General Recommendations for Fertilization of Turfgrasses on Florida Soils1
In many neighborhoods, people envy the individual with the most beautiful lawn and think they cannot grow a lawn of equal quality. That is not necessarily true. A well-maintained lawn only requires some knowledge about fertilization, watering, pest control and mowing. This publication provides basic information about fertilization. By far, the best approach to a proper fertilization program is to start with a soil test, but, if a soil test is not available, these guidelines can be used for a general turfgrass fertilization program.
Essential Elements
All plants require certain chemical elements for proper growth and appearance. Of these nutrients, at least 16 are known to be essential elements. Table 1 lists the 16 known elements and the sources from which plants obtain them. All essential elements except carbon, hydrogen, and oxygen are obtained from the soil and absorbed by plant roots. If inadequate nutrients are available in the soil, turfgrass growth and quality may be limited. However, essential elements can be added to a soil through fertilizer applications.
Essential elements required by lawngrasses.
From Air/Water |
------ From Soil ------ |
|
Macronutrients |
Micronutrients |
|
Carbon |
Nitrogen | Iron |
Hydrogen |
Calcium |
Copper |
| Oxygen | Phosphorus | Manganese |
| Magnesium | Molybdenum | |
| Potassium | Zinc | |
| Sulfur | Boron | |
| Chlorine | ||
Turfgrasses require the macronutrients nitrogen (N), phosphorus (P), and potassium (K) in greatest quantities. Calcium, magnesium, and sulfur are required in smaller quantities. The micronutrients iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), chlorine (Cl), molybdenum (Mo), and boron (B) are required in very minute quantities. Micronutrients are as essential as the macronutrients, but are required in much smaller amounts.
Types of Fertilizers
Fertilizers are identified by analysis and/or brand name. Many common commercial fertilizers are known by their grade, such as 16-4-8, 10-10-10, or 6-6-6. A complete fertilizer contains N, P and K. The numbers indicate the percentage of each of these nutrients. A 16-4-8 fertilizer, for example, contains 16% Total Nitrogen, 4% Available Phosphorus expressed as P2O5 and 8% Soluble Potash expressed as K2O. Thus a 100-pound bag of 16-4-8 would contain 16 pounds of total N, 4 pounds of available phosphate, and 8 pound of potash. These three constituents, N, P, and K, are called the primary plant foods; if all three are present, the fertilizer is referred to as a complete fertilizer. Complete fertilizers, such as 16-4-8, 12-4-8, 10-10-10, and 6-6-6, are commonly used in turfgrass fertilization. Besides the primary elements (N, P and K) the fertilizer may contain secondary plant foods. The secondaries may include Ca, Mg, sulfur (S), Mn, Zn, Cu, Fe and Mo.
Both primary and secondary elements, if present, are listed on the fertilizer label. The label also tells the materials from which the fertilizer has been made. This information appears below the “derived from” statement. An example of a mixed fertilizer containing several different sources of N is shown in Figure 1.
Example of a fertilizer label.
In addition to complete fertilizers, some materials are used almost exclusively to supply N to turfgrasses for rapid growth and dark green color. These materials include soluble forms of N ; ammonium nitrate (34% N), ammonium sulfate (21% N), urea (46% N), calcium nitrate (15.5% N), potassium nitrate (13% N & 44% K2O) and slow-release N sources; Ureaformaldehyde (38% N), Isobutylidene diurea (31% N), Sulfur-coated urea (36-39% N), Nutralene (40% N), and Polyon (40-43% N). Turfgrasses commonly require higher rates and more frequent applications of N source fertilizers than other nutrient sources. In most cases, slow-release N sources can be used to reduce the potential for leaching losses of applied N. In order to obtain the desired growth and color response in most cases, a 70/30 mixture of soluble and slow-release N sources is recommended for use on turfgrasses. It should be pointed out that turfgrasses are one of the most N absorbing efficient ground covers that one can use. When fertilized at the recommended rate and frequency, N leaches very sparingly, if at all, from the turfgrass system. Poor quality, slow-growing and improperly fertilized turfgrasses actually leach much more N than do turfgrasses growing at optimum levels. A quality turfgrass furnishes a complete and uniform cover of the soil surface. The highest quality turfgrass is not necessarily the darkest green or most rapidly growing turfgrass, but the turfgrass that has acceptable color and density without excessive growth. Excess N application can lead to a dark green turfgrass that is growing at excessive rates which will require more frequent mowing and possibly result in contamination of the ground water with nitrate nitrogen.
For Florida turfgrasses, the best yearly fertilization program usually includes a combination of one or two applications of multiple nutrient fertilizations and several supplemental applications of a N fertilizer. Nitrogen fertilization is often based on the desired growth rate and type of turfgrass being grown. Due to past fertilization and the inherent nature of some placeStateFlorida soils, P fertilization is not always required. One should depend on a recent soil test to determine if P is required for optimum turfgrass growth. If your soil test indicates an adequate level of extractable soil P, choose a fertilizer blend that does not contain P as one of the supplied nutrients. That blend would be represented by an X-O-X, such as 15-0-15. Excess P application can result in enrichment of the P status of run-off or leachate waters, and in the euthrophication of adjacent water bodies. Second only to N in total fertilization requirement is K. Potassium influences root growth and water and stress tolerance relationships in turfgrasses and should be maintained at adequate levels for optimum growth. In most turfgrass growth systems, the potassium fertilization program should be based on a recent soil test. Potassium is highly mobile in most of Florida's sandy soils, but an annual soil test is adequate for determining the K fertilization requirement of most turfgrasses grown in the State.
Fertilizer Application
Most fertilizers are applied at a rate determined by the type and amount of nitrogen present in the material. Nitrogen is the nutrient most used by a turfgrass and often the material that burns the turfgrass if applied at excessive rates.
In the past, it was customary to recommend the application of 1 pound of actual nitrogen per 1000 square feet of turfgrass. In light of potential environmental concerns it is now recommended that no more than one half (0.5) pound of the nitrogen in the application be in the soluble form. Thus in order to make an application of 1 pound of actual nitrogen per 1000 square feet of turfgrass you would need to use a blended fertilizer product containing no more that 50% of the total N in soluble form with the rest of the nitrogen originating from a slow-release N source. The pounds of actual N in every fertilizer can be determined by dividing the percent N listed on the label into 100. For example, if applying soluble N from ammonium sulfate, divide 21% (the N content of ammonium sulfate) into 100 to find the number of pounds of ammonium sulfate that will supply 1 pound of N. Since 100 divided by 21 equals approximately five, five pounds of ammonium sulfate would supply one pound of N. Therefore, to apply the equivalent of 0.5 pounds of soluble N per 1000 square feet of turfgrass surface, one would need to apply 2.5 pounds of ammonium sulfate.
Several fertilizer materials are listed in Table 4, and the rate of application for 0.5 pounds of N is already calculated. For example, if using ammonium nitrate on a turfgrass, note that the table lists the rate of application at 1.5 pounds of material per 1000 square feet to apply the equivalent of 0.5 pounds of N. Therefore, if you have a 5000 square foot lawn use 7.5 pounds of ammonium nitrate.
When a soil test of a turfgrass area is not available, Table 5 can be used as a guide for turfgrass fertilization programs at three levels of maintenance for each type of turfgrass for three regions of the state. Note that most programs use a combination of complete fertilizers and nitrogen fertilizers applied during different times of the year. Recall that the complete fertilizer should only be used when the soil test calls for both P and K. When P is not required apply only those nutrients which are recommended by the soil test report.
One program is a basic, or low-maintenance, recommendation that will produce only a minimum quality turfgrass. The second program is a moderate maintenance program which should produce an intermediate-quality turfgrass. The high maintenance program should produce an optimum quality turfgrass with good color and growth characteristics, and should not result in nitrogen leaching losses if the recommendations are followed. The best schedule is the one that produces the quality of turfgrass the individual desires.
To use Table 5, find the particular turfgrass and part of the state that applies to you, then apply the fertilizer indicated during the month(s) recommended. For rates of various materials, refer to Table 4. For example, to obtain a high quality Centipedegrass lawn in Gainesville (central Florida), apply a complete fertilizer (C) like a 16-4-8, 10-10-10, or 6-6-6 (depending on whether or not P and K are recommended by the soil test) in March and September, then apply a slow-release N material like sulfur-coated urea or Milorganite in May. Rates for individual N fertilizer materials are given in Table 4, and the rate for a complete fertilizer is shown at the bottom of the fertilization chart (Table 5).
Organic vs Inorganic Fertilizers
There is much confusion over whether to use organic or inorganic fertilizers on turfgrasses. Both types have advantages and disadvantages; however, the type of fertilizer makes no difference to the turfgrass. Grasses absorb N as nitrate- or ammoniacal-N. Organic N is not used directly by the plant but must first be converted to one of the above chemical forms by soil microorganisms before being taken up by the plant.
The advantages and disadvantages of organic or chemical fertilizers relate to the consumer, not the turfgrass. Inorganic N fertilizers have advantages and disadvantages as listed in Table 2.
Advantages and disadvantages of inorganic nitrogen fertilizer sources.
Inorganic Nitrogen Sources |
|
Advantages |
Disadvantages |
Readily available N |
Leach readily |
Low cost per pound of N |
Danger of fertilizer burn |
| Easily controlled N levels | High salinity potential |
| Little problem of residual N | Must be applied frequently at low rates |
Organic N fertilizers also have advantages and disadvantages that are listed in Table 3. Select a N source after considering the pros and cons of the various forms. A mixture of the two will most likely result in the best response.
Advantages and disadvantages of organic nitrogen fertilizer sources.
Organic Nitrogen Sources |
|
Advantages |
Disadvantages |
Slow-release of N |
May be very expensive per pound of N |
Less subject to leaching loss |
Not released at adequate rate during cool season |
Small danger of turfgrass burn |
Application response may be slow |
May be applied infrequently at high rates |
May contain weed seeds that contaminate turfgrass |
Supplemental Iron Application
Many times turfgrasses, such as Centipedegrass, Bahiagrass and St. Augustinegrass, turn yellow during the summer due to lack of N fertilizer. However, fertilization with N in the summer is not always desirable since this often encourages disease and insect problems. Many times the addition of iron (Fe) to these grasses provides the desirable dark green color, but does not stimulate excessive grass growth which follows N fertilization. Usually, iron sulfate (2 ounces per 3 to 5 gallons of water per 1000 square feet) or a chelated iron source are used to provide this greening effect. The effect from supplemental iron application is only temporary (approximately 2 to 4 weeks), therefore, repeat applications are necessary for summer-long color.
Precautions
All soluble fertilizers may burn the turfgrass if improperly applied. To avoid burn, never apply fertilizer at greater than the recommended rate of 0.5 pounds of soluble N per 1000 square foot per application. If only slow-release N materials are used up to 3 pounds of N can be applied in a single application. Apply P and K only when required based on a recent soil test and do not exceed the recommended rate of application, especially for P. Always apply fertilizers when the turfgrass leaves are dry and water thoroughly after application. Apply enough water to dissolve the fertilizer and move it below the surface. This can generally be accomplished by applying between 1/4 and 1/2 inch of water through the irrigation system which can usually be accomplished by running a typical turfgrass irrigation system for 15 to 20 minutes. Excess irrigation may leach the soluble N below the root zone so great care should be taken not to water too little or too much.
Tables
A guide to rate of fertilizer material to use on Florida turfgrass.
Nitrogen Fertilizers |
%N |
Pounds needed to supply 0.5 pounds of actual N per 1000 sq ft |
|
Soluble N Sources (Inorganic) |
|||
Ammonium Nitrate |
33.5 | 1.5 |
|
Ammonium Sulfate |
20 |
2.5 |
|
Calcium Nitrate |
15.5 | 3.2 | |
Potassium Nitrate |
13-0-44 |
3.8 also 1.7 lbs K2O |
|
| Sodium Nitrate | 16 | 3.1 | |
Nitrate of Soda-Potash |
15-0-16 | 3.3 also 0.5 lbs K2O |
|
Monoammonium Phosphate |
11-48-0 | 4.5 also 2.2 lbs P2O5 |
|
Diammonium Phosphate |
18-46-0 | 2.8 also 1.3 lbs P2O5 |
|
Soluble N Sources (Organic) |
|||
Urea |
45 |
1.1 |
|
Calcium Cyanamide |
21 | 2.4 |
|
Slow-Release N Sources (Synthetic) |
|||
| Ureaform/Nitroform | 38 | 1.3 | |
| Nutralene | 40 | 1.25 | |
| Isobutylidene diurea (IBDU) | 31 | 1.6 | |
| Sulfur-coated Urea | 38 | 1.3 | |
| Polyon | 42 | 1.2 | |
Slow-Release N Sources (Natural Organics) |
|||
| Sewage Sludge | 6-2-0 | 8.3 also 0.2 lbs P2O5 |
|
Cow Manure |
2-0-0 |
25 | |
Poultry Manure |
4-0-0 | 12.5 | |
Cottonseed Meal |
7 | 7.1 | |
Alfalfa Meal |
6 | 8.3 | |
Blood Meal |
3-22-0 |
16 also 3.7 lbs P2O5 |
|
Processed Tankages |
5-10 (varies) | 10 to 5 | |
Garbage Tankages |
2-3 (varies) | 20 to 15 |
|
Some Commercial Sources of Potassium and Phosphorus Fertilizers |
|||
Pounds needed to supply 0.5 lbs of actual Potash or Phosphate per 1000 sq ft |
|||
Potassium Chloride (Muriate of Potash) |
60% K2O |
0.83 | |
| Potassium Sulfate | 50% K2O |
1 | |
Potassium Nitrate |
13-0-44 | 1.1 also 0.1 lbs N | |
| Sulfate of Potash Magnesia | 22% K2O, 11% Mg, 8% S |
2.2 also 0.2 lbs Mg & S | |
| Concentrated Superphosphate | 46% P2O5 |
1 | |
Fertilization guide for turfgrasses maintained without the benefit of a soil test.*
Turfgrass |
Maintenance Level |
Jan |
Feb |
Mar |
Apr |
May |
Jun |
Jul |
Aug |
Sep |
Oct |
Nov |
Dec |
North Florida** |
|||||||||||||
Bahiagrass |
Basic | -- |
-- |
C |
-- |
-- |
-- |
-- |
-- |
C |
-- |
-- |
-- |
Moderate |
-- |
-- |
C |
-- |
SRN |
-- |
-- |
-- |
C |
-- |
-- |
-- |
|
High |
-- |
-- |
C |
-- |
SRN |
-- |
Fe |
-- |
C |
-- |
-- |
-- |
|
Bermuda- grass |
Basic |
-- |
-- |
C |
-- |
SRN |
-- |
-- |
-- |
C |
-- |
-- |
-- |
Moderate |
-- |
-- |
C |
-- |
SRN |
-- |
SRN |
-- |
C |
-- |
-- |
-- |
|
High |
-- |
-- |
C |
SRN |
C |
-- |
SRN |
Fe |
C |
-- |
-- |
-- |
|
Centipede- grass |
Basic |
-- |
-- |
-- |
C |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
Moderate |
-- |
-- |
-- |
C |
Fe |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
|
High |
-- |
-- |
-- |
C |
SRN |
-- |
Fe |
-- |
-- |
-- |
-- |
-- |
|
St. Augustine- grass |
Basic |
-- |
-- |
C |
-- |
-- |
Fe |
-- |
-- |
C |
-- |
-- |
-- |
| Moderate | -- |
-- |
C |
-- |
SRN |
-- |
Fe |
-- |
C |
-- |
-- |
-- |
|
High |
-- |
-- |
C |
-- |
SRN |
Fe |
SRN |
-- |
C |
-- |
-- |
-- |
|
Zoysiagrass |
Basic |
-- |
-- |
C |
-- |
SRN |
-- |
-- |
-- |
C |
-- |
-- |
-- |
Moderate |
-- |
-- |
C |
-- |
SRN |
-- |
SRN |
-- |
C |
-- |
-- |
-- |
|
High |
-- |
-- |
C |
N |
SRN |
-- |
SRN |
-- |
C |
-- |
-- |
-- |
|
Central Florida |
|||||||||||||
Bahiagrass |
Basic |
-- |
-- |
C |
-- |
N |
-- |
-- |
-- |
C |
-- |
-- |
-- |
Moderate |
-- |
-- |
C |
-- |
N |
-- |
Fe |
-- |
-- |
C |
-- |
-- |
|
High |
-- |
-- |
C |
N |
-- |
SRN |
-- |
Fe |
-- |
C |
-- |
-- |
|
Bermuda- grass |
Basic |
-- |
-- |
C |
-- |
N |
-- |
SRN |
-- |
C |
-- |
-- |
-- |
Moderate |
-- |
-- |
C |
-- |
N |
-- |
SRN |
-- |
SRN |
-- |
C |
-- |
|
High |
-- |
-- |
C |
N |
SRN |
-- |
C |
Fe |
SRN |
-- |
C |
-- |
|
Centipede- grass |
Basic | -- |
-- |
C |
-- |
SRN |
-- |
-- |
-- |
-- |
-- |
-- |
-- |
| Moderate | -- |
-- |
C |
-- |
SRN |
-- |
-- |
Fe |
-- |
-- |
-- |
-- |
|
| High | -- |
-- |
C |
-- |
SRN |
-- |
-- |
-- |
C |
-- |
-- |
-- |
|
St. Augustine- grass |
Basic |
-- |
-- |
C |
-- |
-- |
-- |
Fe |
-- |
C |
-- |
-- |
-- |
Moderate |
-- |
-- |
C |
-- |
SRN |
-- |
Fe |
SRN |
-- |
C |
-- |
-- |
|
High |
-- |
C |
-- |
N |
SRN |
-- |
Fe |
SRN |
-- |
C |
-- |
-- |
|
Zoysiagrass |
Basic |
-- |
-- |
C |
-- |
SRN |
-- |
-- |
-- |
C |
-- |
-- |
-- |
Moderate |
-- |
-- |
C |
-- |
SRN |
-- |
-- |
SRN |
-- |
-- |
C |
-- |
|
High |
-- |
C |
-- |
N |
SRN |
-- |
SRN |
-- |
N |
-- |
C |
-- |
|
South Florida |
|||||||||||||
Bahiagrass |
Basic |
-- |
C |
-- |
-- |
-- |
Fe |
-- |
-- |
-- |
C |
-- |
-- |
Moderate |
-- |
C |
-- |
N |
-- |
Fe |
-- |
-- |
-- |
C |
-- |
-- |
|
High |
-- |
C |
-- |
N |
-- |
SRN |
-- |
-- |
-- |
C |
-- |
-- |
|
Bermuda- grass |
Basic |
-- |
C |
-- |
N |
-- |
SRN |
-- |
-- |
C |
-- |
C |
-- |
Moderate |
-- |
C |
N |
-- |
C |
-- |
SRN |
-- |
SRN |
-- |
C |
-- |
|
High |
-- |
C |
N |
SRN |
C |
SRN |
Fe |
-- |
SRN |
-- |
C |
-- |
|
Centipede- grass |
Basic |
-- |
-- |
C |
-- |
-- |
Fe |
-- |
-- |
-- |
C |
-- |
-- |
Moderate |
-- |
C |
-- |
SRN |
-- |
-- |
-- |
-- |
-- |
C |
-- |
-- |
|
High |
-- |
C |
-- |
SRN |
-- |
Fe |
-- |
-- |
-- |
C |
-- |
-- |
|
St. Augustine- grass |
Basic |
-- |
-- |
C |
-- |
SRN |
-- |
SRN |
-- |
-- |
C |
-- |
-- |
| Moderate | -- |
C |
-- |
N |
-- |
SRN |
-- |
SRN |
-- |
-- |
C |
-- |
|
High |
-- |
C |
-- |
N |
SRN |
-- |
SRN |
-- |
SRN |
-- |
C |
-- |
|
Zoysiagrass |
Basic |
-- |
-- |
C |
-- |
SRN |
-- |
SRN |
-- |
-- |
C |
-- |
-- |
Moderate |
-- |
C |
-- |
N |
-- |
SRN |
-- |
SRN |
-- |
-- |
C |
-- |
|
High |
-- |
C |
-- |
N |
SRN |
-- |
SRN |
-- |
SRN |
-- |
C |
-- |
|
* This guide is for turfgrass fertilization under circumstances where a soil test does not exist. In order to properly apply the rate of P and K required, a soil test is required. It is recommended to always soil test. ** The arbitrary dividing line between north and central Florida is a straight east-west line from coast to coast through Ocala, and the dividing line between central and south Florida is a line from coast to coast through Tampa and Vero Beach. C = Complete fertilizer applied at 1.0 lbs N/1000 sq ft containing 50% soluble and 50% slow-release N. N = Soluble N applied at 0.5 lbs N/1000 sq ft. SRN = Slow-release N applied at 1.0 lbs N/1000 sq ft. Fe = Apply Fe to provide dark green color without stimulating excessive growth. For foliar application use ferrous sulfate (2 oz /3-5 gal water/1000 sq ft). If the Fe is applied to an acidic soil, use one pound of iron sulfate per 1000 square feet. If the soil is calcareous, use the container label recommended rate of an iron chelate. |
|||||||||||||
Footnotes
This document is SL 21, one of a series of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date May, 1991. Revised May, 2007. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.
J.B. Sartain, professor, Turfgrass Fertility, Soil and Water Science Department, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611-0510.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal
Opportunity Institution authorized to provide research, educational
information and other services only to individuals and institutions
that function with non-discrimination with respect to race, creed,
color, religion, age, disability, sex, sexual orientation, marital
status, national origin, political opinions or affiliations.
For more information on obtaining other extension publications,
contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service,
University of Florida, IFAS, Florida A. & M. University Cooperative
Extension Program, and Boards of County Commissioners Cooperating. Millie Ferrer-Chancy,
Interim Dean.
