Plant Nutrition, Fertilizers and
Fertilizer Programs for
Florida Golf Courses
L.B. McCarty, J.B. Sartain, G.H. Snyder and J.L. Cisar
University of Florida
Institute of Food and Agricultural Sciences
Florida Cooperative Extension Service
John T. Woeste, Dean
TABLE OF CONTENTS
I. Introduction 1
II. Golf Greens 1
a. Timing 1
b. Nitrogen Rates 2
c. Frequency 2
d. Overseeded Greens 2
e. Nitrogen Sources 3
f. Other Elements 3
g. Micronutrients 3
III. Tees 4
IV. Fairways and Roughs 4
SOIL AND LEAF ANALYSIS 5
I. Soil Analysis Report 5
a. Ratios of Elements 7
II. Leaf Analysis 7
PLANT NUTRITION AND TURF FERTILIZERS 9
I. Plant Nutrition 9
II. Primary Nutrients and Fertilizers 11
a. Nitrogen 11
b. Phosphorus 22
c. Potassium 25
Ill. Secondary Plant Nutrients 26
a. Calcium 26
b. Magnesium 27
c. Sulfur 28
IV. Micronutrients 28
FOLIAR LIQUID FERTILIZATION 31
I. Introduction 31
II. Fluid Fertilizers 32
II1. Slow-Release Sources 33
IV. Application 34
REFERENCES AND ADDITIONAL READING 36
L.B. McCarty, Associate Professor, Environmental Horticulture Department; J.B. Sartain, Professor, Soil and Water Science
Department; G.H. Snyder, Professor, Everglades Research and Education Center, Belle Glade; J.L. Cisar, Associate Professor,
Fort Lauderdale Research and Education Center, Fort Lauderdale.
Bermudagrass, the primary grass used for Florida golf courses, requires ample nutrients for
optimum growth. This, coupled with Florida's extended growing season, high annual rainfall, and
predominately sandy soils, means that Florida courses must have higher inputs to maintain quality turf
than courses in northern states.
Developing one particular fertilization schedule that sufficiently meets the conditions of all
courses within the state is difficult. Player expectations, budget constraints, soils used in construction,
and course location all influence the inputs that constitute a sound fertility program for each course.
Often this complex process is intensified by the demands of professional players for the adoption of
high, sometimes unrealistic standards. Club members, in turn, urge their superintendents to provide
courses with excessively lush conditions, which drives up costs and wastes natural resources.
Soils used to construct golf courses also vary widely throughout the state. In the panhandle,
for example, Cecil type clays often are present; these soils tend to hold water and nutrients adequately
but have low pH levels. In central and coastal areas, sugar sands, which hold water and nutrients
poorly, predominate. In addition to sandy soils, courses in south Florida also may be constructed on
muck-type or limerock-based soils. Limerock-based soils have high pH values; as a result,
micronutrient management becomes very important.
The following is an overview of fertility recommendations for most courses and special situations
in the state. However, course managers should be allowed to determine the fertility programs that best
suit their particular situations.
II. Golf Greens
Determinations of how much and how often fertilizer should be applied are influenced by several
factors. Turf managers for each course should consider the quantity and scheduling of fertilizer to be
applied during the year. Fertilization programs should provide adequate levels of essential nutrients
to sustain growth and acceptable turf quality and color. Improper timing and/or rates of fertilizer
application affect the stress tolerance and recuperative ability of bermudagrass. In addition, disease
occurrence and severity often are closely linked to the amounts of fertilizer applied and the timing of
fertilization programs. For example, dollar spot (Moellerodiscus and Lanzia spp.) and
Helminthosporium leaf spot (Drechslera and Bipolaris spp.) diseases often are correlated with periods
of inactive or slowed turf growth. A fertilizer application containing soluble nitrogen often induces the
turfgrass to outgrow these disease symptoms, eliminating the need for fungicide applications. In
contrast, excessive fertilization of overseeded grasses such as ryegrass (Lolium spp.), roughstalk
bluegrass (Poa trivialis), and bentgrass (Agrostis spp.) often promotes the occurrence of brown patch
(Rhizoctonia spp.) and pythium (Pythium spp.) diseases.
It is important to provide proper fertilization, along with healthy disease- and stress-free turf, to
ensure an acceptable playing surface. In general, excessive fertilization with nitrogen is not only
agronomically detrimental to the turfgrass but also drastically slows the rolling of balls and generates
complaints from players. Exceptions include certain high traffic greens and tees (e.g., par-3) and newly
constructed greens, which require higher nitrogen fertilization to promote turf recovery from ball marks
and concentrated traffic.
Timing is partially based on minimum and optimum temperatures necessary for turfgrass growth.
Table 1 lists growth temperatures for cool- and warm-season turfgrasses. If temperatures are outside
the growth range of the grass, fertilizer applications will be inefficiently utilized by plants that are not
Table 1. Air temperatures affecting turfgrass shoot growth, and soil temperatures at 4
inches affecting root growth.
Shoot Growth Root Growth
Minimum Optimum Minimum Optimum
Turfgrass -----------------------------------F ----------------------
Warm-season grasses 55 80 to 95 50 to 60 75 to 85
Cool-season grasses 40 60 to 75 33 50 to 65
b. Nitrogen Rates
As mentioned, many factors determine the fertilization rates required by a particular golf course.
Due to year-round play, Florida golf greens need from 12 to 24 Ibs N per 1,000 sq. ft. Courses with
sufficient resources, excessive traffic, and elevated player demands need the higher rate range. Course
managers maintaining a less intensive playing surface or operating with limited labor and financial
resources should use nitrogen rates in the lower range. Exceptions to these values may occur. For
example, courses recovering from excessive traffic, pest, or low-temperature stresses or those
establishing new greens may require approximately 25% more nitrogen than the amounts listed.
To maintain optimum color and density during periods of active growth, highly maintained
bermudagrass golf greens need approximately 112 Ib soluble N per 1,000 sq. ft. every 7 to 14 days.
For courses without these resources and those with lower player expectations, bermudagrass can be
maintained adequately when 1/2 Ib N per 1,000 sq. ft. is applied every 2 to 3 weeks. On intensively
maintained courses, higher rates (e.g., 1 Ib N per 1,000 sq. ft. every 7 to 14 days) may be necessary
to encourage quicker turf recovery during times of heavy play. These higher rates can lead to other
problems, however. Excessive thatch can quickly accumulate, putting speeds will be slower due to
the production of more leaf area, and a decrease in turfgrass rooting may result.
d. Overseeded Greens
Once established, overseeded greens should be fertilized every 2 to 3 weeks with 1/2 Ib soluble
nitrogen per 1,000 sq. ft. (plus potassium during the fall and winter). The objective is to provide
enough nitrogen to maintain desirable color but not so much as to weaken overseeded grasses and
promote premature growth of bermudagrass. In addition, the use of highly soluble nitrogen on
overseeded grass often leads to excessive turf growth, slower putting speeds, and the occurrence of
disease (e.g., brown patch or pythium). Many superintendents have discovered that an application of
manganese, and possibly iron, often can substitute for a nitrogen application. Two to three ounces
of an iron source such as ferrous sulfate or 1/2 ounce of manganese sulfate (Epsom salt) in 2 to 5
gallons of water applied per 1,000 sq. ft. provides 2 to 3 weeks of desirable dark green color without
an undesirable flush of growth. Since plants receive these elements only through foliar absorption,
there is a relatively short color response time.
e. Nitrogen Sources
The source of nitrogen used to fertilize golf greens affects the amount applied. Usually, a
combination of soluble and insoluble nitrogen sources is recommended to provide uniform grass
growth. Ureaformaldehyde (Nitroform), IBDU, and SCU often are used to provide slow-release, residual
nitrogen, while a soluble source is used for quicker turf response. During periods of cold weather,
IBDU or soluble sources provide the fastest turf response because they are less dependent on
microorganisms for nitrogen conversion and release. Other considerations involving nitrogen sources
include higher costs for slow-release and natural organic sources than for soluble ones; salinity
hazards associated with the use of ammonium nitrate and ammonium sulfate; and acidifying effects
of ammonium sulfate and ammonium phosphate. With the exception of slow-release (water-insoluble)
materials, single applications of actual nitrogen should not exceed 1 Ib per 1,000 sq. ft. Frequent
application of small amounts of nitrogen (e.g., 1/2 Ib N per 1,000 sq. ft.) is preferred, since this
produces a higher quality turf, avoids growth flushes, and minimizes the potential for leaching. Higher
rates of slow-release nitrogen (e.g., up to 3 Ibs N per 1,000 sq. ft. every 90 days) can be applied
without burn. In most cases, a high-quality turfgrass can be maintained for a 90-day period without
flushes of growth or drastic changes in color when slow-release nitrogen sources are used.
Additionally, slow-release nitrogen sources leach less than soluble ones.
f. Other Elements
Potassium often is called the "health" element; without a relatively available supply of potassium,
turfgrasses are more susceptible to environmental and pest stresses. Root growth also is related to
potassium availability. Unfortunately, potassium does not readily remain in the turfgrass root zone,
especially in greens constructed chiefly with sandy soils. Therefore, potassium should be applied to
golf greens nearly as frequently as nitrogen, but at a rate half to equal that of nitrogen.
Soil phosphorus levels tend not to fluctuate as readily as those of nitrogen or potassium. Soil-
test results should be used to determine the amount needed for a particular course. Usually, 0 to 4
Ibs of phosphorus per 1,000 sq. ft. are needed per year. Phosphorus is generally not very water-
soluble; therefore, if it is needed, application should follow aerification to increase efficiency. This
allows the material to be placed more directly in the root zone. Cool-season turfgrasses have a greater
color response to phosphorus fertilization than warm-season grasses. To take advantage of this, turf
to be overseeded should have a yearly application of phosphorus fertilizer during the cool season.
Regular soil and tissue testing is the best way to prevent many nutrient deficiency problems.
Iron and manganese are two of the most common micronutrient deficiencies encountered by Florida
turf managers. If excessive or indiscriminate amounts of micronutrients are applied or soil pH is
excessively low, however, plant toxicity can occur. For example, turf is sometimes grown on old
vegetable or citrus production fields, many of which were frequently sprayed with fungicides containing
copper, zinc, and/or sulfur. Because these residues (with the exception of sulfur) are relatively
immobile in soils, they have become toxic to turfgrasses in some cases.
Symptoms of micronutrient deficiency can easily be confused with those of pest occurrence or
other stresses. These problems, however, usually are more localized and appear as irregular spots
or in circular patterns. Table 2 offers a starting guideline for spot treating with micronutrients by
spraying them on foliage to the drip point. This topic is covered in more detail in the section of this
publication entitled Plant Nutrient and Turf Fertilizer.
Table 2. Solution used to spot treat for micronutrient deficiencies.
Deficient Ib element per
Micronutrient Fertilizer Source oz/gal 1,000 sq. ft.
Fe iron sulfate 2/3 0.025
Mn manganese sulfate 1/2 0.025
Zn zinc sulfate 1/2 0.01
Cu copper sulfate 1/2 0.003
B borox 0.1 0.001
Mo sodium molybdate 0.01 0.001
Tees, like greens, should be fertilized sufficiently to sustain vigorous recuperative growth, but
not to the extent that wear tolerance is sacrificed. Tees, in general, are maintained almost as
intensively as golf greens. This is especially true for tees constructed with a sand-based profile and
for par-3 tees that receive excessive traffic and damage from ball divots. For most par-4 and par-5
tees, the amount of fertilization can be reduced to approximately half that used for golf greens. For
par-3 tees, the amount of fertilization should range from 3/4 to equal that used for greens. Potassium
application rates should be approximately half those of nitrogen, except where clippings are removed
or when sand-based tees are constructed. In such cases, potassium application rates should equal
those of nitrogen.
IV. Fairways and Roughs
Generally, fairways are maintained with less fertilizer than golf greens because clippings are not
removed during mowing. This results in the recycling of more nutrients and the use of heavier soils
for fairways. In addition, higher mowing heights promote deeper rooting, and less irrigation is applied
that leaches soil nutrients. Nitrogen and potassium fertilization rates should range between 130 and
260 Ibs of nutrient per acre per year. Since such variables as local weather conditions, insect and
disease severity, and overseeding practices will influence exact rates and timing, a range of fertilization
rates is suggested. Phosphorus needs should be based on annual soil tests.
Fertilizer applications should begin in late winter during the flush of new turf growth. In general,
one application of a complete fertilizer is needed during this period and another in the fall. These are
supplemented throughout the year with nitrogen and potassium, as needed, to maintain desirable
color, leaf texture, density, and recuperative ability. In general, these subsequent applications are
made every 5 to 8 weeks on high maintenance courses and every 10 to 12 weeks on low maintenance
courses throughout spring and summer. The last fertilizer application, which should be made
approximately one month prior to anticipated frost in north Florida, should consist of a 1:1 or 1:2
nitrogen to potassium ratio to encourage the formation of desirable carbohydrates. Fertilization in
south Florida or on overseeded fairways should be continued to maintain desirable color but should
not be excessive, since turf that grows slowly is less able to utilize the applied material.
Since roughs are mowed at greater heights than fairways and clippings are returned, fertilization
requirements for roughs are much lower. Roughs are usually fertilized one to three times a year to
maintain color and permit recuperation from pest or traffic damage. Forty Ibs of a soluble nitrogen
source, or 80 Ibs of an insoluble source, are usually applied per acre per application. A complete
fertilizer should be used at each treatment. Obviously, as fertilization amounts increase, so do
maintenance costs associated with mowing and trimming.
SOIL AND LEAF ANALYSIS
Soil testing is a basic practice of turfgrass management. Soil analysis provides information on
relative levels of nutrients, organic matter, pH, soluble salts, and cation exchange capacity. Since
testing laboratories differ in methods of extraction and analysis, it is suggested that turf managers
choose a particular laboratory and use it consistently to minimize the possibility of variation in analysis
techniques.' In most cases, these laboratories use university extraction and analysis techniques and
fertility recommendations. Managers should be certain that the laboratory chosen uses information
based on the calibration of soil test results for the plant material being grown. Recommendations
based on responses of plants other than turfgrass may provide inaccurate results, since the needs of
turfgrass differ from those of most other crops.
I. Soil Analysis Report
Most soil analysis reports list nutrient levels in one of two ways: parts per million (ppm) or meq
milliequivalentt) per 100 grams of soil. Results for the major elements and micronutrients are most
commonly reported in ppm on an elemental basis. An acre of mineral soil with a depth of 6 to 7 inches
weighs approximately 2 million Ibs. To convert ppm to approximate pounds per acre, the ppm value
is multiplied by two.
Soil cations such as calcium, magnesium, potassium, and hydrogen are expressed by their
relative ability to displace other cations. For example, one meq of potassium is able to displace exactly
one meq of magnesium. Cation exchange capacity (CEC) and the total amounts of individual cations
may be expressed in meq/100g.
Using these methods of reporting nutrient levels, laboratories give most soil test readings a
fertility rating of very low (VL), low (L), medium (M), high (H), or very high (VH). Usually, the division
between medium and high is the critical value. Above the high value, plant response to added fertilizer
is not expected; below it, more fertilizer is needed as nutrient levels decrease. Table 3 summarizes
recommended ranges for nutrient levels reported by the Florida Cooperative Extension Soil Testing
Laboratory, which uses the Mehlich-l extractant. The reader should note that there are variations in
the plants, soils, locations, management practices, and laboratory extraction techniques used. Time
and experience are required to establish a baseline from which superintendents can gauge specific
nutrient level fluctuations.
Table 3. Relative response range of soil elements analyzed by Mehlich-1 extractant.
Analysis Acceptable Comments
Nitrogen/ <3% Because nitrogen readily changes in soils, nitrogen availability is difficult to predict. Often
Organic the percentage of organic matter serves as a reserve for many essential nutrients, especially
Matter nitrogen. Therefore, labs list an Estimated Nitrogen Release figure, based on the percentage
of organic matter present, to estimate the pounds per acre of nitrogen that will be released
over the season.
Phosphorus 0 30 ppm Phosphorus absorption is greatest when soil pH is between 5.5 and 6.5.
Potassium 0 60 ppm Generally, higher K levels are required in soils containing high levels of clay or organic
matter. Soils with high levels of Mg may also require higher K applications. Sandy soils
require lighter, more frequent K applications than heavier soils.
Calcium 0 50 ppm In most Florida soils, liming with dolomite to ensure an adequate soil pH for proper plant
(see comment) growth will provide more than adequate concentrations of Ca and Mg. Deficiencies of these
Magnesium 0 20 ppm elements are more common in soils that are sandy or acidic, and/or in soils containing low
(see comment) levels of organic matter.
Soil pH 5.5 6.5 Soil with a pH of less than 5.5 becomes highly acidic and can produce elements toxic to turf.
Alkaline soil pH (>7.0) often limits availability of many minor elements.
Cation 5 to 35 meq/100g CEC measures a soil's ability to hold the cations Ca, Mg, K, H, and Na. CEC generally
Exchange increases in proportion to a soil's organic matter or clay content. Generally, the higher the
Capacity CEC value, the more productive the soil.
Percent Base (See comment) Percent base saturation refers to the proportion of CEC occupied by the cations Ca, Mg, K,
Saturation H, and Na. Base saturation percentages have little value when determining nutrient levels in
Florida's sandy soils.
Iron 12 25 ppm Soil pH and relative levels of such other elements as P are important when interpreting Fe
soil tests. Generally, Fe becomes less available in alkaline or extremely acidic soils, and in
soils with excessively high levels of P or moisture.
Manganese 0 10 ppm Plant response to applied Mn may occur within the following ranges: 3-5, 5-7, and 7-9 ppm
for mineral or organic soils with pH of 5.5-6.0, 6.0-6.5, and 6.5-7.0, respectively. Deficiencies
are more likely to occur on coarse, sandy, acidic soils that receive excessive water.
Zinc 0 3 ppm Plant response to applied Zn may occur within the following ranges: 0.5, 0.5-1.0, and 1-3
ppm for soils with pH of 5.5-6.0, 6.0-6.5, and 6.5-7.0, respectively. Zinc interactions with P
and soil pH can alter needed application rates.
Copper 0 0.5 ppm Plant response to applied Cu may occur within the following ranges: 0.1-0.3, 0.3-0.5, and 0.5
ppm for mineral soils only with pH of 5.5-6.0, 6.0-6.5, and 6.5-7.0, respectively. Copper
deficiencies can occur on alkaline soils; soils containing high levels of organic matter (peat
and muck); soils heavily fertilized with N, P, and Zn; and, in Florida, on flatwood soils
following first cultivation. Toxic conditions may exist when Cu levels exceed the ranges of 2-
3, 3-5, and 5 ppm in mineral soils with pH of 5.5-6.0, 6.0-6.5, and 6.5-7.0, respectively.
Boron 1 1.5 ppm Boron deficiencies occur more commonly on soils that are sandy or alkaline, or those
containing low levels of organic matter. Boron is most soluble (available) under acidic soil
Sulfur See comment Soil S levels, like N levels, are dependent on soil organic matter levels; S levels are erratic
and measurements often yield meaningless results. Soils that are low in organic matter
content, are well drained, have low CEC values, and are fertilized with excessive nitrogen
can develop low S levels. Magnesium sulfate (Epsom salt) applied to leaves will indicate the
presence of S deficiencies by greening up within 48 hours after application.
a. Ratios of Elements
Ratios of various elements can be important for specific chemical reactions. For example, the
carbon to nitrogen ratio of amendments, which generally ranges between 10:1 and 12:1 for soil organic
matter, influences the decomposition and utilization of organic matter. Ratios greater than 20:1 may
result in inefficient breakdown of organic matter due to the lack of nitrogen necessary to sustain soil
organisms. Certain sawdust sources may have a C:N ratio as high as 400:1. Turf managers who use
these as soil amendments should add some nitrogen to the mixture, since sawdust can raise the
carbon to nitrogen ratio to more than 20:1. Similar results also could occur if the nitrogen to sulfur
ratio exceeds 20:1.
II. Leaf Analysis
Tissue or leaf analysis can be used as an additional tool for determining those inputs in turf.
Leaf analysis, along with turfgrass appearance and soil analysis, can be used as a means of
diagnosing the problems and effectiveness of fertilization programs, especially those implemented to
correct micronutrient deficiencies. While soil analysis for some nutrients does not always adequately
indicate their availability to plants, leaf analysis can be used to detect potential nutrient deficiencies
before visual symptoms appear. Leaf analysis also provides a comparison between nutrient levels
available to turf plants and soil test levels and can possibly identify the factors that may interfere with
nutrient uptake to create a deficiency in the plant. In Tables 4-7, leaf analysis has been used to
indicate general ranges for nutrient levels in golf course grasses.
Table 4. Relative nutrient ranges for bermudagrass greens and tees,
from leaf analysis.*
Element Low Sufficient High
----------------------------------- % ---------------------------------------
Nitrogen 3.50- 3.99 4.00- 6.00 >6.00
Phosphorus 0.15 0.24 0.25- 0.60 >0.60
Potassium 1.00 -1.49 1.50 4.00 >4.00
Calcium 0.30 0.49 0.50 -1.00 >1.00
Magnesium 0.10 0.12 0.13 0.40 >0.40
Sulfur 0.15-0.19 0.20- 0.50 >0.60
-------------------------------- ppm -----------------------
Boron 4-5 6-30 >30
Copper 3-4 5-50 >50
Iron 40-49 50-350 >350
Manganese 16 24 25 300 >300
Zinc 15-19 20 -250 >250
*After Jones, Wolf, and Mills.
Table 5. Relative nutrient ranges for
bermudagrass fairways, from leaf
Element Low Sufficient High
-------------------------/---------- % ---------------------------------------
Nitrogen 2.50- 2.99 3.00- 5.00 >5.00
Phosphorus 0.12 0.14 0.15 0.50 >0.50
Potassium 0.70- 0.99 1.00 4.00 >4.00
Calcium 0.30 0.49 0.50 -1.00 >1.00
Magnesium 0.10 0.12 0.13 0.50 >0.50
Sulfur 0.12 0.14 0.15 0.50 >0.50
---------------------------------- ppm ------------------------------------
Boron 4-5 6-30 >30
Copper 3-4 5-50 >50
Iron 40 49 50 350 >350
Manganese 16 24 25 300 >300
Zinc 15-19 20 250 >250
*After Jones, Wolf, and Mills.
Table 6. Relative nutrient ranges for perennial ryegrass, from leaf
Element Low Sufficient High
------------------------------------ % --------------------------------------
Nitrogen 4.00 4.49 4.50 5.00 >5.00
Phosphorus 0.30 0.34 0.35 0.40 >0.40
Potassium 0.70 1.99 2.00 2.50 >2.50
Calcium 0.20- 0.24 0.25- 0.30 >0.30
Magnesium 0.13-0.15 0.16-0.20 >0.20
Sulfur 0.22 0.26 0.27 0.32 >0.32
----- ----------------------- ppm -----------------------------------
Boron <9.0 9-17 >17
Copper 4-5 6-7 >8
Iron <40 40-60 >60
Manganese <2.0 2-10 >10
Zinc 10-13 14-20 >20
*After Jones, Wolf, and Mills.
Table 7. Relative nutrient ranges for
creeping bentgrass, from leaf
Element Low Sufficient High
----------------------------------- % -------------------------------------
Nitrogen <4.5 4.50 6.00 >6.00
Phosphorus <0.3 0.30 0.60 >0.60
Potassium 1.8 2.1 2.20- 2.60 >2.60
Calcium <0.5 0.50 0.75 >0.75
Magnesium <0.25 0.25 0.30 >0.30
----- ------------------------- ppm ------------------------ -
Boron <8 8-20 >20
Copper <8 8-30 >30
Iron <100 100-300 >300
Manganese <50 50-100 >100
Zinc <25 25-75 >75
*After Jones, Wolf, and Mills.
PLANT NUTRITION AND TURF FERTILIZERS
I. Plant Nutrition
Proper fertilization is essential for turfgrasses, enabling them to sustain desirable color, growth
density and vigor, to better resist diseases, weeds and insects, and to provide satisfactory golf course
playability. Turf plants need 16 elements, which are divided into two categories: macronutrients and
micronutrients (Table 8). Macronutrients can be further subdivided into primary nutrients (nitrogen,
phosphorus, and potassium), and secondary nutrients (calcium, magnesium, and sulfur). Carbon (C),
hydrogen (H), and oxygen (0), macronutrients obtained from air and water, are the building blocks for
photosynthesis. When combined in the presence of chlorophyll and light, these three nutrients form
carbohydrates, the sugars that provide plant growth.
6CO, + 12H20 ------------> C6H1206 + 602 + 6H20
carbon water chlorophyll carbohydrates oxygen water
dioxide (or sugars)
Carbon dioxide is absorbed by plants through leaf stomata and water is absorbed through
roots. Therefore, fertilizer practices affecting root growth and function, as well as the opening and
closing of stomata, indirectly influence a plant's ability to produce food, through photosynthesis.
Simple carbohydrates produced from photosynthesis generate more complex compounds, such
as starch and amino acids, which require carbon, oxygen, and hydrogen, in addition to other elements.
These remaining essential elements, absorbed into plants mainly through roots, exist in the soil solution
Table 8. Elements, their most commonly available forms for plant uptake, and primary functions in turfgrass growth.
Element Form(s) Function In Plant Growth
Macronutrlents Oxygen (0) CO2 Through photosynthesis, these elements are converted to simple carbohydrates and
Obtained from finally into amino acids, proteins, protoplasm, enzymes, and lipids.
air and water Carbon (C) CO2
Macronutrients Nitrogen (N) N03 A mobile element within the plant. Used in the formation of amino acids, enzymes,
Obtained + proteins, nucleic acids, and chlorophyll. Generally increases color and shoot growth.
primarily from N4 Conversely, N generally reduces heat, cold, and drought hardiness; disease and
fertilization nematode resistance; wear tolerance; and root growth.
Phosphorus H2PO4" Involved in a carbohydrate transport system in which energy moves to all parts of the
(P) -2 plant to activate growth processes. This function in root development is most vital. P
P4 also hastens plant maturity and is needed for glycolysis, amino acid metabolism, fat
metabolism, sulfur metabolism, biological oxidation, and photosynthesis. In addition, P
influences maturation, establishment, and seed production.
Potassium K+ Essential for control and regulation of various minerals; adjustment of stomatal
(K) movements and water relation; promotion of meristematic tissue and rooting; activation of
various enzymes; protein synthesis; and carbohydrate metabolism. Increases heat, cold,
and drought hardiness; wear tolerance; and disease and nematode resistance.
Secondary Calcium (Ca) Ca+2 Required for cell division (mitosis); important in cell membrane permeability; activates
Nutrients certain enzymes; provides chromosome stability and structure; and enhances
Present in some carbohydrate translocation, formation, and production in the protein-containing portions
fertilizer of mitochondria. Influences absorption of other plant nutrients.
available in Magnesium Mg+2 A component of chlorophyll; assists in the stabilization of ribosome particles and
most soils, (Mg) activates several plant enzyme systems, such as carbohydrate metabolism and cell
and/or as part of respiration.
such as lime, Sulfur (S) SO4-2 Required for the synthesis of the sulfur-containing amino acids cystine, cysteine, and
dolomitic lime, methionine; required for protein synthesis and activation of certain enzymes.
Micronutrients Iron (Fe) Fe+3 Necessary for chlorophyll production; an essential component of iron enzymes and
Most premium Fe+2 carriers. Generally increases color and the growth of shoots and roots.
contain these. Manganese Mn+2, Activates Mangano-enzyme; needed in Photosystem II of photosynthesis; associated with
(Mn) organic salts carbohydrate metabolism, chlorophyll synthesis, phosphorylation reaction, and the citric
Copper (Cu) Cu+2 Connected with the percentage of photosynthesis in plants; found in cytochrome oxidase,
Cu+ essential for plant metabolism and used in production of the enzyme polyphenol oxidase;
used as catalysts in plant metabolism.
Chlorine (CI) CI- Possibly required for photosynthesis of isolated chloroplasts and as a bromide substitute.
Zinc (Zn) Zn+2 Component of the enzyme dehydrogenase, needed for RNA and cytoplasmic ribosomes
in cells, proteinases, peptidases, and IAA synthesis. Involved in the conversion of
ammonium to amino nitrogen.
Boron (B) H3BO3 Facilitates sugar transport through membranes; involved in auxin metabolism in root
HBO.2 elongation and protein and phosphate utilization; influences cell division by controlling
Molybdenum MoO42 Required for the production of amino acids and proteins in the assimilation and reduction
(Mo) processes of nitrogen fixation.
Sodium (Na) Na+ Regulates stomatal opening and nitrate reductase levels. Toxic levels are generally more
problematic than deficiencies.
II. Primary Nutrients and Fertilizers
Nitrogen, phosphorus, and potassium are considered most important because soils typically
are deficient in these elements and they must be applied regularly. Because these elements are
required in the greatest amounts, they are referred to as the primary or essential nutrients or elements.
The numerical sequence on a fertilizer bag refers to the percentages of nitrogen, phosphate (P205),
and potash (K20) the fertilizer contains. Thus a bag of 10-10-10 would contain 10% nitrogen, 10%
available phosphate, and 10% potash.
The secondary elements are calcium, magnesium, and sulfur. Dolomitic limestone provides
deficient soils with calcium and magnesium, while sulfur is added by sulfur-containing fertilizers. Sulfur
also may be provided by acidifying materials such as elemental sulfur, which lowers soil pH, by
desalinization materials such as gypsum, by rainwater containing the air pollutant sulfur dioxide, or by
salts of nitrogen, magnesium, potassium, and various micronutrients. Table 9 shows the effects of
increasing the levels of five essential nutrients on turfgrasses.
While micronutrients are essential elements, plants require them only in small amounts.
Florida's flatwood soils, for example, may not contain ample micronutrients to sustain optimum plant
growth. Due to the high sand content of many golf greens and extremes in soil pH levels (Figure 1),
micronutrient management is somewhat more important for superintendents. Iron and manganese
deficiencies often occur at high pH levels (>7.0) and are sometimes mistaken for nitrogen deficiency.
Since a number of turfgrass specialty fertilizers contain some, or all, of these micronutrients, users
should check product labels carefully before purchasing.
Turf managers consider nitrogen a key element because of its influence on color, growth rate,
density, and stress tolerance. Turfgrasses contain between 20 and 60 g N per kg; the element
constitutes 2% to 6% of the total dry matter. The most often applied element, it is required in larger
quantities than any other element except carbon, hydrogen, and oxygen. However, excessive nitrogen
use creates problems. Excessive amounts of nitrogen increase shoot growth and susceptibility to
selective diseases as well as lowering tolerance to heat, cold, drought, and traffic. Most important,
inordinate use of nitrogen reduces root and lateral shoot growth. Root growth suppression results in
decreased turf tolerance to heat and lessened resistance to nematode damage. In addition, excessive
nitrogen fertilization may adversely affect the environment by contaminating groundwater.
Origins and Losses
Turfgrasses may obtain nitrogen through the decomposition of organic matter and to a limited
extent from the air as nitrogen oxidized by lightning and dispersed by rainfall. In soil, ammonium
(NH4+), nitrate (NO3), and nitrite (N02) are the most important forms of nitrate, originating either from
the aerobic decomposition of organic matter or from the addition of commercial fertilizers. Ammonium
and nitrate are the only forms of nitrogen used by turf plants. No matter what the source of applied
nitrogen (e.g., manure, crop residues, organic matter, or commercial fertilizer), it must be converted to
one of these forms for plant use.
Table 9. Effects of increasing levels of primary and secondary nutrients on turfgrasses.
Increasing levels of
Turf Plant Response N Ph K Fe S Ca Mg
Turf color t 1 1 t
Shoot growth and 11 I T
Rooting 1 I t 1 1 1
Carbohydrate formation It t1 1
Recuperative ability I
Tolerance to heat, cold, I 1 t I
Wear tolerance I t
Nematode tolerance I t
Disease tolerance Lt 1 1 1t
t Ample supply of the nutrient usually increases the specific turf plant response.
1 Excessive nutrient levels usually decrease the specific turf plant response.
II Adequate nutrient levels increase the specific turf plant response, while excessive
amounts decrease the response.
4.0 4.5 5.0 5.5
7.0 7.5 8.0 8.5 9.0
Fig. 1. General relationship between soil pH and availability of soil nutrients to plants. The width of each bar indicates the
relative availability of a particular element as soil reaction (pH) changes (after Sartoretto, 1991).
II Eu.U ,E Un
_ Eu U* nd EINC
Mineralization is the process whereby organic matter, organic fertilizers, and some slow-release
fertilizers are broken down or transformed by soil microorganisms to supply plants with available
ammonium and nitrate. Mineralization is a three-step process involving aminization, ammonification,
and nitrification. Aminization and ammonification are stages of the mineralization process in which
proteins, amines, and amino acids (usually from organic matter or humus) are converted to ammonium,
a source of nitrogen utilized by plants. Mineralization is described in the following equation:
R-NH2 + H20 ------------------ > NH4+ + R-OH + energy
Following mineralization, ammonium nitrogen (NH4+) is absorbed by plants or undergoes further
transformation to become nitrate (NO,). Ammonium nitrogen is the preferred nitrogen source because
additional energy is required to transform nitrate into usable forms by plants and because ammonium
nitrogen is less vulnerable to leaching and denitrification losses. Transformation of ammonium nitrogen
to nitrate nitrogen, referred to as nitrification, is described as follows:
NH4+ + 02 ----------> N02" + 2H+ -----------> N03O + H20
ammonium warm nitrate nitrate
nitrogen temperatures nitrogen nitrogen
Nitrification depends on environmental conditions that favor soil microbiological activity. Warm
temperatures, adequate soil moisture, and soil oxygen are necessary for this activity. However,
nitrification does not readily occur in extreme temperatures (e.g., below freezing or above 1050F), in
saturated or poorly aerated soil, in excessively dry soil, or in soil with a low pH (<4.8). Under such
unfavorable conditions, microorganisms do not perform nitrification and ammonium may accumulate.
Ammonium nitrogen also may become toxic to turfgrasses when they are grown under cool, low-light
conditions that minimize nitrification.
Nitrate nitrogen is readily soluble in water and may be repelled by negatively charged exchange
ions of soil components. Therefore, unless grasses rapidly utilize this form, it may be lost through
leaching if excessive moisture is applied. This may be especially true during the winter, when grass
is not actively growing. In addition to nitrate and water, hydrogen ions (H+) are produced during
nitrification; a reduction in soil pH may be observed when this occurs. This reduction is especially
acute when a high rate of nitrogen is applied to sandy soils low in calcium. These soils are poorly
buffered against changes in pH induced by the acidifying effect of nitrification.
Besides leaching and crop removal, nitrogen can be lost through denitrification and
volatilization. Denitrification, the conversion of nitrate nitrogen to gaseous nitrogen under anaerobic
conditions, can result in the loss of nitrogen into the atmosphere. Certain anaerobic soil organisms
can obtain oxygen from nitrates. They also can obtain oxygen from nitrites in waterlogged soils,
subsequently releasing nitrous oxide and nitrogen gas. Low soil oxygen levels and/or high soil
moisture, alkaline (high-pH) soils, and high temperatures favor denitrification. Applied nitrogen can be
lost through denitrification at the rate of 10% to 30% in compacted, waterlogged soils that have an
especially high pH level (>7.5).
10, tO2, O tO
N03 -----> N02 -----> NO -----> N2O -----> N21
nitrate nitrate nitric nitrous gaseous
nitrogen nitrogen acid oxide nitrogen
Volatilization is the conversion of ammonium nitrogen (NH4+) to ammonia gas (NH3), which
escapes to the atmosphere. If ammonium nitrogen comes in direct contact with free calcium carbonate
in the soil, ammonium bicarbonate is formed. Ammonium bicarbonate, a relatively unstable compound,
decomposes into ammonia, carbon dioxide, and water when exposed to the sun.
NH4+ + CaCO, ----------------> NH3t + HCO^ + Ca+2
ammonium calcium ammonia bicarbonate
nitrogen carbonate gas
Usually, volatilization of ammonia nitrogen can be avoided by incorporating ammonium nitrogen
fertilizer into the soil. In addition, ammonium nitrogen fertilizer can be applied to the surface of a sandy
soil free of lime or calcium carbonate without volatilization of ammonia nitrogen. Further, irrigating with
approximately 1/4 inch to 1/2 inch of water after applying fertilizer will eliminate the potential for
Nitrogen's Effects on Bermudagrass
Nitrogen is one of the most important elements turf managers apply to bermudagrass. In
addition to affecting turf color and growth rate, nitrogen influences thatch accumulation, disease and
insect incidence, cold tolerance, heat and drought stress, nematode tolerance, lime requirements and,
most important to the player, putting speed. Turf managers often measure nitrogen needs based on
turf color, density, and/or amount of clipping. However, it is nitrogen's effects on other aspects of turf
management that often influence the success or failure of a superintendent.
Turf Color, Growth, and Density. When plants are deficient in nitrogen, initially leaf color is an overall
pale yellow-green. This symptom, known as chlorosis, reflects decreased chlorophyll production.
Because nitrogen is a component of chlorophyll, it is essential to chlorophyll manufacture. Chlorosis
due to insufficient nitrogen usually appears first on the lower (older) leaves; eventually, leaf color
changes to yellow as the deficiency symptoms progress to the base of the plant. In addition, growth
rate and density may decrease, resulting in weak turf that has poor recuperative ability.
Other factors also may contribute to or possibly cause symptoms that, to the untrained
observer, appear similar to those of nitrogen deficiency. Chlorosis also may be due to a deficiency
of nutrients such as iron, sulfur, or manganese. Florida sandy soils, many of which are alkaline, often
are deficient in these elements. Compounding this problem, high nematode populations and soils with
poor water-holding capacity can result in reduced rooting and increased water stress. Therefore, turf
managers should determine the cause of chlorosis and turf thinning before indiscriminately applying
nitrogen or micronutrient fertilizer.
In general, nitrogen has a direct bearing on turf growth and recovery from injuries due to divots
or ball marks. In terms of the quantity of clipping matter produced, however, turf growth is a poor
determinant of nitrogen needs. If turf has adequate color and density, clipping matter or weight should
not be universally used as a gauge for nitrogen needs. If turf begins to thin or becomes excessively
damaged, however, turf growth and density may become relatively good indicators of nitrogen needs.
Improper nitrogen fertilization can have an undesirable effect on bermudagrass rooting.
Bermudagrass, in general, uses carbohydrates stored in its roots to support shoot growth. These
carbohydrates are replenished by the products of photosynthesis. If large amounts of nitrogen are
used, excessive shoot growth occurs at the expense of roots. Consequently, these roots may not have
enough time to replenish their carbohydrates before having to support excessive shoot growth when
nitrogen is reapplied. It has been observed that bermudagrass maintained with low levels of nitrogen
has up to twice as much root growth as that maintained at high levels.
In addition to forcing excessive shoot growth at the expense of root growth, high levels of
nitrogen can cause such physiological changes as cell wall thinning, succulent tissue growth, and
reduced root carbohydrate levels. Accordingly, increased susceptibility to stress makes the plant less
Most nitrogen fertilizers are produced synthetically by reacting atmospheric nitrogen and
hydrogen gas. Large amounts of heat and pressure are required to produce ammonia.
N2 + 3H2 pressure ammonia
From the basic ammonia compound, many different fertilizer compounds containing nitrogen
may be manufactured. This compound may be liquefied to form anhydrous ammonia, dissolved in
water to form nitrogen solution (NH40H), or formulated into other inorganic fertilizers.
Table 10. Characteristics of primary nitrogen sources used in turf fertilizers.
Nutrient Percentage Salt Index
S. per Unit of Acidifying
Source N P205 120 Nutrienta Effect Comment
Ammonium nitrate 33 0 0 2.94 Medium Water-soluble; high burn potential;
potential fire hazard.
Ammonium sulfate 21 0 0 3.25 High Water-soluble; contains 24% S; has
greatest acidifying effect of all listed
Calcium nitrate 16 0 0 -Very hygroscopic; contains 19% Ca; fast
acting with high burn potential; N release
is not temperature dependent; used on
sodic soils to displace sodium.
Urea 45 0 0 1.62 Medium Water-soluble; may volatilize if applied to
surface; may leach rapidly if rainfall
occurs immediately after application.
IBDU 31 0 0 0.2 Low Slowly soluble; N release rate is not
temperature dependent but depends on
moisture availability and particle size.
Urea formaldehyde (UF) 38 0 0 0.3 Low Slowly soluble; N release rate is
dependent on temperature and
Sulfur-coated urea (SCU) 32 0 0 0.6 Medium Slowly soluble; N release rate is
dependent on temperature and coating
Milorganite 6 4 0 0.6 Low Activated sewage sludge; N release rate
increases with higher temperatures;
contains micronutrients, especially Fe.
Nitrate of soda 16 0 0 6.06 Basic Water-soluble; has highest burn potential
of all listed materials.
aGenerally, the higher the salt index/unit of nutrient, the higher the burn potential of the particular fertilizer material.
Soluble or quickly available nitrogen sources produce an expedient shoot growth and greening
response. This response occurs approximately 2 days after application, peaking in 7 to 10 days and
tapering off to original levels in 3 to 6 weeks, depending on the application rate and the amount of
water applied following fertilization.
The nitrogen in soluble sources is in one of two forms: ammonium or nitrate. The ammonium
nitrogen form is more susceptible to volatilization but less susceptible to leaching. The nitrate nitrogen
form is more vulnerable to leaching.
Soluble nitrogen sources have salt-like characteristics, in that they dissolve readily in water to
form cations and anions. The greater availability of these ions corresponds with an increased burn
potential in the fertilizer. Burn potential can be lowered by applying the fertilizer only to dry turf
surfaces when the temperature of the air is cooler than 80 F. Watering in soluble nitrogen immediately
following application further reduces the risk of burning plant tissue. Other disadvantages of using
soluble nitrogen sources can be minimized by frequently applying small amounts. Rates at or below
1/2 Ib N per 1,000 sq. ft. will minimize these problems but will increase application frequency and
Advantages of Using Soluble Sources
rapid initial color and growth response
high total nitrogen content
lack of odor
satisfactory nitrogen levels maintained if applied frequently in small amounts
minimum dependence on temperature for availability
low cost per unit of nitrogen
versatility in form: may be applied as a granular or as a liquid
Disadvantages of Using Soluble Sources
high potential for causing foliar burn, especially at higher rates and temperatures
potential for causing undesirable growth surge
relatively short residual plant response, necessitating frequent repeated applications and
increasing labor costs
greater potential for nitrogen loss due to volatility, leaching, and runoff
often difficult to handle
Urea. Urea is one of the most widely used nitrogen sources because it is relatively inexpensive and
completely soluble. It is formed by reacting atmospheric nitrogen with methane to produce ammonia
gas and carbon dioxide. The ammonium is then subjected to high temperature and pressure and
reacted with carbon dioxide to form urea. Once applied, urea is broken down into ammonium
carbonate by the enzyme urease, present in plant tissue and organic matter. Being a cation (a
positively charged ion), ammonium is attracted to negatively-charged clay particles, root hairs, and
organic matter. Direct application of urea to the turf surface can result in conversion of ammonium
carbonate to ammonia and carbon dioxide, resulting in excessive loss, as shown below. This loss can
be avoided by irrigating after urea application to incorporate the nitrogen.
(NH2)2CO ----------> (NH4)2003 -------------> NH3t + CO0
urea H20 ammonia ammonia
Urea has a quick initial release rate of short duration and a high foliar burn potential. Nitrogen
from urea is also subject to leaching and volatilization losses. Urea-based fertilizer programs should,
therefore, include frequent, light applications (< 1/2 Ib N per 1,000 sq. ft.) delivered every 2 to 4 weeks
to reduce the potential for such losses.
Ammonium Sulfate/Nitrate. Ammonium sulfate/nitrate and ammonium phosphate, and potassium
nitrate and calcium nitrate, are other commonly used water-soluble nitrogen sources collectively
referred to as inorganic salts. Once these fertilizers solubilize in soil, ammonium ions can be adsorbed
by the negatively-charged clay or organic matter. As with urea, soil nitrobacteria convert this
ammonium to nitrate, the main form in which it is available to plants. Unlike ammonium sulfate and
phosphate, potassium nitrate and calcium nitrate fertilizers do not need to undergo conversion by
nitrobacteria, since their nitrogen is already in nitrate forms.
Slow-Release Nitrogen Sources
In an attempt to overcome some of the disadvantages of soluble nitrogen sources, fertilizer
manufacturers have developed an array of slow- or controlled-release nitrogen sources. These sources
generally produce a more uniform growth response and a longer residual plant response. They also
have less potential for nitrogen loss and allow a higher application rate than readily soluble sources.
In addition, their burn potentials are lower due to their low salt index values. The application rate at
which these sources release nitrogen may vary with the timing of fertilizer applications, source,
temperature, moisture, pH, and particle size.
Drawbacks of slow-release nitrogen sources include high per unit cost and slow initial plant
response. Some sources also are not adaptable to liquid application systems. Turf managers should
understand the various nitrogen sources and conditions favoring nitrogen release before formulating
their annual fertilizer programs.
Coated, Slow-Release Nitrogen Sources. Coated nitrogen fertilizers consist of urea or other soluble
sources coated with a semipermeable barrier. The nitrogen-release rate is slow because the coating
prevents wetting of the soluble nitrogen source. Release rates depend on coating degradation or on
the physical integrity of the coating.
Sulfur-Coated Urea (SCU). Sulfur-coated urea is formulated by moving granulated or prilled
preheated urea pellets through a stream of molten sulfur by means of a rotating drum. The urea is
then coated (sealed) with a microcrystalline wax, which strengthens the sulfur shell and decreases the
initial rate of urea release, thereby protecting the surface from microbial degradation. After it is coated,
the product is cooled and a diatomaceous earth or vermiculite clay conditioner is applied to further
reduce cracking and to promote sealant stickiness. Urea release consists of a gradual diffusion
through this coating via cracks, pinholes, and imperfections naturally occurring in the surface as the
Because of the lack of uniformity and integrity in the coating process, the urea granules crack
at different times; therefore, they exhibit variable nitrogen release rates. These granules also are
vulnerable to damage during transportation, blending, and application, and to injury due to pressure
from mower reels, rollers, or wheels. Therefore, handling should be kept to a minimum and drop
spreaders avoided when applying urea granules.
The rate of urea diffusion from SCU depends on microorganism activity, particle size, and, as
previously discussed, coating thickness and integrity. Nitrogen release from SCU increases with warm
temperatures, moist soils, and neutral soil pH. These conditions favor soil microorganism activity, as
does a thinner wax coating. Heavy sulfur coatings result in larger fertilizer granules, which release the
nitrogen more slowly. Mower crushing or pickup problems may occur with these larger granules. To
minimize these problems, a finely prilled product with a very uniform nitrogen release rate is produced
for greens application.
SCU applied during the winter may produce turfgrass with a mottled appearance. The intensity
of this mottled appearance is correlated with coating thickness and granule size. Normally it dissipates
within 2 to 4 weeks, depending on the rate of nitrogen application and weather conditions.
While sulfur-coated urea has little effect on soil salinity, it can reduce soil pH slightly because
of the sulfur coating, which also is a sulfur source for plants. Sulfur-coated urea tends to be a low-cost,
slow-release nitrogen source compared with.other coated materials. Leaching and volatilization losses
generally are small, assuming that the application of moisture is not excessive. The nitrogen content
of SCU ranges from 32% to 38%, depending on the thickness of the sulfur coating.
Plastic/Resin-Coated Urea. A relatively new technology similar to that used to produce SCU is a
resin-coating (or polymer-coating) process that involves coating a soluble nitrogen source, such as
urea, nitrate, or ammonium, with resin or plastic. Resin-coated fertilizers rely on osmosis rather than
on coating imperfections to release nitrogen. Low concentrations of salts on one side of the resin or
plastic membrane permit high salt concentrations to diffuse to the other side through the coating. As
the fertilizer particle swells, either the pellet cracks open due to internal pressure, releasing urea, or
urea is forced out through the pores. Since the coating is semipermeable, nitrogen is time-released.
Thus controlled release in resin-coated products is more predictable than in sulfur-coated products,
enabling turf managers to control nitrogen availability to a greater degree. Release rates generally vary
from 70 to 270 days, depending on coating thickness and dissolution of water into the prill.
The major disadvantage of poly-coating is that it costs more than other slow-release fertilizers.
Agriform and Escote are two commercial plastic-coated urea sources.
Multiple coating of urea is a recently developed technique. Urea is coated first with one layer
of sulfur, then with a polymer that further protects nutrients and, in combination with the sulfur layer,
determines the rate of release. Diffusion, the release mechanism of nitrogen, can be regulated by
varying the levels of the coating components. In addition to a controlled release rate, multiple coating
offers better resistance to abrasion than SCU. Dust problems associated with handling the material
are also minimized. Poly-S, a product line from the Scotts Company, is one of the first commercially
available dual-coated fertilizer sources created with this technology.
A nitrogen source marketed under the trade name Poly-N, formulated with a technology similar
to that of Poly-S, consists of two coats of resin instead of one, plus one coat of sulfur. The first resin
coating reacts with the urea, and the second resin coating with the first coating, to form a hard coating
that does not break easily when the product is handled. The coatings are very thin but effective. The
thickness of the coating can be manipulated to produce varying release rates. Dissolution of water into
the prill also controls the nitrogen release rate, but temperature does not appear to greatly influence
Controlled-Release Synthetic Nitrogen Sources. Isobutylidene diurea (IBDU). IBDU is a Japanese
product marketed in the United States by Vigoro Industries under the trade name Par Ex. IBDU is
formed when isobutyraldehyde reacts with urea in an acid solution. The resulting product contains
31% nitrogen, 90% of which is water-insoluble. In the presence of water, IBDU hydrolyzes back to urea
and butyric acid. IBDU's nitrogen-release rate is predominantly affected by soil moisture level and
particle size and is not as dependent on temperature. Higher soil moisture content and smaller particle
size result in a faster release rate. Higher temperatures also increase the rate of nitrogen release,
making it 2 to 3 times higher at 75F than at 50 F. Conversely, organic nitrogen sources and urea-
formaldehyde may exhibit a tenfold decrease in release rate within a similar range of temperatures.
An optimum pH range for IBDU nitrogen release is between 5 and 8, with a significant rate
reduction occurring outside these ranges. Because nitrogen release is independent of microbial
activity, IBDU nitrogen is released more readily during cool weather than other slow-release sources.
Nitrogen release, however, is somewhat dependent on particle size, with finer particles providing a
greater surface area and a faster rate of hydrolysis, the mechanism for nitrogen release. Usually, a
range of particle sizes between 8 and 24 mesh is used to increase the rate of nitrogen release over
a longer period. Particles greater than 2mm in diameter are slow to hydrolyze and are more likely to
be picked up by mowers than smaller particles.
The influence of IBDU on soil salinity and pH is minimal. At excessive rates, however (e.g., 6
Ibs N per 1,000 sq. ft.), ammonia gas may be absorbed by the turf, resulting in temporary chlorosis.
IBDU's reliance on water for nitrogen release may be absent or stimulated at a time when it is least
Ureaformaldehyde (UF). Ureaformaldehyde is a generic designation for several products formed
when urea reacts with formaldehyde, creating first monomethylol urea and then soluble methylene urea
and ureaform. The polymers of methylene urea that make up these products have varying lengths and
range from water-soluble to highly water-insoluble molecules, providing controlled nitrogen release.
The smaller the ratio of urea to formaldehyde, the longer the chain of polymers formed. As the lengths
of polymers and the number of longer polymers increase, solubility decreases, resulting in a slowed
release of nitrogen. For example, a methylene urea with a 1.9:1 urea to formaldehyde ratio is 2/3
water-soluble and 1/3 water-insoluble. Ureaform fertilizers, which contain 38% nitrogen, are
commercially available as Nitroform, Ureaform, and Blue-Chip. These sources are intended for soil
application only and not for use as liquids, except Powder Blue, which can be applied as a suspension.
They are more costly than soluble nitrogen fertilizers.
All UF products depend on microbial breakdown for nitrogen availability. Therefore,
environmental conditions favoring microbial activity (e.g., temperatures >550F, neutral soil pH, and
adequate levels of soil moisture and oxygen) promote nitrogen release. Conversely, low temperatures,
acid soils, and low levels of soil oxygen inhibit the release of nitrogen from UF. Ureaform fertilizers that
contain appreciable amounts of water-insoluble nitrogen polymers do not perform well during cooler
weather. Quickly available sources are usually applied alone or in combination with ureaform fertilizers
during cool periods.
Since water-soluble polymers with shorter chains are readily digestible by soil microorganisms,
they release nitrogen to the soil as ammonium in a relatively short time. Polymers with longer chains
contain water-insoluble nitrogen, which is digested more slowly by soil bacteria. Unlike IBDU and SCU,
which return nitrogen to the soil as urea, methylene urea and ureaform gradually convert nitrogen to
ammonium via mineralization throughout the growing season. Therefore, a lag in nitrogen availability
may occur with the use of UF. Accumulation of "residual" nitrogen may take several seasons and will
result in a more uniform response. During this lag phase, adequate shoot color can be maintained by
applying higher rates of UF or by using a supplemental soluble nitrogen source.
As with any nitrogen source, UF losses due to mowers may be significant, especially
immediately after application. To avoid this problem, grass should be allowed to dry and remain uncut
for several days after application. Alternatively, grass catcher boxes may be removed to allow clippings
and fertilizer granulars to return to the soil surface.
UF loses less nitrogen through leaching and volatilization than do readily available nitrogen
sources. Over time, UF sources are approximately equivalent to soluble sources in terms of nitrogen
use efficiency. Under conditions favoring leaching and volatilization, however, UF sources often are
more efficient. Labor costs for fertilizer applications also must be considered, since UF is applied less
frequently. UF has little effect on soil pH or salinity and its potential for burning is low.
A product similar to UF is Nutralene, a soluble methylene urea source containing approximately
40% nitrogen. It is more readily available than UF because it has less methylation. Nutralene's
mechanism of nitrogen release depends on both microbial activity and hydrolysis. Its rate of nitrogen
release, therefore, is faster than for UF products, but its fertilization effects on turf are of short duration.
Another flowable UF source is FLUF. This source contains 18% nitrogen, 20% to 25% of which
is water-insoluble. The initial response of FLUF is generally slower than that of urea. FLUF also has
a lower potential for foliar burning than urea.
Other Slow-Release Sources. Other slow-release nitrogen sources being developed include Oxamide,
Triazines, and Triazones. Oxamide is a diamine of oxalic acid used in Japan for rice production. A
double urea product containing approximately 31% nitrogen, it is approximately twice as soluble as
IBDU. The release rate is directly related to particle size, hardness, and amount of water present.
Following dissolution, hydrolysis occurs primarily by microbial cleavage of the carbon bonds in the
presence of the enzyme amidase, resulting in the formation of ammonium carbonate. Powdered and
fine particles of oxamide nitrify faster than ammonium sulfate and at a rate similar to that of urea in acid
soils. Their residual effects, however, are not as lasting as those of particles with coarser grades.
When used on turf, oxamide imparts a dark bluish green color. Currently, it is prohibitively expensive.
A pure form of triazine that contains 66% nitrogen is the commercial product Melamine.
Commercial formulations usually consist of a mixture of triazine and urea containing 40%, 50%, and
60% nitrogen. Nitrogen release depends on microbial activity and is generally slow, since the product
contains double carbon bonds that are difficult to cleave (break). Response to Melamine may not
occur for 4 to 6 months. A soluble nitrogen source, such as urea, should be used initially with
Melamine to provide initial color and to encourage breakdown of the product.
Triazones are similar to triazines except that their ring structure does not contain double bonds.
Triazones, which contain approximately 40% nitrogen, can be formulated in a water-soluble form.
Nitrogen release is governed by microbial action.
Natural Organic Nitrogen Sources
Natural organic nitrogen sources usually contain various amounts of either composted material
or human or animal waste products. Manure, sludges, bone meal, humates, and composted plant
residues are traditionally used natural organic nitrogen sources (Table 11). The advantages of using
these sources include a low burn potential due to low water-insoluble nitrogen content, limited effect
on pH, and low rate of loss from leaching. Other advantages are the variety of nutrients these sources
offer in addition to nitrogen, and the potential for improving the physical condition of soils, especially
sandy ones. Also, depending on local supply, natural organic nitrogen sources may be available at
Some factors to consider before using these traditional sources include their low rate of nitrogen
release during cool weather, a result of their limited microbial activity and low nitrogen content. Owing
to this low rate of release, large amounts of material will have to be applied. Other considerations
include the fact that natural organic nitrogen sources are more costly per pound of nutrient than
soluble sources and the possibility that they will be difficult to store and to apply uniformly. This is true
especially when the turf is already established. Some natural organic sources produce an objectional
odor after application and contain undesirable salts, heavy metals, and weed seeds. In general, natural
organic sources such as manures and composted crop residues should not be used on golf greens
because of their potential to hinder soil drainage when large amounts of material are applied.
Table 11. Approximate amounts of macronutrients found in common
organic fertilizer sources.
Nutrient Source N P205 K20
--------------- % --------------
Dried blood 13 2 1
Bone meal, steamed 3 25 0
Dried fish meal 10 7 0
Tankage, animal 7 10 1
Guano, bat 8.5 5 1.5
Cattle manure 2-5 1.5 2
Horse manure 2-8 1-3 2-7
Poultry manure 5-15 3 1.5
Sewage sludge, dried 2 2 -
Sewage sludge, activated 6 3 0.5
Swine manure 7 4 6
Cottonseed meal 7 3 2
Garbage tankage 2.5 3 1
Linseed meal 5.5 2 1.5
Rapeseed meal 5.5 2.5 1.5
Soybean meal 7 1.5 2.5
Tobacco stems 2 0.5 6
Milorganite. A product from the Milwaukee Sewage Commission, Milorganite is the most popular
commercial organic nitrogen source for use on fine turf. Milorganite is an activated sewage sludge
produced when raw sewage is inoculated with microorganisms, aerated to promote flocculation,
filtered, dried, ground, screened, and sterilized. Milorganite contains approximately 6% nitrogen, of
which 92% is water-soluble; 2% phosphorus as P20O; and an array of micronutrients. Milorganite is
characterized by a low potential for burning turfgrass leaves. Due to its uniform release of nitrogen
over a 3- to 4-week period, it has a minimal effect on soil pH and salinity. It also loses little nitrogen
through leaching and volatilization, is a source of iron, copper, and zinc and, due to its dark color,
serves as a soil warmer during cool weather. Lower disease and insect incidence also have been
reported when soluble nitrogen sources have been replaced with Milorganite.
The disadvantages of using Milorganite include its relatively high cost per pound of nitrogen,
its poor winter response in the absence of microorganisms required for nitrogen utilization, and its
relatively short residual nitrogen response. In addition, since Milorganite contains no potassium, it
should be used in conjunction with a potassium source.
Phosphorus, an essential element for plant growth, is involved in the transfer of energy during
metabolic processes. Phosphorus content may range from 0.10% to 1.00% by weight, with sufficiency
values ranging from 0.20% to 0.40% in newly mature leaf tissue. Phosphorus levels below 0.20% are
considered deficient, those above 1.00% excessive. The highest concentration of phosphorus is in new
leaves and meristematic tissue, but the element is readily mobile in plants.
Plants absorb phosphorus largely as the orthophosphate ions H2PO4 and HP04-2, which are
present in the soil solution. H2PO4" ions predominate in acid soils. These ions prevail as soil pH
increases, until conditions become alkaline; P04"3 ions then predominate. Both H2PO4- and HPO4 ions
are found at intermediate pH levels.
H2PO4 <----------> H20 + HP04- <---------> H20 + P043
(acid conditions (neutral soils (alkaline conditions -
soil pH < 6.0) pH 7.0) soil pH > 8.0)
Symptoms of phosphorus deficiency in plants include slow growth and weak, stunted plants
with dark green lower leaves. These older leaves eventually show a dull blue-green color with a
reddish purple pigmentation along leaf blade margins. Eventually, leaf tips turn reddish; this color may
then develop in streaks down the blade. Since phosphorus is fairly mobile in plants, deficiency
symptoms initially occur in older tissue.
Phosphorus deficiency symptoms typically appear when the root growth of turf plants is
restricted. Since root growth is slowed during early spring and fall, phosphorus is not readily
encountered in the soil. Similarly, phosphorus deficiencies often occur during turfgrass establishment,
as a result of the initial restricted rooting of new seedlings.
Cool-season turfgrasses (ryegrasses) tend to respond positively to applications of phosphorus
fertilizer, even in soils containing high levels of phosphorus. On the other hand, the growth rate of
bermudagrass has been observed to decline as a result of excessive phosphorus application. A
reduction in tissue nitrogen content appears to result from the application of phosphorus to soils
containing high levels of extractable phosphorus. In light of these findings, the bulk of annual
phosphorus fertilizer should be applied to ryegrass when turf is overseeded in bermudagrass.
The most commonly used phosphorus fertilizers for turf development include superphosphate,
triple (or treble) superphosphate, and monoammonium and diammonium phosphate (MAP and DAP,
respectively) (Table 12). Superphosphate, which consists of calcium phosphate and gypsum, is
produced by reacting rock phosphate with sulfuric acid. Triple superphosphate is calcium phosphate
formed when rock phosphate is treated with phosphoric acid, while ammonium phosphates are
produced by reacting ammonia with phosphoric acid.
Table 12. Characteristics of primary phosphorus sources used in turf fertilizers.
Nutrient Percentage Salt Index
S per Unit of Acidifying
Source N PI 5 K20 Nutrienta Effect Comment
Monoammonium 11 48 0 2.44 Medium Soluble P source used in many fertilizers.
phosphate (MAP) Provides N and reduces soil pH. Preferred to
DAP when applied to alkaline soils.
Diammonium 18 46 0 2.85 Medium Soluble P source that contains higher N than
phosphate (DAP) MAP and also reduces soil pH. Can cause
significant ammonia losses on alkaline soils.
Superphosphate 0 20 0 0.46 Neutral Contains Ca (18% to 21%) and S (12%) as
Triple superphosphate 0 46 0 0.22 Neutral Concentrated P source containing Ca (13%).
aGenerally, the higher the salt index/unit of nutrient, the higher the burn potential of the particular fertilizer material.
The following formula can be used to calculate the phosphorus content of fertilizers:
As mentioned, the amount of available phosphorus in fertilizers is expressed as P205. To relate
fertilizer phosphorus content to plant phosphorus requirements, it is necessary to perform the above
Due to its low solubility in soil solution, phosphorus does not move or leach readily. Therefore,
phosphorus applications are not needed as regularly as nitrogen applications. A soil test is probably
the best indicator of the phosphorus level in a soil. Indiscriminate application of phosphorus can form
high, unhealthy levels of the element. Iron deficiencies, for example, often occur in soils high in
phosphorus and/or alkaline content. Phosphorus is most readily available to plants when soil pH
ranges from 5.5 to 6.5. At low pH levels (<5.0), soils containing iron and aluminum form an insoluble
complex with phosphorus, such that neither nutrient is readily available to the grass. For example, with
Al and/or Fe, the following reaction can occur:
Sandy soils lacking iron or aluminum, such as those on many golf greens, do not form insoluble
phosphorus complexes. Under these conditions, phosphorus is more available at a lower pH level.
In alkaline soils (pH>7.5), calcium forms insoluble complexes with phosphorus, rendering it
unavailable as dicalcium phosphate [CaHPO4]. Soil pH adjustment may be necessary to prevent the
formation of these complexes, which block the availability of applied phosphorus fertilizer.
Potassium is an essential element not normally associated with a prominent visual response
such as shoot color, density, or growth. However, it does help plants overcome some of the negative
effects of excessive nitrogen fertilization, for instance decreased tolerance to cold, heat, drought,
diseases, and wear. Since an ample supply of potassium increases plants' tolerance to these stresses,
potassium often is called the "health" element. Potassium is directly involved in maintaining plants'
water status, the turgor pressure of their cells, and the opening and closing of stomata. As potassium
concentration in plants increases, tissue water content decreases and plants become more turgid due
to potassium's regulation of stomatal opening. Because potassium provides much of the osmotic
pressure necessary to pull water into plant roots, it improves plants' drought tolerance. Cold tolerance
also is influenced by a plant's phosphorus to potassium ratio. High phosphorus to potassium ratios
in leaf tissue can increase cold temperature damage in St. Augustinegrass and bermudagrass.
The dry matter of leaf tissue consists of 1.0% to 5.0% potassium. Sufficient levels range from
1.5% to 3.0% in recently matured leaf tissue. Potassium deficiency occurs when levels are less than
1.0%, potassium excess when they are greater than 3.0%. Most plants, however, can absorb more
potassium than they need, a phenomenon often referred to as luxury consumption. An inverse
relationship also exists among potassium, magnesium, and calcium in plants. As potassium levels
increase, the first deficiencies to appear are in magnesium; at higher concentrations of potassium,
calcium deficiencies occur. In saline soils, an inverse relationship can occur in which calcium,
magnesium, or sodium ions compete with potassium for uptake by plants.
Potassium deficiency symptoms include interveinal yellowing of older leaves and rolling and
burning of the leaf tip. In later stages of deficiency, leaf veins appear yellow and margins look
scorched. The turf stand will appear thin, with a spindly growth of individual plants. Since potassium
is a mobile element within plants, it can be translocated from older leaves to younger meristematic
tissues if a shortage occurs.
Potassium fertilizer often is referred to as "potash." The name was coined by early settlers, who
produced potassium carbonate for soapmaking by evaporating water filtered through wood ashes. The
ash-like residue in the large iron pots was called potash and the first U.S. registered patent was issued
for this process.
Muriate of potash (potassium chloride), the most commonly used potassium-based fertilizer
(Table 13), is derived from potassium salt deposits that have been mined and processed. These salt
deposits, which developed on land surfaces once occupied by seawater, crystallized as the water
evaporated to become beds of potassium chloride. Potassium sulfate forms when potassium chloride
is reacted with sulfuric acid and potassium nitrate results from the reaction of potassium chloride with
nitric acid. These derivatives are used instead of potassium chloride to reduce the salt index and also
to carry sulfur and nitrogen, respectively.
Table 13. Characteristics of primary potassium sources used in turf fertilizers.
Nutrient Percentage Salt Index
per Unit of Acidifying
Source N P205 KO2 Nutrienta Effect Comment
Muriate of potash 0 0 60 1.93 Neutral Most common K source; high burn potential.
Sulfate of potash 0 0 50 0.85 Neutral Contains 17% S; used instead of KCL to
(potassium sulfate) reduce salt index and to provide S; may not
leach as rapidly as KCL
Potassium magnesium 0 0 18 Neutral Contains 11% Mg and 22% S.
Potassium nitrate 13 0 44 2.44 Basic K source with supplemental N; low salt
concentration, low chloride, fire hazard.
aGenerally, the higher the salt index/unit of nutrient, the higher the burn potential of the particular fertilizer material.
The potassium content of a fertilizer can be calculated with the following formula:
The soluble potassium portion of a fertilizer is expressed as K20. The conversion in the formula
above should be used to determine the quantity of actual potassium supplied in an application.
The form of potassium available for plant use is the potassium ion (K+), which is absorbed
primarily from the soil solution. Although other forms exist, most are unavailable for plant use.
Potassium is not readily held in sandy soils (soils low in CEC) and can be lost by leaching. This is a
problem not always appreciated, especially by growers whose grass is subjected to heavy rainfall or
watering. Soils with an appreciable clay content retain more potassium, since clay particles hold this
Potassium competes with calcium and magnesium for plant access. Soils with high levels of
either or both of these elements need additional potassium fertilization to satisfy plant needs. In sandy
soils, or where turf clippings are not returned, a 2:1 or 1:1 ratio of nitrogen to potassium may be
required to maintain an adequate potassium supply. Frequent, light potassium treatments with these
ratios should be considered with each nitrogen application.
III. Secondary Plant Nutrients
The elements calcium (Ca), magnesium (Mg), and sulfur (S) are required in almost the same
quantities as phosphorus. The functions of calcium include strengthening cell walls to prevent
collapse; enhancing cell division; encouraging plant growth; synthesizing protein; transporting
carbohydrates; and balancing cell acidity. Calcium also improves root formation and growth. Plants
use only the exchangeable calcium ion, Ca+2. Deficiencies occur most frequently in sandy soils, soils
that are extremely acidic (i.e., with pH <5.0), or soils saturated with sodium. Deficiency symptoms
include distorted appearance in young leaves; leaves that turn reddish brown along their margins
before becoming rose-red; and leaf tips and margins that wither and die. Roots are short and
bunched. An excess of calcium may bind other soil nutrients, especially phosphorus, magnesium,
manganese, iron, zinc, and boron, thereby limiting their availability to plants.
Calcium is an immobile nutrient in plants. It does not move from older leaves to new ones and
must be supplied continuously. Calcium is usually added in a liming program or by irrigating with
water high in calcium; in Florida's high-pH soils, this element occurs naturally. Commercial sources
of calcium include calcitic and dolomitic limestone, gypsum, superphosphates, shells, slags, and water
treatment residue (Table 14).
Table 14. Characteristics of primary calcium and magnesium sources used in turf fertilizers.
Nutrient Percentage Salt Index
S- per Unit of Acidifying
Source N P205 K20 Nutrienta Effect Comment
Gypsum (calcium sulfate)
-anhydrite 0 0 0 Neutral Contains 24% S and 41% calcium
oxide; has little effect on soil pH.
hydrated 0 0 0 Neutral Contains 19% S and 33% calcium
oxide; has little effect on soil pH.
Magnesium sulfate (Epsom salt) 0 0 0 Neutral Contains 13% S and 10% Mg.
Potassium magnesium sulfate 0 0 18 Neutral Contains 22% S and 11% Mg.
aGenerally, the higher the salt index/unit of nutrient, the higher the burn potential of the particular fertilizer material.
Magnesium is essential for chlorophyll production in plants. Chlorophyll molecules contain
approximately 7% magnesium. Magnesium also is essential for many energy reactions, for example,
sugar formation, and acts as a carrier of phosphorus. It also regulates the uptake of other plant
nutrients. Deficiencies occur primarily in sandy soils (soils low in CEC) or in soils with extremely high
pH levels, especially when clippings are continuously removed. Deficiencies can occur in soils with
less than 40 Ibs per acre of Mehlich-l extractable magnesium. High calcium and potassium levels also
tend to reduce magnesium uptake.
Magnesium is a mobile element in plants and is easily translocated from older to younger plant
parts as needed. Symptoms of deficiency include a general loss of green color, starting with the
bottom (young) leaves. Veins remain green; older leaf margins turn a blotchy cherry-red color with
stripes of light yellow or white between the parallel veins. Necrosis eventually develops. Sources of
magnesium include dolomitic limestone, sulfates of potash and magnesium, magnesium sulfate (Epsom
salt), oxide, and chelates (Table 14).
Sulfur is essential for selective amino acid production. It is used for building blocks of proteins
and also reduces disease incidence. Sulfur content in leaf tissue ranges from 0.15% to 0.50% of the
The sulfate anion (SO042) is the primary form available in soil solution. Like nitrate, the sulfate
ion can leach from the soil. Deficiencies may occur where grass clippings are removed, excessive
watering occurs, and sandy soils predominate. Initial deficiency symptoms include a light yellow-green
color, with yellowing most pronounced in younger leaves, since sulfur is mobile in plants. Older leaves
become pale, then turn yellowish green in interveinal areas. Leaf tips are scorched along the margins.
Roots tend to be longer than normal and stems become woody. Bermudagrass grown in sandy soils
has been shown to respond to applications of sulfur.
More than 90% of available sulfur is found in organic matter, which has a nitrogen to sulfur ratio
of approximately 10:1. Deficiencies may occur when the nitrogen to sulfur ratio is greater than 20:1
or at high soil pH levels (>7.0). Sulfur may be precipitated as calcium sulfate (CaSO4), while at lower
pH levels (<4.0) the sulfate anion may be adsorbed by aluminum and/or iron oxides. Turf clippings
with a high nitrogen to sulfur ratio ( 20:1) decompose slowly; this may slow thatch biodegradation,
since microorganisms require sulfur to decompose plant residues. Sulfur is supplied as a contaminant
in some fertilizer sources, such as superphosphate. However, many new high-analysis fertilizers
frequently do not contain appreciable sulfur.
In poorly drained, waterlogged soils where soil oxygen is exhausted, SO4-2 and organic matter
containing sulfur can be reduced to toxic hydrogen sulfide (H2S) by sulfate-reducing bacteria.
Excessive application of elemental sulfur to golf greens also may encourage hydrogen sulfide buildup.
Insoluble sulfides also may form when sulfur reacts with soil iron.
Fe+2 + S2 -----------> FeS
sulfide iron sulfide
Turf soils containing toxic levels of hydrogen sulfide or iron sulfate are acidic and commonly
form a "black layer" several inches below the soil surface. They are characterized by the distinct
hydrogen sulfide (i.e., sewer or rotten egg) smell. Low soil oxygen also can cause reductions in
manganese, copper, and iron and produce gray- and blue-colored subsoils. This phenomenon often
occurs in poorly drained soils.
As previously discussed, micronutrients are essential elements needed in relatively small
amounts (e.g., <50 ppm). Many soils in the United States supply micronutrients in large enough
quantities that there is no need for supplements. Other sources of micronutrients occur as impurities
in fertilizers. In Florida, however, soils composed of sand and peat or muck, pockets of soil with high
pH levels and high phosphorus content, poor drainage, and periods of extended, heavy rainfall
contribute to micronutrient deficiencies (Fig. 1). For example, as soil pH is increased, iron changes
from its available (soluble) ionic form to hydroxy ions and, finally, to insoluble or unusable hydroxide,
or oxide forms.
While soil pH has many effects on plants, its greatest influence is probably on the availability
of important nutrients. For example, at lower pH values (<5), aluminum, iron, and manganese are
highly soluble and actually may be present at levels toxic to plants. High levels of aluminum also can
reduce plant uptake of phosphorus, calcium, magnesium, and iron. At higher pH values (>7.0),
nutrients such as iron, manganese, copper, and zinc are less soluble; therefore, they are relatively
unavailable for plant uptake. However, molybdenum (Mo) availability actually increases at high pH
levels. Phosphorus and boron availability also may be hindered by pH values greater than 7.0 (Fig.
1). Marl may become mixed with surface organic soils or peat. Thus these normally acidic organic
soils become neutral or even alkaline due to the liming action of the marl. Many peat or muck sod
farms in south Florida have soils intermixed with marl. These soils are almost always low in magnesium
as well as in potassium, phosphorus, copper, and zinc.
Because many plant functions require more than one element, a balanced intake of
micronutrients is particularly important. Regular soil and tissue testing is the best method of preventing
many nutrient deficiency problems. Deficiencies in iron and manganese are two of the most common
encountered by Florida turf managers. However, if excessive or indiscriminate amounts of
micronutrients are applied or the soil pH value is very low, plants can suffer toxic effects. For example,
turf is sometimes grown on old vegetable or citrus production fields, which formerly were often sprayed
with fungicides containing copper, zinc, and/or sulfur. Because, with the exception of sulfur, they are
relatively immobile in soils, these residues have become toxic to turfgrasses in some cases.
Micronutrient deficiency symptoms can easily be confused with those of pest occurrence or
other stresses (Table 15). Usually, however, these problems are more localized and appear as irregular
spots or in circular patterns. Table 16 offers initial guidelines for spot treating plants by spraying
micronutrients on foliage to the drip point.
OH- OH OH-
Fe+3 -------> Fe(OH) +2--------> Fe(OH)2, -------> Fe(OH)3
(soluble tpH (hydroxy ions in neutral soils) TpH iron hydroxide
in acidic (insoluble in
soils) akaline soils)
Table 15. Forms, deficiencies, and sources of micronutrients: guidelines for turf managers.
Nutrient Deficiency Occurrence Deficiency Symptoms Fertilizer Sources
Iron (Fe) Occurs with soil pH >7.0; excessive Ca, Zn, Chlorosis resembling N deficiency, except Ferrous sulfate (19%-21% Fe and
Mn, P, Cu, and bicarbonate (HCO3) levels in that chlorosis is interveinal and first occurs 19% S); usually foliarly applied;
irrigation water; and poor rooting, poor soil in the youngest leaves, since Fe is limited acidifying effect.
drainage, and cold soils. At low soil pH, P immobile within the plant. Older leaves are
can combine with Fe to form insoluble affected later. N deficiency causes the Ferrous ammonium sulfate (5%
(unavailable) iron phosphate, while at high entire leaf, including veins, to yellow Fe, 16% S, and 7% N); usually
pH, excessive P uptake by plants may simultaneously. Leaves deficient in Fe foliarly applied; also provides
inactivate absorbed Fe. For each increase in finally turn white. Fe chlorosis tends to be some N; moderate acidifying
pH, there is a 100-fold decrease in soluble in randomly scattered spots, creating a effect.
Fe+2. Heavy metals and/or bicarbonates mottled appearance, and looks more
from effluent water or sewage sludge as soil severe when turf is mowed closely; N Chelated iron (6%-7% Fe);
amendments may compete with Fe for plant deficiency develops uniformly over a large longer greening effect than the
uptake. Deficiency symptoms are most area and appears unaffected by mowing. other Fe sources; limited
severe during warm days/cool nights, when acidifying effect.
root growth is insufficient to support shoot
Manganese Occurs in peat and muck soils (insoluble Interveinal yellowing (yellowing between Manganese sulfate (26%-28%
(Mn) complexes are formed); alkaline soils high in veins) in youngest leaves; veins remain Mn).
Ca (for each increase in pH, there is a 100- dark green to olive green color, since Mn
fold decrease in soluble Mn+2); also occurs is an immobile element within the plant;
with low temperatures; poor drainage, small, distinct necrotic leaf spots develop
Excessive Fe, Cu, Zn, K, and Na levels can on leaves; leaf tips may turn grey to white,
reduce Mn adsorption. A Fe to Mn ratio in droop, and wither. On closely mowed turf,
leaf tissue should be at least 2:1. Adjusting mottled or blotchy appearance develops;
soil pH to less than 7.0 usually reduces Mn little or no response to N occurs.
Zinc (Zn) Alkaline soils decrease solubility and Mottled, chlorotic leaves, rolled and thin Zinc sulfate (35% Zn); zinc
availability; excessive soil levels of Cu+2, leaf blades; stunted growth; dark, chelate (9%-14% Zn); zinc oxide
Fe+2, and Mn+2; high soil moisture, desiccated-looking leaves (starting with the (78% Zn).
nitrogen, and phosphate levels. Lower light youngest ones); leaves finally turn white.
intensities reduce root uptake.
Copper (Cu) Deficiency is common in peats, mucks, and Yellowing and chlorosis of leaf margins; Copper sulfate (13%-53% Cu);
highly organic soils because Cu binds tightly leaf tips initially turn bluish, wither and copper oxide (40% Cu); copper
with these. Excessive levels of Fe, N, P, and droop, eventually turn yellow and die; chelates (9%-13% Cu).
Zn and high soil pH encourage deficiency. youngest leaves become light green and
Toxic levels can result from excessive necrotic; plant dwarfing with inward rolling
applications of sewage sludge, use of poultry of leaves, which turn a blue-green color;
manures, copper sulfate, and copper- symptoms progress from the leaf tips to the
containing pesticides such as Bordeau base of the plant. Toxicity symptoms
mixture. Liming to pH 7.0 is the simplest reflecting excessive levels include reduced
means of overcoming Cu phytotoxicity. shoot vigor, poorly developed and
discolored root systems, and leaf chlorosis
resembling iron deficiency.
Boron (B) Organic matter is the principal source of B; Immobile within the plant; thickening, Borax (11% B); fertilizer borate
availability increases with decreasing soil curling, and chlorotic leaves develop on (sodium tetraborate 14%-21%
pH; deficiencies are most common in high dwarf (rosette) plants; chlorotic streaks B).
pH, leached, or very dry soils; Ca decreases develop in the interveinal areas; symptoms
translocation of B in plants. first appear in meristematic tissues.
Molybdenum Availability increases with increasing soil pH; Resembles mild N deficiency with pale Ammonium molybdate (54% Mo)
(Mo) deficiencies are most common in acid sands yellow-green, stunted plants; mottled liquid; sodium molybdate (40%
or highly weathered soils; excessive Cu, Fe, yellowing of interveinal areas then appears Mo); molybdenum trioxide
Mn or sulfate may reduce plants' utilization in older leaves. (66%).
Chlorine (CI) Less available in alkaline soils, or soils high Chlorosis of younger leaves and wilting of Ammonium chloride (66% CI);
in NO and SO4 ; very mobile in acid to plants. calcium chloride (65% CI);
neutral soils. Excessive levels reduce the magnesium chloride (74% CI);
amount of water available to plants, causing potassium chloride (47% CI);
premature leaf yellowing; leaf tip and margin sodium chloride (60% CI). Most
burning; and leaf bronzing and abscission. often applied in large quantities,
along with the potassium source
Table 16. Solution used to spot treat for micronutrient deficiencies.
Deficient Micronutrient Fertilizer Source oz/gal Ib element/1,000 sq. ft.
Fe iron sulfate 2/3 0.025
Mn manganese sulfate 1/2 0.025
Zn zinc sulfate 1/2 0.01
Cu copper sulfate 1/2 0.003
B borox 0.1 0.001
Mo sodium molybdate 0.01 0.001
Chelates, chelating agents, or sequestering agents are cyclic structures of a normally nonsoluble
metal atom and an organic component that become soluble in water when held together. However,
the activity of the metallic ion is decreased in the aqueous solution. Commercially available
sequestered metallic ions are iron, copper, zinc, and manganese. Organic compounds that have the
ability to chelate or sequester these metallic ions include ethylenediaminetetraacetic acid (EDTA);
diethylenetriaminepentaacetic acid (DTPA); cyclohexanediaminetetraacetic acid (CDTA); and
ethylenediaminedi (o-hydroxyphenylacetic acid) (EDDHA).
Sodium, aluminum, arsenic, and silicon are nonessential for turfgrass growth and development.
In general, these elements become toxic at excessive levels and should not be applied in supplemental
FOLIAR LIQUID FERTILIZATION
Foliar liquid fertilization, commonly referred to as foliar feeding, involves the use of a soluble
form of nutrients for plants. Used for more than 100 years, this practice results in more rapid nutrient
utilization and deficiency remediation than soil treatments. However, the response is often temporary.
Since plants require only small amounts of micronutrients, application of these nutrients has been the
most prominent use of foliar sprays. Applying sufficient amounts of macronutrients such as nitrogen,
phosphorus, and potassium without leaf burn also has been difficult. Other advantages and
disadvantages of using foliar liquid fertilization are listed below:
There is no particle segregation, as is common with granulars.
Foliar feeding provides nutrients directly to plants and is not influenced by soil properties.
Nutrients are water-soluble.
Co-application with pesticides is possible.
Fertilizer is generally easier to handle and more quickly applied.
Since the number of bags cannot be counted, the operator and meter must be reliable.
Some solutions may salt out at lower temperatures.
Applying sufficient quantities without causing severe leaf burn may be difficult.
Frequent applications at low rates may be necessary to promote a more lasting turf
response and prevent leaf burn.
Foliar feeding utilizes low fertilizer rates (e.g., 1/8 Ib N or Fe per 1,000 sq. ft.) at low spray
volumes (e.g., 1/2 gal per 1,000 sq. ft.). Low nutrient and spray volumes are used to minimize costs
and to supplement the normal fertilization program with nutrients absorbed directly by turfgrass leaves.
The fertilizer is washed off the leaves at higher spray volumes (e.g., 3 to 5 gal per 1,000 sq. ft.),
resulting in increased root absorption. In this process, called liquid fertilization, fertilizers and pesticides
often are applied together. Although the initial cost of spray equipment for liquid application is higher,
application of liquid fertilizer usually is less expensive than that of granulars.
Fertilization through an irrigation system is termed fertigation. Ideally, this process combines
the two operations to use resources and labor more efficiently. Frequent light applications (e.g., spoon
feedings) of fertilizer are metered into irrigation lines and distributed with irrigation water through
sprinkler heads. Nitrogen and sulfur are the primary elements applied with this method; potassium and
highly soluble forms of iron and zinc also have been used. Fertigation helps maintain a more even turf
color and growth and minimizes the occurrence of color surges that typically follow heavy granular
applications. It also reduces labor costs associated with the frequent applications required for granular
forms. Fertigation also is beneficial on sandy soils subject to nutrient leaching, since heavy fertilizer
applications are avoided.
Lack of uniform application may occur with some irrigation systems. The use of properly
designed irrigation systems and skilled operators will minimize this problem. Salt buildup on soil
surface and shallow turf rooting are other concerns associated with light, frequent fertigation
applications. The use of nitrate solution containing free ammonia or anhydrous ammonia fertilizer
materials with water high in calcium, magnesium, and bicarbonates also may result in precipitant
formation. This can scald plants and plug irrigation equipment. Sulfuric acid often is added in such
instances to prevent the formation of these precipitates.
II. Fluid Fertilizers
The three main categories of fluid fertilizers are as follows:
1. Clear liquid. These are true solutions limited to low analyses, since they will salt out at low
temperatures in high fertilizer grades.
2. Suspension fertilizer. These are mixtures of liquids and finely divided solids that do not settle
rapidly and can be redispersed readily by agitation to yield a uniform mixture. Certain types
of clays usually are added as suspending agents.
3. Slurry fertilizers. These are mixtures of liquids and finely divided solids that settle rapidly without
agitation and form a firm layer in the bottom of the tank. This layer is difficult to resuspend.
A main difference between liquid and dry fertilizers is related to phosphorus solubility. Water
solubility of phosphorus sources in dry fertilizer may vary from 30% in some highly ammoniated
superphosphates to almost 100% in diammonium or monoammonium phosphate. Therefore, granular
phosphorus fertilizers should be used to supplement fertigation fertilizers. Practically all potassium and
inorganic nitrogen sources in both fluid and dry fertilizer have a water solubility of 100%.
Manufacturing of Liquid Fertilizers
In the United States, 40% of all fertilizers are fluid, 60% solid. Mixtures applied in liquid form
total about 30 million tons, with the typical analysis being approximately 9% N, 3.9% P, and 7.5% K.
There are two general methods of manufacturing liquid-mixed fertilizers. The first and most
simplest method, known as the batch process, consists of merely dissolving solid plant-food carriers
such as ammonium phosphates, urea, or potassium chloride in water in proportions that will yield a
final product of the desired grade. The weighed constituents are dissolved in the proper amount of
water with a suitable mixing device. The solution may be heated to facilitate the dissolving process.
The relatively high cost of raw materials generally limits the use of this method to small operations or
to companies engaged in manufacturing specialty grades.
The second, most widely used method is based on neutralizing phosphoric acid with ammonia.
Anhydrous or aqueous ammonia, or ammonia-ammonium nitrate or ammonia-urea nitrogen solutions,
are reacted with phosphoric acid solutions, after which solid sources of nitrogen and/or potash are
added. Potassium chloride is the usual source of potash. The density of most common liquid mixtures
is approximately 10 Ibs per gallon.
The liquid fertilizer applied in foliar feeding enters plants directly by penetrating leaf cuticles or
stomata, then enters the cells. The method enables plants to utilize nutrients more rapidly than does
soil treatment. Research also has shown that the physical form of the nutrient, whether dry or fluid,
has no measurable effect on its agronomic value, such as the total amount of plant growth it produces.
Quickly available nitrogen sources denote rapid availability of nitrogen to turfgrass plants following
fertilizer application. These quickly available nitrogen sources have a high potential for foliar burn due
to their salt-like characteristic of dissolving readily in water to form cations (positive ions) and anions
(negative ions). When these hydrophilic (water-loving) ions are in direct contact with the leaf surface,
they quickly absorb moisture from the plant, giving it a brown, burned appearance. The more free
cations and anions there are in soil solution or on the plant surface, the greater the potential for
fertilizer burn. This problem arises when quickly available liquid nitrogen forms, generally in excess of
1 Ib N per 1,000 sq. ft., are used. Most reports recommend that foliar fertilization occur during periods
of low temperature and relatively high humidity, in the early morning or late evening. Hopefully, new
liquid fertilizer technology will minimize some of these problems.
Because of its water solubility, urea is the most widely used fertilizer material; often it is mixed
with ammonium nitrate or potassium nitrate. Liquid urea is characterized by a quick turf color response
and a medium-to-high burn potential. Frequent application of low rates of liquid urea is required to
promote even turf growth and color and to minimize burn potential. A fine, powdered form of UF also
can be used for liquid fertilization.
An aqueous nitrogen solution marketed as Formolene contains more than half its nitrogen as
monomethylol urea and the remainder as free urea and ammonia. Formolene is a 30-0-2 formulation
containing 3-1/4 Ibs nitrogen per gallon. This is basically a soluble nitrogen source.
III. Slow-Release Sources
Several new materials with better slow-release characteristics are now commercially available.
These materials allow less frequent applications at heavier rates without undesirable surges in growth
or color; they also minimize turf foliar burn potential.
CoRoN. CoRoN is an aqueous solution of many polymethylene ureas and amine modified
polymethylene ureas. CoRoN consists primarily of a straight-chain, amine-modified polymethylene urea
containing two to four urea units; this accounts for approximately 30% of CoRoN's nitrogen content.
Small amounts of methylene diurea and dimethylene triurea are also present; however, the solution
contains no cyclic urea formaldehyde products, such as triazones. No free ammonia and little methylol
urea are included. CoRoN contains a small amount of sodium bicarbonate to protect its near-neutral
pH and sufficient water to safely maintain its 28-0-0 formulation in water. While CoRoN depends on
microbial action for nitrogen release, it has been shown to be effective in the winter due to its relatively
high urea content. Although it tends not to last as long as dry slow-release nitrogen sources, its initial
greenup is quicker.
N-Sure. N-Sure is a liquid nitrogen fertilizer containing triazones and urea in a 0.48:1.0 ratio. N-Sure
may contain 6% methylene diurea and methylol urea by weight. Triazones are stable heterocyclic
nitrogen-carbon ring compounds typically formed under low pH conditions from urea, formaldehyde,
and ammonia. N-Sure contains 30% nitrogen and its nitrogen release rate is microbe-dependent. It
has been demonstrated to be effective during cool weather; however, turf response is not as long-
lasting as with solid, slow-release nitrogen sources.
FLUF. FLUF is another slow-release nitrogen solution source. It consists of cold-water soluble free
urea and methylene diurea, cold-water insoluble, hot-water soluble polymethylene ureas, and small
amounts of hot-water insoluble polymethylene ureas.
A simple irrigation delivery system is probably the best choice for fertilizer application. Such
a system consists of a fiberglass or plastic storage tank with a visual volume gauge, a filter, and an
adjustable corrosion-resistant pump to inject fertilizer into the main irrigation line. If a centrifugal pump
is used for irrigation, the injection pump can be eliminated. Fertilizer is drawn into the suction side of
the irrigation pump, so that some fertilizer is applied with each irrigation. If the injection pump supplies
fertilizer at a constant rate, the irrigation system must be well balanced, with each zone covering
approximately the same land area to ensure that the fertilization rate is also constant. The exception
would be certain areas where it is desirable to fertilize at a heavier rate. Proportioning systems have
been developed that maintain a constant ratio between the volume of liquid fertilizer injected and the
volume of irrigation water applied.
To operate the system, the amount of nitrogen and other nutrients needed per unit of turf area
per unit of time (e.g., Ibs N per 1,000 sq. ft. or per acre applied per month) must be determined. The
rate at which the injection pump must operate can be determined from the concentration of the fertilizer
solution. If necessary, this rate can be adjusted to compensate for unusually high or low amounts of
rainfall that affect irrigation requirements. The visual gauge on the fertilizer tank helps determine how
well the fertilization schedule is being maintained, since the time needed to empty the tank (e.g., a
week, a month, etc.) can be determined in advance. Heavily used areas such as tees and greens often
require greater nitrogen rates than fairways. Various methods can be devised for increasing the rate
of fertilizer applied by irrigation systems on these areas. Such complications, however, may cause
excessive work and more problems. In most cases, fertigation is probably best used to supply a
uniform rate of nitrogen to the entire golf course and traditional granular applications to augment
fertilization on relatively small, heavily used green and tee areas.
Foliar application of micronutrients, notably iron, is commonly employed with foliar fertilization.
All micronutrients except boron and chloride are metals; for all but molybdenum, availability tends to
decline with increasing soil pH. Chloride is unaffected by soil pH. In general, micronutrient fertilizers
may be characterized as being more expensive than macronutrient materials. Usually, however,
micronutrient application rates are low enough that foliar application is feasible. Adding zinc, iron,
manganese, and copper to clear liquid fertilizers is potentially problematic, since precipitation often
occurs when these micronutrients react with phosphates. Chelates of the metal micronutrients can be
mixed with liquids without causing precipitation.
Nitrogen also is added to many micronutrient products to stabilize the solutions. Because
micronutrient solutions can retain elements at higher temperatures, they may become supersaturated.
Upon cooling, micronutrients in the solution may precipitate, forming insoluble compounds. Urea has
been shown to help prevent precipitation and also gives turf a small color boost.
REFERENCES AND ADDITIONAL READING
Bohn, H. L., B. L. McNeal, and G. A. O'Conner. Soil Chemistry. 2d ed. New York: John Wiley and
Brady, N. C. The Nature and Properties of Soils. New York: Macmillan Publishing Co., 1984.
Duble, R. L. Southern Turfgrasses: Their Management and Use. College Station, Texas: TexScape, Inc.,
Emmons, R. D. Turfgrass Science and Management. Albany, N.Y.: Delmar Publishers, Inc., 1984.
Jones, J. B., Jr., B. Wolf, and H. A. Mills. Plant Analysis Handbook. Athens, Ga.: Micro-Macro
Publishing, Inc., 1991.
Kidder, G., and R. D. Rhue. Interpretation of Micronutrient Soil Tests, 1-2. Notes in Soil Science, No.
9. University of Florida Department of Soil Science, 1983.
Sartain, J. B. General Recommendations for Fertilization of Turfgrasses on Florida Soils, 1-4. Soil
Science Fact Sheet, SL-21. University of Florida Department of Soil Science, 1981.
Sartoretto, P. The pH Factor, 1-4. Somerset, N.J.: W. A. Cleary Chemical Corp;,, 1991.
Snyder, G. H. "Fertigation for Managing Turf Nitrogen Nutrition." Proc. GCSAA 50th Inter. Turf. Conf.
and Show (1979): 163-67.
Snyder, G. H., and B. J. Augustin. "Managing Micronutrient Appltdation' on Florida Turfgrass." In
Advances in Turfgrass Fertility, edited by B. J. Joyner; 149-79.,.,Columbus, Ohio: ChemLawn Corp.,
Tisdale, S. L., W. L. Nelson, and J. D. Beaton. Soil Fertility and Fertilizers. eNew York: Macmillan
Publishing Co., 1985.
Turgeon, A. J. Turfgrass Management. Englewood Cliffs, N.J.: Prentice-Hall, 1991.
Turner, T. R., and N. W. Hummel, Jr. "Nutritional Requirements and Fertilization." In Turfgrass,
Agronomy Monograph Series 32, edited by D. V. Waddington, R. N. Carrow, and R. C. Shearman,
382-439. Madison, Wis.: Am. Soc. Agron., Crop Sci. Soc. Am., and Soil Sci. Soc. Am., 1992.
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES, John T. Woeste,
Director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and June
30,1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institutions that
function without regard to race, color, sex, age, handicap or national origin. Single copies of extension publications (excluding 4-H and youth
publications) are available free to Florida residents from county extension offices. Information on bulk rates or copies for out-of-state purchasers
isavailable from C.M. Hinton, Publications Distribution Center, IFAS Building664, Universityof Florida, Gainesville, Florida32611. Before publicizing
this publication, editors should contact this address to determine availability. Printed 10/93.