2 SoilProperties Hayes
Transcript of 2 SoilProperties Hayes
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Important Properties
Color
Texture Structure
Consistence
Shrink-swell Potential Bulk Density
Porosity
Permeability
Infiltration
Drainage Depth
Available Water
Holding Capacity
Reaction
Cation ExchangeCapacity
Landscape Position
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SOIL COLOR Useful tool for providing
information about other
soil properties Organic matter content
Soil minerals
Seasonal high water tables
Appling Series, Granville Co, NC
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SOIL COLOR Useful tool for providing
information about other
soil properties Organic matter content
Soil minerals
Seasonal high water tables
Englehard Series, Hyde Co, NC
High
Low
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SOIL COLOR Useful tool for providing
information about other
soil properties Organic matter content
Soil minerals
Seasonal high water tables
Georgeville Series, Randolph Co, NC
Red color - hematite (iron)
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SOIL COLOR Useful tool for providing
information about other
soil properties Organic matter content
Soil minerals
Seasonal high water
tables
Creedmoor Series, Chatham Co, NC
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SOIL COLOR Munsell Color Chart
Used to identify the soil
color. This chart allows soilscientists to uniformly
describe soil color. In the
field, soil scientists
compare the colors found inthe soil with the color chips
found on the chart.
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SOIL COLOR Redoximorphic Features
Soil colors formed by the
repeated chemical oxidationand reduction of iron and
manganese compounds
resulting from saturation.
Useful for predicting thepresence and depth of
seasonal high water tables
in the soil.
Mattaponi Series, Chatham Co, NC
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Redoximorphic Features Redoximorphic Depletions
Low-chroma (gray) zones
from which iron andmanganese oxide or a
combination of iron and
manganese oxide and clay
have been removed. Thesezones are indications of the
chemical reduction of iron
resulting from saturation.
Creedmoor Series, Chatham Co, NC
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Redoximorphic Features Redoximorphic
Concentrations
Nodules, concretions, softmasses, pore linings, and
other features resulting
from the accumulation of
iron or manganese oxide.An indication of chemical
reduction and oxidation
resulting from saturation.
Creedmoor Series, Chatham Co, NC
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Redoximorphic Features Reduced Matrix
Low-chroma (gray)
horizons from which mostiron oxide has been
removed by leaching. These
horizons are indications of
the chemical reduction ofiron resulting from long-
term saturation.
Cid Series, Chatham Co, NC
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Texture The relative proportions of sand, silt, and clay particles
in a mass of soil.
Used by soil scientists
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Texture Triangle Used by soil scientists to
define the basic textural classes
Field soil scientists frequentlyestimate the texture by feel
using their hands.
For more exact measurements
there are laboratory techniquesthat can determine the exact
amount of sand, silt, and clay.
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Texture Soils containing large
amounts of sandexhibit
little plasticity and cannotretain large amounts of
water or nutrients. They
have large voids between
the particles and canreadily transport water and
air.
Seabrook Series, Hyde Co, NC
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Texture The properties of siltare
intermediate between sand and
clay. Silty soils can retain largeamounts of water but tend to
have moderately slow to slow
permeabilities. Soils high in
silt can present problems for
engineers since they will shiftunder stress and slide and flow
when wet.
Callison Series, Anson Co, NC
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Texture Claysexert a great influence
on soil chemical and physical
properties. Clay particles arechemically active and the
proportion of clay-sized
particles greatly influences soil
physical properties, including
aggregation, porosity, watermovement and storage,
aeration and workability of the
soil.
Vance Series, Granville Co, NC
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Structure The arrangement of
primary soil particles into
compound particles oraggregates.
The type and grade of
structure plays an
important role in the
movement of water within
soils.
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Structure There are eight structural
types commonly
recognized in soil profiles:Granular, single grain,
blocky, prismatic,
columnar, platy, wedge,
and massive.
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Structure Granular - Rounded
aggregates usually less than
1/4 inch in diameter. Theserounded complexes lie loosely
on the surface and are readily
shaken apart. The aggregates
are calledgranulesand the
pattern is calledgranular. Thisis the most common type of
structure found in topsoil.
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Structure Single grainEach
individual soil particle is
separate and there isessentially no structure.
This is only found in very
sandy soils and is the type
of structure commonlyseen in sand dunes at the
beach.
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Structure Blocky- The original
aggregates have been reduced
to blocks, irregularly faced,and basically equal in height,
width, and depth. Blocky
structure is the most common
type of structure seen in the
subsoil (B horizon) in NorthCarolina.
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Structure PrismaticCharacterized by
vertical oriented aggregates or
pillars with flat tops. Theseelongated columns vary in
length with different soils.
Prismatic structure is
commonly seen in soils with
high clay content and inhorizons dominated by high
shrink-swell clays.
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Structure ColumnarCharacterized
by vertical oriented
aggregates or pillars withrounded tops. Theseelongated columns withflat tops vary in lengthwith different soils. Mostcommonly seen in soilsthat have a high sodiumcontent in a dry climate.
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Structure PlatyThe aggregates are
arranged in thin horizontal
plates or sheets. Thisstructure is commonly
found in soil layers that
have been compacted.
Platy structure inhibits thedownward movement of
water.
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Structure WedgeThe aggregates
resemble wedges, thinner
at one end and thicker onthe other. This structure isseen in soils with a highclay content that isdominated by expansiveclays such asmontmorillonite. (2:1clays)
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Structure Affects permeability by
influencing the path by
which water can flowthrough the soil. The type
of structure determines the
number of interconnected
macropores, which readilypermit downward
movement of water.
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Consistence The degree and kind of
cohesion and adhesion that
soil exhibits, and/or theresistance of soil todeformation or ruptureunder applied stress. Fieldevaluations of consistenceusually include ruptureresistance, stickiness, and
plasticity.
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Consistence Rupture resistanceis a
measure of the soils ability to
withstand applied stress. For
this test, moist soil is normally
used. A naturally occurring
soil aggregate is placed
between the thumb and index
finger. Pressure is slowlyapplied to estimate the amount
of force that is required to
rupture a soil aggregate.
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Consistence Stickinessis the capacity
of a soil to adhere to other
objects. Stickiness isestimated at the moisturecontent that displays thegreatest adherence when
pressed between thethumb and forefinger. Thisnormally occurs when thesoil is quite wet.
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Consistence Plasticityis the degree to
which a reworked soil can
be permanently deformedwithout rupturing.
Plasticity is evaluated by
forming a roll (wire) of
soil that is 4 cm long.
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Shrink-swell Potential Shrink-swell potentialis a
measurement of the amount ofvolume change that can occur
when a soil wets and dries. Mostof this volume change is due tothe clay fraction of the soil. Claysswell when wet and shrink whendry. Soils high in 2:1 clays suchas montmorillonite tend to havehigh shrink-swell potentials. Soilshigh in 1:1 clays such as kaolinitetend to have low shrink-swell
potentials.
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Shrink-swell Potential A soil with a highshrink-swell
potential can cause severe
problems when used for urban
development unless the
problem is recognized and
proper engineering precautions
taken. Shrinking and swelling
can buckle roads, crackbuilding foundations and walls,
and even damage plant roots.
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Bulk Density Bulk density is the mass of
dry soil per unit volume,
including the air space. Bulk density has a major
effect on the movement of
air and water in soils.
Soils with high bulk
densities are often
compacted.
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Bulk Density Soil compactionrestricts
rooting depth, which
reduces the uptake ofwater and nutrients by
plants.
NoCompaction
Compaction(plow pan)
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Bulk Density Compactionalso
decreases infiltration,
thereby increasing runoffand the hazard of water
erosion.
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Permeability Permeabilityrefers to the
movement of air and waterwithin the soil.
Permeability rateis the rate atwhich a saturated soil transmitswater, usually expressed ininches per hour. Texture,structure, bulk density, and thetype and connectivity ofmacropores influence
permeability.
Hydraulic conductivityis ameasurement of the amount ofwater that can move downward
through a unit area ofunsaturated soil in a unit oftime.
Saturated hydraulicconductivity (k
sat) is a
measurement of the amount ofwater that can move downwardthrough a unit area of saturatedsoil in a unit of time.
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Infiltration Infiltration is the downward
entry of water into the
immediate surface of the soil
and is influenced by texture,
structure, bulk density, and the
type and connectivity of
macropores.
Soils with a high infiltration
rate are resistant to erosion
because there is little runoff.
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DrainageDrainagerefers to the
frequency and duration of
periods of saturation orpartial saturation. Internal
soil drainage is important
because of its effect on
land use and managementdecisions.
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Drainage An apparent water tableis a
type of saturation in which allhorizons between the upper
boundary of saturation and adepth of 6 feet are saturated.
Apparent water tables arefrequently encountered in low-lying areas where the slope ofthe land is insufficient to
provide good drainage such asflood plains, depressions, andnearly level areas.
Hydeland Series, Hyde Co, NC
Saturated
Zone
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Apparent Water Table
UnsaturatedSeasonal High Water Table
Saturated
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Drainage Aperched water tableis a
water table in a soil in whichsaturated layers are underlain
by one or more unsaturatedlayers within 6 feet of thesurface.
Often caused by a restrictivelayer that has slow or veryslow permeability.
Common in soils that haveclayey subsoils and poorstructure.
Helena Series, Wake Co, NC
Saturated
Zone
Unsaturated
Zone
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Perched Water Table
Seasonal High Water Table
Aquatard Unsaturated
Unsaturated
Saturated
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Drainage The depth to soil water tables
fluctuates throughout the year.
Most of this is due to rainfall
variability and seasonal
changes in the rate of
evapotranspiration.
In North Carolina, the highest
water tables are normallyencountered in the winter and
early spring months.
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Available Water Holding Capacity The capacity of soils to
hold water available for
use by most plants. It iscommonly defined as the
difference between the
amount of soil water at
field capacity and theamount at wilting point.
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Depth The useable depth of the soil is
an important considerationwhen evaluating a soil for a
particular land use. Groundwater can be easily
impacted in soils with ashallow depth to rock.
Root restrictive layersare anypermanent zones in the soilthat restrict the growth of plantroots. Bedrock is the mostcommon root restrictive layer.
Goldston Series, Randolph Co, NC
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Reaction Reactionis a measure of
acidity or alkalinity of a soil.
Acidity or alkalinity is
determined by the amount of
hydrogen and hydroxyl ions in
the soil. When hydrogen ions
outnumber hydroxyl ions the
soil is acidic. In the reversecondition the soil is basic. A
pH scale is used to measure the
level of acidity or alkalinity.
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Reaction In NC, the natural soil pH will
range from 4.0 to 8.0 withmost soils tending to be acidic
with pH values of 4.5 to 6.0. In order to optimize plant
growth, farmers andhomeowners commonly adjustthe pH of a soil by adding soilamendments such as lime. Theamount of lime that needs to beadded should be determined bya soil test.
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Cation-Exchange Capacity Cation-exchange capacity
(CEC) is a measure of the
ability of a soil to hold and
exchange cations. It is one of
the most important chemical
properties in soil and is usually
closely related to soil fertility.
A few of the plant nutrientcations that are part of CEC
include calcium, magnesium,
potassium, and ammonium.
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Landscape Position
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Landscape Position
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Landscape Position
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Landscape Position
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Rich Hayes
Soil Scientist
Aquifer Protection Section
Raleigh Regional Office