Title Page
 Table of Contents
 Session I. Essential plant...
 Session II. Soil testing and plant...
 Session III. Records and plant...
 Session IV. Fertilizer materia...
 Session V. Buying needed nutri...

Title: Soil fertility and fertilizers
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Permanent Link: http://ufdc.ufl.edu/UF00084492/00001
 Material Information
Title: Soil fertility and fertilizers
Series Title: Soil fertility and fertilizers
Physical Description: Book
Creator: Kidder, Gerald,
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
 Record Information
Bibliographic ID: UF00084492
Volume ID: VID00001
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Table of Contents
    Title Page
        Title Page
    Table of Contents
        Page i
        Page ii
        Page iii
    Session I. Essential plant nutrients
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
    Session II. Soil testing and plant nutrient management
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
    Session III. Records and plant nutrient management
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
    Session IV. Fertilizer materials
        Page 21
        Page 22
        Page 23
        Page 24
        Page 25
    Session V. Buying needed nutrients
        Page 26
        Page 27
        Page 28
        Page 29
        Page 30
        Page 31
        Page 32
Full Text




Gerald Kidder
Associate Professor
Soil Science Department

August 1985

Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
Gainesville, Florida, 32611
John T. Woeste, Dean for Extension

0' '/C

Table of Contents

Session I. Essential Plant Nutrients -- What Plants Have to Have and How

1. Plants obtain most of the essential nutrients from the soil.

2. Minerals and organic matter in the soil are the source of

3. The relative quantities of essential nutrients needed by
plants range from very large to minute amounts.

4. The nutrients that are most frequently deficient in soils are
nitrogen, phosphorus, and potassium.

5. Practically speaking, a nutrient is deficient if its addition
as fertilizer produces a desired plant response.

6. Fertilizer is used to correct plant nutrient deficiencies.


Session II. Soil Testing and Plant Nutrient Management -- Deciding What the
Soil Can Supply and What Must Come From Fertilizer

1. Unfertilized soil supplies some or all of each of the
essential nutrients.

2. Soil testing can help predict the fertilizer needs but
observation and records are also important.

3. Soil testing consists of three parts; sample taking,
laboratory testing, and interpretations based on field cor-

4. Routinely, soils are tested for only two or three nutrient

5. The reason for fertilizing is to get a plant yield or growth

6. Observe plant growth and crop production over the long term
and use records to guide fertilization decisions.


Session III. Records and Plant Nutrient Management--A Written Record is Worth
a Lot of Memories.

1. Records are vital in keeping facts straight.

2. Lime and fertilizer records need to include date and rate of
application, materials used, and method of application.

Session IV.

Session V.

3. Soil test records need to include depth, method and date of
sampling, who did the sampling, and the testing laboratory.

4. Record weather, pest problems, and management factors which
may have limited production.

5. Increased measurable yields or measurable quality are the
reasons for applying fertilizers.


Fertilizer Materials -- Supplying the Missing Nutrients

1. There are many materials which can be used as fertilizers.

2. The solubility of the nutrients in a fertilizer material
determines the material's usefulness as a fertilizer.

3. Nutrients and not "fertilizer" should be bought.

4. The cost of fertilization must be calculated on the basis of
applied plant nutrients per unit area of land.

5. The Fertilizer Law gives consumer protection, but the buyer
still needs to beware.


Buying Needed Nutrients -- Formulating the Fertilizer You Need

1. Think nutrients, not fertilizer.

2. Each nutrient applied as fertilizer should give a desired
production response.

3. Calculate one nutrient at a time, considering available
sources, prices, and feasibility of using.

4. The combined ingredients in the specified proportions are the
fertilizer formula.

5. The grade is just a convenient way of expressing the primary
nutrient percentages of fertilizers.

6. The rate of application times the grade gives the rate of
nutrients per acre.

7. Shop for your nutrients and pay yourself the commission with
the satisfaction of a job well done.



Soil Fertility and Fertilizers -- A Five-Session Short Course
for Florida Producers

Gerald Kidder


This publication is composed of the outline and worksheets for a soil
fertility and fertilizer short course to be presented by county Extension
agents. The materials should be used only by agents who have participated in
the in-service training course, given by the author, on use of the outline and
the accompanying worksheets. The materials were not written in the usual
manner of circulars which cover a subject completely enough to be self-
explanatory. Because this circular was not written to "stand alone", there is
danger of misinterpretation if the materials are used without the benefit of
the oral presentation and explanation.
The course is structured in five "sessions," each consisting of an oral
presentation of the subject, a work period in which the provided worksheet is
completed by the participants, and a discussion or debriefing period. Each
session contains planned teaching objectives which are reinforced by the
active participation of the attendees when they complete the worksheet. It is
suggested that about 35 minutes be used for the oral presentation, about 20
minutes for the worksheets, and about 20 minutes for the review or debriefing.
This format uses active participation and repetition to reinforce the points
made in the oral presentation. Good understanding and retention of presented
information are the major objectives of this approach.
The complex nature of soil fertility and fertilizers, the large number of
nutrients and fertilizer materials, and the frequently confusing claims made
about fertilizer products are factors which contribute to the need for a
course such as the one presented here. The emphasis is on fundamentals that
have practical applications for the agricultural producer.
Active participation such as problem solving and "feedback" of informa-
tion helps to clarify concepts and increase the retention of points recently
learned. By participating in all aspects of the short course, attendees should
greatly increase their useful knowledge of the subject of soil fertility and


Session I. Essential Plant Nutrients --
What Plants Have to Have and How Much

1. Plants obtain most of their essential nutrients from the soil.

1.1. Soil is the natural medium for the growth of land
plants and is the source of 13 of the 16 essential
nutrients. Air and water provide the other 3 essential
nutrients (carbon, hydrogen and oxygen).

1.2. An essential nutrient is defined as one which the
organism must have to complete its life cycle.

1.2.1. The 16 essential plant nutrients are shown in
the table below. We will spend some time
reviewing their chemical symbols.

1.2.2. Growth will be limited by the element in
shortest supply in relation to plant needs.

Table I. Plant essential elements.

Element Chemical Where
symbol obtained

carbon C
hydrogen H air and
oxygen 0 water
nitrogen N
phosphorus P
potassium K
calcium Ca
magnesium Mg
sulfur S
iron Fe
manganese Mn soil
zinc Zn
copper Cu
boron B
nolybdenum Mo
chlorine Cl

NOTE: The following memory aid is offered to help you remember
the plant essential nutrients: B. C. HOPKNS CuZn (cousins) CaFe
(cafe) Mg (mighty good) Mn (mighty nice) Cl (closed) Mo (Mondays).

Circular 626.1

2. Minerals and organic matter in the soil are the source of

2.1. Plants take up nutrients that are in the soil solution.
They do not take up solid, particulate matter.

2.2. Most minerals are only slightly soluble in water so
only a small portion is in solution at any one time.

2.3. Organic matter releases nutrients as it is decomposed
by soil microorganisms.

2.3.1. Organic matter is an excellent source of
nutrients and is part of the natural recycling
that occurs in nature.

2.3.2. Added organic matter supplies nutrients, but
large additions are generally impractical in
field situations.

3. The relative quantities of essential nutrients needed by
plants range from very large to minute amounts.

3.1. Carbon, hydrogen, and oxygen are used in large quanti-
ties, but since plants get them from air and water,
they are not usually studied in soil fertility.

3.2. For convenience of discussion the essential nutrient
elements supplied by the soil have been classified as
macro (large) and micro (small), according to the
relative quantities needed.

3.2.1. The 6 macronutrients are nitrogen, phosphorus,
potassium, calcium, magnesium, and sulfur.
They are used in such large quantities that the
soil frequently can't supply enough for the
desired plant growth, i.e. one or more become

3.2.2. The 7 micronutrients are iron, manganese, zinc,
copper, boron, molybdenum, and chlorine.
Deficiencies of micronutrients occur with less
frequency than those of macronutrients. No
naturally occurring deficiencies of chlorine
have been found.

3.2.3. The term "minor element" has been used for
micronutrient in the past. Now "micronutrient"
is preferred because it does not imply "lesser
importance" as does "minor." The use of the
term "trace element" is also discouraged in
plant science.

4. The nutrients that are most frequently deficient in soils are
nitrogen, phosphorus, and potassium.

4.1. Because of the high demand by plants, these three
nutrients are frequently needed in fertilizer. They
have become known as the "primary nutrients" and
fertilizer containing all three is called "complete

4.1.1. The terms are poor ones because they incorrect-
ly imply that these nutrients are more impor-
tant than the others and that a fertilizer is
"incomplete" if it doesn't contain those three
nutrients. For example, legumes don't need
fertilizer N, so a "complete fertilizer" should
not be used on legumes.

4.1.2. By convention, and frequently by law, the
percentages of nitrogen, phosphorus, and
potassium in a fertilizer are expressed in that
order, separated by dashes. Example, 14-9-17.
More on this in a later session.

4.2. Some soils are naturally high in N, P, and K and the
generalization that these macronutrients are always
needed does not hold. For example, nitrogen is plenti-
ful in organic soils, and many soils in Florida are
high in phosphorus because of their mineralogy or due
to years of P fertilization.

5. Practically speaking, a nutrient is deficient if its addition
as fertilizer would produce a desired plant response.

5.1. The desired response depends on the purpose for which
the plant is being grown. For example, a lush-growing
tomato plant which does not fruit is not giving the
desired response even if the plant is dark green and
pretty to look at.

5.2. The desired response may vary with the persons growing
the same species of plants.

5.3. Application of fertilizer where there is no plant
response is unnecessary, wasteful of natural resources,
and can contribute to pollution of water, soil, or air.

6. Fertilizer is used to correct plant nutrient deficiencies.

6.1. Fertilizer provides the nutrients that the soil cannot
supply in sufficient quantities.

6.2. Although the fertilizer is applied to the soil, it is
the plants that are being fertilized, not the soil.

6.3. It makes no sense to apply fertilizer materials to the
soil for other than an expected plant response.

6.4. Too much of a nutrient can be as harmful as too little.


Session I.

Essential Plant Nutrients


1. An essential plant nutrient is defined as: (circle correct answer)

(a) an element which a plant must have in order to complete its
life cycle.

(b) anything which the plant takes up from the soil.

(c) nutrients which animals get when they eat plants.

2. The names of the 16 elements essential to plants are listed in
the table below. An alphabetical listing of their chemical symbols
is at the bottom of the table. Write the chemical symbol of each
element in the blank preceding each name.
Plant Essential Elements

From air
and water



From the soil




B, C, Ca, Cl, Cu, Fe, H, K, Mg, Mn, Mo, N, 0, P, S, Zn.

3. Memorization of the essential elements and their symbols will let
you better understand talks and articles about plant nutrition and
fertilizers. Spend a few minutes learning them or reinforcing what
you already know. You may want to share your memory aids with
others in the group.

4. Use the chemical symbols of the elements to answer the following

a. Which three of the essential elements do plants get primarily
from water and air? and

b. Which three macronutrients are included in a so called
"complete fertilizer?" and .

c. A micronutrient that is so abundant in both soil and water
that there are no recorded, deficiencies of it under natural
conditions is

5. Two of the following statements are true: Circle them.

a. Plant roots take up nutrients that are in the soil solution.

b. Minerals are not important in plant nutrition.

c. Decaying plant and animal matter release nutrients which
growing plants can take up.

d. Everyone fertilizing a particular kind of plant (ex. bahia-
grass) does so to make more money from the crop.

6. Using the information in the table below, label the sections of the
pie graph to show the data graphically.

Relative quantities of the soil-
supplied nutrients in dry plant tissue

Element %

N 49

K 34

P 5

Ca 5

Mg 3

S 3\

Sum of micronutrients
(Fe, Mn, Zn
Cu, Mo, B, & Cl) 1


7. Does the information shown above prove that the macronutrient N is
more essential than the micronutrient Mn?
Explain your answer.

8. The terms "macro" and "micro" refer to the relative quantities of
the nutrients needed by plants, and not to the relative importance
for proper growth and development. Macronutrients are nutrients
used in quantities while micronutrients are used in
quantities. (The terms "minor element" and "trace
element" in plant nutrition are antiquated.)

9. Which one of the following reasons given for applying fertilizer is
being emphasized in this course?

a. To improve the soil.

b. To produce a desired response from plants growing in the soil.

c. To pump some money into the general economy.

d. To obtain the right balance of nutrients in the soil.

10. In which two of the situations described below was a nutrient defi-

a. Application of extra N to 10 rows of corn made the plants
greener, a foot taller, and gave the same grain yield as the
rest of the field where the extra N was not applied.

b. Application of P to soybeans gave no visible response but
produced 3 bushels more per acre than adjacent beans not fertil-
ized with P.

c. Wheat fertilized with 80 pounds of N/acre from ammonium nitrate
produced 35 bushels while adjacent wheat fertilized with 50
pounds of N/acre from ammonium sulfate produced 50 bushels.

d. No yield difference could be measured between areas in a bahia-
grass pasture where a micronutrient mixture had been applied and
where it had not.

11. In Situation C above, which essential element was limiting


Session II. Soil Testing and Plant Nutrient Management--
Deciding What the Soil Can Supply and What
Must Come From Fertilizer

1. Unfertilized soil supplies some or all of each of the essen-
tial nutrients.

1.1. Plant species differ in their nutrient requirements
and their ability to obtain nutrients from the soil.

1.1.1. Naturally occurring plants are examples of
species that can obtain all of their essential
nutrient needs from the soil on which they

1.1.2. Cultivated plants frequently cannot grow
properly in unfertilized soil. This may be
due to the inefficiency of the cultivated
species in foraging for the nutrients or to
the higher nutrient demand where high yields
are being produced. In either of these in-
stances, human production expectations for
the cultivated plants cannot be realized
without addition of nutrients (fertilizer).

1.2. In most soils, the supply of all but a few of the
nutrients- is sufficient for even the high demands
placed on the soil supply by intensive production of
cultivated plants.

1.2.1. For example, few crops need additions of
copper, zinc, boron, iron, manganese, and
molybdenum. The soil supplies all that the
plants need, with a few exceptions.

1.2.2. Deficiencies are usually limited to intensive-
ly grown crops or to special soil conditions.
Unfortunately for us, Florida has many of the
soil and crop conditions which provoke plant
nutrient deficiencies.

1.3. Even when a soil cannot supply all the needs of the
plant, it supplies a portion. The portion can vary
from almost enough to a very small percentage of the
total need.

Circular 626.2

2. Soil testing can help predict the fertilizer needs but obser-
vation and records are also important.

2.1. Soil tests were developed to assist in fertility
management of agronomic crops. They were so
successful they have been used frequently as a cure-
all in situations where their use is not appropriate.
Understanding this point is a major objective of this

2.2. Observation of plant production response to added
nutrients should be a constant task of every grower.

2.2.1. The grower should remember the reason for which
the plants are being grown and the response

2.2.2. For most producers, the cost of getting a
response must be less than the value of
increased production.

2.3. Accurate production records are needed to evaluate soil
fertility and the responses to applied fertilizer.

2.3.1. If a production response to a nutrient is not
being obtained, it is not limiting growth and
may not be needed on that field.

2.3.2. Records allow projection of trends and can help
avoid problems.

3. Soil testing consists of three parts: sample taking, labora-
tory testing, and interpretations based on field correlation.

3.1. The results will be no better than the weakest part. The
picture is not complete unless all parts are there.

3.2. The soil sample must be representative of the field from
which it was taken.

3.2.1. This is the most error-prone part of soil
testing because soil is variable and people are
not always careful.

3.2.2. The sample is very small in comparison to the
volume it represents. Taking 20 cores/20 acres
represents about one millionth of the surface
area. That's like taking 10 people to
accurately represent the population of the en-
tire state of Florida.

3.3. The methods used by the testing laboratory must be
appropriate and the analyses must be done properly.

3.3.1. Different methods exist and some care must be
taken to assure the methods are being used for
conditions for which they were designed.

3.3.2. Reputable laboratories have trained personnel
who control analytical quality and assure re-
liable results.

3.4. Interpretation of test results is what makes soil fer-
tility testing relevant and a tool in plant nutrition.

3.4.1. Beware of the testing lab that doesn't inter-
pret its results.

3.4.2. In order to interpret soil test results in
terms of crop fertilization needs, the yield
responses to applied nutrients under varying
soil test levels and field conditions are in-

3.4.3. Calibration of test results is a long-term pro-
cess that requires years of field trials.

3.4.4. The closer the conditions of the trials resem-
ble the production conditions the more likely
the tests will correctly predict fertility
4. Routinely, soils are tested for only two or three nutrient

4.1. The macronutrients, because they are used in large
quantities, are more likely to be deficient so tests
for them have received the most attention.

4.1.1. Phosphorus and potassium are almost always
tested because they are frequently deficient.

4.1.2. Calcium and magnesium are often tested although
they are less frequently deficient.

4.1.3. Nitrogen and sulfur are seldom determined be-
cause of the dynamic nature of their concen-
trations in soil. The N or S content at the
time of sampling is meaningless in terms of
what will be there during the plant's growing

4.2. Soil tests for micrcnutrients are not generally done
on a routine basis.

4.2.1. Micronutrient deficiencies are less widespread
than are macronutrient deficiencies and testing
is not usually necessary.

4.2.2. Field responses to micronutrients are more dif-
ficult to study and calibrations of soil tests
are generally poorer than are calibrations for
the macronutrients.

4.2.3. Some of the micronutrient elements require dif-
ficult test procedures and cost limits their
widespread use.

5. The reason for fertilizing is to get a plant yield or growth

5.1. This may seem self-evident but the need for fertili-
zation is so well accepted in modern agriculture that
many do not stop to consider this point.

5.2. Plant response is due to individual element needs.

5.2.1. If one essential element is lacking or not in
sufficient supply, the plant will be limited by
that element even though all others are in
abundant supply.

5.2.2. Application of the limiting nutrient will allow
the plant to reach its potential provided some
other non-nutritional growth factor is not

5.2.3. Fertilizing with a nutrient that is not
limiting growth will not make up for a de-
ficiency of a nutrient that is limiting growth.

6. Observe plant growth and crop production over the long term
and use records to guide fertilization decisions.

6.1. Observation of plant growth and study of crop yield
records over several years is a powerful tool in soil
fertility and plant nutrition management.

6.2. Soil test records over a period of years are much more
meaningful than any one test.

6.2.1. Trends can be observed and evaluated in light
of the fertilization and other cultural prac-

6.2.2. The problems of sampling and testing inconsisten-
cies are less serious if results are part of a
historical record than a one shot analysis.

6.3. The integrated analysis of personal observations,
production records, and test records allows the grower
to make the best management decisions for the existing
growing conditions.


Session II. Soil Testing and Plant Nutrient Management


1. No fertilizer was applied in any of the situations described below. Mark
those in which the plants described were obtaining all of the nutrition

a. An oak tree, loaded with acorns, growing in a forest.
b. A pine and palmetto flatwoods typical of much of the Florida
c. Seaoats growing on the beachfront.

2. We discussed in Session I that plants need to take up sufficient quanti-
ties of 16 essential elements. Often only one or two of these elements
are needed as fertilizer. Hydrogen, oxygen, and carbon come from air and
water. What is the source of the other nutrients?

3. Which two of the following are reasons why, when growing in the same soil,
cultivated plants need to be fertilized and native plants do not?

a. Native plants are more efficient foragers for the limited supply of
nutrients naturally present in the soil.
b. Native plants are weeds and weeds don't respond to fertilization.
c. Production expectations for cultivated plants are higher than are those
for native plants.
d. Cultivated plants need some nutrients that are not essential to native
e. It's not economical to fertilize native plants.

4. Match the three aspects of soil testing with an appropriate characteristic
of each.

Sample taking Reliable methods are available and quality
control is generally practiced.

Laboratory testing Years of work are required to correctly accomp-
lish this aspect of soil testing. Tests are
meaningless without this aspect.

Correlation of test Probably the weakest aspect of testing. Lack
results with yields of careful attention and variability of soil
are factors to consider.

5. Circle the four macronutrients (and the accompanying chemical symbol)
which are most commonly measured in soil testing programs.

nitrogen, N phosphorus, P
potassium, K calcium, Ca
magnesium, Mg sulfur, S

6. Mark the following statements either true or false.

a. A deficiency of one essential element can be compensated for by extra
amounts of another.

b. Lack of widespread deficiency of micronutrients is one reason why soils
are not routinely tested for them.

c. Soils are seldom tested for nitrogen (N) and sulfur (S) because inter-
pretation of the results in terms of fertilization needs is complicated
by the transient nature of these elements in the soil.

d. Phosphorus (P) and potassium (K) are most frequently analyzed in soil
testing programs because they are frequently deficient in soils.

e. The primary reason for fertilization of tomatoes is to make the plants
greener and taller.

7. In the following list, circle those items which are tools in soil fertil-
ity and plant nutrition management.

a. Soil test results

b. Records of past fertilization and liming

c. Crop yield records

d. Observations of plant performances

8. In the following illustration, which stave will limit the amount of water
the barrel will hold?


Session III. Records and Plant Nutrient Management--
A Written Record is Worth a Lot of Memories

1. Records are vital in keeping facts straight.

1.1. Plant production is influenced by many factors and
proper analysis can only be done with good records.

1.2. Production records are different from financial re-
cords because they must be kept on a production unit
basis. For example, it is sufficient for tax purposes
to know that 20 tons of lime were purchased but for
production purpose it is necessary to know how many
acres and which fields were treated with those 20

2. Lime and fertilizer records need to include date and rate of
application, materials used, and method of application.

2.1. The rate of application is probably the least docu-
mented of these because fertilizer and lime are ap-
plied in load lots. Amount applied divided by acres
gives rate per acre.

2.2. Dates and method of application are necessary in eval-
uating past performance and for planning future ac-

3. Soil test records need to include: depth, method, and date of
sampling, who did the sampling, and the testing laboratory.

3.1. Soil sampling technique is a critical step and the
person who is sampling should be trained and reliable.

3.2. Sampling procedure influences results obtained and
changes need to be noted for historical purposes.

3.3. Laboratories use different chemical procedures so pro-
per interpretation of results must consider the source
of the test results.

4. Record weather, pest problems, and management factors
which may have limited production.

4.1. It's easy to forget that nutrition is not the only
factor limiting plant growth. Other factors which
frequently limit growth are: too little or too much
water, sunlight, temperature, pests, or poor manage-
ment practices.

4.2. Most fertilization recommendations assume that other
factors are not limiting growth & production. If this
is not the case, the applied nutrients may not give
the expected responses.

5. Increased measurable yields or measurable quality are the
reasons for applying fertilizers.

5.1. If a nutrient was applied as fertilizer and there was
no measurable increase in the desired plant response,
the nutrient wasn't limiting. Weather or some other
growth factor was limiting in that season.

5.1.1. This approach to fertilization is contrary to
the soil build-up philosophy.

5.1.2. Evaluation of records will help decide the
probability of response to the nutrient in
different years.

5.2. Quality may be a desired response, but it too should
be measurable in terms of saleable product or price

5.2.1. Guard against unmeasurable responses.

5.2.2. Records show whether or not increased returns
are being received for the increased costs of
applied fertilizer.


Session III. Records and Plant Nutrient Management


1. Information on three different soybean farming operations are given
below. Which one(s) have sufficient information given to determine:

(a) the rate of potassium application?
(b) the cost per acre of potassium fertilization?
(c) yield of soybeans/acre?

Farm A 86 acres planted to soybeans
fertilized with 0-5-25 grade fertilizer
2100 bushels of beans harvested
fertilizer cost $1806

Farm B 41 acres planted to soybeans
applied 8 tons of 0-6-28
uniformly on the soybean acreage
sprayed twice for insects
used in-row subsoiling
paid $4.00/ton for application of fertilizer
harvested 820 bushels of beans

Farm C 60 acres planted to soybeans
muriate of potash was only fertilizer used
5 tons of muriate (0-0-60) was applied evenly to
soybean land
cost of fertilizer was $180/ton
harvested 1500 bushels of beans

2. Several types of records are listed in the column on the left and exam-
ples of those records are listed in the column on the right. In the
blank, write the letter of the example which corresponds to the record

crop yield a. 3.5 inches in July
soil test result b. 100 Ibs N/acre
rate of nitrogen fertilization c. 31 ppm K
soil sampling record_ d. beggarweed in NW
weed infestation e. 4100 lbs peanuts/acre
fertilizer application method f. broadcast by JP, Inc.
rainfall g. Bob sampled 11 Dec. 82

3. A farmer applied 60 tons of dolomitic lime to a 40 acre field in 1975.
What rate of application should he enter onto the field records?

tons dolomite/acre

4. A potato farmer had very high phosphorus soil tests but was dubious about
a recommendation to not apply phosphorus. He decided to test the recom-
mendation on limited acreage. Thus he picked a 2.4 acre field and left
out the P. In an adjacent 6.2 acre field he applied a total of 350
pounds of P20. He farmed the two fields identically. Yield on the
small field was 7200 pounds of potatoes while yield on the fertilized
field was 18600 pounds. Did he get a response to the applied phosphorus
fertilizer? If so how much?

5. Use the information shown below and that shown on the attached soil test
report to fill in the fertilization portion of the permanent field record
sheet provided.

From a pocket notebook

Soil sampled all fields 0-6" by Jack; 31 Oct 83

15 Dec 83; 20 tons dolomite delivered; 3/4 applied to Ace field

13 Feb 84 Broadcast 6 tons of 9-26-7 on Ace field

21 April 84; 6.0 tons of 21-0-21 delivered; half sidedressed on
Ace field

16.5 acres in Ace field



For more information contact:

date completed: 27 JUL 84


client's identification: 1 lab number: 1484

crop: IRRIG. CORN, 30M/A soil texture: SAND

Both interpretations and recommendations are based upon the soil test
results and research/experience with the specified crop under Florida's
growing conditions.


pH (1:2 S:W): 5.5 A-E BUFFER VALUE: 7.70

MEHLICH I EXTRACTABLE Iv. low I low I medium high Iv. highly off I
+-------------------------+-------+----- -------------- --------scae+
PHOSPHORUS (ppm P) 3 ** I I

SPOTASSIUM (ppm K) 36 *******i*******

MAGNESIUM (ppm Mg) 16 t************** I
+------ -----------------------------------------------
I CALCIUM (ppm Ca) 688


For IRRIG. CORN, 30M/A apply 1.0 tons lime per acre
240 pounds N, 200 pounds P205, and 160 pounds K20 per acre

These footnotes are an integral part of the fertilization recommendation.
PLEASE READ THEM CAREFULLY. They are unique for each soil/crop situation.

SEE FOOTNOTE(S): 105 120 762 763


Field No.

FARM NAME Crop Acres
SOIL TEST Yes No Sampled by: Depth:
Date Tested Lab: __

Results: pH P K Ca___ Mg Micros: 1
Recommendations: Lime (T./A.) N P O__205 K20

NEMATODE Assay Yes No__ Date Tested By:
RESULTS: (Date Sample taken: )
Root knot Spiral Stunt
Sting Lance Ring
Lesion Stubby root Sheath-dagger
Date Calcitic ( ) Dolomitic ( ) Tons/Acre
FERTILIZER APPLIED Mixed, Nitrogen or Other
Date Material-grade Rate/A. Application Me

pm or


Date Material


Application Method/Comments

low adequate high excessive
0 20 days: inches 40-50 days: inches 70 80 days:
20- 30 days: inches 50-60 days: inches 80 90 days:
30- 40 days: inches 60-70 days: inches 90 -100 days:
PEST DAMAGE DURING CROP SEASON (indicate severity of infestation)
PEST Low Mod. High PEST Low

Harvest Date Yield


Mod. High


Session IV. Fertilizer Materials--
Supplying the Missing Nutrients

1. There are many materials which can be used as fertilizers.

1.1. Technically speaking, a fertilizer is any material
which will supply plant nutrients.

1.1.1. To be sold as a fertilizer the
meet the specifications of the

Circular 626.4

material must
state fertilizer

1.1.2. Manures and other organic matter are fertili-
zers but, because their primary nutrient con-
tent totals less than 16%, they must be label-
led "low analysis fertilizer." This does not
mean they are not good sources of plant nutri-

1.2. Some of the more commonly
and their grades are listed

used fertilizer materials
in the following table.

Usual grade

N P205 K20

S- ---

Single macronutrient

anhydrous ammonia
ammonium nitrate
concentrated superphosphate
potassium chloride (muriate)

Multiple macronutrient

ammonium sulfate
diammonium phosphate (DAP)
potassium sulfate
potassium magnesium sulfate




*Sometimes the grade is expressed as 0-0-22-10Mg-22S.

1.2.1. The "grade" of a fertilizer is the percent ni-
trogen, phosphorus, and potassium it contains,
expressed as N, P205, and K20 in that order and
separated by dashes. It is a convenient way of
expressing the primary nutrient content.

1.2.2. Some materials supply only one nutrient element
while others supply two or more.

1.3. These materials may be applied directly or may be
mixed in an almost infinite number of ways to produce
fertilizers of varying compositions.

2. The solubility of the nutrients in a fertilizer material
determines the material's usefulness as a fertilizer.

2.1. Plants take up nutrients from the soil solution.
Thus, the fertilizer must be soluble for the nutrients
to be available.

2.2 Slowly soluble materials (ex., manure, sludge, natural
organic, dolomite, rock phosphate) release their ele-
ments to the soil solution over a period of months or

2.2.1. This has the desirable effect of reducing the
leaching loss of mobile nutrients.

2.2.2. It often has the undesirable effect of re-
leasing nutrients too slowly to supply the
needs of growing plants.

2.3 The cost of slowly soluble nutrients is high in com-
parison to soluble sources. Thus, their use in com-
mercial agriculture is usually limited to special

3. Nutrients and not "fertilizer" should be bought.

3.1. The word "fertilizer" is quite general and a fer-
tilizer can vary drastically in terms of which nutri-
ents and the amount of each that it contains.

3.1.1. Buying fertilizer could be compared to buying
furniture. Beds, tables, chairs, sofas,
desks, and cabinets are all furniture but a
bed is not bought for filing papers any
more than a file cabinet is used for sleeping.
N, P, and Mn are all fertilizers, but applying
N will not do any good if Mn is limiting.

3.1.2. Two fertilizers can contain the same nutrients
but have very different concentrations. Thus
their value in supplying plant nutrients is
proportional to their nutrient content.

3.2. Different nutrients have different economical
values which in turn influence the cost of the

4. The cost of fertilization must be calculated on the basis
of applied plant nutrients per unit area of land.

4.1. Materials with low nutrient content cost less per
pound than those with higher nutrient content but more
must be applied per acre to supply a given level of

4.2 Storage, transportation, and handling costs are usual-
ly calculated on a weight basis. They are higher per
acre for low analysis than high analysis fertilizers
because more weight is needed to get equal amounts of

4.3. Application costs generally reflect the quantity of
material handled and above a certain point usually
increase with increasing weight.

4.4. The true cost of supplementing plant nutrients consid-
ers both application and material costs.

5. The Fertilizer Law gives consumer protection but the buyer
still needs to beware.

5.1. The fertilizer laws were some of the first con-
sumer protection laws.

5.1.1. The antiquated means of expressing phosphorus
and potassium as oxides is a reminder of the
age of the laws.

5.1.2. The laws have generally made it possible for
informed consumers to distinguish legitimate
fertilizers from those of questionable value.

5.2. The subject of organic nitrogen causes much confusion
in Florida.

5.2.1. Organic nitrogen in naturally-occurring materi-
als, such as sewage sludge, becomes available
slowly and thus has a longer lasting effect
than soluble forms. This is a selling point
which has been exploited in the homeowner sec-
tor of fertilizer sales.

5.2.2. Urea is a synthetic organic compound which is
completely soluble and does not have the long
lasting effect of natural organic. Many peo-
ple buy "100% organic nitrogen" fertilizer
thinking it has slowly available properties
when it doesn't.

5.2.3. The advantages of using natural organic in
commercial agriculture is highly questionable.
They should not be recommended except under
very special circumstances.


The concept of "total plant food" can be somewhat

5.3.1. The differences in the cost of individual
nutrients may be lost when the macro nutrient
contents are simply summed. The total "plant
food" content of a 10-5-10 fertilizer is 25%,
the same as that of a 0-5-20 fertilizer. How-
ever, the value of the nutrients in the 0-5-20
is less because of the higher content of the
lower-cost potassium.

5.3.2. The total plant food approach implies that one
nutrient can substitute for the other, which is
not the case.


Session IV. Fertilizer Materials


1. Indicate whether the following statements are True or False.

a. The so called "primary" plant nutrients are nitrogen, phosphorus, and
b. In Florida, mixed fertilizers with less than 16% primary plant nutri-
ents must be labelled "low analysis."
c. Manure can supply important nutrients to plants and is truly a ferti-
lizer even though it does not fit the definition of a commercial
d. The term "primary nutrients" has the same meaning as does the term
e. The solubility of a material is not an important consideration in
determining if it is a suitable fertilizer.
f. A 12-5-20 fertilizer contains 12% nitrogen, 5% K20, and 20% P205'

2. Match the names of these commonly-used fertilizer materials with their
grades shown in the column at right.


a. ammonium nitrate 82-0-0
b. urea 33-0-0
c. anhydrous ammonia ___ 46-0-0
d. diammonium phosphate 18-46-0
e. concentrated superphosphate 0-46-0
f. muriate of potash 0-0-50-17S
g. potassium sulfate 0-0-0-10Mg-14S
h. magnesium sulfate 0-0-60

3. If ammonium nitrate (33-0-0) is selling for $198 per ton and urea (46-0-0)
is selling for $230 per ton, which is the most economical source of

4. If 100 pounds of DAP (diammonium phosphate) and 100 pounds of muriate of
potash were mixed together and spread on an acre, the rate of fertiliza-
tion would be lbs N, Ibs P 05, and lbs K20 per acre.

5. Which rate of urea would most nearly supply 100 pounds of N/acre?

a. 220 lbs urea/acre b. 92 Ibs urea/acre
c. 300 Ibs urea/acre d. 460 lbs urea/acre

6. It costs the same to haul a ton of low grade fertilizer as it does to haul
a ton of high grade material. True or False?


Session V. Buying Needed Nutrients--
Formulating the Fertilizer You Need.

1. Think nutrients, not fertilizer.

1.1. This point has been made before but is repeated here to
emphasize the importance of that approach.

1.2. Over 80% of the fertilizer sold in Florida is blended
for the customer. Thus it is possible to obtain almost
any combination of nutrients if it is requested.

2. Each nutrient applied as fertilizer should give a desired pro-
duction response.

2.1. The purpose of applying fertilizer is to obtain some-
thing in return for the investment.

2.2. The application of nutrients that do not produce a
response is wasteful of resources, could lead to nutri-
tional disorders, and could contribute to pollution.

3. Calculate one nutrient at a time, considering available
sources, prices, and feasibility of using.

3.1. Examples of situations where only one nutrient is needed
will be considered first.

3.1.1. A situation where only nitrogen is to be
applied: topdressing a pasture with 60 pounds of
N in early summer.

Using ammonium nitrate

Divide the pounds of nitrogen needed by the
decimal percent N in ammonium nitrate

60 t 0.335 = 179 lbs ammonium nitrate/acre

Using urea

To calculate how much urea (46-0-0) would be
needed to supply the 60 Ibs of N, divide the
pounds of N needed by the decimal percent N in
the urea.

60 + 0.46 = 130 Ibs urea/acre

Thus, if we apply 179 pounds of ammonium nitrate
or 130 pounds urea/acre we will be applying 60
pounds of the nutrient element N.

3.1.2. A situation where only potassium is to be ap-
plied: preplant fertilization following a le-
gume crop where phosphorus is high (no P needed)
and addition of 100 lbs K20/acre is desired.

Divide the pounds of K 0 needed by the decimal
percent of K20 in muriate of potash (0-0-60).

100 0.60 = 167 lbs 0-0-60 needed to provide
100 lbs K20/acre.

3.2. Calculations involving two or more nutrients will be
considered in this section.

3.2.1. Situation: Nitrogen and potassium are recom-
mended as a sidedressing at 30 pounds N and 30
pounds K20/acre.

Calculate one nutrient at a time. Let's use
ammonium sulfate (21-0-0) as the N source.

30 0.21 = 143 Ibs ammonium sulfate

Using muriate of potash (0-0-60) as the K

30 0.60 = 50 lbs 0-0-60/acre

Thus, the mixture of 143 lbs ammonium sulfate
and 50 lbs muriate of potash
for a total of 193 lbs mixture/acre will
supply the desired 30 lbs N and 30 Ibs K20.

3.2.2. Situation: The recommendation is for 80 lbs N,
20 lbs P205, 90 lbs K20, and 10 Ibs S/acre.

Again we take the nutrients one at a time using
our old friends ammonium sulfate (21-0-0-23S),
concentrated superphosphate (0-46-0), and muri-
ate of potash (0-0-60) as the sources. We will
get the sulfur from the ammonium sulfate and
will not have to add any separate source of S.

80 0.21 = 381 lbs 21-0-0

20 t 0.46 = 44 lbs 0-46-0

90 0.60 = 150 Ibs 0-0-60

10 0.23 = 44 Ibs 21-0-0-23S would provide
the 10 lbs S.

Since we are applying 381 lbs of 21-0-0-23S as
the N source, the S recommendation will be more
than fulfilled.

3.3. There are some combinations of materials which cause
problems and which dealers may not wish to supply.

3.3.1. Segregation is a serious problem when particle
sizes are very different, as is frequently the
case with bulk blended fertilizers.

3.3.2. The physical properties may preclude mixing of
some materials.

3.4 Compare fertilizer prices on the basis of applied nutri-
ents per acre. If other considerations are equal, buy
the most economical source.

4. The combined ingredients in the specified proportions are the
fertilizer formula.

4.1. The formula is the recipe of the fertilizer. It is the
quantity and analysis of the materials in a mixed ferti-

4.2. The ingredients of commercial fertilizers sold in
Florida are listed on the tag. This is not the formula
because the proportions of each ingredient are not

5. The grade is just a convenient way of expressing the primary
nutrient percentages of fertilizers.

5.1. There is nothing magical about the grade.

5.1.1. The concept of a unique grade for a particular
crop (ex., "tobacco special") fails to recognize
the soil's contribution to the crop's nutrition.
It is an antiquated concept which assumes low
soil levels of all primary nutrients.

5.2. The grade of the blend calculated in the previous sec-
tion will be calculated here.

5.2.1. When single materials are used as in Section
3.1.1, the grade is obviously the same as that
of the material.

5.2.2. Where more than one material is used, sum all
the weights and divide the N content by the
total for the percent N. Do the same for the
P 0 and K 0. Example: calculating the grade
of ihe mixture in Section 3.2.1:

143 Ibs 21-0-0
+50 Ibs 0-0-60
193 Ibs total weight of materials

30 Ibs N t 193 lbs total = 15.5% N

30 lbs K20 193 Ibs total = 15.5% K20

The grade of the mixture would be 15.5-0-15.5.
In practice, 7 pounds of filler would probably
be added to bring the total weight to 200 lbs
and the resulting grade would be 15-0-15 (i.e.
30 + 200 = 15%). The same process is followed
for as many nutrients as there are. The fol-
lowing is a calculation of the grade of the mix-
ture described in Section 3.2.2.

381 lbs 21-0-0-23S
44 lbs 0-46-0
150 lbs 0-0-60
575 total weight of materials

80 lbs N 575 lbs total = 13.9% N

20 bs P205 575 lbs total = 3.4 % P205

90 lbs K20 575 lbs total = 15.6% K20

87 lbs S T 575 lbs total = 15.2 % S

The grade would be 13.9-3.4-15.6-15.2S.

Any non-fertilizer material added to round the
grade to whole numbers would result in a
"rounding down." You can't "round up" because
the grade is a guaranteed minimum analysis.

6. The rate of application times the grade gives the rate of nutri-
ents per acre.

6.1. Knowing the grade alone or the rate alone is of little
value. (Ex.,"I applied a 10-3-20." or, "I apply 600
pounds of fertilizer.")

6.2. The calculation is simply a matter of multiplying the
components of the grade by the rate applied per acre.
Example: 500 pounds of 10-3-20 were applied per acre.

500 lbs x 10% N = 50 Ibs N/acre

500 bs x 3% P205 = 15 lbs P205/acre

500 lbs x 20% K20 = 100 lbs K20/acre

6.3. The rate of nutrients per acre is the important item
which should be entered into the field records.

7. Shop for your nutrients and pay yourself the commission with
the satisfaction of a job well done.

7.1. Comparison shopping is good business and can result in
sizeable savings.

7.2. Discussing alternatives with the dealer can lead to bet-
ter understanding of fertilization needs on the part of
the dealer.

7.2.1. Dealer will be more responsive to needs if
clients are knowledgeable.

7.2.2. Products will be stocked and made available when
the market demands are there.

7.3. Unnecessary extras can be eliminated from the fertilizer
bill by well-informed customers.

7.4. Non-quantifiable factors such as reliable service, etc.
need to be considered and evaluated separately from the
fertilizer cost consideration.


Session V. Buying Needed Nutrients


Mark the following 4 statements true or false.

1. The purpose of applying fertilizer is to obtain something in return for
the investment.

2. One hundred pounds of ammonium sulfate (21-0-0) contains 21 pounds of

3. One hundred kilograms of urea (46-0-0) contains 92 kilograms of nitro-

4. If you know Mr. Jones applied a 15-3-19 grade fertilizer, you know the
rate of N he applied.

5. How much muriate of potash (0-0-60) should you apply per acre to provide
80 pounds of K20/acre?

lbs K 0 desired/acre 0.60 K 0 in muriate = _lbs muriate to apply/acre

6. In order to provide 70 pounds of nitrogen in a topdress application,
several sources of N could be used. Draw a line between the N source and
the amount of that source which would supply the 70 lbs N.

anhydrous ammonia (82-0-0) 333 lbs
ammonium nitrate (33-0-0) 85 lbs
ammonium sulfate (21-0-0) 152 lbs
urea (46-0-0) 212 Ibs

7. A recommendation calls for 90 lbs N, 40 lbs P 0 and 100 lbs K20 per acre.
Complete the following form for a one acre batcA of fertilizer.

pounds (33.5-0-0)

pounds concentrated superphosphate (0-46-0)

+ pounds muriate of potash ( )

pounds total material/acre

The producer needs to buy __ tons of this material in order to fer-
tilize ten acres.

8. When 400 pounds of 20-8-20 are applied per acre, there are pounds of
N, pounds of P205, and pounds of K20 applied per acre.

9. Use the steps described on the right side of the page to calculate the
grade of the following bulk blended fertilizer:

956 lbs 33.5-0-0
435 lbs 0-46-0
600 lbs 0-0-60
9 Ibs limestone filler
2000 lb batch total

weight of ammonium
nitrate times
percent of N in it.

Divide by 2000 to
get % N in mixture.

Multiply weight of
concentrated super-
phosphate by percent
of P205 in it.

Divide by 2000 to
get % P205.

Multiply weight of
muriate of potash
by percent of K20
in it.

Divide by 2000 to
get % K20.

Express the grade
in the customary
fashion, i.e.,
%N %P20 %K20.
~25 02

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