. The range of these colors and veinations are illustrated in Plate 6. In severe cases on marly soils the young leaves are small and yellowish to old ivory in color and may be almost free of veination. Such leaves usually shed early, leaving a defoliated effect. In light cases of iron deficiency, the leaf tissue may become green as the leaves mature and the netted effect disappears entirely. This is not unusual on sandy soils, but severe and chronic cases invariably are associated with marly or over-limed soils.
In acute cases, the twigs die back severely in the tree tops and extremes of the branches, showing a marked decrease in tree size. Such trees produce little or no fruit; but other than size of crop, no characteristic fruit symptoms have been associated with iron deficiency'. Although all varieties of citrus are susceptible to iron deficiency, oranges seem to be the most severely affected.
It is quite common to find other deficiencies associated with iron deficiency in citrus. This is particularly true with manganese, magnesium, and zinc. Under such conditions there is definite blending of the individual deficiency patterns in the leaves. Careful examination, however, shows that the specific patterns persist and can be recognized in the presence of others.
Soil Relations: Marl and alkaline soils usually induce iron deficiency. Here again the soil reaction has a positive and controlling effect on the availability of a nutrient. An alkaline reaction reduces the solubility and hence the availability of iron, thereby producing an iron chlorosis. An excess of most carbonates produces an alkaline reaction. This principle accounts for most of the iron chlorosis in all crops, including citrus, and is greatly aggravated in soils with a low content of organic matter.
Light sands often show symptoms of iron deficiency in citrus. This is a result of soil depletion or unavailability of iron, resulting from unfavorable soil reaction or excess of other nutrients.
Treatment: No entirely satisfactory treatment for iron deficiency has been developed for citrus on alkaline soil. The most practical method of treating this deficiency on such soils involves the use of heavy mulching with organic matter and acid fertilizers. The acidulated effect resulting from the acid fertilizer and organic matter will usually bring enough iron in solution to alleviate the trouble in the majority of cases, except where marl extends to the surface.
On alkaline soils soluble iron salts are precipitated too rapidly for root absorption. Furthermore, spraying for iron deficiency has not been as satisfactory with citrus as it has with pineapples and other crops. Recent reports indicate that with appropriate spreaders, iron salts may be successfully used as a spray. In some of the Western states, injection of soluble iron

salts, such as iron citrate or tartrate, directly into the trees has been known to give beneficial results. This treatment usually has to be repeated at somewhat frequent intervals, and is objectionable because of the damage to the wood.
On thin, sandy soils of acid or neutral reaction, iron sulphate applied at the rate of 1 to 3 pounds per tree has given beneficial results. Even here the use of mulches and acid fertilizers will prove helpful. In many cases, applications of manganese, copper and zinc along with iron are beneficial.
Iron Excess: The soluble iron salts such as sulphates and chlorides are acidic in nature, and will burn the foliage and fruit if allowed to come into contact with them. All iron salts become insoluble soon after being incorporated into the soil due to the tendency of iron to form insoluble compounds with other soil constituents and nutrients. For this reason excess iron reduces the availability of phosphates. In practice, it is doubtful that difficulty will be experienced from excess iron except under rather special and very acid conditions. By correcting the soil acidity, the iron is rendered insoluble.
Historical use: Iron deficiency in citrus as well as other crops has been a serious problem in some regions for many decades. This is particularly true in alkaline soils (13). Many investigators (25, 19, 30) have studied this problem and have reported encouraging results in recent years. Records by many growers show that soil applications of iron salts improve fruit color and general tone of the trees.
Deficiency S.vmptoms: Only in rare cases has a deficiency symptom of calcium been reported under field conditions of any crop, and none for citrus. Under controlled conditions, however, calcium deficiency symptom patterns have been described for citrus by Reed and Haas (35), and Bryan (6). These symptoms are characterized by a marked stunted and hard condition of the tree. The flushes of growth are short, with a tendency for the terminal branches to die back. In severe cases the leaves develop a yellowish color at the margins and tips which progresses toward the leaf center and base (Figure 5). In some ways this deficiency resembles a mild case of boron toxicity. The tips of leaves are often blunt and sometimes incompletely developed.
Soil Relations: Of all the soil nutrients, calcium seems to have the greatest controlling or balancing effect. It constitutes over 50% of the active bases in productive soils, being held largely in a replaceable form by the soil colloids (clays and humus). This in a measure represents the available calcium present. Soil acids tend to dissolve the calcium as well as magnesium, thereby^ increasing the intensity of leaching losses, with a resultant lowered fertility. In humid regions the calcium losses from leaching alone are greater than for any other nutrient,

Figure 5. Deficiency Symptoms cif Calcium in Grapefruit Leaves and Trees. (Cuntrolled Cultures.)
Upper: Leaver, showing loss of chlorophyll in tips and edges of leaves. Lower: Normal tree on right contrasted with calcium deficient tree on left.
varying from 200 to 600 pounds or more per acre annually. It is highly desirable to maintain the needed calcium to destroy acids as well as to serve as a balancing agent for biological processes. A rational use of lime is the secret of soil fertility in most areas, including Florida.
Treatment: Only under unusual conditions does the soil require calcium for nutritional purposes to a greater degree than lime for neutralizing soil acids. Although a soil reaction of approximately pH 6.0 is to be desired, it should be distinctly understood that pH alone is not enough, and dependence on it may lead to trouble. Records show that rain water has a favorable pH, but no calcium and magnesium. Ample calcium and magnesium should be the objective, rather than a pH of 6.0 or otherwise. Sands and sandy soils should have as much as 700 to 1000 pounds of calcium and 100 to 150 pounds of magnesium per acre 12 inches of soil. This may be supplied from lime, slag, oyster shells, or dolomite. Heavy soils and soils high in organic mat-

ter should have 50 to 100 per cent more calcium than that required by sandy soils. Dolomite has done more to improve groves, per unit cost, than any other single commodity. It supplies both calcium and magnesium without the risk of loo high pi I values.
Calcium Excess: An excess of calcium in the soil solution rarely occurs, since the sulphate and phosphate of calcium have a low solubility in soil water. An excess of lime carbonate or hydrate on sands produces high pH values which in turn reduces the availability' of manganese, zinc and iron. Many of the unproductive groves in Florida are traceable to excessive amounts of hydrated and carbonated lime (19). Fortunately an excess of dolomite does not produce unfavorable pll values and consequently does not produce the locking effect on the secondary nutrients.
Historical Use: Calcium in the form of lime, shells, ashes, bonemeal. and as a carrier of phosphates in the fertilizer, has been used for many decades. Hut the use of lime on Florida soils came into ill-repute about 1918 following excessive applications to groves. The case of high calcium lime is still a doubtful practive among many Florida growers, but where the secondary elements are applied, its ill effects can be corrected. Since 1933, dolomitic limestone has been used on Florida soils with marked success. Its greatest value lies in the magnesium content and non-injurious effect on the soil reaction, regardless of amounts.
Deficiency Symptoms: Boron deficiency in citrus foliage is. characterized by a marked tendency of the young leaves to wilt, curl and pucker. They have a dull brownish-green color with the absence of luster.
The midrib and lateral veins are chlorotic in young leaves and are usually enlarged with some splitting (Figure 6). Young leaves shed prematurely and the stems show gum formations and often die in irregular areas. The old leaves are often thick, brittle and bronze color, somewhat like magnesium deficiency, and may develop split veins (Figure 7, upper). The branches may have multiple buds with a rosette appearance.
Boron deficient fruit is characterized by small, misshapen, hard fruit which frequently contain brown gummy discoloration in the albedo layer of the rind (Figure 7. lower). The fruit is often lopsided. Gum may be found anywhere in the fruit, which often shows dark spots, dark seed coat, undeveloped seed and marked dryness.
Soil Relations: Although boron deficiency has not been definitely correlated with soil properties, it has been observed on both acid and alkaline soils. Observations indicate that many acid soils in humid regions show distinct boron shortage. Like

fisun 7. Corking of veins and curling of terminal leaves of Grapefruit "A", puckering of lcave:i with corking and splitting of veines "I!" and "C", accompanied bv leathery and brittle conditions with bronze colorations are symptoms of Boron deficiency as reported by Haas.
Lower: Dry discoloration*, abortive seed on left, and hard "rind" with gum formations, right, are Udron deficiency symptoms of fruit as reported by Morris.

Figuro 8. A mi:d case of Huron Toxicity in Grapefruit leaves, showing yellowing of leaves
at tijis ut'.il margins.
other nutrients, the availability of boron is dependent on the soil reaction as well as other nutrients present. Boron deficiency symptoms are more evident during prolonged periods of drought than during normal seasons.
Treatment: Borax has usually been the specific treatment for this deficiency with most annual crops, using 10 to 50 pounds per acre, depending on crop and soil type. This is also true for citrus. In addition, borax may be successfully applied to citrus in a spray, at the rate of 1 pound borax per 100 gallons. Soil applications range from 10 to 25 pounds borax per acre on light sands to as high as 50 pounds per acre on marls and heavy soils. Equivalent amounts of boric acid, fertilizer borate or other boron sources are being successfully used.
Boron Excess: Like copper, boron is poisonous and quickly shows evidence of excess. Yet, there is an optimum range for its usage. 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 California, 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 8 shows a typical case of boron toxicity in grapefruit, which is more sensitive than the orange. Affected leaves frequently show dead areas at tips and leaf margins. In severe cases the leaves shed quickly, followed by successive new flushes of growth which may shed, 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, resinous 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 working 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 types.
Historical Use: Haas (28) and co-workers in California pointed out the symptoms of boron deficiency in the vegetative parts of citrus grown in water cultures (1927, 1930). Later Morris (28) of Rhodesia reported symptoms of boron deficiency in fruit. Observations in recent years indicate that both leaf and fruit symptoms occur in Florida, and experimental records confirm these observations (43). Boron is now used in either sprays or in fertilizers as a general practice in citrus growing in Florida.
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 conditions shown in Figure 9 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 leaf condition in Figure 10 described by Floyd in 1908 as yellow spot is still unknown. It is more associated with grapefruit rootstock and sour rootstock than to rough lemon. Temple oranges are more susceptible than Valencias and Pineapples. It may occur on any variety.
The yellow spot is associated with low calcium in the soil. Leaf analyses reveal that potassium is abnormally high, apparently at the expense of calcium, in yellow spot leaves. The under surface of the yellow spots is resinous, not unlike that in boron toxicity. Boron sprays and high potash seem to aggravate the condition, and calcium seems to correct it.
With additional information, it is logical to assume that these unidentified symptoms and deficiency patterns for other elements such as cobalt, molybdenum, vanadium, etc., will be explained. Vanselow, A. P. and Datta. N. P. (*) of California have recently reported that molybdenum deficiency in lemons was characterized by interveinal chlorosis or mottling of leaves, which extended to leaf edge and became necrotic in advanced cases.
Although the grower may be able to recognize and diagnose deficiency symptoms, it is much better for him to know how to avoid deficiencies than to correct them because citrus trees are considerably impaired in health before visible deficiencies are in evidence.
In order to produce adequate crops, of high quality and avoid deficiencies and wasteful practices, it will be necessary' for growers to study and evaluate each factor affecting production, including the kind and amounts of fertilizers applied on his individual soil. This involves a working knowledge of what the crops actually remove from the soil, what nutrients are lost through leaching processes, and what amounts are needed to provide for tree and cover crop growth. This also involves a knowledge of what nutrients combine with each other and become insoluble and unavailable, and what benefits are derived from cover crops, as well as a knowledge of seasonal absorption as related to time of fertilizer application.
The successful growth of citrus or any crop involves several factors operating simultaneously: namely, (a) Adequate soil moisture, (b) Favorable temperature, (c) Favorable reaction (pH), (d) Favorable soil conditions to promote penetration of fertilizer into the root zone, (e) Pest control, (f) Soil aeration, (g) Ample amounts of organic matter, and (h) Adequate amounts of properly balanced plant nutrients. If any one of these factors is not favorable, all of the others are impaired.
Many growers are successfully practicing these management factors through the use of soil amendments, irrigation,
(*) Jour. Soil Sci. 67:3a-377.

figure lfl.Unidentified Leaf Symptoms. Yellow spots of citrus leaves observed in Florida for many years. It is more marked on grapefruit and sour rootstock than on lemon. Cause unknown.

cultural practices to include cover crops, pest control, and fertilizer applications as needed.
The major problem confronting most Florida growers is that of applying the needed fertilizer nutrients in a balanced form to avoid antagonistic effects and deficiencies. Other citrus areas do not use the poundage of commercial plant food as do Florida growers.
Reliable records indicate that a large per cent of nutrient deficiencies in Florida citrus is traceable to unbalanced and often blind fertilizer practices. This is especially true for growers on sands and sandy soils so common in Florida. Continued fertilizer application on such soils without regard to accumulations, leaching losses, and ratio of absorption is a blind and expensive operation. A cross section of these problems is presented in the following tables which will serve as guides to follow.
The first of these representative data (Table 1) show the nutrient content of citrus as related to fertilizer practices. The data in this table represent averages, and individual cases could be expected to vary as much as 10 to 20'i. From these data, it may be seen that citrus fruits contain about 3 times as much nitrogen as phosphoric acid, and about 1.5 times as much potash as nitrogen. This is a basic starting point regarding the nutrient ratios utilized by citrus. The content of magnesium in the fruit is relatively highalmost that of phosphorusand several times that of the combined amounts of copper, manganese and zinc. This explains the general need of magnesium for citrus. The content of sulphur is also high. But thus far this nutrient has been supplied as a carrier of other nutrients and no need for extra additions have arisen. Calcium is also a carrier of other nutrients and is rarely needed as a nutrient, yet often needed as a soil correctant. Citrus foliage contains remarkably high amounts of calcium, compared to the other nutrients. It is of significant interest to note that citrus fruit contains more boric acid than the combined amounts of copper, manganese and zinc.
Naturally the fruit does not absorb all of the nutrients required to produce the crop. The tree, cover crops, and soil itself absorb considerable amounts. Moreover, leaching takes its toll. Only under very favorable conditions does the fruit absorb more plant food than is applied in the fertilizer, because of leaching losses, fixation and needs of cover crops. Herein lies the secret of good soil management and efficient production. The success of any science depends on the efficient management of the factors involved, and the production of citrus is no exception.

Malnutrition Si/ni ptoms of Citrus 41
In order that a grower may better understand the utilization of his fertilizer nutrients, the data in Table 1 are calculated to give the nutrient requirements for different efficiency levels: namely, 33 '/j per cent each for nitrogen, phosphoric acid and potash, 10 per cent for boron, and 1 per cent each for copper, zinc, manganese and iron. Records show that some groves have an efficiency of less than 10 per cent of the major nutrients and less than 1 per cent of the minor nutrients, while others have an efficiency of over 50 per cent of the major nutrients and 5 per cent of the minor nutrients. As a rule the higher the efficiency, the higher the net profit to the grower.
Groves of low fertilizer efficiency usually mean unprofitable returns and are indicative of one or more vital factors limiting utilization, e. g., moisture, acidity, alkalinity, deficiency, diseases, etc. If copper is deficient in the soil, or its utilization hindered by unbalanced nutrient conditions, the crop will be seriously impaired, even though the actual pounds needed are very small. The same may be true of zinc, magnesium, and even iron. If the soil conditions are favorable and the secondary elements applied in proper amounts the efficiency of the major nutrients is increased, sometimes as much as two to three hundred per cent.
The amounts of representative fertilizer materials needed for 100 boxes of fruit are also listed in Table 1. From these data a grower may calculate the required nutrients for different size crops. For example, 100 boxes of fruit contain on an average, ]0 pounds of nitrogen, 3.5 pounds of phosphoric acid, 15 pounds of potash and 2.5 pounds of magnesium. This means that with 33 per cent efficiency for nitrogen, phosphoric acid, potash and magnesium, 100 boxes of fruit will need 30 pounds of nitrogen, 10 pounds of phosphoric acid. 45 pounds of potash and 9 pounds of magnesium. These are equivalent, respectively, to 200 pounds nitrate of soda, 50 pounds 20' i superphosphate, 75 pounds muriate of potash and 75 pounds of dolomite, or 500 pounds of a 6-2-9-2 (nitrogen, phosphoric acid, potash and magnesium). Conservative estimates indicate that bearing trees require about one-half as much plant food as the fruit consumes. Due allowance should be made for cover crops and leaching losses. If the fertilizer efficiency is less than 25 per cent for the major nutrients, and less than 2'/i for minor nutrients, the practice is wasteful (see footnote Table 1). These data are cited for grower's comparison with his own records.
Table 2 gives the composition of the commonly used commercial fertilizer materials with the pounds needed to give 1 unit or 20 pounds plant food. A working knowledge of these materials will be of great help to one trying to understand his fertilizer problem. They are used in making fertilizer mixtures, and unless a grower is familiar with their composition and properties, it will be difficult for him to intelligently understand fertilizer problems.

Types n( Hunt Nutrients
Chcmica] Forms ml outs ( Reported
Percent nf Nutrients in Fruit, Dry Basis
Approx. Lli-, in
Lbs. NaetH Approximate Ik of
Willi Dilferenl Following Materials
Ffency Lfrdl llcipiiral to Supply
Ik Per Cat Kcdkd Nstrinti
:J3% 57
lerptios. m\
Calcium CaO
55: Dolor
Doric Acid IL0;1 i)i ji; ,7 III'- la ) ill Borax
Minor Copper Cut) 11 jii 17 .7 1% (b ) 2.3# Cop. Sulph.
01 M'HI id! i Plant |W" Nutrients Mang^ Fe,03 InO .0025 II j0OO9 ,HI !5 2,5 13 ,!) r; (b i<; ib ) 7,5: Iron Sulph. ) SJpanj, Sulph,
Zinc ZnO llfi 1 18 Ui If (i) l 'Ik Sulph,
Sodium NiiuO ,115
so, n
as (arners of Other Nutrients
(a) Calculated on basis of in times crop removal, or \% efflciency. (lij Calculated on bails of mi) times crop removal', or If! sffleieitcy.
id Ample anions of sulphur anil chlorine are usually applied as carriers of oilier nutrients, If no sodium nitrate is Included in toiler, sodium may become s limiting factor,
(si Since potasli serves largely as a regulator and catalyst in the plant ami does mil leach as rapidly as nitrogen ami that phosphate* are not subject to leaching losses, a fertilizer analyzing IMI0>l-.U.iiJ-,2J (Nitrogen, Phosphoric Acid, Potash, Magnesium, Manganese Copper, Zinc, Iron, Boric Acid), applied at the rate of approximately J pounds per bus nl fruit annually, will supply the newts for lemon rootstock on sandy lands, Sour root and met ratted would require IJ'I to % mure than tk lemon root on similar soils. Heavier soils such as clays and loams will need more phosphate and leu potash] furthermore, organic soils and soils carrying abundant leguminous (over crops will require lesi nitrogen,

Table I
FERTILIZER MATERIALS Nitrogen I'ertent N I'W Am! I'lTfrnt PjOj l'crcint KlO Lb*. 20 Nitrogen N Rlllin NITROGEN CARRIERS Nitrate of Soda 16 125
Nitrate of soda-potash 14 14 143 143
Nitrate of lime (Calcium nitrate) 15 134
Nitrate of potassium 13 44 46
Cal-Nitro m Oft j: ijj, .,
Sulphate of ammonia "Ammophos" (Ammonium plws.i IXl.d 11.16 21148 125-182 42-160
I'raiiwn k I'rea 4246 44-48
Cyanamide Nitrogen solutions 22 51
37-44 46-54
Dried ground fish k Guano li-in iiiici 334-1
Animal tankage (1) 8.2 8 244 250
Cottonseed meal k Castor meal PIUKI'll \'IT V \IMMl'IK 5-8 25(1-4(111 ..
rllllM tinlH tAKKllKc Bonemeal 2-5 24 Hid 1..... ) 83
Ammoniated Superphosphate 4 16 m 126
Superphosphate (Acid Phosphate) .. 16-26 100-125
Double k triple superphosphates 32-46 .. 56-63
8.16 125-250
Ground phosphate rock (2)
Sulphate of potash-magnesia .. 25
Manure salts 26-36
Kainit ., ,. 14-20
Hardwood ashes .. ,. 2-8
(1) Many organic ammoniates are on the market, such as milorganite,
compost, humus, and so forth. (21 Soft and "Colloidal Phosphates" are also considered as raw phosphates
carrying from 15 to 32 per cent total P..0-, and from 21 to 4'i avail-

Table 3
The- Results Are Expressed in Pounds of Fruit per Tree. Data from Lake Alfred Experiment Station Mimeograph Report, 1938.
Wood : Nitrate
Nitrate of Sulphate of Dried ot' Soda and Nitrate of Soda
Soda** Ammonia" Blood** Sulphate of Sulphate of
Ammonia** Ammonia**
YEAR No. ** Copper Copper No. *** Copper Copper No. *** Copper Copper No. * Copper Copper No. * Copper Copper
1927-28 63 198 138 97 157 88 176 185 33 4
1928-29 133 127 95 153 73 125 100 85 57 37
1929-30 121 133 91 170 166 115 115 168 68 13
1C0-31 158 317 250 375 167 288 198 198 127 98
1931-32 201 378 210 216 154 167 217 244 291 210
1932-33 110 323 77 161 18 124 38 85 59 22
1933-34 250 302 248 235 184 135 223 318 334 340
Sub Total 1036 1778 1112 1407 918 1042 1067 1283 969 724
1934-35 96 318 85 153 70 82 28 Jl. 63 12
1935-36 288 462 33-1 409 381 354 281 461 344 373
1930-37 12 .350, 16 158 28 165 6 86^ 5 201
1937-38 321 567 30 423 285 483 167 582 174 499
'I otals 1753 3475 1577 2550 1683 2126 1549 2456 1555 1812
*Drops not included in averages.
**All plots received steamed boneineal 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.
(a) Plot 10 received till its nitrogen from stable manure until 1930.

The data in Table 3 gives the relative efficiency of different sources of nitrogen used in producing citrus under Florida conditions. Although these data were secured on one soil type (Norfolk sand), they are representative and compare favorably with observations and data from other areas, and are confirme 1 by grower experience. These records cover a ten year period of continuous nitrogen comparison (nitrogen being the only variable), and the data show thai with the addition of copper the inorganic sources were noticeably superior to the organic sources. This has been a debated question for some time, but repeated trials by growers and research workers (*) reaffirm the records that when the needed secondaries and other nutrients are furnished, inorganic nitrogen is superior to organic for citrus in Florida.
From an overall viewpoint it would appear that the natural organic sources of nitrogen would be superior to the inorganic nitrogen on sandy soils in a humid climate, because the organic sources are: (a) less leachable, (b) contain more secondary elements, (c) carry more calcium and magnesium, and (d) have more humus producing materials. However, repeated records by many workers show that pound for pound the inorganic sources of nitrogen when supplemented with needed secondaries are superior to the insoluble organic sources. This is of particular interest to practical growers because the inorganic sources are usually less expensive and more controllable. The records indicate that the organic sources do not furnish enough available nitrogen in the root zone during the critical winter and spring months to take care of needs. Then during summer with more favorable temperature and moisture and less needs, the organic sources become available and are leached. Proper recognition and use of these facts will be of great help to growers.
Unless the leachability and relative losses of plant nutrients are taken into consideration in formulating fertilizer gi*ades on sandy lands in humid regions, the grower cannot escape confusion. The relative rate of leaching losses of the varied nutrients under Florida conditions is given in Tables 4 and 5. The data in Table 4 show the total leachings for a typical twelve month period (1924) from a representative grove soil, receiving different sources of nitrogen.
These records show that insoluble organic nitrogen tends to reduce the total leaching losses, and that calcium losses were greater from superphosphate than from bone meal treatments, and that nitrates, sulphates, magnesium, sodium and potassium leach to a far greater degree than phosphates, iron and am-monical nitrogen, regardless of whether the fertilizer was acid or neutral.
(*) Proc. Fla. State Hort. Soc. 1949.

Figures are in Pounds per Acre, Except Drainage as Noted (a)
TANK NO. No. 1 No. 2 No. :t No. 4
Complete Fertilizer with
Different Sources of Nitrogen Sulphate of Manure Blood Nitrate of
tPiOa from Superphosphate) Ammonia Soda
Total drainage in acre inches 19.7 16.6 12.9 14.1
Total solids 1(5,317.00 6,365.00 8,735.00 1,243.20
Fixed solids 11,777.00 5,572.00 7,353.00 10,954.00
Am monia 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
Phosphoric acid 7.30 3.36 3.68 3.25
Sulphates G.815.00 2,775.00 3,868.00 i.724.uo
Chlorine 115.77 145.24 111.12 269.50
Calcium oxide 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 900.15 782.55 643.80 836.00
Iron oxide 3.77 .99 1.08 1.04
Magnesium oxide 266.40 170.94 123.92
TANK NO. No. r, No. No. 7 No. 8
Complete Fertiliier with
Different Source* of Nitrogen Nitrate of Sulphate of Blood Manure
(PiOs from Hone Meal) Soda of Ammonia
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 r..:;^;'.r.i> 3,437.50 3.135.00
Ammonia 2.02 121.00 9.63 2.7'.'
Nitrites .69 8.19 .68 .46
Nitrates (b) 1,265.00 1,155.00 675.00 555.00
Phosphoric acid 1.65 3.91 1.87 2.94
Sulphates 1168.00 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 -M.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 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 influence in retarding leaching losses.
Table I

LEACHATES 1st 2nd 3rd 4 th 5th 6th 7th 8th 9th I0th
Lakeland Fine Sand
Virgin- receiving 20002T
6-6-6 fertilizer after
10" water applied.
Nitrate Nitrogen p.p.m. Phosphoric Acid 7 1 2 1 2 29 46 14 3 2
0.4 1 0.3 0.2 0.2 0.2 0.3 0.4 0.2 0
Potash 2 1 0.3 0 ii 8 57 45 29 18
Calcium 5 0 4 4 4 25 54 23 8 2
Magnesium 1 1 1 0 1 19 32 11 2 0
Lakeland Fine Sand
Grove -Receiving 2000#
6-6-6 fertilizer after
10" water applied.
Nitrate Nitrogen p.p.m. Phosphoric Acid 84 49 14 6 6 46 34 10 4 3
0.1 0.2 0.1 0.2 0.6 0.3 0.9 4 9 11
Potash 42 21 8 11 8 39 49 28 17 13
Calcium 52 32 19 in 7 17 41 17 6 2
Magnesium :;-! 20 10 2 2 20 23 4 3 1
Leon Fine Sand
Virginreceiving lOno
0-6-6 fertilizer after
10" water applied.
Nitrate Nitrogen p.p.m. Phosphoric Acid 6 4 3 3 2 19 1- 4 1 0.5
3 0.6 0.2 0.8 0.5 10 36 14 6 3
Potash 1 2 3 2 l 12 37 8 3 2
Calcium 6 l 4 g 6 9 15 7 3 3
Magnesium 5 3 1 1 0.6 29 18 1 3 0
Gainesville Sandy Loam
Grovereceiving 2000S?
6-6-6 fertilizer after
10" water applied.
Nitrate Nitrogen p.p.m. Phosphoric Acid 34 16 5 5 4 20 46 13 8 5
0.2 0.1 0.2 0.7 0.4 0.6 0.6 0.6 0.4 0
Potash 14 7 3 8 6 15 38 31 19 10
Calcium 32 17 15 12 9 33 73 57 24 8
Magnesium 16 7 4 2 1 10 34 23 8 2
Blanton Fine Sand
Grovereceiving 20()0#
6-6-6 fertilizer after
10" water applied.
Nitrate Nitrogen p.p.m. Phosphoric Acid 53 22 11 7 6 61 51 11 5 2
0.2 0.3 0.3 0.3 0.5 1 0.3 0.4 09 0.4
Potash 1 i 9 6 8 6 45 70 52 34 20
Calcium 20 17 19 12 34 1 1 27 11 4
Magnesium 39 29 17 9 3 12 10 23 6 2
A 6-6-6 fertilizer applied at the rate of 2000 pounds per acre.
The soils were placed in aluminum tubes 27s" in diameter, 26" long, by passing tube into soil without molesting soil column. The tubes were then placed in racks with appropriate sieves to hold soils in placeand distilled water added at rate of approximately 2 inches at a time. The nutrients were determined in the leachate using standard procedures and technic.
Note that phosphates leach appreciably from Leon fine sand, and potash is retained longer than calcium and magnesium.
Table 5
(Unpublished data from Soil Science Foundation)

The data in Table 5 show that almost 100 per cent of nitrate nitrogen is leached below the 24 inch soil level in typical soils, with 10 inches of water, whereas the same amount of water leached about % of the potash. Only in exceptional cases will the leaching losses be as great from loams and clay soils as from sands.
Growers will profit by carefully studying the data in these tables in formulating fertilizer grades because they show extensive leaching of some nutrients, and relatively none with others. The losses must be restored, otherwise crop production will be hindered. If one nutrient leaches more rapidly than another, it would be reasonable to assume that the one subject to the greatest leaching should be used in proportionately larger amounts. To ignore this principle means an unbalanced soil, and loss to the grower. Furthermore, repeated applications of a nutrient which does not leach will result in the accumulation of such nutrient. This has been confirmed by many workers. Reuther and associates (36) have shown in a quantitative manner the unfavorable effects of high phosphates on the utilization of copper by citrus on sandy soils. The records indicate that it is far better for a grower to keep his soil nutrients balanced, void of extremes, and supplement leaching losses, rather than to use blanket applications year after year.
Records by many workers show that repeated application of high levels of available phosphates on sandy lands tends to build a reserve of phosphates in the soil. The data in Table 6 show that in addition to phosphate accumulation, copper and manganese tend to accumulate with repeated applications. To a certain extent calcium, magnesium and potash accumulate in soils, but nothing like phosphates and copper. If properly managed, the principle of building soil reserves on sands is to be commended, but it is necessary to guard against excesses which result in antagonistic effects.
Too much emphasis can hardly be placed on the influence of soil reaction on the leaching losses. However, pH records are not enough. The amounts of calcium and magnesium in the soil are more important than pH alone. Rain water has an ideal pH, ranging from 5.5 to 6.5, yet it has no calcium.
Strongly acid soils mean dissolving and loss of bases, while alkaline soils mean a locking effect of certain nutrients. The increased losses of calcium and other bases with ammonium sulphate nitrogen in Table 4 are due to the acidulating effects of this material. A reaction of pH 6.0 is considered to be about optimum for citrus on sandy soils. A soil reaction of pH 7.0 or above tends to lock such nutrients as manganese, iron and zinc. These data will prove helpful in studying the factors affecting leaching losses.

Table 6
(5-Yr. Average. Short Research Grove. Unpublished (lata from Soil Science Foundation* I
Replaceable Nutrients** Plot Pounds per Acre6" Soil
Nos. Treatment pH Cal- Magne- Phos Pot-Manga- Cop-
cium sium Acid ash nese per
Rate-, of Phosphate & Potash
17 (a) 6- 0- 8 No P..O- 5.92 216 69 9 51 14.8 4.9
11, 50 6- 0- 8 P.O., from Coll. 5.9 216 64 17 54 12 2.7
(a) 6- 4- 8 Avg. strl. checks 5.76 239 51 31 46 13 2.5
15 ,53 6- 6- 6 40%Org. N Nov-June 5.69 225 38 11 32 12.4 3.1
16, 54 6-12-12 40% Org. N Nov-June 5.62 253 27 68 47 13.3 3.4
10, 48(b) 6- 0- 8 P..O-, once 5 yrs. 5 9 241 58 49 5(1 14 3.6
23, 56 6- 0- 8 P205 from B. Slag 6.6 524 74 214 41 25 5.5
Rates of Potash
24, 67, 68 6- 4- 0 No Potash 6.1 268 76 43 22 10.2 2.6
14, 52 6- 4- 4 40% Org. N Nov-June 5.72 333 53 32 28 12.8 3.2
15, 53 6- 6- 6 40% Org. N Nov-June 5 69 225 38 41 32 12.4 3.1
(a) 6- 4- 8 Avg. std. checks 5.76 239 51 31 46 13 2.5
16, 54 6-12-12 40% Org. N Nov-June 5.62 253 27 (IS 47 13.3 3.4
Rates of Magnesium
38 Std. with no Dolo., no Sol. Mg. 5.3 181 L3 22 43 12.9 4.6
(a) Avg. std. checks 5.76 239 51 31 46 13 2.5
26, 64 Std. with 2 x Mg 5.7 225 64 33 i 1 12.9 2.8
75 Std. with excess Dolomite 6.4 352 89 54 11 14.2 2.6
77 Std. with excess Dolo. & Lime 7.1 1216 99 158 61 17.7 5.8
Rates of Copper
35,72 td. with no Copper 5.8 225 59 33 40 13.2 .5
(a) Avg. std. checks 5.76 239 51 31 46 13 2.5
28, 66 Std. with 2 x Copper 5.7 215 47 29 1 1 12.9 7.6
SO, 55 Std. with 3 x Copper 5.7 234 52 30 54 12.9 10.0
* Soil samples were composites of 16 soil cores per plot, taken 6 inchts deep within one foot of the leaf drip of each tree. ** Available nutrients determined by extracting with sodium acetate, buffered at pH 4.8.
[a) Std. treatment 6-4-8-2-.5-.25-.2-.1. (N-P205-K20-MgO-MnO-CuO-ZnO-BL,0:i, respectively). Because of limited space, a number of words are abbreviated, namely: P20-, for phosphate; Coll. for colloidal phosphate; Avg. std. for average standards; Org. N for organic nitrogen; B. Slag for basic slag; Dolo. for dolomite; Sol. for soluble; Mg. for Magnesium.
(b) Forty pounds per tree of 20 7r superphosphate applied in Feb. 1947 and
34 lbs. per tree in Feb.. 1942.
NotePhosphate, copper and manganese tend to increase with soil ipplication of those nutrients more than for calcium, magnesium and potash.

In a measure, growing citrus on many Florida soils is similar to working with sand cultures in which the nutrients are added in proportions to that required (absorbed) by the crop. The sand culture method of growing plants has been successfully used by many workers. Due allowance should be made for leaching and fixation losses, even on sands. Where this is done, records during the past ten years have shown that the method is profitable. Here again it should be pointed out that attempts to guess at the extent of nutrient reserves and leaching losses, even on sands, are misleading, resulting in unbalanced nutrients and wasteful practices.
Since the availability of many nutrients depends 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 need of another. For example, an excess of potash lowers the availability of magnesium. Table 6. Furthermore, an excess of calcium on sandy soils reduces the availability of zinc, manganese and other bases.
It is generally known that clay and loam soils lower the availability of phosphates by simple combination or chemical precipitation. Heavy clay and loam soils will lock up millions of tons of phosphate by chemical combination and render them unavailable. The reverse of this condition exists in many Florida groves where the content of iron and aluminum is very low, and in some cases the phosphates have accumulated to the extent of hindering the availability of secondary elements. It is interesting to point out that West (47) in Australia first showed that excess phosphates rendered the zinc unavailable. Later, Soil Science Foundation, Lakeland (Figure 2), and others confirmed West's reports. Moreover, records show a greater need for copper to avoid dieback or exanthema on highly phosphated soils than on low phosphated soils. It would be reasonable to assume that where the water soluble phosphorous is high, as is the case in some groves on sandy soils, the available iron, zinc, copper and manganese would be unfavorably affected.
Growers can profitably use these records in formulating their fertilizer grades from year to year. Some modifications will be necessary because of seasonal and soil differences, but when these are accounted for they are better than mere guesses. The practice of using one nutrient to excess and then offsetting its effects by adding other nutrients is poor business.
The effects of nutrient excesses may be classed under several 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 way toward offsetting the ill effects of excesses, especially where carbonates of calcium and magnesium are present, both of which have a balancing effect on other nutrients.
In the case of burning as a result of excess amounts of chlorides, nitrates and sulphates, flooding with water is a practical remedy. Mulching with litter, muck and even soil will be helpful. In most cases the burning effects are temporary, being alleviated by rain.
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, it is not possible to have a highly efficient grove. The optimum or proper balance for all nutrients is not known. But a logical use of the known facts involved will enable a grower to avoid a great deal of waste and erroneous practices.
Numerous analyses over a period of years indicate that available nitrogen is leached from Florida soils because of summer rainsto a greater degree than any other nutrient. This is not true in areas of low rainfall. Furthermore, experimental records by Roy and Gardner (41), show that citrus trees absorb proportionately more nitrogen during the fall and winter than any other nutrient. These finding have a practical value.
Inasmuch as most of the vegetative growth, including bloom and setting of citrus fruit, occur from February to July, it would appear advisable to apply the greater part, if not all, the needed plant food a few months prior to and during this period. This may be done in two or more applications, but records indicate that from one-half to two-thirds of the annual needs should be applied before February 15th. Especially is this true for groves which cannot be irrigated. Where moisture is limited, during the fall and winter period, some time is needed for the fertilizer to penetrate into the root zone. This should be taken into consideration in applying fall and winter fertilizer. Furthermore, insoluble fertilizers are less efficient than soluble forms, because the roots can absorb only soluble forms. And with limited moisture, heavy litter and grass will retard the penetration of fertilizer into the root zone. Under such condition, irrigating and or incorporation of the fertilizer in the soil will prove profitable.
If the records show that a nutrient is needed, it should be applied 30 or 40 days in advance of the growth period, preferably longer in dry soils. If soil records show ample reserves of available nutrients, such as phosphates, magnesium, potash, copper and manganese, there is nothing to be gained by applying them.

Maintenance amounts should be applied sufficiently in advance of the needs to allow penetration and absorption.
Records show that fertilized trees hold fruit and withstand drought and cold better than hungry trees. Furthermore, summer applications of fertilizer are more subject to leaching losses and are not as conducive for the high quality fruit as winter and spring applications, which promote better spring flush and foliage.
Young trees and trees with sparse and unhealthy foliage will need summer fertilizer. Furthermore, heavily loaded trees and cover crop may need summer fertilizer. But if 3/10 to 4/10 of a pound of nitrogen per box has been applied prior to bloom and during spring period, together with other needed nutrients, rarely will any summer fertilizer be needed. The annual needs can be easily calculated from records of tree capacity, using data in Tables 1 and 2.
Unbalanced fertilizer is not only wasteful but leads to deficiency problems and inefficient practices. Records by different workers indicate that a large part of the deficiency problems confronting Florida growers is due to unbalanced fertilizer practices. The conventional nutrient ratios of 1-2-2 and 1-2-3 (nitrogen, phosphoric acid and potash) can be justified only on soils which have a high chemical fixing power for phosphates and potash. Such is not generally true for the sands commonly used for citrus growing in Florida.
The accumulated records during the past two decades show that citrus absorbs approximately three times as much nitrogen as phosphoric acid, and approximately two-thirds as much nitrogen as potash (Table 1). Moreover, repeated records in Florida (Tables 5 and 6) indicate that nitrogen leaches rapidly, and phosphates only sparingly, on sandy lands. If the soil has little or no absorbing power for phosphates, the needs for this element should not be greater than one-third to one-half that of nitrogen ; and if soils contain ample phosphate reserves, additional amounts can hardly be justified. This is true for all nutrients.
The data in Table 6 show that available potash is retained by sands longer than magnesium and calcium. This is partially confirmed by the fact that trees show no ill effects when potash is omitted for twenty-four months or more. The overall interpretation of these leaching data, together with the absorption data, indicate that for the sandy soils under Florida conditions a grower would be entirely safe in applying potash at approximately the same rate as that of nitrogen. (See footnote Table 1). This would furnish the needed potash without causing the replacement of other elements such as magnesium.
To secure a proper phosphate ratio in the fertilizer necessitates a knowledge of the soil reserves of phosphates, especially

sands which have been fertilized for a number of years. As a rule, the initial phosphate application for loam and clay soils should be five or more times that of nitrogen, decreasing the phosphate with time. To a lesser extent this is true for the sands according to the records in the Short Research grove. But as the phosphates accumulate with years of treatment, some of this cumulative material is available. So, it would be profitable for a grower to ascertain the extent of soil reserves. The progressive grower will want to have specific information applicable to his own soil. This can be had only from the measurement of actual soil reserves from time to time. Especially is this true for phosphates, calcium, magnesium and the secondary elements. Records over a period of years show that the cost of such information is more than offset by increased improvement. A general guessing program cannot compete in efficiency with a scientific program. Until more information is available, the suggested nutrient ratio in Table 1 can be safely used in bearing groves on sandy soils under Florida conditions.
The rate of fertilizer application will vary according to soil type, variety and general management practices. As a rule, the fertilizer rate is gauged by its nitrogen content. For many years the rate of fertilizer has been based on the age of the tree and extent of tree spread, but records indicate that the age and tree spread are not the best guides to follow in determining the needed fertilizer. The box capacity of the tree offers a more direct method of determining fertilizer needs than any known factor to date. When this is done with due consideration to variety, rootstock and grove response, efficient and profitable practices have been secured. This can be boiled down to the principle of applying from .3 to .5 pound of nitrogen and other nutrients in proportion to needs, annually, per box capacity of the tree for mineral soils; organic soils will need less nitrogen. Futhermore, soils receiving heavy leguminous cover crops would need less nitrogen. For the bearing groves on typical sandy soils, approximately .3 of a pound of nitrogen per box fruit can be used as a guide for the annual application on rough lemon root. Sour root-stock will need approximately .4 of a pound per box. These rates are equivalent to 6 and 8 pounds of a fertilizer containing 5% nitrogen, or 3 and 4 pounds of a fertilizer containing 10% nitrogen. These rates can be gauged up or down according to tree condition. But it is very important that the tree have approximately one-half of the yearly supply prior to and during the bloom period. If the foliage is sparse or off-color, the rate should be increased accordingly.
Where, growers use greater amounts than these suggested rates, no material gain will be had except in abnormal cases. The problem may be moisture, poor mechanical condition of the soil, disease, or some other factor. Records indicate, however, that some growers use as much as .9 pound of nitrogen, and other nutrients in proportion, to produce a box of fruit.

Characteristic citrus deficiency symptoms of the following nutrients have been described and illustrated: Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, Iron, Copper, Manganese, Zinc and Boron. The illustrations have been carefully chosen and presented in a non-technical form understandable by the average grower. In connection with the deficiency patterns, brief summaries regarding appropriate treatments for the deficiency and excesses are presented, together with the soil relation and historical use.
Representative data dealing with the composition of citrus fruit (fertilizer nutrients), as related to fertilizer practices, are summarized for study along with the leaching data from representative Florida soils. In addition, records of available nutrients in typical soil receiving varied kinds and amounts of fertilizer nutrients have been interpreted in relation to crop needs. Crop needs have been calibrated on the basis of removal with due allowance for leaching losses, cover crop, soil and tree absorption. This has been done to enable the grower to so gauge the rate and time of his fertilizer application for best results, thereby avoiding antagonistic effects of one nutrient on another, deficiencies, and wasteful practices.
Years of experience have demonstrated that a grower can best cope with his nutrition problems by employing a program based on a rational interpretation of crop removal, tree and cover crop needs, leaching losses and soil reserves, rather than by the use of conventional practices, many of which are merely guesses. The scientific plan has proven itself to be more efficient and more economical, besides providing a practical method of avoiding deficiencies and malnutrition problems, as well as avoiding wasteful and inefficient practices.

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 spravs demonstrated. Agr. Gaz. N. S. Wales 48: 571-572, 580. 1937.
4. BRYAN, O. C. Potash deficiency in grapefruit. Florida Grower 43 (1): 14-16. January, 1935.
5. BRYAN, O. C, and DEBUSK, E. F. Citrus bronzinga magnesium deficiency. Florida Grower 45 (2) : 6, 24. February, 1936.
6. BRYAN, 0. C. Deficiency symptom patterns in citrus. Citrus Industry 19 (3): 11-15. March, 1938.
7. 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, 1936.
8. CAMP, A. F. Boron in citrus nutrition in Florida. Citrus Industry 20 (2) : 6, 7, 18. February, 1939.
9. CAMP, A. F. and FUDGE, B. R. Some symptoms of citrus malnutrition in Florida. Fla. Agr. Exp. Sta. Bull. 335, 55 pp. 1939.
10. CAMP, A. F. and PEECH, MICHAEL. Manganese deficiency in citrus in Florida. Proc. Amer. Soc. Hort. Sci. 36: 81-85. 1939.
11. 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.
12. CHAPMAN, H. D., BROWN, S. M., and RAYNER, D. S. Effects of potash deficiency and excess on orange trees. Hilgardia 17 (19). 1947.
13. CHAPMAN, G. W. The relation of iron and manganese to chlorosis in plants. New Phyto. 30:266-283. 1931.
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