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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
16
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.
17
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
19
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
20
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
21
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
23
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
26
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
27
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.
31
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.
32
pH Scale
33
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.
34
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.
35
36
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
41
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.
42
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.
43
Jar Test Example
45
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.
46
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.
47
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