Soil Science CurriculumContent and lab derived from the USDA-NRCS Guides for Educators. Go to https://www.sdsoilhealthcoalition.org/soil-health-buckets/ for the Guides and additional pictures and diagrams.

South DakotaNatural Resources Conservation Service South Dakota FFA

July 2019

Approximately 60 minutes

ObjectivesBy the end of the lesson, students will know or be able to:

•Definesoilaggregate,mycorrhizalfungi,hyphae,plantrootexudates,glycoprotein•Explainwhyasoilaggregateisimportanttosoilhealth•Demonstrateand/ormeasuresoilaggregatestability•Describemanagementpracticesthatsustainorimproveaggregatestability

Materials•3-inchfoamballs•1-inchorsmallerfoamballs•Post-itnotesor3x5indexcards•Slenderwoodendowels,toothpicksand/orcoffeestirrers•Stringlicorice(differentcolors)•Sillystring•Rollofmonofilamentstring(fishingline)•Smallplasticanimals(farmanimalset&jungleanimalset-optional)•Babyorfootpowder•Sinkstrainers(atleast2)•Disposablecerealbowls•Water(aboutaquart)•Flatplasticlidorcuttingboard

Preparatory Work•Printallnecessarycopies•Securepermissiontocollectsoilfromthelandowner(s)•Collectsurfacesoilfromawell-managedcroplandfieldthatisnottilled,andfromonethatisconventionallytilled,about2cupsofeach•Setupatablewithadisposabletableclothorpaper•Providesheetwithdefinitions

Soil Aggregates: Role in soil health and measuring stability

Soil Aggregates: Role in soil health and measuring stability

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Enroll the Participants (Approximately 30 minutes)Handoutabout10-15,3-4-inch-longdowels/toothpicks/stirrers,onesetperstudent;aboutfourtofive3-inchfoamballs,aboutseventononeofthesmallerfoamballs,andtwototheeindexcards/Post-itnotesroughlytornintofourpieces.Haveastudentwithadowelinsertitintothefoamballfromanotherstudent,andplaceonthetablecloth.Haveastudentwithanindexcardpieceplaceitonthedowel(youmayhavetopiercethepaperwithasmallholetogetitstartedonthedowel).Addanotherfoamballto

the other end of the dowel and insert another dowel to one of thefoamballsthatisalreadyattachedtotheotherdowel.Itmayhelptohaveglueonhandandapplytotheendsofthesticksasyoubuildtheaggregate.Theobjectistobuildasoilaggregate“lattice”,somethinglikewhatisshowninFigure1.

Asyouarebuildingthesoilaggregate,explainthatthelargefoamballsrepresentsandparticles,thesmallerfoamballsrepresentsiltparticles,andthePost-itnote/indexcardpiecesrepresentclayparticles.Thedowelsrepresentweakbondsbetweenthesoilparticlesthatwouldnormallybreakveryeasilywhenthesoilgetswet.

Figure 1

Next,handoutafewoftwocolorsofthestringlicorice,andhavethestudentslaythemon/inthelattice.Explainthatonecolorrepresentsmycorrhizalfungi,andtheothercolorrepresentsplantroots.

Thengiveacanofthesillystringtoastudent(ortwocans,onetoeachoftwostudents),andhavethemspraysomesillystringonthesoilaggregate.sillystringrepresentsglycoproteinsthathelpgluethesoilaggregatetogether.

(Optional)Takesomeofthefarmanimalsandjungleanimals,andhavethestudentsplacethemon/inthesoilaggregate.Youcanaskanadditionalquestionaboutwhattheanimalsrepresent.Theyrepresentsoilmicrobesthatmaketheaggregatetheirhome(habitat).Somesoilmicrobesarepredators,likethelionortiger,andsomeareprey,likethesheep.Youcanusepapercut-outanimalsifyoudon’thavetheplasticsonesavailable.

Takeoneendofthemonofilamentstringandtieitofftoa“plantroot”orjustattachittothesoilaggregate,thenrollthestringoutacrossthefloor.Thisrepresentsmycorrhizalfungihypae,whicharebasicallyliketherootsofthefungi.Theyconnecttotheplantrootsandgreatlyincreasetheareaofthesoilfromwhichtheplantrootscangetwaterandnutrients.YoucaninitiallywrapthestringaroundyourarmandexplainthatthehyphaearelikeanIVthatyougetwhenyougointosurgery,andactsthesameway,supplyingfluidsandnutrients/medicinesbetweentheplantsandfungi.

Youcanalsoattachadollarbilltooneofthefoamballs,andwhenyoudestroytheaggregate(below),youcanseethemoney(fertilizer,organicmatter,etc.)erodingaway.

Soil Aggregates: Role in soil health and measuring stability

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Label the Information (Approximately 3 minutes)Reviewandidentifyeachofthesuppliesthatwillbeusedduringthelabactivity.

• Sink strainers• Disposablecerealbowls• Water• Twosoilsamples,onefromno-tillandonefromconventionaltill

Provide the Experience (Approximately 3 minutes)

Reviewthelaboratoryscenariowithstudents.

Alocalfarmerhasbeenfarmingwitharotationofcorn,soybeans,wheat,andsunflowers,andhasbeenpracticingno-tillfor14years.Asoftenaspossible,covercropsareincorporatedintotherotation.Thefarmerrecentlydecidedtorentsomeadjacentlandbutfoundthatthefieldcannotbeenteredintoasearlyasthelandcurrentlybeingfarmed.Waterisoftenpondingintherentedfieldafterarain,anderosionishappening,evenformingsmallgulliesinsomeplaces.

Usethefollowingquestionstofacilitateaconversationwiththestudents:

Whatdoesthesillystringrepresent?Answer:Plantrootsgiveoffexudates,whicharebasicallysugars–sugarissticky,andtheseactlikegluesthathelpholdtheaggregatetogether.Mycorrhizalfungigiveoffglomalin,whichisanother“glue”thathelpsholdtheaggregatetogether.Earthwormsareslimy,andthisslimeisanotherglue–allthesegluesmakethesoilaggregateverystrongandstable.

Whatdoyouthinkwouldhappentotheaggregateifthesoilisdisturbed(tilled)?Answer:Afteryougetsomeanswersfromthestudents,youcandemonstratewhatwillhappenbysmashingthesoilaggregatewithyourhand,andsaythisisadiscorplow.

Whatwillhappentotheindividualsoilparticleswithdisturbance/tillage?Answer:Erosion–youcandemonstratebytakingoneofthefoamballsandrollingitacrossthefloor,andsay“thisislikewindorwatererosion”.Also,thefirstthingtoleaveduringanerosioneventislightorganicmatterparticlesintheairorwater.Youcandemonstratethiswiththebaby/footpowder,bysqueezingthebottleupintotheair–itislikethecarbondioxideleavingwithdisturbancebutyoucan’tseecarbondioxide.

Whathappenstothemycorrhizalfungiandtheirhyphaewithdisturbance/tillage?Answer:Youcandemonstratetheanswerbyshowingthatthehyphaearedisconnectednowfromtheplantroot,andyoucanpulloutalicoricestringandbreakitintopieces.

Thereareotheranalogiesyoucandrawfromthisdemonstration,useyourimagination.

Soil Aggregates: Role in soil health and measuring stability

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Demonstrate the Relevance (Approximately 25 minutes)Steps:1.Fillonesinkstrainerleveltothetopwithsoilfromtheno-tillfield.Asyouarefillingthesinkstrainer,gently

breakapartthesoilintothenaturallyoccurringaggregates.Donotoverlyworkthesoilsampleintofineparticlesorcrushtheaggregates.

2.Repeatstep1withtheconventionaltilledsoilintotheothersinkstrainer.3.Fillthedisposablecerealbowlswithwatertothebrim.4.Placeeachsoilsampleinthesinkstrainersgentlyintothebowlswiththewater.Ensurethattheentire

soilsampleisinfullcontactwiththewater.Letthesamplessoakforapproximately30-60seconds.5.Removeeachsoilsamplefromthebowlsandturnthesampleoverontotheflatplasticlidorplasticcuttingboardsothattheentiresampleremainsonthelid/board.Placethesamplesseveralinchesapart.

6.Raiseonesideoftheboard/lidslightlysothewaterstartstomoveawayfromthesamplesandobservethedifferences.

Thisisonemethodtotestforsoilaggregatestabilityandisalsoknownastheslumptest.Thesamplewithgoodaggregatestabilitywill“standup”higherandtheindividualsoilaggregateswillstillbevisible.Thesamplewithpooraggregatestabilitywilloozedowntheboard/lidandwillbe“soupy”.Oneanalogythatworksisthegoodaggregatestabilitysamplewilllooklikeachocolatebrownie,andthepooraggregatestabilitysamplewilllooklikechocolatepudding.Oftentimesthegoodsamplewillbedarkerthanthepoorersample,andtheywilloftensmelldifferent(thegoodsamplewillhaveanearthysmell,orthesmellafterarain,whilethesmellofthepoorersamplewillbevariable).Figure2showsanexampleoftheresultsofthistest.

Glycoprotein:astickysubstanceproducedabundantlybyhyphaeandsporesofmycorrhizalfungiinsoils–itisanexudateofthefungi;actsasaglueholdingsoilparticlestogetherintoaggregates.

Hyphae:long,branchingfilamentousstructuresofthemycorrhizalfungithattransportwaterandnutrientsfromthesoiltothemainfruitingbodyofthefungiandtotheplantrootswithwhichtheyareassociated–similartotherootsofaplant.

Mycorrhizal fungi:thesearefungithatformasymbioticrelationshipwithplants,andattachtoorintotheplantrootandprovidewaterandnutrientstotheplant–theplantinturnsuppliesfoodtothefungi;theseassociationsgreatlyincreasetheextensionoftherootsintothesoilprofileareainthesoilwhichisavailabletotheplant.

Plant root exudates:thesearepolysaccharidesorbasicallysugarsproducedbyplantrootsthatareusedbymanysoilorganismsforfood,andhelpbuildsoilaggregates.

Soil aggregate:soilparticlesheldtogetherbyorganicmatterandrelatedsubstances.Wellaggregatedsoilshavehigherinfiltrationratesandarelesspronetoerosion.Aggregatesalsoprovidehabitatforsoilmicroorganisms.

Definition

Figure 2