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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

32 Golf Course Management / February 1992


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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.


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-



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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

