Soil Info From USDA

8/8/2019 Soil Info From USDA

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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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1

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.
http://soils.usda.gov/use/hydric/http://soils.usda.gov/use/hydric/


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6

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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7

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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9

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

Documents

Soil Info From USDA