Liming
Turfgrass
Areas
College of Agricultural Sciences
Agricultural Research and Cooperative Extension
1
SOIL REACTION
Liming is the practice of applying an agent to reduce soil acidity
(raise pH) and make soils more favorable for turfgrass growth.
Raising soil pH requires a quantity of liming material that is
determined by the degree of soil acidity as well as the quality
and type of liming material. Although soil acidity is determined by
soil testing, not all soil tests provide accurate information about
how much lime should be applied. Most university and commercial
laboratories, however, will provide sound recommendations of how
much lime needs to be applied to turfgrass areas.
pH SCALE
COMMON SOLUTION
0
Lowest pH for most
mineral soils
Strongly acid
Moderately acid
Slightly acid
Very slightly acid
Very slightly alkaline
Slightly alkaline
Moderately alkaline
Strongly alkaline
What is soil pH?
All soils can be classified as acid, neutral, or alkaline. The degree
of acidity or alkalinity of a soil can be described by a pH value
that ranges from 0 to 14. Any value below 7.0 is considered acid,
a value of 7.0 is neutral, and a pH above 7.0 is alkaline. Thus, a
soil with a pH of 5.8 is acidic, whereas a soil with a pH of 7.9 is
alkaline. See Figure 1.
Soils become more acidic as pH values below 7.0 decrease
numerically. In fact, there is a tenfold increase in acidity for
every decrease by one whole pH unit. For example, a soil with a
pH of 5.5 is ten times more acidic than a soil with a pH 6.5, and
a soil with pH of 4.5 is 100 times more acidic than the soil with
a pH of 6.5. Similarly, for every whole unit increase in pH above
7.0 there is a tenfold increase in alkalinity. Soil pH values are
usually reported to the nearest 1⁄10 of a whole unit on a soil test
report (for instance, 6.2, 7.0, 8.5).
Many plant species show a preference in regard to the soil
pH range. Whereas rhododendrons and azaleas prefer soils in
the range of pH 5.2 to 5.5, cool-season turfgrasses usually grow
best in soils ranging from pH 6.0 to 7.2. Kentucky bluegrass, the
most widely used cool-season turfgrass in Pennsylvania, grows
best when soil pH is between 6.5 and 7.2. Fine fescues, bentgrasses, turf-type perennial ryegrasses, and turf-type tall fescues
are somewhat more tolerant of slightly acidic soils (pH 6.0 to
6.5) than is Kentucky bluegrass.
Highest pH for most
mineral soils
{
{
{
{
{
{
{
{
1
Hydrochloric acid
2
Lemons
Vinegar
3
4
Tomatoes
5
Boric acid
6
7
8
9
Milk
NEUTRAL
Sea water
Bicarbonate of soda
10
Milk of magnesia
11
Ammonia
12
13
Lye
14
Figure 1
The pH scale runs from 0 (most acid) to 14.0 (most alkaline). The pH
values for a number of common substances are shown. Note that soil
pH range extends from approximately 3.5 to 10.5.
Why is liming important?
Soil pH affects turfgrass health by influencing availability of
plant nutrients and other elements, thatch decomposition, some
turfgrass pests, and pesticide activity.
Strongly acidic soils (pH < 5.5) may lead to deficiencies in
calcium, magnesium, or phosphorus and increases in availability of aluminum and manganese in amounts that may be toxic
to turfgrasses. Liming improves plant nutrient availability and
reduces toxicity problems in acidic soils.
In strongly alkaline soils (pH > 8.5), the formation of insoluble
tricalcium phosphate makes the phosphorus unavailable to the
plant. Iron chlorosis, an indication of iron deficiency, may be seen
on some plants growing in soils high in pH. Since most soils in
Pennsylvania are not strongly alkaline, these types of deficiencies
are not often encountered. Exceptions may occur when too much
lime is applied to established turf or to the soil prior to planting.
Many beneficial soil microorganisms do not thrive in strongly
acidic soils. Some of these microorganisms breakdown certain
nitrogen fertilizers, thereby releasing the nitrogen for use by the
turfgrass. Fertilizers containing nitrogen from ureaform, sulfurcoated urea, or natural organic sources are not effective unless certain microorganisms are present in the soil in sufficient quantities.
Soil microorganisms also aid in the decomposition of thatch
and grass clippings. Thatch is the dense accumulation of organic
material on the soil surface beneath the grass. A thatch layer
restricts movement of air, water, nutrients, and pesticides into
the soil. Soil pH in the range of 6.0 to 7.0 increases microbial
activity and helps reduce thatch.
Why do soils become acidic?
Soils become acidic through natural processes and human activities. The pH of most soils is controlled by the amount of rainfall.
In humid areas, such as the northeastern United States, water
from rainfall percolates through the soil, leaching ions such as
calcium and magnesium (which prevent the soil from becoming
more acid) and replacing them with acidic ions such as hydrogen
and aluminum. Other natural processes that increase soil acidity
include root growth and decay of organic matter by soil microorganisms.
Human activities that increase soil acidity include fertilization with ammonium-containing fertilizers and pollution with
industrial by-products such as sulfur dioxide and nitric acid that
enter the soil from acid rain. In most cases, changes in soil pH,
whether they are caused by natural processes or human activities,
occur very slowly. This is the result of the tremendous buffering
capacity (resistance to change in pH) of most mineral soils.
2
Some turfgrass diseases are influenced by soil pH. Although
the reasons for this are not well understood, there is some
evidence to suggest that in very acidic soils the populations of
microorganisms that suppress pathogenic fungi are reduced. In
addition, plants growing in acidic soils may be more susceptible
to disease because they are suffering from nutrient deficiencies
or aluminum toxicity. Conversely, there are at least two turfgrass
diseases (take-all patch and Fusarium patch) that are suppressed
in acidic soils. Fortunately, these diseases rarely cause problems
in home lawns. Optimum pH (6.0 to 7.0) does not prevent turfgrass disease, but it can reduce the severity of infestation.
Acidic soils create conditions that favor growth of certain
weed species. One of the most common and difficult-to-control
weeds, moss, is more prevalent in moderately to strongly acid
soils than in neutral soils or slightly acidic soils. Shepherds
purse is a lawn weed that is a good indicator of moderately to
strongly acidic soils. Although weeds cannot be controlled with
lime applications, applying lime before soils become too acidic
is one means of preventing severe weed infestation.
Research has shown that the activity of some pesticides is
influenced by soil pH. Strongly acidic soils can reduce the
effectiveness of some turfgrass herbicides and insecticides.
How much limestone should be applied?
A lime requirement test is conducted on all turf soil samples sent
to the Agricultural Analytical Services Laboratory at Penn State.
Results of this test will indicate the total amount of limestone
needed to raise the soil pH to the optimum level for your turf.
Established lawns, athletic fields, cemeteries, golf course fairways, and other general turfgrass areas should not receive more
than 100 lb limestone/1,000 sq ft in any single application. Golf
course greens should receive no more than 25 lb/1,000 sq ft/application. If a soil requires more limestone than can be applied in
a single application, semiannual applications are made until the
requirement is met.
When establishing new turfgrass, the total limestone requirement may be applied in a single application if thoroughly
worked into the first 4 to 6 inches of soil prior to seeding.
As you might expect, sources of limestone vary in quality
and, hence, effectiveness. The quality of a liming material is
governed by two main factors: purity and fineness.
Purity
The lime recommendation on the Penn State Agricultural Analytical Services Laboratory soil test report is based on the use of
a liming material that has the same neutralizing potential as pure
calcium carbonate. To put it another way, if your Penn State soil
test report recommends that you apply 50 lb limestone/1,000 sq
ft, it assumes that you will use a lime source that, at 50 lb/1,000
sq ft, will raise the soil pH to the same extent as 50 lb of pure
calcium carbonate/1,000 sq ft would raise the pH. A liming
material that has the same neutralizing potential as pure calcium carbonate has what agronomists call a “calcium carbonate
equivalent” (or CCE) of 100 percent.
The recommended amount of any liming material that is not
equivalent to pure calcium carbonate in neutralizing potential
(100 percent CCE) should be adjusted so that you apply enough
liming material to raise your soil pH to the desired level. All agricultural liming materials sold in Pennsylvania are required by
law to be labeled with their calcium carbonate equivalent. Using
the CCE of your liming material, the actual amount required to
neutralize the acidity in your soil can be calculated as shown
below or read directly from the liming material conversion table.
Is lime needed?
Liming is needed if the pH of your soil is too low for optimum
growth of the turf species you want to maintain. Soil pH can
be determined only by a soil test. Although home test kits can
provide a fairly good indication of soil pH, they cannot provide
meaningful liming recommendations. Kits for collecting and
mailing soil samples to the Agricultural Analytical Services
Laboratory at Penn State are available from all county Penn State
Cooperative Extension offices. Most commercial soil test laboratories also can determine soil pH and provide lime recommendations for turf. Test results showing pH and nutrient status of your
soil sample and recommendations for limestone and fertilizer
applications (if needed) will be mailed to you. Apply limestone
only if your soil test results show a need for it, and never guess
at the amount of limestone needed.
What liming material should be used?
Calculating calcium carbonate equivalent
Agricultural ground limestone is the most widely used liming material for turfgrass areas. It is manufactured by grinding
rock containing high concentrations of calcium carbonate into
fine particles. It can be purchased at most garden supply stores,
hardware stores, farm supply stores, and many supermarkets.
Dolomitic limestone is manufactured by grinding rock containing calcium carbonate and magnesium carbonate. Dolomitic
limestone is recommended when a soil test shows low pH and
deficient levels of soil magnesium.
Pelletized limestone is ground agricultural limestone, calcitic
or dolomitic, that has been aggregated into larger particles to
facilitate spreading and to reduce dust. The aggregates are bound
together by a water-soluble substance that dissolves quickly
when wet.
Other liming materials, such as hydrated lime (slaked lime),
burned lime (quicklime), marl, shells, and blast-furnace slag, are
not recommended for turfgrass areas. Gypsum is not a liming
material.
Actual liming material required = (soil test recommendation/
CCE of liming material) x 100
Example
Soil test recommendation: Apply 75 lb limestone/1,000 sq ft
Liming material label: CCE = 80 percent
Actual liming material required: (75/80) x 100 = 94 lb liming material/1,000 sq ft
As you can see by the above example, you need approximately 20 additional pounds of a liming material with a CCE of 80
percent to raise the soil pH to the same extent as a material with
a CCE of 100 percent.
3
Fineness
Precautions
A liming material must be finely ground to be effective. This
is important because (1) solubility increases as the limestone is
ground finer and (2) limestone affects only a very small volume
of soil around each particle. Therefore, the finer limestone is
ground, the more particles it has, and if there is adequate mixing,
more of the soil comes in close contact with the limestone and,
thus, more of the soil is neutralized.
Pennsylvania law requires that limestone used to make
pelletized lime, agricultural ground limestone, and industrial
by-products meet the following minimum standards:
95 percent through a 20-mesh-per-inch screen
60 percent through a 60-mesh-per-inch screen
50 percent through a 100-mesh-per-inch screen
• Do not use hydrated lime or burned lime on established
turfgrass or turfgrass seedbeds at any time. Both can cause
turfgrass burning; they also stick to shoes and can be tracked
into homes or other buildings.
• Do not lime unless a lime requirement test shows that
limestone is needed.
• Do not expect maximum fertilizer response if the soil is
strongly acidic.
• Apply the total amount of limestone recommended by
the lime requirement test, and take care not to exceed the
maximum recommended amount per application.
• Apply ground agricultural limestone when the air is calm.
Blowing dust may reach places where it is not wanted, and
limestone that blows away is wasted.
Granular limestone (lawn and garden limestone) must meet
the following minimum standards:
95 percent through a 20-mesh-per-inch screen
40 percent through a 60-mesh-per-inch screen
30 percent through a 100-mesh-per-inch screen
• Keep limestone away from plants such as azaleas, rhododendrons, and blueberries that flourish in acidic soil.
A liming material meeting these minimums is considered adequate in most situations. The actual range of particle sizes must
be printed on the label. The calculations and table for adjusting
your recommendations for the CCE of your liming material
assume that the material meets at least these minimum fineness
standards. In selecting a liming material, there is generally
little advantage to using material much finer than the minimum
standards. See Table 1.
How should limestone be applied?
Ground agricultural limestone is sometimes difficult to spread
with a conventional drop-type fertilizer spreader because the
finely ground material tends to bridge over the spreader outlets.
Spinner-type fertilizer spreaders, with frequent stirring in the
hopper, can be used to apply limestone. Limestone can be applied by hand on small areas. For very large areas, commercial
spreader trucks are available for custom spreading.
Pelletized limestone is easily spread with conventional drop
or spinner spreaders.
When should limestone be applied?
Ground limestone may be applied anytime of the year but is
most effective when applied in the fall. Rain, snow, and heaving
of the soil during winter help work the limestone into the soil.
Movement of limestone into the soil is slow, even under the best
of conditions.
When the total amount of limestone needed for turfgrass
maintenance exceeds the amount suggested for a maximum
single application (25 lb/1,000 sq ft) on golf course greens
(100 lb/1,000 sq ft on all other established turf areas), spring
and fall applications at the maximum rate are suggested until the
limestone need is met.
When putting in new seedings, all limestone required may be
applied before seeding, but it must be mixed thoroughly throughout the top 4 to 6 inches of soil.
4
Table 1. Meeting the limestone recommendation on your soil test.
Using the following conversion table: Find your soil test limestone recommendation value in the left-hand column of the table and then read
across that line until you come to the column headed by the percentage of CCE nearest to that of your liming material. The number at that
point is the pounds of liming material required to meet the limestone recommendation on your soil test.
For example: If it is suggested that you apply 100 pounds CCE/1,000 sq ft and the liming material you plan to use contains 85 percent CCE,
you would need 118 pounds of the material you chose to obtain sufficient neutralizing power in your soil.
Because there is no advantage gained by applying more than 100 pounds of CCE/1,000 sq ft in any one application, the table is divided into
three sections suggesting how the total liming material required may be split for most efficient use. (See the right-hand column).
Pounds/1,000 sq ft
of CCE recommended
on your soil test
Percentage calcium carbonate equivalent (% CCE)
of your liming material
70
75
80
85 90
95
100
105
10
20
30
40
50
60
70
80
90
100
14
29
43
57
71
86
100
114
129
143
13
27
40
53
67
80
93
107
120
133
13
25
38
50
63
75
88
100
113
125
12 11
24 22
35 33
47 44
59 56
71 67
82 78
94 89
106 100
118 111
11
21
32
42
53
63
74
84
95
105
10
20
30
40
50
60
70
80
90
100
10
19
29
38
48
57
67
76
86
95
110
120
130
140
150
160
170
180
190
200
157
171
186
200
214
229
243
257
271
286
147
160
173
187
200
213
227
240
253
267
138
150
163
175
188
200
213
225
238
250
129
141
153
165
177
188
200
212
224
235
122
133
144
156
167
178
189
200
211
222
116
126
137
147
158
168
179
190
200
211
110
120
130
140
150
160
170
180
190
200
105
114
124
133
143
152
162
171
181
191
210
220
230
240
250
300
314
329
343
357
280
293
307
320
333
263
275
288
300
313
247
258
271
282
294
233
244
256
267
278
221
232
242
253
263
210
220
230
240
250
200
210
219
229
238
5
Divide total CCE by
the following number
of applications
1
2
3
This publication replaces Special Circular 167 Liming Turfgrass Areas.
Revised by Peter Landschoot, professor of turfgrass science, from Special Circular 167 Liming Turfgrass Areas
by John C. Harper II, professor emeritus of crop and soil sciences.
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