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or recommendations. These texts
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record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
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Copyright 2005, Board of Trustees, University
Bulletin 156 April, 1920
UNIVERSITY OF FLORIDA
Agricultural Experiment Station
SWEET POTATO FERTILIZER
JOHN M. SCOTT
Fig. 12.-Field of sweet potatoes on Florida farm
Bulletins will be sent free upon application to Experiment Station,
BOARD OF CONTROL
J. B. HODGES, Chairman, Lake City, Fla.
E. L. WARTMANN, Citra, Fla.
J. B. SUTTON, Tampa, Fla.
W. W. FLOURNOY, DeFuniak Springs, Fla.
H. B. MINIUM, Jacksonville, Fla.
BRYAN MACK, Secretary, Tallahassee, Fla.
J. G. KELLUM, Auditor, Tallahassee, Fla.
P. H. ROLFS, M. S., Director
J. M. SCOTT, B. S., Vice-Director and Animal Industrialist
J. R. WATSON, A. M., Entomologist
H. E. STEVENS, M. S., Plant Pathologist
C. D. SHERBA4OFF, Ph. D., Associate Plant Pathologist
J. B. THOMPSON, B. S., Forage Crop Specialist
SARAH L. VINSON, Agricultural Editor
R. NEWHALL, Secretary
T. VAN HYNING, Librarian
M. ROUx, Mailing Clerk
F. G. BENDING, Stenographer
A. W. LELAND, Farm Foreman
G. UMLAUF, Gardener
K. H. GRAHAM, Auditor and Bookkeeper
SWEET POTATO FERTILIZER EXPERIMENT
By J. M. SCOTT
The purpose of this experiment, which was started in the
Spring of 1915, was to get information as to which combination
of fertilizers would produce the best yield of sweet potatoes.
The land on which the experiment was conducted had been in
use for six years previous as. a fertilizer experiment with
Japanese cane. The sweet potato experiment occupied the same
plots as did .the Japanese cane, and was fertilized exactly the
same as the Japanese cane.
In this experiment the sweet potatoes were grown from draws
each year. The crop was planted during the last of May and
the first week in June. The same variety of potatoes, Triumph,
were grown each year.
The plots were arranged so that there were three rows of
potatoes in each. The fertilizer was applied on the two middles
as shown below:
Section 1 Section 2 Section 3
The rows marked X were harvested and the yield per acre
computed. This shows that the fertilizer applied to one plot
would have no effect on the yield of an adjoining plot.
The sweet potatoes were not grown on the same plot of ground
for five years continuously but were grown in a rotation as
Section 1 Section 2 Section 3
1915 Sweet Potatoes 1915 Cotton .1915 Corn
1916 Corn 1916 Sweet Potatoes 1916 Cotton
1917 Cotton 1917 Corn 1917 Sweet Potatoes
1918 Sweet Potatoes 1918 Cotton 1918 Corn
1919 Corn 1919 Sweet Potatoes 1919 Sorghum
However, the sweet potatoes, corn and cotton all received the
same kind and amount of fertilizer each year. It will be seen
60 Florida Agricultural Experiment Station
from the rotation that each year the sweet potatoes followed
Table 15 gives the kind and amount of fertilizer applied per
acre. The same number of pounds of fertilizer was not applied
to each plot but the same number of pounds of plant food was
applied to each plot.
The soil on which the experiment was conducted was what
is commonly called high pine sandy soil of only average fertility.
TABLE 15.-FERTILIZERS USED IN EXPERIMENT, AND AMOUNT APPLIED
1 Pounds Per Acre
Kind of Fertilizers Used Plot Plot Plot Plot Plot Plot P
I II III V V VI VII VIII
Dried blood .......................... 112 ........ 112 .......... 112 ......... 112 112
Sulphate of ammonia........................ ...... ... 72 .......... 72 . ..........
Muriate of potash............. 84 84 ........... 84 84 .............. ......
Sulphate of potash......... ................. .. .... ..... .......... 84 84 84
Acid phosphate ..................... 224 224 224 224 224 224 224
Ground lim estone* .......... ......... ......... .......... .......... ................... .......... 2000
"*Applied only in 1915, 1917, and 1919.
The sweet potato fertilizer experiment has been conducted
for five years. This is long enough to be able to draw some con-
clusions as to the effect of fertilizers on the yield of potatoes.
Altho there is some difference in the yield of the different plots
there was little or no difference in the leaf or vine growth. In
other words, the different combination of fertilizers had no
effect on the leaf or vine growth of the crop.
Table 16 gives the yield of sweet potatoes on each plot each
year and also the five-year average.
TABLE 16.-SWEET POTATO FERTILIZER EXPERIMENTS; YIELD PER ACRE
Plot 1915 1916 1917 1918._ 1199 Averae
I .. I 215.6' 1 .3.; 2 "2 .4 113.6 24 0 I 151.8
II ................ 221.6 177.6 240.0 161.6 33.6 166.8
III ................... 99.6 86.4 72.0 60.8 6.4 65.0
IV ..................... 259.6 228.8 294.4 161.6 57.6 200.4
V ...... ......... 252.0 182.6 276.8 249.6 59.2 204.0
VI ................. 216.0 128.0 320.0 163.2 40.0 173.4
VII ..................... 222.0 203.2 251.2 153.6 99.2 185.8
VIII ..................... 269.6 110.4 232.0 153.6 168.0 186.7
Bulletin 156, Sweet Potato Fertilizer Experiment 61
In considering the yields it is best, we believe, to consider only
the five-year averages. If the yield of Plot I is compared with
that of Plot V it will give some idea as to the value of acid
phosphate in a fertilizer for sweet potatoes.
Plot I which received an application of dried blood, 112 pounds,
and muriate of potash, 84 pounds, produced a yield on a five-
year average of 151.8 bushels. Plot V fertilized the same as
Plot I plus 224 pounds of acid phosphate, produced a yield on a
five-year average of 204 bushels. In other words, by the addi-
tion of 224 pounds of acid phosphate the yield of sweet potatoes
was increased 52.2 bushels.
Plot II was fertilized with muriate of potash, 84 pounds, and
acid phosphate, 224 pounds, and produced a five-year average
yield of 166.8 bushels. Plot V was fertilized the same as Plot
II except that 112 pounds of dried blood an acre was applied.
This plot produced a yield of 204 bushels. In other words, an
application of 112 pounds of dried blood was equal to the value
of 39.2 bushels of sweet potatoes. By comparing Plot II and
Plot IV it is seen that an application of 72 pounds of sulphate of
ammonia an acre increased the yield 33.6 bushels an acre, regard-
less of the fact that Plot II which has received no ammonia in
the fertilizer produced a yield of 166.8 bushels on a five-year
average. An application of 112 pounds of dried blood an acre
increased the yield 39.2, and an application of 72 pounds of
sulphate of ammonia increased the yield 33.6 bushels an acre.
This shows that it is profitable to use either dried blood or
sulphate of ammonia in the fertilizer.
The result from Plot III is the most striking. This plot re-
ceived no potash. For the five-year average it produced a yield
of only 65 bushels an acre or 86.8 bushels less an acre than the
next lowest yield. This shows without question the need of
potash in fertilizer for sweet potatoes if a satisfactory yield is
to be obtained.
By comparing the yields of Plot IV and Plot VI it will give a
comparison of the value of muriate of potash and sulphate of
potash. Muriate of potash was applied on Plot IV and sulphate
of potash on Plot VI. Plot IV produced a yield of 200.4 bushels
an acre and Plot VI gave a yield of 173.4 bushels, or a difference
of 27 bushels an acre in favor of the use of muriate of potash.
Comparing Plots V and VII gives some idea of the comparative
value of muriate and sulphate of potash when used with dried
blood and acid phosphate. Plot V received muriate of potash
62 Florida Agricultural E.xp( ri,,,i iat Station
and the yield for the five-year average was 204 bushels an acre.
Plot VII received sulphate of potash and the yield for the five-
year average was 185.8 bushels an acre, a difference of 18.2
bushels an acre.
Plots VII and VIII were fertilized alike except that Plot VIII
was given an application of ground limestone at the rate of 2,000
pounds an acre in 1915, 1917, and 1919. The results in yield
of potatoes an acre are the same, which would indicate that
ground limestone is of no value as a soil corrector for sweet
THE SWEET POTATO AS A FLORIDA CROP
The Bureau of Crop Estimates gives the Florida sweet potato
crop for 1919 as 41,000 acres and a yield of 4,10.0,000 bushels.
On December 1, 1919, they were worth $1.40 a bushel. In other
words, the sweet potato crop of Florida for 1919 had a value of
$5,740,000. If a comparison of the value of the sweet potato
crop is made with other crops in the state it would be seen that
in production and value it is well up in the list.
The following figures give us some idea of the growth of the
crop during the past ten years in Florida.
Year Acres Yield (bushels)
1909 ..........---..................- 22,000--------............................ 2,084,000
1911 ...........................25,000...................3.. ,000,000
1'.11 -7 "*!.'? ..1 1.11 1 :;.-i, ii. 'i .1 10
1 17. 111 111
1919...... ............ 41,000...... .....4,100,000
We do not have the price of sweet potatoes for the above years,
l)i.t on December 1, 1917, the price was $1.15 a bushel. The
same date in 1918, the price was $1.25, and the same date in
1919, $1.40 a bushel.
Notwithstanding the fact that the acreage and production has
increased during the past few years the price has also advanced
The sweet potato is one of the most important crops grown
in Florida. It is a source of food for a large part of the rural
population of the State. It is also used to a large extent for
feeding all classes of livestock. -Few people perhaps realize that
the sweet potato crop in the last few years, in this State, has
been nearly equal in value to that of the upland cotton crop. The
production during the past four years has been one-third to one-
fourth that of the corn crop.
Bulletin 156, Sweet Potato Fertilizer Experiment 63
The sweet potato is very much at home in the South and
especially here in Florida. A well drained warm sandy loam
soil is ideal for its growth. It will grow in a clay soil but the
yields will not be as satisfactory.
There is little doubt but that there will continue to be a
growing demand for good sweet potatoes.
To make this crop profitable it is important that a popular
market variety be given due consideration.
Another point that must be considered is the seed bed. This
must be started in time to get plants large enough for setting at
the proper time. It will require from 7,200 to 8,400 plants to
set an acre. Of course the number required will vary depending
on the width of rows and distance apart in the row.
In bedding sweet potatoes it is sometimes a puzzle to know
just how many to bed to produce plants for a given area. With
most varieties it is not safe under average conditions to count
on more than 2,000 to 2,500 draws from each bushel of potatoes
bedded. However, under ideal conditions, that is with every-
thing favorable, it may be possible to get 6,000 to 8,000 draws
from a bushel. To be on the safe side it would be well to bed
three to four bushels of potatoes for each acre to be planted.
There is also the question as to whether it is best to plant
draws or use vine cuttings. In Florida vine cuttings produce
better marketable potatoes than do the draws, but for an early
summer crop it would be difficult to get vines for planting. For
the crop that is to be planted the latter part of May and early
in June, vine cuttings will be found more satisfactory than draws.
The potatoes produced will be more uniform in size and much
smoother in appearance than those from draws.