TheCarbonFarmingKnowledgeProjectinvolvesaseriesofworkshopstoincreasetheunderstandingof30
independentagriculturaladvisersinsouth-eastAustraliaonreducinggreenhousegasemissions,carboninfarming
systemsandtheEmissionsReductionFund–wherefarmerscanearncreditsforstoringcarbonorreducinggreenhouse
gasemissionsontheirproperties.Theprojecthelpsadvisorspreparetheirclientsforpotentialenvironmental,
economicandsocialbenefitsoffuturecarbonmanagementpolicy.
Session4:SoilCarbon
SummaryofMarch2106advisersworkshoppresentationbyLynneMacDonaldandCliveKirkby,CSIROandBrian
Murphy,NSWOfficeofEnvironmentandHeritage.
ERFmethods
TheEmissionsReductionFund(ERF)allowsfarmerstosell
AustralianCarbonCreditUnitsinreturnforenhancing
carboninagriculturalsoil.Twomethodsareapproved,one
basedondirectmeasurementandonebasedonmodelling
byaqualifiedperson.
Forthedirectmeasurementmethod,itisimportantto
considerthespatialvariabilityacrosstheprojectareato
defineanumberofcarbonestimationareas(CEA).CEAs
shouldtakeintoaccounthowvariationinland-use,
landformandsoiltypemightinfluencesoilcarboncontent.
EachCEAshouldbeashomogenousaspossibletominimise
theerroraroundthemeanandmakeiteasiertomeasurea Figure1:Samplingdepthsformethodsthateffectsoilbulkdensity.
(source:JeffBaldock)
statisticalchangeincarboncontent.
Fordirectmeasurement,acarefulsamplingregimeshouldbeputinplaceforaccurateresults,takingintoaccountthe
numberofrequiredsamplersforeachCEA,sampledepthandsamplepreparationandanalysis.Forexample,ifpractices
areappliedthataffectthesoilbulkdensity,adifferentdepthofcoreshouldbesampledtorepresentanequivalentsoil
mass(Figure1).
Soilorganiccarbonfractions
Itisusefultoconsidersoilorganiccarbonasdifferentcomponents/fractionsthathavedifferentturnovertimes;
1. Particulate(POC):relativelyfreshwithdefinedstructure,decomposesannually.
2. Humic(HOC):noidentifiablestructure,associatedwithminerals,andrelativelystablewithslower
decomposition.
3. Resistant(ROC):highlystablewithturnovertimesgreaterthan100years.
Therelativeproportionsofthesetypesofcarbonaffecthowstableanysequesteredcarboniswithinthesoil.TheCSIRO
areinvestigatingcosteffectivemethodsofmeasuringthedifferentfractions,withthepossiblefutureaimofconsidering
POC,HOCandROCseparatelyintheERF.
Mid-infraredspectroscopyisrapidandcosteffective,butisreliantonacalibrationdataset.TheCSIROcalibration
datasethasbeendevelopedfromanationaldatabasecollectedduringtheSoilCarbonResearchProgram(SCaRP)which
sampledmorethan20,000samplesfrom4,500sites.Themethodisstillindevelopment,performingwellonmostsoils,
butrequiringbettercalibrationforcertainsoiltypes(suchascalcareoussoils).
Soilorganicmatter
Soilorganicmatter(SOM)istheactivematerialinthesoilwithsoilorganiccarbon(SOC)beingonecomponentofSOM.
SOMalsocomprisesofnitrogen,phosphorusandsulphuringenerallyconsistentratiosof1000C:90N:19P:14Sand
alsoincludesoxygenandhydrogen.Commonly,onlytheSOCcomponentinSOMismeasuredandreported.SOMand
SOCarelinkedwithSOMbeingapproximately1.72xSOC.
SOMhasseveralkeypositiveeffectsonsoilphysicalpropertiesandfertility,including:
• Improvedplantavailablewatercapacity,
• Lowerbulkdensity,
• Lowersoilstrengthandcompacteddensity,
• Improvedcationexchangecapacity,
• Increasedbufferingcapacitytoacidification,and
• Sourceofnutrientsforplantgrowth.
Cropresiduebreakdown
Whencropresiduesbreakdown,theyeitherassimilateordisassimilate.Disassimilationisthebreakingdownof
complexsubstancesintosimpleroneswiththereleaseofenergyandCO2,whileassimilationisthebuildingupof
complexorganicmoleculesororganismsandstorageofcarbon
(forexamplemicroorganismsinthesoil)fromsimplerprecursors
(suchasthenutrientsincropresidues).
Therelativedegreeoftheseprocessesdependsontheratiosof
specificelementsinthecropresidues.Soilorganicmatterconsists
oftheseelementsinconsistentratios(1000C,90N,19Pand14S),
soifanyoftheelementsarelimiting(e.g.iftherearelessthan19
Patomsforevery1000Catoms),therewillbeleftovercarbon
whichwilldisassimilateandresultingreenhousegasemissions.
Whentryingtostorecarbon,ifothernutrientsarelimiting,then
Figure2:TrialsinHamiltonshowedthataddingnutrients
increasingthesupplyofthesenutrientcanincreasecarbon
(red)improvescarbonstoragefromstrawasSOC
conversiontoSOM(Figure2).
comparedtostrawalone(green).
Methodstoimprovesoilcarbon
Thebestprocesstoimprovesoilcarboninvolvesthefollowingstrategies:
§ Maximisebiomassproduction,
§ Maximisereturnofthebiomasstothesoil,
§ Improvethequalityofbiomassreturnedtothesoil,
§ Minimisedisturbance,and
§ Improvesoilfertility(nutrition).
ThemaximumlevelofSOM/SOCthatcanbereacheddependsonacombinationofclimateandsoiltype.
Usefulresources
• Methodinformation:Sequesteringcarboninsoilsingrazingsystems.http://www.environment.gov.au/climatechange/emissions-reduction-fund/methods/sequestering-carbon-in-soils
• Managingsoilorganicmatter:http://www.grdc.com.au/GRDC-Guide-ManagingSoilOrganicMatter
Moreinformation:LynneMacdonald,(08)82738111,[email protected];CliveKirkby,0418253003,
[email protected];BrianMurphy,0412261230,[email protected].