Title Page
 Board of control

Title: Citrus fertilizer experiments
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00027144/00001
 Material Information
Title: Citrus fertilizer experiments
Alternate Title: Bulletin 154 ; Florida Agricultural Experiment Station
Physical Description: Book
Language: English
Creator: Collison, S. E.
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville, Fla.
Publication Date: December, 1919
Copyright Date: 1919
 Record Information
Bibliographic ID: UF00027144
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aen3290 - LTUF
18170771 - OCLC
000922781 - AlephBibNum

Table of Contents
    Title Page
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    Board of control
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Full Text

Bulletin 154 December, 1919


Agricultural Experiment Station

ja 24'28



The Station Bulletins will be sent free upon application to the Experiment
Station, Gainesville


J. B. HODGES, Chairman, Lake City, Fla.
E. L. WARTMANN, Citra, Fla.
J. B. SUTTON, Tampa, Fla.
J. T. DIAMOND,* Tallahassee, Fla.
H.B. MINIUM, Jacksonville, Fla.
BRYAN MACK, Secretary, Tallahassee, Fla.
J. G. KELLUM, Auditor, Tallahassee, Fla.


The judicious use of commercial fertilizers in the orange grove
has been one of the important problems confronting the Florida
citrus grower. In the expense involved and the effects upon the
tree and fruit, this problem ranks as of equal importance with
any of the other operations in the grove, such as spraying, har-
vesting, pruning or cultivation. At the time when the work re-
ported in this bulletin was begun, practically no experimental
work in this line had been carried out in the state. The existing
knowledge of the effects of the various fertilizers in use was
entirely the result of the practical experience of the growers
themselves and was of a more or less conflicting nature. In order
to obtain accurate knowledge of the effects of various fertilizers
over a comparatively long period, the experimental work dis-
cussed in this bulletin was undertaken. A young grove was
located on Lake Harris, about three miles from Tavares, in Lake
county, and used for the experiment. The piece of land was
selected with special reference to protection from cold, adapta-
bility to citrus culture and uniformity of type of soil. It is gen-
erally considered that the influence of the fertilizer treatment
given citrus trees may extend over a period of several years after
that particular treatment has been discontinued. In order to elim-
inate this disturbing factor from the experiment it was deemed
advisable to begin with young trees. Accordingly, one year old
budded trees, all of the same variety, especially selected with
regard to uniformity of size, and all from the same nursery,
were used in the work. They were set out in January, 1909, three-
quarters of a pound of bone meal being given each tree.

The objects of the experiment were to determine the effect
of various fertilizers upon the chemical composition of the soll,
upon the growth and composition of the trees and upon the fruit.
The effects of lime and other alkaline materials, and of various
cultural treatments upon the soil and upon the trees were also
objects of study. To supplement the work in the grovvwigth
fertilizers, a number of soil tanks were made use of on thle bigt i
cultural grounds of the Experiment Station. i gsarro rol

The grove was divided into 48 plots of ten trees each. These
trees were Valencia Late on sour stock, and were set 15 by 30

4 Florida Agricultural Experiment Station

I I / I I I 3 I0 3 1

3 2.3 31 33t 7 3 1 I

FgI Daah teliz

Ia I
2. /i3 / 2I , 3 y
a a a 1 1a1 a a a I a a

i g I a a iI S a

P 1 ags i t y l izt
A a w n e e a a as h a
I aia a a I a
a aaI I a I I

I /oa /eat a 1 Z

S a Ammonia, 5 per cent. from sulphate of ammonia.
Standard formula a a Phosphoric acid, 6 per cent., from acid phosphate.
a a i a potash

Bulletin 154, Citrus Fertilizer Experiments 5

Variations from the Standard
Plot 1. Half the standard.
Plot 2. Standard.
Plot 3. Double the standard.
Plot 4. Four times the standard.
Plot 5. Phosphoric acid and ammonia increased by one half.
Plot 6. Phosphoric acid and potash increased by one half.
Plot 7. Ammonia and potash increased by one half.
Plot 8. Phosphoric acid and potash decreased by one half.
Plot 9. Phosphoric acid and ammonia decreased by one half.
Plot 10. Ammonia and potash decreased by one half.
Plot 11. Standard and finely ground limestone.
Plot 12. Standard and air-slaked lime.
Plot 13. Standard and mulch.
Plot 14. Standard.
Sources of Nitrogen
Plot 15. From nitrate of soda.
Plot 16. Half from nitrate of soda, and half from sulphate of ammonia.
Plot 17. From dried blood.
Plot 18. Half from sulphate of ammonia, and half from dried blood.
Plot 19. Half from nitrate of soda, and half from dried blood.
Plot 20. From cottonseed meal.
Plot 21. From cottonseed meal. (With ground limestone.)
Plot 22. Half from cottonseed meal, and half from sulphate of ammonia.
Plot 23. Half from cottonseed meal, and half from nitrate of soda.
Sources of Phosphoric Acid
Plot 24. From dissolved boneblack.
Plot 25. From steamed bone.
Plot 26. From steamed bone. (Double amount.)
Plot 27. From Thomas' slag. (Nitrogen from nitrate of soda.)
Plot 28. From Thomas' slag. (Double amount. Nitrogen from nitrate of
Plot 29. From acid phosphate. (Potash, 7% per cent. in June, 7% in
October, and 3 in February.)
Plot 30. From acid phosphate. (Nitrogen from nitrate of soda. Potash
from hardwood ashes.)
Plot 31. From acid phosphate. (Standard.)
Plot 32. From dissolved boneblack.
Plot 33. From floats.
Plot 34. From floats. (Double amount.)
Plot 35. From floats. (Four times amount.)
Plot 36. From floats. (Four times amount. Nitrogen from cottonseed
Sources of Potash
Plot 37. From low-grade sulphate.
Plot 38. From muriate.
Plot 39. From high-grade sulphate of potash. (With ground limestone.)
Plot 40. From kainit.
Plot 41. From high-grade sulphate of potash. (Standard.)
Plot 42. From nitrate of potash. (Balance of nitrogen from nitrate of
Variations from the Standard
Plot 43. No fertilizer.
Plot 44. Standard.
Plot 45. Standard and mulch.
Plot 46. Standard and clean culture.
Plot 47. Nitrogen from dried blood. Clean culture.
Plot 48. Nitrogen from nitrate of soda. Clean culture.

6 Florida Agricultural Experiment Station

feet. The diagram in Figure 1 shows the relation of the plots to
each other. The fertilizer and other treatment given these forty-
eight plots is shown in Table 1. A standard formula consisting
of 5 percent ammonia, 6 percent phosphoric acid, and 6 percent
potash, was used. In the fall this was changed to 21/2 percent
ammonia and 8 percent potash, the phosphoric acid remaining
the same. The standard mixture consisted of sulphate of am-
monia, acid phosphate, and high grade sulphate of potatsh. As
shown in Table 1 this mixture was varied for different plots by
substituting other sources of the three essential elements for
those in the standard mixture. The standard mixture was used
at first at the rate of 2 pounds per tree three times a year. This
amount was gradually increased so that at the end of the experi-
ment the "standard" plots were receiving an application of six
pounds instead of two.

Soil Subsoil
Insoluble matter ..............-- ............-------- ....-.... ..... 94.09 94.81
Volatile matter .................--------.... .. ----.... .-....... 2.55 1.71
N nitrogen --........................... ...........-- .... .. .033 .018
Phosphoric acid ..-........-- ...... ...........-- ......-...- .10 .09
Potash ........... ...--- ... ...-- ..-.........---...--....------- .047 .025
Soda ........... ..... --------... ..................-----....---- .134 .115
Lime ..............-..---.... ......-.. ---................----- ......--- .13 .17
M agnesia .................................................. .------..... .14 .09
M anganese oxide ....... ................ --- .........- --- .10 .14
Ferric oxide .................... --.......-.......-----.......----- .98 .96
Aluminum oxide ............................. ............... 2.30 2.40
Sulphur trioxide ..............--- ....- .... ..- .............. trace trace
Carbon dioxide ......................---... ........-.......... none none
,P205 N
1st foot ... -----------------------------...... .12 .030
2nd foot ...--..-- .............-...-.....-- ........- ....-.... ....- .10 .015
3rd foot .-.. .... ----------- ------------------------- .09 .013
4th foot ...-....-..-...............-------- ..-- -----------..- -..-- .. .09 .012
5th foot .... .. .... ....................... .......... .09 .009

Plots 46, 47 and 48 were cultivated during the entire year.
Plots 13 and 45 were mulched with a mixture of forest leaves,
grass, etc. The remainder of the grove was cultivated up to
the rainy season (about June 1), and then a cover crop allowed
to occupy the land until in September, when it was either turned
under or cut for hay and the stubble plowed under. During the
early years of the experiment this cover crop consisted of beg-
garweed. The soil finally became too acid to support a good crop
of the beggarweed, and was at first supplemented with cowpeas,
and later on with velvet beans.

Bulletin 154, Citrus Fertilizer Experiments 7


A B C D E F G Ave.
N .029 .040 .033 .033 .037 .030 .028 .033
P205 I .09 .12 .08 .11 .12 .10 .09 .10
N .018 .018 .015 .020 .019 .018 .016 .018
P205 .09 .12 .08 .09 .11 .08 .08 .09

The effects of the various treatments on the trees were meas-
ured by taking at regular intervals the diameter of the trunks
six inches above the bud. Notes on the size, general appearance
and character of growth of the trees were taken from time to
The soil on which the grove is located is a rather coarse reddish
sand of the hammock type, verging on high pine, and rather
dry in character. At the time that the trees were set out com-
posite samples of the soil (0-9 inches) and of the sub-soil (9-21
inches) were taken and analyzed. In one place in the field
samples of the first five feet were taken and the phosphoric
acid and nitrogen contained in the samples were determined.
These analyses are given in Table 2. Samples of the soil and
subsoil were also taken in seven different places in the field and
analyzed for phosphoric acid and nitrogen. These analyses are
given in Table 3. They show that the soil over the field was of
a fairly uniform composition. The analyses of this soil as a
whole indicate that it is somewhat above the average in fertility
as compared with citrus soils in general.

Fi. 2-Setional viw of tanks

Fig. 2.--Sectional view of tanks

8 Florida Agricultural Experiment Station
',*' *" *--------------- /9'- 6 - ---------------- ,

Fig. 3.-Ground plan of tanks
In order to supplement the work with fertilizer in the field,
soil tank experiments were begun on the Station grounds.
By this means it has been possible to more closely measure and
control conditions than where the work has been conducted on
the scale necessary in field experiments. Accurate estimates
of the losses of fertilizing materials in the drainage water under
different systems of fertilizing and the effect of long continued
use of fertilizers on the soil have been possible. In this way much
interesting light has been thrown upon the question of the
capacity of the average sandy Florida soil for retaining the
fertilizing ingredients added to it and which of these materials
are most subject to leaching.
Figures 2 and 3 illustrate the equipment used in the work.
The tanks were constructed of heavy galvanized iron, painted

Bulletin 154, Citrus Fertilizer Experiments 9

inside and out with a chemically-resistant paint. Each tank had
an inside diameter of 5 feet 31/ inches, with a maximum depth
of 41/2 feet, and a surface area of one two-thousandths of an
acre. As shown in the diagram, the bottom of the tank slopes
to one side, where there is a strainer opening into a two inch
tin-lined iron drainage pipe, the length of which is a little over
4 feet. Four such tanks open into a central collecting pit as
shown in Figure 3. Under the ends of the drainage pipes
entering at the four corners of the pit were placed large gal-
vanized cans for collecting the drainage waters. These cans
were coated on the inside with paraffine to prevent any chemical
action of the drainage water upon the metal. The collecting pit,
which is about 8 feet deep and 6 feet square inside, is built of
brick, with a concrete bottom, and is covered. The soil tanks
were sunk in the ground to within a few inches of the tops and
were filled with soil to within 3 inches of the rims. The soil
used was a rather coarse, gray sand of high hammock type. It
is described by the Bureau of Soils as Norfolk sand. In filling
the tanks a layer of quartz pebbles was first placed over the
sloping part of the bottom in order to provide adequate drainage
and to prevent the soil from sifting thru the strainer and filling
the drainage pipe. Above the layer of pebbles was placed 45
inches of soil. In excavating for the tanks the soil was removed
in layers. First a 9 inch layer was removed and placed at one
side by itself. Then the soil was removed in one foot layers, each
foot being kept separate from the remainder. The last foot of
excavated soil was placed in the bottom of the tank, then the
remaining sections ending with the top 9 inches. Thus the
soil rested in the tank as it was in the original state. Each layer
of soil was well packed as it was placed in the tank, the same
weight of dry soil, 8,625 pounds, being used in each. The tanks
were then exposed to natural conditions, the drainage water
leaching thru the soil being collected from time to time as it
became necessary, and analyzed. This treatment was continued
for a period of 10 months during which time the soil received no
fertilizer, the results obtained representing the losses of plant
food from a bare, unfertilized soil. The results show that by far
the greatest loss of plant food falls on the nitrogen of the soil.
The thoro aeration which the soil received when the tanks were
filled would lead to more rapid nitrification of the soil organic
matter and thus to somewhat larger losses of nitrogen in the
drainage water at first, than would occur under natural condi-

10 Florida Agricultural Experiment Station


Sulphate of Nitrate of Drd
Ammonia Sodaed Blood

C3 a 01 -i 'F ZU '30

July 13 74.74 .63 74.11 .85 2.28 72.46 3.05 1.47 73.27 1.96
Aug. 23 .......... 1.18 72.93 1.59 11.32 61.14 15.63 4.16 69.11 5.68
Sept. 5 .......... 4.66 68.27 6.39 20.34 40.79 33.28 11.98 57.13 17.34
Nov. 22 18.69 8.46 78.49 12.40 22.07 37.41 54.21 16.59 59.22 29.05
Jan. 8 .......... 8.12 70.36 10.35 13.26 24.15 35.44 9.35 49.87 15.80
Mar. 12 37.37 5.72 64.64 8.13 2.56 21.59 10.59 2.06 47.81 4.13
April 13 .......... 3.91 98.09 6.05 3.46 55.50 16.04 .43 84.75 .90
June 10 37.37 10.14 87.95 10.34 11.63 43.87 20.95 2.10 82.65 2.48
July 16 .......... 9.64115.68 10.96 7.94 73.29 18.10 1.99118.02 2.41
Aug. 23 .......... 6.43 109.25 5.55 .......... 73.29 ................... 118.02 .........
Oct. 21 18.69 3.191124.75 2.92 3.46 88.52 4.72 1.381135.33 1.17
April 1 37.37 .65 161.46 .52 4.23121.65 4.78 .971171.72 .72
July 14 37.37 1.61 159.85 1.00 2.38119.28 1.95 .271171.45 .16
Aug. 9 ......... ..... 197.23 .......... ...... 156.65 ....-...- ......... 208.82 ..........
Oct. 31 18.69 2.53 213.38 1.28 2.17 173.16 1.39 .22 227.28 .11
Jan. 3 .......... 1.72 211.66 .80 .431172.73 .25 .161227.12 .07
Jan. 24 .......... .56211.09 .27 .291172.44 .17 .271226.85 .12
Feb. 11 .......... .59210.50 .28 .841171.60 .48 .321226.53 .14
Mar. 6 37.37 .79 247.08 .38 .93 208.04 .54 .34 263.57 .15
Aug. 8 37.37 2.33 282.12 .94 4.251241.16 2.05 .27 300.66 .10
Oct. 10 .......... 3.12 279.00 1.11 1.20 239.96 .50 .......... 300.66 .........
Oct. 23 18.69 .......... 279.00 ......... .......... 239.96 .......... .25300.41 .08
Dec. 21 .......... 2.261295.42 .81 2.221256.42 .92 .411318.69 .14
Jan. 6 .......... 2.28 293.13 .77 1.521254.90 .59 .25 318.44 .08
Jan. 25 .......... 2.03 291.10 .69 1.63 253.27 .64 .521317.92 .16
April 5 37.37 1.49 289.60 .51 .86 252.41 .34 .45 317.47 .14
May 17 ......... 1.02 288.58 .35 .......... 252.41 .......... ......... 317.47 ..........

tions. Allowing for this factor, however, the losses of nitrogen
still remain very large. During the 10 month period a loss of
nitrogen equivalent to over 800 pounds nitrate of soda per acre
was noted. The losses of potash and phosphoric acid were much
smaller, in fact, almost negligible. The loss of potash per acre
amounted to about 14 pounds, and phosphoric acid to about a
half pound. These figures show that these two elements of plant
food are locked up in the soil in relatively insoluble forms which
become only slowly available. At the end of this period of 10
months, an orange tree was placed in each tank and fertilized
with a fertilizer of the same formula as that used in the grove
experiment. The trees in all the tanks received the same amounts
of phosphoric acid and potash in the form of acid phosphate and
high grade sulphate of potash, the source of nitrogen only being
varied. The trees in tanks 1 and 2 received sulphate of ammonia,
the tree in tank 3 nitrate of soda, the tree in tank 4, dried blood,

Bulletin 154, Citrus Fertilizer Experiments 11

the same amount of actual nitrogen being used for each tree.
The same amount of fertilizer as was used in the grove was
applied to each tree three times per year. The results of the
analyses of the drainage water collected from these tanks from
time to time are given in Table 4. These figures indicate the
extent to which the nitrogen of the three materials used leaches
thru the soil. These losses are stated here in percentages of the
total amount of nitrogen applied less the amounts lost on pre-
ceding dates. For example, the table shows that on November
22, 1911, the drainage water from the nitrate of soda tank
contained an amount of nitrogen equivalent to over 54 percent
of the total nitrogen which had been applied up to that date,
less the quantity of nitrogen already leached out up to the
same date. In other words, the percentage of loss for each
date was figured on the amount of nitrogen still remaining in
the soil at that date, and not on the total amount which had
been applied.
A study of the table brings out a number of interesting and
important facts. It will be noted that while the loss of nitrogen
varies with the material used, the percentages lost with all three
materials increase from the beginning up to November 22, and
continue large until August, 1913. For the period from July
13, 1911 to July 17, 1913, 41 percent of the sulphate of ammonia
applied to the soil leached thru and was lost in the drainage
water; 72.5 percent of the nitrate of soda, and 38.3 percent of
the dried blood were lost. This interval of about two years
represents a period during which the trees were becoming estab-
lished and when the root system was small and occupied but a
small portion of the soil. Consequently, much of the fertilizer
was not utilized and as a result leached thru the soil and was
lost. The fact that the losses became smaller as time went on
indicates that the larger root systems were able to utilize more
and more of the fertilizer. The table also brings out important
differences in the behavior of the three different sources of
nitrogen in the soil. It will be noted that the largest loss of
nitrogen occurred with the nitrate of soda, the losses from the
other two sources being considerably less. The larger loss of
nitrate of soda is explained by the fact that this material is
very readily soluble in the soil moisture and that the soil has
very little if any power to retain or fix nitrogen in the nitrate
form. Consequently, if the soil is moist and the rainfall is

12 Florida Agricultural Experiment Station

sufficient to more than saturate the soil the nitrate of soda is
immediately dissolved and much of it is carried below the range
of the plant roots. Dried blood and sulphate of ammonia differ
from nitrate of soda in their behavior in the soil.
The nitrogen in these materials is not available for plants
until it is changed to the nitrate form thru the agency of various
soil bacteria in the process known as nitrification. In its original
form the nitrogen of dried blood is not readily soluble in the
soil water, and consequently very little is lost in the leaching
process until nitrification occurs. In this change the organic
nitrogen of the blood is changed first to ammonia, then to the
nitrite and finally to the nitrate form, when it becomes as
readily soluble as the nitrate of soda and is leached out as
readily. Nitrification of the dried blood is a gradual process,
extending over a period of time which may be of several weeks'
duration, depending on soil conditions. Because of this, some
of the nitrogen of dried blood, or for that matter, any similar
organic material, will remain in the soil a considerably longer
time' and be available to the crop over a longer period, than
nitrate of soda. This is especially true where heavy rains occur
after the latter has been applied to the soil.
The behavior of sulphate of ammonia in the soil is different
from either of the two materials already discussed. While this
substance is readily soluble in the soil water the soil has the
power of fixing or absorbing at least a portion of the ammonia,
thus preventing it from leaching away. This takes place thru
chemical means and is common to all soils. Very sandy soils can
absorb only a small amount of ammonia; loam and clay soils
are able to absorb much larger quantities, due mainly to the clay
content of these soils. Therefore, when sulphate of ammonia is
applied to the soil at least a part of the ammonia is absorbed
by this clay present and fixed in a form which is not readily
washed out. This ammonia must be changed, thru the agency of
the nitrifying bacteria of the soil, to the nitrate form. Then
it gradually becomes available to the plant and, of course, is
then subject to leaching. These facts account for the smaller
loss of nitrogen as noted in the table, from the soil receiving
sulphate of ammonia as compared with that receiving nitrate
of soda.
It should be remembered that the three sources of ammonia
here discussed were used side by side, in the same equivalent
amounts, on the same type of soil and under identical conditions
so far as these couldL-e brought about in the experimental work.

Bulletin 154, Citrus Fertilizer Experiments 13

Accordingly, the behavior of each of these materials in the soil
as compared with the others may be taken as strictly compara-
tive not only in this experiment but under all usual conditions
where they are used. The actual amount of each which might be
lost in the drainage on different types of soil and under varied
conditions would in all probability differ more or less from the
results given in the table. However, the fact that nitrate of
soda for instance, leaches thru to a much larger extent than
sulphate of ammonia, would hold true under all ordinary con-
ditions. The important facts brought to light in the experimental
work here described regarding these nitrogenous materials and
which have a practical application in grove fertilization are as
follows: Nitrogen, the most expensive ingredient of fertilizers
under normal conditions and usually the element most deficient
in Florida soils, is the element which is lost in the largest
amounts by leaching.
Tank 1 Tank 3 Tank 4
W +a i S -
S._ ; ."
U2 o o o o 1o o W Wo
July 13 108.86 .10108.76 .0 .30108.6 .40 108.46 .37
Aug. 23 .... .10108.66 .09 .701107.86 .64 .50107.96 .46
Sept. 5 .70107.96 .64 1.20106.66 1.11 .80107.16 .74
Nov. 22 72.57 1.30 179.23 1.20 2.30176.93 2.15 .80 178.93 .74
Jan. 8 ..... 2.40176.83 1.34 4.20 172.73 2.37 1.10 177.83 .61
Mar. 12 54.43 3.50 173.33 1.98 3.90168.83 2.26 2.20175.63 1.24
April 13 2.90224.86 1.67 4.10219.16 2.43 2.00228.06 1.14
June 10 54.43 9.60215.26 4.27 8.40210.76 3.83 5.40222.66 2.37
July 16 ... 11.80 257.89 5.48 4.30260.89 2.04 3.90273.19 1.75
Aug. 23 ------- 10.80 247.09 4.19 ......... 260.89 .................... 273.19 ...
Oct. 21 72.57 11.10 308.56 4.49 12.20 321.26 4.68 5.10 340.66 1.86
April 1 54.43 7.10355.89 2.30 6.80368.89 2.11 6.60388.49 1.94
July 14 54.43 6.501349.39 1.83 6.601362.29 1.79 6.901381.59 1.77
Aug. 9 .-.....-- .--.... 403.82 ......... .......... 416.72 ..........-- ........ 436.02 ..........
Oct. 31 72.57 10.10 466.29 2.50 17.00 472.29 4.08 3.20 505.39 .73
Jan. 3 .......... 16.00 450.29 3.43 22.50 449.79 4.76 6.70 498.69 1.32
Jan. 24 ....... 7.501442.79 1.66 14.70 435.09 3.27 10.90 487.79 2.18
Feb. 11 ........ 7.00 435.79 1.58 11.20 423.89 2.57 13.60 474.19 2.79
Mar. 6 54.43 8.301481.92 1.90 10.20 468.12 2.41 10.201518.42 2.15
Aug. 8 54.43 13.40 522.95 2.78 11.20 511.35 2.39 5.50567.35 1.06
Oct. 10 --..... 19.80 503.15 3.79 6.201505.15 1.21 ......... 567.35..
Oct. 23 72.57 .......... 503.15 .......... ..-....... 505.15 .......... 3.90563.45 .69
Dec. 21 .......... 14.60 561.12 2.90 13.40 564.32 2.65 10.301625.72 1.83
Jan. 6 ..... 12.40 548.72 2.21 11.40 552.92 2.02 8.40 617.32 1.34
Jan. 25 13.40 535.32 2.44 11.80 541.12 2.13 8.10609.22 1.31
April 5 54.43 16501518.82 3.08 13.901527.22 2571 12.00'597.22 1.97
May 17 -.......... 9.601573.25 1.851- .........1581.651 .-.........-- ........1 651.65 .......

14 Florida Agricultural Experiment Station

The various sources of nitrogen differ greatly in their tendency
to leach out of the soil, much more of the nitrogen of nitrate of
soda than of sulphate of ammonia being lost in this way.
The greatest losses take place when heavy rains occur soon
after an application of nitrogenous fertilizers.
These losses decrease to a great extent as the trees become
older and more of the soil becomes permeated with tree roots.
Table 5 shows that a considerable loss of potash has taken
place. The figures in the potash column represent the average
losses for three soil tanks. The losses for the first two years
are small, after which they increase considerably. This would
indicate that during the first period part of the potash applied
was absorbed by the soil, but that after the second year the
soil had reached its maximum capacity for holding the potash
and became saturated, so to speak, so that succeeding applica-
tions were not absorbed to any extent.
It is well known that practically all soils have some power to
retain soluble potash. Sandy soils exhibit this capacity in the
least degree, while heavy clay soils will absorb large amounts.
The power of a soil to fix or absorb potash depends largely upon
the presence of certain silicates which are associated with the
clay present. When absorbed by the soil, water-soluble potash
assumes a form which is not easily leached out by water but
which is still generally regarded as being more available to
plants than the potash combinations originally present. Since
Florida soils as a general rule contain very little clay their power
to absorb potash is limited. In the work here described it was
found that at the end of four years about 30 percent of the
potash applied had leached out, the remaining 70 percent being
used by the trees or absorbed by the soil. In bearing groves the
loss by leaching would undoubtedly be under rather than over
the 30 percent found here.
No table is included to show the loss of phosphoric acid since
this loss has been extremely small. At the end of four years it
was found that only .05 of one percent of the amount applied was
lost in the drainage water. This indicates that the soil is able
to absorb large amounts of soluble phosphoric acid. That this
is true is shown by the fact that the soil used contained 50 per-
cent more phosphoric acid at the end of five years than it did at
the beginning of the experiment.

Bulletin 154, Citrus Fertilizer Experiments 15


Source of
4 Phosphoric Acid S3

1............ Acid phosphate ........ 2859 2633 226 200
2........... Acid phosphate ....... 3601 3002 599 480
3............ Acid phosphate ....... 4532 3449 1083 850
4............ Acid phosphate ......- 4750 3037 1713 1660
5............ Acid phosphate ....... 3701 3037 664 750
6............ Acid phosphate ........ 4080 3449 631 720
7............ Acid phosphate ........ 3513 3002 511 450
8............ Acid phosphate ..... .. 3082 2633 449 300
9............ Acid phosphate .-..... 3720 3238 482 320
10............ Acid phosphate ........ 3213 2895 318 310
11............ Acid phosphate ....... 3783 3356 427 390
12............ Acid phosphate .. .. 3357 3177 180 380
13............ Acid phosphate ........ 3916 3177 739 630
14............Acid phosphate ........ 3659 3356 303 440
15........... Acid phosphate ........ 3396 2895 501 530
16 .........-- Acid phosphate ....... 4372 3469 903 600
17...........Acid phosphate ...... 4286 3794 492 290
18........... Acid phosphate .... 3861 3554 307 280
19............ Acid phosphate ........ 3598 2959 639 450
20............ Acid phosphate ....... 3472 2839 633 310
21........... Acid phosphate -.....- 3456 2839 617 410
22............ Acid phosphate ....... 3516 2959 557 630
23............ Acid phosphate ....... 4210 3554 656 370
24............ Dis. bone black......... 4115 3794 321 430
25............ Steamed bone .......... 3609 3098 511 230
26............ Steamed bone .........- 4524 3651 873 510
27............ Basic slag .............. 3643 3033 610 340
28..........- Basic slag .................. 3901 3236 665 630
29............ Acid phosphate ........ 3559 3236, 323 340
30........... Acid phosphate ....... 3434 3037 397 400
31............ Acid phosphate ........ 4145 3651 494 440
32....-......- Dis. bone black-......... 3530 3098 432 450
33-.......- .. Floats .......................... 3197 2904 293 330
34............ Floats ----............-... .. 4095 3191 904 650
35........... Floats -----.................. 4091 3035 1056 1010
36............ Floats ......... ............ 4466 2795 1671 1400
37........... Acid phosphate ........ 3270 2795 475 420
38............ Acid phosphate ........ 3877 3035 842 540
39............ Acid phosphate ....... 3507 3191 316 420
40.....-..--. Acid phosphate ....... 3529 2904 625 510
41 ... ..... Acid phosphate ..... 3432 2997 435 300
42.......-.. Acid phosphate ..... 3510 2820 690 520
43 ...........No fertilizer ........-..- 3348 3348 0 -30
44............ Acid phosphate ....... 3815 3142 673 380
45........... Acid phosphate ...... 3735 3142 593 490
46.......-.. Acid phosphate ........ 3716 3348 368 320
47 -.......-.. Acid phosphate ........ 3192 2860 332 400
48........... Acid phosphate ........ 3529 2997 532 460

In studying the effect of the fertilizers used on the composition
of the soil, especial attention was given to the phosphoric acid.
Work at the Experiment Station with soil tanks has shown that
the loss of phosphoric acid in the drainage water where acid

16 Florida Agricultural Experiment Station

phosphate was used was so small as to be negligible, and that
practically all the phosphoric acid applied was retained by the
soil. The work with the grove soils has confirmed these results.
Samples of soil from the fertilized plots and from the middle of
the tree rows were taken from time to time to a depth of 9 inches,
and determinations made of the phosphoric acid. Work else-
where has. shown that the greater part of the phosphoric acid
absorbed by soils is retained in the upper plowed soil, so in this
work sampling to a depth of 9 inches was considered sufficient.
The difference between the amount of phosphoric acid in the
soil of the plot and that in the corresponding middle would show
the quantity fixed by the soil. These results for the different
plots are given in Table 6. In order to make the results easily
comparable they have been calculated to pounds per acre. The
figures in the table represent in every instance the average of
the results obtained from three different samplings of soil, the
third being taken in July, 1915. The second column from the
right shows the increase in phosphoric acid content, due to the
absorption by the soil of the phosphate fertilizer applied. It
will be noted that these figures vary considerably among them-
selves, even where the amount and form of phosphoric acid
applied has been identical. This variation can be accounted for
by the difficulty of obtaining samples of soil which are perfectly
representative of the plots. However, it will be noted that those
plots receiving the largest applications of fertilizer also show
the greatest amounts of phosphoric acid retained. Plot 4, re-
ceiving four times the standard quantity of fertilizer shows
the greatest fixation, an increase of 1713 pounds per acre being
noted. The source of the phosphoric acid on this plot was acid
phosphate. Plot 36 receiving the same amount of actual phos-
phoric acid as plot 4, but in the form of floats, shows a gain
practically the same as plot 4. Both these plots show an increase
of over 50 percent. Altho five different sources of phosphoric
acid were used on the plots, the form in which it was used does
not appear to have had any influence on the power of the soil
to absorb this material, the water-soluble form being retained
as thoroly as the insoluble forms.
It is believed that the figures in the last column of Table 6
throw some light on the question as to what forms the phos-
phoric acid assume after being incorporated with the soil. It is
generally agreed upon among soil investigators that the phos-

Bulletin 154, Citrus Fertilizer Experiments 17

phoric acid of the soil exists mainly in three forms, namely, the
phosphates of lime, iron, and alumina. It is generally considered
that the last two forms are much less available toplants than
the first form. Indeed it is held by many that the phosphates
of iron and alumina are but very slightly available because of
their practical insolubility in the soil water. Phosphate of lime,
on the other hand, dissolves slowly in the soil water containing
carbonic acid gas and other weak acids and is thus considered
more available to plants. The fixation of soluble phosphoric acid
in the soil is explained by the fact that it combines with one or
more of the compounds of iron, aluminum or lime present and
thus assumes an insoluble form. It then becomes a matter of
some practical importance to know whether the phosphoric acid
added to the soil assumes the form of the insoluble iron and
aluminum phosphates or the more readily available phosphate of
lime. A method of treatment which it is believed will distinguish
between the different forms has been developed by soil chemists
and has been used to some extent. It depends upon digesting the
soil in a weak solution of nitric acid, which will dissolve the
phosphate of lime present but which has no effect upon the
phosphate of iron and alumina. A given weight of soil was
treated with fifth-normal nitric acid (about 1.26 percent acid)
and the amount of phosphoric acid dissolved out determined, this
dissolved phosphoric acid being regarded as coming entirely
from the phosphate of lime present. The soil samples used were
those on which the total phosphoric acid had been determined as
shown in the table. The results given in the table represent the
difference between the amounts dissolved from the plot soils
and those of the corresponding middles, thus representing the
increase in the acid soluble phosphoric acid of the fertilized
plots, and are calculated to pounds per acre.
Some interesting facts are brought out by comparing these
results with the figures representing the increase in total phos-
phoric acid. Those plots showing the greatest increase in total
phosphoric acid also show the greatest increase in acid-soluble.
Plot 4 again shows the greatest increase, followed by plot 36.
The average increase in acid-soluble phosphoric acid for all the
plots (omitting plot 43) is 494 pounds, as compared with an
average increase in total of 586 pounds. Assuming that the
acid used dissolved out only phosphate of lime and no iron or
aluminum phosphate, these figures indicate that about 80.percent
of the increase in phosphoric acid content in the plots has been
fixed in the form of phosphate of lime.

18 Florida Agricultural Experiment Station

Plot Nitrogen Nitrogen Plot Nitrogen Nitrogen
S in Plot in Middle t in Plot in Middle
1 1140 780 25 1350. 1020
2 1170 990 26 1080 930
3 1080 1050 27 1110 1080
4 810 1140 28 1140 1140
5 870 1140 29 1290 1140
6 1170 1050 30 1020 1080
7 1140 990 31 1230 930
8 1140 780 32 1440 1020
9 1080 840 33 1200 1050
10 990 1110 34 1140 1050
11 1170 990 35 1170 1140
12 1140 1020 36 1230 1050
13 1410 1020 37 1320 1050
14 1440 990 38 1410 1140
15 1410 1110 39 1080 1050
16 1230 840 40 1110 1050
17 1170 960 41 1230 810
18 1260 1080 42 1380 1140
19 1260 1080 43 900 990
20 1230 990 44 1230 1290
21 1320 990 45 1920 1290
22 1350 1080 46 720 990
23 1260 1080 47 780 1140
24 1440 960 48 720 810

Table 7 gives the amount of nitrogen in pounds per acre to a
depth of 9 inches. The soil samples were taken from the plots
and from the middles at the end of the experiment in 1918. One
fact brought out here is the considerably smaller amount of
nitrogen in the clean culture plots, 46, 47 and 48, as compared
with the remaining forty-five plots. The average amount of
nitrogen in these three plots is 740 pounds per acre, as compared
with an average for the others of 1220 pounds an acre, indicating
a loss of 480 pounds or 39 percent. This loss must be attributed
largely to the effects of the continuous cultivation. This practice
leads to more rapid nitrification of the organic nitrogen of the
soil, changing the insoluble nitrogen to the soluble nitrate form
which is easily leached out. This loss of organic matter also
means a decrease in the capacity of the soil for holding moisture
and soluble fertilizers added to it.
The average of the forty-eight soils taken from the middles
is 1030 pounds of nitrogen per acre. It is interesting to compare
this figure with the average of fifteen samplings taken at the
beginning of the experiment in 1909. These samples were taken
at various places over the field and probably give a fair average
of the nitrogen content at that time. The amount of nitrogen

Bulletin 154, Citrus Fertilizer Experiments 19

found in this way was 1080 pounds per acre. This is so close
to the average for the middles (1030 pounds) at the end of the
experiment that it is reasonable to assume that the unfertilized
soil between the tree rows neither gained nor lost in nitrogen
during the ten years. In other words, the loss of nitrogen thru
leaching was counterbalanced by the addition of nitrogen by
means of the leguminous cover crop. The fertilized plots have
gained slightly in nitrogen as compared with the soils from the
middle of the rows. Omitting the clean culture plots and the no
fertilizer plot, the average is 1220 pounds per acre, a gain over
the middles of 190 pounds.
Plot Potash Plot Potash
1 ............................-...... 1620 25 ---.....--.........-----------.. ......... 2160
2 --------.. ---. ----------. 1800 26 ................................. 1530
3 ----.....-.----- .. ---.. ... ---- 2010 27 ---.................. ...... 2070
4 --...--...- -.. -.........- ....... 2040 28 ..--..-.................. ...... ---1950
5 ................ ............. 1740 29 .........----.....-......-...---. 1620
6 ....-- .....- ...... ..--- .. ------ 1830 30 .................................. 2040
7 -....--.....- ............- .. -1740 31 ....................- .....-.... -1950
8 ..- .......-....-- .......----- .. 1740 32 ... ---........-...... ............ 2040
9 ....- .......-- ..-... ..--------- 1830 33 .......----....- ....-- ....-....-.. 1440
10 .-----......-........--.---..------1530 34 .........-- ......... ....... 1950
11 -----...-------...-......----.. 1740 35 .........................- ....... 1530
12 .--. --...... -.------ ...-- ... 1950 36 ....--.......--..... ........ .. 1830
13 .-........-------.... -..-- .... 1830 37 -......-----------------... 1830
14 --------. -.... --------- 1950 38 ....--............-........... .... 2160
15 ..--.---...--...-............ 1620 39 .-...-.... --. ---------... ... 1440
16 --... --....- ... .............. 1740 40 .--- .... --.............. .. ---1680
17 -.--.... --........ ....... 1530 41 ---.... ....................... 1950
18 ............................. .. 1740 42 -----------........... 1830
19 .-..- ...---.......- 2160 43 .......................... 1140
20 .--......------......... 1950 44 -...---...... ............... 1830
21 ..... ...-...........----------- 2250 45 .--...--. ....-- ..--.. ....-.. 1620
22 ...........................-...... 1950 46 ..-- --.....------ ------.. 1620
23 ........ --....---- ............... 1440 47 ----...--.. ----..........- .. 1440
24 .................... ... .. .. .. 2040 48 ......-.......- ... .-...........-.- 1530
Unfertilized soil 1140

The amount of potash present in the different plots at the
end of the experiment in 1918 is given in Table 8. The results
are calculated in pounds per acre to a depth of 9 inches, and
represent the total amount of potash in the soil to that depth.
The unfertilized middles were also sampled, and potash deter-
mined in seven of these soils. The average of these seven soils
amounts to 1140 pounds per acre. By comparing this figure with
those for the various plots, the increase in the latter due to the
potash in the fertilizer may be determined. It will be noted that

20 Florida Agricultural Experiment Station.

Plot Gain Fertilizer Treatment
2 139 Standard.
1 138 One-half standard.
12 136 Standard and air-slaked lime.
13 134 Standard. Mulched.
47 133 Nitrogen from dried blood. Clean culture.
46 132 Standard. Clean culture.
16 130 Nitrogen, % nitrate of soda, % sulphate of ammonia.
45 130 Standard. Mulched.
31 128 Standard.
48 127 Nitrogen from nitrate of soda. Clean culture.
37 127 Potash from low-grade sulphate.
25 127 Phosphoric acid from steamed bone.
22 126 Nitrogen, 7 cottonseed meal, % sulphate of ammonia.
8 125 Phosphoric acid and potash decreased by one-half.
30 124 Acid phosphate, nitrate of soda, hardwood ashes.
41 124 Standard.
6 123 Phosphoric acid and potash increased by one-half.
36 123 Phosphoric acid from floats. (4 times amt.) Cottonseed meal.
35 122 Phosphoric acid from floats. (4 times amt.)
9 121 Phosphoric acid and nitrogen decreased by one-half.
38 120 Potash from muriate.
44 118 Standard.
21 114 Nitrogen from cottonseed meal. Ground limestone.
23 114 Nitrogen, % cottonseed meal, % nitrate of soda.
3 114 Twice standard.
20 113 Nitrogen from cottonseed meal.
26 112 Phosphoric acid from steamed bone. (2 times amt.)
32 112 Phosphoric acid from dissolved bone black.
34 111 Phosphoric acid from floats. (2 times amt.)
42 111 Potash from nitrate of potash. Balance nitrogen, nitrate of
19 110 Nitrogen, % nitrate of soda, % dried blood.
11 110 Standard and ground limestone.
24 110 Phosphoric acid from dissolved bone black.
15 109 Nitrogen from nitrate of soda.
27 109 Phosphoric acid from Thomas slag. Nitrate of soda.
7 108 Nitrogen and potash increased by one-half.
33 107 Phosphoric acid from floats.
18 106 Nitrogen, % sulphate of ammonia, % dried blood.
29 105 7% percent potash in June, 7% in October, 3 in February.
40 104 Potash from kainit.
14 103 Standard.
10 102 Nitrogen and potash decreased by one-half.
43 101 No fertilizer.
28 96 Phosphoric acid from Thomas slag. (2 times amt.) Nitrate of
17 90 Nitrogen from dried blood.
39 88 Standard. Ground limestone.
5 75 Phosphoric acid and nitrogen increased by one-half.
4 65 Four times standard.
all the fertilized plots show an increase over the unfertilized
soil, thus indicating that this soil was able to retain at least
a portion of the soluble potash applied. The average increase
for the forty-seven plots amounts to 660 pounds per acre, or an
increase of over 50 percent for the ten years of the experiment.
A large proportion of the potash in the plot soils is held in

Bulletin 154, Citrus Fertilizer Experiments 21

a very insoluble form, probably largely as feldspar. Treatment
of these soils with strong hydrochloric acid dissolved on the
average only 15 percent of the total potash present.
Rank 1910 1911 1912 1913 11914 1915 1916 1917 1918
1 46 46 46 47 2 2 2 2 2
2 30 47 47 46 1 47 1 1 1
3 45 35 35 36 47 1 46 47 12
4 41 41 41 37 46 13 13 48 13
5 29 44 48 13 13 12 12 12 47
6 24 36 2 41 36 48 47 13 46
7 26 48 36 48 41 36 48 25 16
8 5 37 37 12 12 37 45 46 45
9 13 43 22 22 37 46 25 8 31
10 35 16 44 2 45 22 37 31 48
11 31 22 30 35 48 30 22 37 37
12 22 2 43 30 22 41 36 9 25
13 23 8 42 31 30 25 30 36 22
14 43 42 12 45 44 35 31 11 8
15 47 6 13 38 21 31 41 35 30
16 19 30 1 44 38 21 8 6 41
17 36 45 38 34 43 44 35 22 6
18 42 26 20 8 35 38 11 30 36
19 17 25 31 26 8 45 9 44 35
20 30 38 8 43 9 11 6 45 9
21 21 12 16 21 29 6 16 16 38
22 49 11 34 29 31 43 21 20 44
23 37 19 26 25 23 9 26 24 21
24 14 34 6 23 16 29 29 23 23
25 15 31 29 42 32 23 38 32 3
26 8 33 33 20 42 8 32 29 20
27 27 39 23 32 25 16 23 26 26
28 44 20 11 6 24 32 44 21 32
29 32 24 32 28 20 34 20 38 34
30 34 29 19 1 11 26 24 42 42
31 6 1 45 33 6 24 3 3 19
32 38 7 25 9 39 15 34 19 11
33 35 13 7 11 34 20 19 15 24
34 4 27 21 39 33 42 43 10 15
35 3 9 39 24 26 28 28 14 27
36 25 32 9 19 15 10 42 34 7
37 16 14 24 7 7 3 15 27 33
38 10 23 14 3 3 33 27 33 18
39 18 21 27 10 19 39 33 43 29
40 40 3 3 15 10 19 7 18 40
41 11 5 28 18 14 27 10 7 14
42 21 28 10 14 40 7 14 40 10
43 9 17 40 27 17 14 '18 41 43
44 12 10 15 40 27 40 40 28 28
45 28 40 17 16 18 18 39 17 17
46 2 15 5 5 28 5 17 39 39
47 1 18 18 17 5 17 5 5 5
48 7 4 4 4 4 4 4 4 4

The effect of the various fertilizer treatments used in pro-
ducing growth was measured each year by taking the diameter
of the tree trunks. Table 9 gives the average measurements of

22 Florida Agricultural Experiment Station

the trees in the various plots at the end of the experiment. The
measurements are given in thirty-seconds of an inch. These
figures were obtained by subtracting the original diameter of
the tree when set out from the final measurement at the end of
1918. In each case they are the average of the ten trees in each
plot, and give the actual increase made by the trees. Similar
measurements were taken every year during the continuation of
the experiment. The standing of the different plots from year
to year, beginning with 1910 is shown in Table 10.
In Table 9 the plots are arranged in the order of the increase
in growth made at the end of the ten years, the plot making the
largest-increase being placed at the head of the list. This table
brings out the fact that in this experiment a number of sources
of materials have proven almost equally valuable in producing
growth and that several have had an injurious effect. Among
the fertilizers used on the plots making the most growth no
single source has shown any remarkable superiority over others
used, altho there is a considerable variation in the effect of the
different materials. The results of this work emphasize the fact
that the citrus grower need not be restricted in his choice of
fertilizers to one particular material, but that there are a number
of sources of the three essential elements which can be used to
advantage. It should be stated that the soil on which this ex-
periment was located was somewhat above the average in fer-
tility, especially in phosphoric acid content. This fact has served
to minimize differences which might otherwise have developed
between the fertilizers used and especially the sources of phos-
phoric acid. The behavior of plot 43, which received no fertilizer
during the time the experiment continued brings out the fact
that the soil was unusually well supplied with plant food. How-
ever, a study of the table brings out the fact that the plots making
the best growth have received the standard mixture of sulphate
of ammonia, acid phosphate and high grade sulphate of potash.
Of the best 16 plots, all but one have received acid phosphate as
the source of phosphoric acid. The one exception is plot number
25, receiving steamed bone and ranking twelfth in the list. All
but two plots in these sixteen have received high grade sulphate
of potash as the source of potash. The two exceptions are plot
number 37 receiving low grade sulphate of potash and plot
number 30 receiving hard wood ashes, and ranking eleventh and
fifteenth, respectively. Of the five different sources of nitrogen
used, all are represented in the best 10 plots. Sulphate of am-

Bulletin 154, Citrus Fertilizer Experiments 23

monia, nitrate of soda, and the nitrogen of steamed bone have all
produced good growth. It will be noted that plot number 2,
receiving the standard mixture, stands at the head of the list.
As stated elsewhere, this standard mixture consisted of sulphate
of ammonia, acid phosphate, and high grade sulphate of potash.
This mixture was applied at the rate of 2 pounds per tree three
times per year. The amount was increased as the trees increased
in size, the application finally being at the rate of 6 pounds three
times per year.
Plot number 1, receiving one-half the standard amount, or
at the beginning 1 pound per tree three times per year, shows
practically the same increase in growth as plot 2. Plot number
3, receiving twice the standard amount, or 4 pounds per tree at
the beginning ranks twenty-fifth, while plot number 4, receiving
four times the standard amount or 8 pounds per tree, ranks at
the foot, having made less growth than any of the plots. The
standing of this series of four plots brings out the fact that in
this experiment plot number 1 was receiving about the optimum
amount of fertilizer which it would pay to apply to trees of
this age, and that plot number 2 received the maximum amount
which could be applied without inducing injury. The fact that
plots 2 and 1 made practically the same amount of growth indi-
cates that the former was receiving more. fertilizer than the
trees could profitably use, altho not enough to injure them in
any way. The appearance of these two plots was very similar,
the eye not being able to detect any difference in size, character
of growth, or appearance of the leaves. Plot number 3, receiving
twice the standard amount of fertilizer has developed consider-
able injury. This injury was shown soon after the beginning of
the experiment, was quite severe for several years, but finally
became much less apparent. This would indicate that 4 pounds
per tree three times per year was about the maximum amount of
fertilizer which could be applied to young trees and not kill them
outright. The injury was severe during the first few years but
the trees managed to survive and finally to overcome the inju-
rious effects. The behavior of this plot in thus overcoming the
injurious effects of too much fertilizer is shown in Table 10. It
will be noted that in 1911 and 1912 this plot ranked number forty
in the list. In 1913 and 1914 it rose to thirty-eighth; in 1915 to
thirty-seventh; in 1916 and 1917 to thirty-first; and in 1918
to twenty-fifth. This rise in rank indicates that as the trees
became older they were better able to withstand the effects pro-

24 'Florida Agricultural Experiment Station

duced by too much fertilizer. The early injury, however, re-
sulted in a permanent stunting of the trees. At the end of the
experiment they were about three-fourths as large as the trees
of plots 1 and 2.
Plot 4 shows the maximum injury from the use of too much
fertilizer. These trees were stunted from the beginning and have
made very little growth. By the winter of 1912 half of the
trees in this plot were dead and had to be replaced by others.
In the spring of 1913 the excessive applications were discon-
tinued and from that time on only one pound per tree was used
three times per year. The new trees used to replace those killed
by the fertilizer have failed to make much growth. At the end
of the experiment this plot was less than one-fourth the size
of plots 1 and 2 and consisted of almost worthless trees which
will probably never amount to much. Photographs of plots 2,
3 and 4 are reproduced in Fig. 4.
The behavior of plots number 5, 6 and 7 is interesting in this
connection, because of its bearing on the question as to which
of the fertilizing elements used was chiefly responsible for the
injury produced. In this series of three plots two of the elements
were increased by one-half, the third being used in the standard
amount. In the mixture applied to plot 6 the acid phosphate and
high grade sulphate of potash used was one and one-half times
the amount used in the standard mixture, the sulphate of am-
monia remaining the same as in the latter. Plot 7 received 11/2
times the nitrogen and potash of the standard and plot 5
received 11/ times the nitrogen and phosphoric acid of the
standard. It will be noted that the least amount of growth was
made by plot 5 which ranks forty-seventh in the list. This plot
showed all the signs of severe injury caused by too much ferti-
lizer. In the table showing the rank of the plots by years plot
5 stood forty-first in 1911 and dropped still lower from year to
year, until for the last three years it stood next to the lowest.
Plot 7, where the nitrogen and potash were increased, has
made a better growth than plot 5 but not as much as plot 6.
The latter plot shows no injury from the increased phosphoric
acid and potash used. The trees in plot 7 show some injury
caused by too much fertilizer but the injury is not quite so
marked as in plot 5. The behavior of these three plots brings
out the fact that excessive quantities of nitrogen are much more
injurious than similar quantities of phosphoric acid and potatsh
and that increased ratios of nitrogen and potash are less inju-



Fig. 4.-Plots 2, 3 and 4 show the effect on the orange trees when
too much fertilizer is used
Plot 2 was fertilized with the standard mixture. Plot 3 received twice
this amount and, from the smaller size of the trees shows that some injury
was caused. Plot 4 received four times the standard mixture and consists
largely of new trees, the original trees being practically killed by the
excessive quantities of fertilizer used. Plot 2 is the best plot of the forty-
eight; plot 3 ranked twenty-fifth, and plot 4 forty-eighth.

26 Florida Agricultural Experiment Station


Fig. 5.-Results of plots when two elements in the standard mixture
were increased.
.- :: e..- .f - .-

Fig. 5.--Results of plots when two elements in the standard mixture
were increased.

Bulletin 154, Citrus Fertilizer Experiments 27

rious than similar increases of nitrogen and phosphoric acid.
See Fig. 5 for photographs of these plots.
The mulched plots and the plots which received clean culti-
vation the entire year are among the best in the grove. This
treatment has been of benefit in two ways: by conserving mois-
ture and supplying additional nitrogen. The cultivation thru
the year has led to increased nitrification of the organic matter
of the soil thus liberating a supply of available nitrogen in
addition to that supplied in the fertilizer. Determinations on
several occasions during the early years of the experiment have
shown that these plots contained more nitrates in the soil than
was found in the soil of adjacent plots. The soil on which the
plots were located was naturally a rather dry soil so that the
continuous cultivation and the mulch of dry leaves and weeds
have aided in conserving moisture during dry periods. Table
10 shows that the clean culture plots made more growth than
any others during the early years of the experiment but that
after 1913 they did not do quite so well. This would indicate
that for young trees continuous clean cultivation is of benefit in
promoting good vigorous growth, but after a few years it is
possible to cultivate too much. Determinations made at the
end of the experiment show that the soil of the clean culture
plots has lost about 18 percent of the organic matter due to the
continuous cultivation as compared with the soil of adjacent
plots. (See Fig. 6 for photograph of plot 46.)
Sulphate of ammonia and nitrate of soda are the most com-
monly used sources of nitrogen for citrus trees. They are usually
the least expensive per pound of nitrogen and as a rule have
given the best results in practice. It has been pointed out else-
where that the continued use of sulphate of ammonia increases
the acidity of the soil while nitrate of soda decreases acidity,
and this opposite tendency of the two materials has been pre-
sented as an argument for using them together or alternating
one with the other. Additional important reasons for thus
using them can be given. In the discussion on soil tanks it was
pointed out that the loss of nitrate of soda by leaching was much
greater than sulphate of ammonia, and that the losses were
greatest after heavy rains. In order to get the maximum benefit
from the use of nitrate of soda it should be used in small appli-
cations during the drier season of the year. Its nitrogen being


Fig. 6.-Plot 43, no fertilizer; Plot 32, dissolved bone black;
Plot 46, standard and clean culture
Plot 43 received no fertilizer during the period of the experiment. It
ranks forty-third. On plot 32 dissolved bone black was used instead of
acid phosphate. This plot ranked twenty-eighth. Plot 46 was fertilized
with the standard mixture, and in addition was cultivated thru the entire
year. It ranked sixth at the end of the experiment.

Bulletin 154, Citrus Fertilizer Experiments 29

/' 4 /9'/ /119/ /9/3 19/1 IQff/ I/6 f19r /9/3

3 _-- __




___ Plot 4 Fig. 7.-This figure shows effects of excessive amounts of fertilizer

30 Florida Agricultural Experiment Station

immediately available to the tree it is an excellent material to
use in the spring application of fertilizers. At this time the
tree is preparing to put out the spring growth and produce bloom
and more nitrogen is needed at this time than during any other
period of the year. Nitrate of soda supplies this need in a form
which the trees can use as soon as it is placed in the soil. Later
on in the season if the trees have a yellow color and show lack
of nitrogen a light top dressing of nitrate of soda will usually
be of considerable benefit, not only in putting the trees into
healthy growing condition but in assisting in the development
of the fruit. The only disadvantage likely to occur in using
nitrate of soda in this way comes when it is applied to a very
dry soil. It may remain unused in the soil for some time, until
a rain occurs, making it at once available, and the trees absorb
so much of it that injury results. This is not likely to happen if
small amounts are used. From 2 to 3 pounds of nitrate of
soda to trees bearing ten boxes of fruit may be considered a
rather light application.
Sulphate of ammonia may be expected to be of greater benefit
during the wet season. It has been shown that this material is
much less liable to be leached out of the soil than nitrate of soda.
Therefore, during the rainy season its effects will be more lasting
and extend over a longer period than nitrate of soda. In other
words, it will furnish a more constant and uniform supply of
nitrogen during the wet period. The ammonia of this material
becomes available to the plant only after it has been changed
to the nitrate form thru the process of nitrification. This change
is brought about gradually and thus the effects of the sulphate
of ammonia are extended over a longer period. It will be noted
in Table 9 that plot 16 which received one-half of the nitrogen
in the form of sulphate of ammonia and the other half as nitrate
of soda made a better growth than any plot receiving nitrate of
soda exclusively, 'thus emphasizing the point brought out that
the two materials used together will give better results than
*where nitrate of soda is used alone.
Two plots, 25 and 26, received steamed bone as the source of
phosphoric acid and as this material carried a little over 3
percent ammonia this was taken into account. As the quantity
of steamed bone required to supply the proper amount of phos-
phoric acid furnished less than one-fourth enough nitrogen the
balance was made up of sulphate of ammonia, so that the main

Bulletin 154, Citrus Fertilizer Experiments 31

source of nitrogen for these trees was the latter material. The
behavior of steamed bone as a source of phosphoric acid is
discussed in the section on Sources of Phosphoric Acid.
With one or two exceptions the plots receiving dried blood or
cottonseed meal are not among the best. Plot 47, one of the
best in the experiment, received clean cultivation in connection
with dried blood, during the entire period. It has already been
pointed out that this cultivation was of marked benefit in pro-
ducing growth, especially during the early years of the experi-
ment. On plot 22 cottonseed meal was used in connection with
sulphate of ammonia, the amount of the latter being the same
as was used on plot 1 which ranked second in the series. While
these materials have not brought about any actual injury and,
contrary to the general opinion, have not produced dieback, tlhI
experiment has shown that they should not be relied upon as the
sole source of nitrogen for citrus trees. Experience has shown
that an occasional application of one or the other may be of
benefit probably in stimulating the growth of the beneficial soil
bacteria, but when used continuously they are distinctly inferior
to the mineral sources of nitrogen.
Of the five sources of phosphoric acid used, acid phosphate
has given the best results. The eleven best plots all received
this material. Steamed bone has also given good results, plot
25, which received this material, ranking twelfth in the list..
No explanation can be given for the poor behavior of dissolved
bone black in this experiment. As Table 10 shows, neither of
the two plots, 24 and 32, fertilized with this material, have ever
ranked above twenty-third during the ten years of the experi-
ment. The same thing may be said with regard to plots 27 and
28, fertilized with Thomas slag. These two plots have stood
near the bottom of the list during the ten years' work. The trees
in both these plots have shown evidence of malnutrition, such
as frenching, and in some years have produced but a small
amount of new growth. Plot 28, receiving twice as much
Thomas slag as plot 27, consists on the average of somewhat
smaller trees, showed more frenching from time to time, and in
general showed more pronounced symptoms of poor nutrition
during the period of the experiment than did plot 27.
Plots 33, 34, 35 and 36 were fertilized with finely ground raw
rock phosphate, commonly known as floats. The formulas used

32 Florida Agricultural Experiment Station

were as follows: Plot 33, 5-6-6, from sulphate of ammonia,
floats and high grade sulphate of potash; plot 34, 5-12-6, from
the same materials; plot 35, 5-24-6, from the same materials;
plot 36, 5-24-6, from cottonseed meal, floats and high grade sul-
phate of potash.
At the end of the experiment plots 35 and 36 were receiving
a quantity of floats equivalent to a yearly application of over
1300 pounds per acre. It will be noted that these two plots made
the best growth among the float plots. In 1912 they ranked
third and seventh respectively. From 1913 on they gradually
declined as compared with other plots, until at the end of the
experiment in 1918 they were in the nineteenth and eighteenth
places. Plot 36 made somewhat more growth on the average
than plot 35. The rank of plot 36 from year to year is shown
graphically in Fig. 8. It will be noted that plot 36 was at its
best in 1913, and that from that year on there was a gradual
decline in comparative growth. This decline may probably be
attributed to the inability of the trees to obtain sufficient phos-
phoric acid from the floats to make maximum growth. However,
both 35 and 36 were among the best half of the plots at the
end of 1918.
The better results obtained by the use of acid phosphate over
other sources of phosphoric acid, should in all probability be
attributed to its more ready availability. A large proportion of
the phosphoric acid which it carries is soluble in water, while
such materials as bone, Thomas slag and floats contain no water-
soluble phosphoric acid. So far as known the phosphoric acid
of the soil is absorbed by the plant roots in only one form, namely,
the mono-calcium phosphate, or the so-called water-soluble form
found in acid phosphate. This form contains one part of lime
combined with two parts of phosphoric acid. When acid phos-
phate is added to the soil the mono-calcium phosphate combines
with more lime to form the di-calcium phosphate, or the so-
called "reverted" phosphate, which contains two parts of lime
combined with two parts of phosphoric acid. The reverted form
is fairly soluble in water containing carbon dioxide. Usually
an additional change takes place later on and the reverted form
combines with still more of the lime of the soil and forms tri-
calcium phosphate, containing three parts of lime combined with
two of phosphoric acid. This is the form of phosphoric acid
found in floats and bone.

Bulletin 154, Citrus Fertilizer Experiments 33

/9/0 / ,?(9ft /9/a 3 19,1 / ? /4I /1/7 /9f/






Fig. 8--Comparative growth of plots 27, 43, 32, 36 and 46

34 Florida Agricultural Experiment Station

The thought might occur that since acid phosphate after
being added to the soil ultimately assumes the form of the tri-
calcium phosphate, it would be reasonable to expect as good
results from a direct application of the latter form of material.
The difference in availability is explained by the fact that when
acid phosphate is added to the soil it dissolves in the soil water
and is soon distributed uniformly and widely among the soil
particles. When it changes to the reverted form it remains as
a thin film deposited over the surface of the particles of soil and
thus is in the best possible condition to go into solution thru the
action of the soil water and to- come into contact with the tree
Where the insoluble phosphates are used it is impossible to
obtain as thoro and uniform a distribution of the solid particles
of the material, even if very finely powdered, as it is in the case
of a solution.
The phosphoric acid of steamed bone, altho in the form of
tri-calcium phosphate, is more readily available than the same
form as contained in floats. In the former material the phos-
phoric acid is intimately associated with the organic material
of the bone. When this decays it acts on the insoluble phosphate
and makes it gradually available. Steamed bone has usually
given excellent results as a source both of nitrogen and of phos-
phoric acid, and while not as quick acting as some other mate-
rials, its effects are usually more lasting. It is usually considered
that about one-half of the phosphoric acid of steamed bone be-
comes available the first season, the remainder gradually be-
coming available in succeeding years.

Of the six sources of potash used in this experiment, the high
grade and low grade sulphates and hard wood ashes have all given
excellent results. The best ten plots all received high grade
sulphate of potash. Plot 37 to which low grade sulphate of
potash was applied, ranked eleventh at the end of the work.
The hard wood ashes plot ranked fifteenth. One objection to
the continuous use of the latter material has been brought out
in this experiment, and is discussed in the section dealing with
lime and other alkaline materials. The frenched condition of the
trees brought on by the ashes was not so severe as on other plots,
but was sufficient to interfere somewhat with normal growth.
An occasional application of ashes to citrus trees would probably

Bulletin 154, Citrus Fertilizer Experiments 35

give very little if any trouble. The muriate and the nitrate of
potash gave only fair results. The trees on these two plots did
not produce quite the thrifty, vigorous growth characteristic of
the best plots.
The trees in plot 40, which received kainit as the source of
potash, made very poor growth during the entire period of the
experiment. Compared with plots receiving the high and low
grade sulphate and ashes, they were smaller in size, growth was
less abundant, and appeared much less thrifty and vigorous.
This plot received the same treatment as plot 41 in the next row,
excepting the source of potash, but the trees were not more
than two-thirds the size of those in plot 41.

Table 11 gives the lime requirement of the various plots for
four different dates, samples of soil being taken in March, July,
and December of 1913 and in July, 1915. By the term "lime
requirement" is meant the amount of lime necessary to be added
to the soil to bring about an alkaline reaction. In the method used
the soil is treated with varying quantities of lime water of
standard strength until the proper amount necessary to give an
alkaline reaction is reached. The figures in the table represent
pounds of calcium carbonate (ground limestone) per acre.
Samples of soil were taken from the plots where the fertilizers
had been applied and also in the middle of the tree rows where
the soil had never been fertilized. The difference between the
lime requirement of any plot and the corresponding middle would
show the effect of the fertilizer used on the plot in increasing or
decreasing the acidity of the soil. It will be noted from the
table that plots 11, 12, 21 and 39, receiving ground limestone,
and plot 30, receiving hardwood ashes, all show an alkaline
reaction, due to the effect of these basic materials in neutralizing
the acidity originally present and also that which may have de-
veloped from time to time. Plots 27 and 28, receiving basic slag
and nitrate of soda, show a marked decrease in lime require-
ment as compared with the corresponding checks. Basic slag
has an alkaline reaction and contains usually a small excess of
lime over and above that in combination with the phosphoric
acid in it. This excess of lime is seldom over 5 to 10 percent.
Hence, basic slag in the amounts ordinarily applied in practice
would not supply sufficient lime to neutralize the acid condition
of a sour soil except in a limited degree as is here shown. The

36 Florida Agricultural Experiment Station


Plot No.
lot No. March, 1913 July, 1913 Dec., 1913 July, 1915
____ Plot Middle Plot Middle Plot Middle Plot Middle
1 1600 1070 2140 1070 1600 1070 2140 2140
2 2670 1600 3210 2670 3210 1600 3740 2670
3 2670 1070 3210 2670 3210 2140 4810 2140
4 3210 1070 3740 2140 2670 2140 4810 1600
5 2670 1070 3740 2140 3740 2140 5350 1600
6 4280 1070 3740 2670 3740 2140 4810 2140
7 2670 1600 3740 2670 3210 1600 3740 2670
8 2670 1070 3210 1070 2140 1070 3740 2140
9 2670 1070 3210 2140 2140 1600 2670 1600
10 2670 2140 3210 2670 3210 2140 3210 3210
11 Alk.* 2670 Alk.* 3210 Alk.* 3210 Alk.* 2670
12 Alk.* 2670 Alk.* 3210 Alk.* 3210 Alk.* 4280
13 3740 2670 4280 3210 4280 3210 4810 4280
14 2670 2670 3740 3210 3740 3210 4810 2670
15 2670 2140 3740 2670 2670 2140 2670 3210
16 2670 1070 2140 2140 2670 1600 3740 1600
17 2670 2670 3210 3210 3210 2670 4810 3210
18 2670 2670 3740 4810 2670 2670 4280 2670
19 2670 2140 4280 3210 2140 2670 4280 3740
20 2670 2670 3740 4280 2670 2670 3740 3210
21 Alk.* 2670 Alk.* 4280 Alk.* 2670 Alk.* 3210
22 2670 2140 5350 3210 4280 2670 4280 3740
23 2670 2670 4810 4810 2670 2670 5350 2670
24 2670 2670 5890 3210 3740 2670 4280 3210
25 2670 2670 3740 3740 2670 2670 3210 3210
26 2140 2670 4810 2670 3210 2670 3210 2670
27 1600 2140 2140 3740 2140 2140 1600 2140
28 1070 2670 3210 3740 1070 2670 2140 5350
29 2670 2670 4810 3740 4280 2670 4810 5350
30 Alk.* 2140 Alk.* 3740 Alk.* 2140 Alk.* 2140
31 3210 2670 4810 2670 3210 2670 4810 2670
32 3210 2670 4810 3740 3210 2670 4280 3210
33 2140 3210 3740 2670 2670 2140 3740 3210
34 2140 2140 4280 3210 2670 2670 3740 3210
35 2140 2670 4280 3210 3740 2670 5350 3740
36 2670 2140 4280 4280 3210 2140 3740 2670
37 3740 2140 4810 4280 2670 2140 5350 2670
38 3210 2670 4280 3210 3740 2670 4280 3740
39 Alk.* 2140 Alk.* 3210 Alk.* 2670 Alk.* 3210
40 3210 3210 4810 2670 2670 2140 3740 3210
41 2670 2140 3740 2670 2670 1600 3740 2670
42 2140 2140 3740 2140 2140 1600 2670 2140
43 2140 2670 3740 2670 2140 2140 3210 4280
44 4280 2140 5350 6420 3740 3740 5350 4280
45 4280 2140 7490 6420 5890 3740 6960 4280
46 3210 2670 4280 2670 3740 2140 3740 4280
"47 2670 2140 3740 2140 3210 1600 2670 2140
48 2140 2140 3210 2670 2140 1600 3210 2670
neutralizing effect shown in these two plots is also influenced
by the nitrate of soda used in connection with the basic slag.
Nitrate of soda also has an alkaline reaction in the soil due to
the fact that the N03 or nitrate part of the material is used
up by the tree much faster than the NA or sodium portion.

Bulletin 154, Citrus Fertilizer Experiments 37

This leads to more or less of an accumulation in the soil of the
sodium element, which by combining with the carbonic acid
gas of the soil water forms carbonate of soda, a material having
an alkaline reaction.
The effect of nitrate of soda on an acid soil is also brought
out by a study of the lime requirement of plots 15 and 48 which
received this material as the source of nitrogen. In both plots
the tendency of the nitrate of soda to decrease acidity is clearly
shown. In plot 15 there is an actual decrease in the acid condi-
tion of the soil, while in plot 48 the soda has at least prevented an
increase. In the soil of plot 42, receiving nitrate of potash and
nitrate of soda, the tendency also is for the acidity to decrease.
The well known tendency of sulphate of ammonia to increase
the acid condition of the soil is shown here in the majority of
the plots receiving this material as the source of nitrogen. The
plots showing the highest degree of acidity nearly all receive
this material. It is true that some form of phosphoric acid and
of potash were used on each plot in connection with the sulphate
of ammonia and it might be argued that these materials were in
part responsible for the acid condition present. The work of
other investigators, however, where sulphate of ammonia was
used alone, has shown that this material must be held as the
chief cause of acidity. The absorption and nitrification of the
ammonia of this material is comparatively rapid, being followed
by its final utilization by the tree. This leaves the sulphuric acid
portion in the. soil, thus bringing about acid conditions. The
potash of the muriate and sulphate of potash disappears much
more slowly from the soil as the latter has the power of retaining
for some considerable time the potash or basic element of these
materials. Therefore, while the tendency of these materials
would be to produce in the long run an acid condition, their action
would be much slower than sulphate 'of ammonia. Similarly, it
has been shown that the continuous use of acid phosphate does
not increase acidity. On the contrary, it seems to decrease some-
what the acidity already present in the soil. The figures in
Table 11 for the plots receiving floats or raw rock phosphate
are not very conclusive. In three plots out of four sulphate of
ammonia was used with the floats so that the influence of the
latter on the acidity of the soil would be over-shadowed by that
of the sulphate of ammonia. In general, however, it may be said
that the use of floats Would have a tendency to decrease the

38 Florida Agricultural Experiment Station

acidity of the soil. The various forms of raw rock phosphate
on the market contain more or less carbonate of lime as an
impurity and their influence on the acid condition of the soil
would be proportional to the amount of this material present.
So far as could be noted an acid soil has no injurious effect
on the growth of the orange tree. On some of the most acid
plots in the grove the trees are vigorous and have made very good
growth ranking well up among the best plots in the grove. These
experiments would seem to show that so far as growth is con-
cerned the citrus tree is very little influenced by an acid condition
of the soil. Where a leguminous cover crop is desired during the
rainy season the situation is different. During the early years of
the experiment a beggarweed cover crop was allowed to occupy
the soil during the summer months. After a time the soil became
so acid that a fair stand could not be obtained and cowpeas and
velvet beans were used instead. These crops appear to be much
less susceptible to acidity than beggarweed and will do fairly
well on soils on which the beggarweed almost refuses to grow.
A study of Table 11 brings out the interesting fact that the
acidity varies with the season, being greater in summer than in
winter. The average number of pounds per acre of carbonate of
lime required for the plots receiving the standard mixture of
sulphate of ammonia, acid phosphate and high grade sulphate of
potash is 4360 for the summer months and 3050 for the winter
months, a difference of over half a ton. A probable explanation
of this fact is that during the summer months the high tem-
peratures and abundant rainfall lead to more rapid chemical and
biological changes in the soil. This brings about greater decay
of organic matter and more rapid transformations in the fertiliz-
ing materials present, resulting in a more rapid formation of
Soils may become acid or sour (1) thru an accumulation of
organic acids produced in the decay of vegetable matter; (2)
thru the depletion of the alkaline or basic constituents of the
soil; (3) thru the addition of fertilizers leaving an acid residue
in the soil. Most muck and peat soils are acid in character before
being brought into cultivation. This is also true of many virgin
soils of a more sandy nature. The decay of the vegetable matter
present in such soils leads to the formation of organic acids,
which tend to accumulate, especially if these soils are naturally

Bulletin 154, Citrus Fertilizer Experiments 39

deficient in lime or if they are ill drained. After such soils are
cleared, drained and brought under cultivation this acid condi-
tion disappears to a considerable extent, due to the aeration or
introduction of oxygen into the soil thru cultural treatment.
Where a crop of green material is turned under, as in the prac-
tice of green manuring, the soil may become acid for a time
due to the formation of organic acids in the decay of the vege-
table matter plowed under. In any case where acids are formed
they lead to a depletion of the lime of the soil. It might be said
that all soils tend to become acid in time due to the removal of
lime and other basic materials in the drainage water. Both the
lime in carbonate of lime and that in certain silicate compounds
present in soils are dissolved by the soil acids and are leached
out. When these forms of lime finally disappear from the soil an
acid condition, so far as plant growth is concerned, is produced.
An application of lime in some form is required to bring back
the alkaline reaction. Florida high pine and flat woods soils,
as a general rule, contain relatively small quantities of lime
(usually very little if any in the carbonate form), yet the amount
of this material appearing in the drainage water is surprising.
In experiments carried out by the Florida Experiment Station
it has been found that in the course of 10 months lime equivalent
to 250 pounds of calcium carbonate has leached out and appeared
in the drainage water from an acre of land. Such a loss of lime
if continued for a few years would bring about acid conditions
in the soil.
The use of fertilizers such as sulphate of ammonia, which
leave an acid residue in the soil, is a frequent cause of soil
acidity under Florida conditions. The acid residue combines
with the lime of the soil and changes it to a soluble form which
readily leaches out. In studying the loss of lime where different
sources of ammonia were applied to the soil, the Experiment
Station has found that where sulphate of ammonia was used
the loss was over two times as much as where nitrate of soda
was used. This tendency of nitrate of soda to decrease acidity,
in other words, to conserve the lime of the soil, has already been
mentioned in connection with the discussion of the loss of ferti-
lizers by leaching.
An important feature in the use of these two materials is
thus brought out. It is an advantage to use them together or
alternately, as, for example, nitrate of soda as the source of
ammonia in the spring and sulphate of ammonia in the summer.


Fig. 9.-Phosphate plots
Plots 27 and 28 were fertilized with Thomas slag instead of acid phos-
phate. The source of nitrogen was nitrate of soda. Plot 28 received twice
as much slag as plot 27. The trees in both these plots showed considerable
frenching, plot 28 being much more severely affected. Most of the trees
in plot 28 show the type of growth usually characteristic of badly frenched
trees. Plot 36 received its phosphoric acid in the form of floats, four times
the standard. amount or 24 percent being used in the mixture. At the end of
the experiment this plot ranked eighteenth. Plot 27 ranked thirty-fifth and
plot 28 ranked forty-fourth.

Bulletin 154, Citrus Fertilizer Experiments 41

Thus the nitrate of soda would counteract the acid condition
brought about by the sulphate of ammonia. Other and greater
advantages in thus using the two materials are discussed else-

Lime and other alkaline materials used in this experiment have
proven distinctly injurious to growth. This injury consisted,
in its mildest form, of a light attack of frenching; in the severest
type, of chronic, severe frenching, partial defoliation, and
a permanent retarding of growth, resulting in stunted under-
sized and unhealthy trees. The alkaline materials and the ferti-
lizers used in connection with the plots were as follows:
Plot 11, 5-6-6, from sulphate of ammonia, acid phosphate, high
grade sulphate of potash; ground limestone, 10 pounds per tree.
Plot 12, 5-6-6, same fertilizer treatment as plot 11, with lime-
stone replaced by air-slaked lime, 5 pounds per tree.
Plot 21, 5-6-6, from cottonseed meal, acid phosphate, high-
grade sulphate of potash; ground limestone, 10 pounds per tree.
Plot 27, 5-6-6, from nitrate of soda, Thomas slag, high-grade
sulphate of potash.
Plot 28, 5-12-6, from same materials as plot 27.
Plot 30, 5-6-6, from nitrate of soda, acid phosphate, hard wood
Plot 39, 5-6-6, same treatment as plot 11.
The ground limestone and air-slaked lime were applied in the
spring about two months after the spring application of ferti-
lizers, and were distributed about the tree to about the same
distance from the trunk as the fertilizers. The slag and hard-
wood ashes were applied mixed with the other fertilizers. The
limestone and air-slaked lime were applied every year, beginning
with 1909, until 1913, when the injury produced became quite
noticeable and their use was discontinued for the remainder of
the period of the experiment. The slag and ashes were used
during the entire ten years.
During the early years of the experiment considerable french-
ing was found in all parts of the grove. As the trees suffered
from dieback during these years the frenching was attributed to
the same causes which produced the former disease. In 1913 it
was noticed that the trees on some of the plots receiving alkaline
materials were more severely frenched than the remainder of
the grove. The worst injury was found on the ground limestone

Fig. 10.-Plots 11, 12 and 21, on which lime was used
The plots illustrated here were treated with lime in addition to the
fertilizer. Plot 11 received the standard fertilizer mixture and ground
limestone. Plot 21 received the standard mixture with the sulphate of am-
monia replaced by cottonseed meal and ground limestone in addition. This
plot showed much more frenching than plot 11. Plot 12 was fertilized with
the standard mixture and air-slaked lime in addition. The trees showed
very little frenching.

Bulletin 154, Citrus Fertilizer Experiments 43

plots and on the plot receiving a double quantity of slag. The
trees on the air-slaked lime plot and on the ashes plot also showed
considerable frenching, which, however, almost completely dis-
appeared after 1915, while the trees on the limestone and slag
plots developed the more severe symptoms of the disease, such as
the narrow pointed leaves, partial defoliation, and general un-
thrifty appearance. The disease continued to manifest itself
in this aggravated form in these particular plots, until the clos-
ing out of the experiment. It seriously interfered with normal
growth, the trees on the most severely affected plots appearing
stunted, undersized and unhealthy.
Photographs of plots 11, 12, 21, 27 and 28 are reproduced in
Figs. 9 and 10.
For a more detailed discussion of the injury induced by ground
limestone, the reader is referred to Fla. Exp. Sta. Bulletin No.
137, Injury to Citrus Trees by Ground Limestone, by B. F. Floyd.
In July, 1910, eighteen months after they had been set out,
it was noticed that many of the trees exhibited the early stages
of the disease known as dieback. At this time the symptoms
were mainly the presence of gum pockets and the S-shaped
branching. An examination showed about 78 percent of the
trees thus affected. At the same time the trees presented a
generally unhealthy appearance, much of the growth coming
from the lower parts of the tree and from suckers. No measures
for combatting the disease were adopted at this time, since it
was considered very undesirable to introduce such complications
in the experiment unless absolutely necessary. The grove was
thoroly examined again in March, 1911, and in the fall of that
year when it was evident that the disease had gained much
headway and was causing serious damage. Table 12 shows the
extent to which the grove was affected with the disease. In this
table the number of the plot and the fertilizer treatment is
given, in column I the number of trees in each plot showing
symptoms of dieback in July 1910; in column II those showing
symptoms in March 1911, and in column III those developing
the symptoms in the growth made in the spring of 1911. (The
writer is indebted to B. F. Floyd, Plant Physiologist, for this
The use of organic nitrogenous fertilizers has usually been
regarded as a cause of dieback. A study of Table 12 however,

Plot Different amounts I II III
1 Half the standard ....--........................................... 4 8 6
2 Standard .........--.......---- .... ..........-----------.. 2 4 3
3 Double the standard--................. ...------- ..-- ..-- ... 6 9 5
4 Four times the standard...................----------.--- ------ 9 8 7
5 Phosphoric acid and ammonia increased by one-half... 9 8 4
6 Phosphoric acid and potash increased by one-half.......... 8 9 5
7 Ammonia and potash increased by one-half----................ 10 8 5
8 Phosphoric acid and potash decreased by one-half..--.. 9 10 6
9 Phosphoric acid and ammonia decreased by one-half.... 9 10 7
10 Ammonia and potash decreased by one-half ...............-... 9 7 2
11 Standard and finely ground limestone ---.............................. 7 10 5
12 Standard and air-slacked lime ------------.................................... 9 9 6
13 Standard and mulch--..... -----................................... 7 7 2
14 Standard ................... ......................................... 8 10 3
Nitrogen from different sources
15 From nitrate of soda---.................................... .-----... 9 9 7
16 Half from nitrate of soda, and half from sulphate of
ammonia ......... --.........-- .........................--------- 9 9 8
17 From dried blood..........--......................-........------- 8 8 8
18 Half from sulphate of ammonia, and half from dried
blood ..................................................................... .... 9 8 4
19 Half from nitrate of soda, and half from dried blood.. 7 7 3
20 From cottonseed meal--..... ------- -------......................... 4 4 0
21 From cottonseed meal. (With ground limestone.)........ 6 5 3
22 Half from cottonseed meal, and half from sulphate of
ammonia ........................................--------- ------------- 8 9 2
23 Half from cottonseed meal, and half from nitrate of
soda ......................................------ --.....................--- ------ ................... 10 9 5
Phosphoric acid from different sources
24 From dissolved bone black...............................................-- ...---- 7 10 7
25 From steamed bone........-............................-------.... 10 9 4
26 From steamed bone. (Double amount.)....... -----..................... 9 10 9
27 From Thomas' slag. (Nitrogen from nitrate of soda.).. 8 8 4
28 From Thomas' slag. (Double amount. Nitrogen from
nitrate of soda.) .... ...................- ---------- 4 6 4
29 From acid phosphate. (Potash, 7% percent in June,
7% percent in October and 3 percent in February.) 8 7 1
30 From acid phosphate. (Nitrogen from nitrate of soda.
Potash from hardwood ashes.) ................--------- 4 4 3
31 From acid phosphate. (Standard.).......................-------- 10 10 7
32 From dissolved boneblack...............................-------- 8 9 9
33 From floats ---.. -....--.. -----..............................---- -- 10 10 8
34 From floats. (Double amount.) ......---.........------..... 9 10 6
35 From floats. (Four times amount.) ...........----------- 9 10 4
36 From floats. (Four times amount. Nitrogen from
cottonseed meal.) ..................------------------................. 8 10 1
Potash from different sources
37 From low-grade sulphate-.... -----... .-------------- 9 9 5
38 From muriate ...............-------......-.. .....-.. .---.. ----- 9 8 3
39 From high-grade sulphate. (With ground limestone.) 10 10 7
40 From kainit---...............-.----------..-.................. -- 6 10 6
41 From high-grade sulphate. (Standard.) ............-- ............ 7 9 7
42 From nitrate of potash. (Balance of nitrogen from
nitrate of soda.) ........---....... --------.-----. 8 9 6
Different culture, etc.
43 No fertilizer ... -----..................- ...-............. ---------3 4 0
44 Standard ...----- -----.............-...------------...... ....... 7 10 8
45 Standard and mulch............................. ---------------- 8 8 4
46 Standard and clean culture .......--..-........................... 10 10 10
47 Nitrogen from dried blood. Clean culture----................... 9 10 9
48 Nitrogen from nitrate of soda. Clean culture-..........----. 7 6 3
Total number of trees affected with dieback..................----- 373 1411 1241

Bulletin 154, Citrus Fertilizer Experiments 45

brings out the fact that in this instance plots receiving a strictly
mineral fertilizer were as badly affected with the disease as
were those receiving cottonseed meal, dried blood and other
organic sources of nitrogen. At no time during the progress
of the disease could any definite relation be established between
the disease and any particular fertilizer. In other words, the
disease appeared to be entirely independent of the fertilizers
used. It has been mentioned elsewhere that when they were set
out three-fourths of a pound of steamed bone meal was used
under each tree. It is possible that the organic nitrogen in the
bone meal may have been the primary cause of the disease, but
as every tree in the grove was treated in this way this theory was
impossible of proof.
In the spring of 1912 the disease had reached a serious stage
and it became evident that measures for combatting it must be
taken. The more advanced symptoms, such as bark excrescences,
stained terminal branches, and multiple buds, were quite abun-
dant, and a few trees were in such bad condition that it was
necessary to replace them with others. The fertilizer applica-
tions for the spring and summer of 1912 were omitted and the
trees were sprayed with Bordeaux mixture in February and
April. In order to get at the effect of this spray in controlling
the disease, the fifth tree in every plot was left unsprayed as a
check. In the latter part of the year it was evident that the
disease was much less prevalent than before the treatment. In
January, 1913, B. F. Floyd made a careful examination of the



Affected trees among
sprayed .....-....................... 111 20 10 0 4
Affected trees among un-
sprayed ....---....................... 27 15 13 1 1
Percentage affected trees
among sprayed ................ 25.7 4.6 2.3 0 0.93
Percentage affected trees
among unsprayed ......... 56.2 31.3 27.1 2.1 2.1
Total number trees af-
fected .............................. 138 35 23 1 5

46 Florida Agricultural Experiment Station

trees for symptoms of dieback. Table 13 summarizes his notes
made at that time. This table shows that over 56 percent of the
unsprayed trees still showed dieback in the gum pocket stage as
compared with 25.7 percent of the sprayed trees. While a total
of 138 trees showed this symptom, none were at all severely
affected or were being injured by the disease. The superficial
symptoms such as stained terminal branches, bark excrescences
and multiple buds, were quite scarce. It will be noted that in
November, 1911, 81.7 percent of the trees showed gum pockets,
while in January, 1913, the unsprayed trees showed 56.2 percent
affected. This indicates a decrease in the disease during this
period from causes other than the spray treatment. Probably
the omission of the fertilizer application or other natural causes
were of influence here in bringing about a decrease in the disease.
Nevertheless it may be concluded from the data given that the
Bordeaux treatment was quite effective in this instance in the
control of dieback. In June, 1913, the trees appeared to be
practically free from'the disease, but in June, 1915, slight indi-
cations of it were again noted. Gum pockets were found on the
new growth on 52 trees. They were not numerous on any of
the trees, in most cases a careful search being necessary to find
them. Of the 52 trees affected, 28 were the fifth tree in the
plot, trees which had been left unsprayed at the time of treatment
with Bordedux mixture. No further treatment was given at this
time and the symptoms of the disease disappeared from natural
causes later in the year. From the end of the year 1915 on to
the close of the experiment, no further trouble was experienced
with the disease.


During the first week of February, 1917, a cold wave swept
over the state bringing freezing temperatures, especially on the
3rd and 4th, and causing considerable damage to the citrus and
truck industries.
In the experimental grove temperatures of 21 on the 3rd, and
22 on the 4th were noted. A reproduction of the air and soil
temperature records for the grove for the week ending February
5 is given in Fig. 11. In order to ascertain the extent and
nature of the cold injury the grove was carefully examined dur-
ing the first week of March. It was particularly desired to find
out what effect, if any, the various fertilizer treatment had in
making the trees more or less resistant to cold injury. The

Bulletin 154, Citrus Fertilizer Experiments 47

criteria used in this study were the amount of defoliation, the
number of twigs killed back and the distance to which they were
killed, and the amount and character of the new growth produced
after the freeze.
The individual plots showed considerable variation in the
amount of injury caused by the cold, plots 28, 5, 7, 27, 21, 43 and
39 being the most seriously injured. At the time of the freeze
the trees in these plots were in a weakened and unthrifty condi-
tion, owing to various causes, such as over-fertilization and the
effect of alkaline materials, discussed in detail elsewhere. The
fact that they were unthrifty was undoubtedly the cause of their
more serious injury from cold. It is difficult to express the
degree of injury in definite figures, but these trees showed ap-
proximately 85 percent defoliation, with 70 percent of the twigs
killed back on the average about 9 inches. The new growth
which was coming out was rather scanty and was weak in


Fig. 11.-Reproduction of air and soil temperature records for the grove
during the freeze of February, 1917
These figures may be compared with similar ones for plots
showing the least amount of injury. Plots 2, 1, 47, 48, 12, 13
and 16 were selected for this comparison. These trees averaged
approximately 65 percent defoliation with 30 percent of the
twigs killed back a distance of about 5 inches. The new growth
coming out was considerably more abundant and more thrifty

48 Florida Agricultural Experiment Station

than on the other plots. These figures show that trees in good
healthy condition are more able to withstand a freeze than are
those in an unthrifty condition, and that the former make a
quicker recovery. This statement was borne out by the general
appearance of the trees and their subsequent behavior. No con-
clusive evidence could be obtained indicating that any special
fertilizer treatment among those used on the better plots was
more effective than another in making the trees resistant to


1. In this experiment sulphate of ammonia, acid phosphate,
and high-grade sulphate of potash gave somewhat better
results as measured by increase in growth, than any other
2. Good results were obtained from the use of nitrate of soda
as a source of ammonia, from steamed bone and floats as
sources of phosphoric acid, and from the low-grade sulphate,
hardwood ashes and the muriate, as sources of potash.
3. The use of ground limestone and Thomas slag have caused
injury, indicated by frenching.
4. Clean cultivation thruout the year was of considerable benefit
to young trees, but after a few years leads to a loss of soil
organic matter. It is not a desirable practice with trees over
five or six years old.
5. A large proportion of the phosphoric acid applied in the
fertilizer is retained in the upper nine inches of soil. Prac-
tically none is leached out.
6. Much of the potash applied in the water-soluble form is re-
tained by the soil.
7. Nitrogen, both in the organic and the in-organic form, is
lost in large quantity by leaching as shown by the lysemeter
experiments and by the analyses of the grove soils. There
was a slight increase of nitrogen in all plots excepting the
clean culture and the unfertilized ones.

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