2 soilproperties hayes

8/10/2019 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 minerals


Englehard Series, Hyde Co, NC

High

Low


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Soil minerals


Georgeville Series, Randolph Co, NC

Red color - hematite (iron)


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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




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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




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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

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