Lawn Care/Basics
for Homeowners-Lawn Care/Down to Earth
The physical properties of soils- color, texture,
structure, density, and porosity, and the
clay and organic matter
content- are dominant factors affecting the use of soil. These properties
determine availability of oxygen in soils, movement of water into and through
soil, ease of root penetration, compaction,
erosion, and tillage, and ability of soil
to hold nutrients and pesticides and support a diverse biological community.
Some more localized or specific discussions of soils and soil characteristics
include:
(California) Aeration, Compaction and Drainage
http://ohric.ucdavis.edu/Newsltr/CTC/ctcv11_3.pdf
(Colorado) Soil Sampling
http://www.ext.colostate.edu/pubs/crops/00500.html
(Colorado) Managing Soil Compaction
http://www.ext.colostate.edu/pubs/crops/00519.pdf
(Georgia)
Soil Testing for Home Lawns and Gardens
http://pubs.caes.uga.edu/caespubs/pubcd/L387-w.htm
(Nebraska) Guidelines for Soil Management
http://www.ianr.unl.edu/pubs/soil/g1000.htm
(Nebraska) Management Strategies to Minimize and Reduce Soil Compaction
http://www.ianr.unl.edu/pubs/soil/g896.htm
(Ohio) Soil Compaction and Drainage
http://ohioline.osu.edu/b301/index.html
(Ohio) Software: Soil Fertility Short Course
(1993 DOS program)
http://ohioline.osu.edu/software/soilfsc1.exe
You will receive a self extracting archive file SOILFSC1.EXE.
This file will require 250 Kb of free disk space to download
and an additional 752 Kb of available disk space to unarchive.
(Texas) How to Take A Soil Sample
http://aggieturf.tamu.edu/aggieturf2/soilsample/soilsample1.html
(Wisconsin) Power Point Course: Basic Soil Concepts
http://www.soils.wisc.edu/extension/teachingmaterials/BasicSoilConcepts/index.htm
(Wisconsin) Power Point Course: Phosphorus Basics
http://www.soils.wisc.edu/extension/teachingmaterials/P_Basics/index.htm
Components of a Soil
Soil is composed of four major components: air and water which occupy pore
spaces, and organic and inorganic particles which make up the solid space.
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Soil Horizons
Examination of the soil solid components reveals a range of colors, particle
sizes, and shapes. These properties are used in distinguishing horizons in a
soil profile. A soil horizon may be defined as a layer of soil, approximately
parallel to the soil surface. The soil profile, includes the collection of horizons,
the natural organic layers on the soil surface, and the parent material and
other layers beneath the column that influence the development and behavior
of the soil.
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Soil Color
Color is the most obvious characteristics of soil and provides information
about important soil characteristics such as drainage, organic matter content,
and temperature. Soil color is influenced by the oxidation state of iron and
manganese. Well-oxidized conditions result in colors such as red, brown, and
yellow while grays and blues predominate if insufficient oxygen is present.
Poorly drained soils, characterized by s gray color, created many crop production
problems.
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Soil Texture
Soil texture refers to the relative proportion of the various size groups
(sand, silt, and clay) in a mass of soil. Classes of soil texture are based
on different combinations of sand, silt, and clay. Sand grains are rough and
irregular, depending upon the degree of weathering and have low plasticity,
which refers to the ability of moist soil to be molded. Silt-size particles
are smaller and feel smoother than a sand separate. Clay feels sticky when moist
due to its high affinity for water. Rarely, if ever, do soil samples consist
wholly of one size of material (sand, silt, or clay).
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Density and Pore Space
Bulk density and porosity control water and air movement
and root growth. Bulk density is the weight of a "bulk volume" of soil. Bulk
density includes both solid and pore space- so as we compact a soil pore space
decreases and bulk density increases and adding organic matter usually results
in a more porous soil, decreasing bulk density. Pore space is critical because
this is where roots grow, respire, absorb water and nutrients. It is also where
water is transmitted through and stored in the soil.
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Clay Minerals
The colloidal particles (clays and humus) are extremely small and as such,
they expose a large external surface area per unit mass. They also have an electronegative
charge that aids in the adsorption of water, anions and cations, and organic
molecules on colloidal surfaces.
The importance of clay is that it determines nutrient holding capacity of the
soil. The cation exchange capacity is a measure of the nutrient holding capacity.
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Cation Exchange
Cations (+) are attracted to the negative sites on clay and humus surfaces,
but they can be displaced by (exchanged for) other cations. Cation Exchange
Capacity (CEC) is a measure of the number of negative sites on a unit of soil
(milliequivalents (meq) per 100 grams of soil; e.g. 12 meq/100g).
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Soil Reaction and pH
pH is a method of indicating the concentration of acid (hydrogen ions) in
the water or in a soil solution. A low value indicates higher acidity (for example,
battery acid has a pH of 1) while a higher value indicates a more alkaline (less
acidic) solution (for example, a calcareous soil with high limestone content
may have a pH of 8.0. A neutral pH is 7.0.
pH: is commonly measured with indicator dyes or with pH meters.
Soils that are too acidity affects the availability of nutrients to plants
and needs to be monitored and controlled. Causes of acidity include:
- Leaching by rain over many years is the primary cause in humid climates.
- Application of ammonium forms of N fertilizer (ammonia, ammonium, urea)
releases hydrogen ions.
- Crop removal of basic cations Limestone and gypsum are two common calcium
compounds available to homeowners.
Limestone works to lower pH since water reacts with the calcium to form bicarbonates,
but gypsum reacts with water to form sulfuric acid and will actually lower pH.
The table below offers a field method of estimating the amount of lime needed
in your lawn. It uses pH, texture and organic matter content of the soil.
| Estimated limestone (tons/A0) to restore pH to 6.5. |
| |
Present pH |
| Soil Texture |
Soil Color |
4.5 |
5.0 |
5.5 |
6.0 |
| |
| Sands & Sandy Loam |
Light |
3 |
2 |
1.5 |
0.5 |
| |
Moderately Dark |
5 |
3 |
2 |
1 |
| |
Dark |
8 |
6 |
4 |
2 |
| |
| Loam & Silt Loam |
Light |
4 |
3 |
1.5 |
1 |
| |
Moderately Dark |
5 |
4 |
2 |
2 |
| |
Dark |
6 |
5 |
3 |
2 |
| |
| Clay Loams & Clays |
Light |
5 |
5 |
3 |
2 |
| |
Moderately Dark |
7 |
6 |
4 |
2 |
| |
Dark |
9 |
7 |
5 |
2 |
Acidifying soils or lowering their pH is done mainly to increase solubility
of iron and manganese for plants that can not get adequate supplies from high
pH soils. e.g. azeleas, rhododendron, pin oak trees, some red maple trees, etc.
Common methods of lowering the pH include:
- Powdered sulfur (oxidizes slowly to sulfuric acid)
- Ferrous sulfate or aluminum sulfate
- Sulfuric acid (reacts rapidly and
is expensive - must be handled with care)
- NH4 fertilizers: (NH4)2SO4,NH4NO3, NH3 (NH4)2SO4 produce acid as the NH4+
converts to NO3-and releases pH. Acidifying a soil with fertilizer is a slow,
long term effect.
Acidifying most calcareous soils is not feasible because of the large amount
of calcium magnesium carbonates they contain.
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Soil Organic Matter
Soil organic matter is the organic fraction of soil, including plant
roots, animal and plant residues, and microbial biomass. Organic matter influences
the chemical and physical properties of soils even at the relatively low amount
usually found in soils.
Mineral soils with an adequate supply of organic matter have good tilth (workability).
Organic matter is responsible for 20-30% of the cation exchange capacity of
soils. The original source of organic matter is plant tissue. Soil organisms
decompose these materials and synthesize a dark, amorphous, colloidal mass,
called humus. Humus is the active component of soil organic matter and is responsible
for water retention, nutrient retention and cohesion.
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Salts
High levels of soluble salts such as Na+ can be a severe problem in western
soils and can affect water availability to plants, but salinity is generally
not an issue in humid areas.
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Soil Testing
 |
Image Source: Texas A&M
Turfgrass Program |
You can get soil sample bags and forms from your local county extension office,
or you can use a pint sized plastic bag as your soil sample bag.
Once you have taken the soil sample, seal it in an official sample bag or
a plastic bag. Mail your sample and information sheet to the appropriate Soil
Testing Laboratory along with a check or money order.
Materials Needed:
- Sample Bag (or plastic bag that will hold one pint of soil)
- Spade or Soil Probe
- Plastic Bucket
- Soil Sample Information Form
http://aggieturf.tamu.edu/aggieturf2/soilsample/soilsample2.html
http://aggieturf.tamu.edu/aggieturf2/soilsample/soilsample3.html
http://aggieturf.tamu.edu/aggieturf2/soilsample/soilsample4.html
http://aggieturf.tamu.edu/aggieturf2/soilsample/soilsample5.html
Click here for links to most United States Cooperative
Extension Service Soil Testing websites.
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Soil Modification
Soil modification is the practice of incorporating texture
and structure enhancing materials, which may or may not involve the existing
soil, for the purpose of improving the soil physical and chemical conditions
of the turfgrass root zone. Soil modification
is sometimes done in areas having high clay or high sand content or in areas
that are compacted from heavy traffic.
The amendments normally added to soils are organic matter and sand.
Organic matter increased the water holding capacity of sandy soils. The organic
matter should be well decomposed with an organic matter analysis of at least
90%. The best sources of organic matter for soil modification are peat
moss, sphagnum peat moss, and reed-sedge peat.
The addition of sand to a heavy soil improves the aeration, water
infiltration and water movement, and reduces the tendency for soil compaction.
The best procedure for adding sand to a soil is to mix the soil and sand together
off site and then haul the mix to the area that to be modified. It is virtually
impossible to get a uniform mix by tilling sand into a soil on site.
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Return to:
Lawn Care/Basics
for Homeowners-Lawn Care
Page Updated June 28, 2005
Components
of a Soil