Finding the balance
Core aeration affects turf health, soil physical properties and the playability of golf course greens.
Jeff Atkinson, M.S., and Bert McCarty, Ph.D.
Read this story in GCM's digital edition
A recently core-aerated bermudagrass putting green. Core aeration is necessary to mitigate effects from compaction caused by human and mechanical traffic.
Photo by Bert McCarty
Each growing season,
superintendents are conflicted between the need for core aeration and
commitment to maintaining a consistent, playable putting surface. Over time,
reducing or eliminating core aeration will result in deteriorating turf health,
soil physical properties and soil chemical properties (6). The trick is finding
the balance between providing sufficient soil cultivation to maintain long-term
turf health while limiting disruption to surface playability.
Foot traffic and maintenance
practices such as mowing and rolling are compressive forces that continually
increase compaction. As compaction becomes more severe, the availability of
nutrients, water and oxygen is reduced. Severe compaction leads to accumulation
of toxic levels of carbon dioxide within the soil and increased incidence of
localized dry spot, anaerobic soil conditions, disease and nutrient deficiency.
Using highly stoloniferous
turfgrasses (like ultradwarf bermudagrasses) to increase wear tolerance of
high-traffic areas, such as putting greens, increases the need for frequent
cultivation to prevent excessive thatch accumulation. Thatch is a slowly
decomposing layer of living and dead stems, leaves and roots that develops between
turfgrass shoots and the soil surface (3). A limited amount of thatch is
desirable to provide resilience to turf and act as a buffer for moderation of
soil temperatures (1). Excessive thatch reduces infiltration rate, promotes mower
scalping, localized dry spot and vulnerability to insect and disease damage
Byproducts of microbial thatch
degradation accumulate in the soil and increase total soil organic matter. It
has been suggested when organic matter content of sand-based putting greens
reaches 3%-4% by weight, soil macroporosity begins to decrease (2). Organic matter
accumulation within the root zone increases microporosity, lowers permeability
of the soil, further slows surface infiltration and subsurface drainage,
decreases the amount of water available for plant uptake and impedes gas
†Number of core aeration events/year to reach total surface area affected each year.
‡Topdressing amount was the mathematical equivalent of soil removed from core aeration, or half of this rate.
§In some treatments, two slightly offset passes with the core aerator were necessary to achieve the correct hole spacing.
Table 1. Treatment list showing percent of total surface area affected per year, core aeration events per year and amount of topdressing applied in Clemson, S.C., June–August 2008 and 2009.
Core aeration and topdressing
are cultivation practices used to improve gas exchange, relieve compaction and
slow thatch and organic matter accumulation. Previous recommendations have
stated that removing 20% of the surface area on a yearly basis through core
aeration is necessary to maintain highquality turf (4). Research has not been
able to find the perfect balance among core-aeration programs, turf health and
The goal of this research was to
provide superintendents with a decision-making framework for maximizing
benefits to soil physical properties and turf health from core aeration while maintaining
A field study was conducted at
Clemson University, Clemson, S.C., during the summers of 2008 and 2009 to
evaluate the effect of various core-aeration programs on turf quality and soil
physical properties. All research was conducted on a 10-year-old TifEagle bermuda-grass
research putting green built to USGA recommendations. The experimental design
was developed to explore the effects of removing 15% or 25% surface area per
year through one, two or three core aerations on turf quality and soil physical
Two weeks after treatment removing 25% of the surface area with one core aeration. Increasing the amount of surface area removed through core aeration reduces bulk
density, improves surface water infiltration and decreases surface hardness, while increasing healing time.
Photos by Jeff Atkinson
For each treatment, the
combination of the percentage of surface area removed and the number of core
aerations dictated the tine size and tine spacing. The actual amount of surface
area affected per year varies slightly from the target values because of
mechanical limitations. In some treatments, two slightly offset passes with the
core aerator were necessary to achieve the correct hole spacing. Following each
core aeration, treatments received one of two topdressing rates — either the mathematical
equivalent of soil removed by aerification or half this rate (Table 1).
The first core aerations were
performed on June 1, the second on July 4 (±3 days) (where necessary), and the
third on Aug. 15 (±3 days) (where necessary) of each year, using a tractor-mounted
core cultivator. Topdressing material similar to that used in putting green construction
was measured by volume and applied by shaking it evenly over individual plots.
Topdressing was incorporated by hand with a shop broom.
A 20N-8.8P-16.6K fertilizer was
applied throughout the growing season to provide 1 pound nitrogen/1,000 square
feet (48.42 kilograms/ hectare) each growing month. Plots were mowed five times
per week and maintained at 0.125 inch (3.18 millimeters).
Plots were evaluated for turf
quality, bulk density, surface hardness, thatch depth, soil organic matter
content and surface-water infiltration rate. Turf quality was visually
evaluated every two weeks on a 1-9 scale, where 1 was dead turf; 9 was dark
green, dense turf; and a rating below 7 was unacceptable. Bulk density was
measured at the end of each study year by removing an undisturbed soil core,
drying it in an oven at 221 F (105 C) for 48 hours and then dividing dry soil
core mass by total soil core volume.
†% surface area impacted per year.
‡Averaged across all rating dates.
§Relative surface hardness value quantifies deceleration of 4.96-pound (2.25-kilogram) weight dropped from height of 17.7 inches (45 centimeters).
//Ashed organic weight of thatch layer per square centimeter of surface area.
††Values followed by different letters within the same year are significantly different.
Table 2. Response of turfgrass and soil physical properties to core aeration affecting 25% and 15% surface area per year averaged across all rating dates and number of core aeration events per year in Clemson, S.C., June−August 2008 and 2009.
Surface hardness was determined
as the average of three Clegg impact values (CIV) per plot, a measurement of
deceleration of a 5-pound (2.25-kilogram) weight dropped from a height of 18
inches (45 centimeters). Thatch depth was measured two weeks after each core
aeration by removing four soil cores from each plot and measuring the distance between
shoots above the thatch layer and roots below the thatch layer. Thatch samples were
dried at 221 F (105 C) for 48 hours and weighed. Dry cores were then combusted in
a muffle furnace to provide ashed organic weight and organic matter content determined
by the difference between these two measurements.
Infiltration was measured 14
days (±2 days) after each aerification using a doublering infiltrometer.
Infiltration (inches/hour) is reported as time for water in the center ring to
empty from an initial height of 3 inches (8 centimeters) while maintaining a
consistent hydraulic head in the outer ring.
Topdressing rate did not affect
any measured parameter in either year of the study, and interaction between
percent surface area removed per year and the number of core aerations per year
was inconsistent. The remainder of the article will focus on the effects that the
amount of surface area removed per year and the number of core aerations per
year had on turf quality, bulk density, surface hardness, thatch depth, soil
organic matter content and infiltration rate.
Any conversation about core
aeration includes a discussion of its effect on turf quality. Understanding how
turf quality is affected by the percent surface area removed and the number of
core aerations per year is necessary to properly evaluate the trade-off between
reduction in turf quality and improvement of soil physical properties.
When considering only the amount
of surface area removed per year, turf quality was improved 4% in 2008 and 6%
in 2009 by reducing the amount of surface area removed (Table 2). With less
surface disruption, the turf required less time to fully heal from core-aeration
injury, which contributed to the overall improvement in turf quality.
†Initial aerification occurred on June 1 of each year with subsequent core aeration on July 4 and Aug. 15 (±3 days).
‡Turf quality values range from 9 (ideal turf) to 1 (dead turf).
§Values followed by different letters within the same year and weeks after initial core aeration event are significantly different.
Table 3. Turf quality response over time to 1, 2 or 3 core aerations per year averaged across all amounts of surface area affected per year in Clemson, S.C., June−August 2008 and 2009.
After initial core aeration on
June 1, turf quality was unacceptable (<7) for approximately four weeks in
2008 and six weeks in 2009, regardless of amount of surface area removed. After
these periods, in treatments involving two and three core aerations, turf quality
generally improved but was reduced by subsequent core aerations on July 4 and Aug.
15 (Table 3). In 2008, removing 15% or 25% of the surface area in a single core
aeration initially reduced turf quality more than treatments removing these
amounts through two or three core aeration events.
Although the initial injury
after removing 15% or 25% surface area in a single core aeration may be
unacceptable to some turf managers, turf quality in these treatments was considered
acceptable for more cumulative weeks throughout the study when compared to
treatments with two or three core aerations. In 2009, initial turf-quality
reductions were not as severe because less surface heaving occurred during core
Bulk density or
Soil bulk density is the mass of
dry soil per given unit of soil volume. If interpreted correctly, bulk density
can provide insight into the degree of soil compaction. An excessive increase
in bulk density will result in reduced macroporosity, nutrient and water
availability, oxygen concentration, and speed of surface water infiltration.
Failure to adequately perform core aeration will cause soil to become excessively
dense over time.
The optimal value for bulk
density varies depending on soil texture. For sand-based putting greens, bulk
density should fall between 1.25 to 1.55 grams/cubic centimeter to provide a
balance of soil aeration, water retention, nutrient availability, and oxygen
concentration (5). Bulk density should be a major consideration during the
planning stage of a cultivation program and should be measured every two years.
In this study, bulk density
decreased 5% in 2008 and 4% in 2009 by increasing surface area removed per year
from 15% to 25% (Table 2). Increasing the number of core aerations per year
from one to three reduced bulk density 8% in 2008 (Table 4). In 2009,
increasing the number of core aerations from one to two reduced bulk density
4%. Bulk density was similar between treatments with one and two core aerations
in 2008 and two and three core aerations in 2009. Although the effect of the number
of core aerations per year on bulk density was somewhat inconsistent between
years, bulk density generally decreased as the percent of surface area removed
and the number of core aerations per year increased.
Surface hardness, or firmness,
is a measure of soil compaction and surface cushioning due to thatch
accumulation and soil strength. Since measurements made with the Clegg impact
hammer are a relative barometer of surface firmness, the effects discussed here
should be used during the planning stages of a core-aeration program to
identify the program’s potential effects on playability.
†Relative surface hardness value quantifies deceleration of 4.96-pound (2.25-kilogram) weight dropped from height of 17.7 inches (45 centimeters).
‡Ashed organic weight of thatch layer per square inch of surface area
§Values followed by different letters within the same year are significantly different.
Table 4. Soil physical properties response to one, two or three core aerations per year, averaged across all rating dates and percent of surface area affected each year in Clemson, S.C.,
June−August 2008 and 2009.
Overall, two years of core
aeration were needed before surface hardness was significantly affected by the
percent of surface area removed per year. During 2009, removing 25% of surface
area reduced surface hardness 4% compared to removing 15% of surface area
(Table 2). The effect of the number of core aerations per year on surface
hardness was more consistent between years. Increasing the number of yearly
core aerations from one to three reduced surface hardness 5% in 2008 and 19% in
2009 (Table 4).
Although surface hardness is a
topical indicator of soil compaction, superintendents must consider how
reducing putting surface firmness affects playability. A firm putting surface
may be desirable to encourage fast ball roll speeds and allow predictable ball
action on approach shots for skillful players.
Conversely, a firm putting
surface slows overall play, as fewer balls will hold the green on an approach
shot, causing more strokes to be played around the greens complex.
Because surface firmness affects
playability, it must be considered during the planning stages of a
core-aeration program. Allowing adequate time for firming of the surface is necessary
to provide conditions appropriate for championship play. Although this study quantified
the overall effect on surface hardness of various core-aeration programs across
the growing season, additional research is needed to determine the amount of
time necessary to restore firmness to a desired level after soil cultivation.
Due to the waxy, hydrophobic
nature of thatch, soil moisture management can become challenging when thatch
depth is excessive. Putting green surfaces typically require relatively high
nutrient input to maintain adequate growth. This, in combination with the use
of highly stoloniferous turfgrasses, leads to rapid thatch accumulation in the
absence of proactive cultivation. In this study, neither increasing the percent
of surface area removed per year nor the number of core aerations per year
reduced thatch depth. However, thatch depth did not increase throughout the
study (Tables 2, 4). Further research is needed to determine how other
thatch-cultivation techniques, such as vertical mowing, complement core-aeration
programs and affect surface playability.
Organic matter is the byproduct
of microbial degradation of shoots, thatch and roots. Collecting these
byproducts in the upper soil profile is the driving force behind accumulation of
soil organic matter. Although soil microbe activity should be encouraged,
failure to reduce accumulation of organic byproducts slows soil drainage,
increases microporosity and decreases soil oxygen concentration.
Two weeks after removing 5% of the surface area with one core aeration. Decreasing the amount of surface area removed during core aeration limits improvements in bulk
density, surface water infiltration and surface hardness, while decreasing healing time.
In this study, reduction of soil
organic matter accumulation was not consistent between years. In 2008,
increasing the percent of surface area removed per year or the number of core
aerations per year did not reduce organic matter accumulation. In 2009,
treatments with three core aerations slowed organic matter accumulation 10%
more than treatments with only one core aeration (Table 4); however, overall
organic matter accumulation was not reduced below pre-study levels.
Although research has not
consistently quantified significant reductions in soil organic matter following
core aeration, numerous studies have shown that core aeration prevents organic matter
accumulation above pre-aerification values (6,7,8). Long-term observation of soil
organic matter accumulation is necessary to determine the cumulative effect of
core aeration over several growing seasons.
The resistance water encounters
as it travels through hydrophobic thatch and a compacted soil surface typically
slows water infiltration. Properly constructed putting greens should balance
sufficient drainage with adequate soil water-holding capacity to promote healthy
turf growth. For newly constructed sand-based putting greens, water should
infiltrate the turf surface 10 to 15 inches (25-38 centimeters)/hour
and byproducts of thatch decomposition combine to slow infiltration over time.
As infiltration is reduced, the proportion of water lost through runoff increases,
the amount of plant-available water is reduced, and saturation of the thatch
layer is encouraged. Removing thatch through core aeration has long been relied
on to reduce or slow thatch accumulation, thereby improving infiltration rate.
In this study,
increasing the percent of surface area removed per year did not increase infiltration
speed in 2008 or 2009. Increasing the number of yearly core aerations did not
affect infiltration speed in 2008; however, in 2009 increasing the number of
core aerations from one to two decreased the speed of surface water
infiltration 32%, and increasing the number of core aerations from one to three
decreased surface water infiltration speed 20% (Table 4).
effect of increased infiltration in treatments with only one core aeration in
2009 may be explained by the initial removal of a large percent of surface area
early in the growing season. Increasing the number of yearly core aerations to
remove the same percent of surface area reduces the size and number of channels
opened through the turf surface to facilitate infiltration. When single core-aeration
treatments were repeated in consecutive years (2008 and 2009), numerous channels
to facilitate water movement through the turf surface were opened early in the
growing season, improving season-long infiltration speed.
The research shows
that superintendents should develop core-aeration programs that fit their needs
while keeping in mind agronomic considerations and playability. Generally, as
the number of core aerations per year and the percent of surface area removed
per year increase, soil physical properties improve. As the number of core
aerations per year and the amount of surface area removed per year decrease,
average turf quality across the entire growing season improves, but soil
physical properties show less improvement.
of bulk density, surface- water infiltration, surface hardness, thatch depth
and organic matter accumulation is necessary to identify soil physical properties
in need of amelioration through core aeration. These properties — as well as consideration
of the effects of core aeration on turf quality — should be used to determine amount
and frequency of core aeration necessary to provide a healthy growing
environment for turf.
Developing a framework
for superintendents to balance agronomic practices with maintaining a
consistent playing surface is an ongoing process. Continuing research is needed
to refine timing, spacing and tine size selection to minimize putting surface
disruption while maximizing the benefits gained through core aeration.
Additional research is also needed to gain an understanding of the long-term
effects of various cultivation programs on turf health.
Funding was provided
by the Clemson Agricultural Research Station.
The authors would
like to acknowledge Alan Estes, Ray McCauley and Jeff Marvin for their
assistance conducting this research.
- Butler, J.D. 1965. Thatch: A problem in
turf management. Pages 1-3. In: Illinois Turf
Conference Proceedings, Lemont, Ill. 1965. University of Illinois Cooperative
Extension Service, College of Agriculture and the Illinois Turfgrass
Foundation, University of Illinois, Urbana, Ill.
- Carrow, R. 1998. Organic matter dynamics in the
surface zone of a USGA green: Practice to alleviate problems. USGA Turfgrass
and Environmental Research Summary. Online (http://archive.lib.msu.edu/tic/ressum/1998/15.pdf).
Verified Dec. 10, 2013.
- Engel, R.E. 1954. Thatch on turf and its control. Golf Course
- Hartwiger, C., and P. O’Brien. 2001. Core aeration by the
Green Section Record 39:8-9.
- McCarty, L.B. 2011. Best Golf Course Management Practices.
Pearson Education, Upper Saddle River, N.J.
- McCarty, L.B., M.F. Gregg and J.E. Toler. 2007. Thatch
and mat management in an established creeping bentgrass golf green. Agronomy
- McWhirter, E.L., and C.Y. Ward. 1976. Effect of vertical
mowing and cultivation on golf green quality. Report 2. Mississippi Agriculture
and Forestry Experiment Station, Starkville, Miss.
- Smith, G.S. 1979. Nitrogen and aerification influence on
putting green thatch and soil. Agronomy Journal 71:680-684.
- White, R.H., and R. Dickens. 1984. Thatch accumulation
in bermudagrass as influenced by cultural practices. Agronomy
Jeff Atkinson is a
graduate student and Bert McCarty is a professor in the
school of agriculture, forestry and environmental sciences, Clemson University,