HomeMy WebLinkAboutBest Management Practice Fertilization for Nantucket_201401221138346671Best Management Practice
for
Turf, Tree, and Shrub Fertilization
on
Nantucket Island
February, 2003
Prepared by the Nantucket Landscape Association,
Bartlett Tree Experts and the University of Maryland
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Overview
In 2002, the Nantucket Board of Selectmen and Board of Health have identified the
protection of Nantucket Harbor, and the water quality of the island as the number one
priority for local government on the island of Nantucket, Massachusetts. Naming water
quality protection as a priority comes after a decade of studies have shown possible
nitrate leaching into Nantucket Harbor. While nitrate leaching comes primarily from
septic system run off, both road salt and fertilizer use can contribute to the problem.
In an effort to better understand this environmental concern, The Nantucket Landscape
Association contacted scientists from the University of Maryland, and the Bartlett Tree
Research Laboratories in Charlotte, North Carolina. For several months, a team of
scientists from the University of Maryland, who were involved in the research to protect
the Chesapeake Bay Watershed from nitrate and phosphate pollution, reviewed and
analyzed all pertinent data on Nantucket. In conjunction with the scientists from the
Bartlett Tree Research Laboratories, soil samples of Nantucket were processed, studies
from the Nantucket Golf Course were reviewed, and independent laboratories were sent
data to analyze the results.
Once the review of data was complete, the scientists provided a summary report to the
Nantucket Landscape Association, and the Nantucket Board of Health. This report
provided an overview of all previous reports on the topic, and it provided a recommended
course of action for the professional landscapers on Nantucket to follow in order to assist
the Board of Health with the goal of protecting Nantucket’s watershed. In addition to
providing this report, the scientists from the University of Maryland and the Bartlett Tree
Research Laboratories formally presented their findings at a meeting of the Board of
Health and other island officials in an effort to help all concerned parties understand the
science behind nitrate leaching. At the end of this meeting, the Nantucket Landscape
Association made a commitment to the Board of Health that they would adopt the
fertilization practices recommended by the University of Maryland scientists, which will
substantially reduce the potential for nitrate leaching due to lawn, tree and shrub
fertilization.
To obtain this goal, The Best Management Practice for Turf, Tree, and Shrub
Fertilization on Nantucket was developed. Even though the potential for nutrient runoff
due to fertilization is only a fraction of the concern as compared to the septic system
issue, the Nantucket Landscape Association pledged to do its part to protect the
watershed on the island. This Best Management Practice (BMP) provides guidelines for
landscape fertilization on the environmentally sensitive island of Nantucket, which will
significantly reduce the nutrient input into Nantucket Harbor caused by fertilization.
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Review Committee
Dr. Kevin Mathias, The University of Maryland, Maryland Cooperative
Extension, Turfgrass Extension Specialist
Dr. E. Thomas Smiley, Arboricultural Researcher, Bartlett Tree Experts, Adjunct
Professor, Clemson University
Professor Stanton Gill, The University of Maryland Cooperative Extension
Mr. David Marren, Esquire, Director of Regulatory Affairs, Bartlett Tree Experts
Mr. Michael Misurelli, President, Nantucket Landscape Association
Mr. Martin McGowan, President, Sconset Gardener, Inc.
Mr. Philip Day, President, Nantucket Landscapes, Inc.
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Index
Purpose Page 4
Fertilization of Turfgrass Page 5
Turfgrass Selection Page 5
Soil Nutrient Analysis Page 5
Fertilizer Ratio Page 5
Fertilizer Rates Page 6
Application Timing Page 6
Soil pH Adjustment Page 6
Watering After Fertilization Page 7
Mowing Height Page 7
Soil Aeration Page 7
Organic Matter Incorporation Page 7
Dethatching Page 7
Fertilization of Trees and Shrubs Page 8
Determining Goals and Objectives Page 8
Soil Testing and Plant Analysis Page 8
Foliar Analysis Page 9
Soil Analysis Page 9
Soil Organic Matter Page 10
Cation Exchange Capacity Page 10
Soil Sampling and Analysis Page 10
Fertilizer Selection Page 10,11,12
Salt Index Page 12
Fertilizer Timing Page 12
Fertilizer Application Page 13
Fertilizer Application Area Page 14
Fertilizer Application Area Calculations Page 14,15
Fertilizer Rates Page 15,16
Calibrating Fertilizer Applicators Page 16
About the Authors Page 17
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Purpose
Fertilization may be required on residential and commercial landscapes on Nantucket to
improve the health and longevity of the landscape plants. Without landscape plants,
erosion and other degradation would seriously harm the environment of Nantucket.
However, when fertilizer is applied it should be done using sound techniques, backed by
scientific research, in order to avoid over applications that could lead to environmental
degradation.
This manual provides the landscape managers with information regarding the selection of
turf species, the need for a soil nutrient analysis, fertilizer rates and ratios, the importance
of soil pH adjustment, the influence that watering, mower height, soil aeration, organic
matter, and dethatching can have on reducing nutrient runoff. In addition, practices are
set forth for the fertilization of trees and shrubs.
The purpose of this Best Management Practices is to provide members of The Nantucket
Landscape Association with scientifically researched guidelines to follow in the course of
the fertilization to turf, trees, and shrubs on the island of Nantucket.
Adherence to this document will substantially minimize the potential for nutrient runoff.
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Fertilization of Turfgrass
Introduction
Turf on Nantucket provides many benefits beyond the obvious benefit of aesthetics. It
holds the soil against the forces of wind, acts as a biological filter, it provides a play
surface for families and games, and establishes the basis for many landscapes.
To provide a maximum level of environmental benefit, turfgrass should be maintained on
a regular basis. Following are cultural practices that will provide a high level of benefits
with a minimum of nutrient input.
Turfgrass Selection
Kentucky bluegrass is the predominant lawn grass planted on Nantucket. This species
requires higher levels of nitrogen fertilization (3-4 lbs of N/1,000 sq.ft./Yr). The possible
use of the fine leaf fescues such as hard fescue, sheep fescue and the red fescues in lawn
turf should be further investigated for lower maintenance lawn and turfgrass sites. These
grasses require lower nitrogen requirements (1-2 lbs N/1,000 sq. ft/Yr) and can survive
under lower soil pH conditions.
Soil Nutrient Analysis
Prior to fertilization a soil sample should be collected for nutrient analysis. The analysis
can be conducted by either the University of Massachusetts soil analysis laboratory or a
private laboratory. The analysis should provide data on at least phosphorus, potassium,
calcium and magnesium and soil pH.
Fertilizer Ratio
The fertilizer ratio is the relative amount of nitrogen (N), phosphorus (P) and potassium
(K). The fertilizer analysis is clearly written on all fertilizer labels (N:P:K). The ratio is
calculated by dividing all three numbers by the smallest number on the label. The ratio
should be determined to compensate for deficiencies defined by the soil nutrient analysis.
If a nutrient analysis has not been conducted the proper ratio for an average Nantucket
soil is N - 2 to 3, P – 0 to 1, and K – 1 to 2. Most Nantucket soils do not need phosphorus.
Example fertilizer analysis to select are 30:0:10, 15:0:10, or 6:0:2. Slight variations from
this such as 30:2:9 are acceptable.
A second important number to look for on the label is the amount of Water Insoluble
Nitrogen (WIN). The more WIN a fertilizer has, the less likely it is that nitrogen will
leach into the ground water. Fertilizers with at least half of the nitrogen in a water
insoluble form (>50% WIN of the total N) are preferred on Nantucket. Fast release
fertilizers (<50% WIN of the total N) should only be applied by knowledgeable
professionals.
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Fertilizer Rates
Nitrogen should not be applied at rates that total more than 3 pounds per thousand square
feet annually on turf. Single application rates should not exceed one pound per 1000 sq.
ft. If clippings are not collected, nitrogen rates can be reduced by 25% to 35%. To
calculate fertilizer rate use the following formula:
Application rate (lbs. of N)
Total product needed = % N in product as decimal
Application Timing
Properly timed nitrogen applications will increase uptake by plants and reduce loss to the
environment. For turf there are two schedules that can be used, one using some fast
release fertilizers that should only be applied by professionals and the other using slow
release fertilizers that can be used by homeowners or professionals. They are as follows:
Slow Release Fertilizer N
Rate*
Fast Release Fertilizer
(Professional use only)
N
Rate*
March – mid May ½ to 1
SR
mid March – mid April ¼ FR to
½ SR
June –July ½ to 1
SR
June ½ FR to
1 SR
August - September 1 SR September ½ FR
October ½ FR
October - November ½ to 1
SR
November ½ FR
Rate is based on pounds of nitrogen per 1000 square feet of turf. SR = slow release (>50%WIN), FR= fast
release (<50%WIN).
Soil pH Adjustment
Soil pH adjustment and other nutrients may be required if the soil nutrient analysis
identifies a problem. The optimum soil pH for Kentucky bluegrass is between 6 and 7
while the fine fescues can tolerate slightly lower soil pH. If the soil is acidic dolomitic
limestone is usually recommended. Lime is also used to supply calcium and magnesium.
Typical application rates are up to 25 pounds per thousand square feet on sandy soils and
up to 50 pounds on clayey soils. Micronutrients such as iron and manganese are applied
only if identified to be deficient in a soil analysis.
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Watering After Fertilization
Water is required to move surface applied fertilizer into the soil. The minimum amount of
water to accomplish this is between 1/8 and 1/10th of an inch. Many irrigations systems
can put this amount of water out in 5 to 10 minutes. Additional water either from rain or
irrigation may leach soluble nitrogen based fertilizers deeper into the soil where
environmental quality may be compromised. Therefore, fertilization prior to heavy rain
or longer periods of irrigation should be avoided.
Maintenance practices that increase root depth or enhance the soils nutrient retention will
increase the amount of nitrogen taken up by the plant. Practices such as raising mowing
heights, aeration, organic matter incorporation, and dethatching will produce the desired
effects.
Mowing Height
In general, the taller the grass, the deeper its roots penetrate into the soil. Deeper-rooted
plants are more efficient at taking up nutrients and water. The ideal mowing height range
for turf is 2 to 3 inches.
Soil Aeration
Aeration is the removal of plugs of soil, ½ to ¾ inches in diameter to a depth of 2 to 4
inches. Turf should be aerated annually in the fall.
Organic Matter Incorporation
Organic mater such as compost can be added to the soil/turf after aeration to increase the
water and nutrient holding ability of the soil. The use of mulching mowers rather than
those that collect clippings, will also increase the amount of organic matter in the soil. It
is preferable that clippings not be collected after mowing. This practice however, may
increase the amount of clippings that are tracked into the house for several days after
mowing.
Dethatching
Dethatching is beneficial if the thatch layer develops to a depth of more than ½ inch.
Thatch is an accumulation of slow-decomposing plant parts which exists between the turf
canopy and the soil. This layer may interfere with fertilizer usage and water movement
into the soil. Dethatching is a vertical raking process that removes this accumulation.
Dethatching can be done anytime the ground is not frozen.
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Fertilization of Trees and Shrubs
Introduction
Trees require certain essential elements or nutrients to function and grow. A nutrient is an
element that is involved in the metabolism of a tree or necessary for a tree to complete its
life cycle. For trees growing on a forest site, these elements normally are present in
sufficient quantities in the soil. Landscape trees or urban trees, however, may be growing
in soils that do not contain sufficient available elements for satisfactory growth and
development. Topsoil often is removed during construction. Leaves and other plant parts
are removed in landscape maintenance, disrupting nutrient cycling and the return of
organic matter to the soil. It may be necessary to fertilize or to adjust soil pH to increase
nutrient availability.
Fertilizing a tree can increase growth, reduce susceptibility to certain diseases and
insects, and can, under certain circumstances, help reverse declining health. However, if
the fertilizer is not needed or not applied correctly, it may not benefit the tree at all. In
fact, it may increase susceptibility to certain pests and accelerate decline. Trees with
satisfactory growth and not showing symptoms of nutrient deficiency may not require
fertilization. Trees growing in turf that is heavily fertilized may not require additional
fertilization. It is important to recognize when a tree needs fertilization, which elements
are needed, and when and how they should be applied.
Current practices in the tree care industry are based on what is known as prescription
fertilization – applying only nutrients that have been found to be deficient.
Determining Goals and Objectives
The goal of fertilization is to supply nutrients determined to be deficient to achieve a
clearly defined objective.
Common objectives of fertilization include to
• overcome a visible nutrient deficiency.
• eliminate a deficiency not obviously visible that was detected through soil
or foliar analysis.
• increase vegetative growth, flowering, or fruiting.
• increase the vitality of the plant.
• reduce potential injury from disease or insect infestation.
Soil Testing and Plant Analysis
The most accurate way to determine a tree’s nutrient needs is to obtain laboratory
analyses of the soil and/or leaves. To determine the need for fertilization, three analyses
should be considered:
• foliar nutrient analysis to determine the nutrient content of the leaves
• soil nutrient analysis to determine soil nutrient levels and salt content
• pH analysis to determine the acidity or alkalinity of the soil
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Foliar Analysis
Foliar nutrient analysis is used to determine the current nutrient content of leaves. Results
provide information on which nutrients have been absorbed and translocated within the
plant. This method is the most accurate for determining deficiencies of most elements.
However, it does not provide information on why the nutrients are deficient. Foliar
nutrient analysis usually is significantly more expensive than soil analysis. When foliar
analysis is conducted a soil test should also be run to determine what is in the soil
compared to what is being carried into the foliage. Then the process of determining why
nutrients are not being carried into foliage can be undertaken, if necessary.
Soil Analysis
A soil analysis can give information about the presence of essential elements, soil pH,
organic matter, and cation exchange capacity. This previous sentence is a little confusing.
The pH is important since it influences efficient uptake of fertilizer by a plant. A high salt
index, indicated by a soil test, can cause nutrient uptake problems and induce drought
stress symptoms for certain species of plants. Matching the fertilizer nutrient content to
the deficient elements ensures that the proper nutrients are applied to correct the
deficiency. By adding only the elements required, excess elements will not be added to
the environment. The process of conducting analyses, setting plant health goals, and
selecting a fertilizer to achieve the goal is called prescription fertilization.
Nitrogen is the most commonly deficient nutrient for landscape plants. It is also one of
the most difficult to measure in a soil analysis, because of the numerous forms that
nitrogen can take in the soil (for example, nitrate, ammonium, or urea). Nitrogen also is
rapidly transformed among forms. Even under ideal sampling and testing conditions, the
analyses often do not correlate well with plant response to fertilization. Research has
shown that nitrogen needs to be replenished on an annual basis for healthy plant growth.
Reasonable annual rates of nitrogen fertilization have been established for general woody
plant species, until science can establish the ideal nitrogen amount for each plant species.
The estimated nitrogen release (ENR) is a calculated nitrogen level based on soil organic
matter. This analysis provides the best correlation with plant response of any of the
nitrogen analyses. However, it does not take recent fertilizer applications into account.
Due to the mediocre correlation between soil analysis levels and plant response to
fertilizer, nitrogen recommendations also should be based on foliar nutrient analysis or
visual assessment of the plant, species of plant and the fertilization objective.
Phosphorus (P), potassium (K), magnesium (Mg), and calcium (Ca) levels are determined
using one of several methods of soil extraction. These extraction methods usually are
regionally standardized. Because various laboratories may use different extraction
methods, direct comparison of numbers among laboratories may be difficult.
Interpretation of the results correlates to the probability of plant response to fertilizer
treatment with the element. For example, if the analysis for a given element is “very low”
there is a high probability of plant response to fertilization with that element. Conversely,
if the analysis is “high,” there is a low probability of response to treatment.
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Soil Organic Matter
Soil organic matter (OM) usually is seen as the “blackness” in soil. If high levels of
organic matter are present, there usually will be high levels of beneficial soil
microorganisms and nutrients available to the plant. The reported level is a percentage of
the weight of the soil. Levels of 3 percent or more are preferable for most plants; higher
levels are beneficial for macronutrient availability.
Cation Exchange Capacity
Nutrients are salts that have electrical charges that are either cations or anions. This
electrical charge enables the nutrients to lock onto soil particles until root hairs of plants
can remove them for plant uptake. One of the ways agronomists measure the ability of a
soil to retain charged nutrients is through a measurement of the cation exchange capacity.
(CEC). When CEC values are low, more frequent fertilization may be required, and the
risk of leaching is higher. When the CEC is high, applications should be required less
frequently and the risk of leaching is lower.
Soil Sampling and Analysis
When taking a soil sample, six to ten cores should be taken from representative locations
of the entire area or root zone. Typical sampling depth is to 6 inches, the location of the
majority of fine roots. These cores should be mixed together in a clean, nonmetallic
container or soil sample bag. This procedure will give results that are averaged over the
entire area. Any soil test is only as good as the sample, so it is important to collect a
representative sample of the site. Avoid unrepresentative areas where nutrient levels may
be very high or very low.
A soil analysis will have greater value if done in conjunction with a foliar analysis. In
addition, there is still debate about what levels of various elements are critical for tree
growth. Thus, interpretation may be difficult. One way to facilitate interpretation is to
compare foliar nutrient samples with samples from healthy trees of the same species.
Leaf samples taken from symptomatic areas may help diagnose certain deficiencies or
toxicities. However, a soil analysis or foliar analysis alone can be misleading. It is
possible for certain minerals to be deficient in the leaves but plentiful in the soil and
unavailable due to the soil pH level.
Fertilizer Selection
Macroelements
Fertilizers are available in many forms and combinations. A complete fertilizer contains
nitrogen, phosphorus, and potassium. The fertilizer analysis or guaranteed analysis listed
on the container gives the composition of the fertilizer expressed as a percentage by
weight of total nitrogen (N), available phosphoric oxide (P2O5), and soluble potash
(K2O), always listed in the same order (Figure 2). For example, a fertilizer with an
analysis of 10-3-4 contains 10 percent nitrogen, 3 percent phosphorus, and 4 percent
potassium.
Fertilizers are available in either organic or inorganic forms. Inorganic fertilizers release
their elements relatively quickly when dissolved in water. The available nutrients are in
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the form of inorganic ions, which are adsorbed by oppositely charged sites on the root
membrane. These same ions are also responsible for plant “burn” (when in excess
concentration) by raising the osmotic pressure of soil solution and drawing water out of
the roots.
Organic fertilizers also release inorganic ions but do so more slowly as the molecules are
hydrolyzed or decomposed in the soil. Organic fertilizers are composed of carbon-based
molecules and can be either synthetic or natural. Examples of synthetic organics are
ureaformaldehyde (UF), methylene urea (MU), and isobutylidene diurea (IBDU).
Examples of natural organics are manures, sewage sludge, blood, and bone meal.
Roots absorb most elements in the form of inorganic ions, whether coming from an
organic or inorganic source. An advantage of organic fertilizers is that they must be
converted to inorganic ions before absorption and therefore, they are not leached as
readily from the soil. Organic fertilizers require soil microorganisms to convert nitrogen
to a form useable by plants. The soil microorganism require that soil temperatures be
generally above 50 F for maximum microorganism activity. One advantage of inorganic
fertilizers is that solubility is less affected by temperature so that the rate of availability is
more uniform.
Fertilizers with slow- or controlled-release nitrogen (CRN) should be used when
fertilizing trees. This practice reduces the amount of fertilizer that may be leached and
reduces salt or fertilizer “burn” problems. If slow-release fertilizer is used, more nitrogen
can be applied at a single application . To determine if a fertilizer is slow release, look for
the percentage of water-insoluble nitrogen (WIN) on the label (Figure 2). If at least half
of the nitrogen is water insoluble, the fertilizer is considered slow release. For example, if
a fertilizer label states that the product is 20 percent nitrogen, then the WIN should be at
least 10 percent.
When selecting fertilizers, it is best to work from an individual plant’s nutrient analysis
and apply only the elements that are in short supply. In the absence of soil and/or foliar
analysis, the American National Standard A300 standard states that a fertilizer ratio of
3:1:1 or 3:1:2 should be used. These ratios should be adjusted based on local knowledge,
age, and/or condition for plant, soil, and environmental conditions.
The Other Macroelements: Sulfur, Phosphorus, and Potassium
Sulfur, phosphorus, and potassium occasionally are found lacking in trees and shrubs.
When these elements are to be included in a fertilizer mix, there are many product
options. Rates of application should be guided by soil and/or foliar nutrient analysis.
The Secondary Elements: Calcium and Magnesium
Calcium and magnesium deficiencies typically are found in acidic and sandy soils but
may occur in any soil type. The common treatment for both deficiencies is application of
dolomitic limestone. This fertilizer contains both elements. Rates of application are
determined by soil and/or foliar nutrient analysis and by soil pH level. Because dolomitic
limestone is used to increase soil pH, when applying it for fertilization purposes, rates
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must not be so high that the soil pH is increased beyond the optimal range for the plant
species. Deficinecy of calcium alone calls for the application of calcitic limestone on low
pH soils. In cases where pH is in a suitable range for plant growth but calcium must be
added an application of gypsum may be made to the soil. If magnesium was low but the
pH is suitable then Epsom salts or magnesium sulfate can be applied to the soil to
increase magnesium levels. The objective is maintaining calcium to magnesium ratio of
2: 1 or 3:1. An imbalance in calcium and magnesium levels can induce other nutrient
deficiency symptoms.
The Microelements: Iron, Manganese, Zinc, Boron, and Copper
Microelement deficiencies often are seen on high-pH (alkaline) soils, sandy soils, and/or
soils with naturally low levels of these elements. These deficiencies are very host
specific. They will affect one tree species, but an adjacent tree of a different species may
not be affected at all.
Microelements can be applied to the soil or foliage, or they can be injected into the
xylem. The advantages, limitations, and application techniques for supplementing
microelements are described later. For soil application of iron and manganese, chelated
forms are preferred because they are less likely to be tied up in the soil. Salt forms of
zinc, copper, and boron are often used. Application rates depend on the degree of
deficiency, soil type, and product used.
Salt Index
Salt index is a measure of the relative salinity of a fertilizer. Salts draw water out of the
root system, resulting in less water uptake by the plant. Damage caused by the salt is
referred to as “salt burn” or “fertilizer burn.” Fertilizers with high salt indices have a
greater potential to cause desiccation of plants when applied at the same rate as fertilizers
with low salt indices.
Salt indices rarely are listed on fertilizer labels. To find the salt index of a specific
fertilizer, contact the manufacturer or refer to Table 2. For fertilizing trees and shrubs, a
salt index of less than 50 is preferred to reduce the risk of plant damage.
Fertilizer Timing
Fertilizer uptake in deciduous hardwoods corresponds with the time of root growth. In
general, root growth starts before budbreak and ends after leaf drop. The time of
maximum nutrient uptake is from after budbreak in the spring to color change in the
autumn. Application of quick-release fertilizers should be avoided between leaf drop and
budbreak because uptake is minimal and fertilizer may be leached or volatilized. Quick
release fertilizers should only be applied during the growing season when shoot extension
and leaf enlargement are taking place.
With most slow-release fertilizers, the period of nutrient release is much longer. This fact
makes the seasonal timing of application much less critical. Fall application of fertilizer
to trees not affected by other stress factors is not known to predispose to winter injury.
Slow release fertilizers can be applied at any time except during drought or if the ground
is frozen.
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To prevent fertilizer runoff in the spring, all fertilizer applications should be avoided if
the ground is frozen, and during drought periods when roots will not readily absorb
fertilizers. There is also the additional risk of damage from salts in the fertilizers when
fertilizers are applied during droughts.
Fertilizer Application
Fertilizers can be applied to the soil or foliage, or they can be injected directly into the
xylem of trees. Soil application is the preferred technique. Foliar spray or trunk injections
should be reserved for rare cases when soil application is not effective or not practical to
apply.
Soil surface application of fertilizer is an efficient means of delivering nitrogen to trees or
shrubs. Nitrogen is very mobile in the soil; so as long as there is an adequate amount of
water moving through the soil, the nitrogen will move to the root area. Dry surface
applications are made with carried or wheeled fertilizer spreaders. These types of
spreaders provide an even distribution of the material if moved at a constant speed. To
avoid loss of fertilizer efficacy, applications should be made immediately before
moderate rain or irrigation, whenever possible. An ideal amount of water application after
a fertilization by irrigation or rainfall is 0.5 –1.0 inches. Avoid applications just before a
heavy rain.
Liquid surface application can be made with a variety of spray equipment. To achieve an
even distribution of the fertilizer, a flooding tip or water breaker nozzle is preferred for
surface application.
Although surface application can be effective and inexpensive, there are some use
limitations. Where the fertilizer application area is covered with turf, the turf takes up a
portion of surface fertilizer. Surface applying fertilizer on organic mulch increases the
breakdown rate of the mulch due to an increase in biological activity. On slopes, surface
applied fertilizers are more likely to run off. Phosphorus may not move into the root area
of trees before it is tied up in the soil. In this case, a subsurface application of fertilizer is
preferred. Potassium is intermediate in soil mobility; subsurface application is the
preferred application technique, but surface application may be effective in many cases.
Subsurface, liquid injection is the most common application method used by commercial
arborists. When applying fertilizer with this technique, injection sites should be evenly
spaced within the fertilization area to a depth of 4 to 12 inches. In most cases, injection at
depths less than 4 inches will result in fertilizer bubbling to the soil surface. Injection to
depths greater than 8 inches will result in fertilizer being delivered deeper than the fine
roots of most trees. Fertilizer placed below the actively absorbing roots is likely to leach
away. Therefore, the preferred depth of application is 4 to 8 inches.
The quantity of liquid injected into each hole is typically one to two quarts. Higher rates
often lead to unintentional surface application when the solution bubbles to the soil
surface. At these rates, using a pressure of 150 to 200 psi (measured at the pump), the
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typical distribution radius is 18 inches, which provides good coverage when using 36-
inch spacing.
Fertilizer Application Area
The area in which fertilizer is applied should correspond to the maximum concentration
of fine, absorbing roots in the soil. Generally, these roots are in the upper 6 inches of soil.
On open-grown trees, fine roots are found from near the trunk to well beyond the dripline
of the tree. Beyond the dripline, however, root concentration drops off at a relatively high
rate. Therefore, fertilizer application should be made from near the trunk to near the
dripline.
If soil injecting or using drill-hole techniques, avoid damage to the buttress roots of the
tree when working near the trunk. Do this by avoiding the areas immediately outside the
point where buttress roots enter the soil. Instead, apply between the buttress roots or root
flares.
On trees with a dense canopy, such as Norway maple (Acer platanoides) and pin oak
(Quercus palustris), fine-root density often is higher at the dripline than immediately
inside it, possibly due to the water runoff pattern. On trees with this characteristic,
application beyond the dripline may be beneficial.
Pine (Pinus spp.) and other coniferous trees tend to have a less wide-spreading root
system than hardwoods. On such species, it is not necessary to fertilize all the way to the
dripline.
When fertilizing a group of trees or small woodlot, the entire area within the dripline of
the group should be treated. It is not necessary or desirable to calculate the fertilizer area
for each tree and add them up. Instead, calculate the area for the entire group.
If there is pavement such as sidewalks or streets, or if there is a structure within the
dripline of the tree, this area should be subtracted from the fertilizer application area.
Compensating for these impermeable surfaces by adding additional fertilizer in other
areas is not necessary.
When fertilizing fastigiate (narrow) trees, trees with small canopies, or trees that were
pruned to an unusual shape, the dripline is not a good guide to the area of maximum fine
root concentration. In these cases, a fertilizer application area can be calculated from the
trunk diameter. Multiply the diameter measured in inches at 4.5 feet (dbh) by either 1 or
1.5 to get a number, expressed in feet, to use as the radius measurement for the
fertilization area. For example, a 15-inch dbh tree would have a fertilization area of 15 to
23 feet in radius, depending on the multiplication factor selected.
Fertilizer Application Area Calculations
One of the most important aspects of determining fertilizer rates is correctly calculating
the area where fertilizer will be applied. To make this calculation, the area must be
measured. This measurement usually is done by visualizing the area as either a circle or a
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rectangle. When determining the fertilization area of an open-grown tree, the area is
visualized as a circle with the trunk at the center. The area (A) of a circle is equal to the
radius (r) multiplied by itself then multiplied by 3.14 (A = 3.14 x r x r). A tree with a
dripline radius of 10 feet will have an area of about 314 square feet to fertilize (3.14 x 10
x 10 = 314).
The second method of calculating area is by visualizing a rectangle. To calculate the area
of a rectangle, multiply the length and width of the area.
Fertilizer Rates
The rate of fertilizer to apply should be determined by the landscape goals and the current
nutrient status of the soil. Whenever possible, soil and/or foliar analysis results should be
used to provide information on nutrient status. Without guidance of nutrient analysis, the
following guidelines can be used.
The standard rates for slow-release fertilizer are 2 to 4 pounds nitrogen per 1,000 square
feet, not to exceed 6 pounds of nitrogen per 1,000 square feet annually. Higher rates may
lead to a greater potential for leaching, some pest problems, and runoff. Because of this,
lower rates are preferred, even if frequency of application must be increased to achieve
the objective.
Quick-release fertilizers are not recommended. They should be used only when the
objective of fertilization cannot be met with slow-release fertilizer. Quick-release
fertilizers can readily leach from the root zone. Recommended rates for quick-release
fertilizers are, therefore, lower than those for slow-release fertilizers.
For mature trees, the goal usually is to maintain tree vitality. Trees in good health may
not require fertilization. If nitrogen fertilization is necessary, the maintenance application
rate is 2 to 3 pounds of nitrogen per 1,000 square feet (not to exceed 6 pounds annually).
With established trees that have not reached their mature size, the goal usually is
moderate growth and maintenance of vitality. Rates of 2 to 4 pounds of nitrogen per
1,000 square feet (not to exceed 6 pounds annually) often are recommended when
nitrogen fertilization is needed.
With young trees, the goal usually is rapid growth. To achieve this goal, annual
application of a relatively high rate of fertilizer, within the standard range, often is
recommended.
Fertilization at the time of transplanting is often not recommended. In nutrient deficient
soils, however, new transplants may benefit from incorporation of fertilizer in the backfill
or by surface application over and slightly beyond the root ball. Soil incorporation is
especially important if the soil lacks phosphorus. Nitrogen may benefit many species as
well. Regardless of growth stage, the lower the soil nutrient level, the more response will
be seen from fertilizer application. If fertilizer is applied to recent transplants, it is
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essential that only low-salt-index (< 50), slow-release (WIN > 50 percent) fertilizers be
used.
Rates of phosphorus, potassium, and other elements should be based on soil or foliar
analysis. Elemental sulfur (sulfur powder or pellets) should not be surface applied on turf
at rates greater than 5 pounds per 1,000 square feet or phytotoxicity may occur. On mulch
or bare soil, rates up to 25 pounds are often recommended. Before using sulfur, it is
recommended that phytotoxicity testing be conducted.
Rates of dolomitic limestone are highly dependent on soil analysis. Rates up to 50 pounds
per 1,000 square feet are used in accordance with soil analysis results.
Calibrating Fertilizer Applicators
Liquid soil applicators (both soil injectors and nozzles for surface application) are
calibrated by setting the pressure at the desired level, placing the tip into a calibrated
container such as a bucket or milk jug, and opening the valve for a specific length of
time. After the time period, the valve is closed and the quantity of solution is measured. If
a greater quantity is desired, the calibration procedure is repeated for a longer period, and
the time required to provide the desired quantity of solution is recorded.
Spreader calibration is based on both the flow rate of the fertilizer and the speed of
application. Therefore, when calibrating it is very important to walk or drive at a constant
speed. Fertilizer spreaders usually have calibration numbers engraved near the flow-
control lever. If the fertilizer label designates a calibration number, that setting is a good
place to start the calibration test. Fill the applicator with a measured amount of fertilizer,
then apply the fertilizer over a known area. The application rate is easily calculated by
dividing the weight of the fertilizer applied by the area it was applied to. Several
calibration tests should be conducted to ensure accuracy of the calibration.
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About the Authors
Dr. Kevin Mathias is a Turfgrass Extension Specialist and a Lecturer within the College
of Agriculture and Natural Resources at the University of Maryland. He is responsible
for teaching a number of courses within the area of turfgrass science for the Institute of
Applied Agriculture at the University of Maryland. He has written three laboratory
manuals, and published numerous articles on turfgrass management within professional
and trade journals. He is currently the Education Chairperson for the Maryland Turfgrass
Council, and speaks to local and regional turfgrass and landscape organizations annually.
He received his Ph.D. from the University of Maryland in College Park, Maryland.
Dr. E Thomas Smiley is an Arboricultural Researcher at the Bartlett Tree Research
Laboratories, and an Adjunct Professor at Clemson University. He serves as a technical
advisor for the ANSI A300 Standards for Tree Care Operations Committee, and he is the
Chair of the ISA Best Practices Committee where he has authored the tree care industries
Best Management Practice guidelines for tree and shrub fertilization. He has also
authored numerous books, and articles in the field of arboriculture. He received his Ph.D.
from Michigan State University in Lansing, Michigan.
Professor Stanton Gill
Is a tenured faculty member of the University of Maryland Cooperative Extension
stationed at the Central Maryland Research and Education Center. He is also an adjunct
professor, teaching credited class in the Landscape Technology Program at Montgomery
College in Germantown, Maryland. He serves on the Maryland Arborist Association
board, the Maryland Greenhouse Growers Association board, the Maryland Nursery
Association board, and the educational board of the Landscape Contractor’s Association
of MD/D.C. and VA. He has authored three textbooks, two by Ball Publishing of
Chicago, Illinois and one book in Spanish, published by HortiTecnia Press, Bogotá,
Columbia. He has co-authored a book on CD published and distributed by Horticopia
Company of Purcellville, VA. He is currently leading the publishing effort of 4 other
pathologist and entomologist with Cornell University Press. He has published in 27
refereed science journals and 289 non-refereed trade journals. Presented at over 8
international professional conferences and 214 professional conferences in the United
States.
Mr. David Marren is the Director of Regulatory Affairs for the Bartlett Company. He is
a licensed attorney who monitors regulatory compliance for all Bartlett operations in the
United States, Great Britain, Ireland, and Canada. He is the Chair of the National
Arborist Association’s Governmental Affairs Committee. He is commonly used as a
consulting expert on legal issues concerning the arboriculture industry in legal matters
throughout the United States. He has also testified before Congress on issues relating to
how the government regulates the tree care industry. He received his J.D. from New
England School of Law in Boston, Massachusetts.
Portions of this publication were excerpted from the International Society of Arboriculture’s
Best Management Practice for Tree and Shrub Fertilization.