Recommended fertilizers and nutritional sprays for citrus

Material Information

Recommended fertilizers and nutritional sprays for citrus
Series Title:
Bulletin University of Florida. Agricultural Experiment Station
Reitz, H. J
Place of Publication:
Gainesville Fla
University of Florida Agricultural Experiment Station
Publication Date:
Physical Description:
15 p. : ; 23 cm.


Subjects / Keywords:
Citrus fruits -- Fertilizers -- Florida ( lcsh )
Citrus fruits -- Nutrition -- Florida ( lcsh )
non-fiction ( marcgt )


General Note:
Cover title.
Bulletin (University of Florida. Agricultural Experiment Station) ;
Statement of Responsibility:
compiled by H.J. Reitz ... [et al.].

Record Information

Source Institution:
University of Florida
Holding Location:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
027108251 ( ALEPH )
18272576 ( OCLC )
AEN7051 ( NOTIS )

Full Text

January 1954

SA Contribution from the Citru Experiment Station)

Recommended Fertilizers and Nutritional

Sprays for Citrus

Compiled by

Committee on Fertilizer Recommendations from
Staff of Citrus Experiment Station

Single copies free to Florida residents upon request to

Bulletin 536


Hollis Rinehart, Chairman, Miami
J. Lee Ballard, St. Petersburg
Fred H. Kent, Jacksonville
Wim. H. Dial, Orlando
Mrs. Alfred I. duPont, Jacksonville
George W. English, Jr., Ft. Lauderdale
W. Glenn Miller, Monticello
W. F. Powers, Secretary, Tallahassee
J. Hillis Miller, Ph.D., President'
J. Wayne Reitz, Ph.D., Provost for Agr.3
Willard M. Fifield, M.S., Director
J. R. Beckenbach, Ph.D., Asso. Director
L. 0. Gratz, Ph.D., Assistant Director
Rogers L. Bartley, B.S., Admin. Mgr.3
Geo. R. Freeman, B.S., Farm Superintendent

H. G. Hamilton, Ph.D., Agr. Economist 3
It. E. L. Greene, Ph.D., Agr. Economist 3
M. A. Brooker, Ph.D., Agr. Economist3
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Ar. Economist
D. E. Alleger, M.S., Associate
D. L. Brooke, M.S.A., Associate
M. R. Godwin, Ph.D., Associatei
W. K. McPherson, M.S., Economist
Eric Thor, M.S., Asao. Agr. Economist3
Cecil N. Smith, M.A., Asso. Air. Economist
Levi A. Powell, Sr., M.S.A., Assistant
Orlando, Florida (Cooperative USDA)
G. Norman Rose, B.S., Asso. Agri. Economist
J. C. Townsend. Jr., B.S.A., Agr. Statistician
J. B. Owens, B.S.A.. Agr. Statistician 2
F. T. Calloway, M.S., Agr. Statistician

Frazier Rogers, M.S.A., Agr. Engineer'
J. M. Myers, M.S.A., Asso. Agr. Engineer
J. S. Norton, M.S., Asst. Agr. Engineer
Fred H. Hull, Ph.D., Agronomist 2
G. B. Killinger, Ph.D., Agronomist
H. C. Harris, Ph.D., Agronomist
R. W. Bledsoe, Ph.D., Agronomist
W. A. Carver, Ph.D., Agronomist
Fred A. Clark, M.S., Associate 2
E. S. Horner, Ph.D., Assistant
A. T. Wallace, Ph.D., Assistant 3
D. E. McCloud, Ph.D., Assistant
G. C. Nutter, Ph.D., Asst. Agronomist
I. M. Wofford, Ph.D., Asst. Agronomist

T. J. Cunha, Ph.D., Animal Husbandman 13
G. K. Davis, Ph.D., Animal Nutritionist :
II. L. Shirley, Ph.D., Biochemist
A. M. Pearson, Ph.D., Asso. An. Hush."
John P. Feaster, Ph.D., Asst. An. Nutri.
H. D. Wallace, Ph.D., Asst. An. Husb.h
M. Koger, Ph.D., An. Husbandman 3
J. F. Hentges, Jr., Ph.D., Asst. An. Hush. a
L. R. Arrington, Ph.D., Asst. An. Husb.
A. C. Warnick, Ph.D., Asst. Physiologist

E. L. Fouts, Ph.D., Dairy Technologist 1
R. B. Becker, Ph.D.. Dairy Husbandman '
S. P. Marshall, Ph.D., Asso. Dairy Husb.'
W. A. Krienke, M.S.. Asso. Dairy Tech.O
P. T. Dix Arnold, M.S.A., Asso. Dairy Iuusb. 3
Leon Mull, Ph.D., Asso. Dairy Tech.-
H. H. Wilkowske, Ph.D., Asst. Dairy Tech.:
James M. Wing, Ph.D., Asst. Dairy Husnh.

J. Irancis Cooper, M.S.A., Editor3
Clyde Beale, A.B.J., Associate Editor 3
J. N. Joiner, B.S.A., Assistant Editor
William G. Mitchell, A.B.J., Assistant Editor
Samuel L. Burgess, A.B.J., Assistant Editor
A. N. Tissot, Ph.D., Entomologist'
L. C. Kuitert, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
F. A. Robinson, M.S., Asst. Apiculturist
R. H. Waites, Ph.D., Asst. Entomologist
S. H. Kerr, Ph.D., Asst. Entomologist
Ouida D. Abbott, Ph.D., Home Econ.1
R. B. French, Ph.D., Biochemist
G. H. Blackmon, M.S.A., Horticulturist
F. S. Jamison, Ph.D., Horticulturist3
Albert P. Lorz, Ph.D., Horticulturist
R. K. Showalter, M.S., Asso. Hort.
R. A. Dennison, Ph.D., Asso. 1ort.
R. H. Sharpe, S. Asso. Horticulturist
V. F. Nettles, Ph.D., Asso. Horticulturist
F. S. Lagasse, Ph.D., Horticulturist2
R. D. Dickey, M.S.A., Asso. H'ort.
L. H. Halsey M.S.A., Asst. Hort.
C. Hall, Ph.D., Asst. Horticulturist
Austin Griffiths, Jr., B.S., Asst. Hort.
S. E. McFadden, Jr., Ph.D., Asst. Hort.
C. H. VanMiddelem, Ph.D., Asst. Biochemist
Buford D. Thompson, M.S.A., Asst. Hort.
M. W. Hoover, M.S.A., Asst. Hort.
Ida Keeling Cresap, Librarian
W. B. Tisdale, Ph.D., Plant Pathologist' :
Phares Decker, Ph.D., Plant Pathologist
Erdman West, M.S., Botanist & Mycologist
Robert W. Earhart, Ph.D., Plant Path.2
Howard N. Miller, Ph.D., Asso. Plant Path.
Lillian E. Arnold, M.S., Asso. Botanist
C. W. Anderson, Ph.D., Asst. Plant Path.
N. 1. Mehrhof, M.Agr., Poultry Husb.13
J. C. Driggers, Ph.D., Asso. Poultry Hush.:
F. B. Smith, Ph.D., Microbiologist' 3
Gaylord M. Volk, Ph.D., Soils Chemist
.1. R. Neller, Ph.D., Soils Chemist
Nathan Gammon, Jr., Ph.D., Soils Chemist
Ralph G. Leihty, B.S., Asst. Soil Surveyor
G. D. Thornton, Ph.D., Microbiologist
C. F. Eno, Ph.D., Asst. Soils Microbiologist
H. W. Winsor, B.S.A., Assistant Chemist
R. E. Caldwell, M.S.A., Asst. Chemist34
V. W. Carlisle, B.S., Asst. Soil Surveyor
J. H. Walker, M.S.A., Asst. Soil Surveyor
William K. Robertson, Ph.D., Asst. Chemis't
0. E. Cruz, B.S.A., Asst. Soil Surveyor
W. G. Blue,, PD., Asst. Biochemist
J. G. A. Fiskel, Ph.D., Asst. Biochemist
L. C. Hammond, Ph.D., Asst. Soil Physicist 3
H. L. Breland, Ph.D., Asst. Soils Chem.
D. A. Sanders, D.V.M., Veterinarian 3
M. W. Emmel, D.V.M., Veterinarian 3
C. F. Simpson, D.V.M., Asso. Veterinarian
L. E. Swanson. D.V.M., Parasitologist
WV. R. Dennis, D.V.M., Asst. Parasitologist
E. W. Swarthout, D.V.M., Asso. Poultry
Pathologist (Dade City)


W. C. Rhoades, M.S.. Entomologist in Charge
R. R. Kincaid, Ph.D., Plant Pathologist
L. G. Thompson, Jr.. Ph.D., Soils Chemist
W. H. Chapman, M.S.. Agronomist
Frank S. Baker, Jr., B.S., Asst. An. Husb.
Frank E. Guthrie, Ph.D., Asst. Entomologist
Mobile Unit, Monticello
R. W. Wallace, B.S., Associate Agronomist
Mobile Unit, Marianna
R. W. Lipscomb, M.S., Associate Agronomist
Mobile Unit, Pensacola
R. L. Smith, M.S., Associate Agronomist
Mobile Unit, Chipley
J. B. White, B.S.A., Associate Agronomist


A. F. Camp, Ph.D., Vice-Director in Charge
W. L. Thompson, B.S., Entomologist
R. F. Suit, Ph.D., Plant Pathologist
E. P. Ducharme, Ph.D., Asso. Plant Path.
C. R. Stearns, Jr., B.S.A., Asso. Chemist
J. W. Sites, Ph.D., Horticulturist
H. O. Sterling, B.S., Asst. Horticulturis'c
H. J. Reitz, Ph.D., Horticulturist
Francine Fisher, M.S., Asst. Plant Path.
1. W. Wander, Ph.D., Soils Chemist
J. W. Kesterson, M.S., Asso. Chemist
R. Hendrickson, B.S., Asst. Chemist
Ivan Stewart, Ph.D., Asst. Biochemist
D. S. Prosser, Jr., B.S., Asst. Engineer
R. W. Olsen, B.S., Biochemist
F. V .Wenzel, Jr., Ph.D., Chemist
Alvin H. Rouse, I.S., Asso. Chemist
H Ford, Ph.D., Asst. Horticulturist
L. C. Knorr, Ph.D., Asso. Histologist
R. M. Pratt, Ph.D., Asso. Ent.-Pathologist
W. A. Simanton, Ph.D., Entomologist
E. J. Deszyck, Ph.D., Asso. Horticulturist
C. I. Leonard, Ph.D., Asso. Horticulturist
W. T. Long, M.S., Asst. Horticulturist
M. H. Muma, Ph.D., Asso. Entomologist
F. J. Reynolds, Ph.D., Asso. Hort.
W. F. Spencer, Ph.D., Asst. Chem.
R. B. Johnson, Ph.D., Asst. Entomologist
W. F. Newhall, Ph.D., Asst. Biochemist
W. F. Grierson-Jackson, Ph.D., Asst. Chem.
Roger Patrick, Ph.D., Bacteriologist
Marion F. Oberbacher, Ph.D., Asst. Plant
Evert J. Elvin, B.S., Asst. Horticulturist
R. C. J. Koo, Ph.D., Asst. Biochemist
J. R. Kuykendall, Ph.D., Asst. Horticulturist


W. T. Forsee, Jr., Ph.D., Chemist in Charge
R. V. Allison, Ph.D., Fiber Technologist
Thomas Bregger, Ph.D., Physiologist
J. W. Randolph, M.S., Agricultural Engr.
R. W. Kidder, M.S., Asso. Animal Husb.
C. C. Scale, Associate Agronomist
N. C. Hayslip, B.S.A. Asso. Entomologist
E. A. Woll', M.S., Asst. Horticulturist
W. H. Thames, M.S., Asst. Entomologist
W. G. Genung, M.S., Asst. Entomologist
Robert J. Allen, Ph.D., Asst. Agronomist
V. E. Green, Ph.D., Asst. Agronomist
J. F. Darby, Ph.D., Asst. Plant Path.
V. L. Guzman, Ph.D., Asst. Hort.
J. C. Stephens, B.S., Drainage Engineer-
A. E. Kretschmer, Jr., Ph.D., Asst. Soils
Charles T. Ozaki, Ph.D., Asst. Chemist
Thomas L. Meade, Ph.D., Asst. An. Nutri.
D. S. Harrison, M.S., Asst. Agri. Engr.

F. T. Boyd, Ph.D., Asso. Agronomist
M. G. Hamilton, Ph.D., Asst. Horticulturist
J. N. Simons, Ph.D., Asst. Virologist
D. N. Beardsley, M.S., Asst. Animal Hush.

Geo. D. Ruehle, Ph.D., Vice-Dir. in Charge
D. 0. Wolfenbarger, Ph.D., Entomologist
Francis B. Lincoln, Ph.D., Horticulturist
Robert A. Conover, Ph.D., Plant Path.
John L. Malcolm, Ph.D., Asso. Soils Chemist
R. W. Harness, Ph.D., Asst. Chemist
R. Bruce Ledin, Ph.D., Asst. Hort.
J. C. Noonan, M.S., Asst. Hort.
M. H. Gallatin, B.S., Soil Conservationist 2

Marian W. Hazen, M.S., Animal Husband-
man in Charge 2

WV. G. Kirk, Ph.D., Vice-Director in Charge
E. M. Hedges, Ph.D., Agronomist
D. W. Jones, I.S., Asst. Soil Technologist

R. W. Ruprecht, Ph.D., Vice-Dir. in Charge
J. WV. Wilson, ScD., Entomologist
P. J. Westgate, Ph.D., Asso. Hort.
Ben F. Whitner, Jr., B.S.A., Asst. Hort.
Geo. Swank, Jr., Ph.D., Asst. Plant Path.

C. E. Hutton, Ph.D., Vice-Director in Charge
H. WV. Lundy, B.S.A., Associate Agronomist

G. E. Ricchey, M.S., Agronomist in Charge

E. L. Spencer, Ph.D., Soils Chemist in Charge
E. G. Kelsheimer, Ph.D., Entomologist
David G. A. Kelbert, Asso. Horticulturist
Robert 0. Mlagie, Ph.D., Plant Pathologist
J. 31. Walter, Ph.D., Plant Pathologist
S. S. Woltz, Ph.D., Asst. Horticulturist
Donald S. Burgis, M.S.A., Asst. Hort.
C. M. Geraldson, Ph.D., Asst. Horticulturist


Watermelon, Grape, Pasture-Leesburg
J. MI. Crall, Ph.D., Associate Plant Path-
ologist Acting in Charge
C. C. Helms, Jr., B.S., Asst. Agronomist
L. H. Stover, Assistant in Horticulture
Strawherry-Plant City
A. N. Brooks, Ph.D., Plant Pathologist
A. H. Eddins, Ph.D., Plant Path. in Charge
E. N. McCubbin, Ph.D., Horticulturist
T. M. Dobrovsky, Ph.D., Asst. Entomologist
A. M. Phillips, B.S., Asso, Entomologist0
John R. Large, M.S., Asso. Plant Path.
Frost Forecasting-Lakeland
Warren O. Johnson, D.S., Meteorologist in

SHead of Department
2In cooperation with U. S.
Cooperative, other divisions, U. of F.
On leave

INTRODUCTION .................. ...... ..... ...... .... ..... .... ... .. 5
RECOMMENDATIONS FOR BEARING CITRUS TREES ............................ .. 6
Tim e of Fertilization .....- .. ..... ... .... ....... .... .... ....... 6
Amount of Fertilizer to Use Per Tree ...................................... 6
Elements to be Included in the Fertilizer ........................... 6
N nitrogen .............. .. ................ -- ... .. ...... .... ... 7
Phosphorus ..........- ... .. ...... ....... ..... .. 7
P otassium ..... ............... --.. .... .. ...... -. ........ ..-- .- .. 7
M agnesium ....... ------.......... .... .... .....- .....-- ..-- 8
M anganese -............... ............. ......... 8
Copper ........... ~ ... ..... ....-- .... -- -......- ...- ....- 8
Zinc ...................-.......-............--- ----- .. ........ 9
Boron .........---- --.........-- ...- -.----....------ 9
M olybdenum -.....-- .. ... ... ..... .- ..- ... .... ........ ............. 9
Iron ..................... ........-....-.... ---- -- .. .. ...... .. 10
Calcium ...................... .. -......... -- -.-............ 10
Sulfur ..... .......... ...... .. .... ... .. .. .- .... ... .. ... 10
pH Control --............ ----......---...---.....-- ...- .....--- --------..... ........ 10
Calculation of Fertilizer Rates and Analyses .................. .......-........ 11
NON-BEARING CITRUS TREES ...... .... ..-.... -- ..--- .- ....--- -- .... 13


Recently several conferences have been held by groups in-
terested in establishing the best fertilization practices for citrus
in Florida. These groups have included those staff members of
the Citrus Experiment Station and the U. S. Subtropical Fruit
Field Station who are engaged in citrus nutritional research
work, progressive growers, and representatives of industries
serving the citrus grower. The recommendations in this bulle-
tin were derived by the staff members of the Citrus Experiment
Station who participated in the conferences and are based on
their own extensive studies and on information presented at
these conferences. It is felt that the program presented here-
in is in accord with the general views of the research groups
and is the best practical recommendation which can be devised
from the present fund of information.

INTRODUCTION .................. ...... ..... ...... .... ..... .... ... .. 5
RECOMMENDATIONS FOR BEARING CITRUS TREES ............................ .. 6
Tim e of Fertilization .....- .. ..... ... .... ....... .... .... ....... 6
Amount of Fertilizer to Use Per Tree ...................................... 6
Elements to be Included in the Fertilizer ........................... 6
N nitrogen .............. .. ................ -- ... .. ...... .... ... 7
Phosphorus ..........- ... .. ...... ....... ..... .. 7
P otassium ..... ............... --.. .... .. ...... -. ........ ..-- .- .. 7
M agnesium ....... ------.......... .... .... .....- .....-- ..-- 8
M anganese -............... ............. ......... 8
Copper ........... ~ ... ..... ....-- .... -- -......- ...- ....- 8
Zinc ...................-.......-............--- ----- .. ........ 9
Boron .........---- --.........-- ...- -.----....------ 9
M olybdenum -.....-- .. ... ... ..... .- ..- ... .... ........ ............. 9
Iron ..................... ........-....-.... ---- -- .. .. ...... .. 10
Calcium ...................... .. -......... -- -.-............ 10
Sulfur ..... .......... ...... .. .... ... .. .. .- .... ... .. ... 10
pH Control --............ ----......---...---.....-- ...- .....--- --------..... ........ 10
Calculation of Fertilizer Rates and Analyses .................. .......-........ 11
NON-BEARING CITRUS TREES ...... .... ..-.... -- ..--- .- ....--- -- .... 13


Recently several conferences have been held by groups in-
terested in establishing the best fertilization practices for citrus
in Florida. These groups have included those staff members of
the Citrus Experiment Station and the U. S. Subtropical Fruit
Field Station who are engaged in citrus nutritional research
work, progressive growers, and representatives of industries
serving the citrus grower. The recommendations in this bulle-
tin were derived by the staff members of the Citrus Experiment
Station who participated in the conferences and are based on
their own extensive studies and on information presented at
these conferences. It is felt that the program presented here-
in is in accord with the general views of the research groups
and is the best practical recommendation which can be devised
from the present fund of information.

Recommended Fertilizers and Nutritional

Sprays for Citrus

Compiled by

Most Florida citrus is grown on sandy soils which are ex-
tremely low in natural fertility. Such soils in the virgin state
have low supplies of essential plant nutrients and have such a
low exchange capacity that they can retain relatively small
amounts of exchangeable plant nutrients against the leaching
action of rainfall. For these reasons, citrus crops must be fer-
tilized abundantly and often in order to obtain high production
of good quality fruit.
Citrus will grow under a wide range of nutrition levels and
it is impossible to outline any one program of fertilization that
is better than all others for all conditions. A wide variety of
fertilization programs is now used by citrus growers in Florida,
and many different programs are producing high yields of fruit
of acceptable quality. Obviously, any fertilization program
which is suggested or recommended cannot be expected to sat-
isfy all citrus growers. Furthermore, any such program must
be flexible enough to permit adjustments to meet differing grove
conditions brought about by soil, rootstock, scion, age of trees,
previous programs of fertilization, insect and disease control,
and other factors.
It should be emphasized that the size and quality of the fruit
crop in any one year is not determined by the ratio or poundage
of any single fertilizer application or even of a single year's fer-
tilization. It is determined, rather, by the condition of the
grove, which reflects past grove practices for a period of sev-
eral years. Not only fertilization but also insect and disease
control, irrigation, soil conditions, weather, and other factors
exert an influence.
Recent developments and new research findings in the field
of citrus nutrition make it desirable to issue new recommenda-
tions. These are given in the following sections and are in-
tended primarily for average sandy, well-drained soils low in
organic matter, such as the Lakeland and Blanton sands, and

Florida Agricultural Experiment Stations

for normal, healthy trees. For other soil types modifications
are presented according to available information.

It is known that three applications of fertilizer per year, in
January-February, May-June, and October-November have given
good results in light, sandy soils. These times precede or coin-
cide with the appearance of the three main flushes of growth of
citrus trees. Two applications per year are considered satisfac-
tory on the heavier soils which contain more clay and organic
matter. Where two applications are to be made, one should be in
the winter months, preferably in January or February, and the
other in May or June.

Under ordinary conditions the best guide for determining the
amount of fertilizer to use on mature bearing trees is the past
record of tree yield over a period of several years. The quanti-
ties recommended in this bulletin are based on the number of
standard field boxes (containing about 2.2 bushels) produced by
the tree and provide an ample supply of the elements to take
care of normal growth and yield increases. Trees vary some-
what in fertilizer requirements and there are cases in which
trees on rootstocks other than the common rough lemon may
need as much as 10 percent more fertilizer. Likewise, trees that
have been damaged by freezes, hurricanes, or severe insect
attacks sometimes are benefited by supplemental fertilizer ap-
plications. In case a particular grove has a specific deficiency
this should be corrected and the fertilization should be based
on a reasonable estimate of potential yield.

Research has shown that plants require 15 different chemical
elements for healthy growth. Twelve of these must come from
the soil or from applied fertilizers, soil amendments, or nutrient
sprays. They are nitrogen (N), phosphorus (P), potassium (K),
magnesium (Mg), manganese (Mn), copper (Cu), zinc (Zn),
calcium (Ca), sulfur (S), boron (B), iron (Fe), and molybdenum
(Mo). All 12 of these essential elements are now being applied
1 For general information on fertilizer materials and mixtures, see Fla.
Agr. Exp. Sta. Bul. 506, Nov. 1952, "Know Your Fertilizers".

Fertilizers and Nutritional Sprays for Citrus

to many Florida citrus groves. The other three, carbon, hydro-
gen, and oxygen, are provided by air and water.
Nitrogen.-The percentage of nitrogen is the first figure of
a fertilizer analysis. Apply 0.4 pound of total nitrogen (ex-
pressed as N equivalent on the fertilizer tag) per year per box
of fruit. For example, an 8-box tree would require 3.2 pounds
of nitrogen per year, or 40 pounds of a fertilizer containing
8 percent nitrogen per year.
The nitrogen supply has a pronounced effect on the growth
and appearance of the tree. Nitrogen is easily leached unless
taken up by the tree. As very little reserve supply can be
built up, frequent and ample applications are required to pre-
vent deficiency symptoms.
Phosphorus.-Phosphorus is expressed as P,O, equivalent
(called available phosphoric acid) on the fertilizer tag. It is
usually applied in the form of superphosphate. It leaches very
slowly from sandy soil where the pH is controlled at about 5.5.
Research has shown that mature citrus trees growing on soil
which has been fertilized with phosphorus for several years
will produce high yields of good quality fruit without additional
phosphorus. Consequently, phosphate fertilizers may be omitted
from such groves, at least until such future time as the trees
may show definite need of them. If it is impossible to obtain
enough nitrogen in other forms, it may be necessary to use
ammoniated superphosphate as a source of nitrogen. In this
case, some phosphorus would be applied as a carrier for the
nitrogen, even though the phosphorus was not needed. It may
be desirable under some conditions to apply some phosphorus
for the benefit of a cover crop grown in the grove. Calcareous
or marl soils may also require phosphorus applications. Where
it is needed, apply 0.3 pound of P.05 per year per box of fruit.
Potassium.-Potassium is expressed as KO equivalent (called
potash) on the fertilizer tag. Apply 0.35 pound of KO2 per year
per box of fruit. Excess potassium fertilization may produce
large, coarse, poorly-colored fruit, whereas a lack of potassium
will result in small sizes. The amount of potash applied should
be increased about one-third on high calcium or marl soils, since
high calcium in the soil lowers the uptake of potassium by the
Excessive potassium tends to reduce uptake of magnesium
by the tree, sometimes to the point of inducing magnesium de-
ficiency in the tree.

Florida Agricultural Experiment Stations

Magnesium.-Magnesium is expressed as MgO equivalent
(magnesium oxide) on the fertilizer tag. The form applied
should be water-soluble and is usually applied as a sulfate. It is
recommended that from 0.2 to 0.4 pound of water-soluble MgO
be applied per year per box of fruit. The higher rate should be
used for seedy varieties, where high calcium limestone is used
for pH control, and on calcareous soils. Dolomite, a combination
of magnesium and calcium carbonates, is widely used to control
the soil pH. Because of its magnesium content, less water-
soluble magnesium is required where sufficient dolomite is used
to maintain the soil pH at 5.5 to 6.0 than where high calcium
limestone is used. If magnesium deficiency symptoms appear in
trees on calcareous soils, a separate application of water-sol-
uble magnesium should be made.
Manganese.-Manganese is usually applied as water-soluble
manganese sulfate and is expressed as MnO equivalent (manga-
nese oxide) on the fertilizer tag. On acid soils apply 0.03 pound
of MnO per year per box of fruit. This amount may be re-
duced on old groves where pH has been maintained consistently
at 5.5 or above and which have received regular manganese ap-
plications in recent years. Manganese should not be applied in
the fertilizer on calcareous soils, but should be applied as a
nutritional foliage spray. In the spray use 3 pounds of manga-
nese sulfate and 0.1 pound of hydrated lime per 100 gallons.
For further details on applications of manganese in foliage
sprays, see the current Better Fruit Program Spray and Dust
Copper.-Copper is usually applied as copper sulfate and is
expressed as CuO equivalent (copper oxide) on the fertilizer
tag. Most of the applied copper accumulates in the top six
inches of soil. Soils that contain approximately 50 pounds of
copper per acre six inches need no further additions of copper
in the fertilizer. Recent research indicates that excessive
amounts of copper have accumulated in many grove soils. In
acid soils such excesses of copper are capable of depressing
growth and inducing iron chlorosis in the trees. Some groves
have been found to contain over 600 pounds of copper per acre
in the top six inches of soil. Acid soils low in organic matter
which contain as much as 150 pounds of copper per acre six

These programs may be obtained from the Citrus Experiment Station,
Lake Alfred, the Florida Citrus Commission, Lakeland, or County Agricul-
tural Agents.

Fertilizers and Nutritional Sprays for Citrus

inches of soil are at a potentially dangerous copper level. The
pH of such soils should be maintained at 5.5 to 6, and no further
copper should be applied in the fertilizer. Much higher levels
of copper in calcareous and organic soils can be tolerated with-
out injury to the trees.
Apply no copper in the fertilizer to old groves that have
received copper applications in recent years. Omit copper from
the fertilizer on any grove which received a copper spray for
melanose or scab control.
Zinc.-Zinc should be applied in a nutritional spray once a
year, as either a dormant or a post-bloom spray, using 3 pounds
of zinc sulfate plus 1 pound of hydrated lime per 100 gallons, or
its equivalent in neutral zinc material. For compatibility with
other materials, see spray schedules of the Better Fruit Pro-
gram. Zinc applications in the fertilizer have not consistently
given satisfactory results.
Boron.-Great care should be exercised in the use of boron,
since there is a relatively narrow range between deficient and
toxic levels. It is difficult to find a case of boron deficiency in
Florida citrus, but there are many cases of boron toxicity as a
result of applying too much boron. Boron may be applied as
borax either in a nutritional spray or in the fertilizer, but should
not be applied in both. If applied as a spray, use 1 pound of
borax per 100 gallons. Where it is used in the fertilizer, apply
0.1 unit of B.,O equivalent in a low analysis fertilizer (carry-
ing 4 to 6 percent nitrogen) and 0.2 unit in a high analysis
fertilizer, making only one application per year.
Molybdenum.-Molybdenum foliage sprays are tentatively
recommended to correct molybdenum deficiency, which is com-
monly known as "yellow spot". Yellow spot symptoms usually
appear in the summer and are often particularly severe on trees
on grapefruit rootstock. Spray trees showing mild yellow spot
symptoms on the leaves with 1 ounce of sodium molybdate per
100 gallons, but in severe cases use 2 ounces. Application of
molybdenum sprays should be made in spring and summer, since
sprays applied in October or later in the year usually will not
cause regreening of the yellow spots. However, a late fall spray
or a spring dormant or post-bloom spray will prevent the oc-
currence of yellow spot during the following summer. It is
recommended that molybdenum sprays be applied only to groves
having yellow spot. The occurrence of yellow spot is usually
associated with acid soil. In correcting yellow spot it is es-

Florida Agricultural Experiment Stations

pecially important that the soil reaction be adjusted to pH 5.5
to 6.0 with liming materials and maintained at that level. For
compatibility of sodium molybdate with other spray materials,
see the current Better Fruit Program Spray and Dust Schedule.
Soil applications of molybdenum salts have not been effective in
controlling yellow spot.
Iron.-On acid soils the application of an iron chelate of ethy-
lenediamine tetraacetic acid (FeEDTA) to severely chlorotic
trees is recommended on a trial basis. This should be applied
at the rate of about 20 grams (% ounce) of actual iron per tree.
For example, to apply this amount of iron requires 2/ pound per
tree of a chelate containing 6 percent iron, or 1/ pound per tree
of a chelate containing 12 percent iron.
The iron chelate may be applied alone to the soil around the
chlorotic trees or may be mixed with the fertilizer. Hand appli-
cation of the chelate is recommended if the fruit crop is on the
trees. If it is applied with a fertilizer distributor, either alone
or mixed with fertilizer or other diluent, it may produce severe
burns on any fruit on which the chelate dust settles. This may
result in considerable dropping of fruit. This chelate is not
recommended for calcareous (high lime) soils because large
amounts are required to correct the chlorosis on such soils.
Iron sulfate applied either as a fertilizer or foliage spray has
not been found practical for correcting iron chlorosis and is not
Calcium.-Calcium is usually supplied in sufficient amounts
in either dolomite or high calcium limestone used for pH con-
trol. It is abundant also in superphosphate. Hence, no special
consideration need be given to applying calcium as a fertilizer
element, if sufficient lime or dolomite is applied for pH control
as discussed below.
Sulfur.-Sulfur far in excess of the nutritional needs of citrus
trees is applied in sprays and dusts for mite control and in the
various sulfates used in fertilizer mixtures. Sulfur used in rust
mite control adds to the soil acidity and makes control of soil pH
more expensive. While rust mite control cannot be neglected
because of this, the amounts of sulfur used need not and should
not be larger than recommended in the Better Fruit Program.

It is recommended that the soil pH in groves be maintained
between 5.5 and 6.0 on acid soil types based on samples taken

Fertilizers and Nutritional Sprays for Citrus

in January or February from beneath the drip of the branches.
Sufficient liming material should be applied each year to prevent
the pH from dropping below 5.5. Soil acidity arises from the
use of fertilizer materials leaving acid residues and from the use
of sulfur for pest control. The use of sulfur is a very important
factor, since 31/8 pounds of dolomite are required to neutralize
the acidity resulting from application of 1 pound of sulfur.
The amount of liming materials which must be applied, there-
fore, depends upon the amount of acid-forming fertilizer ap-
plied, the amount of dolomite applied as conditioner or filler in
the fertilizer, and the amount of sulfur used in pest control.
Since variable amounts of acid-forming materials are applied to
different groves, no specific recommendations for rates of appli-
cation of liming materials can be made. However, from 800
to 2,000 pounds of dolomite or lime per acre per year are usually
required to maintain the soil pH at the 5.5 to 6.0 level. Where
the copper content of the soil is high it is essential that the pH
be carefully controlled to reduce copper toxicity.

To illustrate the method of converting pounds of nutrients
per box to pounds of fertilizer per tree and to determine the
fertilizer analysis the following sample calculations are pre-
Assume the following conditions: (1) 0.4 lb. N, 0.35 lb. KO,
0.3 lb. MgO and 0.03 lb. MnO will be applied per box per year.
(2) Average production is six boxes of fruit per tree. (3) The
fertilizer will contain 8 percent nitrogen. (4) One-third of the
year's supply of fertilizer will be applied at this time.

Calculation.-Nitrogen (N)
6 boxes per tree X 0.4 pound N per box per year
2.4 pounds N per tree per year.
2.4 pounds N per tree per year X 0.333 (1/ of annual application) =
0.80 pound N per tree in this application.
0.80 pound N
-10 pounds fertilizer per
0.08 pound N per pound of fertilizer tree in this application.
Potash (KO)
6 boxes X 0.35 pound K2O per box = 2.1 pounds K2O per tree per year.
2.1 X 0.333 (1 of annual application) = 0.70 pound KXO in this application.
0.70 X 100
S71c K,0 in fertilizer.
10 pounds fertilizer to be applied this application

Florida Agricultural Experiment Stations

Magnesium Oxide (MgO)
6 boxes X 0.3 pound MgO per box = 1.8 pounds MgO per tree per year.
1.8 X 0.333 (1s of annual application) = 0.60 pound MgO in this application.
-- X 100 6.0% MgO in the fertilizer.

Manganese Oxide (MnO)
6 boxes X 0.03 pound MnO per box = 0.18 pound MnO per tree per year.
0.18 X 0.333 (1/ of annual application) = 0.060 pound MnO in this
-- X 100 = 0.6/r MnO in the fertilizer.

Combining the percentages obtained by these calculations,
the complete fertilizer analysis would be 8-0-7-6-0.6-03, which if
used at the rate of 10 pounds per tree would provide one-third
of the tree's annual requirement. Other analyses, such as
8-0-8-6-0.6-0 or 8-0-6-6-0.6-0, also would be satisfactory for sup-
plying the tree's requirements.
If it is desired to use a higher analysis fertilizer, analyses
such as 10-0-10-8-0.75-0 or 10-0-8-7-0.75-0 would be satisfactory
if used at 8.0 pounds per tree. Where the use of phosphorus is
advisable, analyses such as 6-5-5-4-0.4-0, 8-6-7-6-0.6-0, 10-8-10-
8-0.75-0 or others similar would be suitable.
Many growers substitute a nitrogen carrier for one of the
regular applications of mixed fertilizer. While there is little
data on which to recommend or condemn such a practice, it is
fairly common. Therefore, a word of caution is warranted.
Applications providing nitrogen only must be included in the
calculations for the yearly total in order to arrive at the true
amount of fertilizer elements applied. For example, the situa-
tion used in the calculation on page 11 can be met over an
annual period by the use of one application of ammonium ni-
trate and two applications of mixed fertilizer provided the mixed
fertilizer contains 50 percent more of the elements other than
nitrogen. One-third of the annual requirement for nitrogen
could be met by applying 2.4 pounds of ammonium nitrate per
tree. Each of the two applications of mixed fertilizer should
then contain one-third of the annual nitrogen requirement and
one-half of the potash, magnesium, and manganese require-


Fertilizers and Nutritional Sprays for Citrus

ments. This could be furnished by 10 pounds per tree of 8-0-11-
9-0.9-0 mixed fertilizer.
To assist in the calculations involving use of fertilizers of
different nitrogen contents, Table 1 has been compiled.

mated Percent Nitrogen in Mixture or Material
Tree- 4 5 6 7 8 10 12 14 16 20.5 33.5

Pounds Fertilizer per Tree per Application
3 10.0 8.0 6.7 5.7 5.0 5.0 3.3 2.9 2.5 2.0 1.2
4 13.3 10.6 8.9 7.6 6.7 5.3 4.4 3.8 3.3 2.6 1.6
5 16.7 13.3 11.1 9.5 8.3 6.7 5.6 4.8 4.2 3.3 2.0
6 20.0 16.0 13.3 11.4 10.0 8.0 6.7 5.7 5.0 3.9 2.4
7 23.3 18.7 15.6 13.3 11.7 9.3 7.8 6.7 5.8 4.6 2.8
8 26.7 21.3 17.8 15.2 13.3 10.7 8.9 7.6 6.7 5.2 3.2
9 30.0 24.0 20.0 17.1 15.0 12.0 10.0 8.6 7.5 5.9 3.6
10 33.3 26.7 22.2 19.0 16.7 13.3 11.1 9.5 8.3 6.5 4.0
11 36.7 29.3 24.4 21.0 18.3 14.6 12.2 10.5 9.2 7.2 4.4
12 40.0 32.0 26.6 22.9 20.0 16.0 13.3 11.4 10.0 7.8 4.8
13 43.3 34.7 28.9 24.8 21.7 17.3 14.4 12.4 10.8 8.5 5.2
14 46.7 37.3 31.1 26.7 23.3 18.7 15.6 13.3 11.7 9.1 5.6
15 50.0 40.0 33.3 28.6 25.0 20.0 16.7 14.3 12.5 9.8 6.0
16 53.2 42.7 35.6 30.5 26.6 21.3 17.8 15.2 13.3 10.4 6.4

To use this table select the estimated yield per tree in the left-hand column and move
right to the column headed by the percentage of nitrogen in your fertilizer mixture or
material The figure found in this column will be the pounds of mixed fertilizer or material
fitting the nitrogen recommendations in this bulletin.


This section concerns primarily the fertilization of non-bear-
ing citrus trees planted on previously uncultivated acid sandy
soils. The soil conditions found in such cases are somewhat
different from those found in heavily fertilized old grove soils.
Uncultivated soils are generally very infertile with respect to
all the essential elements except, in some cases, phosphorus.
Therefore newly planted trees in previously unfertilized soils
should receive regular applications of nearly all essential ele-
ments. Trees in replanted areas or occasional replants in pres-
ent groves should receive appropriate amounts of the fertilizer
mixtures recommended for bearing trees.
Many fertilizer formulas may be very satisfactory on young
trees for a number of years if used in adequate amounts. How-
ever, the most desirable formula should contain only adequate

Florida Agricultural Experiment Stations

amounts of all the elements necessary to produce good tree
growth, and should not contain unnecessary amounts of any
element. It is believed that the following ratio of the elements
will satisfy the requirements of young citrus trees under most
conditions; N-l, P,O--1, KO-1, MgO-1/2, MnO-1/8, CuO-1/16.
The elements in this ratio can be made into fertilizer analyses
such as 6-6-6-3-0.75-0.4, or 8-8-8-4-1-0.5. Higher analysis mix-
tures are usually more economical, but the difficulty of obtaining
uniform application around the root zone is increased. Higher
analysis mixtures should be applied carefully and uniformly
over the soil area to avoid root damage due to high concentra-
tion of soluble salts in localized areas. Use of some organic
nitrogen in the mixture may be beneficial.
On acid soils dolomite or high calcium limestone should be
applied over the entire area at the rate of 1,000 pounds per acre
on new land. The reaction of the soil should thereafter be ad-
justed to pH 5.5-6.0 annually. This practice will be beneficial
to cover crops as well as to the trees.
The rate and number of applications of fertilizer should be
based primarily upon the age of the trees and adjusted in ac-
cordance with tree appearance. Trees should be fertilized every
six weeks during the first two growing seasons. The number of
applications in succeeding seasons may be reduced. Fertilizer
applications should be omitted between November 1 and Feb-
ruary 1. Rate of application during the first season may be rela-
tivey low, due to the limited root system of the tree, but should
be increased materially in succeeding seasons so as to result in
rapid growth of the tree. For approximately the first five years
the emphasis should be strongly upon making tree growth, and
the quality of the crop should be considered a secondary factor.
A suggested schedule of fertilization for a grove planted in the
dormant season is given in Table 2. This schedule may be con-
tinued as long as desired, but when the trees come into bearing
it should be abandoned in favor of the suggested program for
bearing trees.
The fertilizer applications should be supplemented by the use
of nutritional sprays. In most cases it is advisable to make one
application each year of a spray containing 3 pounds of zinc sul-
fate, 3 pounds of copper sulfate and 2.2 pounds of lime per 100
gallons, or equivalent amounts of zinc and copper in neutral
forms. The copper spray is recommended because of the small
amount of copper applied to the soil in the amounts of fertilizer

Fertilizers and Nutritional Sprays for Citrus

used, particularly the first two years. After the fifth year the
nutritional requirements of the trees for copper can be supplied
by copper sprays used for melanose control. If copper sprays
are not applied to non-bearing trees, copper can be supplied by
slightly larger amounts in the fertilizer than indicated in the
above formula. On calcareous soils, or elsewhere if symptoms
of manganese deficiency appear, 3 pounds of manganese sul-
fate and 0.1 pound of lime per 100 gallons or equivalent amounts
of manganese in neutral forms should also be added to the
spray. On calcareous soils the manganese should be omitted
from the fertilizer but more than one spray of manganese each
season may be necessary.


Number of
Year in the Grove Applications Pounds per
Each Year Application

F irst ................................................... 0 .5
S econ d .......................................... 7 1
T hird ........................... 4 2
F ourth .............. ............ ........ 4 2.5
F ifth ........................................ .......... 3 4
Sixth ................................. ......... ... 5'
Seventh ...................... .................. 3 5*

For trees planted after February 1, the number of applications should be correspond-
ingly reduced.
'* Trees bearing more than 3 boxes of fruit should be fertilized in accordance with the
schedule for bearing trees.

If deficiency symptoms of molybdenum, iron, or boron appear,
treatments suggested in the section on bearing trees should be