An Introduction toSOILS OF PENNSYLVANIA—. * ..-..— Sn’.. —

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TeacherEducationSeriesVolume 23, Number4 AGDEX 512

Copiesof this andotherspecialpublicationsof theDepartmentof AgriculturalandExtensionEducationmaybeobtainedby writing to:

Collegeof AgriculturalSciencesPublicationsDistributionCenter

ThePennsylvaniaStateUniversity112AgriculturalAdministrationBuilding I

UniversityPark,PA 16802

An Introduction toSOILS OF PENNSYLVANIA

By BetsieBlumbergInstructionalMaterialsServicesDepartmentof Agricultural andExtensionEducationThe PennsylvaniaStateUniversity

and RobertL. CunninghamProfessorof Soil GenesisDepartmentof AgronomyThe PennsylvaniaStateUniversity

Artist SharonWhitmoyer WaitmanGraduateAssistantDepartmentof AgronomyThe PennsylvaniaStateUniversity

TechnicalEditors GeorgeN. Coller JosephJ. EckenrodeSoil Conservationist Area Soil Scientist

USDA Soil ConservationService

Reviewer JamesE. DiamondAssistantProfessorof Agricultural andExtensionEducationThe PennsylvaniaState University

Departmentof Agricultural andExtensionEducationThe PennsylvaniaStateUniversityUniversity Park,PA 16802

© The PennsylvaniaStateUniversity, 1982

Contents

INTRODUCTION 3

SOIL DEVELOPMENT 4

The Geologic Cycle 4

Weathering 6

Vegetation 8

Climate and Time 8

FORMATION OF PENNSYLVANIA SOILS 10

Bedrock and Topography 10

Parent Material 12

SOIL PROPERTIES 15

Soil Texture 15

Active Fractions 17

Soil Water 18

Soil pH 19

CLASSIFYING SOILS 20

Soil Series 20

County Soil Surveys 20

GLOSSARY 23

INTRODUCTION

An understandingof soils,their development,properties,andusepotential,is both fascinatingandimportant.Thisbook,which focuseson thesoils of Pennsylvania,waswritten to pro-vide suchan understanding.

Thesoil is arecordofthegeologicalandclimatic historyofthe regionwhereit is found. It reflectstheancientpresenceofrock, or rivers,or oceans.It revealstheclimateit haswithstoodand thekind of vegetationit hassupported.Themanyfacetsoftheenvironment— weather,life forms,minerals— areclearlyinterrelatedwhenwestudytheir recordin thesoil, which iswheretheyultimately leavetheir impression.A familiarity withsoil sciencebrings usthis insight.

Sincemanhassettledon thelandscapeof Pennsylvania,he,too, hasmadehis markon thesoil. Hehasturnedover thesur-faceandchangedthevegetationwith his agriculture.Hehasex-cavatedandstrippedtheearthwith his mining activities.And, hehaslargelyobscuredthelandscapewherehehasbuilt cities.However,thekinds ofactivitieshechoosesandwhereheprac-tices themdependon thenatureof thelandhe is exploiting. Forexample,it wasnot at randomthat Pennsylvania’scities grewupatthejunctionsof riverswheretransportationwasconvenientbeforetheageof motorvehiclesandairplanes.Agriculture,animportantindustryin Pennsylvania,is dependableherebecauseof plentiful waterresources,althoughmountainousterrainlimitsits practice.And Pennsylvania’smining industrydevelopedaroundrich naturaldepositsof coalandlimestone.

Not only arethegeneralkindsandlocationsof man’sactivi-tiesdependenton the physicallandscape,butparticularsitesforanyprojectmustbepreciselychosenconsideringimmediatesoilconditions.Wherevera building is erected,wastematerialsde-posited,or thelandscapeotherwisedisturbed,thelocal soil mustbecarefullystudiedandrespectedbecausesoils havetheirownlimitations.Somecannotproviderequiredsupport.Othersmaylacknecessarydrainageor filtration capacity.Andsoil fertility isnotequallydistributed.

Thisbook shouldhelpthereaderto recognizesomeof thepropertiesof local soils, to seehowtheyarerelatedto landscapefeaturesandto thesoil’s history,andto appreciatethelimits andthepotentialof Pennsylvaniasoils.

4

SOIL DEVELOPMENTThe Geologic Cycle

The landscapeof Pennsylvaniaas we seeit todayrepresentsonly amomentin the vastagesof geologictime during which cy-desof landscapebuilding andlandscapeerosionareslowly, butsurely,alwaysin progress.

Soil developsrelatively quickly in termsof geologictime, al-thoughit formsat differentratesin the threekindsof rock: igne-ous, sedimentaryandmetamorphic*.Soil supportsmuchof the lifeon earth.It containsits own microscopiclife forms,anditrecyclesall of thecreaturesthat live anddie on the land.Soil,beingloose,unconsolidatedmaterial,representsthe phasein thegeologiccycle in which the earth’smineralmatteris interactingmostcloselywith life forms.

*Italicized words maybe found in the glossaryon page23.

stream carrying sediments

-~

V . .~ .

—

‘silt’

older lake bed deposits

Figure 1. A stream sorting and depositing its load at its delta, where it enters a lake.

5

The mineralcomponentof the soilwasoncepart of themoltenliquid at theearth’score.As theearthcooled,its surfacehardenedinto solid rock. Today,moltenrock still surfacesasvolcanoes,or spurtsup unseeninto the bedrockbelowthe ground.Outcropsof this cooled,hardenedmoltenrock, known as igneousrock, arefound in southeasternPennsylvania.

Exposedto the assaultsof weatherandtime, solid rockslowly andcontinuallycrumblesanddisintegrates.This weather-ing processproducestheunconsolidatedmineralmaterial inwhich soil forms. On astablelandscape,soil developsandma-turesin this materialdirectlyabovetheweatheringrock. On anerodingterrain,it is carriedawayby waterandeventuallyflowsinto the sea.

Watersortstransportedparticlesby size,separatingsand,silt, andclay (Fig. 1). The water-borneandsorteddepositsaccu-mulate,arecompressed,andhardenover long periodsof time.Carbonates,substanceswhich arecompletelydissolvedin water,ultimately precipitateout assolids, forming limestone.Clay de-positsbecomeshale,silt becomessiltstone,andsandbecomes

- lake surface

t

~ clays

dissolved carbonates

silt .1

6

sandstone.Eventuallyin geologictimewhat wasoncetheseabot-tom risesandbecomesthesedimentaryrockof dry land.

Exposedatthe earth’ssurface,sedimentaryrockweathersanew.Butwhereit lies deepwithin theearth,greatheatandpressurefurtherhardenandchangeit into metamorphicrock.Whengeologiceventsbring metamorphicrock to thesurface,ittoo will slowly weather,form soil materials,erodeaway,andeventuallyform rockagain,as the cycle continues.

WeatheringSoil formationstartswith weathering,which happensto

barerock aswell asto buriedrock. Severalfactorsbring aboutweathering:

1. Temperaturefluctuation,which causesexpansionandcontraction.

2. Erosionby water,wind, andice.3. Plantroots growing into tiny cracks,causingthemto

spread.4. Chemicalreactionsof soil mineralswith water andair.You mightexpectsoils to havethe samecompositionas the

rock from which theyoriginate.However,in the transformationof rock to soil, mineralsundergosomany changesthat thesoilminerals,althoughremainingrepresentativeof theoriginal rockminerals,usuallychangetheir composition.For example,by thetime limestonerockbecomessoil, it containsno calcite(CaCO,),thepredominantmineral in thatrock. Becausecalciteis highlysoluble,it dissolvesin humid climates,leavingjust insolubleim-purities,which becomethe limestonesoil. Only anestimated5percentof theoriginal limestonerock remains.Thusa5-inchlayerof limestonesoil representstheweatheringof 100 inchesofbedrock.

Soil, however,is morethanjust weatheredrock. Organicmat-ter is anotherimportant component.Organicmatterincludesthedecomposinganddecomposedpartsof animalandplant mate-rial andamultitude of soil organisms,mostlymicroscopic.Themicroorganismscontributeto theweatheringof mineralsandthebreakdownof organicresidues.

The mediumin which soil developsis calledparentmaterial.This material is usuallyweatheredrockin Pennsylvania,but inbogsandmarshesit is decayedorganicmatter.Parentmaterialmayalsobe loosematerial,gravel,for example,depositedalongrivers andstreamsduringfloods. Within theparentmaterial,processessuchas leachingandredistributionof mineralstakeplace.Theseprocessesresult in thedifferentiationof horizonsbelowthe surface(Fig. 2),visible whenthe landis excavated.

7

The topsoil, whichhasthe mostorganicmatterandis theroot zone,is calledthe A horizon.The nextlayer, thesubsoil orB horizon,containshigher concentrationsof clay andis denserthanthe A horizon. TheC horizon is the parentmaterial— thealteredorganicdepositor the weatheredbedrock.Bedrockis thelast layer,the R horizon. Thedepthandthicknessof the hori-zonsvary with eachsoil.

Figure 2. A soil profile: the different soil horizonsin soil color and texture can be distinguished.

are visible on the sides of this pit where changes

x

N

0

20 -

cm

60

cm

8

VegetationMaturesoil developsslowly. Whenit staysin placefor a long

time, vegetationbeginsto grow on the surface,providingor-ganicmatterfrom litter anddeadroots,anddarkeningthe soilnearestthe surface.As organicmatter accumulates,conditionsbecomeincreasinglyfavorablefor plant growth.

The kind of vegetationgrowingon thesurfaceaffectsthedevelopmentof the soil below. Grasseshaveextensiverootsys-tems,a largeportionof which die off andarereplacedby newshootseachseason.After manyyears,grassesgive topsoilawell-aerated,crumblystructureandhigh levelsof organicmatter(Fig. 3). The soilsof the Midwest are highly productive,largelybecausetheyweregrasslandsfor manycenturiesbeforetheywere farmed.

Pennsylvaniamayoncehavehadsomegrasslands,but in re-cent timesit hasbeenmostly forested.Treescontributeorganicmatterlargelythroughthe annualfalling of leavesratherthanthroughtheir root systems.Thus forestsoils tendto havealayerof dark, mattedorganicresidueoverthe surface,with arela-tively low level of organicmatterwithin the soil (Fig. 4).

Not only doesvegetationcontributeto soildevelopment,italsorevealsmuchaboutsoil conditions.To thrive, manyspeciesrequireparticular rangesof soilmoisture,texture,andacidity(pH). For example,wetandneutralsoil favorscattailsandteasel.Wherethe soil is acid, rhododendronandlaurel bushesthrive.Knowledgeof wild vegetationcanbe an index to soil properties.

Climate and TimeClimateis amajor influenceon the rate of soil development.

Pennsylvaniahasahumidclimate, with anannualrainfall ran-ging from 34 to 50 inches.Its soils reflect centuriesof rainwaterflowing throughthem,slowly breakingdown minerals.Whensolublecomponentssuchasthe alkalineions— calcium,magne-sium,andpotassium— arecarriedoff to the groundwater,soilfertility dirr~inishesandacidity increases.

Rain alsoveryslowly carriesdown from the topsoil thesmallestsoilparticles,the fine clays. Thesesettlein the subsoil,makingit finer-textured(moreclayey) thanthe topsoil. Overtime, the recognizablydifferent horizonsdevelop.

Maturesoilhasits own soil structurewhich is composedof ag-gregatesof sandandsilt heldtogetherby clay andorganicmat-ter. If you takea handfulof maturesoil andlet it spreadoveryour palm,you will noticethatit falls into little angularor crum-bly lumps.Thesestructuralunits,or peds,aretheproductof cen-tunesof development.

9

Heat,aswell asrainfall, acceleratestheprocessof soil devel-opment.BecausePennsylvaniahasahumid temperateclimate,with seasonalfluctuationsandannualfreezing andthawing,thesurfaceis continually subjectto expansionandcontractionandthe effectsof water. Thesefactorsresult in asoil thathasgreatermaturity— pedologicage— thanthatof the sameinitial parentmaterialdevelopingin the Arctic for the samelengthof time.However,no soil in Pennsylvaniais asmatureastheoldesttropi-cal soils.

Ap(plow ~or

A horizon

B horizon

Figure 3. Profile of a grasslandsoil. Note the thick A horizon.

o horizon (surface litter)

A horizon

B horizon

C horizonFigure 4. Profile of a forest soil.Note the litter on the surface andthe thin A horizon.

10

FORMATION OFPENNSYLVANIA SOILS

Bedrock and TopographyPennsylvaniasoilsaretheproductof the generalforcesof

weathering,vegetation,climate,andtime working on thepartic-ular parentmaterialandtopographyof the region.

Many different typesof bedrockunderliePennsylvania. .

Bedrockandits weatheringcharacteristicsarenot only responsi-ble for thenatureof the developingsoil, but alsoinfluencethetopographyof the landscape.As Figure 5 shows,bedrockandto-pographygenerallycorrespondacrossthe state.

At thesoutheasternandnorthwesternedgesof Pennsyl-vania,soils arenot derivedfrom massiverock, but from sandsdepositedwhenthis landwasonceseashore.Coastaldepositslikethesearefound on flat, openlowlands.The sandsweatherandaccumulateorganicmatterto becomesoil. TheWilliamson soilsof Erie Countywereformed from coastaldeposits.Thesesoilsarewell suitedto growing vegetablesandfruit.

In thesoutheasternpart of thestate,abandof very old met-amorphicrock lies underthe soil. This bedrock— schist,gneiss,andquartzite— is the oldestoutcropin thestate.Formedin thepre-Cambrianeramore than600million yearsago,it is the rem-nantof mountainsoncehigher than theRockies.Thesegreatmountainsweatheredawayvery slowly to form therolling topog-raphy found in MontgomeryCountytoday.

Wheresiltstoneoccursin southeasternPennsylvania,it con-tainsveinsof very hardigneousrock. Theseintrusionsweathermoreslowly thanthe siltstone,leavingrocky depositswhichin-terferewith agriculture.

Underlyingthe restof thestateis sedimentaryrock— shale,sandstone,andlimestone— formedfrom materialdepositedinlakesandseasoncepresentin Pennsylvania.Low mountainridgesandvalleysrun northeastandsouthwestacrosscentralPennsylvania.Thistopographyis the resultof aseriesof geo-logic eventswhich occurredafter the shale,sandstone,andlime-stonesedimentsformed. Horizontal layersof rock were up-turned,wrinkled, andfolded. Subsequenterosionof thisconvolutedsurfaceexposedthe upturnedlayers, creatingthelandscapeweseetoday.

Pennsylvania’sridgesandvalleys areevidenceof thediffer-ential ratesof weatheringof the layers. Sandstone,thehardestandmostchemicallyresistantsedimentaryrock, forms the ridgecaps.Limestone,the leastresistant,formsthe valleys.Shale,ofintermediateresistance,underliesthe slopes(Fig. 6).

Ccnca)

0~00~I-0)

00~

0-oC(U00•0a)

~0a)

-Ca)

0)

12

Parent MaterialWhenbedrockbecomestheparentmaterial for the soils de-

velopingon it, it is thesourceof importantsoil properties.Forexample,sandstonesoils, which tendto becoarse,dry out sofastthatthey do not supportmanycrops.Limestonesoilsin theval-leysaregenerallyfertile andproductive— the.bestagriculturalsoils in Pennsylvania,suchas the HagerstownandDuffield soilsin LancasterCounty,arelimestonesoils. Shalesoilsare fine-texturedandtendto be acidic andlow in nutrients— with largeadditionsof fertilizer, theyarefarmed.On mountainsidestheyoften supportmixed forests.

Much of the landoverlyingshaledepositshasbeenruinedby strip mining, becauseshalecontainsPennsylvania’srich coalbeds.Strip mining removesall the rock andsoilmaterialabovethe coal,andthenbackfills thedepletedmine with crushedrock,calledminespoil. Becausethesoil surfaceis gone,almostnothinggrowson the mine spoil, leavingabarrenwastelandwhicherodesandclogsup streams(Fig. 7).

More acreagehasbeendisturbedby strip mining in Pennsyl-vaniathanin anyotherstate.Legislationpassedin 1971 requiresthat topsoilbe replacedat future stripmines. Researchersareworkingon methodsof economicallytreating thebareminespoil, whichis often veryacid, infertile, andtoo coarsefor plantgrowth,andareidentifying speciesthataretolerantto spoil con-ditions. Eventuallytheyhopeto revegetatelanddisturbedbefore

limestone 1971.Parentmaterialcanbe classifiedaccordingto its history, as

transportedor residual.Residualsoilshaveformedin their pres-entlocation. On gently rolling uplands,residualsoil is likely to

shale be well developedandproductive,as is the Chestersoil ofChesterCounty,which producescornandtobacco.However,

while residualsoils formedon steepslopesaredeep,theyare not

suitablefor cultivation with modernequipment.In Pennsylvania,

sandstone vastforestsrepresentthe bestuseof steepmountainsidesbe-

causetheyprovide a coverthatminimizeserosion.

limestone valley

‘ \ ,.—~,--

N/1k:; ~<i ~ /

I

Figure 6. A cross-section of a small portion of ridge and valley topography showing resistant rockat the top of the ridges and faster weathering rook in the valley.

shale footslopes

sandstone ridges

13

Theforcesof ice, water,wind, andgravity carrysmallparticlesas well as rocksacrossthelandscape.Soil forms in thistransportedmaterialdepositedover the original soil or bedrock.Transportedparentmaterialcanbe glacial, aeolian,colluvial, oralluvial in origin.

The onceglaciatednortherncornersof Pennsylvaniahaveglacial featuressuperimposedon older topography.Glacial tilldepositsconsistof rock materialof all kindsandsizes,from boul-ders to clay, broughtin by the ice andleft whereit standstoday.Outwashfeatures,madeof materialcarriedandsortedby waterflowing from themelting glacier,arefoundon relatively opentopography.

Becausetheyhaveverycompacted,firm subsoil,glacial tillsoils generallyhavedrainageproblems.They arenot well suitedto row-crop agriculture,but makegoodpastureandhayland.The Volusiasoils of TiogaCountyareglacial till soils.

Parentmaterialdepositedby thewind is calledaeolian,orbess,material.Chalfontsoil, found in BucksCountyandlargelyusedfor row crops,is anexample.Loesssoils are not widespreadin Pennsylvania,but in the midwestthegreatgrasslandsdevel-opedin besssoils. The bess,which providesanoptimumsoiltexture,combinedwith the effectsof growinggrassesovertime,createdsomeof the richestagriculturalsoil on earth.

While transportedparentmaterialssuchasaeolianor glacialdepositscoverlargeregions,othersareonly transportedlocally.Footsbopesof themountainsin Pennsylvaniaare often createdbyrockwhich hastumbleddown from above.Suchloose rock mate-rial is calledcolluvium.The forestedBuchanansoil of CentreCounty is formedfrom sandstonecolluvium.

Figure 7. A commonlandscape at the site ofabandoned strip mined land.

F’s

14

Becausecolluvial soilshaveaproblematicfeaturecalledfragipans,theyare often usedfor pasturesratherthanfor devel-opment.Fragipans,also found in glacialtill soils, aresubsoillayersof exceptionallydensematerialwhich maybea few inchesto severalfeet thick (Fig. 8). Theyarerelatively impermeabletowaterandimpenetrableto plant roots; hencethe soil abovethemis oftenwaterlogged.Fragipansinterferewith anykind of landusefor whichdrainageis important.Residentialdevelopmentofthesesoils requiresartificial drainageandasewagetreatmentsystem.

In river andstreamvalleys,alluvium— sedimentcarriedbyflowing water— is depositedduringfloods. Newparentmateri-alsarecontinuallyaddedto existingdeposits.This new materialkeepsthesesoils fertile aswell aspedologicallyyoung. Alluvialsoils,while good for farming,aregenerallyhazardousfor build-ing becausethey aresubjectto flooding. TheLinden soils alongtheSusquehanna,periodicallythe site of devastatingfloods, areanexample.

Observingthe landscapefeaturesaroundyouis agood wayto determinethekind of parentmaterialwhich formedthe soilon which you arestanding.

Figure 8.

Soil profile showing afragipan at the bottom ofthe B horizon. Thefragipan is characterizedby bleached verticalstreaks which form apolygonal pattern inhorizontal cross-section. Onthe right is a cut-away of thefragipan.

A horizon

B horizons

15

SOIL PROPERTIESSoil Texture

Onceformedby variousenvironmentalprocesses,soils haveanumberof importantpropertiesof their ownthatdeterminetheir potentialuses.

Soil particlesof varioussizeshaveporespacesbetweenthemthatalsovaryin size.Particle-sizedistribution,alsocalledsoil tex-ture, determineshowreadilyair andwaterwill passthrough,beheld,or beblockedby the soil.

Plantsarequite sensitiveto the textureof thesoil environ-ment.The soil shouldboth retainmoistureandallow air circula-tion. The idealagriculturalsoil compositionis 45 percentmin-eral, 5 percentorganicmatter,and50 percentporespace.Foroptimum plantgrowth,half of the porespacesshouldbe filledwith water,half with air.

Soundfoundationsfor buildingsandroadsrequireasoiltexturewhich providesadequatebearingstrengthanddrainagecharacteristics.Wastedisposalsystemsrequiregooddrainageandenoughfine material(seethe activefraction, page17) to filterout toxinsbeforethey reachthegroundwaterandthewatersupply.

Soil texturecanbe felt by rubbingthe soil betweenthethumbandfingers. With practice,onecantell approximatelywhatpercentageof eachparticlesizemakesup agiven soil, andwhereit belongson the textural triangle(Fig. 9). Particleslargerthan2 mm arecalled coarsefragments.Soil~-size particles,referredto as fine earth,are lessthan2 mmin diameterandaredivided further into sand,silt, andclay.

The termssand,silt, andclay referonly to size,not to the chemicalmakeupof the particles,whichmaybe the samefor clay as for sand.Sandparticlesare 2 mm to 0.05mm in diameter,andsandysoil feelsgritty betweenthe fingers. Siltparticlesare 0.05 to 0.002mm in diameter;siltfeelssilky or floury. Clay particlesaresmallerthan0.002mm in diameter.Moist clay feelssticky andslickwhenrubbedbetweenthefingers.

sand and silt particlesforming air filled pores

waterfilled pores

physical compositionof an ideal soil

greatly enlargedcross-section

clay coating sand ~grains with plant root coating sand grains

16

100

90

80

70CLAY

~ 60

TheFigure 9. Textural Triangle

40 SANDY This diagram is used to identify the texture of a soil. ToCLAY LOAM SILTY CLAY ‘~ use it, locate the appropriate percent clay on the clay

scale, and silt on the silt scale. Follow the linesinward. Clay lines run parallel to sand scale; silt

SANDY LOAMSILT lines run parallel to clay scale. The lines will

0

=‘SAND ‘ SAND -~ intersect in the compartment which represents00 ~ -s ~ ~ ‘5 0

% SAND the texture of a given soil.

All of thesesizesseemvery smallto us. Nonetheless,acoarsesandis 1,000timeslarger thanacoarseclay,andthisdif-ferencehasagreatimpacton the behaviorof waterandair mol-eculesmaking their way throughthe soil.

Sincesandsarethe largestparticlesin the soil, theycreatelargeporespaces.A sandysoil drainsrapidly andremainssoftor light so thatrootscaneasilypenetrateandspread.However,soil composedof too muchsandwill not hold enoughwateror ~ CLAYnutrientsfor goodplant growth. Becausesandhashigh bearing <0.002mmstrength,it makesastablefoundationfor building.

Silt allows theoptimalamountof soil waterretentionandsoil air circulation for agriculture.Silt-sizedparticlesare readily SILTcarriedby the wind, sobesssoils (page13) aresilty soils. 0.002mm— 0.05mm

Clay contributeswater-holdingcapacityin soils.Becauseclayis sofine,water moleculescling to its surfacesandareheldtightly within its tiny pores.Clays coat largersoil particlesandbindthem together,creatingaggregates.Soil havingwell-definedaggregatesandthereforewell-defineddrainagechan-nelsis saidto havegoodstructure.

Soil containingahigh percentageof clay is consideredheavybecauseit createsdragon the plow as well as on plant roots try-ing to penetrateit. If the soil containstoo muchclay, watermay ~neverdrain throughit. Whensuchsoils arewet, the small pores/

collapseif anythingheavypresseson the surface,suchas feetalongapathor tireson adirt roador cornfield. Compac- ~ ~tion smashesthe soil aggregatesandclosesthe channels SAND

/ OOSmm—2mm’for air andwater, destroyingthe soil structure.The sur-facebecomesimpermeable,slippery,andmuddywhenwet,andhardandcrackedwhendry. Becauseplantscannotgrow \

tin compactedsoil, awell-worn pathwill not become Vovergrown.Clay soils do not makegoodbuilding foundationsbecause

theyarelikely to changevolumeandcrackasmoisturecontentchanges. ~-~--- —

17

sand grain

clay particles with tightlyheld coating of water

H +

Active FractionsClay andorganicmatterbothhavearemarkableandimpor-

tantpropertythatmakesthem theactivefractionsof the soil.Clays aresotiny that they havemoresurfacethantheyhavein-ternal mass.Thus,electricalforceswhich hold the crystallineclayparticlestogetherarefelt alongtheir surface.Electricallychar-gedions dissolvedin the soil waterareattractedor repelledbythe chargeson the clays(Fig. 10).

Forexample,apositivelychargedpotassiumion floating insoilwaterwill be attractedto anegativelychargedsite on clay. Ifthe potassiumion is morestronglyattractedto thesite thantheion occupyingthat site, thetwo will exchangeplaces.The potas-siumwill adhere,or becomeadsorbed,to the clay, andtheion itreplaceswill be free to flow with thewater.This propertyoftradingions is calledtheexchangecapacityof the soil (Fig. 11).

Organicmatterin soilhasa far greaterexchangecapacitythanhasclay. It is foundon humus— clay-sizedparticlesof or-ganicmatter.Although the productof decomposition,humusisveryresistantto further breakdown.Pennsylvaniasoils usuallyhavemuchlesshumusthanclay.

Clay andhumusinteractwith materialswhich areintro-ducedinto the soil. Fertility dependsupon the activefraction ad-sorbingandholdingnutrientsby ion exchange.Applied fertili-zerdoesnot drain throughasoil with adequateclay andorganicmatter,but is retainedandmadeavailableto the plants.

This samepropertyexplainshow soil canrenovatewasteprod-ucts.Wheneffluent from asepticsystem,for example,is re-leasedinto the soil, claysadsorbundesirablesubstances,pre-ventingthemfrom beingwashedinto the groundwater.Eventuallymicroorganismsdecomposethesesubstances,render-ing themharmless.

si~

$ -~

H +

1~

Figure 10. Diagram representing ion exchange insoil. Hydrogen ions adsorbed on clay surface.

Figure 11. Hydrogen ions have exchangedplaces with ions in soil solution (soil water).

j

18

Soil WaterAfter aheavyrain, excesswaternormally drainsaway.

Waterleft after adayor so makesthe soilmoist,but not wet.The dynamicsof the active fraction occurin thismoisture,whichis not a free liquid, but acoatingaroundandbetweensoilparticles.

Moistureandtexturedeterminesoil strengthor consistency.Up to apoint, sandysoil becomesfirmer as watercontentin-creases.The waterfills the emptyporespacesandactsasaweakadhesivebetweenthe particles.A clay soil becomessofteraswater is addedbecausewaterinterfereswith the attractiveforcesbetweenthe clay solids.

The balancebetweenparticlesizeandwatercontentis criti-cal both for engineeringandagriculturalusesof soil. An illustra-tion of this delicaterelationshipis found in theright combina-tion of waterandkaolin clay, acombinationboth plasticandcohesiveenoughfor molding into pottery.

Drainageconditionsareoften indicatedby soil color. Wheredrainageis poor andthe soil is saturatedfor part of theyear(usually in spring),patchesof grayandorangediscolorations,calledmottles,appear.Their presenceanddepthmayrevealshal-low bedrock,thepresenceof a fragipan,or soil containingtoomuchclay.

Soil Drainage Classes

Figure 12. Relationship of drainage conditions to landscape position. Vegetation also indicatesdrainage conditions.

moderatelywell-drained

somewhatpoorly-drained

19

Drainageis often relatedto landscapeposition (seeFig. 12).Whereastheuplandandupperslopesareusuallywell drained,the low spotsarepoorly drained.Drainageis an importantfactorin land-usedecisions.Buildingson poorly drainedsitesarelikelyto havewetbasements,andsepticeffluentcannotdrainaway.

Soil pHA soil pH of 6.5 is optimal for mostcrops.Acid soilsrequire

liming to raisethe pH for goodcropproduction.Pennsylvaniasoils usuallyhavealower, or moreacidic, pH becausetheabun-dantrainfall leachesout alkalineions.Acrossthis continent,an-nualaveragerainfall decreasesfrom eastto west.Forexample,45 inchesof rain fall in Pennsylvania,and 10 inchesfall in Colo-rado.As aresult, soils rangefrom acid in the eastto neutralinthe midwestto alkalinein the westernstates(Fig. 13).

The effect of rainfall on soilpH is agoodexampleof howsoil-forming factorssuchasclimate, time, parentmaterials,vege-tation, andtopographyhavecreatedPennsylvaniasoils.Thesefactorsimposelimitations on landuse,but our understandingandimaginationareultimatelythe limiting factorsin theappro-priate andproductivedevelopmentof the landscape.

Figure 13. Diagram showing relationship of rainfall, vegetation, soil profile, and soil pH acrossthe United States.

Colorado (100th meridian) Pennsylvania10” rainfall 20” rainfall 45” rainfall

(wheat belt) (corn belt)

desert short tallshrubs grasses

alkaline soilspH>7

neutral soils acid soilspH<7

20

CLASSIFYING SOILS

Soil SeriesSoils havebeenclassifiedinto orders,suborders,great

groups,subgroups,andfamilies. Pedologicalage,temperatureandwaterregimes,andspecialfeaturessuchasfragipans,aresomeof the characteristicson which the systemis based.

A local soil hasacombinationof traitsuniqueto it, suchasparentmaterial,texture,drainagecharacteristics,horizonse-quence,andlandscapeposition. A given soil is likely to be foundover alimited geographicregionwhereverthe samebedrockandlandscapepositionarefound. it is ordinarily associatedwithotherlocal soils on associatedbedrockand landscapepositions.Suchan individual soil hasits own name(e.g.,Duffield, Volusia,or Conotton)andis calledasoil series (seeFig. 14).

County Soil SurveysThe Soil ConservationServiceof the U.S. Departmentof

Agriculture surveysandmapsthesoils of the United States,andpublishessurveyreports.Soil surveyscontainvaluabledataaboutlocal soils,including maps,yield potentialsfor eachsoil se-ries, limitationsfor development,anddetailedsoil-identifyingfeatures.Surveysfor mostcountiesin Pennsylvaniahavebeencompletedandareavailable.You cangetoneby requestingitfrom your countyagent,your representativein Congress,oryour local office of the Soil ConservationService.Soil surveysforeverycountyin Pennsylvaniawill be availableby 1989.

A bulletinwith detailedtabularinformationfor the soils ofPennsylvaniacanbe orderedfrom: AgronomyExtension,106Agricultural AdministrationBuilding, The PennsylvaniaStateUniversity, University Park,PA 16802.Ask for SoilsofPennsyl-vania— TheirExtent,Classification,Characteristics,and Uses.

21

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] GLOSSARY 23

active fraction — componentof the soil havingan ion exchangecapacity,specificallyclayandor-ganicmatter

adsorb — collect andadhererelatively looselyon a surface

aeolian — wind borne

alluvium — river-bornedepositof rock andfine particles

bedrock — solid rock mantle underlyingsoil or transportedrock material

calcareous — soil or rock materialwith high calciumcarbonatecontent

clay — a) particlesize lessthan0.002mmb) soil containingmorethan45 percentclay, lessthan40 percentsilt, andless than45

percentsand

colluvium — adepositof rock fragmentsandsoil materialaccumulatedat thebaseof steepslopesas aresultof gravitationalaction

exchange capacity — interchangebetweenan ion in solutionandanotherion on the surfaceofanysurface-activematerialsuchasaclay or organiccolloid

fragipans — naturalsubsurfacelayerswith highbulk densityrelativeto the soil above,seeminglycementedwhendry, somewhatbrittle whenmoist; low in organicmatter,mottled,slowly orvery slowly permeableto waterandoften showingbleachedcracksforming polygons

glacial till — unstratifiedglacial drift depositeddirectly by the ice andconsistingof clay, sand,gravel, andbouldersintermingledin any proportion

horizons (soil horizons) — layers of soil or soil material approximatelyparallel to the surface,occurring naturally,anddistinguishablefrom adjacenthorizonsby differencesin color, tex-ture, quantityof organicmatter,etc. Simplifiedhorizondesignationsare:0 = the surfacelit-ter, A = topsoil,root zone,B = subsoil,containingmoreclay andlessorganicmatterthanA,C = parentmaterial,andR = bedrock

igneous rook — rock formedfrom the coolingandsolidification of moltenrock, andthat hasnotbeenchangedappreciablysinceits formation

bess — materialtransportedanddepositedby wind andconsistingprimarily of silt-sizedparticles

metamorphic rock — rock derivedfrom pre-existingrocksbut differing from them in physical,chemical,andmineralogicalpropertiesasa resultof naturalgeologicprocesses,principallyheatandpressure,originatingwithin the earth.The pre-existingrock mayhavebeenigneous,sedimentary,or anotherform of metamorphicrock

mine spoil — shatteredrock materialremovedto makeway for mining operationsandreplacedatthe site whenthemine is abandoned

24

mottles — spotsor blotchesof different color or shadesof color interspersedwith thedominantcolor

organic matter — anyorganisms,alive or dead,andanymaterialderivedtherefrom

outwash — water-sortedglacial materialdepositedby glacialmeltwater

peds — unitsof soil structureformedby naturalprocesses

pedologic age — maturity of asoil in termsof its developmentalcharacteristicsratherthanitschronologicalage

parent material — unconsolidatedand moreor lesschemicallyweatheredmineralor organicmat-ter from which the soil developed

residual soil (residuum) — unconsolidatedandpartly weatheredmineralmaterialsaccumulatedby disintegrationof rock in place

sand — a) particlesizebetween2 mm and0.05mmb) soil containingmorethan84 percentsand

sedimentary rock — rock formedfrom materialsdepositedfrom suspensionor precipitatedfromsolution, usuallymoreor lessconsolidated

silt — a) particlesizebetween0.05 mm and 0.002mmb) soil containingmorethan80 percentsilt andlessthan 12 percentclay

soil pH — alsosoil reaction— the negativelogarithmof thehydrogenion activity of asoil. The de-greeof acidity (or alkalinity) of asoil asdeterminedby asuitableindicator ataspecifiedmois-ture contentor soil waterratio, andexpressedin termsof thepH scale

soil series — the basicunit of soil classification,beingasubdivisionof afamily andconsistingofsoils which areessentiallyalike in all majorprofile characteristicsexceptthe textureof the Ahorizon

soil structure — combinationor arrangementof soil particlesinto largerunits, or peds

soil texture — relativeproportionsof varioussoil sizedparticlescharacterizing-asoil, as describedby the classesof soil textureshownon the texturaltriangle

strip mining —mining techniqueinvolving removalof all rock, soil, andplant materialabovethedesireddeposit.Whenthe mine is abandoned,thedisturbedmaterial is replacedin the pits,leavingthe surfacewithout soilor plant cover.

Land Use in Pennsylvania(MA = million acres)

*

N,

N

N.

Forest/

(at least 40% stocked with trees)N

55.3%

(15.9 MA) ~--‘~Open Forested La d(less than 40% stocked with trees)7.3% (2.1 MA)

ermanent Pasture~“ 3.6% (1 MA) ~

-.,,,..-.—

/ ~ Harvested CroplandOther 13.4%

Abandoned> (3.9 MA)(cities, farmsteads, Cropland ~roads, etc.)

N

K.. 12% (idle for more~ MA) than 10 years)

8.4%(2~4~MA)

From “Open andForestedUplandRangefor BeefProduction”,FinalResearchReportfor the PennsylvaniaDepartmentof Agriculture,projectno. 2128,Collegeof Agriculture,The PennsylvaniaStateUniversity, 1981.

PENNSTATECollegeof AgriculturalSciencesCooperativeExtension

Wheretradenamesappear,nodiscriminationis intended,andnoendorsementby theCooperativeExtensionServiceis implied.

Issuedin furtheranceof CooperativeExtensionWork, Acts ofCongressMay 8andJune30, 1914,in cooperationwith theU.S.Departmentof AgricultureandthePennsylvaniaLegislature. L.F.Hood, Directorof CooperativeExtension,ThePennsylvaniaStateUniversity.

The PennsylvaniaStateUniversityis committedto thepolicy thatallpersonsshallhaveequalaccessto programs,facilities, admission,andemploymentwithout regardto personalcharacteristicsnotrelatedto ability, performance,orqualificationsasdetenninedbyUniversitypolicy orby stateor federalauthorities.ThePennsylvaniaStateUniversitydoesnot discriminateagainstanypersonbecauseofage,ancestry,color,disabilityor handicap,nationalorigin,race,religiouscreed,sex,sexualorientation,orveteranstatus.Directallaffirmativeactioninquiriesto theAftinnativeActionOffice, ThePennsylvaniaStateUniversity,201Willard Building,UniversityPark,PA 16802-2801.

R1M192 U.Ed. 83-179