Whole Document Navigator (Click Here)    ---------------------------------- Top of Document INTRODUCTION TABLE OF CONTENTS - Session I. Essential Plant Nutrients -- What Plants Must Have and How Much - Session II. Soil Testing and Plant Nutrient Management -- Deciding What the Soil Can Supply and What Must Come From Fertilizer - Session III. Records and Plant Nutrient Management -- A Written Record is Worth a Lot of Memories - Session IV. Fertilizer Materials -- Supplying the Needed Nutrients - Session V. Buying Needed Nutrients -- Formulating the Fertilizer You Need - Answers to Worksheets Session I -Essential Plant Nutrients -- What Plants Must Have and How Much -Essential Plant Nutrients -- Worksheet Session II -Soil Testing and Plant Nutrient Management -- Deciding What the Soil Can Supply and What Must Come From Fertilizer -Soil Testing and Plant Nutrient Management -- Worksheet Session III -Records and Plant Nutrient Management -- A Written Record is Worth a Lot of Memories -Records and Plant Nutrient Management -- Worksheet Session IV -Fertilizer Materials -- Supplying the Needed Nutrients -Fertilizer Materials -- Worksheet Session V -Buying Needed Nutrients -- Formulating the Fertilizer You Need -Buying Needed Nutrients -- Worksheet Footnotes Disclaimer Copyright Infomation

Soil Fertility and Fertilizers: A Five-Session Short Course for Florida Producers ¹

Gerald Kidder²

INTRODUCTION

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 are best used by agents who have participated in the in-service training course given by the author on use of the outline and accompanying worksheets. The materials are not written in the usual manner of circulars which cover a subject completely enough to be self-explanatory. Because this circular is 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 information 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 fertilizers.

TABLE OF CONTENTS

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

1. Plants obtain most of the essential nutrients from the soil.
2. Minerals and organic matter in the soil are the source of nutrients.
3. The relative quantities of essential nutrients needed by plants range from 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.

WORKSHEET

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 also are important.
3. Soil testing consists of three parts:
   1. sample taking.
   2. laboratory testing.
   3. interpretations based on field correlation.
4. Routinely, soils are tested for only two or three nutrient elements.
5. The reason for fertilizing is to get a plant yield or growth response.
6. Observe plant growth and crop production over the long term and use records to guide fertilization decisions.

WORKSHEET

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.
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. The reasons for applying fertilizers are to increase measurable plant yields or measurable quality.

WORKSHEET

Session IV. Fertilizer Materials -- Supplying the Needed 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.

WORKSHEET

Session V. 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 make up the fertilizer formula.
5. The grade is just a convenient way of expressing the primary nutrient percentages of fertilizers.
6. The rate of application multiplied by the grade gives the rate of nutrients per acre.
7. Shop for your nutrients and pay yourself the commision with the satisfaction of a job well done.

WORKSHEET

Answers to Worksheets

Session I. 1. a. 2. C, H, O, N, P, K, Ca, Mg, S, Fe, Mn, Zn, Cu, B, Mo, Cl, Co, Ni. 4a. C, H, O. 4b. N, P, K. 5. a & c. 7. No. Both are essential, but plants need larger quantities of N than Mn. 8. large & small. 9. b. 10. b & c. 11. S.

Session II. 1. a, b, & c. 2. soil. 3. a & c. 4. 5. P, K, Ca, & Mg. 6. F, T, T, T, & F (Tomatoes are primarily grown for their fruit). 7. a, b, c, & d. 8. N.

Session III. 1a. Farms B & C. 1b. Farm C. 1c. Farms A, B, & C. 2. e, c, b, g, d, f, & a. 3. 1.5. 4. No. There was no additional yield from P fertilizer.

Session IV. 1. T, T, T, F (Ca, Mg, & S are also macronutrients.), F, & F (It contains 5% P₂O₅ and 20% K₂O). 2. c, a, b, d, e, g, h, & f. 3. urea. 4. 18, 46, & 60. 5. a. 6. T.

Session V. 1. T. 2. T. 3. F (One hundred kg of 46-0-0 contains 46 kg of N.). 4. F (You also need to know the amount of fertilizer applied to calculate the rate.). 5. 80 & 133. 6. 85 lb of 82-0-0, 212 lb of 33-0-0, 333 lb of 21-0-0, and 152 lb of 46-0-0. 7. 269, ammonium nitrate, 87, 167, 0-0-60, 523, and 2.6. 8. 80, 32, & 80. 9. 320, 0.16 or 16%, 200, 0.10 or 10%, 360, 0.18 or 18%, and 16-10-18.

Session I

Essential Plant Nutrients -- What Plants Must Have and How Much

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

1.1 Soil is the natural medium for the growth of land plants and is the source of 15 of the 18 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 18 nutrients essential for all higher plants are shown in Table 1. You are encouraged to know the chemical symbols for these elements since they are commonly used in fertilizer literature.

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

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

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 Tons per acre of manure, biosolids, or urban plant debris must be applied to supply typical crop nutrient needs.

• 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 quantities, 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 according to the relative quantities needed - macro nutrients (large quantities required) and micro nutrients (small quantities required).

3.2.1 The 6 macronutrients are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Some 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 deficient.

3.2.2 The 9 micronutrients needed by all higher plants are iron, manganese, zinc, copper, boron, molybdenum, chlorine, cobalt and nickel. Deficiencies of micronutrients occur with less frequency than those of macronutrients.

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 became known as the "primary nutrients" and fertilizer containing all three is called "complete fertilizer".

4.1.1 The terms are poor ones because they incorrectly imply that these nutrients are more important than the others and that a fertilizer is "incomplete" if it doesn't contain these 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 plentiful 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 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.

Table 1. Plant essential elements.

Element	Chemical symbol	Where obtained
carbon	C	air and water
hydrogen	H	air and water
oxygen	O	air and water
nitrogen	N	soil
phosphorus	P	soil
potassium	K	soil
calcium	Ca	soil
magnesium	Mg	soil
sulfur	S	soil
iron	Fe	soil
manganese	Mn	soil
zinc	Zn	soil
copper	Cu	soil
boron	B	soil
molybdenum	Mo	soil
chlorine	Cl	soil
cobalt	Co	soil
nickel	Ni	soil

Essential Plant Nutrients -- Worksheet

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 18 elements essential to all higher plants are listed in Table 2 . An alphabetical listing of their chemical symbols is at the bottom of the table. Write the chemical symbol of each element next to each name.

Table 2. (Question 2). Plant essential elements.

From air and water	From the soil
	Macro- nutrients	Micro- nutrients
___carbon	___nitrogen	___iron
___hydrogen	___phosphorus	___manganese
___oxygen	___potassium	___zinc
	___calcium	___copper
	___magnesium	___boron
	___sulfur	___molybdenum
		___chlorine
		___cobalt
		___nickel
B, C, Ca, Cl, Co, Cu, Fe, H, K, Mg, Mn, Mo, N, Ni, O, 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 questions:

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 ____.

• 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 releases nutrients that growing plants can take up.

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

• 6. Using the information in Table 3 , label the sections of the pie graph ( Figure 1 ) to show the data graphically.

Table 3. (Question 6). Relative quantities of the soil-supplied nutrients in typical dry plant tissue.

Element	%
N	49
K	34
P	5
Ca	5
Mg	3
S	3
Sum of micronutrients: (Fe, Mn, Zn, Co, Cu, Mo, Ni, B, + Cl)	1

Figure 1. (Question 6).

• 7. Does the information shown in Table 3 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 deficient? _______ and _______

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 the P-fertilized beans produced 3 bushels more per acre than adjacent beans which were not fertilized 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 bahiagrass pasture where a micronutrient mixture had been applied and where it had not.

• 11. In Situation C of Question 10, which essential element was limiting production?

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.

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 grow.

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 instances, 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 intensively 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 only a small percentage of the total need.

• 2. Soil testing can help predict the fertilizer needs but observation 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 course.

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 desired.

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, that nutrient 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, laboratory testing, and interpretations based on field correlation ( Figure 2 ).

• Figure 2. The soil testing picture is made up of three interrelated parts.

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 15 people to accurately represent the population of the entire 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 Each method has conditions that must be met for the results to be valid.

3.3.2 Reputable laboratories have trained personnel who control analytical quality and assure reliable results.

3.4 Interpretation of test results is what makes soil fertility testing relevant and a tool for plant nutrition management.

3.4.1 Beware of the testing lab that doesn't interpret 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 indispensable.

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

3.4.4 The closer the conditions of the trials resemble the production conditions the more likely the tests will correctly predict fertility needs.

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

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 It has been difficult to develop a meaningful test for N because of the dynamic nature of N in soil. Only under carefully defined conditions at the time of sampling is the N content meaningful in terms of what will be there during the plant's growing season. As a result, N is not routinely determined in soil fertility tests.

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

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

4.1.4 Sulfur, like N, is seldom determined because of its dynamic nature in soil. Also, chemical analysis for S is quite difficult.

4.2 Soil tests for micronutrients 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 difficult to study and calibrations of micronutrient soil tests are generally poorer than are calibrations for the macronutrients.

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

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

5.1 This may seem self-evident but the need for fertilization 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 ( Figure 3 ).

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

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

Figure 3. The stave barrel analogy. The amount of water the barrel can hold is limited by the shortest stave--in this case, K.

• 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 practices.

6.2.2 The problems of sampling and testing inconsistencies are less serious if results are part of a historical record than a one time 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.

Soil Testing and Plant Nutrient Management -- Worksheet

• 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 necessary.

a. An oak tree, loaded with acorns, growing in a forest.

b. A pine and palmetto flatwoods typical of much of the Florida landscape.

c. Seaoats growing on the beachfront.

• 2. We discussed in Session I that plants need to take up sufficient quantities of 18 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 needed 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 plants.

e. It's not economical to fertilize native plants grown as a crop.

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

a. sample taking

b. laboratory testing

c. correlation of test results with yields

____Reliable methods are available and quality control is generally practiced.

____Years of work are required to correctly accomplish this aspect of soil testing. Tests are meaningless without this aspect

____Probably the weakest aspect of testing. Lack 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. The transient nature of nitrogen (N) and sulfur (S) in soil complicates interpretation of test results in terms of fertilization needs.

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

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 fertility 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 illustration in Figure 4 , which stave will limit the amount of water the barrel will hold? ______

Figure 4. (Question 8).

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 records 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 tons.

• 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 documented of these because fertilizer and lime are applied in load lots. Amount applied divided by acres gives rate per acre.

2.2 Dates and method of application are necessary in evaluating past performance and for planning future actions.

• 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 proper interpretation of results must consider the source of the test results.

• 4. Record those 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 management 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 buildup philosophy. Additionally, the buildup philosophy is questionable on economic and environmental grounds.

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 received.

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.

Records and Plant Nutrient Management -- Worksheet

1. Information on three different peanut 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 peanuts/acre? _______

• Farm A

• 86 acres planted to peanuts

• fertilized with 0-5-25 grade fertilizer

• 172 tons of peanuts harvested

• fertilizer cost $1806

• Farm B

• 41 acres planted to peanuts

• applied 8 tons of 0-6-28 uniformly on the peanut acreage

• sprayed twice for insects

• paid $4.00/ton for application of fertilizer

• harvested 114,800 lbs of nuts

• Farm C

• 60 acres planted to peanuts

• muriate of potash was only fertilizer used

• 5 tons of muriate (0-0-60) was applied evenly to peanut land

• cost of fertilizer and application was $180/ton

• harvested 180,000 lbs of nuts

• 2. In Table 4 , several types of records are listed in the column on the left and examples 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 type.

Table 4. (Question 2). Types and Examples of Farm Records.

___crop yield	a. 3.5 inches in July
___soil test result	b. 100 lbs 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. 01

• 3. A farmer applied 60 tons of dolomitic lime to a 40 acre field in 1997. 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 recommendation 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 P₂O₅ . He farmed the two fields identically. Yield on the small field was 7,200 pounds of potatoes while yield on the fertilized field was 18,600 pounds. Did he get a response to the applied phosphorus fertilizer? If so how much? ______ lbs potatoes/acre

• 5. Use the information shown below and that shown on the soil test report in Figure 5 to fill in the fertilization portion of the permanent field record sheet shown in Figure 6.

From a pocket notebook:

• Soil sampled all fields 0-6" by Jack; 31 October 01

• 15 December 01; 20 tons dolomite delivered; 3/4 applied to Ace field

• 13 February 02 Broadcast 6 tons of 9-26-7 on Ace field

• 21 April 02; 6.0 tons of 21-0-21 delivered; half sidedressed on Ace field

• 16.5 acres in Ace field.

Session IV

Fertilizer Materials -- Supplying the Needed Nutrients

• 1. There are many materials that can be used as fertilizers.

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

1.1.1 To be sold as a fertilizer the material must meet the specifications of the state fertilizer law.

1.1.2 Manures and other organic matter are low analysis fertilizers.

1.2 Some of the more commonly used fertilizer materials and their grades are listed in Table 5 .

Table 5. Some commonly used fertilizer materials and their grades.

Fertilizer material	Usual grade	N	P2O5	K2O
Single macronutrient		- - - - - - - - - - - - % - - - - - - - - - - -
anhydrous ammonia	82-0-0	82	0	0
ammonium nitrate	33.5-0-0	33.5	0	0
urea	46-0-0	46	0	0
concentrated superphosphate	0-46-0	0	46	0
potassium chloride (muriate)	0-0-60	0	0	60
Multiple macronutrient
ammonium sulfate	21-0-0	21	0	0
diammonium phosphate (DAP)	18-46-0	18	46	0
potassium sulfate	0-0-50	0	0	50
potassium magnesium sulfate	0-0-22*	0	0	22
* Sometimes the grade is expressed as 0-0-22-10Mg-22S.

1.2.1 The "grade" of a fertilizer is the percent nitrogen, phosphorus, and potassium it contains, expressed as N, P₂O₅ , and K₂O in that order and separated by dashes. It is a convenient way of expressing the NPK content.

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

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

1.3.1 Bulk blending is an economical means of producing customized combinations of nutrients but care must be taken to assure product quality.

1.3.2 Uniform composition is a desirable characteristic of granular and fluid fertilizers.

• 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 (e.g., manure, biosolids, natural organics, dolomite, rock phosphate, slow release fertilizers) release their elements to the soil solution over a period of months or years.

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 releasing nutrients too slowly to supply the needs of growing plants.

2.3 The cost of slowly soluble nutrients is usually high in comparison to soluble sources. Thus, their use in commercial agriculture is usually limited to special situations.

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

3.1 The word "fertilizer" is quite general and a fertilizer can vary drastically in terms of which nutrients 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 fertilizer.

• 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 the same level of nutrients.

4.2 Storage, transportation, and handling costs are usually 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 nutrients.

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 considers 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 consumer protection laws.

5.1.1 The antiquated means of expressing phosphorus and potassium as oxides is a reminder of the history 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 materials, 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 sector 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 organics. Many people buy "100% organic nitrogen" fertilizer thinking it has slowly available properties when it doesn't.

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

5.3 The concept of "total plant food" can be somewhat deceiving.

5.3.1 The difference in the cost of individual nutrients may be lost when the macronutrient 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. However, the value of the nutrients in the 0-5-20 is less because of the higher content of the lower-cost potasium..

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

Fertilizer Materials -- Worksheet

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

a. The so called "primary" plant nutrients are nitrogen, phosphorus, and potassium.

b. A bulk blended fertilizer is produced by mixing together two or more dry fertilizer materials to obtain a desired combination of plant nutrients in a single mixture.

c. Manure can supply important nutrients to plants and is truly a fertilizer even though the concentration of nutrients is relatively low.

d. The term "primary nutrients" has the same meaning as does the term "macronutrients".

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 5% K₂O, 20% P₂O₅ , and 12% N.

• 2. Using Table 6 , match the names of these commonly-used fertilizer materials listed on the left, with their grades listed in the column on the right. In the blank, write the letter of the fertilizer material which corresponds to the grade.

Table 6. Commonly used fertilizers and their grades.

Fertilizer material		Grade
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 $230 per ton and urea (46-0-0) is selling for $285 per ton, which is the most economical source of nitrogen? _____________________

• 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 fertilization would be _____lbs N, _____lbs P₂O₅ , and _____lbs K₂O per acre.

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

a. 220 lbs urea/acre

b. 92 lbs urea/acre

c. 300 lbs 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 70% 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 production response.

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

2.2 The application of nutrients that do not produce a response is wasteful of resources, could lead to nutritional disorders, and could contribute to environmental 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 the early summer.

Using ammonium nitrate

Divide the pounds of nitrogen needed by the decimal percent N in ammonium nitrate (33.5-0-0).

60÷ 0.335 = 179 lbs ammonium nitrate/acre

Using urea

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

60 ÷ 0.46 = 130 lbs urea/acre

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

3.1.2 A situation where only potassium is to be applied: preplant fertilization following a legume crop where phosphorus is high (no P needed) and addition of 100 lbs K₂O/acre is desired.

Divide the pounds of K₂O needed by the decimal percent of K₂O in muriate of potash (0-0-60).

100 ÷ 0.60 = 167 lbs 0-0-60 needed to provide 100 lbs K₂O/acre.

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

3.2.1 Situation: Nitrogen and potassium are recommended as a sidedressing at 30 pounds N and 30 pounds K₂O/acre.

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

30 ÷ 0.21 = 143 lbs ammonium sulfate

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

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 lbs K₂O.

3.2.2 Situation: The recommendation is for 80 lbs N, 20 lbs P₂O₅ , 90 lbs K₂O, and 10 lbs 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 muriate 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 ÷ 0.46 = 44 lbs 0-46-0

90 ÷ 0.60 = 150 lbs 0-0-60

10 ÷ 0.23 = 44 lbs 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 nutrients 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 fertilizer.

• 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 shown.

• 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 section 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 P₂O₅ and K₂O. For example, in Figure 7 we calculate the grade of the mixture in Section 3.2.1.

Figure 7. Grade calculation of mixture in Section 3.2.1.

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. Figure 8 is a calculation of the grade of the mixture described in Section 3.2.2.

Figure 8. Grade calculation of mixture in Section 3.2.2.

80 lbs N ÷ 575 lbs total = 13.9% N

20 lbs P₂O₅ ÷ 575 lbs total = 3.4% P₂O₅

90 lbs K₂O ÷ 575 lbs total = 15.6% K₂O

87 lbs S ÷ 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 will 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 nutrients 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. For example, 500 pounds of 10-3-20 were applied per acre.

500 lbs × 10% N = 50 lbs N/acre

500 lbs × 3% P₂O₅ = 15 lbs P₂O₅ /acre

500 lbs × 20% K₂O = 100 lbs K₂O/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 better 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.

Buying Needed Nutrients -- Worksheet

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 nitrogen.

• 3. ___ One hundred kilograms of urea (46-0-0) contains 92 kilograms of nitrogen.

• 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 K₂O/acre?

____ lbs of K₂O desired/acre ÷ 0.60 K₂O 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. Using Table 7 , draw a line between the N source and the amount of that source which would supply the 70 lbs N.

Table 7. Sources of nitrogen and amount of those sources.

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 lbs

• 7. A recommendation calls for 90 lbs N, 40 lbs P₂O₅ and 100 lbs K₂O per acre. Complete the following form for a one acre batch 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 fertilize ten acres.

• 8. When 400 pounds of 20-8-20 are applied per acre, there are pounds of N, pounds of P₂O₅ , and pounds of K₂O applied per acre.

• 9. Use the steps described below to calculate the grade of the bulk blended fertilizer in Figure 9 :

Figure 9. Bulk blended fertilizer.

• Multiply weight of ammonium nitrate times percent of N in it.

• Divide by 2000 to get % N in mixture.

• Multiply weight of concentrated superphosphate by percent of P₂O₅ in it.

• Divide by 2000 to get % P₂O₅ .

• Multiply weight of muriate of potash by percent of K₂O in it.

• Divide by 2000 to get % K₂O.

• Express the grade in the customary fashion, i.e., % N - % P₂O₅ - % K₂O.

Figure 5. Soil Test Report.

Figure 6. Crop Record.

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Footnotes

1. This document is Circular 626, one of a series of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First Published September 1984. Last revised: July 2002. Please visit the EDIS Web site at http://edis.ifas.ufl.edu.

2. Gerald Kidder, Professor, Soil and Water Science Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611-0290.

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The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.

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Copyright Information

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