Soil Preparation to Establish

Healthy Turf

Presented at the Sustainable Turfgrass

Management for Landscape Professionals

Workshop in Sacramento, California

by Bill Baker

Soil Physical Problems

• Compaction

• Heavy clay

• Too sandy

• Poor drainage (percolation)

• Low infiltration rate

• Low organic matter content

Soil Structure

• Structure refers to the way soil particles clump

together into larger units

• These large units are called aggregates

• Aggregates that occur naturally in soils are called

peds

• Clumps of soil caused by tillage are called clods

• Structure can alter the effects of texture

• Compaction = reduction of aggregates

Soil Texture

• Soil texture describes the proportion of three sizes of

soil particles sand (large), silt (medium), and clay

(small).

• The three particle groups are called “soil separates”.

• Soils should also be about 50 percent open space

(pores) – about half of which should be filled with

water and the other half air.

• Ideally, soils should also include about 5 percent

organic matter.

Comparison of Particle Sizes

Very coarse sand = 2.00 - 1.00 (mm)

Coarse sand = 1.00 - 0.50 (mm)

Medium sand = 0.50 - 0.25 (mm)

Fine sand = 0.25 - 0.10 (mm)

Very fine sand = 0.10 - 0.05 (mm)

Silt = 0.05 - 0.002 (mm)

Clay = < 0.002 (mm)

Effects of Texture (particle size)

• Surface area

- small particles have more surface area

- high surface area = greater H2O capacity

• Number and size of pore spaces

- large particles have larger pores

- small particles have smaller pores

- water drains rapidly through large pores

Sand Particles

• Sand is the largest soil separate

• Composed mainly of weathered grains of quartz

• Almost all sand sizes are visible to the eye

• Gritty to the touch

• Grains do not stick together

• Sandy soils have poor nutrient and moisture holding

capability

Silt Particles

• Silt is the medium size soil separate

• Silk particles are silky or powdery to the touch

like talc

• Like sand, silt particles do not stick together

• Silt has the best ability to hold large amounts of

water in a form that the plant can use

Clay Particles

• Clay is the smallest soil separate

• Mostly in the form of tiny, sheet-like crystals

• Clay results from chemical reactions between

weathered minerals to form tiny particles of new

minerals

• Clay can bond nutrients chemically to their

surfaces

Particle Density

• Refers to the weight and density of the soil

without the pore spaces

• Think in terms of a soil being a solid block instead

of a permeable mixture of particles

Bulk Density

• Refers to the mass of a volume of undisturbed,

oven-dry soil

• Bulk density measurement includes pore space

• Bulk densities of mineral soils depend mostly on

the pore space

• Organic soils are much lighter

Soil Porosity

• Soil porosity = total pore space

• Measure of the soil volume that holds air and

water

• Porosity increases at finer textures

• The porosity of sand is less than clay

Permeability

• Refers to the ease at which air, water, roots move through soil

• Permeability depends partially on the number of pores, but the size and continuity of the pores is more important

• Large pores (macropores) occur between large particles

• The rate of water movement in soil (hydraulic conductivity) relates directly to permeability

Infiltration Rates of Different

Soils

Measured in inches per hour

Sand-coarse 1.00-8.00

Sand-very fine 0.50-3.10

Sandy loam 0.40-2.60

Loam 0.08-1.00

Clay loam 0.04-0.60

Clay 0.01-0.10

Site Preparation – Soil Amendments

ADD SOIL AMENDMENTS IF:

• The soil is compacted

• The soil is heavy clay

• The soil drains poorly

• The soil is very sandy

• You want to minimize irrigation

• You want to have superior turf for years to come

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Mulch versus Compost

• Compost is an organic feedstock materials that has

been decomposed and stabilized through biological

decomposition

• Organic mulches are used as a soil cover and

generally have not been decomposed - but composts

can easily fill this role.

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Uses of Composts in Turf

• Incorporate into existing soil

• Mix into new growing mediums

• Apply as component in topdressing

• Seed cover

• Mulch

• Cosmetic appeal

Benefits of Compost to Turf

• Improves soil structure

• Improves soil fertility

• Adds beneficial soil micro-organisms

• Reduces irrigation requirements

• Improves commercial fertilizer utilization

• Suppresses plant diseases

• Reduces off-site transport of pollutants

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Composition of Composts

• Vegetative Based Composts – improve soil

structure but add limited amounts of nitrogen

• Animal Based Composts – this category is

primarily manures and they are high in nitrogen but

add only minimal improvements to soil structure

• Biological Solids – this is domestic waste and

performs similarly to manures

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Advantages Over Non-

Composted Organics

• Will not draw nitrogen from the soil

• Will not generate unpleasant odors

• Will not be a carrier for weed seeds

• Will not support pathogenic organisms

Non-composted can be defined as materials that have not gone through a

decomposition (decay) process

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Disadvantages of Composts

• Composts are generally higher in salts and pH then native soils or other amendments

• Compost quality is inconsistent in the marketplace and greatly depends on credibility of the supplier

• The soil structure improvements derived from composts are most effective in the first 5 years and diminish in following years

Selecting Quality Composts

• Watch for visible contaminants

• Should have a pleasant aroma

• What is the texture and appearance

• Is the particle size appropriate and uniform

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Terms Associated with Composts

by Successive Stages of Improvement

• “Green” - unprocessed or early stages

• “Active” - decomposition is incomplete

• “Stabilized” - completed decomposition

• “Mature” - recombined into humus

• “Cured” - colonized by beneficial org.

Compost Analysis

Considerations

• pH of compost

• Salt concentration

• Moisture content

• Organic matter content

• Water holding capacity

• Trace heavy metals

• Nutrient content

FIELD GUIDE TO VERIFYING SOIL QUALITY AND DEPTH

IN NEW LANDSCAPES – Washington State BMP Manual

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Sand Amendments

• Sands have the advantage of being permanent in

altering soil structure

• Purchase from a reliable source – sands can be very

high in pH or have contaminants

• Sands will not retain nutrients, but this may not be a

problem if the soil has an original high clay content

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Sand Amendments2

• Sands should be “washed” or “double-washed” to

remove clays and fine sediments.

• Sands should also have been “screened” to remove

pebbles and rocks

• Sand suppliers should be able to provide a “spec”

sheet on the material

• Adding too little sand may do more harm than good

Soil Chemical Problems

• Alkalinity – High pH

• Acidity – Low pH (not us)

• High Sodium

• High Total Salts

• Low Fertility

• Ion Toxicity

Site Preparation – Soil Tests

CONDUCT A SOIL TEST IF:

• Soils in your region are known to be problematic

• There are identified water quality issues

• Other turfgrass sites and landscapes in the area are in

decline or under stress

• You want to be sure you always putting down the

correct nutrients

Soils and Irrigation Water

• Soils and irrigation water are two parts of the same puzzle.

• In many cases we analyze the same properties in both the soil and water.

• Whatever problems we see with the irrigation water

we can soon expect to see in the soil.

• Existing issues with the soil will be compounded if similar problem are found in the irrigation water.

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pH Definition

The pH, or “potential of Hydrogen” is the scale that

measures the relative acidity or alkalinity of a

solution. Solutions are measured from zero (totally

acid) to fourteen (totally alkaline) and seven is

neutral.

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pH Scale

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How the pH Scale Works

Like the Richter scale that's used to rate

earthquakes, the pH scale is not linear. The

intervals between numbers is logarithmic, which

means every number on the scale shows ten times

less H concentration than the number below. Soil

with a 5 is ten times more acidic than soil with a

pH of 6.

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Cation Exchange Capacity (CEC)

• Any element or molecule with a positive charge is

called a cation

• Basic cations include calcium (Ca+2), magnesium

(Mg+2), potassium (K+1) and sodium (Na+1)

• Acidic cations include hydrogen (H+1) and aluminum

(Al+3).

• The amount of positively charged cations a soil can

hold is described as the CEC and is expressed in

milliequivalents per 100 grams (meq/100g) of soil.

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Plant Nutrients

Element Chemical Symbol

Source Available

Form

MAJOR

Largest

quantity

Nitrogen

Phosphorus

Potassium

N

P

K

S-F

S-F

S-F

NH4+ , NO3

-

HPO4= , H2PO4

-

K+

SECONDARY

Medium

quantity

Sulfur

Calcium

Magnesium

S

Ca

Mg

S-F

S-F

S-F

SO4=

Ca++

Mg++

MINOR

Smallest

quantity

Iron

Manganese

Boron

Copper

Zinc

Molybdenum

Chlorine

Fe

Mn

B

Cu

Zn

Mo

Cl

S-F

S-F

S-F

S-F

S-F

S-F

A-W

Fe++ , Fe+++

Mn++

H2BO3-

Cu++

Zn++

MoO4=

Cl-

Carbon

Hydrogen

Oxygen

C

H

O

A-W

A-W

A-W

CO2=, CO3

=

H+

Many forms

S = Soil, F = Fertilizer, A = Air, W = Water

Soil Preparation – Pre-plant

Fertilizers

WHY USE PRE-PLANT FERTILIZERS?

• They are high in phosphorous – an important nutrient

for root development

• Phosphorous is difficult to infuse in the soil profile

later

• The fertility will be almost immediately available to

the new sod

• New turf requires 25 – 50% more fertility the first

year

Site Preparation - Conditioners

• Add a soil conditioner if the soil test results

recommends it

• Add a conditioner absent a recommendation if you

just want to have some insurance against soil

problems and improve the soil long-term

• A safe, and almost always helpful, conditioner is

gypsum at 25 lbs. per 1,000 square feet

Site Preparation – Incorporating

amendments, conditioners, and Pre-

Plant Fertilizers

• All materials can be mixed into the soil at the same

time.

• Mix to a full 6 inch depth

• Use a roto-tiller or do it by hand with a shovel.

• Roll and water thoroughly after mixing to stabilize

the soil and start the breakdown of the materials

Classifying Soils by Percentages

of Sand, Silt, and Clay

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Performing a Jar Test

• A reasonable estimate of the amounts of sand, silt,

and clay can be determined by filling a quart-size

jar half full of soil and the other half water.

• Add a teaspoon of soap solution to break up water

and soil tension. Shake thoroughly and let it set

long enough to settle out.

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Performing a Jar Test2

Sand

Most of the sandy particles sink and form a layer on

the bottom, and the water looks fairly clear.

Silt

The silt fraction will settle on top of the sand and

before the clay. It will be noticeably darker than the

other two soil types.

Clay

The water is cloudy with a thin layer of particles on

the bottom. The tiny clay particles take ages to settle.

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Jar Test Example

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Conducting a Soil “Feel Test”

• Determining Your Soil Type The "Feel Test" can help you determine your soil type.

• Take just enough moist soil to rub between the thumb and fingers.

• Rub it back and forth several times and feel it very carefully.

• Clay soils will be slick and smooth, with little or no grittiness.

• Sandy soils will be gritty and will not stick together well.

• Loamy soils will stick together easily, but not like a clay soil. Loam will feel moderately gritty.

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Loam Soils (or Sandy Loams) are

Preferable for Plant Growth

• Loam soil is a mix of sand, silt or clay, and organic matter.

• Feel: Loam soils are loose and look rich. When squeezed in your fist, moist loam will form a ball which crumbles when poked with a finger.

• Infiltration: Loam is the best soil for infiltration of rainwater and for healthy vegetation. Loam soils normally absorb water and store moisture well. Loam soils can be sandy (preferable) or clay (less desirable) based, and will vary in moisture absorption and retention.

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Defining Loams by Percentages of

Sand, Silt, and Clay

Central Ranges of Percentages for Loams as

defined on the

Soil Pyramid

• Loam = 40% Sand / 40% Silt / 20%Clay

• Sandy Loam = 70% Sand / 20% Silt / 10% Clay

• Clay Loam = 30% Sand / 30% Silt / 40% Clay