Front Cover
 Table of Contents
 The fertilizer tag
 Sources of plant foods in...
 What happens to fertilizers in...
 Materials other than standard mixed...
 Calculation of fertilizer...
 Back Matter
 Back Cover
 Historic note

Group Title: Bulletin - University of Florida Agricultural Extension Service ; 177
Title: Know your fertilizers
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00020516/00001
 Material Information
Title: Know your fertilizers
Series Title: Florida, University, Gainesville, Agricultural Extension Service. Bulletin 177
Physical Description: 25 p. : illus., tables. ;
Language: English
Creator: Volk, G. M ( Gaylord M )
Publisher: University of Florida, Agricultural Extension Servi ce
Place of Publication: Gainesville
Publication Date: 1962
Subject: Fertilizers   ( lcsh )
Fertilizers -- Florida   ( lcsh )
Genre: non-fiction   ( marcgt )
General Note: Cover title.
General Note: "This is a revision of Agricultural Experiment Station bulletin 506."
 Record Information
Bibliographic ID: UF00020516
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 01730683
 Related Items
Other version: Alternate version (PALMM)
PALMM Version

Table of Contents
    Front Cover
        Page 1
    Table of Contents
        Page 2
        Page 3
        Page 4
    The fertilizer tag
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
    Sources of plant foods in fertilizers
        Page 10
        Page 11
        Page 12
        Page 13
    What happens to fertilizers in the soil
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
    Materials other than standard mixed fertilizers frequently used for side-dressing or other special purposes
        Page 21
        Page 22
        Page 23
        Page 24
    Calculation of fertilizer formulas
        Page 25
        Page 26
    Back Matter
        Page 27
    Back Cover
        Page 28
    Historic note
        Page 29
Full Text
Bulletin = 177


Gaylord M. Volk

Ferti lize

SWT. 100 LBS.

February 1962

_-^-. { ..... ,



THE FERTILIZER TAG .......... ..-.................. .... ---... .... 5

SOURCES OF PLANT FOODS IN FERTILIZERS .................. ................- 10

W HAT HAPPENS TO FERTILIZERS IN THE SOIL ............................ ................ 14

LIME .............. .......... ...................... 19

A PPENDIX ...............------ .... .................................. .. ... 21

Materials other than standard mixed fertilizers frequently used for
side-dressing or other special purposes ..................... ........--....- 21

Calculation of fertilizer formulas ............... ......................... 25

This is a revision of Agricultural Experiment Station Bulletin

(Acts of May 8 and June 30, 1914)
Agricultural Extension Service, University of Florida,
Florida State University and United States Department of Agriculture, Cooperating
M. O. Watkins, Director

Know Your Fertilizers


Plants need at least 15 different chemical elements for their
growth processes. They require large quantities of carbon, hy-
drogen and oxygen, which they obtain from air and water. Ni-
trogen, potassium, phosphorus, calcium, magnesium and sulfur
also are used in considerable quantity by the plant. These ele-
ments may not be present in sufficient supply or in the proper
form. For example, air is four-fifths nitrogen gas, but only
the clovers and similar leguminous plants carrying nodule bac-
teria on their roots can use it. All other plants must have
nitrogen in combined forms such as is found in nitrate salts,
ammoniacal salts and certain other fertilizer materials.
In addition to the elements mentioned above, there is a group
of elements-iron, copper, manganese, zinc, boron and molyb-
denum-that are all essential for normal plant growth but
needed only in very small quantities. The majority of soils have
enough of these elements, but our sandy soils may show defi-
ciencies. In some instances the nature of the soil limits their
availability to the plant.
Whenever any element is in short supply for plant growth,
it must be furnished by some type of fertilization for economical
crop production.
The chemistry of fertilizers and their reaction with the soil
is very complex. The following discussion purposely omits the
use of chemical terms and symbols other than those appearing
on the fertilizer tag or as used in the Florida Commercial Fer-
tilizer Law. However, this simplified presentation covers most
of the essential facts. It is based on a careful interpretation
of the underlying chemistry of fertilizers and soils.
The chemical symbols used on the fertilizer tag to designate
various plant food constituents may be confusing to readers who
have had an introduction to chemistry. For example, nitrogen
is listed on the tag as the element, N; while phosphorus is given
as the oxide, P.O,, and called phosphoric acid.
Florida Fertilizer Law designates the fertilizer constituents
simply as Primary Plant Foods or Secondary Plant Foods. This
terminology will be used in the discussion to follow. There is
some objection on the part of plant physiologists to the use of

Florida Agricultural Extension Service

the term Plant Food to designate fertilizer constituents, but
historical use in the fertilizer industry has set the precedent
for present usage.
Soil reaction (pH) plays a vital part in fertilizer efficiency.
It refers to the degree of acidity (sourness) or alkalinity (sweet-
ness) of a soil. To have a simple numerical measure, the pH
scale has been adopted. At pH 7.0 a soil is neither acid nor
alkaline, but neutral. As values decrease from pH 7.0 soil
acidity increases. As values rise above 7.0 soil alkalinity in-
Virgin Florida soils range from pH 3.8 (very acid) to pH
8.0 or slightly higher (alkaline). The strongly acid condition
is encountered in certain acid peats, mucks and palmetto flat-
woods. The alkaline condition is usually associated with marl
Most crops grow best in the range pH 5.5 to 6.2, except
legumes, which may respond to a higher pH. In some instances
a low pH may be required for disease control.

Figure 1.-A Florida land pebble phosphate rock mine. (Photograph
courtesy American Agricultural Chemical Company.)

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Know Your Fertilizers

There is a wealth of information on the Florida fertilizer
tag. This information, if understood by the grower, can often
prevent needless expenditure for materials containing unneces-
sary elements, or crop losses resulting from the use of materials
lacking in some essential plant food.
A discussion of the fertilizer tag and what it means in terms
of practical use and economy of fertilizers will be presented un-
der the following headings:
1. The fertilizer tag.
2. Sources of plant foods in fertilizers.
3. What happens to fertilizers in the soil.
4. Lime.

Fertilizers differ in composition, depending upon how much
of each of the different plant foods they contain and the source
of these nutrients. A 100-pound bag of 3-8-8 1 analysis ferti-
lizer contains three pounds of nitrogen, eight pounds of avail-
able phosphoric acid and eight pounds of water-soluble potash.
If the fertilizer contains six pounds of nitrogen, eight pounds
of phosphoric acid, and four pounds of potash, it has the analysis
6-8-4. The first figure always indicates nitrogen, the second
phosphoric acid and the third potash. These are the available
primary plant foods. These figures are percentages or units in
fertilizer terminology. A 3-8-8 contains only one-half as much
nitrogen, but twice as much potash, as a 6-8-4. Obviously these
two fertilizers would not serve the same purpose.
Some fertilizers are very similar in analysis; from these
approximately the same amounts of nitrogen, phosphoric acid
and potash may be applied to the crop by changing the amount
of fertilizer used per acre. When comparing one fertilizer anal-
ysis with another, it usually is best to keep the nitrogen con-
stant, because plants are very sensitive to deficiencies or ex-
cesses of this plant food.
For example, if 15 100-pound bags of a 5-7-5 have been
used in the past, 15 times 5-7-5-or 75 pounds of nitrogen, 105
pounds of phosphoric acid and 75 pounds of potash-were used.
To determine how this compares with a 6-8-8, divide the 75
pounds of nitrogen by six (the pounds of nitrogen in a bag of

1 In certain instances other numbers may be added to the analysis. They
refer to secondary elements as follows: N-P2O.-K20-MgO-MnO-CuO. Thus,
5-6-6-0-0.75-0 indicates that 0.75% MnO has been added to the 5-6-6.

Florida Agricultural Extension Service

6-8-8). This gives 121/ bags of 6-8-8 as necessary to provide 75
pounds of nitrogen. At eight pounds each of phosphoric acid
and potash per bag of 6-8-8, the 121/2 bags would supply 100
pounds of phosphoric acid and 100 pounds of potash. Twelve
and a half bags of 6-8-8, therefore, would supply five pounds
less phosphoric acid but 25 pounds more of potash and an equal
amount of nitrogen.2
The grower must decide whether the substitution of 121/2
bags of 6-8-8 for 15 bags of 5-7-5 is permissible.3 If the change
is acceptable, the cost of 15 bags of 5-7-5 should be compared
to the cost of 121/2 bags of 6-8-8 to determine if a saving is
made. Other factors involved will be discussed later, but in
general the fertilizer requiring the smallest number of bags or
pounds per acre will be most economical, even though the cost
per bag is higher.
The formula for the available primary plant foods in a 6-8-8
fertilizer would appear on the fertilizer tag in percentage (%)
as follows:

Total Nitrogen, not less than.........------......--..........-- 6.00%
-------------------------------------- ----- -----------%
------------------------------------ .--- --- --- -- ------------%
... ..----------.-------------.. .. ..-- -...... ..-- -----
.--- ... .....-- -...----------...--...-......-...--- -%
Available Phosphoric Acid, not less than............................. 8.00%
------------.--. ------------------------.. ..- ..- .. -- %
Water-Soluble Potash, not less than.................................. 8.00%

In addition to the primary plant foods there are secondary
plant foods. These are reported in a similar manner at the
bottom of the tag if they are guaranteed present. The com-
monly recognized secondaries include calcium, magnesium, cop-
per, manganese, zinc, boron, iron, sulfur and molybdenum.4
There are certain required statements of forms and sources of
both primary and secondary plant foods which must appear

2 This method of visualizing the analysis probably will be the easiest to
remember and to use by the grower who buys limited amounts of fertilizer
and would like to have a method of comparing fertilizer analyses and costs.
Fertilizer formulation based on units and percentages is given in the Ap-
3 Arbitrarily increasing or decreasing phosphoric acid or potash applied
to a crop by more than one-fourth probably is not an economical practice
for crops where fertilizer requirements have been well established.
SThese are reported as oxides, except sulfur, which is reported as the

Know Your Fertilizers

on the tag. An example of the above tag filled in as required
by law might read as follows:

Total N nitrogen ........................................... 6.00% 1
Nitrate Nitrogen ........................................ .75% 2
Ammoniacal Nitrogen .......................... 2.25% 3
Water-Soluble Organic Nitrogen ............ 2.10% 4
W ater-Insoluble Nitrogen .................-...... .90% 5
Available Phosphoric Acid .............. ............ ........ 8.00% 6
Insoluble Phosphoric Acid ........................... .20 7
W ater-Soluble Potash ................................................ 8.00% 8
Total Available Primary Plant Food ........................ 22.00% 9
Chlorine not more than ---.......................... 3.00% 10
Derived from: Castor Pomace, Tankage, Ammonium Nitrate, 11
Sulfate of Ammonia, Urea, Ammoniated Superphosphate, 12
Sulfate of Potash, Muriate of Potash and Sulfate of 13
Potash-Magnesia. 14
Derived from Secondary Plant Foods: 15
Total Magnesium as MgO, not less than ................ 2.00% 16
Water-Soluble Magnesium as MgO, not less than.... 2.00% 17
Copper Sulfate as CuO, not less than ............................. .50% 18

The line numbers do not appear on the tag but are inserted
by the writer for easy reference in the discussion to follow.

Figure 2.-Aerial view of rock phosphate washing plant. (Photograph
courtesy Davison Chemical Company.)

Florida Agricultural Extension Service

It will first be noted that the lines 1, 6 and 8, are the per-
centages making the analysis as already discussed. Line 9 is
the total of these three figures. If this total is relatively high
it will indicate a high analysis fertilizer. There is no set di-
viding line, but fertilizers with a total of more than 24% would
usually be classed as high analysis fertilizers.
Lines 2, 3, 4 and 5 list the types of nitrogen which make up
the 6.00% total nitrogen. This is one of the most important
statements on the tag and will be discussed in the next section.
Line 7 gives the insoluble phosphoric acid. This form of
phosphoric acid is not included in the 8.00% available phos-
phoric acid of line 6, but is in addition to it.
Line 10 gives the maximum percentage of chlorine. Chlo-
rine ordinarily is not valued as a plant food in the fertilizer. It
may be injurious to certain crops, such as tobacco and potatoes,
or in plant bed fertilizers if high percentages are present, but
small amounts may be beneficial under some conditions.
Lines 11 to 14 list the materials from which primary plant
foods were obtained. This statement is of value to the grower
if only one source of a given plant food is listed or if a given
form of nitrogen is supplied only by one material. Where a
plant food or form of nitrogen comes from more than one ma-
terial a statement of sources is of limited value.
Lines 15 to 18 show the method of reporting secondary plant
foods. A knowledge of the source of these secondary plant foods
is important in order to know their availability to the plant.
The order and methods by which the sources of plant foods
are reported on the tag may vary to some extent with different
tags, but there should be no confusion if the above example tag
is thoroughly understood.
Conditioners and Fillers.-The amount of various fertilizer
materials which are required to supply the primary and secon-
dary plant foods in a ton of a given formula usually do not total
2,000 pounds when mixed together. The remaining portion is
made up of conditioner or filler or both. A conditioner is a ma-
terial that helps prevent a fertilizer from becoming so moist or
so hard on standing that it will not drill properly. Conditioners
may also supply some of the plant foods in the formula.
Filler is the term applied to a material added to fill out the
ton of weight. It often consists of dolomite, raw phosphate or
sand. It usually has certain conditioning value, but contains
no significant amount of available primary plant food.

(See Table 2 also for other nitrogenous materials.)

Percentage Composition (See text for meaning of symbols.)
Material I I I
_____ N P.O | K2O CaO MgO S Na2O Other

Ammonium sulfate ...................... 20.5 23
Ammonium sulfate-nitrate ........ 26 11
Ammonium phosphate ................ 11-21 46-48
Ammonium nitrate plus lime .... 20.5 23(10.5*) (7*)
Basic slag ................................ 8 40 5 3 MnO
Borax ........................................ 12 36 B20s
Cyanamid ................................. ... 20.6 53
Calcium sulfate .......................... 32 18
Calcium nitrate ........ ................. 15.5 36
Copper sulfate .................----- 12 30 CuO
Castor pomace ...............- .......... 5.4 1.5 1.3
Cotton bur ash ........................... 3 40 10 4 2 5 C1
Emjeo ....................................... 27 22
Fish scrap ........... ....................... 8 6
Guano (Peruvian) .................. 12 11 2.4 12 1 1
Iron sulfate copperass) --. --- 11 33 Fe20.
Magnesia (seawater) ..-...- 93
Magnesium sulfate ..--........... 30 24
Manganese sulfate ........................ 13 30 MnO
Muriate of potash ........................ 60 44 Cl
Nitrate of soda .......................... 16 36 to
Nitrate of soda-potash ........... 15 14 18
Phosphate rock ............................ 33 44
Potassium nitrate .................... 13 44
Sewage sludge (activated) ........ 5 4.6 0.4 2 0.9 1
Sodium molybdate ........................ 19 58 MoOs
Sulfate of potash ......................... 48 18 2 C1
Sulfate of potash-magnesia ...... 25 18 22 1 1 Cl
Sul-Po-Mag ............................... 22 18 22 1 1 Cl
Superphosphate, regular ............ 20 23 9
Superphosphate, cone. .............. 47 20 2
Tankage, animal .......................... 8 10
Tee-Man-Gam ........................ 16 37 MnO
Tobacco stems ...................... 2.2 6
Zinc sulfate ............... ............-- 12 45 ZnO

If conditioned with dolomite.

Florida Agricultural Extension Service


The sources of the various available plant foods in fertilizers
differ to some extent in various parts of the country. The fol-
lowing discussion applies to Florida; relatively low analyses are
still common, but the usage of high analysis fertilizers requiring
concentrated materials is increasing.
Some materials carry more than one plant food or form of
plant food (Table 1). For example, ammoniated superphosphate
may carry nitrate nitrogen, ammoniacal nitrogen and phosphoric
Nitrate Nitrogen.-This form of nitrogen in mixed fertilizers
comes mainly from ammonium nitrate, ammoniated superphos-
phates, nitrate of soda and nitrate of soda-potash (Table 2).
Ammoniated superphosphate is prepared by spraying ammoniat-
ing solutions on superphosphate. Ammoniating solutions used
at present generally contain ammonium nitrate or urea or both,
and ammonia gas dissolved in water.

Percent Rate of
Fertilizer Material Nitrogen Nitrogen
Nitrate of soda ........................................... 16.2 Very rapid
Nitrate of soda-potash .................................. 15.0 Very rapid
Nitrate of potash .....-.................................. 13.2 Very rapid
Calcium nitrate ............................................ 15.5 Very rapid
Ammonium nitrate ......................-................. 33.5 Very rapid
Ammonium nitrate plus lime** .................. 20.5 Very rapid
Ammonium nitrate solutions .-................. 16-21 Very rapid
Ammonium sulfate-nitrate ............................ 26 Very rapid
Ammonium phosphate .................................... 11-21 Rapid
Anhydrous ammonia .............. ................... 82 Rapid
Aqua ammonia ............................... ......... 24 Rapid
Ammoniated superphosphate ...................... Variable Rapid
Ammonium sulfate ........................................ 20.5 Rapid
U rea ............................................................ 45-46.6 R apid
Cyanam id ............................................. ....... 20.6 R apid
Cottonseed meal* ......................................... 6.7-7.4 M moderate
Castor pomace* ....................... ............... 4.1-6.6 Moderate
Dried blood* ........ ..-- ...... .. 9.0-14.0 Moderate
Hoof meal* .................................... ..... .. 10.7-15.6 M moderate
Dry fish scraps* ............................... ...... 6.5-10.0 Moderate
Peruvian Guano* ..........---- ---------- .. 12 Moderate
Sewage sludge (activated)* ....................... 4.1-6.4 Moderate
Ureaform ... .................... 38 Moderate
Beetle scrap dust .................................... .. 19.0 Slow
Processed tankages* ..................................... 5.0-10.0 Slow
Raw bone meal* ........................................... 3.3-4.1 Very slow
H ull m eals* ...................................................... 1.2-3.0 Very slow
Beetle molded scrap .............. ............. .. 19.0 Very slow
Garbage tankage* ..............-......... ........ ..... 2.5-3.3 1 Very slow
Natural organic.
** A-N-L, Cal Nitro, Calcium ammonium nitrate, etc.

Know Your Fertilizers

The nitrogen in ammonium nitrate is one-half ammoniacal
nitrogen and one-half nitrate nitrogen. All of the nitrogen in
nitrate of soda and nitrate of soda-potash is in the nitrate form.
Calcium nitrate and nitrate of potash also carry all of their
nitrogen in the nitrate form, but are little used in Florida mixed
fertilizers at present. Crops can use the nitrate nitrogen from
different sources equally well.
Ammoniacal Nitrogen.-This form of nitrogen comes mainly
from ammoniated superphosphate, sulfate of ammonia and am-
monium nitrate. The ammoniacal nitrogen in ammoniated super-
phosphate is from the ammonia gas dissolved in the ammoniat-
ing solution and the ammonia portion of the ammonium nitrate.
All of the nitrogen in sulfate of ammonia is in the ammoniacal
form. Ammonium phosphate also carries all ammoniacal nitro-
gen and is often used in high analysis fertilizers. The ammonia-
cal nitrogen from different sources is equally usable by crops.
Water-Soluble Organic Nitrogen.5-This form of nitrogen

5 The name "organic nitrogen" refers to nitrogen of the type found in
organisms such as plants and animals. It includes certain of the nitro-
genous compounds now made synthetically.

Figure 3.-Receiving sodium nitrate from Chile at a Florida port.
(Photograph courtesy Wilson & Toomer Fertilizer Company.)

Florida Agricultural Extension Service

has been supplied mainly from urea and calcium cyanamide in
the past. The urea is made by chemical processes, but is identi-
cal with urea nitrogen found in the urine of animals. Calcium
cyanamide is a chemical combination of lime and nitrogen.
Both urea nitrogen and cyanamide nitrogen change to am-
moniacal nitrogen within a few days after application to the
soil when applied in the amounts usually found in mixed ferti-
lizers. For this reason, the water-soluble organic nitrogen re-
ported on the fertilizer tag should be considered as the equiva-
lent of ammoniacal nitrogen. The practice of including it in a
statement of total organic nitrogen is misleading to the grower,
who wants the resistance to leaching and extended period of
availability attributed to water-insoluble nitrogen.
Water-Insoluble Nitrogen.-This form of nitrogen comes al-
most entirely from natural organic sources, such as the various
seed meals, tankages and sewage sludge products. A small
amount of water-insoluble nitrogen may come from synthetic
materials.6 The rate at which the insoluble nitrogen from differ-
ent materials becomes available to the crop varies widely. In-
soluble nitrogen is a very high-cost form of nitrogen. It should
not be confused with the water-soluble organic form of nitrogen.
Insoluble organic nitrogen is costly also in another way, since
only a third to half of the insoluble nitrogen now used in ferti-
lizers is available within a reasonable length of time, while up
to 80 percent of soluble forms of nitrogen may be utilized by
an annual crop.
Available Phosphoric Acid.-This form of phosphorus comes
mainly from superphosphate, ammoniated superphosphate and
concentrated superphosphate (double or treble). These ma-
terials are made by treating raw rock phosphate with acids or
heat to make the phosphorus more available to the plant. High
analysis fertilizers may contain considerable amounts of am-
monium phosphate. The available phosphoric acid from these
different materials is about equally usable by the crop.
Insoluble Phosphoric Acid.-This form of phosphorus must
not be confused with available phosphoric acid. It is largely
composed of rock phosphate or waste pond phosphate added
as filler, or the part of the rock phosphate that was not con-
verted to the available phosphoric acid form by acid or heat
treatments. This form of phosphoric acid is more slowly avail-

See Ureaform in Appendix.

Know Your Fertilizers

able to the plant, but over a long period of time does have
certain value and is therefore reported on the tag.7
Water-Soluble Potash.-Potash comes mainly from muriate
of potash, sulfate of potash magnesia, nitrate of soda potash
and sulfate of potash. Cotton bur ash contains potash in the
form of carbonate. The water-soluble potash from different
sources is equally usable by the crop.
Chlorine.-This element comes almost entirely from muri-
ate of potash.8 Other forms of potash, such as sulfate of pot-
ash, sulfate of potash magnesia and nitrate of soda potash, are
used if it is desirable to reduce the chlorine content of a ferti-
Secondary Plant Foods.-Considerable care must be used in
reading a fertilizer tag to determine the amounts of secondary
plant foods guaranteed. These secondaries may be from var-
ious sources that differ widely in availability to the plant. The
water-soluble forms usually are the important sources in a
mixed fertilizer,9 but certain insoluble forms are now receiving
wide acceptance.
Magnesium always is given as both water-soluble and total
with the symbol MgO. Water-soluble magnesium usually is
derived from sulfate of potash-magnesia or magnesium sulfate.
Other secondaries of importance, with their symbols and com-
monly used water-soluble sources, are as follows:

Plant Food Symbol Derived from
Copper CuO Copper Sulfate
Manganese MnO Manganese Sulfate
Zinc ZnO Zinc Sulfate
Boron BsOa Borax, Borate
Iron Fe2sO Iron Sulfate, Chelated iron
Molybdenum MoO. Sodium Molybdate
Sulfur S Superphosphate, sulfate of potash
magnesia, ammonium sulfate 10
Sodium Na.O Nitrate of soda 10
Calcium CaO Calcium sulfate, superphosphate

It also indicates whether or not raw phosphate has been the form of
filler used and if the amount is significant. Multiplying by 100 will give
an estimate of the amount of waste pond phosphate filler that might have
been used per ton, or multiplying by 60 gives the equivalent of high grade
rock phosphate.
SWhen potash is supplied from crude salts such as kainit, manure salts
or sylvinite, the amount of chlorine added with the source of potash usually
is considerably higher than when supplied only from muriate.
Some common sources of primary and secondary plant foods are listed
in Table 1.
1" These usually are not selected deliberately to supply the element in-

Florida Agricultural Extension Service

Insoluble forms of secondaries quite widely used are copper
oxide, magnesium oxide, manganese oxides, calcite and dolomite
limes, and frits. The latter consists of single or various com-
binations of elements dissolved in a glasslike matrix and reduced
to a fine powder.
Chelated iron (iron EDTA) is now becoming a common source
of this element. (See Appendix.)
Base Goods.-This term is frequently encountered in discus-
sion of fertilizer mixtures. It generally refers to a mixture of
several fertilizer materials, usually superphosphate, with ma-
terials containing nitrogen or potash or both. This mixture,
after curing, is used as a base to which more materials may be
added to make different analyses.

Nitrate Nitrogen.-Nitrate nitrogen dissolves readily in wa-
ter and moves freely in the soil with the movement of water.
It is not held by the soil particles. For this reason, heavy leach-
ing rains may remove the nitrate form of nitrogen. On the
other hand this characteristic of nitrate nitrogen makes it a

Figure 4.-Nitric acid plant for the production of ammonium nitrate.
(Photograph courtesy Lion Oil Company.)

." -4 .i :'-;

Know Your Fertilizers

favored side dressing, because the nitrogen moves more freely
into the root zone than other forms of nitrogen. Nitrate nitro-
gen is the form of nitrogen most universally preferred by plants.
Ammoniacal Nitrogen and Soluble Organic Nitrogen.-Solu-
ble organic nitrogen is converted to ammonia nitrogen in from
one to seven days under most soil conditions. For practical pur-
poses it may be classed with ammoniacal nitrogen.
Ammoniacal nitrogen dissolves readily in water. It differs
from nitrate nitrogen in that it is held by the soil particles
and free movement through the soil is largely prevented. Move-
ment of ammoniacal nitrogen through a strongly acid soil is
more rapid than through a slightly acid soil. Therefore, proper
liming to reduce soil acidity (sourness) will help reduce the
leaching loss of ammoniacal nitrogen by heavy rains.
Most plants can use ammoniacal nitrogen to some extent,
but usually bacteria convert the ammoniacal nitrogen to nitrate
nitrogen in a period of one to four weeks. Plants then use the
nitrate nitrogen so formed. If the soil is strongly acid, the
bacteria do not work well, and certain types of plants may
suffer from lack of the nitrate form of nitrogen. Soil that is
saturated with water, very dry or too cold also is slow to convert
ammoniacal nitrogen to nitrate nitrogen. For this reason ni-
trate nitrogen is favored for rapid penetration of cold soils when
side dressing in late fall, winter and early spring.
Because ammoniacal nitrogen tends to be retained near the
surface of the soil when it is applied as top dressing, special at-
tention should be given to liming to offset the concentration of
acidity as nitrification takes place. Samples for pH should be
taken of the surface two-inch layer of soil by itself. Samples
below this depth also should be taken. One pound of ammonia-
cal nitrogen may require up to six pounds of lime to prevent in-
crease of acidity in the shallow surface soil and maintain opti-
mum conditions for nitrification.11
Water-Insoluble Nitrogen.-Water-insoluble nitrogen cannot
be used directly by the plant but must be converted to ammonia-
cal nitrogen by the soil organisms. This conversion proceeds
gradually, and for this reason insoluble nitrogen is more slowly

11 Recent work has shown that gaseous loss of ammonia from urea top-
dressed on light sandy soil or on turf is appreciable even in the acid pH
range. It also has been noted that surface liming promotes ammonia loss
from top-dressed ammonium sulfate and increases loss from urea still more.
Lime should be mixed into the soil whenever practical to do so. For max-
imum nitrogen efficiency urea should always be incorporated, and top dress-
ing of ammoniates on top-dressed lime avoided if practical.

Florida Agricultural Extension Service

available to a crop and less subject to leaching loss by heavy
rains. It was a favored form of nitrogen in the past when its
cost was comparable to other forms of nitrogen.
The conversion of insoluble nitrogen proceeds more rapidly
in some materials than in others. In some it is so slow as to
make them of little value as fertilizers. Many materials are
pretreated with heat or chemicals to increase this speed of con-
version to usable nitrogen in the soil. A list of nitrogenous
fertilizer materials is given in Table 2, with an estimated rate
of availability of their nitrogen.
Most natural organic nitrogen carriers have part of their
nitrogen in soluble form. This portion appears under the ni-
trate, ammoniacal and water-soluble forms on the fertilizer tag.
The usable insoluble nitrogen in a fertilizer is very high in cost
as compared to other sources. It should be requested only if a
real need exists. The practice of side dressing with cheaper
nitrogen while the crop is growing usually eliminates the need
for high amounts of insoluble nitrogen at planting.
Insoluble nitrogen is especially valuable for lawns, turf and
certain ornamentals, as rapid uptake of nitrogen by the plants
is prevented. This reduces the intense flush of growth immedi-
ately after fertilization and to some extent, the unsightly ap-
pearance of spotty growth due to uneven spreading.
Relative amounts of insoluble nitrogen from different sources
are not reported on the fertilizer bag. This makes it impossible
to determine which forms are being used in significant quanti-
ties if more than one source is reported.
Phosphoric Acid.-All forms of phosphoric acid are strongly
held by the soil against loss by leaching, unless the soils are
strongly acid white or gray sands. Moderate liming largely cor-
rects this condition in the flatwoods soils.
Available phosphoric acid is readily usable by the crop on
all soils. Soils that are red or yellow in the surface or subsoil
tend to hold phosphoric acid so strongly that in the second or
third year after application the availability of the residual phos-
phorus may be much lower than for black or gray soils, making
the amount of phosphorus to be added to maintain fertility of
the red and yellow soils somewhat larger than for black or gray
Insoluble phosphoric acid is more slowly available to the
crop than is available phosphoric acid. It is more rapidly avail-
able on the moderately to slightly acid soils than on slightly acid

Know Your Fertilizers

to high lime soils. For this reason available phosphoric acid
has been favored in the past for rapidly growing crops receiv-
ing a drill application at time of planting, while the use of ground
rock phosphate has been confined largely to pastures.
Sulfur is known to be deficient in many soils in the South-
east. The main source of this element in the past has been reg-
ular superphosphate, which is about half calcium sulfate. If
ground rock phosphate or concentrated phosphates are to be
used continuously on a given area, sooner or later sulfur may
have to be applied to replace that removed by the crops.
Potash.-Potash is held in the soil much as is ammoniacal
nitrogen. In sandy soils it may be moved down out of the root
zone of shallow rooted crops to some extent, but apparently
much of it can be recovered by deep rooted crops.
Secondary Plant Foods.-Calcium, magnesium, copper, zinc,
manganese, iron and molybdenum are held in the soil in various
manners. Copper, zinc, manganese, iron and molybdenum are
held so strongly under certain conditions that they may be rela-

Figure 5.-Mine site and refinery for potash salts near Carlsbad, New
Mexico. (Photograph courtesy American Potash Institute.)

Florida Agricultural Extension Service

tively unavailable to crops. Chelates and frits have been de-
veloped to partially offset this strong inactivating ability of
the soil. In iron chelate, the only chelate which has been of
practical success for soil usage, the iron is protected in soluble
form within a complex molecule until taken into the plant, where
it is broken down and the iron utilized. With frits the ele-
ments are held in a slowly soluble form in a glasslike matrix
and released at a speed that allows the plant to compete more
readily with the soil than is the case with more soluble forms
of the elements.
Water-soluble sulfur and boron may move much like nitrate
nitrogen and be leached away. Almost all of the primary and
secondary plant foods may be tied up to some extent in the soil
microorganisms and organic matter (humus) and later be re-
leased to a crop when the organisms die or the organic matter
Fertilizer Injury.-High chlorine will reduce crop quality or
injure sensitive crops such as tobacco and potatoes in the field,
or cause injury to plant beds.
Too much usable nitrogen in the soil at one time may cause
leaf burn and injure the roots. The accumulation of soluble
salts from fertilizers or by irrigation with salty water will pre-
vent intake of water by the plant and reduce yield.
In general, the more sandy the soil and the drier the soil,
the more severe will be the injury from a given amount of ex-
cess chlorine, nitrogen or total salts. Irrigating the crop to keep
the soil moisture high and to wash out some of the soluble salts
is the best method of correction in the field or in the plant bed.
Fertilizer Acidity.-Most fertilizers are acid-forming. This
acidity may be overcome by adding dolomite to the fertilizer
during mixing or by liming the soil. On the average, one ton
of fertilizer requires about 200 pounds of dolomite to neutralize
this acidity.
While it is preferable that the proper amount of dolomite be
added during mixing, many fertilizers are sold without this be-
ing done. With certain high analysis fertilizers it is not possible
to add dolomite without reducing the amount of primary plant
food in the analysis. For this reason, the acidity of the soil
should be determined every few years and lime added if neces-
12 Recognition of the possibility that high acidity may develop in the vi-
cinity of the fertilizer band and enhance the solubility of aluminum with
its potential toxicity has led to renewed interest in banding lime and ferti-
lizer together.

Know Your Fertilizers

The effect of fertilizer acidity on the subsoil is of primary
concern with certain deep rooted crops such as citrus. Appar-
ently the effect of fertilizer materials on subsoil acidity is closely
associated with the amount of ammonia nitrogen or urea they
Agricultural Limestone.-Liming materials are used for the
control of soil acidity and to supply calcium and magnesium.
Agricultural limestone, which is ground, crushed or pulverized
limestone rock, is used to the largest extent for this purpose.
It consists of calcium cabonate and may also carry magnesium
carbonate, and is reported on the tag as percentages of these two
compounds present. Eighty-four pounds of magnesium carbon-
ate is equal to 100 pounds of calcium carbonate in neutralizing
soil acidity.
Proper liming of strongly acid soils increases the efficiency
of almost all plant foods added in the fertilizer, as well as making
many of those already held by the soil more available to the
crop. Much of the calcium and magnesium applied as lime is
lost by leaching, especially where heavy fertilization is practiced.
The recognition of potential toxicity of aluminum and signifi-
cant mobility of phosphorus in sandy soils in the strongly acid
range reemphasized the need of proper liming of these soils.
The highest rate of reaction of lime with the soil is not
always the best rate. Sufficient fine material should be present
to make the immediate correction of acidity desired, and there-
after the coarser material continues slow reaction to help main-
tain a desirable pH. This is becoming increasingly important
on pastures as well as ornamental turf in recognition of the need
to incorporate more lime during renovation processes in order
to reduce the need for supplemental top dressing at a later date.
Limestones containing appreciable amounts of magnesium

3 Ammonia moves into the subsoil in combination with acid ions, espe-
cially sulfate where sulfur sprays are used. Conversion of the ammonia to
nitrate leaves a strong residue of acidity from the acid ions, enhanced even
more if the nitrate is not taken up by subsoil roots. Adequate liming large-
ly controls production of acidity by this process in the tilled surface soil,
but is relatively ineffective in the subsoil because of the slow movement of
lime. Calcium nitrate and sodium nitrate are equally effective in retarding
the development of subsoil acidity but pH values for subsoils must be in-
terpreted with caution where sodium is involved because of its exaggerating
effect on the pH determination. Soluble salts in the soil have a marked ex-
aggerating effect in the opposite direction, toward increased acidity. The
latter is thought to be caused by replacement of hydrogen ions and active.
tion of aluminum.

Florida Agricultural Extension Service

carbonate (not less than 30 per cent) are called dolomite. The
magnesium is of value where this plant food is deficient in the
soil. Dolomite is somewhat slower in correcting soil acidity than
are limestones containing little or no magnesium.
The screen test as reported on the tag is very important in
determining the value of agricultural limestone-the finer the
material the more rapid is its reaction with the soil. Agricul-
tural limestone usually has a fineness such that about 85 per-
cent passes a 20-mesh 14 screen and 60 percent passes a 60-mesh
screen. By regulation, 90 percent must pass a 10 mesh and 70
percent pass a 20 mesh screen.
Hydrated Lime.-Hydrated lime is made by burning lime-
stone to quicklime and then slaking with water. It may consist
of calcium hydroxide or of mixtures of calcium hydroxide and
magnesium hydroxide and is so reported on the tag. The mag-
nesium hydroxide is of special value where magnesium is needed
in the soil.
Hydrated lime is used to a considerable extent for special
purposes. It reacts much faster with the soil than agricultural
limestone; therefore, more care is required in its use. Hydrated
lime should not be used at more than one-half the rate recom-
mended for agricultural limestone.
Lime Requirement.-Particular care should be exercised in
sampling soils and determining pH for lime requirement. Sur-
face applied lime moves into the soil very slowly. Therefore,
pastures and other areas where tillage is nil or shallow should
be sampled to the appropriate depth of probable mixing of the
lime, with a second sample taken at lower depth to represent the

Number of wires per inch.
'~ The presence of fertilizer salts usually will give a pH value that is too
low, and the presence of sodium a value that is too high as usually inter-
preted for liming recommendations. Some attempt is now being made to
mask out these effects by deliberate addition of soluble salts in the pH de-
termination, but data on correlation of this method are still inadequate to
allow widespread use.

Know Your Fertilizers



Actomag (Selectively Calcined Dolomite).-This is a mix-
ture of finely divided magnesium oxide and calcium carbonate.
A typical analysis shows 27 percent magnesia. The rate of
availability of magnesium is intermediate between magnesium
sulfate and dolomite. It is used where magnesium especially is
needed by a crop.
Ammonium Nitrate.-This material is used as a top-dressing
or side-dressing where nitrogen only is needed. It contains
about 33 percent nitrogen and is used in much the same manner
as nitrate of soda, but is more concentrated and should be used
at a lower rate. One-half of the nitrogen is the same as that
in nitrate of soda and the other half is the same as that in sul-
fate of ammonia.
Ammonium Nitrate plus Lime.-This material, sold under
various trade names (A-N-L, Cal-Nitro, Calcium Ammonium
Nitrate, Nitro Lime), is ammonium nitrate to which either cal-
cic or dolomitic lime has been added to condition the material
and reduce the nitrogen content to 20.5 percent nitrogen. The
mixture is non-acid-forming and supplies calcium or, in the
case of dolomite conditioner, both calcium and magnesium in
addition to the ammoniacal and nitrate nitrogen.
Anhydrous Ammonia.-This material is ammonia gas under
pressure and cannot be used except with special apparatus.
Usually it is injected into the soil behind a chisel-like implement.
It contains 82 percent ammoniacal nitrogen.
Basic Slag (Thomas Slag).-Basic slag contains 8 to 25 per-
cent of phosphoric acid. In addition, 100 pounds of basic slag
are equal to about 70 pounds of limestone for the correction of
soil acidity. Basic phosphate slag is a name applied to basic
slag containing not less than 12 percent phosphoric acid, of
which 80 percent is approximately equal in availability to phos-
phoric acid of superphosphate.
Calcium Sulfate (Landplaster, Gypsum).-This material is
used primarily as a source of sulfur when sulfur is needed but
not supplied in the usual manner by superphosphate or sulfates

Florida Agricultural Extension Service

of ammonia or potash. It is not a liming material for reducing
soil acidity.16
Chelates.-Chelates of trace elements, of which iron EDTA
or EDTA-OH are the most common, consist of the element held
in the center of a large organic molecule in a manner that pro-
tects the element from immediately reacting with the soil and
becoming unavailable before the plant has a chance to absorb
it. Apparently the plant takes up the entire molecule under
some conditions and then releases the iron or other nutrient
within the plant.
Collodial Phosphate (Waste Pond Phosphate).-This is finely
divided raw mineral phosphate or phosphatic clay. If the phos-
phoric acid content is 20 percent or more, it is approximately
equal to ground rock phosphate on an equivalent phosphoric
acid basis. For example, 300 pounds of 20 percent collodial
phosphate would equal 200 pounds of 30 percent ground raw
rock phosphate. (See Rock Phosphate.)
Cottonseed Meal.-(See Natural Organics.)
Cyanamid (Calcium Cyanamide).-This material carries 20.6
percent nitrogen. The special precautions given by the manu-
facturer must be followed to prevent injury from the use of
this material. The nitrogen is synthetic, non-protein organic
nitrogen and should not be confused with natural organic.
Frits.-Frits of trace elements consist of one or more of
the elements dissolved in molten glass-like material. This mass
is cooled by dropping in water to fracture it, and then ground to
powder. The nature of the glass-like matrix and the fineness
of grinding determines the rate of solubility in the soil and the
rate of release of trace elements in the frit. Certain frits have
shown considerable promise for improved availability of ele-
ments that are either easily leached or rendered unavailable by
the soil.
Gypsum.-(See Calcium Sulfate.)
Milorganite.-This is activated sewage sludge of about 6.2
percent nitrogen and 3.5 percent phosphoric acid. Its nitrogen
is about 60 percent as available as nitrate and ammoniacal forms.
Most forms of natural organic nitrogen used at present have a
much lower rate of availability. The direct use of high cost

1 When applied to acid soils the immediate effect is an increase in the
acidity of the soil solution, but the ultimate effect after leaching has been
effective is a reduction of soil acidity. This becomes apparent especially in
strongly acid subsoils.

Know Your Fertilizers

natural organic usually is not an economical practice except for
landscaping, turf maintenance, plant beds or certain special
Nitrate of Soda (Sodium nitrate).; Nitrate of Soda-Potash;
Nitrate of Potash (Potassium nitrate).-These materials all
carry only the nitrate form of nitrogen and are widely used for
side- or top-dressing. They carry from 13 to 16 percent nitrate
nitrogen. In addition, nitrate of soda-potash carries 14 percent
potash, and nitrate of potash carries 44 percent potash.
Nitrogen Solutions.-(See Solution Fertilization.)
Nutritional Sprays; Physiological Sprays.-(See Solution
Rock Phosphate.-This material consists of finely divided
phosphate rock and contains from 27 to 44 percent phosphoric
acid in insoluble form. It is moderately available to plants on
slightly to moderately acid soils and almost unavailable in high
lime soils. It is widely used as a soil builder. It is used to some
extent on pastures but is not suitable as a sole source of phos-
phorus for rapidly growing row crops.
Rock Potash.-Pulverized granite, green sand and similar
materials carry potassium in the form of feldspars or glauconite,
which are highly insoluble potassium-bearing minerals. The
rate of availability of potash is so low as to render these materials
economically valueless as compared to the usual sources of wa-
ter-soluble potash.
Solution Fertilization.-Numerous fertilizer materials and
mixtures on the market are intended to be dissolved in water
and applied as sprays to the leaves while the crop is growing
or by dipping the roots or by pouring in the holes in transplant-
ing. They are made from ordinary fertilizer materials which
have been purified and concentrated to reduce insoluble residues.
These practices have a sound basis of fact but cannot be gen-
erally recommended because they are of economic value only for
very special conditions. These fertilizer materials may be used
also in the dry state like ordinary fertilizers, but they usually
are so concentrated that great care is necessary in reducing the
application to avoid injury to the plants.
Recently the use of solutions of ammonium nitrate, urea
and aqua ammonia or mixtures of these have come into quite
widespread use in some areas. They are sprayed or dribbled on
the surface of the soil or turf, except in the case of aqua am-

Florida Agricultural Extension Service

monia, which must be incorporated in the soil much like anhy-
drous ammonia. The use of ammonium nitrate and urea solu-
tions produces about the same results as would equivalent ap-
plications of dry materials. A possible advantage lies in ease
of handling solutions by pumps and spray rigs. Also, materials
do not need conditioning which is usually necessary to produce
pellets for dry application. The special precautions necessary
to prevent possible poisoning of stock or burning of vegetation
must be followed. Volatile loss of ammonia from surface-applied
urea also may be a factor. (See footnote 11.)
Starter Solutions.-(See Solution Fertilization.)
Sulfate of Ammonia (Ammonium Sulfate).-This material
contains about 20 percent nitrogen, all in ammoniacal form,
but no other primary plant food. Ammoniacal nitrogen does
not penetrate to the root zone as readily or give as quick a
response as does nitrate nitrogen when used as a side- or top-
dressing. On the other hand, ammoniacal nitrogen does not
leach out as readily when heavy rains occur. For this reason
it is used where quick response is not vital to the crop.
Urea.-Urea contains 45 to 46 percent water-soluble organic
nitrogen that is usually converted to ammoniacal nitrogen with-
in one to three days after application to the soil. It is called an
organic nitrogen but should not be confused with natural or-
ganics or insoluble nitrogen. It is a very concentrated form of
nitrogen and difficult to use at a light rate of application, even
when conditioned, unless the analysis is reduced by adding a
An impurity, biuret, usually is found in prilled urea as a
result of heating in the pelleting process. Fertilizer urea for
general usage contains not more than 2.5 percent biuret, be-
cause it is toxic to plants if present in significant quantity.
For crops known to be exceptionally sensitive, and for spray
usage, special low biuret urea such as crystal urea is available.
Ureaform.-This is a relatively new form of water-insoluble
nitrogen containing about 38 percent nitrogen made by chemi-
cally combining urea and formaldehyde for fertilizer use. It
releases nitrogen to a crop more slowly than do soluble forms
of nitrogen. Tests of the various ureaforms now offered for
sale are inconclusive, showing efficiency varying from that of
good natural organic to less than half this value, depending on
the conditions of the tests. The current high cost of ureaform

Know Your Fertilizers

largely restricts usage to turf, ornamentals and similar cul-

The fertilizer analysis shows the percentages of Nitrogen
(N), Available Phosphoric Acid (P20O) and Potash (K20) in
that order. Thus a 6-8-7 contains 6% nitrogen, 8% phosphoric
acid and 7% potash; or 120 pounds of N, 160 pounds of P205
and 140 pounds of K,O per ton. Analyses may then be com-
pared as to the amount of plant foods per ton of fertilizer.
One percent of plant food is also called one unit of plant
food and is equal to 20 pounds of that plant food per ton of fer-
Assume that we wish to use sulfate of ammonia to supply
two of the six units of nitrogen in the 6-8-7. Table 1 shows
sulfate of ammonia to have 20.5% nitrogen. The calculations
2,000 20.5 (%) = 98 lbs. of ammonium sulfate to give
one unit of nitrogen.
2 x 98 lbs. = 196 Ibs. of ammonium sulfate needed for 2
units of nitrogen.
Or a grower may wish to know how much copper sulfate
was used in a mixture showing 0.5' CuO. The calculations are
the same. Table 1 shows copper sulfate as having 30% CuO.
2,000 30 ( ) = 66.7 lbs. per unit.
0.5 (units) x 66.7 = 33 lbs. of copper sulfate per ton.
Fertilizer formulation tables usually show the number of
pounds of various fertilizer materials necessary to give one
unit of plant food per ton of mixed fertilizer.

Some attempts are being made at present to develop a ureaform type
of water-insoluble nitrogen right in the fertilizer mixture by adding urea
and formaldehyde together in solutions at the time of ammoniation of the
superphosphate. To date there has been inadequate testing of materials so
manufactured, and they should be accepted with caution or used on a trial


For Your Future

in Agriculture

Let the



The University of Florida College of Agriculture is
equipped and staffed to give you the best possible train-
ing in

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College of Agriculture
University of Florida
Gainesville, Florida

S2 36 0 4


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source

site maintained by the Florida
Cooperative Extension Service.

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