Soil Science Curriculum · • Roll of monofilament string (fishing line) • Small plastic animals...
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Content 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 Dakota Natural Resources Conservation Service South Dakota FFA July 2019 Approximately 60 minutes Objectives By the end of the lesson, students will know or be able to: • Define soil aggregate, mycorrhizal fungi, hyphae, plant root exudates, glycoprotein • Explain why a soil aggregate is important to soil health • Demonstrate and/or measure soil aggregate stability • Describe management practices that sustain or improve aggregate stability Materials • 3-inch foam balls • 1-inch or smaller foam balls • Post-it notes or 3x5 index cards • Slender wooden dowels, toothpicks and/or coffee stirrers • String licorice (different colors) • Silly string • Roll of monofilament string (fishing line) • Small plastic animals (farm animal set & jungle animal set - optional) • Baby or foot powder • Sink strainers (at least 2) • Disposable cereal bowls • Water (about a quart) • Flat plastic lid or cutting board Preparatory Work • Print all necessary copies • Secure permission to collect soil from the landowner(s) • Collect surface soil from a well-managed cropland field that is not tilled, and from one that is conventionally tilled, about 2 cups of each • Set up a table with a disposable tablecloth or paper • Provide sheet with definitions Soil Aggregates: Role in soil health and measuring stability
Transcript of Soil Science Curriculum · • Roll of monofilament string (fishing line) • Small plastic animals...
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.
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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.
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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
