• TABLE OF CONTENTS
HIDE
 Front Cover
 Credits
 Table of Contents
 Introduction
 Plan of experiments
 Fertilizer analyses
 Amounts of fertilizer per acre
 Percentage of nitrogen from organic...
 Sources of nitrogen
 Muriate vs. sulfate of potash
 Manganese
 Other soil amendments
 Summary
 Acknowledgments














Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 352
Title: Fertilizer experiments with potatoes on the marl soils of Dade County
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 Material Information
Title: Fertilizer experiments with potatoes on the marl soils of Dade County
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 352
Physical Description: Book
Language: English
Creator: Fifield, W. M.
Wolfe, H. S.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1940
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Bibliographic ID: UF00027669
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Source Institution: University of Florida
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Table of Contents
    Front Cover
        Page 1
    Credits
        Page 2
    Table of Contents
        Page 3
    Introduction
        Page 3
    Plan of experiments
        Page 4
        Page 5
        Page 6
    Fertilizer analyses
        Page 7
        Page 8
        Page 9
        Page 10
    Amounts of fertilizer per acre
        Page 11
        Page 12
        Page 13
    Percentage of nitrogen from organic sources
        Page 14
        Page 15
        Page 16
    Sources of nitrogen
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
    Muriate vs. sulfate of potash
        Page 25
    Manganese
        Page 25
        Page 26
        Page 27
        Page 28
    Other soil amendments
        Page 29
        Page 30
        Page 31
        Page 32
        Page 33
        Page 34
        Page 35
        Page 36
        Page 37
    Summary
        Page 38
        Page 39
    Acknowledgments
        Page 40
Full Text

December, 1940


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


Fertilizer Experiments With Potatoes

On The Marl Soils of Dade County

By W. M. FIFIELD and H. S. WOLFE


h.c


Fig. 1.-Washing and grading potatoes at the Sub-Tropical Experiment Station.

Single copies free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


Bulletin 352


~'~5~3
2~j





EXECUTIVE STAFF BOARD OF CONTROL


John J. Tigert, M. A., LL.D., President
of the University3
Wilmon Newell, D.Sc., Director3
Harold Mowry, M. S. A., Asst. Dir.,
Research
J. Francis Cooper, M.S.A., Editor3
Jefferson Thomas, Assistant Editors
Clyde Beale, A.B.J., Assistant Editor3
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Manager3
K. H. Graham, Business Manager3
Rachel McQuarrie, Accountant3
MAIN STATION, GAINESVILLE
AGRONOMY
W. E. Stokes, M.S., Agronomist'
W. A. Leukel, Ph.D., Agronomists
Fred. H Hull, Ph.D., Agronomist
G. E. Ritchey, M.S., Associate2
W. A. Carver, PH.D., Associate
John P. Camp, M.S., Assistant
Roy E. Blaser, M.S., Assistant
Fred A. Clark, B.S.A., Assistant
ANIMAL INDUSTRY
A. L. Shealy, D.V.M., Animal Indus-
trialist:'
R. B. Becker, Ph.D., Dairy Husbandman3
E. L. Fouts, Ph.D.. Dairy Technologists
W. M. Neal, Ph.D. Asso. in An. Nutrition
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian3
N. R. Mehrhof, M.Agr., Poultry Hus-
bandman3
W. G. Kirk, Ph.D., Asso. An. Husband-
man3
D. J. Smith, B.S.A., Asst. An. Hush.
P. T. Dix Arnold, M.S.A., Asst. Dairy
Husbandman3
.L. Rusoff, Ph. D., Asst. in An.
Nutrition3
O. W. Anderson, M.S., Asst. Poultry
Husbandman'
L. E. Mull, M.S., Asst. in Dairy Tech.
SOILS
R. V. Allison, Ph.D., Chemist'1
Gaylord M. Volk, M.S., Chemist
F. B. Smith, Ph.D., Microbiologists
C. E. Bell, Ph.D., Associate Chemist
H. W. Winsor, B.S.A., Assistant Chemist
J. Russell Henderson, M.S.A., Associates
L. H. Rogers, M.S., Asso. Biochemist
Richard A. Carrigan, B.S., Asst. Chemist
ECONOMICS, AGRICULTURAL
C. V. Noble, Ph.D., Agricultural
Economist' a
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Associate
ECONOMICS, HOME
Ouida D. Abbott, Ph.D., Home Econ-
omistx
Ruth Overstreet, R.N., Assistant
R. B. French, Ph.D., Asso. Chemist
ENTOMOLOGY
J. R. Watson, A.M., Entomologisti
A. N. Tissot, Ph.D., Associate
H. E. Bratley, M.S.A., Assistant
HORTICULTURE
G. H. Blackmon, M.S.A., Horticulturist'
A. L. Stahl, Ph.D., Associate
F. S. Jamison, Ph. D., Truck Hort.3
R. J. Wilmot, M.S.A., Fumigation
Specialist
R. D. Dickey, M.S.A., Asst. Horticulturist
J. Carlton Cain, B.S.A., Assistant
Horticulturist
Victor F. Nettles, M.S.A., Assistant
Horticulturist
F. S. Lagasse, Ph.D., Horticulturist2
H. M. Sell, Ph.D., Asso. Horticulturist2
PLANT PATHOLOGY
W. B. Tisdale, Ph.D., Plant Pathologist' 3
George F. Weber, Ph.D., Plant Path.3
L. O. Gratz, Ph.D., Plant Pathologist
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Asst. Botanist


H. P. Adair, Chairman, Jacksonville
W. M. Palmer, Ocala
R. H. Gore, Fort Lauderdale
N. B. Jordan, Quincy
T. T. Scott, Live Oak
J. T. Diamond, Secretary, Tallahassee
BRANCH STATIONS
NORTH FLORIDA STATION, QUINCY
J. D. Warner, M.S., Agron. Acting in
Charge
R. R. Kinkaid, Ph.D., Asso. Plant Path.
Elliott Whitehurst, B.S.A., Assistant An.
Husbandman
Jesse Reeves, Asst. Agron., Tobacco
CITRUS STATION, LAKE ALFRED
A. F. Camp, Ph.D., Horticulturist in
Charge.
John H. Jefferies, Asst. in Cit. Breeding
Michael Peech, Ph.D., Soils Chemist
B. R. Fudge, Ph.D., Associate Chemist
W L. Thompson, B.S., Associate
Entomologist
F. F. Cowart, Ph.D., Asso. Horticulturist
W. W. Lawless, B. S., Asst. Horticulturist
R. K. Voorhees, M.S., Asst. Plant Path.
EVERGLADES STA., BELLE GLADE
J. R. Neller, Ph.D., Biochemist in
Charge
J. W. Wilson, Sc.D., Entomologist
F. D. Stevens. B.S., Sugarcane Agron.
Thomas Bregger, Ph.D., Sugarcane
Physiologist
Frederick Boyd, Ph.D., Asst. Agronomist
G. R. Townsend, Ph.D., Plant Pathologist
R. W. Kidder, M.S., Asst. An. Husbandman
W. T. Forsee, Ph.D., Asso. Chemist
B S. Clayton, B.S.C.E., Drainage En-
gineer2
F. S. Andrews, Ph.D., Asso. Truck Hort.
SUB-TROPICAL STA., HOMESTEAD
W. M. Fifield, M.S., Horticulturist Act-
ing in Charge
S. J. Lynch, B.S.A., Asst. Horticulturist
Geo. D. Ruehle, Ph.D., Associate Plant
Pathologist
W. CENTRAL FLA. STA.,
BROOKSVILLE
W F. Ward, M.S., Asst. An. Husband-
man in Charge"
FIELD STATIONS
Leesburg
M. N. Walker, Ph.D., Plant Pathologist
in Charge
K. W. Loucks, M.S., Assistant Plant
Pathologist
Plant City
A. N. Brooks, Ph.D., Plant Pathologist
Hastings
A. H. Eddins, Ph.D., Plant Pathologist.
E. N. McCubbin, Ph.D., Asso. Truck
Horticulturist
Monticello
Samuel O. Hill, B.S., Asst. Entomologist'
Bradenton
Jos. R. Beckenbach, Ph.D., Truck Horti-
culturist in Charge
David G. Kelbert, Asst. Plant Pathologist
Sanford
R. W. Ruprecht, Ph.D., Chemist in
Charge, Celery Investigations
W. B. Shippy, Ph.D., Asso. Plant Path,
Lakeland
E. S. Ellison, Meteorologist2
B. H. Moore, A.B., Asst. Meteorologist2

THead of Department
'In cooperation with U.S.D.A.
3Cooperative, other divisions, U. of F.








FERTILIZER EXPERIMENTS WITH POTATOES ON THE MARL
SOILS OF DADE COUNTY
By W. M'. FIFIELD and H. S. WOLFE*

CONTENTS
Page Page
Plan of Experiments ...... 4 Sources of Nitrogen .17
Fertilizer Analyses .............. 7 Muriate vs. Sulfate of Potash 25
Amounts of Fertilizer per Acre. 11 Manganese 25
Percentage of Nitrogen from Other Soil Amendments 29
Organic Sources ........ 14 Summary 38

INTRODUCTION

The marl soils of southern Dade County which are used for
potato production are of a peculiar calcareous formation quite
unlike those of any other soils in the United States. They are
alkaline, ranging from a pH of about 7.5 to about 8.5. Mechanical
analysis would classify this soil as a uniform silt loam, but chem-
ical analysis shows over 90 percent of calcium carbonate. Sand
is present only in very small percentage, and organic matter
constitutes about 5 percent. This marl, a sedimentary deposit,
varies throughout the area from a depth of a few inches to about
four feet and is underlaid with a porous limerock. In limited
areas muck is found with the marl, particularly in the numerous
small sink or pot hole formations and other low places.
The marl is interspersed throughout with remains of tiny
shells, evidently similar to those from which it originally was
derived. It is relatively low in natural fertility and in organic
matter, but soil moisture, rising through capillarity from the
water table near the surface during the winter season, ordin-
arily is sufficient for a good crop.
Some farms in the area are located on the higher, fairly
well drained soils which are seldom flooded in summer, and
others on lower-lying fields subject to flooding during part of
the summer rainy season. Extensive drainage by means of
canals and ditches in recent years has reduced the danger from
sudden floods but, at the same time, occasionally has contributed
to a lack of soil moisture in times of drouth. At present the
water table ordinarily is found from two to four feet below the
surface during the major part of the growing season, which in
this section extends from November to March.

Rotation of crops is not practiced generally in growing po-

*Formerly Horticulturist in Charge, Sub-Tropical Experiment Station.








FERTILIZER EXPERIMENTS WITH POTATOES ON THE MARL
SOILS OF DADE COUNTY
By W. M'. FIFIELD and H. S. WOLFE*

CONTENTS
Page Page
Plan of Experiments ...... 4 Sources of Nitrogen .17
Fertilizer Analyses .............. 7 Muriate vs. Sulfate of Potash 25
Amounts of Fertilizer per Acre. 11 Manganese 25
Percentage of Nitrogen from Other Soil Amendments 29
Organic Sources ........ 14 Summary 38

INTRODUCTION

The marl soils of southern Dade County which are used for
potato production are of a peculiar calcareous formation quite
unlike those of any other soils in the United States. They are
alkaline, ranging from a pH of about 7.5 to about 8.5. Mechanical
analysis would classify this soil as a uniform silt loam, but chem-
ical analysis shows over 90 percent of calcium carbonate. Sand
is present only in very small percentage, and organic matter
constitutes about 5 percent. This marl, a sedimentary deposit,
varies throughout the area from a depth of a few inches to about
four feet and is underlaid with a porous limerock. In limited
areas muck is found with the marl, particularly in the numerous
small sink or pot hole formations and other low places.
The marl is interspersed throughout with remains of tiny
shells, evidently similar to those from which it originally was
derived. It is relatively low in natural fertility and in organic
matter, but soil moisture, rising through capillarity from the
water table near the surface during the winter season, ordin-
arily is sufficient for a good crop.
Some farms in the area are located on the higher, fairly
well drained soils which are seldom flooded in summer, and
others on lower-lying fields subject to flooding during part of
the summer rainy season. Extensive drainage by means of
canals and ditches in recent years has reduced the danger from
sudden floods but, at the same time, occasionally has contributed
to a lack of soil moisture in times of drouth. At present the
water table ordinarily is found from two to four feet below the
surface during the major part of the growing season, which in
this section extends from November to March.

Rotation of crops is not practiced generally in growing po-

*Formerly Horticulturist in Charge, Sub-Tropical Experiment Station.





















Fig. 2.-Summer growth of weeds on a South Dade farm. Note
growth in relation to height of tractor.
tatoes in Dade County, where the same field usually is planted to
potatoes every year. However, the fields used for potatoes dur-
ing the winter months produce a heavy green manure crop of
weeds (Fig. 2) or of a legume such as velvet beans (Fig. 3) or
sesbania during the spring and summer. This is plowed under
in the fall.
PLAN OF EXPERIMENTS
The experiments described in this bulletin mostly were
carried out on the East Glade farm of the Sub-Tropical Experi-
ment Station, located about six miles east of Homestead on the
north side of the Homestead or North Canal. The soil on this
farm is typical of the better potato soils of the area, being fairly
high, well drained and about three feet deep. Other experiments
described were performed in other sections of the adjoining
area, known as South Allapattah Gardens, where in the 1938
season about 7,500 acres of potatoes were planted.
Practically all of the potatoes now planted in Dade County
are of the Bliss Triumph variety, and all of these experiments
were performed with it. In general throughout the tests seed
pieces were 1% ounces in weight and were spaced 9 inches apart
in the rows. The earlier work was with 36-inch rows, and the
later with 38-inch rows. This size and spacing required from
28 to 30 bushels of seed per acre.
When the Station was first established in 1930 its equipment,
staff and facilities were exceedingly limited and remained so
for a number of years. Accordingly, although nearly all of the
growers were using machine planters and fertilizer distributors,
the early Station experiments had to be fertilized and planted





Fertilizer Experiments with Potatoes


Fig. 3.-Summer growth of velvet beans on a potato farm at South
Allapattah Gardens. Note high water in the ditch.
by hand. Later, as equipment was obtained, a change to ma-
chine methods was accomplished.
In planting and fertilizing by hand, furrows of about three
inches in depth were opened with a garden tractor, after the
field had been plowed and disked. The fertilizer was carefully
weighed out and distributed in the furrow uniformly. The fur-
rows were then closed and in about two days reopened for plant-
ing, thereby mixing the fertilizer with the soil. Planting was
done by hand with the aid of marking chains to insure proper
seed piece spacing. Four-row plots, each 1/72 acre, were planted
by this method. At harvest time the outside rows of each plot
and 5 feet from each end of the two center rows were discarded
to eliminate any possible competitive effect between treatments.
The comparison of treatments has been based on the yields
obtained from the remainder of the plots (1/180 acre) after the
discarded portions were eliminated.
Later, when machine planting was adopted, fertilizer was
distributed in two continuous narrow bands, approximately at
the same level as the seed piece and two inches from it on either
side. The distributor was adjusted as accurately as possible for






Florida Agricultural Experiment Station


each mixture. A single-row, assisted-feed planter was used.
Plots harvested for data with this method each consisted of a
single row, 75 feet long (1/184 acre). In all cases border plots
were planted around the field, and except where otherwise in-
dicated buffer rows were planted between treatment plots. Furth-
ermore, about 80 to 85 feet of row were actually planted, the
ends being trimmed off at harvest to eliminate errors due to
starting and stopping the planter. Variations from these meth-
ods occurred in some of the cooperative tests. These exceptions
are described under headings of the tests involved.
All of the fertilizer mixtures used on the Station farm were
hand mixed. In order to provide a uniform basis of interpreta-
tion, all of the test mixtures described in this publication have
been converted to a nitrogen basis, according to the 1935 Florida
fertilizer law, but early work as reported in the Station's Annual
Reports was done with formulas in which the nitrogen was ex-
pressed as ammonia.
Replicate plots of all treatments were used, varying in num-
ber in different tests, but always arranged in a randomized
manner. Time of planting, cultivation and spraying for foliage
diseases and insects were uniform throughout each test. The
vines were allowed to die before the tubers were dug.
All results are reported in terms of yield of No. 1 tubers (in-
cluding both A and B sizes) per acre. It was found that the
yield of No. 1 tubers, which always ran 85 to 95 percent of the
total yield, closely paralleled total yields, and, accordingly, rela-
tive results were the same. Grading was done in later years at
the Station farm (Fig. 1) with a standard hand grader equipped
with official-sized grading chains. Formerly it was done in the
packinghouse of the South Florida Potato Growers' Association.
Throughout this bulletin the term "significant" will be used
often in discussing differences between yields. Where two aver-
age yields differ only slightly, it is conceivable that the differ-
ences could be due to other factors than the two fertilizers being
tested. Statisticians have worked out methods for use with
prescribed plot technique which enable the research worker to
determine fairly well whether the difference in average yields
obtained is due to the difference in fertilizers being tested, or to
other variables. If the differences can be attributed to the fer-
tilizers they are said to be "significant." If the differences ap-
parently were caused by variables other than the fertilizers they
would not be significant.





Fertilizer Experiments with Potatoes


In this bulletin statistical significance was determined by a
mean difference in yield being at least 2.2 times as large as its
standard error. In a few tests, "Student's" methods were used.
The methods used are all described by Love'. The statistical
computations and constants are not shown in the tables except
where publication of the odds by "Student's" method is helpful
for interpretation.
FERTILIZER ANALYSES
The most common potato fertilizer analysis used in Dade
County at the time the Station was established (1930) was a 4-
8-52, with about 50 percent of the nitrogen derived from organic
sources. Experiments soon were begun using the 4-8-5 as a base
or control, to determine if a different analysis would give better
results.
The first experiments, begun in 1930 on the Station farm,
consisted of doubling and halving the percentages of N, P and K.
respectively, from the amounts in the common 4-8-5 analysis.
All fertilizers had 50 percent of the N derived from organic
sources, each contained manganese, and all sources of ingredients
were the same for each formula. Each mixture was applied at
the rate of 1,500 pounds per acre by hand and was tested in
quadruplicate plots, except in 1930-31 when duplicate plots only
were used. The tests were conducted on a field in which pota-
toes had been grown previously only one, the preceding (1929-30),
season.
As the work progressed the 4-4-5 treatment was discarded
because certain accidental variables occurred which rendered
the data valueless.
The average yields for all replications of each treatment
(except 4-4-5) are recorded in Table 1.
TABLE 1.-AVERLAGE YIELDS OF No. 1 TUBERS BUSHELSS PER ACRE) FROM THE
1930-33 FERTILIZER ANALYSIS TESTS.
Treatment 1930-31 1931-32 1932-33 Average
4-8 -5 140 170 200 170
4-16-5 142 177 218 180
4-8 -2V1 138 166 195 167
4-8 -10 136 193 209 180
2-8 -5 138 172 201 170
8-8 -5 115 150 186 150
2 4% nitrogen (N), 8% phosphoric acid (P), 5% potash (K).

1 Love, H. H. Application of statistical methods to agricultural re-
search. The Commercial Press, Ltd. 1938.





8 Florida Agricultural Experiment Station

In each of the three seasons the high nitrogen plot (8-8-5)
yielded significantly lower than any of the other treatments,
indicating that the additional nitrogen was not only a needless
expense but actually harmful. The differences in yield between
the other treatments were not very great, but the 3-year average
indicated a slightly higher yield for the high phosphate (4-16-5)
and high potash (4-8-10) treatments. On the strength of this,
and the fact that the low nitrogen treatment (2-8-5) yielded as
well as the standard treatment (4-8-5), a new analysis, 3-12-8,
was selected as embodying some of the trends indicated by the
general results of the test. The cost and source of ingredients
of this 3-12-8 were comparable to those of the 4-8-5.

The new 3-12-8 analysis then was tested with the 4-8-5 in
succeeding years. The first of these tests was conducted on the
Station farm in 1934-35. Each analysis was tested at the rate of
1,000, 1,500 and 2,000 pounds per acre, respectively, applied by
hand. The yields from four replications of each treatment were
averaged, with the results shown in Table 2, Series 1934-35.


TABLE 2.--AVERAGE YIELDS OF No. 1 TUBERS BUSHESS PER ACRE) IFROMI THE
1934-36 FERTILIZER ANALYSIS TESTS.

Series Analysis Rate per Acre (lbs.) Yield per Acre
4-8 -5 1,000 167
3-12-8 1,000 171
1934-35 4-8 -5 1,500 199
3-12-8 1,500 186
4-8 -5 2,000 194
3-12-8 2,000 197

Estes 3-12-8 2,000 248
4-8 -5 2,000 237

3-12-8 1,500 279
1935-36 4-8 -5 1,500 278
3-12-8 2,000 289
4-8 -5 2,000 287



Analysis of the data showed that there was no significant
difference in yield between the two analyses, even though at the
1,500-lb. rate the 4-8-5 showed a little higher average yield than
the 3-12-8.

Another test was conducted the same year on the commer-
cial farm of J. H. Estes. About an acre was planted (by machine)






Fertilizer Experiments with Potatoes


with each analysis at the rate of 2,000 pounds per acre, and from
each acre 20 representative plots were harvested at random. The
yields from the 20 plots of each treatment were averaged with
the results shown in Table 2, Series Estes.
In this test a slight but not significant increase in average
yield was noted for the 3-12-8 treatment.
Another test was made the following year (1935-36) on the
Station farm. The 3-12-8 and 4-8-5 analysis were tested in quad-
ruplicate plots at rates of 1,500 and 2,000 pounds per acre, applied
by machine. The average yields are given in Table 2, Series
1935-36. Again, no significant difference in yield was obtained
between the two analyses.
Since it was apparent that no appreciable differences in yield
were being obtained from analyses varying as widely as a 4-8-5
and a 3-12-8, it was thought wise to test differences in analysis
on a more intensive scale. Accordingly, a new series of tests was
instituted on the Station farm in 1937-38, in which the percent-
ages of phosphoric acid and potash in a basic 4-8-4 formula were
increased progressively, alone and in combination. The nitrogen
was not varied, but kept constant throughout at 4 percent, of
which half was derived from organic sources.
Data were secured from six replications of each of the 12
treatments, planted by machine. All fertilizer was applied at
the rate of 1,500 pounds per acre, and all of it contained man-
ganese. The average yield from each treatment is given in
Table 3, for each year.

TABLE 3.-AVERAGE YIELD OF No. 1 TUBERS (BUSHELS PER ACRE) FROM TIHE TREAT-
LENTS COMIPOSING THE FERTILIZER ANALYSIS TESTS, 1937-39.

Analysis 1937-38 1938-39
4-8-4 330 174
4-8-6 331 169
4-8-8 334 176
4-8-10 333 171
4-12-4 342 172
4-.12-6 327 179
4-12-8 339 182
4-12-10 331 168
4-16-4 329 169
4-16-6 323 174
4-16-8 336 172
4-16-10 341 179

The yields were extremely high the first year of this test and
fairly low the second (a dry) year. Each year, however, a sur-
prising similarity in yield was obtained from all 12 treatments,





























Fig. 4.-Portion of the 1937-38 potato fertilizer analysis tests. Note
uniform vine growth among all plots.

and the small differences in yield between them were found not
to be significant. In other words, no significant increase in yield
was obtained from increasing the phosphoric acid beyond 8
percent, or from increasing the potash content beyond 4 percent.
No difference was noted in vine growth or quality of tubers
between treatments either year (Fig. 4).
It should be noted that this last experiment was conducted
on land which had been fertilized and planted in potatoes for
five successive preceding years. Since the authors have noted
indications that some fertilizer residue tends to carry over from
one year to another in these marl soils, there is a possibility
that sufficient residual phosphate and potash were present to
offset additional quantities added in the higher analyses. Since
the lowest analysis tested (4-8-4) yielded as well as the highest
(4-16-10), it would seem desirable to test even cheaper formulas,
especially in view of the good results from the 2-8-5 and 4-8-22
analyses as shown in Table 1, on land with no previous history
of potato culture.
These analysis tests, conducted over a period of years, in-
dicate that there seems to be no justification for using analyses,






A r'tililzcr Lp .rVinllclits uwit/i Potatoce


to be applied at rates of about 1,500 to 2,000 pounds per acre, with
more than 3 or 4 percent nitrogen, 8 percent phosphoric acid
and 4 or 5 percent potash.

AMOUNTS OF FERTILIZER PER ACRE
The rate at which fertilizer should be applied per acre is,
of course, influenced greatly by the analysis of the fertilizer.
At the time these experiments were begun a 4-8-5 analysis was
the one most commonly in use. Therefore, it was used exten-
sively for the basic tests. A few other analyses were used from
time to time. The tests were distributed over a number of
years and over a number of different farms, in order to get as
comprehensive data as possible.
The first test was performed on the Station farm in 1933-34.
The fertilizer was distributed in the furrows by hand and mixed
with the soil two days before the seed pieces were planted.
Four treatments were used, 500, 1,000, 2,000 and 3,000 pounds
per acre, respectively, of a 4-8-5 analysis, in which two-thirds
of the nitrogen was from organic sources. Four replications
of each treatment were planted. The average yields from each
treatment are shown in Table 4, Series A.
The 2,000-pound rate yielded higher than any of the other
treatments. It yielded enough more than the 1,000-pound rate to
justify the additional cost. The reduced yield of the 3,000-pound
rate was probably due to injury of the potato sprouts, as it was
noted that these plots showed slower emergence than did the
others. This injury might not have occurred had the fertilizer
been distributed by the machine band method, or had it been
applied in the furrows earlier before planting.
Another test was conducted on the Station farm the same
year in connection with another experiment. A 4-8-5 was also
used in this test, but in one series 33 percent of its nitrogen was
derived from organic sources, and in the other 66 percent was
so derived. Each mixture was applied by hand at both 1,000-
pound and 2,000-pound per acre rates. The plot arrangement
was similar to that of the previous test. The replicate yields
were averaged with the results given in Table 4, Series B.
With both types of mixture, the 2,000-pound rate signifi-
cantly outyielded the 1,000-pound rate. A comparison of the 33
percent and 66 percent mixtures will be presented later (Table
7, Series 1933-34).






Florida Agricultural Experiment Station


In another test on the Station farm in 1933-34 nitrate of soda
was compared with sulfate of ammonia as sources of inorganic
nitrogen in a complete 4-8-5 analysis, and muriate of potash
with sulfate of potash as potash sources in the same analysis.
Each treatment was tested at both 1,000 and 2,000 pounds per
acre, in triplicated plots, with the results given in Table 4,
Series C.

TABLE 4.-AVERAGE YIELDS or No. 1 TUBERS (BUSHELS PER ACRE) FOR VARIOUS
RATES OF APPLICATION FOR 4-8-5 FERTILIZER, 1933-34.
Series Rate per Acre (lbs.) Fertilizer Variable Yields per Acre
500 Standard mix 176
A 1,000 Standard mix 203
2,000 Standard mix 222
3,000 Standard mix 202
1,000 33% Organic N 184
B 2,000 33% Organic N 197
1,000 66% Organic N 203
2,000 66% Organic N 222
1,000 Inorg. N as Nitrate of Soda 165
2,000 Inorg. N as Nitrate of Soda 164
1,000 Inorg. N as Sulfate of Ammonia 181
C 2,000 Inorg. N as Sulfate of Ammonia 197
1,000 Potash all as sulfate 204
2,000 Potash all as sulfate 222
1,000 Potash all as muriate 207
2,000 Potash all as muriate 209

These data are not harmonious. The nitrate of soda plots
showed no increase in yield for the higher rate of application.
The sulfate of ammonia showed a statistically significant in-
crease. The sulfate of potash plots also showed such an increase
for the 2,000 pounds application, but the muriate plots did not.
The comparison of these sources of nitrogen and potash as they
in themselves affect yields will be discussed later.
The following year (1934-35) the first test was repeated in
revised form on the Station farm. The 500-pound rate was
eliminated and a 1,500-pound rate was added. Also another
analysis, 3-12-8, was added, and this was tested at 1,000, 1,500
and 2,000-pound rates. In both mixtures the nitrogen was de-
rived two-thirds from organic sources. Four replications were
used and the fertilizer again was applied by hand. The results
from Table 2 are given again for convenience in Table 5, Series
1934-35.
The results indicate that with both analyses the average
yields of the 1,500-pound rate were about as good as those of
the 2,000-pound rate. The higher yield of the 2,000-pound rate






Fertilizer Experiments with Potatoes


of 3-12-8 was found, upon analysis of the replicate plot data,
to be not significant. In the 4-8-5 test the 3,000-pound rate out-
yielded the lower rates, and with both analyses the 1,000-pound
rate was outyielded by the higher rates.
This same year (1934-35) another test was carried out, this
time on the commercial farm of J. M. Holferty. A 4-8-5 analysis
(50% of nitrogen from organic sources) was used, applied by
machine. Approximately one acre was planted at each of two
rates, 1,300 and 2,000 pounds per acre. At digging time 10
plots, each 100 feet long, were selected at random for harvest
from each block. The No. 1 tubers were graded from each
replicate plot and averaged, with results given in Table 5, Series
Holferty A. In this instance, the 2,000-pound rate significantly
outyielded the 1,300-pound rate.
In another field of the same grower, another similar test was
performed two weeks later. The results are found in Table 5,
Series Holferty B. This time, although the 2,000-pound rate
showed a slight increase in average yield over the 1,300-pound
rate, the difference was not statistically significant and thus ap-
plication of the additional 700 pounds of fertilizer was not
justified.
Another test was performed on the Station farm in 1935-36,
comparing 1,500 and 2,000-pound rates of both a 4-8-5 and a
3-12-8 analysis (each with nitrogen 66%' from organic sources).
Six replications of each were planted. This time the fertilizer
was applied by machine. The data were averaged for the various
replications, as shown in Table 5, Series 1935-36.
TABLE 5.-AVERAGE YIELDS Or No. 1 TUBERS (BUSHELS PER ACRE) FOR VARIOUS
RATES OF FERTILIZER APPLICATION, 1934-36.
Series Rate per Acre (Ibs.) Analysis Yields per Acre
1,000 4-8-5 167
1,500 4-8-5 199
2,000 4-8-5 194
1934-35 3,000 4-8-5 226
1,000 3-12-8 171
1,500 3-12-8 186
2,000 3-12-8 197
Holferty A 1,300 4-8-5 179
2,000 4-8-5 209
Holferty B 1,300 4-8-5 212
2,000 4-8-5 224
1935-36 1.500 4-8-5 278
2.000 4-8-5 287
1,500 3-12-8 279
2,000 3-12-8 289





Florida Agricultural Experiment Station


Here, with both analyses, the 2,000-pound rate slightly out-
yielded the lesser rate in average yield but the differences were
not great enough for statistical significance. Therefore, the ex-
pense of the extra 500 pounds of fertilizer was not justified.
In 1937-38 still another Station farm test was made of the
1,500 and 2,000-pound rates, in connection with testing 4-8-5
mixtures in which 33, 50 and 66 percent, respectively, of the
nitrogen was derived from organic sources. The fertilizer was
applied by machine. Four replicate plots were planted, and
their yields averaged, as given in Table 6.
TABLE 6.-AVERAGE YIELDS OF No. 1 TUBERS (BUSHELS PER ACRE) FOR VARIOUS
RATES OF APPLICATION OF A 4-8-5 FERTILIZER, 1937-38.
Rate per Acre (lbs.) % of N from Organic Sources Yields per Acre
1,500 33 302
2,000 33 305
1,500 50 304
2,000 50 311
1,500 66 289
2,000 66 296

Again in this test a slightly increased average yield was ob-
tained from the heavier fertilizer application but the increase
was too small for statistical significance.
It is apparent that no single rate of application will give the
same results in all seasons or under all conditions in the same
season. The data of these experiments generally agree, however,
that 1,000 pounds of 4-8-5 per acre is probably not sufficient for
best results, and that 3,000 pounds is probably too much. There
is more definite agreement that the correct amount is from
1,500 to 2,000 pounds per acre. In the great majority of instances
no significant yield differences were obtained between these two
amounts, and certainly, that being the case, the 1,500-pound
rate would be the more profitable for regular use. In a season
in which higher prices than usual might be expected, or in
an unusually wet season, or on soil more moist than that occur-
ring on the Station's East Glade farm, it is possible that the
2,000-pound rate would be more profitable. It should be pointed
out here that the rates of application discussed refer only to the
generally used analyses of 4-8-5 and 3-12-8, and not to mixtures
containing higher or lower concentrations of plant food.
PERCENTAGE OF NITROGEN FROM ORGANIC
SOURCES
Since the percentage of nitrogen derived from organic
sources markedly affects the expense of mixed fertilizers, ex-







Fertilizer Experiments with Potatoes


periments were begun in the fall of 1933 to study the effect on
yields of varying this percentage in a standard 4-8-5 analysis.
The first year's test was limited to a comparison of 33 and
66 percent of the nitrogen so derived. All sources of ingredients
of the two fertilizers were similar, and both included manganese.
Nitrogen was derived from cottonseed meal, fish scrap and
sulfate of ammonia, phosphate from superphosphate, and potash
from sulfate of potash. Each treatment was replicated three
times and the fertilizer was applied by hand. Each mixture was
applied at both 1,000 and 2,000-pound rates per acre. The re-
plicate plot yields were averaged to obtain the data shown in
Table 7, Series 1933-34. In this test, the 66 percent treatment
outyielded the 33 percent treatment at both rates of application
and significantly enough to offset the additional cost of the 66
percent mixture.

TABLE 7.-AVERAGE YIELDS OF NO. 1 TUBERS (BUSHELS PER ACRE), RESULTING
FROM VUSE OF A 4-S-5 FERTILIZER WITH VARYING PERCENTAGES or NITROGEN
DERIVED FROM ORGANIC SOURCES.


% of N from
Organic Sources


33
66
33
66
33
66


Rate per Acre
(lbs.)


1,000
1,000
2.000
2,000
1.500
1,500


33 1.500
1935-36 50 1.510
66 1,500
33 1.500
1936-37 50 1,500
66 1,500
33 1,500
50 1.510
1937-38 66 1.500
33 2.000
50 2.000
66 2.000


Yields per Acre
184
203
1]7
222
208
199
276
280
278
194
184
182
302
304
289
305
311
296


The following year (1934-35) both percentages were again
tested but this time only at 1,500 pounds per acre. Other factors,
including application of the fertilizer by hand, were the same
as in 1933-34. The average yields are given in Table 7, Series
1934-35. These yields are not significantly different, and since
the 33 percent mixture was cheaper, it was therefore more
profitable.


Series


1933-34


1934-35






Florida Agricultural Experiment Station


The following year (1935-36) the same tests were repeated
with similar procedure, except that the number of replications
was increased to 10. In addition, a 50 percent treatment was
included. The average yields are given in Table 7. Here again
the yields were not significantly different, and the 33 percent
treatment again was most profitable.
In the 1936-37 season the same experiment was repeated with
technique similar to that of the previous year. The average
yields are shown in Table 7. Again this year the 33 percent
treatment yielded as well as the others and was therefore most
profitable.
All treatments were repeated in the 1937-38 season, this
time each mixture being applied at both 1,500 and 2,000-pound
rates per acre. Also, this year the fertilizer was applied by
machine, with eight replications of each plot. Average yields
are given in Table 7. Again this year, and at both rates, the
33 percent treatment yielded as well as either of the others, and
therefore again was most profitable.
Thus, in four of the five years of testing, the 33 percent
mixture yielded as well as the mixtures containing a higher
percentage of N derived from organic sources.
A factor considered most important in selecting the more
slowly available sources of nitrogen, and the percentage of them
used in the fertilizer, is amount of rainfall. Therefore, for com-
parative purposes, the rainfall data including these five years,
as recorded officially at the Sub-Tropical Experiment Station
for the respective crop seasons, are given in Table 8.
There seems to be no definite relation of treatment results
to rainfall during the seasons in which these tests were con-
ducted. The first season (1933-34) higher yields were received
from the 66 percent mixture. That year an unusually heavy
rainfall occurred in October, but the potato plots were not
planted until December 8, so that there is not much likelihood
of the October rain exerting much influence on the crop. In
the 1935-36 season the plots were planted December 2. The
season from planting to harvesting (March 18) was even wetter
than in 1933-34, and yet the 33 percent mixtures yielded as well
as those containing higher percentages of N derived from organic
sources.
These tests were conducted over seasons which varied con-
siderably in amount of rainfall, so that it seems quite logical to
conclude from them that ordinarily, with other factors equal,






Fertilizer Experiments with Potatoes


mixtures containing no more than 33 percent of their nitrogen
from organic sources should give as satisfactory results as those
of higher percentages thus derived. Of course, these conclusions
are drawn from experiments in which the organic sources of
nitrogen were limited to two typical water-insoluble organic,
fish scrap and cottonseed meal.
TABLE 8.-MONTILY AND TOTAL R.\IrALL (IN INCHES) RECORDED DURING THE
CROP SEASONS FROI-M 1932 TO 1940, HOMESTEAD, FLORIDA.*

Total
October November December January February March (6 months)
1931-32 6.95 1.85 0.26 3.21 0.47 0.92 13.66
1932-33 12.90 4.15 0.81 1.39 0.20 3.05 22.50
1933-34 22.95 1.39 0.33 2.00 0.94 2.13 29.74
1934-35 3.22 0.37 0.41 0.23 0.25 0.53 5.01
1935-36 7.41 5.51 0.69 2.50 4.59 4.83 25.53
1936-37 3.37 3.52 0.89 0.65 2.70 4.41 15.54
1937-38 7.41 0.37 0.55 2.69 0.81 1.72 13.55
1938-39 4.41 2.44 0.71 0.93 0.56 0.09 9.14
1939-40 16.79 0.95 1.80 1.02 2.44 2.93 25.93

* None of the potato tests described in this bulletin was planted before
November 10 in any year.
Additional experiments were conducted on sources of nitro-
gen, in which mixtures containing all water-soluble nitrogen
were compared with those containing 50 percent of their N from
numerous organic sources. These are described below.
SOURCES OF NITROGEN
These investigations were begun in the fall of 1933, when a
comparative study of sulfate of ammonia and nitrate of soda,
as inorganic sources of nitrogen in complete fertilizer, was
started. The first series of trials was conducted over a period
of four years. A 4-8-5 fertilizer was used throughout. The first
three years it was applied in the furrow by hand and the last
year by machine. The first year it was applied at the rate of
2,000 pounds per acre. In each of the next three years it was
applied at 1,500 pounds per acre.
The nitrogen of the fertilizer was derived 25 percent from
fish scrap, 25 percent from cottonseed meal, and 50 percent from
either sulfate of ammonia or nitrate of soda, according to the
mixture tested. In other words, 50 percent of the nitrogen was
derived completely from one or the other of these two inorganic
sources.
The first year (1933-34) three replications of each treatment
were planted. The second (1934-35) year, four, the third






Florida Agricultural Experiment Station


(1935-36) year, 10, and the fourth (1937-38) year, six replications
were used. The tests were not planted in 1936-37. The repli-
cate plot yields for each treatment were averaged each year
and the average annual yields are given in Table 9.

TABLE 9.-AVERAGE YIELDS OF No. 1 TUBERS (BUSHELS PER ACRE) FROM FERTILIZER
TREATMENTS COMPARING INORGANIC SOURCES OF NITROGEN IN COMPLETE
FERTILIZERS.

Source 1933-34 1934-35 1935-36 1937-38 Average
Nitrate of soda 164 191 284 305 236
Sulfate of ammonia 197 199 278 292 241

There was no appreciable difference between the two treat-
ments except in the first year, when sulfate of ammonia yielded
better than nitrate of soda. Just why this difference should
have occurred the first year is not explainable on a rainfall
basis, or on any other readily apparent basis. At any rate,
since the four-year average indicates no significant difference
in yield between the two, and since the first year's data were in
favor of sulfate of ammonia, it is logical to conclude that this is
probably the better source for these soils, especially since its cost
per unit of nitrogen was lower than that of nitrate of soda.
A more comprehensive test of nitrogen sources was begun
in the fall of 1937. A number of water-soluble and water-insolu-
ble sources were tested in a 4-8-5 complete fertilizer, with man-
ganese added. The source of phosphoric acid (superphosphate)
and potash (sulfate of potash) remained the same for all treat-
ments, except for allowances made for the small quantities of
these elements carried by some of the organic.
Although most ordinary commercial potato fertilizers contain
a number of organic sources of nitrogen, it was decided arbi-
trarily in this experiment to test the sources singly, deriving
half the nitrogen from sulfate of ammonia and half from the
organic source being tested. The materials thus tested were
cottonseed meal, fish scrap, blood-and-bone tankage, dried blood,
milorganite and urea. In addition, a cyanamid test was included,
but since 50 percent of cyanamid nitrogen was considered too
much, the nitrogen in this treatment was derived 20 percent
from cyanamid and 80 percent from sulfate of ammonia. Five
other treatments were included. In three of these, all (100 per-
cent) of the nitrogen was derived from sulfate of ammonia,
nitrate of soda or ammonium phosphate, respectively. In the





Fertilizer Experiments with Potatoes


fourth, the regular Station control 4-8-5 formula was used in
which 25 percent of the nitrogen was derived from cottonseed
meal, 25 percent from fish scrap and 50 percent from sulfate of
ammonia. The nitrogen in the last treatment was derived half
from nitrate of soda and half from sulfate of ammonia. Thus in
all there were 12 treatments.
Urea and cyanamid are synthetic organic which resemble
the inorganic nitrogen sources more closely than they do the
natural protein organic, in availability to plants and in solubility
in water. They may be distinguished for our purposes as water-
soluble organic, in contrast to the older water-insoluble types
like cottonseed meal and fish scrap.
The composition of the 12 fertilizer treatments as they were
mixed at the Station is given in Table 10.
All of the fertilizers were applied at the rate of 1,500 pounds
per acre with a machine distributor. The first year eight repli-
cations of each treatment were used. In the second and third
years the number was reduced to six. Each plot harvested for
data consisted of one row 75 feet long. The rows were spaced
76 inches apart (twice the ordinary distance), but in converting
the yield data to an acre basis, a plot was considered arbitrarily
as 75 feet x 38 inches or 1/184 acre.
This departure from ordinary plot technique deserves brief
discussion. In placing the rows twice the ordinary distance
apart the object was simply to eliminate planting of the buffer
rows. Satisfactory evidence from previous observations indicated
that there would be no competitive effect between roots and
fertilizers in adjacent plots. In converting the data to an acre
basis it was recognized that while the plots actually were 75 feet
x 76 inches, from a practical standpoint conversion on this
basis would yield values far below normal commercial yields.
and this would be misleading, since the actual yields per plant
were quite normal. As the object of the test was to determine
merely the relative effect of the various treatments, and not the
absolute value of each, the only sensible procedure was to con-
vert the yields on a normal basis of 38-inch rows. The fertilizer
and seed, as well as the yields, were computed on the latter
basis. The average yields for each year are given in Table 11.
A primary consideration in the selection of nitrogen sources
for potato fertilizers has been their performance in relation to
soil moisture. Growers usually consider that the water-insoluble










TABLE 10.--CoMPOSITION, IX POUNDS PER TON, OF THE FERTILIZERS COMPOSING THE SOURCE OF NITROGEN TESTS, 1937-40.


0a
E M 0 M u
Treatment, with the Per- S d o 0 H
centage N each Source Con- < ,
tributes to the Total N in 0 ., 0 W 0
the Formula o C4
Oto oo |0 ,00 o |o &O c g
Io -o |i j, .0 .o go S, go ^o '- 0^ |

Sulfate of ammonia 100% 381 ---- 800 209 100 510
Nitrate of soda 100% 534 800 209 100 357
Nitrate of soda 50% 190 267 800 209 100 434
Ammonium phosphate 100% 500 300 209 100 891
Cottonseed meal 50% 190 615 --. 755 190 100 150
Fish scrap 50% 190 421 740 209 100 340
B & B tankage 50% 190 615 680 209 100 206
Dried blood 50% 190 308 800 209 100 393
Urea 50% 190 95 800 209 100 606
Milorganite 50% 190 696 730 209 100 75
Cyanamid 20% 305 76 800 209 100 510
Control-cottonseed meal 25 %,
fish scrap 25% 190 308 210 745 200 100 247
: Balance of N from sulfate of ammonia.






Fertilizer Experiments with Potatoes


TABLE 11.-AVERAGE YIELDS OF No. 1 TUBERS (BUSHELS PER ACRE) FROM THE
VARIOUS SOURCE-OF-NITROGEN TREATMENTS, USING A 4-S-5 ANALYSIS AT 1,500
POUNDS PER ACRE.
Fertilizer
Nitrogen Source Cost 1937-38 1938-39 1939-40 Average
1,500 Pounds
100% from sulfate of ammonia $17.96 237 144 249 210
100% from nitrate of soda 19.35 240 144 246 210
50% from nitrate of soda* 18.65 242 149 239 210
100% from ammonium
phosphate 22.38 242 151 247 213
50% from cottonseed meal* 21.84 256 145 241 214
50% from fish scrap* 22.64 246 150 239 212
50% from blood-and-bone
tankage* 22.55 263 150 257 223
50% from dried blood* 23.16 256 148 255 220
50% from urea* 18.37 249 155 238 214
50% from milorganite* 22.33 246 170 255 224
20% from cyanamid* 18.35 252 145 237 211
25% from fish scrap, 25% cotton-
seed meal 22.24 245 154 236 212
Balance of N from sulfate of ammonia.
sources are best in a wet year. Referring back to Table 4 and
to the seasons 1937-38 through 1939-40, it will be noted that these
seasons were quite variable with regard to rainfall. The 1937-38
season may be considered as intermediate, with a total of 13.55
inches. The 1938-39 year was a dry one, with only 9.14 inches,
as was reflected in the lower yields. The 1939-40 season was an
unusually wet one, with rainfall well distributed throughout
the growing season. Thus it may be considered that the test
was run under conditions which varied considerably from dry
to wet. With all of this variation, the yields did not vary much
among the treatments, and therefore the experiment was termi-
nated with the 1939-40 test.
The results first will be discussed by individual years. It
was found that a minimum difference in yield of 7 bushels per
acre was necessary for significance in the 1937-38 data. There-
fore, the treatments sulfate of ammonia, nitrate of soda, the
combination of these two, ammonium phosphate, fish scrap,
milorganite and the fish scrap-cottonseed meal combination as
a group may be considered as all having yielded about alike.
Slightly higher yielding were urea and cyanamid and a little
higher yielding than these were tankage, dried blood and cotton-
seed meal. The yields of all 12 treatments were so nearly alike,
however, that fine distinctions in yield differences are hardly
justified.
It was found that at least a 6-bushel difference was required
for significance in the 1938-39 data. On this basis, all of the






Florida Agricultural Experiment Station


treatments except urea, milorganite and the fish scrap-cottonseed
meal combination yielded about alike. The latter three may be
considered as higher yielding than some of the others, but only
the milorganite significantly outyielded all of the others.
In 1939-40 a 7-bushel difference was found necessary for
significance. This year milorganite, dried blood and tankage
stood out as being significantly highest yielding, although minor
significant differences occurred between some of the other
treatments, and a few-sulfate of ammonia, nitrate of soda and
ammonium phosphate-yielded almost the same as these three
water-insoluble organic.
From this brief consideration of the yearly data it will be
noted that while certain trends in yield differences appear, the
differences in most cases are so small as to leave some doubt
as to their practical application. Conclusions can best be drawn
from the data secured by averaging the treatment yields over
the three-year period.
For these data (last column, Table 11) it was found that a
difference of more than 4 bushels per acre was necessary to
establish significance. On this basis the treatments sulfate of
ammonia, nitrate of soda, the sulfate of ammonia-nitrate of soda
combination, ammonium phosphate, cottonseed meal, fish scrap,
urea, cyanamid and the fish scrap-cottonseed meal combination
all yielded about alike. Yielding slightly but significantly
higher were milorganite, tankage and dried blood.
In order to help determine the relative profitableness of the
treatments, the fertilizer cost per bushel of potatoes produced
was determined from these data for each season. The costs are
shown in Table 12.
TABLE 12.-FERTILIZER COST PER BUSHEL OF POTATOES FROM TIE VARIOUS SOURCE
OF-NITRO"EN TREATMENTS. (ARRANGED IN ORDER OF AVERAGE COST BASED ON
AVERA.;E YIELD FOR TREE YEARS.)


50% fror
100% fror
20% fror
50% fror
100% fror
50% fror
50% fror
50% fror
50% fror


Nitrogen Source 1937-38 1938-39 1939-40
n urea* $ .073 $ .119 $ .077
n sulfate of ammonia .076 .125 .072
n cyanamid* .073 .127 .077
n nitrate of soda* .077 .125 .078
n nitrate of soda .081 .133 .079
m milorganite* .091 .131 .088
m blood-and-bone tankage* .086 .150 .088
n cottonseed meal* .085 .151 .091
n dried blood* .090 .156 .091


25% from fish scrap, 25% cottonseed
meal*
100% from ammonium phosphate
50% from fish scrap*


Average
$ .086
.086
.087
.089
.092
.100
.101
.102
.105


.091 .153 .094 .105
.092 .144 .091 .105
.092 .151 .095 .107


* Balance of N from sulfate of ammonia.






Fertilizer Experiments with Potatoes


Each year, and for the three-year average, the fertilizer
cost of producing a bushel of No. 1 potatoes was less from the
water-soluble sources-urea, sulfate of ammonia, cyanamid and
nitrate of soda-than from the other sources.
Since it has already been shown that cottonseed meal, am-
monium phosphate, fish scrap and the fish scrap-cottonseed
meal combination were significantly outyielded by milorganite,
dried blood and tankage, there is no question but that the latter
three were more profitable than these others, which cost about
the same.
In comparing milorganite, dried blood and tankage with the
cheaper sources-urea, sulfate of ammonia, cyanamid and nitrate
of soda-however, a little more difficulty occurs.
Considering the first three treatments as one group and
the latter four treatments as another group, by averaging the
data for each it is calculated that the first, or insoluble materials,
group required $4.17 per acre more of fertilizer cost to produce
an additional 11 bushels of No. 1 potatoes. These potatoes had
an undug field value of about 82 cents per bushel according to
Howard and Steffani3, or $9.02 for the 11 bushels. Thus the extra
$4.17 cost for fertilizer of the first group returned an increased
yield worth $9.02, as compared with the second group, or a dif-
ference of $4.85 per acre in favor of the more insoluble organic
nitrogen group.
The above calculations are presented for the benefit of
those who are interested in knowing just what the profit and
loss of the various treatment groups were under the conditions
in which the experiments were performed. From a broader and
more practical viewpoint, however, the authors believe that
definite conclusions on the basis of these particular "cost and
returns" data alone are not warranted, because conditions are
almost never the same in any two years. Fertilizer costs, yields
and returns vary considerably. Furthermore the calculations
are based on average yields, which in themselves are only sig-
nificant within certain limits, as already pointed out. Also it
must be recognized that as yields increase on an acre of land,
the costs per bushel for land rent, machinery use, spray mater-
ials, seed, labor and supervision decrease, which probably would
more than offset small increases in fertilizer cost.
It would seem more sensible, therefore, to consider the re-

3 Howard, R. H. and C. H. Steffani. A study of potato farming in
Dade County. Florida, seasons 1934-35 to 1938-39. Fla. Agr. Ext. Ser.
Mimeo. Circ. Dept. Agr. Econ. Potatoes AE4. 1939.






24 Florida Agriciultural Experiment Station
suits in more general terms. From this standpoint it is concluded
that in general as used in this experiment, the fertilizer sources
milorganite, blood-and-bone tankage (medium grade) and dried
blood slightly outyielded the other sources. The differences in
yield, although small, were profitable for the three-year period
based on cost and returns data cited but in certain of the years
some of the water-soluble sources were equally as profitable.
It would seem wise to continue the use of either milorganite,
dried blood, or blood-and-bone tankage in fertilizers for potatoes
in Dade County for the present. There is no evidence to indi-
cate that any one of these three is better than the other. Since
prices fluctuate from time to time, whichever one is cheaper
per unit of nitrogen at the time of purchase is the one to choose.
Sulfate of ammonia and nitrate of soda yielded alike, as sole
sources of nitrogen, and no advantage was demonstrated from
combining the two on a half and half basis. Price differential
per unit of nitrogen would accordingly determine the preference
for use in potato fertilizers in this area.
Ammonium phosphate was the least economical of the water-
soluble nitrogen sources tested. Although its performance was
quite satisfactory, its use cannot be recommended because of its
higher cost. It is possible, however, that it might be a desirable
source for use in high analysis fertilizers, which were not in-
cluded in the scope of this test.
The use of urea and cyanamid is worthy of consideration.
They both produced yields in the upper range of the water-solu-
ble sources, and both sources were among the treatments show-
ing least fertilizer cost per bushel. Since many growers are of
the impression that urea leaches less readily from the soil than
do some of the other water-soluble sources, this would give it an
apparent advantage in wet seasons, especially if an entirely
water-soluble fertilizer is desired. No data are available for
Dade County soils on the leaching properties of urea.
The relatively good showing of the 20 percent cyanamid
treatment is noteworthy. Some fertilizer manufacturers would
like to use a small amount of this ingredient in their mixtures
because of its conditioning effect. The data of this experiment
indicate that there should be no objection to this practice so far
as potato fertilizers for these soils are concerned.
The performances of cottonseed meal and fish scrap indicate
that they are less desirable than the other water-insoluble sources
tested, and, because of their present higher cost, show no econ-
omical advantage over the water-soluble sources with which
they were also compared.






Fcrtilizcr Expcriments w-ith Potatocs


MURIATE VS. SULFATE OF POTASH
There has been a great deal of debate among growers as to
the relative merits of muriate and sulfate of potash for potato
fertilizers. A series of experiments was begun in the fall of 1933,
testing these two ingredients. Each was used as the sole source
of potash in a regular 4-8-5 fertilizer, with manganese. The rest
of the mixture in each case was composed of sulfate of ammonia,
fish scrap, cottonseed meal and superphosphate.
The first two years, four replications of each treatment were
planted. The third year 10 replications and the last year six
replications were used. The first three years the fertilizer was
applied by hand. The last year it was applied by machine. The
tests were not conducted in 1936-37. The first year a ton per
acre was used, but in each of the other three years the fertilizer
was applied at the 1,500 pound rate. The plots were on different
ground each year.
The replicate plot yields each year were averaged and the
annual average yields from each treatment are given in Table 13.
TABLE 13.-AVERAGE YIELDS OF NO. 1 TUBERS (BISIELS PER ACRL) FROM PLOTS
COMPARING THE MI-RIATE AND SU-LATE FORM AS SOURCE Or POTASI IN A
4-8-5 FERTILIZER.
Source 1933-34 1934-35 1935-36 1937-38 Average
Sulfate of potash 222 199 278 298 249
Muriate of potash 209 189 281 301 245

The data of Table 13 indicate only slight differences in yield
of tubers between the two sources of potash, and these differ-
ences were found not to be statistically significant. The findings
of this experiment indicate that either source may be used with
equal results.
It should be noted that each year these tests were carried
out in a different field. Just what effect would be had by using
either source continually on the same field remains to be de-
termined.

MANGANESE
As a result of the pioneering work of Skinner and Ruprecht4
and of leading growers, most of the potato growers in the Home-
stead area were using manganese sulfate in their fertilizers by
the time the Sub-Tropical Experiment Station was established

4 Skinner, J. J., and R. W. Ruprecht. Fertilizer experiments with
truck crops. Fla. Agr. Exp. Sta. Bul. 218, 1930.






Fcrtilizcr Expcriments w-ith Potatocs


MURIATE VS. SULFATE OF POTASH
There has been a great deal of debate among growers as to
the relative merits of muriate and sulfate of potash for potato
fertilizers. A series of experiments was begun in the fall of 1933,
testing these two ingredients. Each was used as the sole source
of potash in a regular 4-8-5 fertilizer, with manganese. The rest
of the mixture in each case was composed of sulfate of ammonia,
fish scrap, cottonseed meal and superphosphate.
The first two years, four replications of each treatment were
planted. The third year 10 replications and the last year six
replications were used. The first three years the fertilizer was
applied by hand. The last year it was applied by machine. The
tests were not conducted in 1936-37. The first year a ton per
acre was used, but in each of the other three years the fertilizer
was applied at the 1,500 pound rate. The plots were on different
ground each year.
The replicate plot yields each year were averaged and the
annual average yields from each treatment are given in Table 13.
TABLE 13.-AVERAGE YIELDS OF NO. 1 TUBERS (BISIELS PER ACRL) FROM PLOTS
COMPARING THE MI-RIATE AND SU-LATE FORM AS SOURCE Or POTASI IN A
4-8-5 FERTILIZER.
Source 1933-34 1934-35 1935-36 1937-38 Average
Sulfate of potash 222 199 278 298 249
Muriate of potash 209 189 281 301 245

The data of Table 13 indicate only slight differences in yield
of tubers between the two sources of potash, and these differ-
ences were found not to be statistically significant. The findings
of this experiment indicate that either source may be used with
equal results.
It should be noted that each year these tests were carried
out in a different field. Just what effect would be had by using
either source continually on the same field remains to be de-
termined.

MANGANESE
As a result of the pioneering work of Skinner and Ruprecht4
and of leading growers, most of the potato growers in the Home-
stead area were using manganese sulfate in their fertilizers by
the time the Sub-Tropical Experiment Station was established

4 Skinner, J. J., and R. W. Ruprecht. Fertilizer experiments with
truck crops. Fla. Agr. Exp. Sta. Bul. 218, 1930.






26 Florida Agricultural Experiment Station

in 1930. The usual amount of manganese sulfate added was 200
pounds per ton but some growers were using as much as 400
pounds per ton. Experiments were started by the Station in the
fall of 1931 to determine the effect on yields of lesser amounts
of manganese, and of the residual effect of manganese.
RATE OF APPLICATION
A series of plots was laid out on the East Glade farm to be
continued over a period of years. Four manganese treatments
(65 percent manganese sulfate) were included: 0 lbs., 50 Ibs., 100
Ibs. and 200 Ibs. per ton of 4-8-5 fertilizer, respectively. The
fertilizer was applied at the rate of 1,500 pounds per acre and was
distributed in the furrow by hand. The test included three repli-
cate plots of each of the four treatments. Average yields from
each treatment are given in Table 14.
TABLE 14. YIELDS OF No. 1 TUBERS (BUSITELS PER ACRE) RESULTING FROM VARIOUS
RATES OF APPLICATION OF MANGANESE SULFATE PER TON OF 4-8-5 FERTILIZER.
Season 0 lbs. 50 lbs. 100 lbs. 200 lbs.
1931-32 128 126 155 147
1932-33 195 237 228
1933-34 174 196 216 199
1934-35 137 139 146 133
Average 159 174 186 159

The data are quite consistent in showing that 100 pounds of
manganese sulfate per ton (75 pounds per acre) was equally as
good as, if not better than, the greater and lesser amounts tested.
In order to check these results on a commercial scale, sev-
eral cooperative tests were carried out with growers.
The first of these was conducted on the farm of W. J. Vick
ir 1934-35. Eleven rows, each one-fourth mile long, were planted
;n the regular commercial manner for each treatment, and each
treatment was replicated once. The regular basic fertilizer was a
4-8-5 applied at 1,500 pounds per acre. The three treatments
consisted of 100, 150 and 200 pounds per ton, respectively, of 65
percent manganese sulfate mixed with the fertilizer. Ten strips
each 50 feet long were harvested at random from each plot and
averaged for each treatment to obtain the data shown in Table
15 (Vick). The data show clearly that the 100-pound rate yielded
slightly better than the higher rates of manganese application.
Another test was conducted in 1935-36 on a commercial scale
on one of the farms of F. C. Peters, Inc. This farm, by the way,
had never before had applications of manganese, so far as the
owner knew. Approximately one-quarter acre was planted with






Fertilizer E.xperiLments with Potatoes


TABLE 15.-AVERAGE YIELDS OF No. 1 TUBERS (BUSHELS PER ACRE) RESULTING FROM
VARIOUS RATES OF APPLICATION OF MANGANESE SUI.FATE PER TON OF 4-8-5
FERTILIZER IN COOPERATIVE TESTS.

Lbs. of Manganese Sulfate per Ton
Cooperator 100 150 200
Vick 235 219 216
Peters 244 245 244

each of the three manganese (65 percent) treatments, 100, 150 and
200 pounds per ton. The 4-8-5 fertilizer to which the manganese
had been added was applied by machine at the rate of one ton
per acre. Ten sub-plots, each 2 rows 50 feet long, were harvested
at random from each treatment plot. The average yields are
also given in Table 15 (Peters). The data show no significant
differences in yield among the three treatments, again indicating
the 100-pound rate to be as effective as the higher rates.
This particular test has further significance in view of the
idea among some growers that more than 100 pounds of man-
ganese sulfate per acre is needed for potatoes on "new" land.
Apparently this idea is erroneous.
RECENCY OF APPLICATION
Experimental work was also started on the Station's East
Glade farm in the fall of 1931 to study the residual effect of man-
ganese over a four-year period. The plots, each 1/72 acre in
size and each with three replications, were established with per-
manent boundaries for the four-year period. A 4-8-5 fertilizer.
applied by hand at the rate of 1,500 pounds per acre, was used
each year. When manganese applications were made, 65 percent
manganese sulfate was mixed directly with the fertilizer, at the
rate of 100 pounds per ton.
Five basic treatments were included. Manganese was ap-
plied to four of the plots the first year and omitted from the
fifth. The second year manganese was applied to Plots 1, 2 and
3 and omitted from 4 and 5. The third year only Plots 1 and 2
received manganese, and the fourth year only Plot 1. Thus by
the end of the fourth year data had been secured from plots
receiving no manganese for four5, three, two and one years, re-
spectively, and at the same time from plots receiving manganese
for no, one, two, three and four years in succession, respectively.
The replicate yields of No. 1 tubers of the various treatments

6As a matter of fact these plots, to the writers' knowledge, had received
no manganese for at least eight years.






Florida Agricultural Experiment Station


have been averaged and are given in Table 16. Figures in italics
indicate where manganese had been applied.
TABLE 16.-YIELDS OF NO. 1 TUBERS (BUSHELS PER ACRE) AS RELATED TO RECENCY
OF APPLICATION OF MANGANESE SULFATE.
Treatment 1931-32 1932-33 1933-34 1934-35
A 134 161 157 142
B 155 183 186 146
C 148 203 179 145
D 145 215 196 148
E 149 217 216 160

The yields fluctuated from year to year as is expected of
different seasons. The data show consistently that each year the
yields were higher in the plots receiving manganese that year.
Because of the normal yield fluctuations from year to year, the
data are difficult to interpret from the standpoint of residual
effects. Only a generalization can be made-that there is a ten-
dency for the effect of manganese to continue somewhat into
the second and possibly into the third year after its application,
but that for all practical purposes, however, manganese should
be applied each year, through a period of at least four years.
Two years later (1937-38) another experiment was conducted
on another section of the farm, to which manganese had been
applied for at least five years in succession. Replicate plots
(six each) with and without manganese (75 pounds per acre)
were compared for yield. This year the fertilizer was applied
by machine. The average yields, from Table 20, are given in
Table 17 (1937-38). The addition of manganese did not increase
the yield.
TABLE 17.-AVERAGE YIELDS OF NO. 1 TUBERS (BUSHELS PER ACRE) OBTAINED WVITH
AND WITHOUT MANGANESE IN A STANDARD 4-8-5 FERTILIZER ON LAND WHERE
MANGANESE HAD BEEN APPLIED FOR SEVERAL YEARS.
Season Control Manganese
1937-38 292 292
1938-39 142 139

Again in 1938-39 the test was repeated in another field
which had received manganese annually for at least seven years.
Plots with and without manganese were planted as before, with
the results (from Table 21) given also in Table 17 (1938-39).
These data also show no increase in yield resulting from the
application of manganese.
The results of these experiments indicate that for the first
four years, at least, manganese sulfate should be applied annual-






Fertilizer Experiments with Potatoes


ly, but that after a period of five years or more of successive
applications, the manganese content probably may be omitted
entirely from the fertilizer one year without decreasing the
yields. The data here presented indicate not only that manganese
exhibits some residual effects, but also that there may result an
accumulation of it in the soil from year to year in a form avail-
able to the potato plant. It is possible, of course, that the residual
effect of manganese becomes more pronounced when the fertilizer
is applied by machine in the band method than by hand where
it becomes more thoroughly mixed with the soil.
It is worthy of note that fairly good yields of potatoes were
obtained during several years of growing them without adding
any manganese on land with no previous history of manganese
applications (treatment A, Table 16). Although the addition of
manganese with the fertilizer increased the yields profitably, its
omission resulted only in lessened yields and slightly smaller
vine growth (Fig. 5). No other characteristic foliage symptoms
of manganese deficiency were noted.

OTHER SOIL AMENDMENTS
The results obtained with manganese naturally promoted
a parallel interest in other soil amendments. Accordingly, some
experiments with these were started on the Station farm in 1934,
to determine if the addition of any of these other elements might
exhibit a beneficial effect on potato yields. The first trials were
of a more or less preliminary nature and included tests of zinc,
copper, iron and magnesium, as well as manganese in various

Fig. 5.-The 1932-33 potato manganese test. The plot in the background
received 100 pounds of manganese sulfate; that in the foreground no
manganese for two years.






Florida Agricultural Experiment Station


combinations. The materials used as sources of these elements
and amounts applied per ton of fertilizer were as follows:
1. Zinc-from 89 percent zinc sulfate @ 75 pounds per ton.
2. Copper-from bluestone crystals (copper sulfate) @ 100
pounds per ton.
3. Iron-from copperas (ferrous sulfate) @ 125 pounds per ton.
4. Magnesium-from commercial epsom salts (magnesium sul-
fate) @ 300 pounds per ton.
5. Manganese-from 65 percent manganese sulfate @ 100 pounds
per ton.
6. Calcium-from gypsum (calcium sulfate) @ 1000 pounds per
ton.
All of these ingredients, in whatever combination they were
used, were mixed with a regular 4-8-5 fertilizer (50 percent of
N from organic sources), which was applied by hand at the rate
of 1,500 pounds per acre. Thus the elements were applied per
acre at three-fourths the amounts listed above.
The test the first year was composed of 14 treatments, applied
to land which had had manganese applications for several years
previously. The treatments are listed in Table 18 in their order
of yield of No. 1 tubers. The plots consisted of single rows, 50 feet
long and 38 inches apart, and each treatment replicated 16 times,
in two series of 8 plots each. The tubers from each replicate plot
were graded and the data converted to an acre basis and averaged
for each treatment, with results shown in Table 18.
TABLE IS.-AVERAGE YIELDS OF NO. 1 TUBERS (BUSIHELS PER ACRE) FROM THE
TREATMENTS COMPOSING THE 1934-35 MICRO-NUTRIENT ELEMENT TESTS.


Elements Added to 4-8-5 Fertilizer

Manganese-zinc-copper
Manganese-zinc -copper-iron
Manganese-zinc
Manganese-magnesium
Iron-zinc
Zinc
Manganese-magnesium-zinc-iron-copper
Iron-zinc-copper
Manganese-copper
Manganese-calcium-zinc-iron-copper
Iron
Iron-copper
Copper
Manganese (control)


Increase
Yield Over Odds
Control
237 38 4298:1
227 28 71:1
223 24 121:1
223 24 121:1
217 18 27:1
216 17 43:1
216 17 17:1
215 16 14:1
205 6 2:1
201 2
199 0
196 3
192 7
199


According to the data of Table 18, a number of the treat-
ments showed average yields somewhat higher than the control
or manganese treatment.





Fertilizer Experiments with Potatoes


The data were analyzed statistically by "Student's" t test.
Significance of differences in yield over that of the control plot
is indicated in the column "odds". Odds of 30:1 or better are con-
sidered satisfactory for significance. On this basis the first six
treatments listed in Table 18 may be considered as having signi-
ficantly outyielded the control treatment, since the one treat-
ment with odds of 27:1 closely approaches the arbitrary 30:1
standard.
A striking fact is that most of the combinations including
zinc are represented in these six treatments, indicating that ap-
plications of zinc sulfate may be beneficial on these soils. This
is especially indicated by the fact that zinc alone and the zinc-
manganese combination outyielded manganese alone.
The addition of copper and iron in combination with man-
ganese and zinc did not significantly increase the yield over that
obtained by adding the latter two alone, and since iron and
copper alone or together did not increase the yield, the data of
this test indicate they were not beneficial.
Evidence is provided that the addition of magnesium sulfate
with manganese was beneficial, although when magnesium was
added to the larger combination of manganese-zinc-iron-copper,
the yield was lower than that of a similar mixture without mag-
nesium.
The only mixture in which calcium sulfate was added failed
to show an increase over a similar mixture without it.
The following year (1935-36) an experiment was conducted
on different ground comparing the effects on yield of adding 89
percent zinc sulfate to the fertilizer at the rate of 50 pounds per
ton, with and without manganese. The regular 4-8-5 fertilizer was
applied by hand at the rate of 1,500 pounds per acre. Ten replica-
tions of each treatment were used. The average yields from each
treatment are given in Table 19 (Series 1935-36). No increase in
yield was obtained from the zinc applied in this experiment.
The next year (1936-37) similar tests were conducted with
zinc sulfate (89 percent) at the rates of 5, 25 and 50 pounds per
ton, and with magnesium sulfate (commercial epsom salts) at
rates of 25, 100 and 400 pounds per ton. A control treatment of
100 pounds of manganese sulfate was included also. The fertilizer
to which they all were added was the regular 4-8-5 mixture con-
taining 100 pounds of manganese sulfate per ton, and it was
applied by hand at the rate of 1,500 pounds per acre. Each of the
seven treatments was replicated 10 times. The average yields





Florida Agricultural Experiment Station


TABLE 19.-AVERAGE YIELDS OF NO. 1 TUBERS (BUSHELS PER ACRE) OBTAINED IN
TESTS OF VARIOUS MICRO-NUTRIENT ELEMENTS ADDED TO STANDARD 4-S-5
FERTILIZER, 1935-37.
Series Elements Added Yields
Manganese (100)* (Control) 278
1935-36 Manganese (100) and zinc (50) 277
Zinc (50) 270
Manganese (100) (Control) 182
Zinc (5) 187
Zinc (25) 189
1936-37 Zinc (50) 184
Magnesium (25) 191
Magnesium (100) 185
Magnesium (400) 187
SFigures in parentheses refer to pounds of the compound added per ton
of fertilizer.
are given for each treatment in Table 19, Series 1936-37. Here
again the zinc failed to increase the yield over the manganese
treatment and magnesium also had no beneficial effect. The
small differences in average yields are not significant.
The following year (1937-38) the micro-nutrient element
tests were expanded to include more treatments and the fertili-
zer was applied by machine. This year five replications were
planted of each treatment in a randomized block arrangement,
with each treatment replicate paired with a control plot. The
buffer rows, planted between treatment and control plot rows,
were fertilized with the control mixture. Zinc sulfate (89 per-
cent), copper sulfate (crystal bluestone), iron (commercial fer-
rous) sulfate, iron (technical ferric) citrate, and magnesium
sulfate (commercial epsom salts) were used this season in various
combinations with and without manganese. The field in which
the test was conducted had been planted annually to potatoes
for at least the five preceding years, with manganese applica-
tions made each year.
All ingredients were added to the regular 4-8-5 mixture,
which was applied at the rate of 1,500 pounds per acre. The
control mixture was this same 4-8-5 with no manganese added.
The treatments tested and the average yields from them and
from their respective control plots are given in Table 20.
Statistical analysis of the data from which this table was
compiled involved the use of "Student's" Z test, as applied to a
paired plot arrangement. Odds of less than 30:1 are not consid-
ered significant.
Zinc at the 25-pound rate, both alone and in combination





Fertilizer Experiments with Potatoes


TABLE 20.-AVERAGE YIELDS OF NO. 1 TUBERS (BUSHELS PER ACRE) OF THE TREAT-
MENTS AND OF THEIR RESPECTIVE CONTROL PLOTS, 1937-38 MICRO-NUTRIENT
ELEMENT TESTS.
Ave. Increase
Elements Added to 4-8-5 Fertilizer Treatment Control of Treatment Odds
Yield Yield Over Control
Zinc (75) manganese (100)* 310 285 25 23:1
Zinc (75) manganese (100) iron
sulfate (125) 308 280 28 36:1
Iron (ferric) (134) 304 290 14 73:1
Zinc (25) manganese (100) 304 278 26 60:1
Zinc (25) 303 285 18 49:1
Zinc (75) 300 290 10 4:1
Magnesium (400) manganese (100) 299 290 9 3:1
Iron (ferrous) (125) 299 276 23 44:1
Iron (ferrous) (125) manganese (100) 294 293 1 1:1
Zinc (75) copper (100) manganese
(100) 292 281 11 21.1
Manganese (100) 292 292 0 0
Zinc (75) iron (ferrous) (125) copper
(100) manganese (100) 285 279 6 6:1
:' Figures in parentheses refer to pounds of the compound added per ton
of fertilizer.
with manganese, increased yields markedly. No explanation can
be offered for the poor results with zinc at 75 pounds, where
the increase was not significant.
Manganese failed to increase yields when applied alone.
When applied with zinc the increase was not appreciable over the
yield of zinc (25) alone. This failure might be expected, in view
of the continual manganese applications made in previous years
on the field where these tests were made.
Iron salts, both ferric and ferrous, increased yields signifi-
cantly when applied alone, but not in combination with other
elements. Iron added to zinc and manganese did not increase
the yield over that of the latter two alone, nor did its addition
with manganese increase the yield. The lack of increase from
iron in combination with other elements is difficult to understand
and no explanation is offered.
Neither magnesium nor copper caused increase in yields.
Another series of experiments along these same general lines
was conducted in 1938-39. The 4-8-5 fertilizer, to which the
various amendments were added, was applied by machine as
before, at 1,500 pounds per acre. Five replications were planted
of each treatment and its respective paired control plot on land
which had received manganese for the preceding seven years.
Zinc sulfate was added at 5, 25 and 75 pounds per ton, iron
(ferrous) sulfate at 125 pounds and magnesium sulfate at 25





Florida Agricultural Experiment Station


and 400 pounds per ton. Copper sulfate and iron citrate were not
used this year but boron, in the form of borax, was added at the
rates of 12 and 24 pounds per ton. The treatments and average
yields from them and from their respective control plots are
given in Table 21.
It was found that none of the small differences in average
yields this year were significant. Thus this year manganese,
magnesium and zinc were of no effect in increasing yields. Like-
wise no increase was obtained from either iron or boron.

TABLE 21.-AVERAGE YIELDS OF No. 1 TUBERS (BUSHELS PER ACRE) OF THE TREAT-
MENTS AND OF THEIR RESPECTIVE CONTROL PLOTS, 1938-1939 MICRO-NUTRIENT
ELEMENTS TESTS.
Average Increase
Ingredients Added to 4-8-5 Fertilizer Treatment Control of Treatment
Yield Yield Over Control
Zinc (75) manganese (100)* 156 144 12
Iron (125) manganese (100) 155 142 13
Zinc (25) manganese (100) 149 140 9
Zinc (5) manganese (100) 148 142 6
Boron (12) manganese (100) 147 142 5
Magnesium (25) manganese (100) 144 137 7
Zinc (75) iron (125) manganese (100) 143 143 0
Iron (125) 141 142 1
Manganese (100) 139 142 3
Magnesium (400) manganese (100) 136 143 7
Boron (24) manganese (100) 132 139 7

Figures in parentheses refer to pounds of the compound per ton of
fertilizer.
SUMMARY OF MICRO-NUTRIENT ELEMENT STUDIES
Considering the experimental results over a period of years,
the data are rather convincing in establishing that the addition
of iron sulfate, copper sulfate and magnesium sulfate to the soil
in fertilizer form is not to be recommended as a general practice
in growing potatoes on these marl soils. In occasional instances
their use resulted in slight increases in yield but the evidence is
strong enough otherwise to indicate that their use in the amounts
tested, even as yield "insurance," is unwarranted.
The use of calcium sulfate, or gypsum, will be discussed
later. It did not increase the yield in the 1934-35 test.
Boron, used only one year at two different rates of applica-
tion, failed to improve the yields.
The evidence is not so convincing concerning the use of zinc
sulfate. In two of the five seasons zinc increased the yields
significantly and the increases, although not very large, were
profitable. This success is not to be ignored, although the fact






IFrtilizcr Expcriimints wt,7ith Potati's


that its addition to the fertilizer in the majority of years did not
result in increased yields scarcely permits its recommendation
for general use. The nature of zinc deficiency in these soils is
not yet understood and it is not known if deficiencies occur in
some years and not in others. Certainly the method of adding
zinc needs further study. As in the case of manganese, no obvious
symptoms of deficiency which could be attributed to zinc have
been observed. It is possible that this element, as well as some
of the others, may better be applied as a foliage spray, and ex-
periments are now under way at this Station to determine this
point.
Since this experiment was conducted with an ordinary 4-8-5
fertilizer with 50 percent of its nitrogen derived from organic
sources, the results might not be applicable in instances where a
radically different fertilizer program is followed. Also the fact
that benefits from adding these various micro-nutrient elements
have not been pronounced up to the present time does not
exclude the possibility that their use may be required later on
after intensive potato cropping has progressed year after year
on the same land.
In addition to the more complete experiments thus far
described a number of minor tests were carried out with sulfur,
-'i.iur and manure.
SULFUR
Since the soil of this area is alkaline it seemed logical to
determine what effect applications of sulfur might have on the
resultant yields of potatoes. Accordingly, a test was conducted
in 1932-33, in which a control 4-8-5 fertilizer treatment applied
at 2,000 pounds per acre was compared with a similar treatment
to which had been added 1,000 pounds of dusting sulfur per acre,
applied in the furrows by hand with the fertilizer two days
before planting. The resultant average yields from three replica-
tions of each treatment are given in Table 22, Series 1932-33.
No change in yield resulted from the addition of sulfur.
The effect of the sulfur on the pH of the soil was not determined
this season, but in 1938 Ruehle", in studies of potato scab, applied
1,000 pounds of sulfur per acre in a similar manner and found
that the pH was changed slightly but the change was of short
duration.

6Ruehle, G. D. Control of potato diseases in Dade County. Fla. Agr.
Exp. Sta. Ann. Rept. 1938, p. 191.






Florida Agricultural Experiment Station


TABLE 22.-AVERAGE YIELDS or No. 1 TUBERS (BUSHELS PER ACRE) RESULTING FROA'
USE OF VARIOUS AMOUNTS OF SULFUR WITH A STANDARD 4-8-5 FERTILIZER.
Series Treatment Rate per Acre Yields
1932-33 Sulfur 1,000 pounds 195
Control 197
1938-39 Sulfur 4,000 pounds 125
Control --- 149
Filler Sulfur 123 pounds 140
Phos-rock 123 pounds 139

In 1938-39 a cooperative test was carried out on a field
which had produced poor crops of potatoes due to its sea salt
content. Analysis of the soil showed a chlorine concentration of
about 4,000 parts per million in the surface and 1,100 p.p.m. at the
2 to 4-inch depth. The analysis was made by the Department of
Chemistry and Soils of the Florida Experiment Station at Gaines-
ville. Sulfur was among the materials tested on this soil. It was
broadcast over the surface at the rate of 2 tons per acre and
disked in the day before planting. A 4-8-5 fertilizer was applied
at planting time at the rate of one ton per acre. Resultant average
yields per acre from this test are given in Table 22, Series 1938-
39. In this case sulfur actually reduced the yield.
This same year a test was conducted on the Station farm in
which two 4-8-5 fertilizer mixtures, identical except for their
filler material, were compared. One was made up in the ordinary
manner, using raw rock phosphate as filler, and the other with
flowers of sulfur as filler. Each filler was added in the amount
of 164 pounds per ton, and the complete fertilizers were applied
at the rate of 1,500 pounds per acre by machine. Each plot was
replicated five times. The replicate yields were averaged for
each treatment and are also found in Table 22, Series Filler.
In this test the yields were the same for both treatments.
These three experiments, then, indicate that no increase in
yield of potatoes may be expected from the addition of sulfur in
the amounts and by the methods tested.
GYPSUM
The effect on yields of applying commercial calcium sulfate
(gypsum or landplaster) was also studied over a period of years,
as the result of preliminary tests in pot cultures which showed
a stimulating effect of calcium on growth of tomato plants in
marl soil.
In 1932-33 gypsum was applied to the furrows by hand at
the rates of 1,000 pounds per acre, along with a regular 4-8-5






Fertilizer Experiments with Potatoes


fertilizer applied at 2,000 pounds per acre. This treatment was
compared with a similar one without gypsum added. Three repli-
cations of each were planted and the resultant average yields
are found in Table 23 (1932-33). The difference between these
two yields was too small to be of significance.
The following year gypsum was again applied with a 4-8-5
mixture by hand at two different rates. The treatments, each
replicated four times, and their average yields are given in
Table 23 (1933-34) also. This time small but significant increases
in yield could be attributed to the gypsum, but it is extremely
doubtful if the additional cost and labor of applying the gypsum
were justified.

TABLE 23.-AVERAGE YIELDS F0 NO. 1 TUBERS (BUSIIELS PER ACRE) OBTAINED IN
TRIALS OF GYPs-r ADDED TO REGULAR 4-8-5 FERTILIZER.
Series Treatment Rate per Acre (lbs.) Yields

1932-33 Control 2000 196
Control + gypsum 2000 + 1000 202
Control 2000 198
1933-34 Control + gypsum 2000 + 1000 217
Control 1000 172
Control + gypsum 1000 + 500 187
1934-35 Mixture 1500 227
Mixture gypsum 1500 + 750 201
1938-39 Control 2000 149
Control + gypsum 2000 + 4000 132

Another test in 1934-35 has already been described (Table
18). Gypsum at 750 pounds per acre was added with a 4-8-5
mixture (at 1,500 pounds) containing manganese, zinc, copper,
and iron, and compared with a similar treatment without gypsum.
The results are given again in Table 23 (1934-35) for comparison.
In this test gypsum decreased the yield.
The cooperative experiment of 1938-39 in the field with a
high chlorine content, which contained the sulfur experiment,
also contained a treatment in which gypsum was broadcast at
the rate of 2 tons per acre and disked in prior to planting.
Average yields per acre of the 10 replications of the gypsum and
control plots are included in Table 23 (1938-39). Again in this
experiment gypsum failed to increase the yield.
Thus, it is concluded that the addition of gypsum in the
amounts tested to these marl soils is not justified from the stand-
point of increasing potato yields.





Florida Agricultural Experiment Station


MANURE
A series of replicated plots was planted in 1932-33 to test the
effect on yield of adding stable manure to the soil. Stable manure
was broadcast over the plots at the rate of 6 tons per acre and
disked in prior to planting. The potatoes in the manure and
control plots both were fertilized with a ton per acre of 4-8-5
containing 100 pounds of manganese sulfate. The average yields
are given in Table 24 (1932-33). The manure significantly in-
creased the yield, but at local manure prices (about $5 per ton)
the treatment was not profitable.
TABLE 24.-AVERAGE YIELDS OF NO. 1 TUBERS (BUSHELS PER ACRE) OBTAINED IN
TRIALS or MANURE APPLIED IN ADDITION TO STANDARD 4-8-5 FERTILIZER CON-
TAINING MANGANESE.
Series Treatment Rate per Acre (tons) Yields
1932-33 Control 1 196
Control + manure 1 + 6 220
1938-39 Control 1 149
Control + manure 1 + 8 162

Again in the 1938-39 season manure was added as one of
the treatments on the salty land to which the sulfur and gypsum
were applied. In this experiment stable manure was broadcast
uniformly at the rate of 8 tons per acre and disked in just prior
to planting. The potatoes were fertilized in the regular commer-
cial manner with a ton of 4-8-5 containing 100 pounds of man-
ganese sulfate. Average resultant yields of tubers are given in
Table 24. Again the manure increased the yield but not enough
to warrant the additional cost.
These two experiments indicate that stable manure has a
beneficial effect on yields, but as applied in these tests its
additional cost was prohibitive. Incidentally, in neither test did
the percentage of potato scab (Actinomyces scabies (Thax.) Giissow)
increase. There was practically no scab in any of the plots.

SUMMARY
Fertilizer experiments conducted at the Sub-Tropical Ex-
periment Station over a period of 10 years are reported in which
analyses, amounts, sources of nitrogen and potash, and applica-
tions of manganese and other soil amendments were studied as
affecting yields of Bliss Triumph potatoes grown on the marl
soils of Dade County, Florida.
Analyses varying from a 2-8-5 and 3-12-8 to 8-16-10 were
tested. The results indicate that for mixtures to be applied at
rates of about 1,500 to 2,000 pounds per acre there is no justifica-





Fertilizer Experi ments with Potatoes


tion for increasing the analysis beyond 3 or 4 percent nitrogen,
8 percent phosphoric acid and 4 or 5 percent potash.
Experiments with ordinary 4-8-5 and 3-12-8 analyses showed
that the correct amounts of these to apply was from about 1,500
to 2,000 pounds per acre, and in most instances the most profit-
able amount was 1,500 pounds.
In four of the five years of testing a 4-8-5 mixture in which
33 percent of the nitrogen was derived from organic sources
yielded as well as mixtures containing a higher percentage of
nitrogen so derived. No definite relation of treatment yields to
monthly rainfall during the crop season was observed during the
five years over which these tests were conducted.
The source-of-nitrogen tests indicated that the organic
materials milorganite, blood-and-bone tankage (medium grade)
and dried blood slightly outyielded the other sources, and profit-
ably so. No significant differences in yield were obtained among
these three. Fish scrap, cottonseed meal, urea and cyanamid
yielded slightly less, and about the same as mixtures containing
all their nitrogen from ammonium phosphate, sulfate of am-
monia or nitrate of soda. No advantage was demonstrated from
combining the latter two materials. Likewise a fish scrap and
cottonseed meal combination yielded no better than mixtures in
which these materials were used separately.
The urea and cyanamid treatments both produced yields
in the upper range of the water-soluble sources, and both were
among the treatments showing the lowest fertilizer cost per
bushel.
No significant differences in yield were obtained when sul-
fate of ammonia and nitrate of soda were compared as inorganic
sources of nitrogen in a 4-8-5 formula containing 50 percent of
its nitrogen from organic sources.
Likewise no significant differences in yield were obtained
between the sulfate and muriate forms of potash as sources of
potash in a similar 4-8-5 fertilizer.
Applications of 100 pounds of 65 percent manganese sulfate
per ton of fertilizer gave as good yields as greater amounts.
It was found that on "new" land applications of manganese sul-
fate should be made annually for at least the first four years.
After a period of five or more years of successive applications,
however, results indicated that the manganese content of the
fertilizer could be entirely omitted at least one year without
decreasing the yield.





Florida Agricultural Experiment Station


Applications of magnesium sulfate (epsom salts), copper
sulfate (bluestone), iron sulfate copperass), borax, iron citrate,
sulfur and calcium sulfate (gypsum) failed to increase yields
profitably. There were some seasons when zinc sulfate increased
yields but results were too inconsistent to warrant its general
recommendation as a fertilizer ingredient.

Stable manure increased the yields slightly when applied at
6 to 8 tons per acre with commercial fertilizer, but not sufficient-
ly to justify the cost.

ACKNOWLEDGMENTS
The Board of County Commissioners of Dade County assisted by
appropriating part of the funds for these experiments each year since
the 1935 season. Dr. G. D. Ruehle supervised much of the spraying of
the plots in later years, and Messrs. L. R. Toy, Ivan Moser, Lloyd Field
and Roy Nelson assisted with much of the field work involved in conduct-
ing the tests.
Messrs D. P. Blake, Jr., Luther Chandler, F. M. Dolan, J. H. Estes,
J. M. Holferty, F. C. Peters, Frank Rue and W. J. Vick, growers, kindly
cooperated in some of the tests reported. County Agent Charles Steffani
also assisted with the cooperative work.
The Redland District Chamber of Commerce provided six acres of
test plots for some of the experiments conducted in 1932-33.




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