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Group Title: Bulletin - University of Florida. Agricultural Experiment Station ; no. 298
Title: The reaction of zinc sulfate with the soil
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00027107/00001
 Material Information
Title: The reaction of zinc sulfate with the soil
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: 43 p. : charts ; 23 cm.
Language: English
Creator: Jones, H. W
Gall, O. E ( Owen E )
Barnette, R. M
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1936
 Subjects
Subject: Zinc sulphate   ( lcsh )
Soils -- Zinc content -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Bibliography: p. 42-43.
Statement of Responsibility: by H.W. Jones, O.E. Gall, R.M. Barnette.
General Note: Cover title.
Funding: Bulletin (University of Florida. Agricultural Experiment Station) ;
 Record Information
Bibliographic ID: UF00027107
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000924376
oclc - 18212438
notis - AEN4994

Table of Contents
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    Personnel
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    Table of Contents
        Page 3
        Page 4
    Main
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Full Text



Bulletin 298


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA
WILMON NEWELL, Director








THE REACTION OF ZINC SULFATE

WITH THE SOIL


By
H. W. JONES
O. E. GALL
R. M. BARNETTE


TECHNICAL BULLETIN









Bulletins will be sent free to Florida residents upon application to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


June, 1936









EXECUTIVE STAFF
John J. Tieert, M.A., LL.D., President of
the University
Wilmon Newell, D.Sc., Director
H. Harold Hume, M.S., Asst. Dir., Research
Harold Mowry, M.S.A., Asst. Dir., Adm.
J. Francis Cooper, M.S.A., Editor
Jefferson Thomas, Assistant Editor
Clyde Beale, A B.J., Assistant Editor
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager
K. H. Graham, Business Manager
Rachel McQuarrie, Accountant

MAIN STATION, GAINESVILLE

AGRONOMY
W. E. Stokes, M.S., Agronomist**
W. A. Leukel, Ph.D., Agronomist
G. E. Ritchey, M.S.A., Associate*
Fred H. Hull, Ph.D., Associate
W. A. Carver, Ph.D., Associate
John P. Camp, M.S., Assistant

ANIMAL HUSBANDRY
A. L. Shealy, D.V.M., Animal Husbandman**
R. B. Becker, Ph.D., Dairy Husbandman
W. M. Neal, Ph.D., Asso. in An. Nutrition
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian
N. R. Mehrhof, M.Agr., Poultry Husbandman
W. W. Henley, B.S.A., Asst. An. Husb.*
W. G. Kirk, Ph.D., Asst. An. Husbandman
R. M. Crown, M.S.A., Asst. An. Husbandman
P. T. Dix Arnold, B.S.A., Assistant Dairy
Husbandman
L. L. Rusoff, M.S., Laboratory Assistant
Jeanette Shaw, M.S., Laboratory Technician
CHEMISTRY AND SOILS
R. W. Ruprecht, Ph.D., Chemist**
R. M. Barnette, Ph.D., Chemist
C. E. Bell, Ph.D., Associate
R. B. French, Ph.D., Associate
H. W. Winsor, B.S.A., Assistant
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural Economist**
Bruce McKinley, A.B., B.S.A., Associate
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Assistant
ECONOMICS, HOME
Ouida Davis Abbott, Ph.D., Specialist**
C. F. Ahmann, Ph.D., Physiologist
ENTOMOLOGY
J. R. Watson, A.M., Entomologist**
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
HORTICULTURE
A. F. Camp, Ph.D., Horticulturist**
G. H. Blackmon, M.S.A., Horticulturist and
Associate Head of Department
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph.D., Truck Horticulturist
R. J. Wilmot, M.S.A., Specialist, Fumigation
Research
R. D. Dickey, B.S.A., Assistant Horticulturist
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist**
George F. Weber, Ph.D., Plant Pathologist
R. K. Voorhees, M.S., Assistant***
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Assistant Botanist
Stacy O. Hawkins, M.A., Assistant Plant
Pathologist
SPECTROGRAPHIC LABORATORY
L. W. Galdum, Ph.D., Biochemist
L. H. Rogers, M.A., Spectroscopic Analyst


BOARD OF CONTROL
Geo. H. Baldwin, Chairman, Jacksonville
Oliver J. Semmes, Pensacola
Harry C. Duncan, Tavares
Thomas W. Bryant, Lakeland
J. T. Diamond, Secretary, Tallahassee


BRANCH STATIONS
NORTH FLORIDA STATION, QUINCY
L. 0. Gratz, Ph.D., Plant Pathologist in
Charge
R. R. Kincaid, Ph.D., Asso. Plant Pathologist
J. D. Warner, M.S., Agronomist
Jesse Reeves, Farm Superintendent
CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Horticulturist in Charge
John H. Jefferies, Superintendent
W. A. Kuntz, A.M., Assoc. Plant Pathologist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Asst. Entomologist
EVERGLADES STATION, BELLE GLADE
A. Daane, Ph.D., Agronomist in Charge
R. N. Lobdell, M.S., Entomologist
F. D. Stevens, B.S., Sugarcane Agronomist
Thomas Bregger, Ph.D., Sugarcane Physiologist
G. R. Townsend, Ph.D., Assistant Plant
Pathologist
J. R. Neller, Ph.D., Biochemist
R. W. Kidder, BS., Assistant Animal
Husbandman
Ross E. Robertson, B.S., Assistant Chemist
B. S. Clayton, B.S.C.E., Drainage Engineer*
SUB-TROPICAL STATION, HOMESTEAD
H. S. Wolfe, Ph.D., Horticulturist in Charge
W. M. Fifield, M.S., Asst. Horticulturist
Geo. D. Ruehle, Ph.D., Associate Plant
Pathologist
W. CENTRAL FLA. STA., BROOKSVILLE
W. F. Ward, M.S.A., Asst. An. Husbandman
in Charge*


FIELD STATIONS

Leesburg
M. N. Walker, Ph.D., Plant Pathologist in
Charge
W. B. Shippy, Ph.D., Asso. Plant Pathologist
K. W. Loucks, M.S., Asst. Plant Pathologist
J. W. Wilson, Ph.D., Associate Entomologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
Cocoa
A. S. Rhoads, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist
Monticello
G. B. Fairchild, M.S., Asst. Entomologist***
Bradenton
David G. Kelbert, Asst. Plant Pathologist
C. C. Goff, M.S., Assistant Entomologist
Sanford
E. R. Purvis, Ph.D., Assistant Chemist,
Celery Investigations
Lakeland
E. S. Ellison, Ph.D., Meteorologist*
B. H. Moore, A.B., Asst. Meteorologist*

In cooperation with U.S.D.A.
** Head of Department.
*** On leave.















CONTENTS
PAGE

IN TRODUCTION ..-......... ............................ .... .............. ....... 5

METHODS OF EXPERIMENTATION ............... ......................................... 6

D eterm nation of Zinc .............. ................... ......... ..................... 6

Application of Zinc Method to Soils ............------............................ 7

THE REACTION OF ZINC SULFATE WITH NORFOLK SAND ............................... 12

THE INFLUENCE OF ORGANIC MATTER ON THE FIXATION OF ZINC BY NOR-

FOLK SAND .-.... .-- --.......................... ......... .. ............... 14

THE INFLUENCE OF SUPERPHOSPHATE AND COLLOIDAL PHOSPHATE ON THE

FIXATION OF ZINC BY NORFOLK SAND ........................................ ....... 16

FIXATION OF ZINC BY SEVERAL SOIL TYPES ............................... ................... 18

WATER SOLUBLE AND REPLACEABLE ZINC IN SOILS RECEIVING FIELD APPLI-

CATIONS OF ZINC SULFATE ............................................ ......... ... 25

Field Crop Experiments ................. ............ -.-. ...- .. ................. 25

Citrus Soil at Lake W ales ............... ........................................ 27

Tung Oil Soil at Gainesville ................. ........... ... .. ................ 27

Satsuma Soil at Gainesville ....................... ......... .............. 30

DISCUSSION OF EXPERIMENTAL RESULTS ..............-...............-.......-. 32

TOXICITY OF REPLACEABLE ZINC IN NORFOLK SAND .................................... 38

SUM M ARY ........... ..... ....... ........ ........... ................................. ............ 40

LITERATURE CITED ......................- .......... ..... ....... .................. ..... 42












THE REACTION OF ZINC SULFATE

WITH THE SOIL

By
H. W. JONES, O. E. GALL and R. M. BARNETTE

INTRODUCTION
The stimulating and toxic actions of zinc compounds on plant
growth have been studied in soil, sand and water cultures.
Brenchley (10)1 has reviewed the greater portion of the litera-
ture up to 1925 on the quantities and distribution of zinc in
plants and soils, and its stimulating and toxic actions. More
recently interest in the effect of zinc compounds on plant growth
has been increased due to the discoveries that they correct cer-
tain manifestations of malnutrition in some plants. Some of
the most promising results have been obtained by Alben, Cole
and Lewis (1) (2), Finch and Kinnison (16), Demaree, Fowler
and Crane (15), Chandler, Hoagland and Hibbard (12), (13),
and Johnson (19). These workers report a favorable response
of the pecan, peach, apple, walnut, plum, citrus fruits, apricot
and grape to the application of soluble zinc compounds to the
soil or in a spray on the foliage.
In this State, Allison, Bryan and Hunter (3) and Allison (4)
reported a transitory stimulation of plant growth by zinc sulfate
when applied to raw peat soils of the Everglades. Mowry (22)
and Mowry and Camp (23) have found zinc sulfate a corrective
for a malnutrition known as "bronzing" of tung trees. Camp
(11) extended these studies to include the treatment of mottled
leaf of citrus. Barnette and Warner (6) and Barnette, Camp,
Warner and Gall (7) obtained a favorable response in increased
growth and prevention of a chlorotic condition by the applica-
tion of zinc sulfate under several agronomic plants, especially
corn.
Because of the indicated value of zinc compounds for the cor-
rection of certain physiological disturbances in plants growing
in Florida soils, a knowledge of the reaction of zinc compounds
with these soils is highly desirable. There is the possible danger
of the accumulation of toxic concentrations of zinc in the soil
from repeated use. In addition, the residual effect of the appli-
1 Italic figures in parentheses refer to "Literature Cited" in the back of
this bulletin.






Florida Agricultural Experiment Station


cation of zinc compounds is especially important for their eco-
nomical use under general field crops.
The reaction of zinc compounds with the soil and similar sys-
tems has been studied for a number of years. One of the most
valuable contributions is Baumann's (8) study of the reaction
and toxicity of zinc compounds in the soil. He cited the early
work of von Gorup-Besanez (18), who in 1863 showed the
capacity of soil to fix zinc from solutions of its compounds, and
of Freytag (17), who established the exchange reaction between
the zinc of a zinc sulfate solution and the replaceable calcium,
magnesium, sodium and potassium of the soil. Baumann
concluded from his experiments that there are several factors
influencing the fixation of zinc in the soil. Organic soils had the
greatest fixing power for zinc: clay and calcareous soils ranked
second, while sandy soils had a very low fixing capacity. The
conclusion was reached that insoluble humicc acids", "free humic
acids", zeolites, aluminum hydroxide, and calcium and mag-
nesium carbonates were the soil constituents capable of removing
zinc from solutions of its salts. Kappen and Rung (20) and
Kappen and Fischer (21) found that zinc replaced other cations
from permutite, from certain natural silicates and from the
cosloidal matter of the soil. The zinc in turn could be replaced
from these materials by the potassium ion of a potassium chlor-
ide solution. Chandler, Hoagland and Hibbard (13) found a
great variation in the fixing power of California soils for zinc.
They concluded that clay, organic matter and salts are the most
important factors in its fixation by the soil.
During the past two years a systematic study has been made
of the fixing powers for zinc of representative Florida soils.
Several combinations of zinc in the soil have been differentiated
and factors influencing its fixation have been studied.

METHODS OF EXPERIMENTATION
Determination of Zinc.2-The method used for the determina-
tion of zinc in these studies depends upon the reaction of potas-
sium ferrocyanide with zinc salts in the presence of a low con-
centration of potassium ferricyanide with diphenylbenzidine as
an internal indicator. The method is essentially that described
by Cone and Cady (14). The diphenylbenzidine forms a blue
oxidation product with potassium ferricyanide in the presence
2 The senior author was supervised and assisted by Dr. L. W. Gaddum
of the Florida Agricultural Experiment Station in a critical study of the
method for the determination of zinc.







The Reaction of Zinc Sulfate With the Soil


of zinc salts. The oxidation product is reduced by the first excess
drop of potassium ferrocyanide and the color changes from blue
to a very pale green or almost yellow. In the absence of zinc
salts no blue color is produced by a dilute solution of potassium
ferricyanide with the indicator.
It was found that iron interferes with the determination be-
cause of the blue color of the ferricyanide which is formed in the
presence of potassium ferrocyanide. Thus, if iron is present,
the blue color of the indicator is masked and the end point can-
not be determined. Iron was the only element studied which
interfered with the color change of the indicator.
Studies were made on the separation of iron and zinc com-
pounds, and a satisfactory procedure was developed. It con-
sists of precipitating the iron as ferric hydroxide in an excess
of ammonium chloride and ammonium hydroxide and separating
by filtration and washing. A satisfactory separation of iron and
zinc by this procedure was possible even when iron was present
in quantities four to five times as great as zinc.
This method is sensitive and satisfactory for the determina-
tion of as little as 5 milligrams of zinc. Smaller quantities may
be estimated by the addition of measured quantities of a stand-
ardized zinc sulfate solution to insure the development of the blue
color with the indicator. Subsequent titration and proper ad-
justment for the added zinc permits the approximate determina-
tion of smaller quantities.
Application of Zinc Method to Soils.3-When soluble zinc salts
are added to the soil, three types of compounds are formed: 1,
those combined with soil constituents to form water soluble
compounds; 2, those in combination with the colloidal complexes
(replaceable); and 3, those combined with the phosphates and
carbonates and other soil constituents to form more nearly in-
soluble compounds.
Of these groups of zinc compounds in the soil, the water soluble
and the replaceable are the most readily determined. Normal
solutions of either ammonium chloride or ammonium acetate
are used often for the replacement of cations from the colloidal
complexes of acid soils. The comparative quantities of zinc re-
placed by solutions of these two salts have been determined.

3 In discussing the reaction of zinc sulfate with the soil, the results are
expressed as m. e. (milliequivalents) of zinc per 100 grams of air-dried
soil. Milligrams of zinc per 100 grams may be calculated by multiplying
m. e. by 32.69. The expression, "per 100 grams of air-dried soil" has been
omitted frequently in the text, but it is understood.







Florida Agricultural Experiment Station


One-hundred-gram samples of an air-dried Norfolk sand were
treated with 100 milligrams of zinc as zinc sulfate. The samples
were brought to 25 percent moisture content and allowed to stand
for four days. This moisture content insured favorable distri-
bution of zinc sulfate in the soil. The samples were transferred
to filters and leached with water until the percolates gave no
test for the sulfate ion. The soil was then leached with either a
normal solution of ammonium chloride or ammonium acetate.
Zinc was determined in the percolates. The comparative results
of the displacement of zinc from the soil by ammonium chloride
and ammonium acetate are given in Table 1.
TABLE 1.-COMPARISON OF THE DISPLACEMENT OF ZINC FROM NORFOLK
SAND BY NORMAL AQUEOUS SOLUTIONS OF AMMONIUM CHLORIDE AND
AMMONIUM ACETATE.
Soluble zinc
Volume of Ammonium Ammonium
leachate chloride acetate
pH 5.62 pH 6.45
ml. m.e.* m.e.
500 1.146 0.711
1,000 1.260 0.882

m.e. per 100 g. air-dried soil.
Average of seven determinations.

The data in Table 1 show that 62 and 70 percent as much zinc
was leached from 100 grams of Norfolk sand by 500 and 1,000
milliliters, respectively, of normal ammonium acetate solutions
as was removed by the same amounts of normal ammonium
chloride solutions. The first 500 milliliter portions of the solu-
tion removed the greater part of replaceable zinc. The larger
quantities of zinc removed by the ammonium chloride solution
may be attributed to its lower pH.
A preliminary study was made of the fixation of zinc by the
soil when added in various ways. First, the admixture of soils
with zinc sulfate solutions was tried. One-hundred-gram por-
tions of air-dried Norfolk sand were mixed with 250 milliliters
of zinc sulfate solutions. The mixtures were shaken frequently
and the soil was allowed to remain in contact with the zinc sul-
fate solutions for 18 hours. They were then filtered and the zinc
determined in the filtrate. The decrease in the concentration of
the zinc sulfate solutions after contact with the soil was used as
a measure of total quantities of zinc fixed by the soil. The soils








The Reaction of Zinc Sulfate With the Soil


were washed with distilled water until free from soluble sulfates.
Then they were leached with two 1,000 milliliter portions of a
normal ammonium chloride solution. The zinc content of the
ammonium chloride leachates was determined and used as a
measure of the replaceable zinc. The quantities of zinc fixed
by the soil and removed by the normal ammonium chloride solu-
tion are recorded in Table 2.

TABLE 2.-FIXATION OF ZINC FROM MIXTURES OF 100 GRAMS OF AIR-DRIED
NORFOLK SAND AND 250 MILLILITERS OF SOLUTION OF ZINC SULFATE.


in 250 ml. fixed in
solution 100 grams
of soil

0.399 0.380
0.793 0.694
2.300 1.283
3.829 1.533

7.667 1.874
15.072 1.978
23.084 2.167
30.371 2.502
38.171 2.540

45.656 3.073
53.534 3.290
60.900 3.309


m. e. of zinc
|replaced from
100 g. of
soil by 1000
ml. N. NHCl

0.284
0.546
1.044
1.240

1.398
1.546
1.513
1.586
1.641
1.655
1.647
1.692


Total quantities of


zinc fixed reached a maximum of 3.290


milliequivalents per 100 grams of air-dried soil. This concentra-
tion was reached upon the addition of 53.534 milliequivalents of
zinc in 250 milliliters of solution.
The first liter of normal ammonium chloride solution removed
substantially all of the replaceable zinc from the soil. The second
liter removed only 3.82 percent as much zinc as the first liter.
From these results it appears adequate to use one liter of normal
ammonium chloride for the removal of replaceable zinc from
100 grams of sandy soils.
The quantities of zinc removed from the soil by a normal
ammonium chloride solution increased with an increase in the


replaced by
2nd 1000 ml.
of N. NHlC1

0.014
0.015
0.039
0.045
0.055
0.058
0.053
0.068
0.063

0.066
0.066
0.065


replaced by
2000 ml. of
N. NHICl

0.298
0.561
1.083
1.285
1.453
1.604
1.566
1.654
1.704
1.721
1.713
1.757







Florida Agricultural Experiment Station


concentration of the zinc sulfate in the mixtures until a concen-
tration of 15.072 milliequivalents of zinc was reached. This
concentration corresponded to 1.604 milliequivalents of replace-
able zinc.
The fixation of zinc by Norfolk sand from the direct addition
of zinc sulfate to a weighed quantity of soil was next studied.
One-hundred-gram portions of air-dried Norfolk sand similar
to that used in the previous study were weighed into beakers.
Solutions of zinc sulfate were added to give a range of 0.153 to
30.590 milliequivalents of zinc. The soil samples were main-
tained at a 25 percent moisture content. The beakers were
covered with watch glasses and stored for four days at room
temperature, after which the samples were transferred to filters
and leached with 1,000 milliliters of distilled water. Two addi-
tional leachings each with 500 milliliters of water were made.
Following the leaching with water, 1,000 milliliters of a normal
ammonium chloride solution were percolated through each sam-
ple. The zinc content of the water and normal ammonium chlor-
ide percolates was determined by the titration method. The
results of these determinations are given in Table 3.
TABLE 3.-FIXATION OF ZINC UPON THE DIRECT APPLICATION OF ZINC
SULFATE TO 100 GRAMS OF NORFOLK SAND MAINTAINED AT 25 PERCENT
MOISTURE FOR ONE WEEK.
m. e. of zinc per 100 grams of air-dried soil.
I fixed in
added as leached by water I replace- removed
zinc 1st addi- I 2nd addi- | able and by 1000
sulfate 1000 ml. tional tional Total insoluble ml. N.
500 ml. 500 ml. II form NHIC1

None 0.011 0.003 0.003 0.017 ........ 0.050
0.153 0.011 0.010 ........ 0.021 0.132 0.099
0.306 0.013 0.004 0.004 0.021 0.285 0.211
0.459 0.026 0.006 0.006 0.038 0.421 0.322
0.765 0.079 0.008 0.007 0.094 0.671 0.529
1.530 0.413 0.017 0.017 0.447 1.083 0.897
2.294 1 0.900 0.034 0.021 0.955 1.339 1.121
3.059 1.519 0.027 0.024 1.570 1.489 1.256
15.295 13.135 0.043 0.043 13.221 2.074 1.592
22.943 21.177 0.049 0.045 21.271 i 1.672 1.654
30.590 29.072 0.056 0.049 29.177 1.413 1.670







The Reaction of Zinc Sulfate With the Soil


From these data it is apparent that most of the water-soluble
zinc is leached from the soil by the first liter of distilled water,
there being only very small quantities leached by subsequent
washings.
Total quantities of zinc fixed in the soil were obtained by the
difference in zinc content of the water leachates and the quan-
tities added to the soil. The amount of zinc fixed by the soil in
replaceable and insoluble forms increased with the quantities
added up to 15.295 milliequivalents. The maximum amount
fixed was 2.075 milliequivalents per 100 grams. The discrepan-
cies in the results obtained with higher concentration were due
to errors in sampling.
The quantity of replaceable zinc also increased with an in-
crease in the amount of zinc sulfate up to 15.295 milliequivalents
of zinc. The maximum quantity of replaceable zinc retained by
the Norfolk sand was around 1.592 milliequivalents. The higher
concentrations of zinc sulfate failed to increase significantly the
amounts of replaceable zinc.
Another series of samples was prepared by the direct addi-
tion of zinc sulfate to 100-gram portions of air-dried Norfolk
sand. The samples were brought to a 25 percent moisture con-
tent and allowed to dry for 21 days in the laboratory and then
leached with w-ater and a normal ammonium chloride solution as
in the previous series. Results were similar to those obtained in
the preceding series. Determinations of fixed and replaceable
zinc for the three methods are summarized in Table 4. Results
obtained from the application of approximately 0.399, 0.765,
2.294, 15.295, 22.943 and 30.590 milliequivalents may be di-
rectly compared for the different methods. The figures for total
zinc fixed agree satisfactorily for concentrations of zinc sulfate
up to 22.943 milliequivalents. With this concentration and above,
the total quantity of zinc retained by the soil from the mixture
was definitely higher than that fixed by the direct application of
zinc sulfate to the soil. The quantities of zinc removed by 1,000
milliliters of normal ammonium chloride solution were practically
constant, regardless of the method of handling the soil.
These preliminary experiments are of value in the formulation
of a procedure for determining the reaction of the soil with solu-
ble zinc compounds. While the mixture method provides a more
intimate contact of zinc sulfate with the soil, at the same time
this method does not approximate field applications of soluble
zinc compounds to the soils of the humid region. Therefore, the
procedure adopted for future studies was as follows: 100 grams







Florida Agricultural Experiment Station


of air-dried sandy soils and correspondingly smaller amounts of
heavier mineral and organic soils were weighed into beakers.
Concentrations of zinc varying from 0.153 to 30.590 milli-
equivalents per 100 grams of soil were added in the form of a
standard zinc sulfate solution. The samples were adjusted-with
distilled water to a moisture content which insured contact of
the zinc sulfate and the soil and maintained at this moisture con--
tent for at least four days. Then they were transferred to filters
and leached with 1,000 milliliters of distilled water, followed by
1,000 milliliters of a normal solution of ammonium chloride.
The zinc and calcium contents of the water and ammonium chlor-
ide leachates were determined. Thus the water soluble zinc and
calcium, the replaceable zinc and calcium and the total quantities
of zinc fixed by the soil were determined.
TABLE 4.-COMPARISON OF FIXATION OF ZINC BY NORFOLK SAND FROM
SUSPENSIONS, FROM DIRECT ADDITION OF ZINC SULFATE TO MOIST SOIL,
AND FROM DIRECT ADDITION AND DRYING OF SOIL.

m. e. of zinc per 100 grams air-dried soil
Total fixed Replaced by 1,000 ml. N. NH4C1
added as added to Iadded to
zinc added moist added to moist
sulfate from directly samples mixtures moist soil and
mixtures to moist and dried soil dried
soil 21 days 21 days

0.399 0.380 0.284
0.459 0.421 0.430 0.322 0.320
0.765 0.671 0.691 0.529 0.521
0.793 0.694 0.546
2.294 1.339 1.424 1.121 1.132
2.300 1.283 1.044
15.072 1.978 1.546
15.295 2.074 2.042 1.592 1.616
22.943 1.671 1.841 1.654 1.690
23.084 2.167 1.513
30.371 2.502 1.586
30.590 1.413 1.326 1.670 1.687


THE REACTION OF ZINC SULFATE WITH NORFOLK SAND
Results of a study of the reaction of Norfolk sand with varying
concentrations of zinc sulfate are given in Table 5 and Fig. 1.
Total quantities of zinc fixed, replaceable zinc, the calcium ren-
dered water soluble and the replaceable calcium in the soil ex-








The Reaction of Zinc Sulfate With the Soil


pressed as milliequivalents of the respective elements per 100
grams of soil are given for each concentration of the zinc sulfate.

TABLE 5.-THE TOTAL QUANTITIES OF ZINC FIXED, THE REPLACEABLE ZINC,
THE WATER SOLUBLE CALCIUM AND REPLACEABLE CALCIUM IN THE RE-
ACTION OF NORFOLK SAND WITH ZINC SULFATE.


m. e. of zinc per
air-dried soi


added as
ZnSO4

None
0.153

0.306

0.459

0.765
1.529
2.294

3.059

7.645
15.290
22.935
30.580


fixed by
soil


0.153
0.291

0.440

0.706
1.220

1.495

1.676
2.040
1.977
2.035
2.155


100 g.

removed by
N.NH4C1

0.086
0.205

0.324
0.355

0.593
0.994
1.098
1.358

1.686
1.750

1.786
1.750


m. e. of calcium per 100 g. of
air-dried soil


water
soluble

0.092

0.239

0.210

0.270

0.439
0.779
1.058

1.238

1.497
1.617
1.677
1.817


removed by
N.NH4C1

1.697
1.567

1.487

1.417
1.288

0.928

0.699
0.599
0.339
0.250
0.230
0.170


Total

1.789

1.806
1.697

1.687

1.727
1.707
1.757

1.837

1.836
1.867
1.907
1.987
! ___


These results brought out some very interesting and important
correlations between the fixation of zinc in the soil and the re-
placement of calcium from the organic and inorganic colloidal
complex of the soil. At low zinc sulfate concentrations, which
correspond more nearly to the application of zinc compounds to
sandy soils, there was a fixation of zinc in the replaceable form
with a near equivalent exchange for the calcium of the colloidal
complexes. This relationship held for the concentrations of 0.153
to 0.459 milliequivalents of zinc. At concentrations of 0.459
milliequivalents and above, there were larger quantities of total
fixed zinc than replaceable zinc. The maximum quantities of
zinc fixed and in the replaceable form were reached at a concen-
tration of 7.645 milliequivalents of added zinc. This Norfolk
sand fixed a total of approximately 2.000 milliequivalents of
zinc per 100 grams of air-dried soil, of which about 1.700 milli-
equivalents were in the replaceable form. Quantities of calcium
replaced by a normal ammonium chloride solution bore an inverse







Florida Agricultural Experiment Station


relationship to quantities of water soluble calcium. The total
quantity of calcium, in both water soluble and replaceable forms,
was practically constant.



. L.B,1






5 000










Olby, me, ZV Ujaj>- 5 -1 ol. Y- 10 -- d.---t
Fig. 1.-Quantities of fixed and replaceable zinc, replaceable and water
soluble calcium in 100 grams of air-dried Norfolk sand treated with differ-
ent amounts of zinc sulfate.

THE INFLUENCE OF ORGANIC MATTER ON THE
FIXATION OF ZINC BY NORFOLK SAND

Baumann (8) found that the organic matter of the soil was
one of the most active constituents in the fixation of zinc. He
isolated humicc acids" from soils by treatment with sodium
hydroxide and precipitation of the humicc acid" with hydro-
chloric acid. After solution and reprecipitation, he found that
humicc acids" which contained only traces of bases, fixed 0.476
grams of zinc per 100 grams. Soils containing large quantities
of organic matter fixed zinc in large quantities from its soluble
salts.
The influence of organic matter on the fixation of zinc was
studied by the addition of saw-grass peat to Norfolk sand. The
saw-grass peat, obtained from the Everglades Experiment Sta-
tion at Belle Glade, was slightly acid in reaction with a high re-
placeable base content. The organic matter content of the Nor-







The Reaction of Zinc Sulfate With the Soil


folk sand was increased by the addition of 1 gram of air-dried
saw-grass peat to 100 grams of air-dried soil, and the fixation
curves for zinc were determined. The results of this study are
given graphically in Figure 2.
1 500-


:: /




3.000- /
L7 -









R^.ooj F- I Z, 1 n N o.tk S a-a 1% 1 -
F /... La .,.....






965
Fig. 2.-Influence of the addition of 1 gram of saw-grass teat on the
total zinc fixed and the replaceable zinc of a Norfolk sand treated with
different amounts of zinc sulfate.

This graph shows that the addition of organic matter in the

form of saw-grass peat had very little influence on the fixation
of zinc from low concentrations of zinc sulfate. Below a con-
centration of 0.765 milliequivalents, the total quantities of zinc
fixed were practically the same for the Norfolk sand and the
Norfolk sand with the saw-grass peat. Above this concentra-
tion, the Norfolk sand with the saw-grass peat fixed more zinc
than the Norfolk sand alone. The quantities of replaceable zinc
retained in the Norfolk sand with and without additions of saw-
grass peat remained practically constant up to a concentration
of 1.529 milliequivalents. Above this concentration, the quan-
tities of replaceable zinc in the Norfolk sand with the saw-grass
peat were higher than those held in this form by the Norfolk
sand alone. The approximate maximum quantities of total and
replaceable zinc were reached at a concentration of 7.645 milli-
equivalents for both Norfolk sand and the Norfolk sand with the






Florida Agricultural Experiment Station


saw-grass peat. At this concentration 2.050 milliequivalents of
zinc were fixed by the Norfolk sand and 3.350 milliequivalents
by the Norfolk sand with saw-grass peat. The quantities of
replaceable zinc at this concentration were 1.700 milliequivalents
per 100 grams of air-dried Norfolk sand and 2.400 milliequiva-
lents for the Norfolk sand with saw-grass peat. Thus, the
addition of saw-grass peat to Norfolk sand materially increased
the total fixing power and the replaceable zinc content. These
results are in keeping with the findings of earlier investigators.

INFLUENCE OF SUPERPHOSPHATE AND COLLOIDAL
PHOSPHATE4 ON THE FIXATION OF ZINC
BY NORFOLK SAND
Zinc phosphate [Zn3 (P04)2] is practically insoluble in water.
By the intimate contact of superphosphate and soluble zinc
compounds, as in their simultaneous application in the drill,
there is a possible formation of zinc phosphate in the soil. To
study this reaction, superphosphate and zinc sulfate were added
together to 100-gram portions of Norfolk sand. The samples
were brought to a moisture content favorable for contact of
the superphosphate and zinc sulfate and allowed to stand for
one week, after which they were transferred to a filter and
leached with 1,000 milliliters of water. The water soluble zinc
was determined and the total quantities of zinc fixed were cal-
culated. The results of this study are given in Table 6.
TABLE 6.-EFFECT OF SUPERPHOSPHATE UPON THE SOLUBILITY OF 2.294
MILLIEQUIVALENTS OF ZINC AS ZINC SULFATE ADDED TO 100 GRAMS OF
NORFOLK SAND.

Superphosphate m. e. of zinc per 100 grams of soil
added per 100 Soluble in Fixed as
grams soil 1,000 ml. water insoluble
None 0.838 1.456
1 g. 0.636 1.658
2 g. 0.588 1.706
5 g. 0.303 1.991
1 Corrected for soluble zinc in untreated soil.
4 Colloidal phosphate is a finely divided material associated with the hard
rock phosphate deposits of Florida. Some of the chemical and physical
properties of colloidal phosphate are described in an unpublished thesis,
"A chemical study of colloidal phosphate," by E. R. Purvis, University of
Florida, and in the published article of K. D. Jacob, L. T. Alexander and
H. L. Marshall in the Journal of Industrial and Engineering Chemistry
22: 1392-1396. 1930.







The Reaction of Zinc Sulfate With the Soil


Addition of superphosphate with zinc sulfate to Norfolk sand
decreased the content of water soluble zinc and increased the
total fixation of zinc. The total quantities of zinc fixed by the
soil increased and the water soluble zinc decreased progressively
with the larger amounts of superphosphate in the soil.
The various combinations of phosphorus found in colloidal
phosphate probably more nearly approach those found in the
soil than those of any other concentrated form of natural phos-
phates. While the exact combinations are not known, most
likely the phosphorus forms a series of complex compounds with
iron, aluminum, calcium, magnesium and perhaps silicon.
Definite quantities of colloidal phosphate containing approxi-
mately 24 percent P205 were weighed into beakers and treated
with 3.090 milliequivalents of zinc as zinc sulfate. The suspen-
sions were stirred frequently and allowed to stand over night.
They were then filtered and washed with water to a volume of
250 milliliters. The zinc in the washings was determined and
the quantities fixed by the colloidal phosphate calculated from
the changes in concentration of the zinc sulfate after contact
with the phosphate. The quantities of soluble and fixed zinc
are given in Table 7.
TABLE 7.-THE FIXATION OF ZINC FROM ZINC SULFATE SOLUTIONS BY
COLLOIDAL PHOSPHATE.
3.059 milliequivalents of zinc per 250 milliliters of solution.
Zinc fixed
Weight of Zinc leached Zinc per gram
colloidal by 250 ml. fixed colloidal
phosphate water phosphate
g. m. e. m. e. m. e.
None 3.090 .. ..
0.5 2.972 0.077 0.154
1.0 2.904 0.155 0.155
2.0 2.705 0.354 0.177
3.0 2.584 0.475 0.158
4.0 2.442 0.617 0.154
5.0 2.360 0.699 0.140
Average ..... ............. ........ 0.156

The total quantities of zinc fixed increased from 0.077 milli-
equivalents by 0.5 gram of colloidal phosphate to 0.699 milli-
equivalents by 5 grams. The quantities of zinc fixed per gram






Florida Agricultural Experiment Station


of colloidal phosphate varied from 0.140 to 0.177 milliequivalents,
averaging 0.156 milliequivalent.
A further study was made of the effect of colloidal phosphate
on the fixation of zinc in Norfolk sand. Three series of treat-
ments were used: (1) no colloidal phosphate, (2) 1 gram colloidal
phosphate and (3), 2 grams of colloidal phosphate per 100 grams
of soil. Different concentrations of zinc sulfate were added to
each of the series. The soils were adjusted to a favorable
moisture content for the contact of the phosphate and zinc sul-
fate, allowed to stand for a week and the quantities of water
soluble and replaceable zinc determined. The results of this
experiment are given in Table 8.
At a concentration of 0.306 milliequivalents of zinc per 100
grams of soil, colloidal phosphate had very little effect on the
water soluble, total fixed, and replaceable zinc contents of Nor-
folk sand. Above this concentration, the water soluble zinc
was decreased by the addition of 1 and 2 grams of colloidal
phosphate. Total zinc fixed was increased by the colloidal phos-
phate. The replaceable zinc content of the soil was not affected
greatly by the colloidal phosphate until a concentration of 2.294
milliequivalents of zinc was reached. At this concentration and
above, the replaceable zinc content of Norfolk sand was in-
creased by the addition of colloidal phosphate. It may be con-
cluded from this study that phosphates similar to those found
in the soil may react with soluble zinc compounds and increase
the fixation of zinc.

FIXATION OF ZINC BY SEVERAL SOIL TYPES
The reaction of zinc sulfate with five different soils has been
studied by the method outlined. The soil types studied were (1)
a Greenville sandy loam from Plains, Georgia; (2) a Norfolk
fine sand from Quincy; (3) a Norfolk sand from Gainesville;
(4) a saw-grass peat from Belle Glade; and (5) a marl from
Homestead. These last four soil samples were collected in Flor-
ida. Samples of the surface soil of each of the several types
were used. Results of partial chemical and physical analyses of
these soils are given in Table 9. The mechanical analyses were
made by the hydrometer method of Bouyoucos (9). The results
obtained from the study of the reaction of the three acid mineral
soils and zinc sulfate are shown graphically in Figures 3, 4,
5 and 6.
Figure 3 shows the total amounts of zinc fixed by the Green-
ville sandy loam and Norfolk sand from different concentrations













TABLE 8.-EFFECT OF COLLOIDAL PHOSPHATE ON THE FIXATION OF ZINC BY NORFOLK SAND.
Water soluble zinc Total zinc fixed Replaceable zinc
m. e. zinc Colloidal phosphate Colloidal phosphate Colloidal phosphate
added to per 100 g. soil per 100 g. soil per 100 g. soil
100 g. soil None 1 g. 2 g. None 1 g. 2 g. None 1 g. 2 .

None 0.006 0.012 0.012 ..... 0.024 0.037 0.027
0.306 0.012 0.024 0.021 0.300 0.294 0.297 0.226 0.226 0.199
0.765 0.125 0.116 0.095 0.646 I .0(;61 0.682 0.514 0.575 0.5:15
1.52) 0.489 0.440 0.367 1.046 1.101 1.171 0.);i) 0.921 0.878
2.294 0.929 0.875 0.752 1.371 1.411 1.554 1.095 1,189 1.242
3.059 1.572 1.572 1.480 1.491 1.499 1.591 1.217 1.321 1.352
7.645 5.980 5.843 5.598 1.671 1.814 2.059 1.481 1.30 1.756
















TABLE 9.-PARTIAL CHEMICAL

Soil




Greenville sandy loam .....................

Norfolk fine sand ................... ..........

Norfolk sand .................................

Saw-grass peat ....................................

M arl2 .............................


AND PHYSICAL ANALYSES OF SOIL SAMPLES USED IN


pH Loss on
Ignition

%
5.40 5.70

5.26 3.64

5.60 2.26

6.16 87.76

7.45 47.12


N


%
0.073

0.055

0.045

2.85

0.394


P205
SI

%

0.072

0.036

0.574

0.178

0.061


Replace-
able Ca.

m. e.

2.089

1.424

1.697


ZINC FIXATI

Sand


ON STUDIES.

Silt Clay


% %

18.5 13.1

9.5 6.2

1.5 2.2


1 Contained a few scattering fragments of shell.
2 Contained 39.07% CO,.


---






The Reaction of Zinc Sulfate With the Soil


of zinc sulfate. At a concentration of 1.529 milliequivalents of
zinc per 100 grams of soil the quantities of zinc fixed by these
two soils were practically identical. Above this concentration
the Greenville sandy loam fixed larger quantities of zinc than
the Norfolk sand. The maximum quantity of zinc fixed by the
Norfolk sand was approximately 2.000 milliequivalents. This
amount was reached at a concentration of 7.645 milliequivalents
of added zinc. The maximum fixation by the Greenville sandy
loam was not reached at a concentration of 22.935 milliequiva-
lents of zinc, 3.000 milliequivalents being fixed at this concen-
tration.
35o.



5}t -------------------------------------------------






S100- a
8 I

T /y










0. aaa j .6 3'_ Ijha. Y- 100 r. i. dn'a -t
Fig. 3.-Comparative total quantities of zinc fixed by 100 grams of an
air-dried Greenville sandy loam and a Norfolk sand treated with different
amounts of zinc sulfate.

From Fig. 4 it may be observed that there is very little differ-
ence in the replaceable zinc content of the three soils at con-
centrations of zinc lower than 1.529 milliequivalents. Above
this concentration the Greenville sandy loam had the highest
replaceable zinc content, and was followed by Norfolk sand and
Norfolk fine sand. The maximum replaceable zinc content of
the Greenville sandy loam was approximately 2.900 milliequiva-
lents and that of the Norfolk sand and the Norfolk fine sand
about 1.800 milliequivalents per 100 grams of air-dried soil.






Florida Agricultural Experiment Station


0 '65 m1e Zn added s ync msulpllh e r 1m l de sol
Fig. 4.-Comparative quantities of replaceable zinc retained by 100 grams
of an air-dried Greenville sandy loam, a Norfolk fine sand and a Norfolk
sand treated with different amounts of zinc sulfate.

The water soluble and the replaceable calcium contents of the
soils are shown graphically in Figures 5 and 6, respectively. At
a concentration of 1.529 milliequivalents of added zinc, there
was very little difference in quantities of calcium rendered soluble
by the zinc sulfate from the three soils. Above this concentra-
tion more calcium was made soluble from Greenville sandy loam
and Norfolk sand than from Norfolk fine sand, the Greenville
soil showing the greatest amount.
Replaceable calcium content of the untreated soils was 2.089
milliequivalents for Greenville sandy loam, 1.697 milliequivalents
for Norfolk sand and 1.424 milliequivalents for Norfolk fine sand.
Figure 6 shows that there is a rapid change to the soluble form
of replaceable calcium with the lower concentrations of zinc
added to the soil, over half being rendered soluble by a concen-
tration of 3.059 milliequivalents of zinc per 100 grams of soil.
Higher concentrations of zinc replaced only small additional
amounts of calcium.
There are several interesting observations which may be made
from the reaction of zinc sulfate and these three acid mineral
soils. With low concentrations of zinc sulfate most of the zinc








The Reaction of Zinc Sulfate With the Soil 23






I Gr,,ud,.IL S0tJ Loom -
Nooolk FL- S --oo
No.olk Sanel






100 -





1 0.00 -






oioo 'Z9 059
o '.es nc l5 a Y 100 m a d
Fig. 5.-Comparative quantities of water soluble calcium in a Greenville
sandy loam, a Norfolk fine sand and a Norfolk sand treated with different
amounts of zinc sulfate, on the basis of 100 grams of air-dried soil.


0olI / \ 00 15Z5 229
o.45f -1 ,
01o J m.e. Zn a idpd. as jln .sa phale pe 100 m. air died. sdm
Fig. 6.-Comparative quantities of replaceable calcium in a Greenville
sandy loam, a Norfolk fine sand and a Norfolk sand treated with different
amounts of zinc sulfate, on the basis of 100 grams of air-dried soil.






Florida Agricultural Experiment Station


apparently combines with the soil in a replaceable form. At
these concentrations, the amount of calcium rendered soluble
and the zinc in replaceable form are nearly equivalent. At higher
zinc sulfate concentrations, Greenville sandy loam with a higher
clay and replaceable calcium content fixed appreciably more zinc
than Norfolk fine sand and Norfolk sand. The Norfolk fine sand
and the Norfolk sand were quite similar in their reaction with
zinc sulfate. The fine sand had a higher clay and organic matter
content but a lower replaceable calcium content than the sand.
Results of the study of the reaction of zinc sulfate with saw-
grass peat and with marl are given in Table 10. Only the water
soluble zinc and the total fixed zinc content of the soils were de-
termined.

TABLE 10.-THE FIXATION OF ZINC FROM ZINC SULFATE BY SAW-GRASS
PEAT AND MARL.


Marl soil
Water
soluble
zinc


m. e.

0.031

0.012

0.024

0.028

0.021

0.024

0.037

0.052

0.239

1.095

2.386

5.451


Saw-grass
S Water
Fixed soluble
zinc zinc

m. e. m. e.

........ 0.098

0.153

0.306 0.061

0.459

0.765 0.141

1.529 0.177

2.288 0.141

3.038 0.128

7.437 0.171

14.226 0.316

20.580 0.494

25.160 0.739

1.615

2.202

S 3.163
3.763


Zinc added
as ZnSO4 per
100 g. soil


m. e.

None
0.153

0.306

0.459

0.765

1.529

2.294

3.059

7.645

15.290

22.935

30.580

38.237

45.885

53.533
61.180


peat

Fixed
zinc

m. e.




0.306


0.722

1.450

2.251

3.029

7.572

15.072

22.539

29.939

36.720

43.785
50.468

57.515






The Reaction of Zinc Sulfate With the Soil 25

The very great zinc fixing power of these soils may be at-
tributed to the calcium carbonate of the marl and the base
saturated organic matter of the saw-grass peat. The zinc sul-
fate reacting with the marl soil forms insoluble zinc carbonate
and calcium sulfate. In the saw-grass peat the zinc combines
with the organic constituents. Even with the application of
30.580 milliequivalents of zinc as zinc sulfate, the maximum
fixing power of the marl for zinc was not reached and 61.180
milliequivalents were insufficient to bring about the maximum
fixation in the saw-grass peat. These concentrations correspond
to 1 and 2 percent of zinc in the respective soils. The signifi-
cance of the differences in the fixing power of different soils
will be discussed later.

WATER SOLUBLE AND REPLACEABLE ZINC IN SOILS
RECEIVING FIELD APPLICATIONS OF ZINC SULFATE
Field experiments conducted by the Departments of Horticul-
ture, Agronomy, and Chemistry and Soils offered an opportunity
to study the action of zinc sulfate in field soils.
A special soil sampler was designed for field use. The sampler
consists of a heavy brass tube 3 1/16 inches in diameter. The
tube has a heavy flange around the top which assists materially
in shoving it into the soil and also prevents it from going deeper
than three inches. This sampler takes an approximately con-
stant volume of soil and may be conveniently lifted from the
soil with an ordinary trowel. Sandy soils may be sampled rapidly
and effectively with this apparatus.
Samples were collected from four different field experiments
where zinc sulfate had been applied to the soil. After they
were brought into the laboratory and allowed to air-dry, the
samples were screened through a 2 millimeter round holed alum-
inum sieve. One hundred grams of the screened soils were
leached first with a liter of water and then with a liter of normal
ammonium chloride solution. Zinc was determined in leachates.
Field Crop Experiments.-The Departments of Agronomy and
Chemistry and Soils cooperating have a series of 24 plots where
the effect of zinc sulfate on the growth of various field crops is
being tested. The treatments consist of no zinc sulfate plots
and plots with three different rates of application of 89 percent
zinc sulfate replicated six times in the field. The zinc sulfate
was applied in the drill row on March 29, 1934, before the crops
were planted. Sub-samples were obtained with the special







Florida Agricultural Experiment Station


sampler from 27 different places in the drill of each plot to
depths of 0-3 and 3-6 inches on April 3, 1934. The sub-samples
were mixed thoroughly to form a composite and the sample for
analysis was carefully taken from this mixture. The quantities
of water soluble and replaceable zinc found in these samples are
expressed in milliequivalents per 100 grams of air-dried soil in
Table 11.


TABLE 11.-WATER


SOLUBLE AND REPLACEABLE ZINC IN SOIL FROM
FIELD CROPS.


ZnSO4 applied per
acre in row





None







5 pounds







15 pounds







60 pounds


Averag,


Plot
No.



1
5
11
15
20
24
e...........

2
6
12
16
19


Average...........

3
7
9
13
18
I 22
Average ..........

4
8
10
14
S17
21
Average.-.........


m. e. zinc per 100 grams
0-3 inches 3-6 inches
SSoSolubl I Soluble
Soluble in Soluble in
in water I N.NHCl | in water N.NH,Cl

0.009 0.025 0.009 0.032
0.010 0.025 0.003 0.033
0.012 0.021 0.006 0.033
0.011 0.020 0.004 0.022
0.010 0.028 0.009 0.023
0.009 0.021 0.008 0.023
0.010 0.023 0.007 0.028


0.013
0.010
0.008
0.012
0.013
0.010
0.011

0.008
0.012
0.010
0.016
0.020
0.019
0.014

0.128
0.231
0.038
0.074
0.109
0.138
0.119


0.029
0.030
0.040
0.047
0.039
0.039
0.038

0.032
0.102
0.059
0.129
0.084
0.097
0.084

0.455
0.543
0.302
0.364
0.480
0.377
0.421


0.014
0.009
0.006
0.009
0.009
0.001
0.008

0.006
0.003
0.006
0.008
0.009
0.008
0.007

0.006
0.004
0.008
0.009
0.009
0.006
0.007


0.027
0.025
0.029
0.031
0.031
0.025
0.028

0.028
0.033
0.036
0.034

0.028
0.032

0.029
0.055
0.020
0.023
0.012
0.031
0.029


89% zinc sulfate applied March 29, 1934.
Soil samples collected April 3, 1934.


These data were obtained from the analysis of soil samples
collected within a week after the application of zinc sulfate to
the soil. There was no rainfall between the dates of application
and sampling. The water soluble zinc content of the soil was






The Reaction of Zinc Sulfate With the Soil


increased very little by the 5 and 15 pound per acre rates of
application of zinc sulfate. The 60 pound per acre rate increased
the water soluble zinc content of the 0-3 inch depth of the soil
from 0.010 to 0.119 milliequivalents. The replaceable zinc con-
tent of the soil was increased with an increase in the rate of
zinc sulfate applications; being 0.023 milliequivalents for the
untreated soil, 0.038 for the 5-pound rate, 0.084 for the 15-
pound rate, and 0.421 for the 60-pound rate. Neither the water
soluble nor the replaceable zinc content of the 3-6 inch soil depth
was affected at the date of sampling. This may be attributed
to the lack of rainfall between the dates of application and
sampling.
Citrus Soil at Lake Wales.-The soil sampled at Lake Wales is
a Norfolk sand (deep phase) which is coarse in texture and
almost devoid of organic matter. The grove is planted to orange
and grapefruit trees of varying ages. Zinc sulfate was broad-
cast in the zone of fertilizer application. Six sub-samples were
taken in this zone one month and seven months after the zinc
sulfate applications and composite for analyses. The water
soluble and replaceable zinc contents of the variously treated
soils are given in Table 12.
At the end of these periods the water soluble zinc content
of both depths of soil was increased very slightly, or not at all,
by the applications of zinc sulfate. The replaceable zinc content
of the 0-3 and 3-6 inch soil depths was increased by applications
of zinc sulfate. The maximum quantity of zinc fixed in the re-
placeable form in the surface soil of this coarse sand with large
zinc sulfate applications is small in comparison to that fixed by
finer textured soils. Evidently the water soluble zinc leached by
rain from the surface soil was fixed partially in the replaceable
form in the lower soil depths.
Tung Oil Soil at Gainesville.-Mowry (22) in 1932 applied zinc
sulfate to several tung trees on the Agricultural Experiment
Station Farm at Gainesville. This application has been fol-
lowed by others at different dates to trees in the same planting.
The planting is located on Norfolk and Hernando fine sands.
Samples of soil were collected from selected trees of this plant-
ing in June 1934. Eight sub-samples of soil were collected from
each tree and composite for analysis. The dates of application
of zinc sulfate, the total quantities of zinc added, the quantities
of water soluble and normal ammonium chloride soluble zinc
in the 0-3 and 3-6 inch depths of soil are given in Table 13.










TABLE 12.-WATER SOLUBLE AND REPLACEABLE ZINC IN SOIL FROM CITRUS GROVE.

m. e. per 100 grams air-dried soil


Date of
application




Sept. 1, 1933


March 2, 1934





March 2, 1934
(9


ZnSO,
applied
per tree


None

1 lb.

5 lb.

10 lb.

15 lb.

20 lb.

1 lb.

2 lb.

5 lb.


4 10 Ib.

Each sample a composite of 6 subsamples taken in the
Sampled April 11, 1934. 89% zinc sulfate was used in


0-3 inches
SSoluble in
Soluble N.NHCl1
in water solution

0.010 0.033


O.uu8

0.009

0.015

0.014

0.013

0.013

0.012


0.073

0.137

0.168

0.161

0.175

0.072

0.108


0.012 0.146

0.023 0.212

zone of applications.
this experiment.


3-6

Soluble
in water

0.006

0.008

0.017

0.012

0.012

0.017

0.009

0.009

0.011

0.034


inches
Soluble in
N.NHXC1
solution

0.026

0.025

0.059

0.079

0.086

0.118

0.030

0.038

0.038

0.059


No. of trees
sampled





TABLE 13.-WATER SOLUBLE AND REPLACEABLE ZINC IN SOIL FROM TUNG TREE GROVE.


Tree Number Single applica-
Hill Row tion of ZnS04

11 1 None
11 2
11 3
14 1
14 2
Average
2 1 220 gm.1
1 1 "
Average
1 10 220 gm.1
1 14 "
Average
7 1
7 2 110 gm.2
7 3
7 4
7 5
7 6
Average
5 1
5 2 220 gm.2
5 3
5 4
5 5
5 6
SAverage
15 11 1 lb.2
15 13
Average
Samples collected June 26 and 27, 1934.


m. e. per 100 grams of air-dried soil
0-3 inches 3-6 inches
Dates of Total zinc ap- Soluble in Soluble in Soluble in Soluble in
applications plied as sulfate water N.NHaCl water N.NH.C1
m. e. m. e. m. e. m. e.
0.012 0.049 0.004 0.027
0.012 0.024 0.001 0.021
0.012 0.030 0.006 0.034
0.009 0.021 0.008 0.030
0.011 0.015 0.008 0.024
0.011 0.028 0.005 0.027
7/28/32 49.9 g. 0.012 0.174 0.008 0.061
0.015 0.189 0.011 0.125
| 0.014 0.182 0.009 0.093
8/5/32 49.9 g. 0.012 0.168 0.006 0.058
0.014 0.193 0.008 0.098
0.013 0.180 0.007 0.078
S9/19/32 0.009 0.342 0.009 0.058
3/11/33 158.4 g. 0.012 0.162 0.008 0.070
| 6/23/33 0.009 0.199 0.008 0.049
4/13/34 0.014 0.511 0.009 0.159
0.011 0.272 0.009 0.043
0.014 0.480 0.012 0.122
0.011 0.328 0.009 0.083
9/19/32 0.017 0.453 0.008 0.079
3/11/33 237.6 g. 0.019 0.508 0.004 0.104
[ 4/13/34 0.006 0.226 0.006 0.043
0.021 0.575 0.012 0.189
0.024 0.774 0.012 0.330
0.030 0.850 0.012 0.281
0.019 0.564 0.009 0.171
S6/26/33 326.6 g. 0.017 0.416 0.006 0.110
4/13/34 0.019 0.355 0.009 0.144
0.018 0.385 0.008 0.127


I ZnSO,-7H0: 2 ZnSO,






Florida Agricultural Experiment Station


These data show that in general the zinc sulfate applications
had very slightly increased the water soluble zinc content of
the soil in both the 0-3 inch and the 3-6 inch soil depths at the
date of sampling. A total of 49.9 grams of zinc applied as zinc
sulfate in July and August 1932 increased the replaceable zinc
content of the 0-3 inch soil depth from 0.028 to approximately
0.180 milliequivalents in 1934, and from 0.027 milliequivalents
to approximately 0.086 milliequivalents for the 3-6 inch depth.
Total applications of 158.4 grams and 237.6 grams of zinc as
zinc sulfate given at intervals between August 1932 and April
1934 increased the replaceable zinc content of the 0-3 inch soil
depth to 0.328 and 0.564 milliequivalents respectively in June
1934; the replaceable zinc content of the 3-6 inch soil depth
was increased also. The total application of 326.6 grams of zinc
in June 1933 and April 1934, increased the replaceable zinc
content of the 0-3 inch soil depth to 0.385 milliequivalents and
that of the 3-6 inch depth to 0.127 milliequivalents in June 1934.
The discrepancy between these results and those obtained for
the 237.6 gram application of zinc may be attributed to soil vari-
ations, lack of sufficient samples and difference in weather con-
ditions.
Satsuma Soil at Gainesville.-The soil samples in a Satsuma
grove receiving applications of 89 percent zinc sulfate in March
1934 were similar to those of the tung tree grove. Samples
were taken at three dates after the application of zinc sulfate
to the soil. Table 14 gives the results of the determinations of
water soluble and replaceable zinc in Satsuma soils treated with
zinc sulfate on March 15, 1934. Samples were taken on March
21, June 7 and October 3, 1934.
Two hundred grams of zinc sulfate per tree applied on March
15, 1934, increased the water soluble zinc content of the 0-3 inch
soil depth from 0.008 to 2.062 milliequivalents, on March 21, 1934,
while two pounds per tree further increased it to 4.978 milli-
equivalents. On the same date, the replaceable zinc content of
the 0-3 inch soil depth was increased from 0.023 to 0.645 and
0.956 milliequivalents for the 200-gram and two-pound applica-
tions, respectively. There was no rainfall between the dates
of application and sampling. As the zinc sulfate had been worked
mechanically into the soil, the water soluble and replaceable
zinc contents of the 3-6 inch soil depths were increased by the
zinc sulfate applications but not to the extent of the 0-3 inch
depth.













TABLE 14.-WATER SOLUBLE AND REPLACEABLE ZINC IN SOIL FROM SATSUMA GROVE.


['FoI'im of zinc
in soil


Zinc soluble

in water


Zinc soluble in

normal NH,C1

solution


89'/ zinc sulfate
applied per tree on
March 15, 1934


None .........

200 gin. per tr

2 Ibs. per tree


N one ........

200 gm. per tr

2 lbs. per tree


March1 June2
21/34 7/34
0-3 inches


m. e. m
-... .. ....-... I 0 .0 0 8

ee ........... 2.062 0.

... ....... 4.978 0


.................. 0.023

ee ...-....... 0.645 0

................ 0.956 0.


.e.


.016

.060




.309

.647


1 Average of 6 samples from untreated trees and 12 individual samples
2Average of 6 composite samples from 6 trees. Each composite made
Rainfall: March 15 to 21, none; March 21 to June 7, 14.58 inches.


Date of
October2
3/34


m. e.


0.017

0.0:36




0.191

0.487


Sampling
March
21/34


m. c.
0.014

0.014

0.100


0.025

0.099

0.149


June
7/34
-6 inches

m. e.


0.024

0.130




0.131

0.212


from each of 3 treated trees.
up of 8 individual samples.
June 7 to October 3, 22.59 inches.


October
3/34 Z


e. 0.


0.013

0.156 6




0.103

0.235
a.







Florida Agricultural Experiment Station


The samples collected on June 7 showed an entirely different
relationship of the water soluble and replaceable zinc. The
water soluble zinc content of the 0-3 inch depth receiving the
200-gram application of zinc sulfate had decreased from 2.0262
milliequivalents on March 21 to 0.016 milliequivalents on June
7. During this period, the water soluble zinc content of the
soil receiving two pounds of zinc sulfate decreased from 4.978
to 0.060 milliequivalents in the surface three inches. The re-
placeable zinc content of this soil depth also decreased during
this period.
The water soluble zinc content of the 3-6 inch depth of the
soil receiving the 200-gram application of zinc sulfate decreased
from 0.041 to 0.024 milliequivalents between March 21 and June
7. The water soluble zinc increased in the 3-6 inch depth of the
soil receiving the two-pound application of zinc sulfate. The
replaceable zinc content of the 3-6 inch depth increased for both
applications of zinc sulfate. The 14.58 inches of rain falling
between March 15 and June 7 had washed out practically all of
the water soluble zinc from the surface three inches of soil and
a portion of this zinc had been fixed in the replaceable form in
the second three inches of soil. The replaceable zinc content
of the surface three inches also had been decreased during this
period.
On October 3, the quantities of water soluble and replaceable
zinc in the surface three inches of soils treated with zinc sulfate,
with one exception, had decreased below those found on June 7.
The soil with the two-pound application of zinc sulfate still
showed the highest water soluble zinc content. Replaceable zinc
content of the second three inches was lower on October 3 than
on June 7 for the soil receiving the 200-gram application of zinc
sulfate. On the other hand, replaceable zinc content of the 3-6
inch depth of soil receiving the two-pound application of zinc
sulfate increased progressively from March 21 to October.

DISCUSSION OF EXPERIMENTAL RESULTS
The series of laboratory studies on the reaction of zinc sulfate
and the soil, together with observations on soils receiving appli-
cations of zinc sulfate in the field, are of value in the interpreta-
tion of observations on plant response to zinc and in formulating
a more rational use of soluble compounds of this metal on various
soils. In discussing these results it seems desirable to review
briefly the most important observations made in these studies






The Reaction of Zinc Sulfate With the Soil


and then consider their relationship to plant responses in the
field.
When soluble zinc and the soil react, there are three classes
of compounds formed, (1) water soluble, (2) combinations with
the colloidal portion of the soil (replaceable zinc) and (3) water
insoluble and non-replaceable zinc combinations such as car-
bonates, phosphates and more complex compounds.
The entrance of zinc into the organic and inorganic colloidal
complex of the soil is essentially a replacement of cations. Cal-
cium is the predominating replaceable base in the acid mineral
soils of Florida as shown by Barnette and Hester (5) and this
cation evidently is easily replaced by zinc. That other cations
such as potassium, sodium, magnesium, etc., are also replaced
by zinc has been shown by other workers (17). In the three
acid mineral soils studied, a large proportion of the total quan-
tities of zinc fixed by the soil from zinc sulfate was in the re-
placeable form. When dilute concentrations of zinc sulfate
react with acid mineral soils, practically all of the zinc is taken
up by the soils in a replaceable form and thus rendered tempor-
arily insoluble to water. Evidence presented in the study of
the fixation of zinc by different soils and observations made on
field soils emphasize the importance of replaceable zinc in acid
mineral soils.
Soluble zinc compounds in acid soils and particularly in sands
are apparently readily leached into the lower depths of the soil
where they are fixed either in a replaceable form or an insoluble
form or are further leached. A very large and definite increase
in the water soluble zinc content of acid mineral soils over an
extended period after the application of zinc sulfate was not
observed in the laboratory and field experiments. While a rela-
tively high concentration of water soluble zinc may be present
immediately after the application of zinc sulfate to the soil,
this is soon reduced by leaching rains. After being leached,
soils treated with relatively large quantities of zinc sulfate often
show very low concentrations of soluble zinc which, however,
are higher than those found in untreated soils. Apparently the
replaceable zinc of the soil is the source of this increased water
soluble zinc in soils treated with zinc sulfate and subsequently
leached artificially or by rains.
Zinc compounds not removed from the soil by water and a
normal ammonium chloride solution are considered insoluble zinc
compounds. Insoluble zinc compounds formed in the soil upon
the addition of zinc sulfate are evidently quite varied in com-






Florida Agricultural Experiment Station


position. Apparently these compounds are formed in the acid
mineral soils when high concentrations of zinc sulfate react
with the soil or after the major portion of the replaceable bases
of the soil have been displaced from the colloidal complex by
zinc. It is difficult to imagine that these insoluble zinc com-
pounds are a readily available source of zinc or very materially
affect plant growth.
Addition of organic matter in the form of saw-grass peat
definitely increased the fixation of zinc in replaceable and in-
soluble forms in Norfolk sand. The increase in replaceable zinc
may be attributed to the replaceable calcium, magnesium, etc.,
added in the saw-grass peat. The increase in insoluble zinc may
be attributed to the combination of the soluble zinc sulfate with
the saw-grass peat to form insoluble organic compounds. These
results are in keeping with those obtained in 1885 by Bau-
mann (8).
Superphosphate and colloidal phosphate in contact with zinc
sulfate in the soil decreased the water soluble zinc and increased
its fixation in the soil in an insoluble form.
Several characteristics of soils influenced the fixation and
solubility of zinc from zinc sulfate. Total quantities of zinc
fixed in the insoluble and replaceable forms by a Greenville sandy
loam were definitely higher than those of a Norfolk fine sand
and a Norfolk sand. The higher clay, organic matter and re-
placeable base content of the Greenville soil was without doubt
responsible for the greater fixation of replaceable and insoluble
zinc by this soil. A Norfolk sand with a higher replaceable cal-
cium content was able to fix more replaceable zinc than a Nor-
folk fine sand, despite the finer texture of the latter. A marl
soil containing the equivalent of about 80 percent calcium car-
bonate fixed very large quantities of zinc in the insoluble form.
Saw-grass peat which was about neutral and contained some
undecomposed shells, rendered very large quantities of zinc in-
soluble when treated with zinc sulfate.
Examination of field soils to which zinc sulfate applications
had been made shows that the water soluble zinc content of the
soil may be increased by the application of 15 pounds or more
of zinc sulfate per acre. Any very large increases in water
soluble zinc were temporary, while small consistent increases
were observed following most applications. The replaceable zinc
content of field soils to which zinc sulfate had been applied was
increased definitely over that of untreated soils. This was found
to be true for both the 0-3 inch and 3-6 inch soil depths.







The Reaction of Zinc Siulfate With the Soil


From the experimental evidence, the replaceable zinc of the
soil is one of the most important forms of zinc in acid mineral
soils. That some Florida soils retain very little zinc in the re-
placeable form is emphasized by the low replaceable zinc con-
tent obtained for a Norfolk coarse sand (deep phase) from
Lake Wales following large applications of zinc sulfate.
Results of these laboratory and field observations may be
correlated to some extent with plant response following the
application of zinc sulfate to the soil. The results with citrus,
reported by Camp (11) in 1934 were as follows: "In experiments
on the very sandy soils in Polk and Highlands counties the
results from zinc sprays have been outstanding. Results from
soil treatments have been much more irregular than has been
the case with tung trees. In some cases no visible result was
obtained from soil applications; whereas, in others, application
of from five to 15 pounds per tree broadcast brought good
response. Applications ranging from one-fourth to two pounds
as used for tung oil and Satsumas in the vicinity of Gainesville
gave little or no benefit, while excellent reactions were obtained
from the use of sprays. Whether the zinc salt is leached out of
the very sandy soils too quickly or is tied up by something in
the soil remains to be determined. So far sprays seem to be
much more sure and effective than soil applications for citrus."
The analysis of the Norfolk coarse sand (deep phase) for
water soluble and replaceable zinc following the application of
zinc sulfate are interesting in this connection. This coarse sand
had a low water soluble and replaceable zinc content both in
the 0-3 and 3-6 inch soil depths despite the application of as
much as 20 pounds of zinc sulfate per tree. The soluble zinc
apparently is leached from this deep coarse Norfolk sand with
very little fixation in the replaceable form.
In 1930, Newell, Mowry and Barnette (24) described a mal-
nutrition of the tung oil tree called "bronzing" which occurred
in some of the older plantings in Florida. Their observations
were as follows:
"The only correlation with a soil condition is found in the
total phosphate content of the soil and the appearance of the
disturbance, etc.
"Thus a definite correlation is to be seen between the phos-
phate content of the soil and the development of the bronzed
condition. The bronzing of the leaves and the malgrowth were
correlated with the depth and character of the soil above the
phosphatic lime rock underneath, etc."






Florida Agricultural Experiment Station


Mowry and Camp (23) in their preliminary report on the use
of zinc sulfate for the correction of bronzing write about the
same planting as follows:
"One of the oldest large plantings, made in 1924, on rolling
lands which in some parts are high in phosphatic material, has
consistently shown large amounts of bronzing. It was on this
property that the first results were obtained from zinc treat-
ments, as previously noted. However, more extensive treat-
ments started here in 1933 did not show consistent results and
in no case were marked results visible until late in the growing
season. It was at first thought that this variable response was
due primarily to the age and hardness of the trees which reduced
their ability to respond to treatment. There is some indication
at present, however, that it may be due to the soil condition
and that some other method of application may be desirable."
A natural phosphate (colloidal phosphate) when added to a
Norfolk sand in relatively large concentrations decreased the
solubility of zinc and increased its fixation from zinc sulfate.
The increased fixation of zinc by the addition of colloidal phos-
phate to a Norfolk sand indicates that those soils which are
formed from phosphatic materials or contain large quantities
of these materials are capable of fixing large quantities of zinc
in an insoluble form and thus decreasing its solubility in the
soil.
Laboratory experiments on the influence of superphosphate
on the water soluble and total quantities of zinc fixed indicate
that superphosphate may decrease the water soluble and in-
crease the fixation of zinc in an insoluble form by a Norfolk sand
when applied in contact with zinc sulfate. Results of corn yields
obtained from nine field experiments (7) in which zinc sulfate
was applied mixed with an inorganic fertilizer made from nitrate
of soda, superphosphate, and muriate of potash substantiate
the results of these laboratory experiments. The response of
corn to the application of zinc sulfate was decreased definitely
by the use of zinc sulfate in an inorganic fertilizer containing
large quantities of superphosphate as compared with the response
from a combination without superphosphate. These results in-
dicate that under some conditions the simultaneous application
of zinc sulfate and superphosphate in an inorganic fertilizer
mixture may not be desirable.
Field observations on plant responses emphasizing the im-
portance of the residual zinc content of the soil have been ob-
tained during the current planting season. In experiments on







The Reaction of Zinc Sulfate With the Soil


the Agricultural Experiment Station Farm, applications of 12
pounds of 89 percent zinc sulfate in 1934 were apparently as
effective in improving the white bud condition of corn in 1935
as an additional 12 pounds of zinc sulfate applied in the row
in 1935. In this experiment care was taken to place the rows
as nearly as possible in the same location in 1934 and 1935. These
results have been substantiated by observations made on a field
in which experimental plots with and without zinc sulfate were
established in 1934, and where no additional applications of
zinc sulfate were made in 1935. The plots receiving no zinc
sulfate in 1934 showed definite symptoms of "white bud" of
corn in 1935, while those receiving an application of 12 pounds
in 1934 showed no symptoms in 1935 despite the fact that no
additional applications were made. Residual effect of the ap-
plication of zinc sulfate to acid mineral soils apparently may
be attributed to the slowly soluble replaceable zinc held in the
soil following this application.
Finally, possible toxicity of zinc fixed in the soil is of interest
to those using zinc compounds for the prevention and correction
of the malnutrition of plants. Baumann (8), in his very thor-
ough study of the reaction of zinc compounds with the soil,
attributed the great divergence of toxic limits of zinc obtained
by different workers to the wide difference in fixing power of
soils for zinc. Thus, a much lower concentration of zinc was
found to be toxic in sandy soils than in humus and marl soils.
These observations were correlated with the fixing power of
soils for zinc. From Baumann's results as well as from results
presented in this study, it appears that organic and marl soils
have a very much greater fixing power for zinc than have sandy
soils.
Results reported by many workers as reviewed by Brenchley
(10) and others point to the fact that very insoluble zinc com-
pounds such as the oxide, carbonate, phosphate, sulphides, etc.,
are seldom toxic to plant growth. On the other hand, the very
toxic character of water soluble zinc compounds in water cul-
tures, sand cultures and soils with low fixing power often has
been proved.
The laboratory and field experiments reported above show
that water soluble zinc is readily leached from open textured
sandy soils and toxic concentrations of soluble zinc in field tests
were found very seldom. The soluble zinc content of the soils
is low except immediately following the application of soluble
zinc compounds and before leaching rains have fallen. The very






38 Florida Agricultural Experiment Station

insoluble zinc combinations formed in mineral soils with high
concentrations of soluble zinc compounds are not toxic to plant
growth under ordinary conditions. However, very little informa-
tion is available on the toxic limits of the more soluble and mobile
replaceable zinc in acid mineral soils.

TOXICITY OF REPLACEABLE ZINC IN NORFOLK SAND

The surface soil of a Norfolk sand from the Agricultural Ex-
periment Station Farm was used for toxicity studies. A quantity
of the air-dried sieved soil was treated with a high concentra-
tion of zinc sulfate solution in the coffee urn type of glazed
earthenware pots. The soil was brought to a favorable moisture
condition for the contact of the zinc sulfate and soil and allowed
to stand for a week. The excess zinc sulfate was washed from
the soil with distilled water and the zinc treated soil spread in
thin layers to dry.
Small glazed earthenware pots holding 1,200 grams of soil
were used for the vegetation experiments. Different proportions
of untreated and zinc-treated Norfolk sand were used to give
a range of replaceable zinc from none to 1.376 milliequivalents
per 100 grams of air-dried soil. The higher limit was approxi-
mately the saturation point of the replaceable zinc for this Nor-
folk sand.
Seven series of cultures for each replaceable zinc concentra-
tion were established in the greenhouse. Ammonium nitrate
was applied at the rate of 100 pounds per acre (2,000,000 pounds
of soil) to all cultures. Chemically pure mono-calcium phosphate,
potassium sulfate, calcium carbonate and calcium sulfate were
added to different series in the concentrations indicated in Table
15. All cultures were established in duplicate. An optimum
soil moisture for plant growth was maintained by frequent
weighing and additions of distilled water. Two crops of corn
and cowpeas (five plants per culture) were grown for four weeks
each. The top growth of the corn and cowpeas was harvested
and the dry weight (100 C) of the plants from each pot ob-
tained. Average relative weights were calculated on the basis
of weights obtained from cultures with no replaceable zinc and
are given in Table 15.
Growth of cowpea seedlings was definitely stunted by con-
centrations of 0.482 milliequivalents of replaceable zinc per 100
grams of soil. At this concentration, examination of the roots
showed that nodulation had been decreased. At a concentration








TABLE 15.-RELATIVE WEIGHTS OF COWPEAS AND CORN GROWN IN NORFOLK SAND WITH DIFFERENT AMOUNTS OF
REPLACEABLE ZINC.


Application bf fertilizing salts


I m. e. replaceable Zn. per 100 g. air-dried soil
I None 0.069 0.138 0.206 0.275 0.482 0.688 I 1.376

Cowpeas


NH4NO, (100 lbs./A) -.. ................. ............ ...
CaH2PO (233 lbs./A) ........................
+ K=SO, (100 lbs./A) ........................
+ + CaH.PO, (233 lbs./A) ........
+ CaCO, (1000 lbs./A) --...-..........-..
+ CaSO4 (500 lbs./A) .-..-.-.-- ........-
+ CaSO4 + CaH2PO, (233 lbs./A)

A average ..--. ......................- .. ......... ..-


100 96 91 86 92
100 97 92 84 96
100 107 100 100 87
100 106 89 89 94
100 87 87 79 80
100 110 100 97 94
100 .. 104 105 91

100 100 95 91 91


Corn

NHlNO, (100 lbs./A) ....................................... .. .. 100 91 98 ..... 102 110 99
+ CaH2PO, (233 lbs./A) -.........-...... 100 113 110 122 122 110 121
+ KSO, (100 lbs./A) .......... ..... ..-- 100 101 92 99 102 88 96
+ + CaH-PO (233 lbs./A) .......... 100 119 100 98 105 108 98
+ CaCO, (1000 lbs./A) ........................... 100 102 110 110 110 108 96
+ CaS04 (500 lbs./A) .......................... 100 103 105 97 90 94 94
+ + CaH.PO, (233 lbs./A) ....... 100 98 103 95 103 86

Average ............ ................... ... 100 102 101 105 102 102 97


71 61
74 61
75 62
75 66
78 61
68 47
68 51

73 58






Florida Agricultural Experiment Station


of 1.376 milliequivalents, no nodules were found on the roots
and the young plants made practically no growth after germina-
tion and the formation of two to four leaves. The plants re-
mained green until the edges of the leaves began to curl and
die. Finally the leaves dropped off and the plants were left
barely alive. Germination of the cowpeas was not affected by
the zinc concentrations proving toxic to top growth.
Corn seedlings showed no injury until a concentration of
1.376 milliequivalents of replaceable zinc was reached. At this
concentration the blades turned yellow between the veins which
developed an intensified green color. Injured seedlings had
several blades but remained very small as compared with the
other seedlings. Germination of the corn was not affected by
toxic concentrations of replaceable zinc.
Among the fertilizer salts used, calcium carbonate was the
only one to offset the toxicity of replaceable zinc. Applied at
the rate of 1,000 pounds per acre, calcium carbonate definitely
decreased the toxicity of the high concentrations of replaceable
zinc.
SUMMARY
1. The method of Cone and Cady for the titration of zinc
with potassium ferrocyanide in the presence of potassium ferri-
cyanide and with diphenylbenzidine as an internal indicator has
been used for the determination of zinc in water and normal am-
monium chloride extracts of soils. The method may be applied ac-
curately for the determination of 5 milligrams of zinc, with fairly
accurate estimations of smaller quantities. Iron, the most import-
ant element interfering with the determination, may be satis-
factorily separated by precipitation as the hydroxide in the
presence of an excess of ammonium chloride and ammonium
hydroxide. The separation of iron and zinc by this method
has been found to be satisfactory up to a concentration of iron
four to five times as great as that of zinc.
2. When zinc compounds are applied to and react with the
soil there are three general types of compounds found: (1)
water soluble zinc compounds, (2) combinations formed by the
reaction of soluble zinc compounds and the organic and inorganic
colloidal complex of the soil (replaceable zinc), and (3) com-
binations insoluble in water and not in combination with the
colloidal complexes of the soil (not replaceable). The formation
of replaceable zinc combinations in the soil is apparently an ex-
change of the water soluble zinc with the cations of the organic






The Reaction of Zinc Sulfate With the Soil


and inorganic colloidal complexes of the soil. In acid mineral
soils, calcium predominates as an exchangeable cation in the
colloidal complex. When low concentrations of soluble zinc
compounds react with the soil, the major portion of the zinc
enters into combination with the colloidal complexes and may
be replaced by a normal ammonium chloride solution. Under
these conditions there is a near equivalence between the re-
placeable zinc of the soil and the calcium removed from the
colloidal complex. When high concentrations of soluble zinc
compounds react with the soil, the zinc is found present not
only in water soluble and replaceable forms but also in an in-
soluble form. After the major portion of the exchangeable
bases are replaced by zinc, the zinc enters into this insoluble
form in the soil.
3. Organic matter, clay, replaceable bases, carbonates and
phosphates were found to influence the fixation of zinc in the
soil. Superphosphate in contact with zinc sulfate in the soil
decreased the solubility of the zinc and increased the fixation
of insoluble zinc.
4. A marl and a peat soil fixed very much greater quantities
of zinc in an insoluble form than did acid mineral soils.
5. The water soluble zinc content of acid mineral soils was
increased in most instances by row and broadcast applications
of zinc sulfate. The greatest increase occurred immediately after
application. Water soluble zinc leached into and was fixed in
part by the lower soil depths. Applications of zinc sulfate to
field soi's increased the replaceable zinc content of the 0-3 and
3-6 inch soil depths.
6. In a Norfolk sand, zinc was found to be toxic to cowpeas
at a concentration of approximately 0.482 milliequivalents per
100 grams of air-dried soil and to corn at 1.376 milliequivalents
per 100 grams. Calcium carbonate decreased the toxic action
of replaceable zinc.







Florida Agricultural Experiment Station


LITERATURE CITED

1. ALBEN, A. 0., J. R. COLE and R. D. LEWIS. New Developments in
treating pecan rosette with chemicals. Phytopath. 22: 979-981.
1932.

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The Reaction of Zinc Sailfate With the Soil


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