Fertilizers and fertilization

Material Information

Fertilizers and fertilization
Series Title:
Bulletin, University of Florida Food and Resource Economics Dept. ; 183
Volk, Gaylord. M.
University of Florida, Cooperative Extension Service, Institute of Food and Agricultural Sciences
Publication Date:


Subjects / Keywords:
Nitrogen ( jstor )
Fertilizers ( jstor )
Nitrates ( jstor )

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Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
58749992 ( OCLC )


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Full Text
Bulletin 183
June 1972
and Fertilization

Professor of Soils


% P205


Institute of Food and
Agricultural Sciences
University of Florida

% K20




The Fertilizer Tag .. ........ 4

Sources and Characteristics of Plant Foods 8

Lime and Soil Acidity ................ ..... 14

Liquid Fertilizers ... ..... ........ 16

Manures and Composts ... .. 17

General Principles of Fertilization ......19

Pollution Potential of Fertilizers 24


CALCULATION OF FERTILIZER FORMULAS ... ........ .......................... .. .. 29

Originally printed as Experiment Station Bulletin 506,
1952, revised 1955. First printing of Extension Bulletin
177, 1962; second printing, 1964; third printing, 1965;
fourth printing and revision June 1966; fifth printing April
1967; and this major expansion as Bulletin 183.

(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, University of Florida and United States
Department of Agriculture, Cooperating, Joe N. Busby, Dean

Fertilizers and Fertilization
Gaylord M. Volk'

Plants need at least different of fertilization for economical
chemical elements for their growth crop production.
. processes. They require large The chemistry of fertilizers and
quantities of carbon, hydrogen, and their reaction with the soil is very
oxygen, which they obtain from complex. The following discussion
air and water. Nitrogen, potas- purposely omits the use of chem-
sium, phosphorus, calcium, magne- ical terms and symbols other than
slum, andsulfur also are used in those appearing on the fertilizer
c;niderale quantityy the plant tag or as used in the Florida Com-
Chlorine also may be beneficial. mercial Fertilizer Law. However,
'T~ eseelements may not be pres- this simplified presentation covers
ent in sufficient supply or in the most of the essential facts.
proper form. For example, air is The chemical symbols used on
four-fifths nitrogen gas, buT only the fertilizer tag to designate var-
tne clovers and similar leguminous ious constituents may be confusing
plants with nodule bacteria in their to readers wo avean inroduc-
roots can use it. All other plants on to chemistry or example,
must have nitrogen in combined nitrogen is listed on the tag as the
form such as is found in nitrate elemreirttN; while phosphorus is
salts, ammoniacal salts, and cer- given as TRe oxide, P20, and called
ta other fertilir ma phosphoric acid2; and potassium as
In addition to the elements men- the oxide, K20, and called potash.
tioned above, there is a group of Florida Fertiizer Law desig-
elements-iron, copper, mangan- nates the fertilizer constituents
ese, zinc, boron, and molybdenum simply as Primary Plant Foods or
-that are all essential for normal Secondary Plant s This erm-
plant growth but needed only in inology will be used in the discus-
very small quantities. The major- sion to follow.
ity of soils have enough of these Soil reaction (pH) plays a vital
elements, but our sandy soils may part in fertilizer efficiency. It re-
show deficiencies. In some in- fers to the degree of acidity (sour-
stances the nature of the soil ness) or alkalinity (sweetness) of
limits their availability to the a soil. To have a simple numeri-
plant. cal measure, the pH scale has been
Whenever any element is in adopted. At pH 7.0 a soil is
short supply for plant growth, neither acidnoralkaline, but neu-
it must be furnished by some type tral. As values decrease from pH
SProfessor of Soils (Soil Chemist) IFAS.
'Phosphate' is a more accurately descriptive term.

7.0 soil acidity increases. As val-
ues rise above 7.0 soil alkalinity

Virgin Florida soils range from
pH 3.8 (very acid) to pH 8.0 or
slightly higher (alkaline). The
strongly acid condition is encoun-
tered in certain acid peats, mucks

and palmetto flatwoods. The al-
kaline condition is usually associ-
ated with marl or other calcareous
Most crops grow best in the
range pH 5.5 to 6.5. However, in
some instances a low pH may be
required for disease control.

There is a wealth of information phosphoric acid, and the third
on the Florida fertilizer tag. This potash. These are the available
information, if understood by the primary plant foods. The figures
grower, can often prevent needless are percentages or units in fertili-
expenditure for materials contain- zer terminology. A 6-8-8 contains
ing unnecessary elements, or crop only three-fourths as much nitro-
losses resulting from the use of gen, but four times as much avail-
materials lacking in some essential able phosphorus as 8-2-8. Ob-
plant food. viously these two fertilizers would
Fertilizers differ in composition not serve the same purpose.
depending upon how much of each Some fertilizers are very similar
of the different plant foods they in analysis; from these approxi-
contain and the source of these mately the same amounts of nitro-
nutrients. A 100-pound bag of 6- gen, available phosphoric acid, and
8-8 analysis tertiiz contains potash may be applied to the crop
pounds oiLfTtogen, 8 pounds of by changing the amount of fer-
available phosphoric acid, and 8 tilizer per acre.6 Fertilizer formu-
pounds sof water-solub poitash.- If lation based on units and percent-
the -ertilizer contains 8 pounds of ages is given in the appendix.
nitrogen, 2 pounds of available The formula for the available
phosphoric acid, and 8 pounds of primary plant foods in a 68-8
potash, it has the analysis 8-2-8. tilizer would appear on the fertili-
The first figure always indicates zer tag in percentage (%) as fol-
nitrogen, the second available lows:
3 The importance of the pH determination is its indicator significance of lime re-
quirement and of current or potential availability of nutrient elements in the soil.
(The fact that pH, per se, is a quantitative measure of hydrogen ion concentra-
tion is of no practical significance in the buffered soil system).
4 In certain instances other numbers may be added to the analysis. They refer
to secondary elements as follows: N-P.Os-KO-MgO-MnO-CuO-B20.. Thus, 6-8-8-
0-0.75-0-0 indicates that 0.75% MnO has been added to the 6-8-8.
When comparing one fertilizer analysis with another, it usually is best to keep
the nitrogen constant, because plants are very sensitive to deficiencies or excesses
of this plant food. For example, if twenty 100-pound bags of a 6-8-8 have been
used in the past, 20 times 6-8-8-or 120 pounds of nitrogen, 160 pounds of avail-
able phosphoric acid, and 160 pounds of potash-were used. To determine how
this compares with a 10-10-10, divide the 120 pounds of nitrogen by 10 (the
pounds of nitrogen in a bag of 10-10-10). This gives 12 bags of 10-10-10 as
necessary to provide 120 pounds of nitrogen. At 10 pounds each of phosphoric
acid and potash per bag of 10-10-10, the 12 bags would supply 120 pounds of
available phosphoric acid and 120 pounds of potash. The grower must decide
whether a substitution is permissible and economical.

Total Nitrogen, not less than ....---.......---- -......

Available Phosphoric Acid, not less than ....

Water-Soluble Potash, not less than .. ... -

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 commonly recognized
secondaries include calcium, mag-
S nesium, copper, manganese, zinc,
boron, iron, sulfur, and molyb-
denum.G Of these, manganese, cop-

per, zinc, boron, iron, and molyb-
denum are frequently referred to
as micronutrients.7 There are cer-
tain required statements of forms
and sources of both primary and
secondary plant foods which must
appear on the tag. An example of
the above tag fiNed in for nutrients
that are guaranteed might read as


Total Nitrogen ............
Nitrate Nitrogen ..... --.--
Ammoniacal Nitrogen ...........
Water-Soluble Organic Nitrogen
Water-Insoluble Nitrogen .
Available Phosphoric Acid .....
Insoluble Phosphoric Acid .. -
Water-Soluble Potash ..
Total Available Primary Plant Food
Chlorine not more than ......

..-. .. 6.00% 1
.75% 2
2.25% 3
2.10% 4
.90% 5
....- 8.00% 6
.20% 7
... 8.00% 8
.. 22.00% 9
3.00% 10

Derived from: Caster Pomace, Tankage, Ammonium 11
Nitrate, Sulfate of Ammonia, Urea, Ammoniated 12
6 These are reported as oxides, except sulfur, which is reported as the element.
SThe use of the terms 'minor' and 'trace' is now discouraged.




Superphosphate, Sulfate of Potash, Muriate of
Potash and Sulfate of Potash-Magnesia.
Statement of Secondary Plant Foods:
Total Magnesium as MgO ..........................
Water-Soluble Magnesium as MgO --- ......-
Copper as CuO -..-- ......................-..

Derived from: Magnesium sulfate and Copper sulfate

The line numbers do not appear
on the tag but are inserted by the
writer for easy reference in the
discussion to follow.
It will first be noted that the
lines 1, 6, and 8, are the percent-
ages making the analysis as al-
ready 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 dividing line, but fertili-
zers 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, giving the insoluble phos-
phoric acid, is optional. This form
of phosphoric acid is not included
in the 8.00% available phosphoric
acid of line 6 but is in addition to
Line 10 gives the maximum per-
centage of chlorine. Chlorine or-
dinarily is noiT-Vued s a plan
i6 n -ie fJertilizer. 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 con-

Lines 11 to 14 list the materials
from which primary plant foods
were obtained. This statement is
of value tothe 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 material a statement of
sources is of limited value.
Lines 15 to 19 show the method
of reporting secondary plant foods.
A knowledge of 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 re-
ported may vary to some extent
with different tags, but there
should be no confusion if the above
example tag is thoroughly under-
Conditioners and Fillers.-The
amount of various fertilizer ma-
terials which are required to sup-
ply the primary and secondary
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 material that helps
prevent a fertilizer from becoming
so moist or so hard on standing
that it will not drill properly. Con-

2.00% 16
2.00% 17
.50% 18

I. A

(See Table 2 also for other nitrogenous materials.)
Percentage Composition (See text for meaning of symbols.)
Material N PO1 [ KO CaO MgO S Na O Other

Ammonium sulfate ......................
Ammonium sulfate-nitrate ..........
Ammonium phosphate ..............-
Ammonium nitrate plus lime .....
Basic slag (Thomas) ...............
Basic slag (Open hearth) .........
B orax ... ... ..- .. ..... ....
Calcium sulfate ... ... ........
Calcium nitrate .... ....---
Copper sulfate .... ....... ..
Castor pomace ..............- ........-
Cotton bur ash ....--......-...-.......
Em jeo .. ...... ....... ..-
Fish scrap ............ ........
*4 Guano (Peruvian) -..-...--...-
Iron sulfate copperass) ...............
Magnesia (seawater) .......
Magnesium sulfate .........
Manganese sulfate -.....--- ..
Muriate of potash ........-............
Nitrate of soda .........-- ..
Nitrate of soda-potash ..............
Phosphate rock ..............
Potassium nitrate ....-- .....
Sewage sludge (activated) .......
Sodium molybdate .....................
Sulfate of potash ....................
Sulfate of potash-magnesia .........
Sul-Po-Mag .....- .........
Superphosphate, regular ..........
Superphosphate, cone.- ..----.
Tankage, animal .......................
Tec-Man-Gam .........- ------
Zinc sulfate .............. ---- -





5.4 1.5 1.3
5.3 28

11 2.4

4 MnO

12 36 B203

30 CuO

5 C1

33 FeOOa

30 MnO
44 C1

19 58 MoO3
2 C1
S 11 C1
S 11 C1

37 MnO
45 ZnO

* If conditioned with dolomite.

ditioners may also supply some of mite, raw phosphate or sand. It
the plant foods in the formula. usually has certain conditioning
Filler -i the term applied to a value, but contains no significant
material added to fill out the ton of amount of available primary plant
weight. t often consists of dolo- food.


The sources of the various avail-
able plant foods in fertilizers differ
to some extent in various parts of
the country. The following dis-
cussion applies to Florida; medium
analyses are still common, but the
usage of high analysis fertilizers
requiring concentrated materials is
Some materials carry more than
one plant food or form of plant
food (Table 1). For example, am-
moniated superphosphate may car-
ry nitrate nitrogen, ammoniacal


Fertilizer Material

Nitrate of soda ...............
Nitrate of soda-potash ...
Nitrate of potash ... .
Calcium nitrate .. .. ........
Ammonium nitrate ..... ...
Ammonium nitrate plus lime**
Ammonium nitrate solutions ..
Ammonium sulfate-nitrate ......
Ammonium phosphate ..........
Anhydrous ammonia ...........
Aqua ammonia ....... .............
Ammoniated superphosphate ....
Ammonium sulfate ...........
U rea ... .......... .. ...
Cottonseed meal* .....
Castor pomace* ..... .....
Hoof meal* ...........
Dry fish scraps* ........
Peruvian Guano* ...........
Sewage sludge (activated)*
U reform ..... .......-- .. ..........
Beetle scrap dust ................
Processed tankages*
Raw bone meal*
Hull meals* .. ... .........
Beetle molded scrap ....
Garbage tankage* ....

nitrogen, and phosphoric acid.
Nitrate Nitrogen.-This form of
nitrogen in mixed fertilizers comes
mainly from ammonium nitrate,
ammoniated superphosphates, ni-
trate of soda, and nitrate of soda-
potash (Table 2). Ammoniated
superphosphate is prepared by
spraying ammoniating solutions on
superphosphates. Ammoniating so-
lutions used at present generally
contain ammonium nitrate or urea
or both, and ammonia gas dis-
solved in water.


...... 11-21
S 82
S 24
S 12
...... 19.0
.... 2.5-3.3

Rate of
Very rapid
Very rapid
Very rapid
Very rapid
Very rapid
Very rapid
Very rapid
Very rapid
Very slow
Very slow
Very slow
Very slow

SNatural organic.
** A-N-L, Cal Nitro, Calcium ammonium nitrate, etc.

The nitrogen in ammonium ni-
trate is one-half ammoniacal nitro-
gen and one-half nitrate nitrogen.
All of the nitrogen in nitrate of
soda and nitrate of soda-potash is
in the nitrate form. Calcium ni-
trate and nitrate of potash also
carry all of their nitrogen in the
nitrate form. Calcium nitrate is
little used in Florida mixed fertil-
izers at present. Crops can use the
nitrate nitrogen from different
sources equally well.
Nitrate nitrogen dissolves read-
ily in water and moves freely in
the soil with the movement of
water. It is not held by the soil
particles. For this reason, heavy
rains may cause leaching loss of
nitrates. On the other hand this
characteristic of nitrate nitrogen
makes it a favored top or side
dressing when rapid movement in-
to the root zone is needed, or as
an inclusion in the band to serve
as a mobile starter fertilizer at

Ammoniacal Nitrogen. This
form of nitrogen comes mainly
from ammoniated superphosphate,
sulfate of ammonia, and ammo-
nium nitrate. The ammoniacal ni-
trogen in ammoniated superphos-
phate is from the ammonia gas
dissolved in the ammoniating solu-
tion and the ammonia portion of
ammonium nitrate which may also
be a constituent of the solution.
All of the nitrogen in sulfate of
ammonia is in the ammoniacal
form. Ammonium phosphate also
carries all ammoniacal nitrogen
and is often used in high analysis
fertilizers. The ammoniacal nitro-

gen from different sources is equal-
ly usable by crops.
Ammoniacal nitrogen dissolves
readily in water. It differs from
nitrate nitrogen in that it is held
by the soil particles and free move-
ment through the soil is retarded.
Movement of ammoniacal nitrogen
through a strongly acid soil usu-
ally is more rapid than through a
slightly acid soil. Therefore, prop-
er liming to reduce soil acidity
will help reduce the leaching loss
of ammoniacal nitrogen by heavy
Most plants can use ammoniacal
nitrogen, but usually bacteria con-
vert 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
are not efficient, and certain types
of plants may suffer from lack of
nitrate form of nitrogen. Soil that
is saturated with water, very dry,
or too cold also is slow to convert
ammoniacal nitrogen to nitrate ni-
trogen. For this reason nitrate ni-
trogen is favored for rapid pene-
tration of cold soils when side
dressing late fall, winter, and early
Because ammoniacal nitrogen
tends to be retained near the sur-
face of the soil when it is applied
as top dressing, special attention
should be given to liming to offset
the concentration of acidity pro-
duced as nitrification takes place.
One. pound of ammoniacal nitrogen
may require up to 6 pounds of lime
to prevent increase of acidity and
maintain optimum conditions for

" Solonaceous crops (potatoes, tomatoes, tobacco, etc.) usually respond to a higher
than average ratio of nitrate to ammonium than most crops, apparently as a
requirement for mobilizing calcium into the plant.

Water Soluble Organic Nitro-
gen.9-This form of nitrogen is
supplied mainly from urea.10 The
urea is made by chemical proc-
esses, but is identical with urea
nitrogen found in the urine of
Water-soluble nitrogen changes
to ammoniacal nitrogen within a
few days after application to the
soil when applied in the amounts
usually found in mixed fertilizers.
For this reason, the water-soluble
organic nitrogen reported on the
fertilizer tag should be considered
as the equivalent 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.
Gaseous loss of ammonia from
solid urea top-dressed on light
sandy soil or on turf may be ap-
preciable under certain conditions.
(See Appendix)

Water-Insoluble Nitrogen.-This
form of nitrogen comes almost
entirely from natural organic
sources, such as seed meals, tank-
ages, and sewage sludge products.
A small amount of water-insolu-

ble nitrogen comes from syn-
thetic materials-primarily urea-
Relative amounts of insoluble
nitrogen from different sources
are not reported on the fertilizer
tag. This makes it impossible to
determine which forms are being
used in significant quantities if
more than one source is reported.
Water-insoluble nitrogen cannot be
used directly by the plant but must
be converted to ammoniacal nitro-
gen by soil organisms. The con-
version proceeds gradually. For
this reason, insoluble nitrogen is
more slowly available to a crop
and less subject to leaching loss by
heavy rains.
The conversion of insoluble ni-
trogen 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 conversion to usable nitrogen in
the soil. A list of nitrogenous fer-
tilizer materials is given in Table
2, with estimated rates of avail-
ability of their nitrogen."
Most natural organic nitrogen
carriers have part of their nitrogen
in soluble form. This portion ap-
pears under the nitrate, ammoni-

" The name "organic nitrogen" refers to nitrogen of the type found in organisms
such as plants and animals. It includes certain of the nitrogenous compounds now
made synthetically.
10 Some urea nitrogen and water-soluble non-urea nitrogen is present in urea-
forms. See Ureaform in Appendix.
" Recent tests with activated sludge and Peruvian guano showed that the water-
insoluble portion that was potentially available to plants was largely converted
to nitrate within four weeks. On the other hand, good ureaforms (Uramite,
Nitroform) showed a marked extended availability of the water-insoluble nitr
gen. But the grower should use extreme caution to avoid ureaforms derived b,
processing industrial wastes of the plastics industry. Such processing, including
ultrafine grinding, apparently will result in an activity index above 40, 1
under crop tests the water-insoluble nitrogen is so unavailable as to be relative
worthless as a fertilizer material.
Retarded availability of water-insoluble nitrogen has been achieved by encap-
sulation but is not of practical significance to date.

acal, and water-soluble forms on
the fertilizer tag. The usable in-
soluble nitrogen in a fertilizer is
very high in cost as compared with
other sources, since only a third
to a half of the insoluble nitrogen
now used in fertilizers is available
within a reasonable length of time.
It should be requested only if a
real need exists. Side-dressing
with cheaper nitrogen while the
crop is growing, along with the
control of nitrogen release afforded
by decomposing crop residues usu-
ally eliminates the need for in-
soluble nitrogen at planting.
Insoluble nitrogen is valuable for
lawns, turf, and certain ornamen-
tals as uptake of nitrogen by the
plants is less rapid. This reduces
the intense flush of growth im-
mediately after fertilization. Much
of the beneficial response to natu-
ral organic may be due to the sec-
ondary elements they usually con-

Available Phosphoric Acid.-
This form of phosphorus comes
mainly from superphosphate, am-
moniated superphosphate, and con-
centrated superphosphate (double
or treble). These materials are
made by treating raw rock phos-
phate with acids or heat to make
the phosphorus more available to
the plant. High analysis fertilizers
may contain considerable amounts
of ammonium phosphate. The

available phosphoric acid from
these different materials is about
equally usable by the crop.12
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
corrects this condition in the flat-
woods 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 avail-
ability of the residual phosphorus
may be much lower than for black
or gray soils, thus the amount of
phosphorus to be added to main-
tain fertility of the red and yellow
soils is somewhat larger than for
black or gray soils.13

Insoluble Phosphoric Acid. -
This form of phosphorus must not
be confused with available phos-
phoric 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 converted to the available
phosphoric acid form by acid or
heat treatments.14 This form of
phosphoric acid is more slowly
available to the plant, but over a
long period of time does have cer-
tain value and is, therefore, re-
ported on the tag. It is more
rapidly available on the moderately
to slightly acid soils than on

2 However, recent information raises a question as to the degree of reversion of
phosphate by relatively high ammoniation of superphosphates, and subsequent
reduction of availability of the phosphorus. The effect would be least with band
placement in acid soils and greatest in broadcast use on calcareous soils.
13 Assessment by soil analysis, of the contribution of accumulated phosphorus in
the soil, is second only to pH and associated calcium-magnesium balance deter-
mination in importance.
" It also indicates whether or not raw phosphate was 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.

slightly acid to high lime soils. The
use of ground rock or waste pond
phosphate has been confined large-
ly to pastures.
Many soils in the Southeast are
deficient in sulfur. The main
source of this element in the past
has been ordinary superphosphate,
which is about half calcium sul-
fate. If ground rock phosphate or
concentrated phosphates are to be
used continuously on a given area,
eventually sulfur may have to be
supplied from another source to re-
place that removed by the crops.

Water-Soluble Potash.-Potash
comes mainly from muriate of pot-
ash, sulfate of potash magnesia,
nitrate of soda potash, nitrate of
potash, and sulfate of potash. Cot-
ton bur ash contains potash in the
form of carbonate. The water-
soluble p o t a s h from different
sources is equally usable by the
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 re-


Plant Food



covered by deep-rooted crops.
Chlorine.-This element comes
almost entirely from muriate of
potash.15 Other forms of potash,
such as sulfate of potash, sulfate
of potash magnesia, nitrate of pot-
ash, and nitrate of soda potash, are
used if it is desirable to reduce
the chlorine content of a fertilizer.

Secondary Plant Foods.-Con-
siderable care must be used in
reading a fertilizer tag to deter-
mine the amounts of secondary
plant foods guaranteed. These sec-
ondaries may be from various
sources that differ widely in avail-
ability to the plant. The water-
soluble forms usually are the
important sources in a mixed
fertilizer,1" but certain insoluble
forms are now receiving wide ac-
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 mag-
nesium sulfate. Other secondaries
of importance, with their symbols
and commonly used water-soluble
sources, are as follows:

Derived from

Copper Sulfate
Manganese Sulfate
Zinc Sulfate
Borax, Borate



Iron Fe20 Iron Sulfate, Chelated iron
15 When 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 con-
siderably higher than when supplied only from muriate.
" Some common sources of primary and secondary plant foods are listed in
Table 1.





Insoluble forms of secondaries
quite widely used are copper oxide,
magnesium oxide, manganese ox-
ides, calcite and dolomite limes,
and frits. 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-
tively unavailable to crops. Avail-
ability of these elements tends to
be reduced as pH increases into the
alkaline range, except for molyb-
denum which may be rendered in-
creasingly unavailable as the soil
approaches strong acidity.
Chelates and frits have been de-
veloped to partially offset this
strong inactivating ability of the
soil. In iron chelate, the only che-
late 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 elements are held in a slowly
soluble form in a glasslike matrix
and then 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 nitro-

Sodium Molybdate
Superphosphate, sulfate of
potash-magnesia, ammo-
nium sulfate17
Nitrate of soda17
Calcium sulfate, superphos-

gen 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 released to a crop when
the organisms die or the organic
matter decomposes.

Base Goods.-This term is fre-
quently encountered in discussion
of fertilizer mixtures. It generally
refers to a mixture of several fer-
tilizer materials, usually super-
phosphate, with materials contain-
ing nitrogen or potash or both.
This mixture, after curing and
grinding, is used as a base to which
more materials may be added to
make different analyses.

Bulk Blending.-This term is
still poorly defined, but it refers
in general to dry mixtures of
straight, high-analysis materials
intended primarily for immediate
short haul bulk delivery and broad-
cast application before significant
deterioration of physical or chemi-
cal makeup takes place. The pres-
ent trend is toward the use of ma-
terials which have been selected
for granule sizes and gravities that
will not unduly segregate during
bulk transit, and that will respond
uniformly to centrifugal broad-
cast spreading.

" These usually are not selected deliberately to supply the element indicated.

Fertilizer Injury.-High chlorine
will reduce crop quality or injure
sensitive crops such as tobacco and
potatoes in the field, or cause in-
jury to plant beds.
Too much usable nitrogen in the
soil at one time may cause leaf
burn and injure the roots. The ac-
cumulation of soluble salts from
fertilizers or by irrigation with
salty water will prevent intake of
water by the plant and reduce
In general, the more sandy the
soil and the drier the soil, the more
severe will be the injury from a
given amount of excess 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 fertil-
izers are acid-forming. This acidity
may be overcome by adding dolo-
mite to the fertilizer during mix-
ing or by liming the soil. On the
average, one ton of fertilizer re-
quires about 200 pounds of dolo-
mite to neutralize this acidity.
With certain high analysis fertil-
izers it is not possible to add
dolomite wit h o u t reducing the
amount of primary plant food in
the analysis.
If the acidity of the soil is deter-
mined every few years and lime
added when necessary, it is ques-
tionable that addition of lime to
fertilizer mixtures at the expense
of concentration is justified.


Agricultural Limestone. Lim-
ing materials are used for the con-
trol of soil acidity and to supply
calcium and magnesium. Agricul-
tural limestone, which is ground,
crushed, or pulverized limestone
rock, is used to the largest extent
for this purpose. It consists of
calcium carbonate and may also
carry magnesium carbonate, and is
reported on the tag as percentages
of these two compounds present,
within limits established by law.
Eighty-four pounds of magnesium
carbonate is equal to 100 pounds
of calcium carbonate in neutraliz-
ing soil acidity.
Limestones containing appreci-
able amounts of magnesium carbo-
nate are called dolomite. The mag-

nesium is of value where this plant
food is deficient in the soil.'8
The screen test as reported on
the tag is very important in deter-
mining the value of agricultural
limestone; the finer the material
the more rapid is its reaction with
the soil. By regulation, 90% must
pass a 10 mesh, 80% pass a 20
mesh, and 50% pass a 50 mesh

Hydrated Lime.-Hydrated lime
is made by burning limestone to
quickliine and then slaking with
water. It may consist of calcium
hydroxide or of mixtures of cal-
cium hydroxide and magnesium
hydroxide and is so reported on the

8 The type of lime to use, whether calcic or dolomitic, is determined by the cal-
cium-magnesium balance in the soil at the time the initial pH determinations
are made, unless the high magnesium requirements of the crop automatically
precludes the use of low magnesium lime.
" Number of wires per inch.

Hydrated lime is used to a con-
siderable extent for special pur-
poses. It reacts much faster with
the soil than agricultural lime-
stone; therefore, more care is re-
quired in its use. Hydrated lime
should not be used at more than
one-half the rate recommended for
agricultural limestone.

Reaction in the Soil.-Proper
liming of strongly acid soils not
only increases the efficiency of al-
most all plant foods added in the
fertilizer, but makes 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 prac-
The recognition of potential tox-
icity of aluminum and significant
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 im-
mediate correction of acidity de-
sired. Thereafter, the coarser ma-
terial continues slow reaction to
help maintain a desirable pH. This
is becoming increasingly impor-
tant on pastures as well as orna-
mental turf in recognition of the
need to incorporate more lime dur-
ing renovation processes in order
to reduce the need for supple-
mental top dressing at a later date.
Lime should be mixed into the soil
even if only to a shallow depth if
practical to do so.
Particular care should be exer-

cised in sampling soils and deter-
mining pH for lime requirement.
Surface applied lime moves into the
soil at a relatively slow rate.
Therefore, pastures and other
areas where tillage is nil or shallow
should be sampled to the appro-
priate depth of probable mixing of
the lime, with a second sample
taken at lower depth to represent
the subsurface.20
Very fine lime, well mixed with
the soil, will produce a maximum
pH within about one month. Stand-
ard agricultural limestone, mixed
with the soil by discing in the con-
ventional manner, usually does not
show maximum effect for about 6
months. Therefore, pH determina-
tions are misleading if taken be-
fore such an interval has passed.
It also has been noted that up to
one-half of the limestone may still
be undissolved in the soil when
maximum pH is reached, although
it will gradually react thereafter
to help maintain this pH. This
undoubtedly is due to slow reaction
of coarser particles and to the
somewhat non-homogenous mix-
ture of lime and soil that is inevi-
table even with acceptable methods
of application.
The total lime requirement es-
tablished as necessary to arrive at
a desired soil pH may be impracti-
cally high, and the indicated lime
best not applied in one application.
The heterogenous nature of the
soil-lime mixture following applica-
tion is such that application of
more than two tons at one time
is seldom justified, because plant
roots will selectively respond to the
micro environment in the vicinity
of the lime concentrations most

" The presence of fertilization salts usually will give a pH value that is too low
as interpreted for liming recommendations.

suited to their needs.
If more than two tons of lime
are indicated, then a period for re-
action adjustment and soil pH
check usually should intervene be-
tween applications. Excessive lim-
ing can interfere with micronu-
trient availability and create or
enhance the problem. On the other
hand, liming to pH 7.0 is some-
times recommended to help alle-
viate toxicity due to high copper
residues in the soil.

Subsoil Acidity.-The effect of
fertilizer acidity on the subsoil
where incorporation of lime is im-
practical is of primary concern

with deep-rooted crops. Apparently
the effect of fertilizer materials on
subsoil acidity is closely associated
with the amount of ammonium
nitrogen or urea they contain.21
Ammonium moves into the sub-
soil usually in combination with
sulfate, chloride, and nitrate, es-
pecially if the surface soil is. mod-
erately to strongly acid. Conver-
sion of ammonium to nitrate in the
subsoil leaves a strong residue of
acidity. Adequate liming of the
tilled surface soil tends to hold
ammonium more efficiently in the
surface as well as promote conver-
sion of the ammonium before it


Plant nutrients supplied in fluid
form consist primarily of low pres-
sure nitrogen solutions and anhy-
drous ammonia, with small but
increasing usage of solution mix-
tures. Slurries consisting of solid
and liquid materials stabilized in
clay suspensions have been devel-
oped, but currently they are unim-
portant in Florida. Certain com-
plete mixtures have been developed
around the usage of polyphos-
phates, with urea as a primary
source of the nitrogen. These mix-
tures show promise but currently
constitute only a very small per-
centage of total usage of fertilizer
Low pressure fluids are usually
applied with dribble equipment of
some type. Liquid application in
this manner is now being combined
with dry application by tailgate
centrifugal spreaders so that nitro-

gen solutions and dry potassium
chloride, for example, may be ap-
plied in one operation.
Anhydrous ammonia is trans-
ported in liquid form under high
pressure, but during application it
converts to gas at an injection tip
within the soil. To date it does
not have the wide acceptance in
Florida that it does in the midwest
and the Mississippi delta. The es-
sential injection procedure appar-
ently is not readily acceptable for
many Florida soil conditions and
cropping systems. The medium
pressure aqua solutions of am-
monia are little used.
At present about one-third of
the nitrogen used for direct appli-
cation in Florida is as low pressure
nitrogen solutions, predominantly
of 32% N, with the nitrogen de-
rived about equally from urea and
ammonium nitrate. Anhydrous am-

21 Calcium nitrate and sodium nitrate are equally effective in retarding the de-
velopment of subsoil acidity, but pH values for leached subsoils must be inter-
preted with caution where sodium is involved because its presence gives pH
values that are too high as usually interpreted for comparative purposes.

monia accounts for about another
tenth of the nitrogen used for di-
rect application.
Crops respond to plant foods ap-
plied in solution in about the same
manner as to application of dry
materials. Response to anhydrous
ammonia injected into the soil may
be somewhat different than to
other ammoniacals or urea be-
cause the anhydrous ammonia
held by the soil is highly immobile,
and the high alkalinity occurring
at the injection site may cause a
delay in conversion rate of am-
monium to nitrate, as compared
with ammoniacal salts or the ini-
tially mobile urea.
The 32% nitrogen solution as
well as anhydrous ammonia show
excellent promise for expanded
usage in the future. Both are
ideally adapted to custom applica-
tion. The first has an excellent bal-
ance of three-fourths ammoniacal
equivalent and one-fourth nitrate
nitrogen. The presence of ammo-
nium nitrate in the solution tends
to temporarily activate soil acidity
which largely prevents gaseous
loss of ammonia nitrogen from the
urea (See Urea in Appendix) when
applied to bare soils in the acid
range of pH. A 21% nitrogen
solution made from ammonium ni-
trate is also an excellent material,
but may cause trouble by salting
out in the applicator during cold
Loss of ammonia nitrogen when

the 32% solution is applied to well-
developed sod can be appreciable
under certain conditions. Also,
burning of the grass following ap-
plication of nitrate-bearing solu-
tions, especially the 21% ammo-
nium nitrate, is apparently
accompanied by some form of gas-
eous nitrogen loss. The 32% urea-
ammonium nitrate solution and
the 21% ammonium nitrate solu-
tion should give comparable results
if applied to recently cut or grazed
dry turf that has not been re-
cently top limed. Both materials
are economically acceptable for
topdressing pastures under these
conditions. Low pressure nitro-
gen solutions are best covered
after application to tilled soils, but
allowing them to remain on the
surface is acceptable if covering
is impractical. Solutions made
from urea alone should always be
covered or watered in.
Anhydrous ammonia is highly
regarded for areas and crops where
injection is economically practical,
because the basic cost per unit of
nitrogen is the lowest of all mate-
rials. Its preplant or side-dress
usage on row crops in tilled soils
where drawbar pull is low is com-
paratively more economical than
usage in heavy turf where both
drawbar pull is high and jet loss
of ammonia before closure of the
injector slit can be appreciable.
Nevertheless, usage on pastures is
practical and should continue to


Animal manures and organic
composts usually are used prima-
rily for their soil-conditioning val-
ue, and secondarily for their plant
food content. An exception is

chicken manure, which if unleach-
ed is quite high in plant food per-
centages and requires judicious
usage to avoid burning.
The rate at which the nitrogen

in manures and composts becomes
available depends to a large extent
on the ratio of nitrogen to carbohy-
drates (cellulose, etc.) in the ma-
terial. Until the carbohydrates
have been reduced by microorgan-
isms to a relatively low level,22
activity of the microorganisms will
continue to keep the nitrogen tied
up in their life processes and not
allow it to become readily avail-
able to growing plants.
Composting is the process of al-
lowing or aiding the microorgan-
isms to reduce carbohydrate of a
material until it becomes so low as
to be limited as an energy source.
In the process, the material is
much reduced in volume. At ap-
proach to termination, decomposi-
tion of the dead organisms releases
the nitrogen they have been re-
cycling. The controlled release of
nitrogen afforded by decomposing
field crop residues is essentially
a composting process.
A true compost is a material in
which carbohydrates are reduced
to the extent that when added to
the soil the material will release

available nitrogen at a significant
rate, or at least not reduce the ef-
fectiveness of added fertilizer ni-
trogen. Organic materials which
have not reached this stage of de-
composition should not be called
composts. For example, so-called
garbage compost which has been
allowed to compost only a few days,
until the readily active waste pro-
teins are destroyed and the mater-
ial made sanitary for further dis-
posal, is only a slightly composted
product without the characteristics
of a true compost.23 The majority
of the cellulose is still intact and
the material will cause acute ni-
trogen starvation of plants, similar
in effect to applications of straw
or sawdust, unless supplemented
heavily with fertilizer nitrogen.
It is impractical to compost low
nitrogen-high carbohydrate mater-
ials for agricultural usage without
initially adding fertilizer nitrogen
to them. A well composted material
usually is black in color with vis-
ual identity of all but the coarse
fractions of the original materials
lost during composting.

Following are approximate analyses of four animal manures:
Percentage Composition on Dry Basis* (litter free)

Phosphoric Acid Potash
Nitrogen (P205) (K20


Rate of Nitrogen

Very slow

*About 4 pounds of fresh manure equals 1 pound of dry.
" In general, a carbon to nitrogen ratio of ten to one (C/N = 10) is considered
to be the dividing point although this can vary widely depending on the com-
position and coarseness of materials.
" The composting process of even readily compostable materials such as manures
or green plant residues takes 6 to 8 weeks.

Horse manure is called a 'hot'
manure because it is high in un-
digested carbohydrate and will
heat excessively in a pile. Cows
and sheep are ruminants. The
carbohydrate is much reduced in
the rumen of the animals, there-
fore, the nitrogen in the manure
is more readily available to a crop.
Fresh cow, sheep, and chicken ma-
nure, undiluted with litter, will not
cause nitrogen starvation.
Commercial dried cow, sheep,
and chicken manures are excellent
products for direct usage. Manures
which have been taken from un-
covered corrals or feedlots where
leaching has occurred and that
have been diluted with litter may
be relatively low in nitrogen and
potassium but nevertheless are
good soil conditioners although
weed seeds may be introduced by
All manures, and especially
horse manure, are improved by
composting. Inter-layering about

6 inches of manure with 2 inches
of soil into a pile several feet high,
maintained in moist condition for
6 to 8 weeks, makes an excellent
product when the pile is mixed for
The practice of incorporating
non-toxic organic rather than
concentrated fertilizers in trans-
planting fruit trees and ornamen-
tals is excellent. Sewage sludges,
manures, steamed bone meal, and
mature composts can be mixed di-
rectly with the soil before setting
the plants. The nutrients in these
materials are primarily in a form
that resists leaching from the fre-
quent watering essential to suc-
cessful transplanting, yet are re-
leased at a controlled rate more
suitable to the initially limited re-
quirements of the plant as com-
pared with the ready availability
of nutrients in concentrated com-
mercial fertilizers with their high
toxicity potential.


The various methods of applying
fertilizers are dictated by the
physical characteristics of the ma-
terials or mixtures, as well as econ-
omy, crop culture, interactions
with the soil, or simply by con-
venience. It is usually more eco-
nomical to place materials where
they are most accessible to the
plants, other factors being equal.
Thus, there is band placement for
row crops, localized broadcasting
for developing tree crops, pre-
plant broadcasting for solid-plant-
ed crops, and nutritional spray
application of micronutrients for
direct foliar sorption.
Prior to, or at planting time,

fertilizers may be incorporated
into the soil to the desired depth,
or be surface-applied and covered
by tillage. Thus, potential limita-
tions due to gaseous loss of am-
monia, or positional restrictions of
slowly mobile elements are largely
avoided. After planting, the crop
becomes a limiting factor. It can-
not be disturbed materially, and it
may be sensitive to physical con-
tact with fertilizer materials; or
the expanding crop simply utilizes
the space initially used for cultural
Specific cultural practices devel-
oped for various crops will not be
discussed in this publication. Only

the basic factors involved in the
general types of practices will be
analyzed for their role in fertilizer

Band vs Broadcast Incorpora-
tion.-Band placement of fertilizer
originated because it was found
that young plants in the row need-
ed nutrients more rapidly than
broadcast fertilizer would supply
them. To avoid toxicity that re-
sulted from contact with the down-
ward growing primary roots of the
seedlings or transplants, or burn-
ing of the upward growing point
it was found advantageous to place
double bands on the sides of the
row, preferably slightly below
planting depth. Developing lateral
roots do not penetrate a fertilizer
band to their detriment but only
approach it to the extent of their
tolerance to the environment of
the band. Toxicity largely arises
as a result of movement of toxic
concentrations of materials out of
the band area, probably with water
movement, into an area closer to
the plant as the roots there create
a water deficit. Leaching down-
ward into a root zone under in-
fluence of rains, or upward under
influence of surface evaporation
may also move soluble constituents
into a root zone, but simple dif-
fusion out of the band without sig-
nificant water movement may be
of little importance in toxicity
Band placement has an advan-
tage over broadcast application in
maintaining availability of some
elements, notably phosphorus and
certain micro-nutrients, which un-
der many conditions tend to be
fixed by the soil in competition

with plant uptake. The higher
acidity and concentration of salts
in the band are primarily respon-
sible. The acidity remains largely
localized at the band. It is not very
effectively reduced by adding lime
to the fertilizer prior to usage. The
lime does eventually react but it
is a somewhat latent action.
Placing only a minimum amount
of fertilizer in the band-so-called
s t a r t e r fertilizer-and the re-
mainder broadcast or later side
dressed, is an excellent practice,
but in general it is not widely used
because of the economy of the sin-
gle operation, and the possibility
of lowered efficiency of broadcast
or top dressed phosphorus. The
value of the practice is recognized
when slowly mobile elements such
as phosphorus, etc. are band-placed
at planting, but a significant por-
tion of the potassium and nitrogen
withheld for later application.
Broadcast application of com-
plete fertilizers and mixing with
the soil prior to land forming and
row planting is an excellent prac-
tice where culturally acceptable.
It distributes the work load and
can take maximum advantage of
the economy of bulk spreading and
the use of nitrogen solutions for
row crops. The use of anhydrous
ammonia under similar conditions
should dodge the row, or if cross-
row injected, usually precede
planting by about two weeks to
avoid toxicity. Anhydrous am-
monia is injected too deep to be
readily distributed by tillage.
Broadcast incorporation has the
advantage of eliminating the zone
of concentrated materials. On the
other hand, the reduction of avail-
ability of certain elements when

homogenized throughout the tilled
soil becomes of major importance,
particularly with acid soils high in
iron and aluminum, or with soils
containing lime, such as the marls.
The humus and certain clay col-
loids of soils have an exchange
mechanism that will retard the
mobility of most nutrients except
nitrate, sulfate, and boron, holding
them in readily available form.
When this mechanism is relatively
limited in quantity-as in sands
of low humus content-it can be
overloaded by the concentration
brought about by band placement.
The leaching of potassium and am-
monium can be significantly higher
from band-placed fertilizers than
from fertilizers broadcast on such
soils. Broadcasting takes maxi-
mum advantage of the retaining
power of the exchange mechanism.
When the highly mobile unused
residues of sulfate, chloride, and
nitrate are present in the soil and
subjected to leaching by heavy
rains, they carry with them the
nutrient elements, calcium, mag-
nesium, potassium, and ammoni-
um. If a soil is kept properly limed
to control soil acidity and to keep
the calcium balance high, the re-
sulting leaching balance is such
that this cheap element will move
predominantly in the leaching
water as compared with the more
costly elements, potassium and
ammonium nitrogen. Magnesium
reacts similar to calcium in this
process. It is a factor in favor of
our present high analysis mate-
rials that the amounts of sulfate
and chloride may be low, and the
leaching potential accordingly less.
Ridge-row planting results in
certain characteristics of fertilizer

movement that differ from those
of flat-row planting. Less water
penetrates the ridge row than a
flat row under intensive rains. As
a result, leaching from band-placed
nitrogen in the ridge may be sig-
nificantly less than from flat plant-
ing. Water tends to run rapidly
off the ridge into the alley and
penetrates there or runs off as sur-
face drainage.
On the other hand inverted
leaching, which is the movement
upward of soluble constituents and
deposition on the surface during
dry periods, may leave salts con-
centrated on or near the surface of
the ridge. A flushing rain can then
erode the materials to the alley be-
fore significant moisture penetra-
tion takes place. Of the various
nutrient elements, nitrate nitrogen
is particularly subject to this
movement. If rain following a dry
period is gentle and penetrating,
and the accumulation of soluble
salts on the ridge is enhanced by
inherently high soil salinity such
as may be present in certain coast-
al soils, the amount of salts re-
entering the soil in a concentrated
front can result in toxicity to the
Tillage operations that progres-
sively build or maintain the ridge
during the growing season modify
this picture, both by covering sur-
face-positioned salts and by re-
turning any portion persisting in
the alley back onto the ridge.

Surface Application of Dry Ferti-
lizers.-Surface application ranges
from the relatively low concentra-
tion of simple broadcasting to the
high concentration of surface
banding under plastic film. With

tree crops application starts close
to the transplant and expands with
tree growth, usually to a few feet
beyond the tree spread, until it
eventually reaches simple broad-
casting at tree maturity.
The factors determining toxicity
and leaching apply about equally
to surface-applied and incorporated
materials, depending on intensity
of application, with the notable ex-
ception of application under plastic
film. Where plastic strips are used
to cover the soil in the vicinity of
the row, a heavy single application
of fertilizer may be surface-applied
or slightly incorporated after the
crop is established but just before
the plastic is put in place. The low
potential for development of toxic-
ity-considering the large amount
of fertilizer used-is unique.
Downward leaching with surface
penetrating water is eliminated or
restricted. Only diffusion may be
significant. Apparently the plant
roots concentrate to absorb nutri-
ents just below or around the
fringes of the toxic zone, but do
not penetrate the fertilizer band.
Moisture for such a culture must
move into the row from the alley
or up from sub-irrigation.
A characteristic of plants that is
still little appreciated is their abil-
ity to sorb nutrients from the soil
without an available supply of wa-
ter at the sorption location. Roots
will maintain themselves or readily
penetrate a non-toxic dry soil, if by
exudation of water they can devel-
op or maintain a relative humidity
near 100% by translocating mois-
ture through the plant from a zone
of higher moisture content. Nitro-
gen and potassium especially, but
apparently not phosphorus, can be

sorbed by the roots against the
outflow of moisture from them to
the soil. The use of plastic creates
an ideal environment for this phe-
nomenon to function, although it
is suspected that it also plays an
important role at the upper fringes
of rising moisture during drought
periods even without plastic.
Except for placement under
plastic, surface application of nu-
trients is generally somewhat
less efficient than incorporation,
whether broadcast or concentrated
on only a portion of the soil area.
Uncovered nutrients must move
down to the root zone. Ammonium
converts to more mobile nitrate at
a relatively slow rate in the shal-
low surface because of extended
periods of low soil moisture. The
more immobile elements such as
phosphorus, copper, zinc, iron, and
manganese tend to be held above
the active root zone, particularly
if the soil pH is maintained at the
level usually preferred for crop
production, or following surface
liming. Actively decomposing sur-
face organic matter probably alle-
viates the condition to some extent
by promoting greater mobility and
by encouraging development of
supplementary shallow roots dur-
ing moist periods.
Root pruning by tillage, which
in the past has been thought of as
being detrimental to plants and
therefore to be avoided, probably
is a less inhibiting factor than re-
stricted nutrition that accompa-
nies uncovered surface applica-
tion. Pruned roots are rapidly
replaced by new growth into the
disturbed soil.
Solid urea, or a purely urea so-
lution, is not recommended for un-

covered surface application unless
followed by sprinkler irrigation,
because of the high potential for
loss of ammonia as the urea con-
verts to ammonium. (See Urea in
Appendix.) This can take place
even on acid soils if they are sandy
and low in humus content. The
fact that these losses occur erratic-
ally because they are so markedly
affected by precipitation pattern
often masks the real importance
of the problem. A naturally high
pH, such as exists in high lime
soils, or a similar condition
brought about by surface liming
enhances ammonia loss from urea
and may even bring it about for
ammonium sulfate, or urea-ammo-
nium nitrate solution, which are
otherwise acceptable materials for
surface application.
With soils having a significant
layer of decomposing organic de-
bris, such as under forest cover,
gaseous loss of ammonia from sur-
face-applied urea does occur, but
usually in unimportant quantities.
Controlled burning apparently re-
duces even this potential by tem-
porarily reducing the activity of
the enzyme system responsible for
conversion of urea. The urea per-
sists longer following burning, al-
lowing a longer period for rain to
move it into the soil. Even that
small portion of urea which may
be retained by the forest canopy is
not subject to significant ammonia
volatilization, although a small but
measurable quantity may be lost
as gaseous ammonia.

Liquid Application. Commer-
cial low-pressure liquid materials
or mixtures may be applied either
broadcast or concentrated in

bands. Interactions with the soil,
and crop responses will be similar
to those of dry materials, with the
possible exception that toxicity
and leaching potentials may be
slightly lower because of the gen-
erally lower level of sulfate and
chloride in liquid mixtures as com-
pared with dry mixtures of medi-
um analysis.
Dry materials may be dissolved
in an injector system for appli-
cation with overhead irrigation
water. Application by overhead
irrigation is generally less uniform
than dry application with non-
centrifugal spreaders unless the
irrigation system gives a very uni-
form distribution of water. Small
irregularities in distribution are
not critical for tree crops with
their widespread root system, or
for pastures which usually are fer-
tilized below the maximum.
The place where irrigation in-
jection must receive critical eval-
uation is with lawn grasses, golf
greens, and annual high-return
crops fertilized to obtain maxi-
mum production. Rotary sprinklers
which must overlap to give cover-
age are of questionable value for
such usage. In general, the ap-
plication of fertilizer materials
through irrigation equipment is
not widely accepted. Injection of
nutrients into water used for sur-
face flooding, row irrigation, or
sub-irrigation is not recommended
for Florida soils.
Certain fertilizer materials may
be applied in solution or precip-
itated suspension as nutrient
sprays for foliar sorption. Other
than micronutrients, only urea is
used at present, and only in minor
amounts as an addition to spray

solutions which already are jus-
tified for other reasons. Certain
nutritional micronutrients are reg-
ularly sprayed on tree crops, but
the deliberate application of mac-

ronutrients as nutritional sprays
has not proved to be profitable as
compared with other methods of


The pollution potential of the
various fertilizers are of consider-
able interest, especially in connec-
tion with eutrophication of natural
lakes and impounded waters. The
potential for detrimental pollution
by plant foods or fertilizer salts
other than phosphorus and nitro-
gen, generally is of negligible im-
portance to the quantities originat-
ing from the fertilizers per se.
Nitrate nitrogen moves readily
through the soil, and its contribu-
tion can be significant where an
extensive root system is lacking or
dormant, especially under condi-
tions where a shallow water table
is controlled by ditch or tile drains.
The significance of penetration of
nitrate through an extensive soil
profile to a deep aquifer under
judicious fertilization has not been
adequately evaluated, but the low
level of nitrates usually found in
deep-aquifer water even in highly
developed agricultural areas sug-
gests that the problem exists or
might develop in the future only
under exceptional conditions.
Only a small percentage of nitro-
gen passes an active, well-devel-
oped root system. Thus, broadcast-
ing fertilizer over an area only
partially covered by plant roots
such as in immature orchards, pro-
motes greater leaching loss than
where the fertilizer is confined to
the area of root expansion. Nitro-
gen application during periods of
crop dormancy would also enhance

leaching losses.
There is an initial difference in
mobility of ammoniacal, nitrate,
and urea nitrogen when first ap-
plied to the soil, but the mobility
of ammoniacal and urea nitrogen
prior to their nitrification is de-
layed only temporarily. This con-
stitutes a significant factor in their
favor only where heavy leaching
rains follow application of the fer-
tilizer within a few days.
The movement of phosphorus
through mineral soil profiles usual-
ly is negligible in neutral to slight-
ly acid soils, but in acid sands
movement becomes progressively
more active as acidity increases be-
low about pH 5.5. This range usu-
ally is not acceptable for crop pro-
duction. An exception, as yet
unevaluated for pollution potential,
is phosphorus fertilization of pines
on strongly acid flatwoods soils.
This is a relatively recent develop-
ment in phosphorus usage which
may become extensive, but which,
because of the low level of phos-
phorus application, may contrib-
ute little to pollution. The move-
ment of fertilizer phosphorus from
cropped organic or sandy soils fol-
lowing heavy fertilization within a
few feet of a drainage ditch or im-
mediately over shallow tile is an
unevaluated possibility. The major
way that phosphorus moves into
drainage channels is by surface
soil erosion.
Soluble constituents, such as ni-

States, may be moved in significant
quantities by surface runoff fol-
lowing initially intensive rains es-
pecially under ridge-row culture,
but under gentle rains nitrates
usually are moved down into the
soil before surface water runoff
occurs. A major contributor of
both nitrogen and phosphorus to
drainage water is surface move-
ment of manure from pastures, or
followingg manure top dressing of
,the soil where incorporation is im-
. practical.
What could be termed pollution
Sof the soil by buildup of retained
fertilizer constituents to a toxic

level applies primarily to copper
and possibly molybdenum under
injudicious usages. However, there
is no reason for this to take place
with our present knowledge and
technology, although in the past a
problem with copper developed in
some instances. The buildup of
phosphorus in the soil is not detri-
mental, per se, to plants. In fact,
phosphorus compounds apparently
have a desirable buffering action
in sandy soils. However, the in-
creased pollution potential result-
ing from movement under surface
erosion of such enhanced concen-
trations must be recognized.


Ammonium Nitrate.-This material is used as a top-dressing or
side-dressing where nitrogen only is needed. It contains about 33.5%
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 sulfate 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 calcic or dolomitic lime
has been added to condition the material and reduce the nitrogen
content to 20.5% nitrogen. The mixture is non-acid-forming and sup-
plies 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 pres-
sure and cannot be used except with special apparatus. Usually it is
injected into the soil behind a chisel-like implement. It contains 82%
ammoniacal nitrogen.
Basic Slag (Thomas Slag).-Basic slag averages about 15% avail-
able phosphoric acid. In addition, 100 pounds of basic slag are equal
to about 70 pounds of limestone for the correction of soil acidity.
Open hearth basic slag averages about 10% available phosphoric acid.
Calcium Nitrate (Prill Cal).-Crystalline calcium nitrate takes up
moisture from the air too readily to be conveniently used for side
dressing. Prill Cal (15.5% N) is a relatively new calcium nitrate
product that contains 1.2% ammoniacal nitrogen. It is quite stable
and makes an excellent nitrate side dressing.
Calcium Sulfate (Landplaster, Gypsum).-This material is used pri-
marily as a source of sulfur when sulfur is needed but not supplied
in the usual manner by superphosphate or sulfates of ammonia or
potash. It is not a liming material for reducing soil acidity.24
Chelates.-Chelates of micronutrients, of which iron EDTA is the
most common, consist of the element held in the center of a large
organic molecule in a manner that protects the element from im-
mediately reacting with the soil and becoming unavailable before
the plant has a chance to absorb it. Apparently the plant takes up

2" 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 sub-

the entire molecule under some conditions and then releases the iron
or other nutrient within the plant.
Colloidal Phosphate (Waste Pond Phosphate).-This is finely di-
vided raw mineral phosphate or phosphatic, clay. If the phosphoric
acid content is 20% or more, it is approximately equal to ground rock
phosphate on an equivalent phosphoric acid basis. For example, 300
pounds of 20% colloidal phosphate would equal 200 pounds of 30%
ground raw rock phosphate. (See Rock Phosphate.)
Frits.-Frits of micronutrients consist of one or more of the ele-
Sments 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 de-
termines the rate of solubility in the soil and the rate of release of
micronutrients in the frits. Certain frits have shown considerable
promise for improved availability of elements 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% nitro-
gen and 3.5% phosphoric acid. Its nitrogen is about 60% 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 natural organic usually is not an economical
practice except for landscaping, turf maintenance, plant beds, or cer-
tain special crops.
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 contain from 13 to 16% nitrate nitrogen. In addition, nitrate
of soda-potash is 14% potash, and nitrate of potash is 44% potash.
Nitrogen Solutions.-(See Solution Fertilization.)
Nutritional Sprays; Physiological Sprays.-(See Solution Fertiliza-
Rock Phosphate.-This material consists of finely divided phosphate
rock and contains from 27 to 44% 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 phosphorus 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 availabil-
L ity of potash is so low as to render these materials economically
valueless as compared to the usual sources of water-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 transplanting. They are made
from ordinary fertilizer materials which have been purified and con-
centrated to reduce insoluble residues. These practices are of eco-
nomic value only for very special conditions. The 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.
Solutions of ammonium nitrate and urea-ammonium nitrate have
come into quite widespread use for direct application.
Starter Solutions.-(See Solution Fertilization.)
Sulfate of Ammonia (Ammonium Sulfate).-This material contains
20.5% 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% water-soluble organic nitrogen
that is usually converted to ammoniacal nitrogen within one to three
days after application to the soil. It is called an organic nitrogen
but should not be confused with natural organic or insoluble ni-
trogen. It is a very concentrated form of nitrogen and difficult to
use at a light rate of application.
Urea is converted to ammonium by the enzyme urease, produced
by microbiological activity. If urea is surface-applied to moist soil,
or surface application to dry soil or turf is followed by only light,
non-penetrating rains, appreciable nitrogen loss as ammonia gas
might occur.
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% biuret, because 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 crys-
tal urea is available.
Ureaform.-This is a material containing about 38% nitrogen made
by chemically combining urea and formaldehyde for fertilizer use.
It releases nitrogen to a crop more slowly than do soluble forms of
nitrogen. Approximately one-third of the nitrogen is rapidly avail-
able, one-third moderately available, and one-third so slowly avail-
able that it must be built up to considerable quantity in the soil to
release nitrogen in significant amount. Tests of the various urea-
forms now offered for sale show that the best are superior to natural

organic in prolonging the supply of available nitrogen. The current
high cost of ureaform largely restricts usage to golf greens, orna-
mentals, and similar cultures.25

The fertilizer analysis shows the percentages of Nitrogen (N),
Available Phosphoric Acid (P205), and Potash (K20) in that order.
Thus, a 6-8-8 contains 6% nitrogen, 8% phosphoric acid, and 8%
potash; or 120 pounds of N, 160 pounds of P205, and 160 pounds of
K20 per ton. Analyses may then be compared as to the amount of
plant food 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 fertilizer.
Assume that we wish to use sulfate of ammonia to supply two of
the six units of nitrogen in the 6-8-8. Table 1 shows sulfate of
ammonia to have 20.5% nitrogen. The calculations are:
2,000 20.5 (%) = 97.6 lbs. of ammonium sulfate to give one unit
of nitrogen.
2 X 97.6 lbs. = 195 lbs. 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.
2 At present a ureaform type of water-insoluble nitrogen is being made right
in the fertilizer mixture by adding urea and formaldehyde together in solutions
at the time of ammoniation of the superphosphate. If precisely done, an accept-
able form of ureaform nitrogen is developed.

(Acts of May 8 and June 30, 1914)
Cooperative Extension Service, IFAS, University of Florida
United States Department of Agriculture, Cooperating
Joe N. Busby, Dean