Soils 101 and
Understanding the Soil Analysis
Michael J. Curry, BS, PLA, ASLA
GreenSite, Inc.
m.curry@greensiteinc.com
The Ideal Soil Composition
The Soil Ecosystem It is important to understand the complex
relationships within the living system known
as soil. Soil environments vary by location
in terms of content, structure and chemical
make-up.

Critical aspects of soil
 Physical properties
 Structure, Texture, and Density
 Soil Profile
 Soil layers interface
 Chemical properties
 pH, EC, CEC, C:N, and Nutrients
 Organic properties
 Organic Matter
 Soil Biology
Soil TextureRefers to the relative proportion
of mineral particles, of various
sizes in a given soil.
Soil Texture
Soil Structure and Aggregation

Structure refers to the arrangement of soil
particles, their shape, size and stability.

This plays a major role in how the soil functions.

Large aggregations called Peds!

Sand, silt, clay, and OM particles glued together
Bulk Density or Compaction Bulk density is a measure of a soils mass per unit volume of
soil. It is used as a measure of soil wetness, volumetric
water content, and porosity. Factors that influence the
measurement include; organic matter content, soil porosity,
and the soil structure. These factors will in turn control
hydraulic conductivity.
 Bulk density is used to used to calculate the total porosity.
 The higher the bulk density the more compacted the soil.
 A soil that has a well developed structure will become less
dense as porosity increases; as a result the bulk density of
the soil will decrease.
Permeability and Porosity

Permeability (aka-Saturated Hydraulic Conductivity (ksat) & Infiltration
Rate) is the ability of water to move down through soil and at what rate.

Soil porosity is the quantity of voids in a soil sample.

Permeability and Porosity are directly influenced by the soils texture,
structure, and density as well as the type and distribution of organic
matter.

The number of pores as well as the size of pores affect permeability.
Larger pores allow for more movement and more readily available water
for plant growth, but smaller pores do not. However, the largest pores are
not necessarily most conducive to growth.

Soils with a fine texture hold more water but medium-textured soils are
actually best for growing plants.
Soil Density and Effects of Compaction
Type of Material
Bulk Density (grams/cm3)
Normal soils
1.0 to 1.6
Soils with restricted root growth
1.4 to 1.6
Bricks
1.4 to 2.3
Soil commonly found at construction sites
1.7 to 2.2
Total Pore Space %
Bulk Density (grams/cm3)
58
1.1
55
1.2
51
1.3
47
1.4
43
1.5
40
1.6
36
1.7
Chemical Properties
 The chemical composition of soils are important in soil and plant
health. These affect how nutrients circulate through soil.
 Chemical composition depends on pH or acidity content, soil
structure and the chemical activities that take place between soils,
soil organisms, and plants.
 The chemical properties of soil are easier to modify than physical
properties, especially after the soil is installed.
 Therefore, design emphasis should be placed on soil physical
properties.
Nutrients
There are 14 plant
nutrients that are
essential for plant
growth.
 There are only 3 that
you need to worry about
most of the time.
 Nitrogen
 Phosphorus
 Potassium
pH
•
pH is one of the most important chemical properties. It affects
nutrient availability and microbial activity. Most plants and
microorganisms prefer a pH range of 6-7.
•
pH is a measure of the active hydrogen in soil. The presence or
absence of hydrogen determines whether the soil is acidic or
alkaline.

It is important to know the optimum pH range for the plants to be
grown, however…

Don’t expect a pH range of 6-7 if you are in the SW US or along
the limestone belt from Western Massachusetts to Iowa. You
probably won’t get there.

Plants tend to be more tolerant to alkaline, rather than acidic
soils.
Buffer pH (or Buffer Index)
• Buffer pH is the resulting sample pH after a liming material is added.
This liming material is called the buffer solution and it acts as an
extremely fast- acting lime. Each soil sample receives the same
amount of buffering solution; therefore the resulting pH is different
for each sample. To determine a lime recommendation, we look at
the difference between the original soil pH and the ending pH after
the buffering solution had reacted with the soil.
• If the difference between the two pH measurements is large, it
means that the soil pH is easily changed, and a low rate of lime will
be sufficient. If the soil pH changes only a small amount after the
buffering solution has reacted, it means that the soil pH is difficult to
change and a larger lime addition is needed to reach the desired pH
for the crop.
Lowering pH
 Know that lowering pH of alkaline soils is difficult and often unnecessary.
 Sulfur products can be used but this is not sustainable.
 Nutrient deficiencies associated with high pH are often not present. This
depends on the sensitivity of the plant (e.g. Pin Oak). It may be more
economical and effective to treat for nutrient deficiencies with fertilizer
rather than continually trying to adjust the pH.
 Bio-Stimulants can also be used to aid the plant in nutrient uptake
 You have to know what is driving the pH up. If you have even a small
amount of free calcium carbonate in the soil, reducing the pH will be
impractical, if not impossible!
Excess Carbonate
• This measures the amount of free limestone in the soil.
• This test is reported as: Very Low, Low, Medium, High, Very High. As
the rating increases so the amount of free limestone.
• Changing the amount of excess carbonate in the soil is difficult and
economically impossible to do. However, it can be important in
herbicide selection as well as selection of fertilizer application
techniques.
Soluble Salt or Salinity (EC) 
Electrical Conductivity (EC) is a measure of the level of soluble
salts a soil contains.

Problems with irrigated soils can occur when there are elevated
evaporation rates and low rainfall. This causes salts to build up.

Buildup can also occur due to irrigation water, compost, manure
and fertilizers.

It is possible to leach the salt by gradually applying surplus
water.
Saturated Paste Extract dSm or mmho/cm
Low
Moderate
High
Very high
< 1.5
1.6-3.9
4-5
>5
Exchangeable Sodium (Na)
High sodium levels in the soil can result from poor drainage and
soil compaction issues.

Excess sodium in soil can impede plant roots from taking in
important minerals such as calcium, potassium and magnesium.

You can manage high levels of sodium by maintaining optimal
levels of calcium in the soil.

Gypsum, or calcium sulfate, is often used in sodic soils to remove
sodium and help balance pH levels.

Sodium Index is a measure of the portion of the CEC occupied
by sodium; a sodium level of less than 15% is acceptable and
levels of greater than 15% are excessive and harmful to plants not
adapted to saline conditions.
Cation Exchange Capacity (CEC) The total amount of
exchangeable cations that a
particular material or soil can
adsorb at a given pH.
 Exchangeable cations are held
mainly on the surface of colloids
of clay and humus, and are
measured in milligramequivalents per 100 g of material
or soil.
 In general, the higher the CEC,
the higher the soil fertility.
Carbon to Nitrogen Ratio

The C/N ratio (C:N) or carbon-to-nitrogen ratio is a ratio of the
mass of carbon to the mass of nitrogen in a substance. Carbonto-nitrogen ratios are an indicator for nitrogen limitation of plants
and other organisms.

The carbon to nitrogen ratio for natural soils is typically between
10:1 and 20:1.

High C:N causes Nitrogen draft or pulling N out of the soil to feed
the decomposition process.
Percent Base Saturation

The ratio of quantity of exchangeable bases to cation exchange
capacity. It is a measure of the amount of electron charges that
are occupied by the cations: primarily calcium, magnesium, and
potassium vs. aluminum and hydrogen.

A high base saturation reduces soil acidity (or increases
alkalinity) and increases supply of other plant nutrients.

By comparing the actual percent with the suggested percentage
an idea of which kind of soil amendment (Lime, Gypsum, Sulfur)
may or may not be needed.
Nitrate (NO3)
• Nitrate-Nitrogen is the amount of available nitrogen present in the
soil at the time it was analyzed in the laboratory.
• Because of it's solubility it can leach rapidly on various soil
conditions. This mobility makes it difficult to predict how much
nitrogen will be present through out the growing season.
• However, it can be a useful tool for determining nitrogen utilization
efficiencies at the end of the growing season.
Phosphorus (P)
 Two types of phosphorus extractions are used for analysis, type is
determine by the soil pH.
 If pH is < 7.2 a Bray I extraction is used, > than 7.2 an Olsen
extraction is used.
 The interpretation of the two methods are different, the following
table defines the two.
Rating
bray p (pH<7.2) ppm
olsen p (ph>7.1) ppm
Low
1-15
1-19
Low to Adequate
15-25
10-15
Adequate
26-40
16-24
High
> 40
> 24
Potassium (K)
• Potassium is a cation which is held on the soil's exchange sites.
• The form of potassium extracted is the readily available K.
• The following table provides a generalized interpretation for
potassium. Soil textures have a great influence on it's availability.
With sand textures high levels of K may be difficult to obtain
because of it's ability to leach.
Rating
Low
Potassium (ppm)
1-120
Low to Adequate
121-190
Adequate
191-300
High
> 400
Zinc – Manganese – Copper - Iron
Below are the tables which gives a general interpretation for these
micro-nutrients.
Rating
Zinc (ppm) Manganese (ppm)
Copper (ppm)
Iron (ppm)
Low
0.1 - 0.8
0.1 - 2.5
0.1 - 0.4
0.1 - 4.5
Low to Adequate
0.9 - 1.2
2.6 - 4.0
0.5 - 0.9
4.6 - 7.0
Adequate to High
1.3 - 3.0
4.1 - 12.0
1.0 - 2.0
7.1 - 20.0
> 5.0
> 50.0
> 2.0
> 70.0
High
Sulfur - Boron
• Below are the interpretation tables for sulfur and boron.
• Both of these elements are soluble in water and subject to leaching.
Rating
Sulfur (ppm)
Boron (ppm)
Low
1-4
0.1 - 0.5
Low to Adequate
5-9
0.0 - 0.9
10 - 25
1.0 – 1.5
> 25
> 2.0
Adequate
High
Organic Properties & Soil Biology
A soils organic matter is derived from living things. Decomposer
organisms in the soil break down the wastes and remains of
plants, animals and other organisms, a process that enriches the
soil with nutrients, such as nitrogen and phosphorus, and creates
humus. Not only is humus a key component of soil structure, it
also retains water and nutrients that plants and other organisms
in the soil need.
A soil ecosystem's health depends on having adequate
organic matter
So an ongoing supply
of fresh organic matter
is needed to replace
what the living things
in soil consume.
Organic Properties & Soil Biology
Soil microorganisms play a critical role in soil health. Fungi and
bacteria decompose organic material, and some work symbiotically
with plants, providing them with nitrogen or enabling them to absorb
more water and nutrients (mycorrhizae).

The activity of soil organisms is influenced by soil temperature,
available oxygen, soil pH, and the amount and type of organic matter.

Microbial activity increases with temperature, available oxygen, and
with the introduction of organic matter as the energy source to support
microbial growth.

Any activity or practice that encourages soil microbial activity
will enhance soil health!!!
Soil Sampling and Testing Laboratories Sampling methods and the lab you use will vary depending on the
material, and what you are testing for.
 There are many things to consider, among them are:
 Chemical Properties
 Physical Properties
 Biological properties
 Toxic compounds
 Particle size and distribution
 Structural capacity
 In stockpiles
 In place at grade
 Etc…
Soil Test Analysis
 Determine what tests you will need to be
performed on the samples.
 Determine what lab you will need to send the
samples to.
 Be sure the samples are collected according to
the quantity and method required by the lab,
and the testing to be performed.
 Submit with plenty of lead time for the specific
project.
Soil Sampling
 Promotes environmental quality and stewardship, encourages plant
growth and health by diagnosing and providing appropriate rates and
recommendations for fertilizer and amendments, and SAVES MONEY!
 A soil sample must be taken at the right time and in the right way. The
tools used, the area sampled, the depth and the correct mix of the
sample, the information provided, and packaging all influence the
quality of the sample.
 Sample and test soil before starting any new planting.
 Sample and test existing and established areas every 3-4 years.
Soil Testing
Know that there are different methods
for soil testing that will produce different
results. And different labs often come up
with varying results even when using the
same test methodologies.
You should use a lab that you and/or your soils consultant are familiar
and confident with. You will get used to reading a test report you see
the same format and methodologies over & over.
What is important is the interpretation. Soil test labs and consultants
should make interpretations on the results relative to the test methods
they are using.
Sampling Tools-
Soil Sampling
Understanding the Soil Analysis Report
 Reading and understanding a soil analysis test report can be a
challenge because the information is detailed and complex, but it
can help you optimize treatment and how you amend and maintain
the soil.
 Correctly using a soil analysis report aids in using the right amounts
of fertilizers, chemicals, and amendments.
 Working with a good lab and soils consultant that can provide you
with explanations and recommendations is particularly helpful.
The D50 size, called the median grain size, is the grain diameter for which half
the sample (by weight) is smaller and half is larger.
Uniformity Coefficient Cu = D60/D10 is 60. Should be 2-4 in a sand based mix.
The higher the value, the less uniform, and the greater potential for packing.
Organic Matter Amendment
 Supports soil organisms Restores soil life
 Buffers pH, acid or alkaline
toward optimal 6.3-6.8
 Reduces bulk density
(compaction)
 Improves water holding
capacity
 Improves soil structure
 Increases CEC, nutrient
storage and availability
 This will happen…over time!
Restore soil life to restore soil functions
 Soil biology and the benefits:













Improve soils structure
Natural nutrient cycling
Increased nutrient uptake
Plant disease protection
Reduction of pests
Elimination of synthetic inputs
Bio-filtration
Erosion control
Stormwater detention and moisture retention
Reduction of water use
Increase in living diversity in the landscape
Increase in carbon sequestration into soil
Quicker plant acclimation
Organic matter (Carbon) kickstarts the soil ecosystem
by providing food and home for organisms!
What is % Organic Matter????
 OM is reported in a lab test by loss-onignition method.
 Most composts and plant materials are
30-60% OM by this method (or 40-70%
mineral).
 Know the characteristics of the
materials you are working with and
match the C:N and nutrients of the
amendment to your plant needs
Amending Soils with OM Adding 10% compost (by moist volume) into the soil
does not increase the Soil Organic Matter (SOM) by
10%. It will raise the tested SOM by only 1-3%
(depending on the organic content of the compost, and
it’s dry density relative to the heavier soils density).
 Use coarse compost or Pine Bark fines to amend clay
and other fine textured soils.
 Add most compost to the upper 8-12” of soil to mimic a
natural profile. Rip a little compost deeper when
subsoiling to restart the soil life.
 Too much compost too deep in the soil profile promotes
anaerobic conditions
One “Size” does not fit all
You may need multiple organic soil amendments
Fine OM
Coarse OM
References and Resources

Urban, James. Up by Roots, International Society of Arboriculture, 2008

Soil Science Society of America
www.iheartsoil.org

Turf and Soil Diagnostics
www.turfdiag.com

AgSource Harris Laboratories
www.agsource.com

Soil and Plant Laboratory
http://waypointanalytical.com/

Michael J Curry, BS, PLA, ASLA , GRP
m.curry@greensiteinc.com