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by James C. Thomas C.P.Ag.
To many people, "sand is sand." On a golf course, however, sands can
be as different as night and day. While it may be tempting to save money
by using bunker sand as a soil amendment or topdressing, the physical
properties of a bunker sand may not be suitable in a root zone. Also,
a root zone sand may be woefully unsuited for use in a bunker.
Superintendents must evaluate several characteristics of any sand before
using it on the golf course. Properly selected sands will help ensure
healthy greens. Happy golfers and playable bunker lies.
How big are the grains?
Sand grains in both bunkers and root zones should be predominately
in the "medium" and "course" ranges, which means their particle sizes
generally range from 0.25 millimeter to 1 millimeter.
You can use USGA's sand-content recommendations for a finished root-zone
mixture as a preliminary tool in selecting acceptable root-zone sands
because sand comprises 80 percent or more of most mixes.
Root-zone sand should contain no more than 3 percent gravel (particles
2 to 4 millimeters in diameter) by volume. Sands free of gravel are ideal,
while those containing more than 3 percent gravel are likely to damage
mower blades and bed knives. Ideally, a root-zone sand should contain
60 percent or more medium- and coarse-sized particles and no more than
10 percent total of gravel and very coarse (1- to 2-millimeter) particles.
The sand may also contain up to 20 percent of particles in the fine (0.1-
to 0.25-millimeter) range with an additional 5 percent or less in the
very fine (0.05- to 0.15-millimeter) range.
Since very-fine sand acts much like silt and clay particles, root-zone
sand should contain no more than 10 percent very fine sand, silt and clay
combined. Use of excessively fine sand results in root zones that are
slow to drain and poorly aerated. Fine sand also requires careful management
to prevent black layer.
Bunker sand needs to be cleaner than root-zone sand and should contain
no more than 3 percent silt and clay. Bunker sand with more than 3 percent
silt and clay may crust over or "setup" frequently, requiring repeated
maintained to keep the sand in playable condition.
Because golfers often blast sand from greenside bunkers onto putting
surfaces, ideal bunker sands are limited to less than 3 percent gravel
and 7 percent very-coarse particles. Bunker sands with greater amounts
of gravel and very-coarse particles will damage mowers, reduce putting
quality and slow play on the course. An ideal bunker sand should also
contain greater than 65 percent of its particles in the medium and coarse
ranges (0.25 to 1.0 millimeter) and less than 25 percent in the 0.05-
to 0.25-millimeter range.
Particle shape
Determine particle shape by looking at a sand sample under a microscope
or hand lens. The predominate particle shape may be either angular, sub-angular,
sub-rounded or rounded, depending upon the sharpness of the edges and
corners of the particles. The particles are also rated for sphericity,
with "ball-shaped" particles rating high in sphericity and very elongated
or flat-shaped particles rating low.
Particles with either a sub-angular or sub-rounded shape and medium
sphericity are preferred in root zones. Highly angular sands tend to pack
tightly and may injure turf roots, while highly rounded sands may be loose
and unstable during turf establishment, causing problems with footprinting
and tracking. In contrast, the desired bunker sand shape is angular with
a low degree of sphericity. The sharp angles and corners of an angular
sand help it resist movement under impact from a golf ball, thus resulting
in fewer buried balls, which reduces complaints from players.
Color
Generally, sand color is of little importance for a root zone since
it's quickly covered by the turf and isn't seen except for short periods
immediately after topdressing or aerification. Bunker sands, on the other
hand, are continuously exposed, and sand color adds an important aesthetic
appeal to most golf courses. The contrast of a clean sand against a healthy
green turf is important to break up the monotony of large turf areas,
and well-designed bunkers add definition and challenge to each golf hole.
Generally, light-colored sands are preferred for bunkers use. The most
common colors seem to be white, light brown, yellowish brown and light
gray. While some clubs use a pure white sand to provide dramatic contrast
in colors, tans or light browns are more natural, easier to maintain and
are easier to play from because they reflect and glare less. Pure white
sands can be hard to keep clean and often turn tan with age because of
contamination from grass clipping, leaves and other foreign materials
that are washed or blown into the bunkers.
Occasionally, other considerations may override color, and unusually
colored bunker sands may be acceptable. Such was the case at the Jack
Nicklaus designed Old Works course in a depleted Montana copper mine,
where the bunkers contained black slag instead of sand. The on-site availability
and the stability of the slag material combined with its very high resistance
to partially burying golf balls in the "fried-egg" lies makes for a good
bunker sand, even though the black color is unusual. Given the choice
between a sand that plays well with few buried balls and one that looks
good but plays poorly, our preference should be for the playability of
the sand.
Crusting and setup
Golfers tend to frown on bunkers with crusted setup sand. Crusting
is the formation of a thin, hard shell on the sand surface, much like
the upper crust of a pie shell. Setup is the formation of a thick crust
as deep as water penetrates. Calcareous sand and sands with excess silt
and clay particles have the greatest tendency to crust and setup. A severe
tendency to crust or setup requires more frequent raking to keep the sand
in playable condition. Thus, ideal bunker sands are free of both crusting
and setup.
Chemical composition
Since 1970, researchers have reported that quartz sand (commonly called
silica sand) is preferred for use in both greens construction and bunkers
because of its hardness, which makes it resistant to further weathering
and helps it retain its original shape. Softer sands, particularly those
derived from limestone, create special problems that require special management
by the superintendent.
As soft, calcareous sands weather calcium carbonates dissolve
and migrate in the green. The carbonates act as weak cementing agents
and have been known to precipitate, forming restrictive layers above the
drain systems of putting greens. In addition, the calcium carbonates will
increase the amounts of crusting and setup in the bunker sands and thus
require more frequent raking to keep bunkers in playable condition.
Furthermore, as the carbonates dissolve from the sand, the
particle size of the sand may gradually degrease, causing a reduction
in both water flow and the amount of air-filled porosity. Calcareous sands
tend to have alkaline pH values which, depending on the severity of the
pH, may limit the availability of micronutrients. Thus, adjustments in
the fertility plan must compensate for this. Because of these various
problems, quartz is the preferred mineral for all golf course sands.
Buried balls
Another problem unique to bunker sands is the potential for golf balls
to partially bury in a fried-egg lie. Golfers tend to complain about "soft
sand" when their scorecards record extra strokes from digging out of such
lies.
A Test can reveal the potential for sands to form fried-egg.
A standard quantity of air-dried bunker sand is placed in the test vessel
and stirred. The force required to press a golf ball halfway into the
sand is measured and compared with a table of values allowing the sand
to be rated as having a very low, slight, medium or high potential for
burying golf balls. Ideal bunker sands give a reading of 2.4 kilograms
per square centimeter or above on a pocket penetrometer, indicating a
very low tendency to bury golf balls landing in bunkers.
Hydraulic conductivity
Saturated hydraulic conductivity is a measure of the rate at which water
will pass through sand. Good root-zone mixtures have conductivities of
6 to 24 inches an hour as specified by the USGA.
This allows playing surfaces to drain rapidly and have adequate
aeration to promote grass rooting. In addition, sand based root-zone mixtures
need to meet other criteria, including pore size distribution, as set
forth by the USGA.
No standards have been established for the conductivity of
a bunker sand, although inadequate drainage is an oft-discussed problem
of bunkers. And because bunker sand is frequently blasted onto nearby
putting surfaces, it seems reasonable that a bunker sand should have a
minimum conductivity of 20 inches an hour, with rates preferred.
Unlike root-zone mixtures, there is no upper limit to an
acceptable hydraulic conductivity of a bunker sand.
Over time, bunker sands inevitably are contaminated with
silt and clay particles from the base and edges of the bunkers, as well
as soil, dust and organic debris washed or blown into the bunkers. These
contaminants not only discolor the sand, but also clog pore spaces and
bind sand particles together. This reduces water conductivity and increases
water retention and the potential for crusting and setup. So it's best
to start with sand having high conductivity to reduce the effects of future
contamination.
Ask golfers
Care is essential in choosing the proper sands for a golf course.
Evaluate sands used in root-zone mixtures or topdressing for their particle-sized
distribution, shape and physical measurements (saturated hydraulic conductivity,
density and pore size distribution). Evaluate bunker sands for particle-size
distribution, shape, color, crusting and setup, hydraulic conductivity
and their potential for burying golf balls. If the choice comes down to
two or three bunker sands with similar test results, it's often a good
idea to establish some test areas and get your members opinions about
which sand they prefer.
While the ideal particle sizes of root-zone and bunker sands
are similar, bunker sands should be more angular, have less silt and clay,
should not crust or setup and should be resistant to the formation of
fried-egg lies. Consider the investment of time and lab testing as "doing
your homework" before spending thousands of dollars and countless work
hours to purchase and install large volumes of sand on your golf course.
This can pay big dividends in the form of happy golfers,
fewer complaints to the superintendent and less maintenance to keep the
course in top condition.
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