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Understanding Soils
Physical Problems
Of Coarse-Textured Soils
Awareness of the problems inherent in a
particular type of soil is an important stepin the development of a sound management program.
Sandy or coarse-textured soils,
whether they are natural or con-
structed, are used on many high
traffic sites because they exhibit better soil
physical properties than do soils with
appreciable silt or clay (or both).Of course, one would expect a root
zone medium developed to USGA Green
R.N. Carrow is a professor of turfscience in the department of agronomy.
28
Section specifications for golf greens to
resist compaction and have ample mac-
ropores for water movement, gas
exchange and root penetration.
Robert N. Carrow, Ph.D.University of Georgia
However, sandy soils vary considerably
in their physical properties, so certain soil
physical problems can occur on them.
Many physical problems on sandy soils
are caused by one or more of several fac-
tors that will be discussed in this
presentation.
Awareness of specific problems on a
site is prerequisite to development of
sound management programs.
Although this discussion will focus on
soil physical properties, problems due to
adverse chemical or biological soil
properties also can occur. Adverse chem-
ical and biological problems will not be
Continued on p. 32
Calf Course Management / February 1992
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Understanding Soils
Continued on p. 34
A common approach to improving
water holding capacity in coarse-textured
soils is to add 5 to 15 percent by volume
of well-decomposed organic matter.
Excessive moisture retention and low aer-
ation can occur if too much organicmatter is used.
Many different organic sources can be
used if they are well-decomposed, have
a good particle size for mixing and do not
contain excessive fines. Common organic
sources used on turf sites are various
peats, decomposed rice hulls and com-
posted sewage sludge.
Addition of silt or clay or both will
enhance water retention. However, too
much can easily seal the macropore
channels. In high sand content media -
more than 80 percent sand - particlesare in direct contact with other sand par-
ticles. This produces a rigid matrix that
resists compaction. Relatively small quan-
tities of silt and clay can accumulate at
points of sand particle contact and begin
to seal off pore channels necessary for
water movement.
Silts are especially effective in sealing
and decreasing pore continuity. For this
reason, the USGA Green Section specifi-
cations limit silt to less than 5 percent and
clay to less than 3 percent by weight.
Soils with sand content between 65
and 85 percent are especially prone to
poor water movement. These sandy soils
have considerable silt and clay to seal
many pores but too much sand to allow
good structure formation. Structure
develops when clay, silt, organic matter
and sand particles start to aggregate into
structural units that open up new macro-
pores. High sand content inhibits forma-
tion of strong aggregates.
Due to the presence of smaller pores,
very fine sands retain more water than do
coarser sands. However, adding very fine
sand to a medium-to-coarse sand is not
recommended. Although it would help
increase water retention, infiltration and
percolation rates would decline as the
smaller particles filled the macropores.
Inorganic amendments - calcined
clays, expanded shale, processed vermic-
ulite mica and porous ceramics - are
sometimes used to enhance water reten-
tion. To be effective these amendments
should:
Retain water in pores within the par-
ticles that are large enough to then
Surface Area per
1 Grama
-inches2-
2
4
7
14
35
70
1,240,000
90
720
5700
46,000
722,000
5,776,000
90,260,853,000
Common Physical Problems
Concrete sand - usually contains a
wide particle size range of sands and fine
gravel.
Mason's (mortar) sand - similar to
a concrete sand but without the fine
gravel. Dune sand - obtained from a wind
or water deposited sand dune. Often has
a fairly narrow particle size range.
River sand - can vary from very uni-
form sand to sand with considerable fines,
derived from rivers.
Thus, general sands are not named by
well-defined particle ranges but by source
or construction use. They mayor may not
be good for root zone mixes.
from p. 28
Particle
Diameter
-mm-
2.00 - 1.00
1.00 - 0.50
0.50 - 0.25
0.25 - 0.10
0.10 - 0.05
0.05 - 0.002
Below 0.002
Low Water Holding Capacity
The most common problem with
coarse-textured soils is low water holding
capacity. Available water for plants in
sands may range from 0.4 to 1.5 inches
of water per 12 inches of depth when
organic matter content is less than 1 per-
cent (by weight) and there is no perched
water table. As a result, drought stress
occurs unless frequent irrigation is
practiced.
Sand, silt and clay contents of sandy soils
Composition
{Percent by Weight}
Sand Silt Clay
85-100 0-15 0-15
70-90 0-30 10-30
45-85 0-50 15-55
Sand separate classes compared to silt and clay
Number ofParticles
Per Gram
Soil Classification
Sand
Loamy sand
Sandy loam
Texture Class
Separate
Sand
Very coarse sand
Coarse sand
Medium sand
Fine sand
Very fine sand
Silt
Clay
a 1 lb. soil = 454 grams.
Soil scientists classify soils in 12 differ-
ent texture classes based on their percent
sand, silt and clay. The three texture
classes with the highest quantity of sand
are sand, loamy sand and sandy loam.
Obviously, a soil can be called "sandy"
but still contain considerable silt and clay.
Physical properties can vary dramatically
- even between two soils within the
same texture class.
The classification of sand separates isbased on the diameter of the particles.
Sand particles range from 0.05 to 2.00
mm in diameter - a 40-fold range.
Therefore, a very coarse sand will not
have the same properties as a very fine
sand.
General names are often used instead
of the official separate classification
(USDA system) to identify a sand.
Because these names have no legal
meaning, the terms are general. Some
common general names for sand types
include:
discussed but are listed for reference in
an accompanying table.
COARSE SOILS
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Understanding Soils
Soil Biological Problems
1. All soils, fine-textured or coarse-textured, can contain weed seeds, dis-
ease organisms, and harmful insects, small animals, and worms.
2. Low microorganism population. Sands are likely to contain fewer
microorganisms than fine-textured soil.
3. Less diversity of microorganisms than fine-textured soils. This creates
the potential for microorganism population balances to be easily shifted
from beneficial to pathogenic.
4. Nematodes. Many nematodes prefer sandier soils.
Primary chemical and biological problems on sandy soils
Soil Chemical Problems
1. Nutrient deficiencies and imbalances.
2. Low CEC (cation exchange capacity), which contributes to low nutrient
retention, low buffering capacity and high leaching potential.
3. Improper soil pH affecting nutrient availability.
4. Salt-affected.
Saline - most serious on sands.
Sodic.
Saline / sodic.
5. Presence of free CaC03 that acts as a buffer system in alkaline sands
and contributes to nutritional problems.
6. Toxic compounds from heavy metals, allopathic substances, herbicides,
etc., are potential problems due to low buffering capacity of mostsands.
release the water to the turf plant.
Not accumulate salts in internal
pores.
Retain their physical structure and
not deteriorate.
Be cost competitive with various
organic amendments at application rates
sufficient to achieve comparable water
retention.
Barriers that inhibit drainage increase
water retention in sands. In the USGA
Green Section specifications for golf
greens, a distinct interface is formed
between the coarse sand (1-2 mm dia.)
and pea gravel (6-10 mm dia.) layers.
This interface impedes drainage, thereby
increasing water content in the root zone.
Water is retained around the coarse sand
by adhesion-cohesion, while few inter-
connecting water films exist between the
coarse sand and gravel because of the dis-
tinct differences in particle sizes.
Only after water "ponds" a few inches
Water is retained around the
coarse sand by adhesion-
cohesion, while few water
films exist between the
coarse and gravel layer ..
Effective application rates.
Total and plant-available water
retained.
Longevity of the materials.
Influence of soil solutes on actual
versus potential water absorption.
The potential for salt accumulation.
Other procedures can be utilized to
influence root zone water content or
availability .
Careful overhead irrigation that does
not increase the ability of the sand toretain water but does allow for frequent
addition can be used.
Sub-surface irrigation has been
attempted but is especially difficult on a
sandy medium. This is because capillary
rise in sands is less than in a soil with
appreciable amounts of silt or clay. As a
result, very careful placement of water
emitters is required.
Sands have slow, unsaturated water
flow through water films around sand par-
ticles. This may limit water availability
during high demand periods, although
sands do have very high saturated flow
rates. As a result, if output is increased
Continued on p. 38
are not new types of compounds,
although particular chemicals are continu-ally being developed because polymers
can be formulated in many different
lengths, co-linked, and be formulated in
conjunction with other substances. In
fact, several PAMs and one PVA were
evaluated in a USGA supported project
for influence on moisture retention of
sands in 1978 (Agron. Journal
70:p.317-321) and no influence was
found.
Limited additional research with poly-
mers has been conducted until recently.
As more results are published, the poten-
tial for these materials may become
clearer. However, important questions
stillmust be answered. They concern the
following:
of water table control. Other procedures
to adjust water table level to allow capil-
lary rise of water to the roots have been
used in flat sod fields but not on golf
courses.
In recent years, water absorbing poly-
mers have been promoted to enhance
water holding capacity in turfgrass soils.
Polymers are formed by combining two
or more smaller molecules into a larger
chain-like molecular structure. Examples
include natural polymers such as starches,
and synthetic polymers such as poly-
acrylamides (PAM), polyvinyl alcohols
(PVA) and polyacrylates.
Contrary to popular belief, polymers
above the interface will drainage occur.
Once drainage starts, it is rapid throughthe large pores.Thus, this unique type of
barrier enhances water retention while
maintaining good drainage.
The Purr-Wick construction system
uses an enclosed ceil method system to
prevent drainage until water reaches a
certain level. This level can be adjusted
as needed. This is essentially a method
from p. 32COARSE SOILS
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Understanding Soils
The different layers of a USGA specifi-cation green result in the development ofa perched water table at the coarse sand-pea gravel interface.
sand content sites, where the surface area
of the sands is limited. Organic coatings
form on sand particles that become highly
water repellent. Typically, the hydropobic
zone is 1 to 4 inches in depth and errati-
cally situated on a site with affected and
unaffected areas side by side.
Wetting agents are used to rewet
High salt content
in sandy soils dramaticallyinfluences plant water
availability.
hydrophobic sands. Core aeration for cre-
ation of areas for water to collect and
rewet adjacent soil is frequently used in
conjunction with wetting agents. Nor-
mally, wetting agent treatment must be
repeated because the organic coatings
are not eliminated. Keith Karnok of the
University of Georgia has been refining
some treatments that may allow for dis-
solution of the coatings for a more per-
manent solution.
As in any soil, a high water table can
be present in a sand and result in exces-
sive moisture. Each site should be evalu-
ated to determine whether the water table
is naturally high or whether a perched
water table has occurred due to a layer
impeding drainage.
Improper contouring that channels
water to low spots can lead to two
problems on sand: a wet area on which
water stands and a dry site from which
water came. Many times improper con-
touring enhances other problems such as
layering or a high water table.
One common example of poor con-
touring is golf greens with "pockets" that
have no surface drainage. These pockets
often collect fines over time and become
susceptible to scald and intracellular
freezing.
Proper contouring is best achieved
prior to turf establishment.
"Hard" sands are a frequent complaint
of turf managers for the first 1 to 3 years
after turf establishment. The problem alsoContinued on p. 40
Managing Sandy Soils
Hydrophobic (water repellent) sandscan be a major problem on very high
ing salt build-up. When leaching, the
quantity of water required depends upon
the water quality, existing level of salts
present in the soil, salt tolerance of the
turf and the amount of water that goes
toward evapotranspiration versus leach-
ing (Le. arid climates require more total
water).
Layers
Presence of fine-textured layers within
the sand root zone is another common
soil physical problem. As previously men-
tioned, even small quantities of silt or clay
can seal a zone within a sand if the parti-
cles accumulate at a microsite.
Layers can result from many sources
but common ones are from installation of
sod, use of a topdressing medium with
fines, and wind and water deposition.
Sometimes a clay lens (an area of silt or
clay deposition) is present deeper in the
sand soil profile because it formed as the
soil developed.
Calcite formation at the soil surface
due to irrigation water with high calcite
(calcium carbonate) content is another
type of layer. This can seal the surface
and reduce infiltration.
Acidification of the irrigation water to
dissolve the calcite layer is effective, but
the soil should be observed so that the
layer doesn't form at the bottom of rou-
tine irrigation water penetration depth.
Salts of various types can accumulate
on the surface of soils in arid regions
when sufficient capillary rise occurs. As
the water moves to the soil surface it car-
ries solutes that are precipitated out as thewater evaporates, forming a layer.
Management of layers is accomplished
primarily through prevention of layer for-
mation and routine cultivation. Other
methods such as leaching of solutes or
acidification of irrigation water may be
appropriate in certain situations.
from p. 34COARSE SOILS
High Salt Content
High salt content in sandy soils dra-
matically influences plant water availabil-
ity. Solutes reduce plant water availabil-
ity by attracting water films by adhesion
forces - primarily hydrogen bonding.
by emitters to create saturated conditions,
the water rapidly drains downward out of
the root zone.
Finally, any management practice per-
formed to enhance rooting depth pro-
vides more water to the plant, even
though soil water content is not altered.
This can occur even though total soil
water content remains unaffected.
High sodium content is detrimental insands primarily because it adds to the
total salinity. Although few structural
aggregates are present in sands, high
sodium causes dispersion of any silt and
clay present. This material may then
migrate to the depth of routine irrigation
and re-form as a mini-layer. By contrast,
the major effect of high sodium in a fine-
textured soil is the destruction of struc-
ture. Reduction of water availability is a
secondary consideration.
Leaching with excess water and the
use of better quality irrigation water arethe primary cultural methods of alleviat-
38 Golf Course Management / February 1992
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Understanding Soils
... A surprising variety of soil physi-cal problems can still occur on what
we classify as sandy soils or sandy
root zone media.
The wide range of particle sizes classi-
fiedas
sands contributes toa
number ofphysical problems.
can occur on older sites. These sands donot have much resiliency, exhibit high ball
bounce, and when on an athletic field
they have little "give."
Hard sands occur for several reasons.
On new greens, organic matter added
does not provide the same degree of res-
liency that occurs after turfgrass roots
have grown. Bentgrasses especially
develop a high mass of roots in the sur-
face inch. Also, new greens do not have
thatch, which contributes to resiliency.
Sands that are more angular than
rounded in shape tend to fit together toform a rigid matrix. This matrix has less
pore space than one formed with
rounded sands. As a result, water move-
ment is not as good.
Construction specifications for high
sand root zone mixes normally indicate
the use of sands with a narrow particle
size distribution. For example, sands with
75 percent of the particles in two adja-
cent particle size ranges are preferred.
This ensures good pore space distribution
as long as very fine sands are avoided.
on golf greens and athletic fields that have
high sand content root zone mixes. Sands
that are round and in a narrow particlesize range - such as one with 70-80 per-
cent of particles in one size range - feel
soft and do not provide good traction.
These sands do not have enough fine par-
ticles to limit particles shifting.
Other problems can contribute to soft
soils, but they occur primarily on fine-
textured soils. These include waterlogged
conditions and slippage zones. Obviously,
high traffic and sharp tuming create more
surface stability problems on any soil
regardless of texture.
Solutions to working with soft sandsinclude:
Avoiding sands that are too
uniform.
Adding organic matter to aid in
stabilization.
Promoting good root development.
In special situations, using root zone
stabilization materials such as VHAF (ver-
tical, horizontal and angular fibers) or
Netlon mesh.
Maintaining good moisture during
times of high traffic. Moist but not satu-
rated sands have appreciably more rigid-ity than do dry sands.
In conclusion, we often think of sandy
soils as possessing good soil physical
properties. They do in comparison to
fine-textured soils subjected to traffic.
However, a surprising variety of soil phys-
ical problems can still occur on what we
classify as sandy soils or sandy root zone
media.
Management of sandy soils has its
challenges. Turf managers will continue
to find that sands and sandy soils can beextremely variable growing media. 0
Water holding capacity of sandy soils canbe increased with the addition of organicmaterials. On-site mixing, however, may
result in incomplete integration ofmaterials.
They plug many of the macropores
formed by a medium-to-coarse sand.
Sands with wide particle size distribu-
tions are harder because the particles fit
together into a more dense media. This
occurs whether the fine particles are very
fine sand, silt, clay or a combination.
Many concrete and mortar sands are hard
if they are used for growing turf because
of their wide particle size ranges.
Organic content, whether it is
achieved by the addition of organic
matter or by roots helps soften hard sands
to some extent. Thatch development of
% to Y 2 inch also will create resiliency.
However, hard sands that are the result
of a wide particle size distribution or the
presence of excessive fines continue to
exhibit poor water movement and remain
hard when dry. Topdressing with a
rounded sand in the medium-to-coarse
range improves conditions over time if
performed in conjunction with core
aeration.
"Soft" sands that have a tendency toshift create another problem, especially
from p. 38COARSE SOILS
40 Golf Course Management / February 1992