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Environmental Study Group November 30, 2004 Soil Characterization


Environmental Study Group November 30, 2004 Soil Characterization & Sampling for Effective Surface Reclamation of Saltwater-Impaired Soils – PowerPoint PPT presentation

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Title: Environmental Study Group November 30, 2004 Soil Characterization

Environmental Study Group November 30, 2004
Soil Characterization Sampling for
EffectiveSurface Reclamation of
Saltwater-Impaired Soils
Soil Characterization Sampling for
EffectiveSurface Reclamation of
Saltwater-Impaired Soils
  • Gilbert J. Van Deventer, PG, NMCS, REM
  • gil_at_trident-environmental.com
  • Trident Environmental, PO Box 7624, Midland TX
  • Office 432-682-0808
  • Fax 432-682-0727
  • Mobile 432-638-3106
  • Website Address www.trident-environmental.com

Sources of information Remediation of
Salt-Affected Soils at Oil and Gas Production
Facilities, API Publication No. 4663, Oct.
1997 The Nature and Properties of Soils, by
Nyle C. Brady, 1990, 10th Edition, McMillan
Publishing Co. Seeding Rangeland, by Tommy C.
Welch, et al, April 1994, Texas Agricultural
Experiment Station
Soil Characterization
  • Physical Components
  • Important Soil Properties
  • Soil Horizons
  • Slope and Erosion Susceptibility
  • Drainage
  • Soil Chemistry
  • Water
  • Climate

Sampling for Effective Surface Reclamation of
Saltwater-Impaired Soils
  • Onsite Assessment and Sampling

Soil Characterization
Very important to characterize the soil because
we need to know the health, maturity, properties
of the soil, and other site conditions if we are
to be able to improve or restore the surface.
Physical Components
Soil has four physical components. A typical
soil consists of approximately
Therefore, about 50 of a soil is pore space is
occupied by either water or air.
Important Soil Properties
Texture - relates to the size of individual soil
particles (gravel, sand, silt, clay) and how they
are apportioned.
loam - mixture of sand, silt and clay
  • clay soils (low permeability)
  • sandy soils (high permeability)
  • loams have good drainage
  • Hard horizon may result in perched
  • water conditions

Soil Texture Triangle
Important Soil Properties
Color -- depends on
  • organic content -- makes soil dark
  • Fe-oxide content -- makes soil red
  • Al-oxides, CaCO3 -- light colors
  • Greenish, dark gray, bluish colors or mottles
    (splotches of light color in dark soil) indicate
    prolonged wetness.

Structure -- shape of aggregates in soil may
influence direction of percolation through soil
  • Soil particles bound in stable aggregates are
    resistant to erosion and indicative of relatively
    large and beneficial macropores in the soil.
    These macropores help the soil efficiently take
    in rainwater and air which are essential to the
    survival of most plants and animals.

Soil Horizons
Soil Profile and Horizons
O horizon -- abundant organic matter (OM) dark
colored. OM gt50 by weight.
A horizon -- considered topsoil or primary root
zone. Has the greatest biological activity and
richest in plant nutrients. Internal biotic
activities, including plant growth, help bind
soil particles together into stable structural
units called aggregates. Region from which
materials (esp. calcite, iron oxide, clays) are
removed (eluviation) lighter color than O, but
still contains OM.
B horizon -- subsoil material moved from A
horizon may accumulate here (illuviation) color
depends on presence of iron oxide, calcite, or
clay (any of these may be abundant) lighter
color than A. Little OM, fewer plant roots, and
much less biological activity than topsoil.
Usually has the highest proportion of clay which
greatly restricts downward migration of water.
C horizon -- partially altered parent material,
but looks similar to parent material. Contains
esentially no OM or illuviation of clay material
from above. Has been subjected to chemical
weathering by water percolating through the soil.
Soil salts, carbonates, and reprecipitated
silicates often concentrate and become cemented,
further decreasing porosity.
R horizon -- (regolith) consolidated geologic
bedrock material such as sandstone or limestone.
Not considered to have been sufficiently
weathered to be described as part of the soil.
Example of translocation (movement of materials
within the soil profile)
  • Eluviation - or washing out of carbonates from A
    horizon to B horizon

  • Illuviation or washing in of material and
    calcification (CaCO3)
  • from A and C horizon to B horizon

  • Decalcification - removal of calcium from C
    horizon to B horizon by chemical transformation

The 12 soil orders (soil types) are listed below
in the sequence in which they key out in Soil
Taxonomy Gelisols - soils with permafrost
within 2 m of the surface Histosols - organic
soils Spodosols - acid forest soils with a
subsurface accumulation of metal-humus
complexes Andisols - soils formed in volcanic
ash Oxisols - intensely weathered soils of
tropical and subtropical environments
Vertisols - clayey soils with high shrink/swell
capacity Aridisols - CaCO3-containing soils of
arid environments with subsurface horizon
development Ultisols - strongly leached soils
with a subsurface zone of clay accumulation and
lt35 base saturation Mollisols - grassland
soils with high base status Alfisols -
moderately leached soils with a subsurface zone
of clay accumulation and gt35 base saturation
Inceptisols - soils with weakly developed
subsurface horizons Entisols - soils with
little or no morphological development
  • Characteristics of Aridisols
  • Of the twelve soil orders for soil types,
    Aridisols are probably the most common in west
    Texas and southeast New Mexico.
  • They are characterized as dry soils generally
    light in color and low in organic matter.
  • They have a horizon of accumulation of calcium
    carbonate (calcic), gypsum (gypsic), soluble
    salts (salic), or sodium (sodic).
  • Except where there is groundwater or irrigation,
    the soil layers are moist only for short periods
    of the year.
  • These short moist periods may be sufficient for
    drought-adapted desert shrubs and annual plants,
    but much less so for many varieties of perennial
    grasses or conventional crops.
  • If groundwater is present near the surface,
    soluble salts often accumulate to levels that
    most crop plants cannot tolerate.
  • The major land use for Aridisols are for
    rangeland. They are not generally suitable for
    cropland as they have a naturally low fertility.
  • Where irrigation water is available, Aridisols
    can be highly productive however,they must be
    carefully managed to prevent the accumulation of
    soluble salts.

Aridisols are further broken down into suborders
Map of Aridisols in the United States
Aridisols have a limited availability of soil
moisture for sustained plant growth. The
redistribution and accumulation of soluble
materials in some layers of the soils are common.
Calcid Aridisol with a calcic horizon. The parent
materials have a high carbonate (caliche) content.
Slope and Erosion Susceptibility
Erosion is problematic where sloping occurs and
potentially severe with slopes gt 8 because it
results in loss of topsoil
Erosion and Slope Controls
  • Rapid establishment of vegetation
  • Berming
  • Terracing
  • Prevention of runon and runoff
  • Leveling
  • Erosion-control fabrics
  • Mulching
  • Contour tillage
  • Hydromulching
  • Biodegradable nets

The ability of a soil to drain is very important
especially because salts must be able to move out
of the soil root zone in order to remediate the
Soil internal drainage is affected by soil
texture, pore size distribution, and low
permeability layers.
Drainage categories as created by the USDA-NRCS
are described as
  • Excessively Drained - Water drains so rapidly
    that the soil retains relatively little water and
    plants are frequently in drought stress.
  • Well Drained - Water drains readily but not
    rapidly allowing for sufficient water to be
    available for mesophytic plants (plants which
    require a moderate amount of water) during most
    of the growing season.
  • Moderately Drained - Water is removed somewhat
    slowly during some periods of the year. Growth of
    mesophytic plants is limited.
  • Poorly Drained - Water is removed very slowly and
    soil is usually wet. Without drainage
    enhancements, excessive wetness is growth
    limiting to mesophytic plants. One or more of the
    following factors substantial rainfall, minimal
    slope or depression area, high water table, fine
    soil texture or low permeability layer, or
    minimal macropores.

Soil Chemistry
The soil solution (liquid phase of a soil)
dissolves and allows other plant nutrients to
move toward plant roots. In order for a plant to
survive it must have an appropriate amount of
each of the plant nutrients as listed below.

Soil Chemistry
Sources of Nutrients in the Soil Organic matter
Most soil nutrients are contained in the soil
organic matter. To make these nutrients available
the organic matter must be decomposed..
Adsorbed nutrients These are the nutrients
that are held on the soil colloid. This is the
major source of nutrients for the plants, and is
the source that is most easily controlled by man.
Soil minerals (includes clay minerals) These
are the nutrients that are in the parent
materials. These nutrients may become available
through weathering, however this is a very slow

Soil Chemistry
The salts in saline soils are primarily chloride
(Cl-) and sulfate (SO4-2) anions that pair with
calcium (Ca), magnesium (Mg2), sodium (Na),
and potassium (K) cations. Once deposited or
released in the soil whether by by natural or
man-made means, the salts are brought to or near
the surface through micropores by upward-moving
water, which then evaporates, leaving the salts
behind. Unfortunately, high levels of these salts
cannot be tolerated by most crop
plants. Detrimental effects on plants stem not
only from the high salt contents but also from
the level of sodium in the soil, especially in
relation to levels of calcium and magnesium. High
exchangeable sodium levels are detrimental both
physically and chemically.
Because of the situations outlined above four
primary chemical properties should be measured to
characterize salt-affected soils
  • pH
  • 2 Electrical Conductivity (EC)
  • 3 Exchangeable Sodium Percentage (ESP)
  • 4 Sodium Absorption Ratio (SAR)

Chemical Properties
pH - is a measure of the degree of soil acidity
(H dominant) and alkalinity (OH- dominant). The
soil pH controls many chemical and biological
functions of soils and plants, especially in
relation to nutrient availability for plant
In the above diagram the denser the band shade,
the greater the availability for that particular
plant nutrient, as the shading diminishes
nutrient availability decreases.
Chemical Properties
Electrical Conductivity (EC) - measures the
ability of the salt in the soil solution to
conduct electricity which correlates indirectly
to the concentration of salt in soil. Units are
commonly expressed in decisiemens per meter
Normal (non-saline and non-sodic) soils typically
have a pH ranging from 6.5-7.2 pH units and an EC
value of 2-6 dS/m.
Traditionally, the pH and EC measurements are
made in a suspension of soil in water (usually a
ratio of 11 or 12). Although this method is
suitable for quick screening in the field, for
saline soils it is better to determine pH and EC
on a saturated paste of the soil because the
moisture content of the paste is sufficiently
near that of the soil to make the measured pH
more meaningful.
Chemical Properties
Exchangeable Sodium Percentage (ESP) - identifies
the degree to which the exchange complex is
saturated with sodium.
Cation exchange capacity (CEC) - The number of
cation positive charges retained by 100 grams of
soil. The CEC is a measurement of the total
amount of exchangeable cations that can be held
by the soil. Soil clays and organic matter have a
relatively large number of negative charge sites
which retain cations in dynamic equilibrium with
the soil solution. CEC gives an indication of the
soils potential to hold plant nutrients.
Exchangeable sodium - amount of sodium on cation
exchange sites or in the soil solution that can
participate in the cation exchange process in
Normal soils typically have an ESP between 13-15
Chemical Properties
Sodium Adsorption Ratio (SAR) - is a measure of
the relative competitiveness of sodium versus
calcium plus magnesium for adsorption onto clay
cation exchange sites. It is calculated as
Normal soils typically have a SAR between 13-15
One problem with the overdependence on using SAR
is that it is merely a ratio of dissolved
cations, and is completely unrelated to the total
amount of sodium in the soil or the CEC of the
soil. This is important because we want to know
the total amount of sodium in the soil when
calculating the quantity of chemical amendments
required to remediate the soil. For this reason,
ESP is the preferred over SAR in order to
calculate required chemical amendments.
ESP SAR when either are lt40 (soil at
Chemical Properties
Saline Soils and Osmotic Potential
Osmotic Potential - The force which causes
dissolved constituents to retain water molecules.
Highly saline soil water competes with the plants
for water molecules because of the high osmotic
potential it creates.
Sodic Soils and Soil Dispersion
Soil Dispersion - is the reverse process of
aggregation. Dispersion is a detrimental
electrochemical process in which soil clay
particles repel each other, that is physically
move apart, and clog soil pores. Unless soil
salinity is also high dispersion will occur in
soils having excess sodium.
To a great extent, climate determines the type of
soil present as it dictates the frequency,
duration, and quantity of precipitation and
evaporation, as well as the extremes and duration
of temperature and wind.
These factors have a major impact on the fate and
transport of salts in the soil. Most chemical
reactions occur at a faster rate with increasing
After a rainfall, a portion of the rainwater
percolates downward through the soil dissolving
and carrying soluble salts. During evaporative
periods, soil-pore water reverses course and
moves back upward through the soil bringing
dissolved salts back to the surface. Since salts
do not evaporate, they continue to concentrate at
the soil surface during evaporation of soil water.
Water is critical to plant growth because it
provides the transportation medium in which
nutrients are delivered to plants. As stated
earlier, a typical soil contains about 25 water
in its pore spaces. The pore spaces can be full
of water, but rarely contain less than 10 water,
even when very dry.
Mean Annual Total Precipitation in Texas
Salt and Drought Tolerance of Native Grass Plants
Common to west Texas
The traditionally accepted objective criteria for
remediation of saline and/or sodic soils for all
plants has been to decrease the salinity and ESP
to lt4 dS/m and 15, respectively. However, the
presence of naturally saline and sodic
environments and the halophytic plants which
thrive naturally in these soils indicates that
more elevated levels of salts can be an
acceptable remediation goal.
Source Seeding Rangeland, Tommy Welch, et al,
April 1994, Texas Agricultural Experiment Station
Law of the Minimum
Whether a primary or secondary macronutrient or,
a micronutrient, the Law of the Minimum holds
the most growth-limiting nutrient will limit
growth, no matter how favorable the nutrient
supply of other elements. For example, a
deficiency of Fe or Mn (most common in soils
containing calcium carbonate) can severely limit
plant growth in spite of adequate N, P, and K.
This concept also applies to other requirements
for active plant growth.
Stave Concept
Assessment and Sampling Activities
  • Compile pertinent information concerning release
  • Draw site map that includes pertinent features,
    structures, and affected area
  • Collect Soil Samples
  • Test and observe soil sample characteristics

Assessment and Sampling Activities
Compile pertinent information concerning release
  • Site identification (Lease No.) and legal
    location (section, township, range,latitude,
    longitude, etc.)
  • - Land use (agricultural, grazing, industrial,
  • - Date of Release (if known)
  • Amount of release (if known)
  • Cause of release (if known)

Assessment and Sampling Activities
Draw site map that includes pertinent
features, structures, and affected area__
  • Features roads, fence line, surface
  • water bodies, property lines, etc.
  • Structures tank batteries, pipelines, etc.
  • Horizontal and vertical extent of the
  • salt-affected area
  • - Topography, drainage, and slope
  • characteristics
  • - Native vegetation types (and crops if
  • applicable)
  • - Sample locations and field measured
  • values (pH, EC, chloride, soil type, etc)

Useful Forms
Source Remediation of Salt-Affected Soils at Oil
and Gas Production Facilities, API Publication
No. 4663, Oct. 1997
Assessment and Sampling Activities
Collect Soil Samples for both Field Measurements
and Lab Analysis
  • Hot spot composites (0-1 ft and 1-2 ft)
  • (Deeper samples may be required)
  • Avg condition composite (0-1 ft and 1-2 ft)
  • Background (0-1 ft and 1-2 ft)

(No Transcript)
Assessment and Sampling Activities
Test and observe soil sample characteristics
  • Determine depth of saltwater penetration
  • Identify soil horizons and note thickness
    (particularly topsoil and A horizon.
  • Identify soil texture, color, structure and
    quantify sand, silt, clay content

- Measure pH, EC, and chloride concentration in
the field from samples comprised of a suspension
of soil in water (usually a ratio of 11 or 12).
These quick screening measurements will be
useful in choosing which and how many samples
will be submitted for laboratory analysis.
- Submit samples for laboratory analysis of CEC,
SAR, ESP, OM, cations(Ca, Mg, Na, K, S) and
anions (SO4, Cl), moisture content, pH, and EC.
(No Transcript)
Saturated Paste Extract
The moisture content (weight of soil moisture
divided by dry weight of soil) at which pH, EC,
SAR, ESP values are measured is very important
because the ratio of less soluble salts (Ca and
Mg) to more soluble salts (Na) increases with
increasing moisture content.
The saturated percentage represents the maximum
moisture content at which dissolved nutrients are
available to plants. The saturated percentage is
achieved when all soil pores are completely
filled with water, but there is no water in
excess of that amount. For this reason the method
of preparing a saturated paste is recommended to
allow measurements of pH, EC, SAR, ESP, and
soluble ions.
Preparing a saturated paste extract requires
allowing the water to equilibrate with the soil
for at least an hour and extraction by inducing a
vacuum or positive pressure.
Fortunately, if this is too time consuming and
burdensome to do in the field it may be more
convenient to have an experienced laboratory do
this work for you since they will be performing
the analyses anyway.
Soil Testing Laboratories
Texas AM University Soil, Water and Forage
Testing Laboratory 345 Heep Center College
Station, TX 77843-2474 979-845-4816 http//soiltes
Texas AM University Soil Crop Sciences
Department College Station, TX 77843-2474 979-845-
7295 http//soildata.tamu.edu/
Texas Plant Soil Lab, Inc. 5115 W. Monte
CristoEdinburg, TX 78539956-383-0739http//www.
Source Remediation of Salt-Affected Soils at Oil
and Gas Production Facilities, API Publication
No. 4663, Oct. 1997
Source Remediation of Salt-Affected Soils at Oil
and Gas Production Facilities, API Publication
No. 4663, Oct. 1997
Source Remediation of Salt-Affected Soils at Oil
and Gas Production Facilities, API Publication
No. 4663, Oct. 1997
Cow manure showing proper fiber and moisture
content indicating balanced feed.
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