soil info from usda
TRANSCRIPT
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United StatesDepartment o
Agriculture
NaturalResources
ConservationService
From theSurace DownAn Introduction to Soil Surveysor Agronomic Use
Second Edition
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Credits
Cover photo courtesy o Frankie F. Wheeler and Larry Ratli, retired soil scientists.
Figures 1, 2, 12, 21, 22, 23, 27, and 28 created by the U.S. Department o Agriculture,
Natural Resources Conservation Service (or Soil Conservation Service).
Figures 3, 4, 5, 6, 7, 8, 13, 14, 15, and 20 reprinted rom Soils o the Great Plains,
by Andrew R. Aandahl, by permission rom the University o Nebraska Press.Copyright 1982 by the University o Nebraska Press.
Figures 9 and 19 courtesy o Edgar White, Natural Resources Conservation Service,Harrisburg, PA.
Figure 10 courtesy o John Kimble, retired soil scientist.
Figures 11, 16, 17, 18, and 25 are rom the authors (William Brodersons) collection.
Figure 24 created rom Evaluating Missouri Soils, by Dr. C.L. Scrivner and James C.
Baker. Circular 915, Extension Division, University o Missouri-Columbia.
Figure 26 courtesy o Douglas Wysocki, Natural Resources Conservation Service,
Lincoln, NE.
Cover
Prole o Segno ne sandy loam, a Plinthic Paleudal. Note the characteristic blocks o
plinthite at a depth o 30 inches.
Nondiscrimination Statement
The U.S. Department o Agriculture (USDA) prohibits discrimination in all itsprograms and activities on the basis o race, color, national origin, age, disability, andwhere applicable, sex, marital status, amilial status, parental status, religion, sexual
orientation, genetic inormation, political belies, reprisal, or because all or a part o anindividuals income is derived rom any public assistance program. (Not all prohibited
bases apply to all programs.) Persons with disabilities who require alternative meansor communication o program inormation (Braille, large print, audiotape, etc.)
should contact USDAs TARGET Center at (202) 720-2600 (voice and TDD). To lea complaint o discrimination, write to USDA, Director, Oce o Civil Rights, 1400Independence Avenue, S.W., Washington, D.C. 20250-9410 or call (800) 795-3272
(voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer.
First edition printed in1991;revised in1994, 2001, and 2003
Second edition printed in 2010
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Contents
Introduction ....................................................................................................................1
Section 1: What are soil horizons? ............................................................................2Section 2: How is soil ormed? ..................................................................................7
Section 3: What are the soil-orming processes? ....................................................11
Soil survey inormation ................................................................................................14
Section 4: Soil properties ........................................................................................14Section 5: Management interpretations ..................................................................20
Section 6: General soil inormation .........................................................................23Section 7: Detailed soil inormation .........................................................................26
Location o inormation ................................................................................................27Section 8: Location o soil properties and interpretations .......................................27
Reerences ..................................................................................................................30
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Many o our lies activities and pursuits arerelated to and infuenced by the behavior
o the soil around our houses, roads,septic and sewage disposal systems, airports, parks,
recreation sites, arms, orests, schools, and shopping
centers. What is put on the land should be guided bythe soil that is beneath it.
Like snowfakes, no two soils are exactly the same.Surace and subsurace soil eatures change across
landscapes (g. 1). A grouping o soils having similarproperties and similar behavioral characteristics is
called a series. A series generally is named or a townor local landmark. For example, the Mexico series is
named or a town in north-central Missouri. More than21,300 soil series and 285,200 soil map units havebeen named and described in the United States, and
more are being dened each year.When soils are mapped, soil series are urther
divided into phases according to properties that areimportant to soil use, such as texture o the surace
layer and slope. These phases o soil series all have acharacteristic behavior. The behavior o the individualphase is applicable no matter where the soil is
observed.One o the main reerences that can help land
users determine the potentials and limitations o soilsis a soil survey. The List o Surveys by State (http://
soils.usda.gov/survey/printed_surveys/) indicates theavailability o soil survey inormation in paper copies,in PDF les on CD or on the Web, and in tables and
reports in Web Soil Survey (http://websoilsurvey.nrcs.usda.gov/). A soil survey is prepared by soil scientists
who determine the properties o soil and predict soilbehavior or a host o uses. These predictions, oten
called soil interpretations, are developed to help userso soils manage the resource.
A soil survey generally includes soils data or onecounty, parish, or other geographic area. During a soil
survey, soil scientists walk over the landscapes, boreholes with soil augers, and examine cross sections
o soil proles. They determine the texture, color,
structure, and reaction o the soil and the relationshipand thickness o the dierent soil horizons. Some soils
are sampled and tested at soil survey laboratories orcertain soil property determinations, such as cation-
exchange capacity and bulk density.The intent o this publication is to increase user
understanding o soils and o the content o soilsurveys and supplemental interpretations that are
important to agronomic programs.Prociency in using soil survey data requires
a basic understanding o the concepts o soil
development and o soil-landscape relationships.These topics are covered briefy in the next three
sections.
From the Surace DownAn Introduction to Soil Surveys or
Agronomic Use, Second Edition
United States Department o Agriculture, Natural Resources Conservation Service,
Soil Survey Sta1
1 First edition (1991) by William D. Broderson, retired soil scientist. Sections 7 and 8 in the second edition (2010) by Jim R. Fortner, soil
scientist, USDA, Natural Resources Conservation Service, National Soil Survey Center, Lincoln, Nebraska.
Introduction
Figure 1.Facts about soil.
http://soils.usda.gov/survey/printed_surveys/http://soils.usda.gov/survey/printed_surveys/http://soils.usda.gov/survey/printed_surveys/http://websoilsurvey.nrcs.usda.gov/http://websoilsurvey.nrcs.usda.gov/http://websoilsurvey.nrcs.usda.gov/http://websoilsurvey.nrcs.usda.gov/http://soils.usda.gov/survey/printed_surveys/http://soils.usda.gov/survey/printed_surveys/ -
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Section 1: What are soil horizons?
Soils orm in bedrock residuum or in materialdeposited by ice, wind, water, or gravity.Layers, called horizons, orm over time in the
soils. These layers are evident where roads have beencut through hills or streams have scoured through
valleys and in other areas where the soil is exposed.Where soil-orming actors are avorable, ve or six
master horizons may be in a mineral soil prole (g.2). Each master horizon is subdivided into speciclayers that have a unique identity. The thickness
o each layer varies with location. Under disturbedconditions, such as intensive agriculture, or where
erosion is severe, not all horizons will be present.
Young soils have ewer major horizons. An example isthe bottom-land soil in gure 12 (shown in section 2,page 7) and the deep loess soil in gure 3.
The uppermost layer in an undisturbed soil maybe an organic horizon, or O horizon. It consists
o resh and decaying plant residue rom suchsources as leaves, needles, twigs, moss, lichens,and other organic material. Some organic materials
were deposited under water (gs. 4 and 5). The
subdivisions Oa, Oe, and Oi are used to identiy levelso decomposition. The O horizon is dark because olarge amounts o accumulated humus.
Below the O horizon is the A horizon. The A horizonis mainly mineral material. It is generally darker thanthe lower horizons because o varying amounts o
humied organic matter (gs. 6 and 7). This horizonis where most root activity occurs and generally is
the most productive layer o soil. It may be reerred toas a surace layer in a soil survey. An A horizon thatFigure .A soil prole with ve major horizons.
Figure 3.Somewhat excessively drained Colby
soil ormed in loess. A horizon (0 to 8 inches)
o grayish brown silt loam; AC horizon (8
to 16 inches) o pale brown silt loam; C
horizon (below 16 inches) o pale brown silt
loam. Aridic Ustorthent. Western Nebraska,
eastern Colorado, Kansas, South Dakota, and
Wyoming.
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has been buried beneath more recent deposits is
designated as an Ab horizon (g. 4).The E horizon generally is bleached or whitish
(gs. 8, 9, and 10). As water moves down through thishorizon, soluble minerals and nutrients dissolve andsome dissolved materials are washed (leached) out.
The main eature o this horizon is the loss o silicateclay, iron, aluminum, humus, or some combination o
Figure 4.Poorly drained Cathro soil. Thick Oa
and Oe horizons (0 to 37 inches) o organic
material developed rom a continuous high
water table. A buried Ab horizon (37 to 45
inches) o black loam. Terric Haplosaprist.
Northeastern Minnesota, northern Wisconsin,
northern Michigan, and upper New England.
these, leaving a concentration o silica sand and siltparticles.
Below the A or E horizon is the B horizon, orsubsoil (gs. 6 and 8). The B horizon generally is
lighter colored, denser, and lower in content oorganic matter than the A horizon. It commonly is
the zone where leached materials accumulate. TheB horizon is urther characterized by the materials
that make up the accumulation. In a Bt horizon, orexample, clay has accumulated. This accumulationis indicated by the letter t in the horizon designator.
Other illuvial concentrations or accumulations includeiron, aluminum, humus, carbonates, gypsum, and
silica. A B horizon that does not have recognizableconcentrations but has color or structure dierent romthose o adjacent horizons is called a Bw horizon.
Still deeper in the prole is the C horizon, orsubstratum (g. 3). The C horizon may consist o
material with less clay than the overlying horizons,or it may consist o other less weathered sediments.
Partially disintegrated parent material and mineral
particles are in this horizon. Some soils have a sotbedrock horizon that is given the designation Cr (g.
11). A C horizon described as 2C consists o dierentmaterial, generally o an older age than the horizons
that overlie it.The lowest horizon, the R horizon, is bedrock (g.
11). Bedrock can be within a ew inches o the suraceor many eet below the surace. Where bedrock is verydeep and below the normal depths o observation, an
R horizon is not described.
Figure 5.Surace o a very poorly drained soil that has
many depressions.
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Figure 6.Moderately well drained Pawnee soil ormed in till.
The A horizon is 14 inches thick. The Bt horizon, between
depths o 14 and 3 inches, is dark brown clay that has
prismatic structure. Pockets o white, sot lime are at a
depth o 53 inches. Oxyaquic Vertic Argiudoll. Nebraska
and northeastern Kansas.
Figure 7.Well drained Ferris soil. The A horizon is olive clay
about 6 inches thick. Pale olive clay is between depths
o 6 and 60 inches. Cracks are lled with surace soil
material to a depth o 4 inches. Chromic Udic Haplustert.
Texas and Oklahoma.
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Figure 9.Moderately well drained Exum soil ormed in loamy
Coastal Plain sediments. A grayish brown A horizon (0
to about 6 inches); a light brownish gray E horizon (6 to
10 inches); thick, yellowish brown, very strongly acid Bt
horizons to a depth o 6 eet. Aquic Paleudult. Maryland,
North Carolina, South Carolina, and Virginia.
Figure 8.Well drained Wallace soil ormed in sandy deposits
on old sand dunes, lake benches, and outwash plains.
This soil has an A horizon (0 to about inches) o dark
grayish brown sand; an E horizon ( to 10 inches) o
white sand; and a Bhsm horizon (10 to 6 inches) o dark
reddish brown, brown, and yellowish brown, massive
and cemented ortstein. The B horizon has illuvial
concentrations o organic matter, aluminum, and iron.
Typic Durorthod. Northern Michigan and New York.
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Figure 10.Poorly drained Felda soil ormed in sandy marine
material. A grayish brown and light gray E horizon is
between depths o 5 and 4 inches. An irregular boundary
is between the E horizon and the Bt horizon, which is at a
depth o 4 inches. Arenic Endoaqual. Florida.
Figure 11.Well drained Hambright soil ormed in amorphous
material derived rom basic igneous rocks. The content o
rock ragments is about 50 percent to the Cr horizon, at
a depth o 15 inches. Fractured basalt (R horizon) is at a
depth o 19 inches. Lithic Haploxeroll. Caliornia.
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Section : How is soil ormed?
Figure 12 shows common landscapes. Soilsorm through the interactions o climate,living organisms, and landscape position as
they infuence the decomposition and transormationo parent material over time. Figure 12 shows how
soil proles change rom weakly developed to welldeveloped with time. Generally, soils on older terraces
or second bottoms have a developed B horizon,unlike recent soils on rst bottoms. The recent soilsmay have strata varying in thickness, texture, and
composition and may have begun accumulatinghumus in the surace layer.
Dierences in climate, parent material, landscape
position, and living organisms rom one location toanother and the amount o time the material has beenin place all infuence the soil-orming process.
Five soil-orming actors
Parent materialClimate
Living organismsLandscape positionTime
Parent materialParent material reers to the great variety o
unconsolidated organic material (such as resh peat)
and mineral material in which soil ormation begins.Mineral material includes partially weathered rock; ash
rom volcanoes; sediments moved and deposited bywind, water, or gravity; and ground-up rock depositedby glacial ice. The material has a strong eect on
the type o soil that orms and the rate at which itorms. Soil ormation may take place more quickly in
materials that are more permeable to water (g. 8).Dense, massive, clayey materials can be resistant to
the processes o soil ormation (g. 7). In soils thatormed in sandy material, the A horizon may be alittle darker than its parent material, but the B horizon
tends to have a similar color, texture, and chemicalcomposition (g. 13).
Climate
Climate is a major actor in determining the kind oplant and animal lie on and in the soil. It determines
the amount o water available or weathering mineralsand or transporting the minerals and elementsreleased.
Figure 1.Landscape position, climate, time, living organisms, and parent material infuence soil
ormation.
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Figure 15.Well drained Olton soil ormed in mixed alluvial
and eolian material. Ap horizon (0 to 6 inches) o brown
loam; Bt horizon (6 to 3 inches) o reddish brown clay
loam; whitish calcium carbonate below the Bt horizon.
Aridic Paleustoll. Texas and New Mexico high plains.
Warm, moist climates encourage rapid plant
growth and thus high organic-matter production.Also, they accelerate organic-matter decomposition.
The opposite is true or cold, dry climates. Under the
control o climate, reezing, thawing, wetting, anddrying break parent material apart.Rainall causes leaching. Rain dissolves some
minerals, such as carbonates, and transports themdeeper into the soil. Some acid soils ormed in parent
material that originally contained limestone. Rainallcan also be acid, especially downwind rom industrialprocesses.
Living organisms
Plants aect soil ormation by supplying upperlayers with organic matter, recycling nutrients rom
lower to upper layers, and helping to control erosion.
In general, deep-rooted plants contribute more to soilormation than shallow-rooted plants because the
passages they create allow greater water movement,which in turn aids in leaching. Leaves, twigs, and bark
rom large plants all onto the soil and are brokendown by ungi, bacteria, insects, earthworms, and
burrowing animals. These organisms eat and breakdown organic matter, releasing plant nutrients. Some
change certain elements, such as sulur and nitrogen,into usable orms or plants.
Microscopic organisms and the humus they
produce act as a kind o glue, holding soil particlestogether in aggregates. Well-aggregated soil provides
the right combination o air and water to plant roots.
Landscape position
Landscape position causes local changes inmoisture and temperature. When rain alls on a
landscape, water begins to move downward by theorce o gravity, either through the soil or across
the surace to a lower elevation. In an area whereclimate, living organisms, parent material, and time
are held constant, the drier upslope soils may be quitedierent rom the wetter soils at the base o the slope,where water accumulates. The wetter soils may have
reducing conditions that will inhibit proper root growthor plants that require a balance o soil oxygen, water,
and nutrients.The steepness, shape, and length o slopes are
important because they infuence the rate at whichwater fows into or o the soil. I unprotected, the moresloping soils may become eroded and thus have a
thinner surace layer. Eroded soils tend to be lessertile and have less available water than uneroded
soils o the same series.
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Aspect aects soil temperature and moisture. Inmost o the continental United States, soils on north-acing slopes tend to be cooler and wetter than soils
on south-acing slopes. These dierences aectseedling emergence and the rate o plant growth.
Soils on north-acing slopes tend to have thicker Aand B horizons.
Time
Time is required or horizon ormation. The longer a
soil surace has been exposed to soil-orming agents,such as rain and growing plants, the greater the
development o the soil prole. Soils in areas o recent
alluvial or windblown material and soils on steepslopes where erosion has been active may show verylittle evidence o horizon development (g. 3).
Soils on the older, stable suraces generallyhave well dened horizons because the rate o soil
ormation has exceeded the rate o geologic erosionor deposition (g. 6). As soils age, many originalminerals are destroyed. Many new ones are ormed.
Soils become more leached, more acid, and moreclayey. In many well drained soils, the B horizons tend
to become redder as iron accumulates with time (gs.8 and 15).
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relocated to the lower slope positions or deposited onbottom lands can increase or decrease the productive
use o the soils in those areas.Translocations
Translocation is the movement o soil material romone place to another. In areas o low rainall, leaching
oten is incomplete. Water starts moving down throughthe soil, dissolving soluble minerals as it goes. Thereis not enough water, however, to move the minerals
all the way through the soil. When the water stopsmoving and then evaporates, salts are let behind. Soil
layers with accumulations o calcium carbonate orother salts orm in this way. I this cycle occurs enough
times, a calcareous hardpan can orm.
Upward translocation and lateral movement occurin some soils. Low-lying soils can have a high water
table, even i they are in dry areas. Evaporation at thesurace causes water to move upward (g. 16). Salts
are dissolved on the way. They are deposited on thesurace as the water evaporates (g. 17).
Transormations
Transormations are changes that take place inthe soil. Micro-organisms that live in the soil eedon resh organic matter and change it into humus.
Chemical weathering changes the parent material.Some minerals are destroyed completely. Others are
changed into new minerals. Many o the clay-sizedparticles in soil are actually new minerals that orm
during soil development.
Other transormations can change the orm ocertain materials. Iron oxides (erric orm) usually
give soils a yellowish or reddish color. In waterloggedsoils, however, iron oxides lose some o their oxygenand are considered reduced. The reduced orm o
iron (errous) is easily removed rom the soil throughleaching. Ater the iron is gone, the leached zone
generally is grayish or whitish (g. 8).Repeated cycles o saturation and drying create
mottles (splotches o colored soil in a matrix o a
dierent color). Part o the soil is gray because ironoxide is reduced or lost, and the part in which the iron
oxide is not removed or reduced is browner (gs. 18and 19). During long periods o saturation, gray-lined
root channels develop. These may indicate a possible
loss o iron caused by enhanced microbial activityollowing an addition o humus rom decayed roots.
Figure 17.Salinity-alkalinity problem caused by poor internal
soil drainage. Caliornia.
Figure 18.Munsell soil color. The soil block on the let has
gray reduced colors. The one on the right has reddish
oxidized colors.
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Figure 19.Moderately well drained Mattapex soil, wet phase,
ormed in marine sediments. Dark grayish brown A horizon
(0 to 6 inches); brown BE horizon (6 to 1 inches); yellowish
brown, strongly acid Bt horizon (1 to 36 inches). Common
light brownish gray mottles are in the part o the Bt horizon
between depths o 1 and 36 inches. A C horizon is at a depth
o 36 inches. Aquic Hapludult. Maryland, Delaware, Virginia,
and New Jersey.
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Section 4: Soil properties
Soil survey publications describe a numbero properties that pertain to agriculture.Some properties, such as slope gradient
and actors K and T, relate to erosion. Others relateto plant growth. These include depth to layers that
restrict root development, available water capacity,salinity, and the capacity o the soil to retain and
release plant nutrients. Some properties relate to theability o the soil to retain soluble substances that may
cause pollution o ground water. These include organicmatter and pH, which aects the need or additions olime. Alteration o some properties, such as slope, can
improve the suitability o a site. For example, properly
constructed terraces can shorten the slope length andthus reduce the hazard o erosion or the grade orirrigation. The ollowing paragraphs describe the major
soil properties that aect the suitability o a soil or anumber o specic uses.
Available water capacity (AWC)
Available water capacity is an estimate o how
much water a soil can hold and release or use bymost plants, measured in inches o water per inch o
soil. AWC is infuenced by soil texture, content o rockragments, depth to a root-restrictive layer, organic
matter, and compaction. It is used in schedulingirrigation and in determining plant populations. Thetype o soil structure can infuence the availability o
water to plants and the rate at which water is releasedto plant roots. A soil with a tillage pan may not allow
roots to penetrate and extract the deeper water.
Bedrock and other restrictive layers
There are 20 kinds o restrictive layers recognizedin soil surveys. Examples are cemented pans,
permarost, dense layers, layers with excessivesodium or salts, and bedrock.
Bedrock is the solid rock under the soil and parent
material (g. 11). In areas where it is exposed atthe surace, it is reerred to as rock outcrop. The
depth rom the soil surace to bedrock infuences thepotential o the soil or plant growth and agronomic
practices. Sot bedrock consists o material thatcan be ripped. A shallow depth to bedrock resultsin a lower available water capacity and thus drier
conditions or plants. It also restricts the rooting depth.Five depth classes are dened or use in soil
surveys (table 1).
Table 1.Depth classesVery shallow ................................ Less than 10 inches
Shallow ................................................10 to 20 inchesModerately deep ..................................20 to 40 inchesDeep ....................................................40 to 60 inches
Very deep ....................................More than 60 inches
Calcium carbonate
Calcium carbonate (CaCO3) infuences the
availability o plant nutrients, such as phosphorusand molybdenum. Iron, boron, zinc, and manganesedeciencies are common in plants grown in soils
that have signicant levels o calcium carbonateequivalent, especially in the surace layer. Soil texture
infuences the levels at which these decienciescommonly occur. Sensitive crops may show
deciencies even at low levels (0.5 to 2.0 percent).
Cation-exchange capacity (CEC)
Cation-exchange capacity is the ability o a soilto hold and exchange cations. It is one o the most
important chemical properties in soil and generallyis closely related to soil ertility. A ew o the plant
nutrient cations include calcium, magnesium,potassium, iron, and ammonium.
Generally, as CEC levels decrease, more requentand smaller applications o ertilizer are desirable.Smaller applications o ertilizer on soils that have low
CEC levels may reduce ertilizer loss to surace andground waters, lessening the impact on water quality.
In many highly weathered, naturally acid soils, CEC islower when pH is lower and higher when pH is higher.
Drainage class (natural)
Drainage class reers to the depth, requency, and
duration o periods o saturation or partial saturationduring soil ormation. Seven classes o natural
drainage are used in soil surveys. They range rom
excessively drained to very poorly drained (g. 5).
Erosion factor (K)
The soil erosion actor (K and Kw) is a relative
index o the susceptibility o bare, cultivated soil toparticle detachment and removal and transport by
rainall. It can be computed rom particle size, organicmatter, saturated hydraulic conductivity, and structure.
K values range rom 0.02 to 0.64 or more. Thehigher the value, the greater the susceptibility. Soils
Soil Survey Information
Sections 4 through 7 describe the agronomic soil inormation published in soil surveys or contained in the FieldOfce Technical Guide o the Natural Resources Conservation Service.
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that have more silt and very ne sand are generallymore erodible than other soils because o weakerbonding. K is adjusted downward or the percent o
rock ragments in each layer. K values are calculatedvalues that indicate the erodibility o the ne-earth
raction, or the material less than 2 millimeters insize. They are used in the Revised Universal SoilLoss Equation2 (RUSLE2). Kw estimates indicate
the erodibility o the whole soil, including the rockragments. Kw criteria are used in the determination o
important armland, including prime armland.
Erosion factor (T)
The T actor is the soil loss tolerance used in theRUSLE2. It is dened as an estimated maximum rateo annual soil erosion that will permit crop productivityto be sustained economically and indenitely. The
ve classes o T actors range rom 1 ton per acreper year or very shallow soil to 5 tons per acre per
year or very deep soil, which can more easily sustainproductivity than shallower soils.
Flooding
Inundation by overfowing streams (g. 20) or
runo rom nearby slopes may damage crops or delaytheir planting and harvesting. Scouring can remove
avorable soil material. Deposition o soil material canbe benecial or detrimental. Soil stratication (g. 16)
is an indication o deposition by fooding. Long periodso fooding reduce crop yields. Table 2 gives therequency and duration classes used in soil surveys.
Table 2.Flooding frequency and duration classes
Flooding requency classes
None: Near 0 percent chance in any year, or less
than 1 time in 500 years
Very rare: Less than 1 time in 100 years but more
than 1 time in 500 years
Rare: Nearly 1 time to 5 times in 100 years
Occasional: 5 to 50 times in 100 years
Frequent: More than 50 times in 100 years but
less than a 50 percent chance in all months oany year
Very requent: More than a 50 percent chance inall months o any year
Flooding duration classesExtremely brie: 0.1 hour to 4.0 hours
Very brie: 4 to 48 hours
Brie: 2 to 7 days
Long: 7 days to 30 days
Very long: 30 days
Onsite investigation may indicate that a map unitdescribed as subject to fooding has areas that are
now protected against fooding.
Potential for frost action
Potential or rost action is the likelihood o upwardor lateral movement o soil through the ormation oice lenses. Estimates are made rom soil temperature,particle size, and soil water states. Frost can break
compact and clayey layers into more granular orms.It can also break large clay aggregates into smaller
aggregates that are more easily transported bywater and wind. Frost heaving can harm improperly
designed conservation structures and can destroytaprooted perennial crops.
High water table
A seasonal high water table is the highest averagedepth o ree water during the wettest season. The
ground water level, or water table, may be high yearround or just during periods o heavy rainall. Howhigh the water table rises and how long it stays at that
height aect the use o the soil. A perched water tableusually occurs in areas where a hardpan, claypan, or
other dense layer retards deeper water penetration. Awater table that rises above the surace is considered
ponding.
Organic matter
The content o organic matter is estimated or
each soil layer. A content o 1 percent organicmatter is equivalent to 0.6 percent organic carbon.Organic matter promotes granulation, good tilth,and water inltration; increases porosity; lowers
bulk density; reduces plasticity and cohesion; andincreases the available water capacity. It has a high
cation-adsorption capacity, and it releases nitrogen,phosphorus, and sulur as it decomposes.
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Permeability
Permeability reers to the ability o soil to transmitwater or air. In soil surveys, the term permeability
indicates saturated hydraulic conductivity, which isinfuenced by texture, structure, bulk density, andlarge pores. Soil structure infuences the rate o water
movement through saturated soil, in par t, by the sizeand shape o pores. Granular structure readily permits
downward water movement, whereas platy structurerequires water to fow more slowly over a much
longer path (g. 21). Permeability aects drainagedesign, irrigation scheduling, and many conservationpractices. Permeability classes are shown in table 3.
Table 3.Permeability classes
Class Rate (in/hr)
Impermeable...................................................20
Figure 0.Flooding along the Missouri River.
Reaction
Soil pH is an expression o the degree o acidity oralkalinity o a soil. It infuences the availability o plant
nutrients. Compared to a neutral soil (pH 7.0), a veryacid soil (pH less than 5.0) typically has lower levelso nitrogen, phosphorus, calcium, and magnesium
available or plants and higher levels o availablealuminum, iron, and boron. At the other extreme,
i the pH is too high, the levels o available iron,manganese, copper, zinc, and especially phosphorus
and boron may be low. A pH above 8.3 may indicate asignicant level o exchangeable sodium.
Rock ragments
The size and percentage o rock ragments in thesoil are important to land use. Rock ragments reducethe amount o water available to plants and may
restrict some tillage operations. Particles larger than2 millimeters in diameter are called rock ragments.
Those 2 millimeters to 3 inches in diameter are calledpebbles or gravel; those 3 to 10 inches in diameterare called cobbles; and those more than 10 inches in
diameter are called stones or boulders.
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in reduced aeration and permeability and increasedsusceptibility to erosion. Higher values may indicate
surace conditions that take on a puddled appearance.Amendments, such as gypsum (CaSO4), along with
irrigation and drainage can improve the unavorable
soil condition in many areas.
Slope
Slope is the gradient o an elevation change. Arise o 10 eet in a horizontal distance o 100 eet is
a slope o 10 percent. Ranges o slope assigned tomap units represent practical breaks on the landscape
that are important or the use and management othe survey area (g. 22). Terraces, irrigation, and
tillage practices are all considered. For example,
terraces can help to control erosion in some areaswhere slope is more than about 1 or 2 percent;
thus, a separation o 0 to 2 percent and more than2 percent or the same kind o soil may be used in
mapping. Slope classes are not site specic, however,and or conservation planning, onsite investigation is
necessary to determine the slope.
Soil texture (USDA)
Texture is determined according to the relativeproportions o sand, silt, and clay in the soil (g. 23).
Figure 24 illustrates the relative sizes o the threemajor soil particles.
Sandy soils tend to be characterized by lowstrength and a greater susceptibility to wind erosion
and less water available to plants than soils o othertextures. In addition, trenches and banks are highlysusceptible to caving, which may pose a saety
hazard. Water may pipe through terraces and otherwater impoundments.
Clayey soils generally have more available water
than sandy soils. Loamy very ne sands and loamyne sands, however, can hold moderate amounts
o available water. Generally, the cation-exchangecapacity increases with increases in content o clay
and organic matter. Soils that have large amounts oclay x more phosphorus than soils that have lessclay. The type o clay also aects phosphorus xation.
Clayey soils that are high in content o montmorillonitetend to have the greatest capacity to shrink and swell
(gs. 7 and 25). They retain large quantities o water,which aect tillage practices and can contribute to soil
creep or landslides in sloping areas. MontmorilloniticFigure .Slope classes.
Figure 3.USDA soil texture classes.
Figure 4.The relative sizes o sand, silt, and clay.
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or other smectitic clays also have strong adhesiveproperties that bond particles together.
Silty soils have a higher available water capacitythan sandy soils. In the absence o clay particles, silty
soils have lower adhesive properties. Piping throughterraces, levees, and pond embankments can be aproblem. Trenches may cave, particularly in saturated
soils.In organic soils the term muck or peat is used
in place o textural class names (g. 4). Muck is
well decomposed organic soil, and peat is raw,undecomposed material. The word mucky is used asan adjective to modiy a texture class. An example ismucky loam.
Adjectives describing rock ragments also are usedto modiy a texture. For example, some Hambright
soils (g. 11) have very cobbly layers.
Subsidence
Organic soils oten subside when drained becauseo shrinkage rom drying; loss o ground water, which
physically foats the organic material; soil compaction;and oxidation o the material. Subsidence creates an
uneven surace. Periodic surace smoothing or gradingmay be needed to maintain adequate irrigation
systems. Draining and oxidation o the organic
Figure 5.Deep, wide cracks are common during dry periods
in Vertisols. Maxwell soil. Typic Haploxerert. Caliornia.
material contribute large amounts o carbon to theatmosphere.
Some mineral soils subside because o lowering oground water tables; removal o zones o soluble salts,such as gypsum and calcium carbonate, through
leaching; and melting o ice lenses in rozen soils.
Wind erodibility group (WEG) and wind erodibility
index (I)
WEG is a general grouping o soils with similarproperties aecting their resistance to soil blowing.Soil texture, size o soil aggregates, presence o
carbonates, and the degree o decomposition inorganic soils are the major criteria used in grouping
the soils. The groups are numbered 1 through 8. The
number 1 represents sandy soils, which are the mostsusceptible to wind erosion (g. 26), and the number8 represents gravelly or wet soils that are not subjectto soil blowing. The wind erodibility index (I) is an
estimate o soil loss in tons per acre per year. It is oneo the criteria used in the determination o important
armland, including prime armland.
Figure 6.Evidence o erosion on a sandy soil partially
protected by surace gravel.
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Section 5: Management interpretations
Soil surveys commonly identiy the moreimportant soil characteristics that determinethe soil-related limitations that aect
arming. Interpretations or arming include soilproductivity, placement o the soil in management
groups, and presentation and evaluation o a numbero soil properties aecting use. The interpretations
are designed to warn o possible soil-related hazardsin an area. Table 5 displays important soil propertyinormation related to agronomic interpretations. The
ollowing paragraphs describe some o the majoragricultural interpretations.
Soil productivity
Productivity o the soil is the output or yield peracre o a specied crop or pasture species under
a dened set o management practices. I the landis irrigated, yields are provided or irrigated andnonirrigated conditions. Management practices are
usually dened or each class.A high level o management provides necessary
drainage, erosion control, protection rom fooding,proper planting rates, suitable high-yielding varieties,
appropriate and timely tillage, and control o weeds,plant diseases, and harmul insects. This managementalso includes avorable pH and optimal levels o plant
nutrients; appropriate use o crop residue, manure,and green manure crops; and harvesting methods that
ensure the smallest possible loss. For irrigated crops,the irrigation system is adapted to the soil and crops
and good-quality irrigation water is uniormly appliedas needed.
Irrigation
For most crops, the most avorable soils or
irrigation are deep, nearly level, and well drained.They are characterized by good surace permeability
and a high available water capacity. Irrigation water
or rainwater can perch on a tillage pan, reducing theamount o oxygen in the root zone and increasing the
amount o nitrogen lost to the atmosphere.Important considerations aecting the design o
irrigation systems are easible water application rates,ease o land leveling, drainage i necessary and its
eect on the soil, the hazard o erosion, equipmentlimitations caused by steep slopes or rock ragments,and fooding.
Slope aects the perormance o an irrigationsystem. Flood or urrow irrigation is used mainly onsoils having slopes o less than 3 percent. Wheel lines
and center pivots work well on slopes o as much as7 percent but with increasing diculty. Drip systems
work well even on steep slopes.Most irrigated crops grow well i the rooting depth
exceeds about 40 inches. A shallower root zone has a
lower amount o available water, thus requiring morecare in crop management and irrigation. Shallow
soils, sandy soils, and soils that have rock ragmentsrequire more requent irrigation than deep and ner
textured soils. Frequent, light irr igation on ne textured
soils helps to prevent cracking and thus reduces theamount o water lost through evaporation (g. 25).
Chemical characteristics can be important. Salinityis particularly a problem where drainage conditions
are unavorable or the removal o soluble salts byfushing. Where only small dierences in slope and
elevation occur, salt-laden water can increase salinityand alkalinity in low areas (g. 17).
Drainage
Drainage is the removal o excess water rom
soil. Determination o which soils meet the denitiono hydric soil and wetland is needed to prevent
draining o wetlands.Soils that have intermediate saturated hydraulic
conductivity (permeability) respond well to subsuracedrains, open ditches, or a combination o these.In areas that have large amounts o excess water,
drainage can be improved by smoothing or shapingthe surace o the soil, provided that trac-induced
surace compaction is remedied. Smoothing orshaping increases runo and reduces the amount o
water to be disposed o by internal water movement.Stoniness, slope, silty soil low in content o clay,
and physical soil barriers aect the installation and
unctioning o the drainage system. Caution is neededin areas o unstable soils. Silty soil material low in
content o clay tends to move into and clog subsuracedrains that are not adequately protected by lters.
Coarse textured soils are unstable and may bedroughty ater drainage. Some wet soils have suldesthat oxidize on exposure to air, causing extreme
acidity ater drainage. Drainage water high in reduced
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iron may precipitate a slime that plugs drainagelines. Wet organic soils subside ater drainage.
The eective rooting depth is an indicator o the
depth to which soils can be drained. In deep soilswithout root-restrictive layers, depth is not a limitation.
I a massive clayey layer or other root-restrictive layeroccurs in the soil, eective drainage is more dicult.
I drainage is impaired by a restrictive layer, trenchingand installation o drain tiles are needed.
Erosion-control practices
The need or erosion control depends on the
hazard o erosion and the cultivars grown. Somecrops, such as hay and pasture, protect against
erosion. For others, such as row crops, specicmanagement practices are needed. The practices
to be used should be selected only ater onsiteinspection. In some areas adequate erosion controlcan be achieved by simple application o one o
the general practices. In other areas two or threedierent practices may be needed. In addition to cover
crops, stripcropping, conservation tillage, terraces,diversions, and grassed waterways, other measures
may be appropriate.
Other management interpretations
Some soil surveys, or addenda to the surveys,have special tables on important agronomic soil
interpretations. A ew tables show the potential o soilsor a specied use, such as the potential or cropland.
Table 5 identies soil properties that infuenceagronomic uses.
Soil properties
Agronomic
use
Organic
matter
Flooding Texture Bedrock
or pan
pH Subsid-
ence
Cation-
exchange
capacity
CaCO3
Slope Bulk
density
Perme-
ability
Potential
or rost
action
Available
water
capacity
Salinity/
alkalinity
Water
table
Wind
erodibility
group
Erosion
actors K
and T
Tillage
suitability Plant
adaptability Erodibility:
Wind
Water
Irrigation
Drainage
Crop yield
productivity Conservation
practices Land use
capability
A bullet () indicates that the soil property aects the selected agronomic use.
Table 5.Soil survey inormation that infuences agronomic uses
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Some tables group soils or specic programs, suchas hydric soils, highly erodible lands, land capabilityclassication, and prime or unique armland.
Hydric soils ormed under conditions o saturation,fooding, or ponding long enough during the growing
season to develop anaerobic conditions (lack ooxygen) in the upper part (6 to 10 inches). Thepresence o hydric soils is one o three parameters
needed or a site to be considered a wetland orFederal wetland protection programs and legislation.
The presence o hydric soils can also be used toidentiy areas suitable or wetland restoration. Soil
eatures that occur because o anaerobic conditions
are used to conrm that a soil is hydric.The national hydric soils list identies map units
that have components o hydric soils. A copy o theocial hydric soils list can be downloaded rom the
ollowing Web site: http://soils.usda.gov/use/hydric/.An interpretive map based on the hydric soils list
can be created or an area o interest (AOI) in WebSoil Survey. Ater creating an AOI, click on the Soil
Map tab. From the Soil Data Explorer tab, click onSuitabilities and Limitations or Use. Open LandClassications, and select Hydric Rating by Map Unit.
Highly erodible soil and potentially highly erodiblesoil are listed in Section II o the NRCS Field Oce
Technical Guide. The criteria used to group highlyerodible soils were ormulated using the Universal
Soil Loss Equation and the wind erosion equation.The criteria are in the National Food Security ActManual. Soil use, including tillage practices, is not a
consideration.Areas dened as highly erodible can be held to
an acceptable level o erosion by ollowing approvedpractices in a conservation plan. Various conservation
practices, such as crop residue management,reseeding to grasses, contour arming, and terraces,are used in conservation planning to reduce soil loss,
maintain productivity, and improve water quality.Land capability classes and, in most cases,
subclasses are assigned to each soil. Theysuggest the suitability o the soil or eld crops or
pasture and provide a general indication o theneed or conservation treatment and management.Capability classes are designated by either Arabic
or Roman numerals (I through VIII), which representprogressively greater limitations and narrower choices
or practical land use (g. 27).
Capability subclasses are soil groups within one
class. They are designated by adding a small letter,e, w, s, or c, to the class numeral, or example,
IIe. The letter eshows that the main hazard is therisk o erosion unless close-growing plant cover
is maintained; wshows that water in or on the soilintereres with plant growth or cultivation (in somesoils the wetness can be partly corrected by articial
drainage); sshows that the soil is limited mainlybecause it is shallow, droughty, stony, saline, or sodic;
and c, used in only some parts o the United States,shows that the chie limitation is climate that is very
cold or very dry.In class I there are no subclasses because the
soils o this class have ew limitations.
Prime armland and other important armlandare identied by map unit name in the table Prime
Farmland and Other Important Farmlands in WebSoil Survey. Prime armland is land that has the
best combination o climatic, physical, and chemicalcharacteristics and landscape eatures or producingood, eed, orage, ber, and oilseed crops.
Unique armland is land other than prime armlandthat has the soil and climate characteristics needed
or the production o specic high-value crops, suchas citrus, tree nuts, olives, cranberries, ruit, and
vegetables. Nearness to markets is needed.Farmlands o statewide and local importance are
used or the production o ood, eed, ber, orage, and
oilseed crops. They do not meet the criteria or primearmland or unique armland.
Figure 7.Landscape with land capability classes outlined.
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Section 7: Detailed soil inormation
The Web Soil Survey (WSS) at http://websoilsurvey.nrcs.usda.gov/app/providesthe public with access to the most current
ocial soil survey inormation. This Web applicationaccesses the national SSURGO data in the Soil
Data Mart. WSS users can outline their local areao interest (AOI) within a survey area or can selectthe whole soil survey area as the area o interest.
I necessary, the AOI can cross traditional soilsurvey area boundaries. Various navigation tools are
available to help the users navigate to the generalarea o their AOI. WSS also allows the users to
import an AOI boundary rom their local Geographic
Inormation System (GIS). Recent aerial photographyis used as the background or displaying the soil
survey data in WSS.Ater selecting an AOI, the user has the option
o viewing the soil map and list o map units or theAOI. The list includes the acreage and percent o the
AOI or each map unit. The user has the option todisplay either the traditional local map unit symbol or
a nationally unique map unit symbol on the maps andin generated reports.
A description o each map unit is available in WSS.
Areas delineated on the soil maps are not necessarilymade up o just one type o soil but generally
include smaller areas o contrasting soil types. Thecomposition o each map unit is shown in the map unit
description.Thematic maps can be displayed or a variety
o soil properties and interpretive ratings or the
delineated soils. Maps o interpretive ratings displaythe limitations or suitability o each map unit ora particular land use. For each map displayed, a
summary table showing the results is generated. Theunderlying SSURGO data can be downloaded or the
dened AOI in standard ormat.Standard tabular soil reports also can be generated
or the AOI. These reports look much like the tables
that have been included in the traditional hard copysoil survey publications.
The various maps and tabular reports that the userselects can be printed individually or compiled into
a Custom Soil Resource Report via the Shopping
Cart option. The output reports are compiled into astandard PDF le or download to the users local
computer. The maps can be printed at various scalesand on various sizes o paper, depending on what
printer options the user has locally. Larger AOIs canbe tiled to multiple pages or printing. This capability
allows users to get just the content that they want orneed to answer their particular resource management
questions.Soil surveys provide sucient inormation or
the development o resource plans, but onsite
investigation is needed to plan intensive uses o smallareas. Some useul inormation that is not included
in WSS is available in Section II o the NRCS FieldOce Technical Guide (FOTG). The electronic version
o the FOTG can be accessed at http://www.nrcs.usda.gov/technical/eotg/.
http://websoilsurvey.nrcs.usda.gov/http://websoilsurvey.nrcs.usda.gov/http://www.nrcs.usda.gov/technical/efotg/http://www.nrcs.usda.gov/technical/efotg/http://www.nrcs.usda.gov/technical/efotg/http://www.nrcs.usda.gov/technical/efotg/http://websoilsurvey.nrcs.usda.gov/http://websoilsurvey.nrcs.usda.gov/ -
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Included are a variety o national interpretationsas well as various state-specic interpretations. Notall interpretations are included or all areas o the
nation. Some may not be applicable to all areas. Also,not all soil properties are populated or all areas.
For example, inormation about salinity likely is notincluded or an area where salinity is not an issue.
Generated ratings that can be displayed as
thematic maps in WSS are organized in a series oolders on the Suitabilities and Limitations tab.
Specic soil properties or interpretations aresometimes dicult to locate within the WebSoil Survey (WSS) application. To assist the
user, WSS includes a search unction that allows theuser to type in a soil property name or keyword. The
tool returns a series o links that the user can clickon to go directly to the desired inormation. The linksmay include general descriptive inormation, thematic
maps, or tabular reports, as shown in the ollowingimage.
Section 8: Location o soil properties and interpretations
Location o Inormation
Section 8 describes where soil inormation can be ound.
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8
The Soil Properties and Qualities tab has a similararrangement o olders and individual themes thatallows the user to generate a thematic map o an
individual soil property or quality.
Each older has one or more interpretive ratings, asshown or Building Site Development in the ollowingimage.
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The Soil Reports tab is organized in a similar ashion. These reports are tabular soilreports with ormats similar to those that have traditionally been included in publishedhard copy soil surveys.
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Reerences
Andrew R. Aandahl. 1982. Soils o the Great Plains. University o Nebraska Press.
Huddleston, J. Herbert, and Gerald F. King. 1984. Manual or Judging Oregon Soils.Oregon State University Extension Service, Extension Manual 6.
Scrivner, C.L., and J.C. Baker. 1975. Evaluating Missouri Soils. Circular 915, Extension
Division, University o Missouri-Columbia.
Smith, C.W. 1989. The Fertility Capability Classication System (FCC): A Technical
Classication System Relating Pedon Characterization Data to Inherent FertilityCharacteristics. Doctoral Thesis. Department o Soil Science, Nor th Carolina State
University, Raleigh, Nor th Carolina.
Soil Survey Division Sta. 1993. Soil Survey Manual. Soil Conservation Service. U.S.
Department o Agriculture Handbook 18. Available online (http://soils.usda.gov/technical/manual/).
United States Department o Agriculture, Natural Resources Conservation Service.
National Soil Survey Handbook, title 430-VI. Available online (http://soils.usda.gov/technical/handbook/). Accessed 1/20/2010.
United States Department o Agriculture. 1988. From the Ground Down: An
Introduction to Soil Surveys. Soil Conservation Service. Columbia, Missouri.
http://soils.usda.gov/technical/manualhttp://soils.usda.gov/technical/manualhttp://soils.usda.gov/technical/manualhttp://soils.usda.gov/technical/handbookhttp://soils.usda.gov/technical/handbookhttp://soils.usda.gov/technical/handbookhttp://soils.usda.gov/technical/handbookhttp://soils.usda.gov/technical/manualhttp://soils.usda.gov/technical/manual