Royal Swedish Academy of SciencesAmounts, Dynamics and Sequestering of Carbon in Tropical and Subtropical SoilsAuthor(s): ...
WimG. Sombroek, Freddy0. Nachtergaele and Axel HebelAmounts, Dynamics and Sequesterinof Carbon in Tropical and Subtropical...
Unesco Soil Mapof the World(2, 3) was used to estimatetheextent of each soil unitin the mappingunits.A studyof about400 so...
tentsthatvarybetween 13 kg m-2,for the veryclayey soils, andtotal8 kg m-2 for the sandy or moderatelydeep soils, with theu...
............................... ................. ............................... .. ......M---M g :wAN......................
............. .... .... .. ..................... .........xom: X yx---------- ---- ..............m m d--- ----------.........
dayvegetativecover;thatof deeperlayersis largelybeyondtheinfluenceof the vegetation.Therearemanystudies(42-44) on thesoil ...
Some examples of thevariation in amount and rMvertical distribution oforganic matter in tropicaland subtropical soils. Fl1...
andcropresidues,andespecially througha morevigorousrootgrowth.Nutrientsmaycome in shortsupplyatsuchhigherratesof biomasspr...
3?:.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.4~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1rDiffe...
References and Notes1. Bouwman,A.F. (ed.). 1990.Soils andtheGreenhouseEffect.Proceedingsof theInter-nationalConferenceon S...
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Amounts, dynamics and sequestering of carbon in tropical and subtropical soils

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Amounts, dynamics and sequestering of carbon in tropical and subtropical soils

  1. 1. Royal Swedish Academy of SciencesAmounts, Dynamics and Sequestering of Carbon in Tropical and Subtropical SoilsAuthor(s): Wim G. Sombroek, Freddy O. Nachtergaele, Axel HebelSource: Ambio, Vol. 22, No. 7, The Royal Colloquium (Nov., 1993), pp. 417-426Published by: Springer on behalf of Royal Swedish Academy of SciencesStable URL: http://www.jstor.org/stable/4314120 .Accessed: 15/06/2011 23:43Your use of the JSTOR archive indicates your acceptance of JSTORs Terms and Conditions of Use, available at .http://www.jstor.org/page/info/about/policies/terms.jsp. JSTORs Terms and Conditions of Use provides, in part, that unlessyou have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and youmay use content in the JSTOR archive only for your personal, non-commercial use.Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at .http://www.jstor.org/action/showPublisher?publisherCode=springer. .Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printedpage of such transmission.JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range ofcontent in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new formsof scholarship. For more information about JSTOR, please contact support@jstor.org.Springer and Royal Swedish Academy of Sciences are collaborating with JSTOR to digitize, preserve andextend access to Ambio.http://www.jstor.org
  2. 2. WimG. Sombroek, Freddy0. Nachtergaele and Axel HebelAmounts, Dynamics and Sequesterinof Carbon in Tropical and SubtropicalSoilsL] < 3.6 3.6-7.5 7.6-15.0 15.1-35.0 in >35.0Figure 1. Soil organic carbon pool in kg C m-2up to I m depth.The organiccarbon pool inthe upper 1 m of the worldssoilscontains 1220 Gtorganic carbon, 1.5 times the total forthestanding biomass. In the widespread deep soils in thetropicsthe carbon stored below 1 m may add about 50 GtC.Thecontributionsofcharcoal, roots and soil fauna should beadded to these totals. The much less dynamic carbonate-carbon pool amounts to 720 Gt C. Changes in land use,particularlybyclearing of forests, reduce organic carbon by20 to 50% inthe upper soil layers, but littleindeeper layers.On the other hand, there are indications that a human-inducedenrichmentofsoil organic mattercan be maintainedover centuries. Research on the causative soil processesshould be supported, because an improved understandingof this phenomenon might lead to better managementstrategies and sound programs to stimulate organic carbonstorage and fertilitylevels in tropical and subtropical soils.Recent research data on the C02 fertilizationeffect and theassociated antitranspirationeffect due to an increase ofC02inthe atmosphere indicate that a positive influence on soilorganic carbon levels can be expected.INTRODUCTIONSoil carbonis an importantpartof the terrestrialcarbonpool.Itssize hasbeenestimatedbetween700 and3000 Gt C (1 Gt =i015 g C) as organiccarbonand 780 to 930 Gt C as calciumcarbonate.Othercarbonpoolsaretheoceans(38 000 GtC),fossilcarbonreserves(6000 GtC), CO2in theatmosphere(720 GtC),andbiomassof plants(560 to 835 GtC) (1).Thebeneficialeffects for agriculturalproductionof soil car-bon in its organicform(freshorganicmatter,humus)arewell-known: source of nutrientsgradually becoming available toplants;increasedaggregatestability;increasedmoisturestoragecapacityandincreasedmicrobialdiversityandactivity.Higherpercentagesgenerallyimprovethe chemical, physical andbio-logical statusof the soil. In spite of this, soundorganic-mattermanagementpracticesremaintheexceptionratherthantherule,particularlyin tropicaland subtropicalenvironments.More re-cently, soil organic matterhas received attentionin scientificcircles for its role in the sequestrationof the greenhouse gasCO2,andtheemissionof C02, CH4andN20.Theobjectivesof thisarticleareto refinecurrentestimatesoftheorganicsoil carbonpools by usingtherecentlycorrectedanddigitizedFAO/UnescoSoil Mapof the World(2), to emphasizethe role of sound organic-mattermanagement,to explore thepossibilitiesfor soil-carbonsequestering,andto drawattentionto possible effects of global climaticchangeon the soil-carbonpool.CARBONPOOLSINTHEWORLDAverage Soil Carbon Contents Based on the FAO/UnescoSoil Map of the WorldOrganic CarbonEstimatesofthestorageoforganiccarboninsoilsonaglobalscalevarybetween700 and3000 GtC(1, 3-1 1).Thislargevariationisexplainedby thedifferencein basemapsselected(FAO/UnescoSoilMapof TheWorld,HoldridgeLifeZones,VegetationMaps)andthe variousassumptionsmadeaboutsoil attributesdirectlyrelatedto thetotalcontentof organic-matterpersoil typesuchasorganicmattercontentanddistributionin the soil profile,bulkdensityof soil layers,andaveragesoil depths.In the present approach,the correctedand digitized FAO/AMBIOVOL.22 NO. 7, NOV. 1993 417
  3. 3. Unesco Soil Mapof the World(2, 3) was used to estimatetheextent of each soil unitin the mappingunits.A studyof about400 soil profiles groupedper FAO soil unitgave an indicationof the rangeandmedianvalues for organic-carboncontentandbulkdensityfor each soil unit(Table 1). These medianfigureswere used to calculatethe total soil organic-carboncontentforeachmappingunitandwerecorrectedforanassumedsoil depthas indicatedby specific soil phases or soil names on the map:Lithosols(10 cm), RendzinasandRankers(30 cm), petrocalcic,petrogypsic,duripanand petroferricphases (half 75 cm deep,half 30 cm deep), lithic phases (30 cm deep). Othersoils wereconsidered100cm deep.Litterlayerswerenotconsideredinthecalculation,butHistosols wereincluded.Theapplicationof thismethodologyyieldeda globalestimateof about1220Gtorganiccarbon.Thisfigureis somewhatlowerthanmost recently publishedestimates (1400-1700 Gt C) butvery close to the one obtainedby using soil informationandHoldridgelife zones (1270 Gt C; 13). The resultsfor the worldarepresentedin Figures1and2. Individualcountryresultswerealso estimatedandareavailablefromthe authorsuponrequest.Theyvaryfromabout2.5 kg m-2forcountriesin aridareas(e.g.Libya,Mauritania)to about25 kg m-2in FinlandandSweden.Itshouldbe notedthatourestimateis significantlylowerthantheone resultingfroma recentstudyby a USA teamof soil sci-entists (14). They arrivedat 1576 Gt of organiccarbonin theworldssoils to I-m depth.The difference is due to the use ofanothersoils database, viz. a world mapof majorsoil regionspreparedby the USDA Soil ConservationService, still in press(15). It uses the USDA Soil Taxonomysystemof classification(16) ratherthanthe FAO-Unesco one, and dataof 1000 indi-vidualsoil profilesof 45, mainlytropicalcountries,in additionto 15000 profiles of continentalUSA. The divergency of thefiguresshouldbe due to differencesin the criteriafor soil clas-sification,mappingscales, degree of representativenessof soilprofilesused anddegreeof incorporationof new soil inventoryinformation.The discrepancymay be solved in the nearfutureby contactsbetweenFAO, USDA andISRIC(the InternationalSoil Reference and InformationCentre of Wageningen, TheNetherlands),underthe aegis of the IGBPStandingCommitteeon DataandInformationSystems. FAO andISRICarealreadyengagedin updatingof its georeferencedsoil databaseforLatinAmerica;thedataon thatregionfortheexisting 1:5Mapof thatregionare35-yearold, andin themeantimemuchimprovedin-formationhas become availablethroughthe efforts of nationalsoils resources institutionsin most of the regions, especiallyconcerningthe Amazonregion.Organic Soil Carbon Distribution with DepthCalculationsof theorganiccarbonpool intheworldssoils havetraditionallyprovided results to 1 m depth. This facilitatescomparisonof resultsbuthasthedisadvantagethatnotthewholesoil-carbonpoolistakenintoconsideration.Thereislittlescientificjustificationtoconsideronlythefirst 1mof thesoil profileinthecalculation,becausemanysoilsaredeeperandcontainconsiderableamountsof carbon(organicandinorganic)inthesubsoil.Indeed,althoughorganic-carboncontentsgenerallydecreasewithdepthinsoils (withtheexceptionof somealluvialandorganicsoils),thecontributionof carbonin the deep subsoil-below 1 m-to thetotalcarbonpool is importantparticularlyin soils of the tropicsandsubtropicswhicharegenerallydeepto verydeep.It was pointedout (17, 18) thatthe age of soil organiccarbonincreases with depth. This indicates that in the tropical soilsdeeper layers contain an appreciableamount of soil organicmatteras stable,relativelyinerthumuswhich would not be af-fected by a changein landuse. Detailedanalysesof the carbonprofiles in these soils supportthatfinding. Indeed,the organiccarboncontent in the uppermeter of the majortropical soilsVertisols, Andosols, Ferralsols,Arenosols, Acrisols and Luvi-sols is 53, 66, 69, 77, 80 and 82%,respectively,of the amountcontainedup to 2 m depth(Table2). This implies thatthe totalglobalamountof soil carbonis largerthanthe 1220Gtestimatedfortheupper1m andmaybe as muchas 1270 GtC, takingintoaccounttheproportionof these deeptropicalsoils.A calculationon about30 soil profiles of the Amazon areasampledduringFAO forest inventoriesin the early 1960s andsome morerecentsurveysshow thatmorethan90%of the up-land (terrafirme) soils, Ferralsolsand FerricAcrisols mainly,with samplingdown to 200 cm or morehave total carboncon-.. .. ... ... . ..................................... .................... . . ........ . ... . . ..................... . ................. ....................... ................................................. ............ .... .. .. ... ... ... ................. .. ... . ..... ..... ............................................ . .. ........ .......... .. .... .... .. . .... .. ..................................Up,. .... .... .... .... ... ....... ..... . ........ . . ....... .. ....... . . ...... . . .......... ... .......... ... . .. ................. ....................................... ........ ... ... ... ................. .. .... ... .. .. ............... II .. ................... ........ .... ... . ....... ....... .... ........ .................. .............................................. . . ............................... ...... ....... ............. ..... ... .... .... .................. ..... .. ....... .............. ......... . .. .......... .. . ... .......................................................................... 1-1.1-11.1-1...... .... ............................... ... ... . .. ... .......................... .S......... .... .... ... ....... ...... . . .13. . ........ . ........ .... ......... .aR............... .... .... ......... ............I...... .... 2-1::-44- . ................. ... .... ......... .... ............ .............. ................................................ . ......... ..................... gp. ........................ ............ .......... ..................................................... ....... .. ..................... .... ....... ..... ... ...... ............... ............ .... ....... ........... ............ .. .... .... .. .. .... ............. . .......... .... . ... . ....... ... .... ... ... ..... . ........... . . ....... . ....................................... .. .... . .. .... ... .... .... - - - - - -............................................... . ...... ....... .............................. . ........ ... ... ....... ................ .... . ... ..... ................ .. .......-..................................... ... ... ... ........ r%p - --- --- -------418
  4. 4. tentsthatvarybetween 13 kg m-2,for the veryclayey soils, andtotal8 kg m-2 for the sandy or moderatelydeep soils, with theupper25 cm accountingfor only one thirdof the amountsto 2m depth (43% of amountsto 1 m depth), unless the soils areshallow or imperfectly drained(19, 20). These data comparewell with recentcalculationson carboncontentof all recordedsoil profile analyses carriedout in the frameworkof the radarsupportednatural-resourcesurveysof the BrazilianAmazon inthe 1970s (21). A similarcalculationfor 53 profilesof Suleimiseries, a Vertisol occupying extensive areas of Sudan centralclayplain(22) showedthattotalcarboncontentswerestrikinglyuniform,withall horizonsto 1.5 m depthcontributingevenly tothe total pool of soil carbonand contents in deeper layers di-minishingby one third.The churningprocesses thatcharacter-ize these smectitic soils arelargelyresponsiblefor the homog-enizationof the organic-carbonprofile.Consequently,the con-tributionof the upper25 cm to the carbonpool is only about13%of the whole profile down to 2-m depth(26%of the totalto 1-mdepth).In Arenosolsthe soil textureis by definitioncoarse (sandorloamysand),andthese soils normallycontainverylittleorganiccarbon.However,dueto deeppercolationof rainwaterthiscar-boncontentremainsremarkablyuniformbelow the top 25 cm.If analyzedto 2 m depth,the topsoil contributionof Arenosolstothetotalcarbonpool is about40%of the total(halfof the to-talto 1m).A different picture emerges for non-ferralic Acrisols andLuvisols,which areextensive in the tropicsin savannaandsa-vanna-forestareas.In these soils, contributionof deep subsoilcarbonis less, andthebulkof thecarbonpool is concentratedinthetop25 cm.Note thatin Histosols the upperlayers are stronglyconsoli-datedduringcultivationby compactionand settling undertheinfluenceof gravity after drainage.Therefore,arbitrarydepthboundariesto express carboncontent do not make muchsense in these soils, and directestimationof carbonlost by ac-celeratedoxidationis essential,as well as the estimationof thetotalcarbonstock down to theunderlyingmineralsubstratum,regardlessof thedepthatwhichthisoccurs.Soil Organic Carbon VersusBiomass CarbonTheglobalbiomasscarbonpoolhasbeenestimatedat about835Gt C (23), althoughthis figureremainsdebateddue to the ge-neral lack of agreement ondefinitionsof vegetation typesandintheabsenceof anadequateglobal landcover and land usemap.On a global basis the soilcarbonpoolcomprisesabout1.5times the carbon stored in thevegetation.Matchingsoil groupswiththenormal(simplified) ecosystemtypes under which they occurleads to the following results(Table 3). Soils contain nearlyas muchcarbonas the vegeta-tion underrainforest,but con-siderably exceed the biomasscarbonin otherecosystems, byFigure 2. Percentages of land with different organic carbon classes forAfrica, America and Asia in kg C m-2up to 1 m depth._~~~~~~~~~~~~~~~~~~~~~~~~~~~.... ..._ ......... .........__I,. .. . ____,l. . . . . . . . . _ . . . . . . ., . . .. . . ... ... ... ... ...Il!|l. . . . _. . . . . . . . . . .}_ !-_... . . . . . . . . . . .....E_!.t_.............:::::::::::::::::::::::::1..... . ........ ... .. . . . ... ...:::::::::::::Zi_ki>~~~~~~~~~~~~~~~~.t . W=_.. . . .j,, X:..::..::.:::-: -:...Asia....> 35 1. 5 76_1 . . ..:....:..g...:...:...:....:.:e...:.>: :e.:::.>::.: :::.::0: :::0: : m: ::. ..: :e O:C: :... :0.: :.:e: :e.:e:..:..: ::.:: .: .: :::: :::: .: - ::::: :: ::: ::::: ::s:::::.. ....:0:"::.....:::::* ! ! *!.i!>,!-!"^,,8:*2-s!::-s-0OtCO?oo3;8<c;us*M-!8<,,e?8>i?~~~~~~~~~~~~~~~~::o?.z?.z?o?.o:uous;abe!>. : !; ~~~~~....... ... ... ... ...................S .... ... ... .... .. ... ... SSS|..?SS....r . ...y ...# ..<sl ... ............... tws... ...;8s# @u u X S : # #b ee e WSn x 8 ................_,,.. . G.....I,--, . .. _1_i l?1 s -|#oZR S .- ..XRl .. .. .fg > X r- e b w .3....... . ... .. ...........m S S& s^ R , ER |.R?-@WOXPSSSRXwXw(XBNBb2SwbRRSa..ZSa=XwWNO#SwwpMu#O>#bxp.WTssonSR:axe.wSRSWjww.m-SYS-Z-----...-OO<O>XOM@S2#8aNlE8ors1ae!2g!1!!~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~?2XXZ.: a2S|.s||8#Ro.<.>.oiii_# |~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~AMBIOVOL.22 NO. 7, NOV. 1993 419
  5. 5. ............................... ................. ............................... .. ......M---M g :wAN..............................................-------------min=Mga factor2 to 10. Note thatthe figurefor tropicalforestgiven by(24)-18 kg C m-2-and quotedby (12) is controversial.16 kgC m-2is usedforglobalmodellingas well (25). FortheAmazonregiona figureof 11.7 kg C m-2 is given (26). It can be arguedthateven thelatterfigureis stilltoo highdueto biasof theforestsamplingtechniquesappliedin the area(20).Carbonate CarbonCarbonatecarbonhas received little attentionin carbon-cycleresearch.Schlesinger(27)concludedthatindesertandsemidesertareas where the accumulation of pedogenic carbonates ispronounced,carbonatecarbonexceedsorganiccarbonbyafactor10ormore.Inotherclimaticregionssoils prevailwithoutanyorwithonlylittlecarbonatedueto solubilizationandleachingof thecarbonatesthatmayhavebeen presentin the weatheringparentmaterialorbroughtalongby dustorflowing water.Heestimatedtheglobalcarbonate-carbonpool in soils atbetween780 and930GtC.To estimatetheglobalcarbonatecarbonstocksin soils in amannerconsistentwiththeorganic-carbonestimates,theaveragecarbonate-carboncontents for soil types given by Schlesinger(27) wereusedincombinationwiththesoil unitareascalculatedfromthe mappingunitsof the digitizedSoil Mapof the World.Resultsforcontinentsandmajorpartsof continentsarepresentedin Tables4 and5.We arriveat an estimated global carbonate-carbonpool insoils of 720 Gt C. This is slightly less thanSchlesingers esti-mate,butcan be explainedby differencesin soil areaestimatesbetweenthetwo approaches.Indeed,desertareashavea signifi-cantextentof sanddunes androcks which arecountedas soilsin the Schlesinger approachand are excluded in the presentstudy. However, a certain underestimationin our approachshould be noted:we did not consider soils which may be cal-careous, but for which this characteristicis not consideredintheirtaxonomicname,e.g. certainArenosolsin the 1974 FAO/Unesco Legend (3, Vol. I). Also, soils developed on coral areprobablynot adequatelyrepresentedon the Soil Map of theWorld.For converting carbonateto carbon, all carbonatewas as-sumedto contain 12%C (thecase for CaCO3),consideringthatdolomiteandMgCO3areof minorimportanceon a global scalecomparedwith calciumcarbonate.No attemptwas madeto es-timatecarbonin carbonaterocks.ProblemsSeveralproblemsrelatedto theestimationof theglobalorganic-carbonpool deservemoreattention.Some of thesehavealreadybeentoucheduponintheprevioussection,suchasdifferencesinapproachesforareaestimatesandtheuseofdifferentkindsofbasemaps.Inthisrespectanintegratedapproachusing soil, climaticandland-usedatain combinationwould probablyyield thebestresults. However, the lack of an adequateland-use map willremainamajorconstraintforsuchanapproachinthenearfuture.The establishmentof global pointdatabases by internationalresearchand modelling organizationssuch as IGBP (Interna-tional Geosphere-BiosphereProgramme)and others, deservessupportas theywill allowbettercarbonestimatesby soil typeorvegetationtypeto be madein duecourse.The use of organiccarbonandrelatedparametersto inferthefertilitystatus,organicmatterturnoverandbiological activityintropicalecosystems remainsproblematic,becausethe causalorstatisticalrelationshipsbetweenthemarepoorlyknown.This isdue to the paucityof investigationson the subject,but also tolackof standardizationin methodsandlackof linkagewith ma-jor soil units. Recent researchwithin the TSBF (TropicalSoilBiology andFertilityProgramme)of Unesco/IUBS/ISSSandatnational researchinstitutionsaims to demonstratethe impor-tanceof soil organicmatterin general.Recommendationson theuse of standardizedlaboratorymethodsforthedeterminationoforganiccarbon,soil respiration,litterdecomposition,nitrogenmineralization,root length and distribution,etc. are given in(28).A majorproblemremainsthe lack of sufficientdataon bulkdensityof soil horizons.Organiccarbonandcalciumcarbonatedeterminationsareconsideredroutineanalyses in soil surveys,butaredone on weight basis. Bulk densitiesareonly rarelyde-termined,however,andas thesevaluesarecrucialto recalculatecarbon data on a kg m-2 basis, this lack hampers consistenttreatmentof results.Bulkdensitiescanbe estimatedwitha vari-able level of confidence (29). However, the wide variationofbulkdensitiesas a functionof themoisturecontentatwhichit isdetermined,is anaddedproblem,especiallyforsoil groupssuchas Vertisols.Weathering-resistantcharcoalhasbeen identifiedas one kindof soil carbonthatis rarelyif evermeasured.Withtheexceptionof specialpurposestudies(30) suchcharcoalpieces areignoredby soil laboratories, because only the fine-earth fractions(smallerthan2 mm aftersieving) areanalyzed.Forinstance,itis indicated(31) thatcharcoalresultingfrom burningthroughlightningorearlyAmerindianoccupationis commonin thesoilsof the Amazon basin under naturalrainforests.For a well-drained("terrafirme")soils of the upperRio Negro areaof theColombianandVenezuelanAmazonregionthecharcoalcontentvariesfrom3 to 24 t/ha,with33 to 86%of it concentratedin theupper50 cm (32). Undercurrentshiftingcultivationpracticesin420 AMBIOVOL.22 NO. 7, NOV. 1993
  6. 6. ............. .... .... .. ..................... .........xom: X yx---------- ---- ..............m m d--- ----------............,,mgMWzp iWR5,10R:t,-m .......................................... . ......... ......gqgv IEMg-Zsx:1c...... ... ... ... ......tropicalforest areas,and in savannaecosystems subjectto re-peatedburning(naturalorhuman-induced),thetotalaccumula-tion of charcoalpieces in the soil can be very substantial,butagain,factualmeasurementsarerare(33).A finalproblem,particularlyrelevantwhensoil mapsareusedas a basisfor carbonestimations,is the lack in most soil classi-fication systems of due attentionto topsoil characteristicsingeneraland humus characteristicsin particular.The develop-mentof a propertopsoil characterizationas proposedby FAO(34) is worthwhile,not only for a betterunderstandingof theagriculturalpotentialof thesoil butalsoforecological studiesonaglobalscale suchas thepresentone.FACTORSINDUCINGCHANGESINSOILCARBONLEVELSTheambientorganic-mattercontentin the soil is determinedbythesupplyof soilorganicsubstances,includingsoil substancesofthe precedingyears and newly added undecomposedorganicmaterials,combinedwiththerateof decomposition.The supplydependsontheinsituproductivityintermsofbiomassproductionand on man-madeadditionalorganic inputs. Decomposition,whichcanbe measuredin termsof CO2productionby thesoil, isinfluencedby variousbiotic andabioticconditions.The factorscontrollingsupplyanddecompositionhavebeenreviewedintheliterature(35-37). Some factorsof particularimportanceforthetropicsandsubtropicsarebrieflydiscussedin thefollowing.EnvironmentalConditionsTheactualsoil organic-mattercontentandits changeswithtimearestronglyinfluencedby the interactingfactorsclimate,reliefandparentmaterial,floraandfaunaandby the soil itself.A combinationof high temperaturesand large amountsofprecipitationinducesenhanceddecompositionrates.Therefore,in thehumidtropicsthose ratesarehigh unless soils areimper-fectly drainedand oxygen deficiencies reduce decompositionrates.This situationfrequentlyoccurs in valleys and depres-sions. For instance,an overlay of the wetlands map of Africa(FAO,unpublished)with the organiccarbonmap reveals thatrelationship.The decreaseof soil organic-mattercontentin thehumidtropicsdue to decompositionis counteractedby a largesupplyof organic substancesfrom biomass productionunlessthevegetationis cleared.Frequentdryingandmoisteningof the soil-often occurringin thesemi-aridtropics-also bringsaboutrapiddecompositionof organic substances. Soils derived from volcanic materials(Andosols) have much highercarboncontents thansoils fromotherparentmaterials,mainlybecausethestrongbondsbetweenamorphousmineralconstituentsanda majorpartof the organicmatterinhibitsits decomposition.Relief, nutrientstatus(in par-ticular phosphorus), vegetative productivity and soil fauna(earthworms,termitesin thetropics)affectamountanddistribu-tion of organiccarboncontentin theprofileandtype of organiccompoundsformed,butarenotdiscussedin detailhere.Coastalareasoften exhibitecological conditionsthatdeviatefromtheirsurroundings.Lower riverplains and deltas have nearlyeverywherelargeamountsof soil organicmatter,formedin situ ordepositedwiththe sediments(andthen occurringirregularlywith soil depth),even whereadjacentuplandsoils arelow in organicmatter,as inaridclimates.Human-induced FactorsThekindof landuse stronglyinfluencesthe amountsof organiccarbon in the soil. Any land use in the long run leads to anequilibriumin soil organic-mattercontents.Conversionsof landuse candrasticallychangeorganic-mattercontents(38).Land-use and ManagementThe clearingof forests or woodlandsandtheirconversionintofarmlandin the tropicsreducesthe soil-carboncontent,mainlythroughreducedproductionof detritus(Table3), increasedero-sionratesanddecompositionof soil organicmatterby oxidation.Variousreviews (e.g. 1, 27) agreethatthe loss amountsto 20 to50%of theoriginalcarboninthetopsoil,butdeeperlayerswouldbe little affected,if atall.It was calculated(39) thatdeforestationin the tropicscauseda netreleaseof between0.1 and0.3 GtC soil carbonperyearintheyearsaround1980(comparedwithamountsbetween0.3 and1.3GtC by burninganddecayof clearedvegetation,and5.3 GtC peryearby fossil-fuel consumption).The decreaseof organicmatterin topsoils can have dramaticnegativeeffects on waterholdingcapacityof the soil, on struc-turestabilityandcompactness,nutrientstorageandsupplyandon soil biological life such as mycorrhizasand nitrogen-fixingbacteria(38, 40). Otherpropertiesbeing equal,thereis often aclearcorrelationbetweenorganic-carboncontentin topsoilsandcropyields, also in semiaridareas(22).The dynamics of organic carbon in the various systems oflanduse afterdeforestationneedsto be systematicallystudiedtomakemorereliableprognosesfor the futuredistributionof car-bon pools in the world.In a studyof representativesoil profilesforthewhole of Brazilit was shown(41) thatonly thehumusofthe topsoil (A horizon)is in directequilibriumwith the presentAMBIOVOL.22 NO. 7, NOV. 1993 421
  7. 7. dayvegetativecover;thatof deeperlayersis largelybeyondtheinfluenceof the vegetation.Therearemanystudies(42-44) on thesoil nutrientdynamicsunderthe shiftingcultivationsystemof cropping,in its variousforms,fromwhichthe soil-carbonbehaviourcanbe derivedforthatlanduse.Less systematicobservationshavebeenmadeon theorganic-carboncycling underpermanentcrops,especially treeperenni-als suchas oil palmandrubber.Pasturesare an increasingly widespreadland-use type fol-lowingdeforestation,establishedeitherimmediatelyorafteroneor morecycles of shiftingcultivation.In the lattercase the or-ganic-mattercontentsremainlow. However,pastureestablish-ment immediately after deforestation,especially when usingspecies with high percentagesof below-groundbiomass pro-duction,may actuallyincreasethe soil organic-mattercontent.This is confirmedby several studies in the BrazilianAmazon(45) and elsewhere in Latin America (46) and in East Africa(47). Twenty years old pasturesin the Rondonianpartof theBrazilianAmazonprovedto haveto 50%moresoil carbonstockto 30 cm depth,in comparisonto forestedsoils of the samena-ture.It shouldbe notedthatthis does not yet fully compensatefor the loss of carbonstoragein the above-groundbiomass,andthe economic value of the establishedgrasslandsmay be short-lived. This because it is difficult to maintainthe palatibilityofsuchgrasslandsaftera numberof yearsbecauseof the growingcompetitionof various species (woody herbs;hardyperennialgrasses). Some of these species, such as Imperatacylindrica("alang-alang",cogon grass) do provide a protective groundcoverandarelativelylargeamountof above-andbelow-groundcarbonstorage,butdirectbenefitsforthehumanpopulationsarenil, except wherethe grassis used forthatchingorpapermanu-facture.An interestingalternativeis the developmentof inten-sive livestockproductionatthe marginsof tropicalforests,em-ployingpreseminalcropwithhighbiomassproductionpotential(sugar-cane,forage trees) for the feeding of livestock speciesmanagedin confinement(48).Applicationof fertilizerinducesenhancedbiomassproductionandmay thereforeresultin largercarboninputsin the topsoil.When organicfertilizersare applied-household refuse, urbanwaste, agro-processingwaste, greenmanure,forestlitteror sodfrom landelsewhere-then the effect on a longer-termbasis isobvious.Theage-oldPlaggensoils of TheNetherlands,Flandersand NorthernGermanyareperhapsthe best-knownexamples,Figure3. RelationshipbetweenPercentagesof SoilOrganicCarbonandCationExchangeCapacity(CEC)interra-preta-do-lndiosoilprofilesof the Amazonregion.(AdaptedfromSombroek,1966.Fiveprofiles;nonsettleduponnowadays.m.e./100 g soil40 -A AAA30 -O20a ]0 1 2 -3 4 5 6_.- Organiccarbonbut similarsoils exist in the tropics and subtropicsin spite ofhigherdecompositionrates.A case in point(16) arethe "terra-preta-do-Indio"soils onhighriverbanksandotheruplandsin theAmazonregion.Thesesoils, originallyaspoorchemicallyasthesurroundingkaolinitic soils, were purposely enriched by theearly Amerindianpopulation with organic matter from sur-rounding land or aquatic grasses and phosphates-the latterfrom hunting and fishing-and they have maintained theirhighertrophiclevel even aftertheirabandonmentcenturiesago.The few analyses availablefor these soils indicatenot only adoublingof the organic-mattercontentin the upper0.5 to 1 mbutalso ahighercation(nutrient)exchangecapacitythanwouldbe expectedfromthesumof thecolloidalactivityof theorganicmatterand the kaolinitic clay mineralsindividually.A stablecomplexof theaddedorganicmatterandthekaolinite,underin-fluence of the addedphosphorusand possibly colloidal silica,may be the cause (Fig. 3). A recentstudy(41) indicatesthatonthese"terra-preta-do-Indio"soils theCO2productionis lowerascomparedto comparableadjacentsoils withouthumusenrich-ment. This possibly is inducedby a higherstabilityof the soilorganic matter.This conclusion supportsthe idea that stablecomplexesof organicmatterandkaolinitemayoccur.Someba-sic researchon theseterra-pretasoils mayprovideaclueto whatspecific land-managementpracticesareneededto emulate,in afew years time ratherthanin centuries,this increasedfertilitylevel andstableorganic-carbonstorage.Liegel indicatesthatsoil carbonaccumulationratesby pur-posefulsoil managementin PuertoRico arecomparableto thosein temperateregions(46). Therearenumerousexamplesof soilorganicmatterenrichmentunderintensiveirrigatedricecultiva-tion and underhydromorphicsoil conditions in general. Pur-posely stimulatingthiswouldhoweverincreaseemissionsof thegreenhousegas methane(anpossibly also of nitrousoxide) un-dertheprevailingsoil andwatermanagementpractices.EFFECTSOFCLIMATECHANGECO2Fertilization EffectThereareseveralreviews on the likely effect of the anticipatedhuman-inducedglobal climatic change on soil conditions ingeneral, and its carbon pool in particular(1, 51, 52). Mostattentionhasbeendevotedto thelikely negativeeffects of risingtemperatures:more rapid breakdownof soil organic matter;decreasingsoil moisturestoragebecauseof lowerprecipitation/evapotranspirationratioswithconsequentlyless newproductionof organicmatter;depletionof plantnutrientsdue to increasederosion, againentailingless organicmatterproduction;loss ofessentialsoil floraandfauna,includingsymbioticorganismsandthe anticipatedshiftingof agroecologicalzones, with slowerorunbalancedlitterdecomposition;andloss of landduetosea-levelrise,causinga decreasein terrestrialbiomassproduction.However,recentexperimentson thebehaviorof plantsunderelevated atmosphericCO2levels, in greenhouses,in open-topfield chambersas well as in free-airCO2enrichment(FACE)field experiments,coupled with observationson plant growthnear sites with naturallyhigh CO2concentrations(some vol-canic lakes) all pointto a substantiallyhigherprimaryproduc-tion, above-groundand below-ground, especially of the so-called C3 plants(CO2fertilizationeffect) anda moreeconomicuse of water by plants, especially those of the C4 type (CO2antitranspirationeffect). Under a doubled atmosphericCO2concentrationthis increasemay be 30%oor morein bothcases,and slightly higher temperaturesmay furtherstrengthentheseeffects (61-63).The CO2fertilizationeffect is likely to have a significantim-pact on plantgrowthin the humidtropicsin a CO2enrichedat-mosphere,yielding extra soil organic matterthroughlitterfall422 AMBIOVOL.22 NO.7. NOV. 1993
  8. 8. Some examples of thevariation in amount and rMvertical distribution oforganic matter in tropicaland subtropical soils. Fl1. Very low amount, withgradualverticaldecrease -i.concentrated in topsoil(luvic Arenosols, Amazon,1Brazil).2. Fairamount, with gradualverticaldecrease (rhodic :3. Fairlyhigh amount, withgradual vertical decrease ~~~~.(xantho-humic Ferralsol,southern Brazil).4. Highamount,withvery ;LOngradual vertical decrease .-(humic Nitisol, Kenya).5. Highamount,concentrated in subsurfacehorizon (humic Alisol, -Brazil). ..6. Fairlyhigh amount,regularlythroughout theprofile (eutric Vertisol,Ethiopia).7. Highamount, irregularlythroughout the profile(mollic Andosol, Ecuador).8. Highamount in uppersubsoil (dystric Planosol, tUruguay).9. Highamount irregularly insubsoil (carbic Podzol,Amazon, Brazil).A ~~~~~~~~~ .~~~~~~~ 9
  9. 9. andcropresidues,andespecially througha morevigorousrootgrowth.Nutrientsmaycome in shortsupplyatsuchhigherratesof biomassproduction,butthiscan,inprinciple,be redressedbylarger applicationsof fertilizers and promotionof integratedplant-nutritionsystems in agro-ecosystems.Therearesome in-dications that in naturalecosystems higher atmosphericCO2concentrationinducesmoremycorrhizalactivitystimulatingre-lease of occludedphosphorus,morebiologicalnitrogenfixationfromthe air,andmorepotassiumreleaseby increasedweather-ing of the saprolitebelow the soil (56, 63, 64). According tosome estimates (61) the CO2fertilizationeffect would alreadyhavecontributed,by 10%ormore,to the approximatedoublingof theworldwideagriculturalproductivityin thepast 100years.The CO2antitranspirationeffect would be of particularsig-nificance in the semiaridregions of the tropicsand subtropics:plants would grow more vigorously with the same amountofwater, and some plant growth would become possible wherehithertothe land surfaceis bare,due to climate- or salinity-in-ducedaridity.A bettergroundcover would be the result,limit-ing soil-erosionhazards,loweringthe soil-surfacetemperaturesandprovidingfreshorganicmatterforincorporationin the soil.The two plant physiological effects of higher atmosphericCO2concentrationswill in practicebe counteractedandlimitedby a numberof associatedfeaturesof Global Change,such ashigherUV-B values, highertropospheric03, temperaturesneartheupperlimitforgraindevelopment,etc. (62, 63).Thereis still some doubtaboutthe persistenceof the effectsover successive generationsof annuals,andthe laterstages oflife of perennials-including forests-and hence the experi-mental data recording will have to extend over many years,partlyin costly field set-ups in naturalor plantedforests. Buteven if theneteffectwill be only afractionof theexperimentallyobtainedgrowthincreasesof 30%or more, an increasein soilorganiccarbonstoragemay be expected in an environmentofhigheratmosphericCO2.Threeyearsonly of FACEexperimen-tation with cotton, using 13C,showed that 10%of the soil or-ganiccarbonin theupper30 cm was "new"(58).Carbon Sequestering in SoilsOnthebasis of the admittedlyfew indicationson thepossibilityto increase carbon storage in tropical soils by adaptedland-managementtechniquesthatemulatethealreadyhuman-enrichedsoils, combinedwith the existence of the CO2fertilizationandantitranspirationeffects, we herebyplea for furtherresearch.Inagriculturalecosystemspotentialstudiesshouldincludecorrelatingtotalsoilcarbonandaccumulationrateswithclaycontentandsoilmineralogy,relatingobservedtotalcarbonpools to past/presentcroppingsystems andlanduse changes anddeterminingwhichkinds of soils are most suitablefor carbon/nitrogenstoragebyfungi and other rhizosphere organisms (46). In particularexperimentationon the terra-pretaenrichmentprocess and thesubsequentdevelopmentofalarge-scalefieldprogramtostimulateorganiccarbonstoragein tropicalandsubtropicalsoils is highlydesirable.Fortemperateareasthereareanumberof historicalexamples.A recentpublicationof the US EnvironmentProtectionAgency(63) gives an overview of practical possibilities for carbonsequesteringin arablesoils, mainlythroughconservationtillagetechniques.Ofthese,theno-tillmanagementtechniques-leavingnearly all of the crop residues on the land, with minimumdisturbanceonly at seeding the next cropwould be the mostpromising,because it reduces soil temperature,increases soilmoistureand stimulatessoil faunato transportthe residueun-derground.Theideawastakenupinasimulationstudy(64)forthemain agriculturalsoils of the formerSoviet Union: Completeconversionof all climaticallysuitableland(181 M. ha)to no-tillmanagement,resultingin a 10%increasein soil carbon,wouldimply a sequesteringof 3.3 Gtof carbon.No-till soil managementin the tropicsandnon-tropicsseemsfeasible,too,thoughsomesoils needtobecultivatedregularlytoprovidea good seebed ("tilth"),andburningof the residuesofsomecropsisrequiredtopreventthesurvivalofdiseasesandpestsin monocultures.In additionto no-tilling, as much as feasiblewithinthe local transportfacilities, urbanandperi-urbanwasteandsludgeshouldbeusedbecauseofitsinherenthighconcentrationof organiccarbonandplantnutrients.Insteadof thiswastebeingdissipatedinaquaticsystemsandultimatelyincoastalwatersandsediments, it should be processed on the spot and separatedacordingto its quality,includingits contentsof pollutants,andmade thereupon availableto improvesoils in ruralareason apermanentbasis. Algae or grassy aquaculturesmay be anintermediatestageof suchaprocessingof wasteforaproductionfactorin agriculture.A majorfield programin the above senscouldbe startedin the moist lowlandsavannazones of West orSoutheasternAfrica,aspartofFAOsinternationalschemefortheconservation and rehabilitationof African lands (ISCRAL).Especially when in combination with additionalphosphorussupply-for instancethroughtheapplicationof locallyavailablerockphosphates-it wouldservetwo purposes:theresilienceoftropicalsoilsandtheirproductivecapacityforastronglygrowinghumanpopulationwould be improved,and there would be asubstantialsequesteringof carbonin soils which,by its natureisof a morepermanentcharacterthanstoragein living vegetation.It would form an automaticand gradually strongerbrakingmechanismontheanticipatedhuman-inducedriseofatmosphericco2.Theaboveis nota pleafora "business-as-usual"use of fossilfuels.Amorefrugaluseofthisnon-renewableresource,especiallyin alreadyindustrializedcountriesof temperatezones, remainsessentialtoslackenthecurrentriseof atmosphericCO2tosuchanextent that adverse effects of human-inducedglobal climaticchange,suchas sealevelriseandintensificationof local climatevariability,maybe keptdownto manageableproportions.CONCLUSIONS(i) The organic-carbonpool in the upper1 m of the worldssoils is 1220 Gt, 1.5 times higher than that of the standingbiomass(naturalvegetationandcrops).Inthe soils undertropi-cal rainforeststhis pool is about equal to that of the above-groundbiomass.(ii) In the tropicsmany soils aredeep andthe storageof or-ganiccarbonbelow 1m depthis substantial;about50 Gtof theglobal pool of carbonis storedat between 1 and 2 m depthintropicalsoils.(iii) Charcoalstoragein manytropicalandsubtropicalsoils isnotinsignificant,even in soils underpristinevegetation,butit israrelymeasuredquantitatively.(iv) In the tropicaland subtropicaldrylandregions the car-bonate-carbonstoragein soils amountsto about720 Gt;it is lit-tle dynamic.(v) The short-termdynamics of organic carbonare largelyrestrictedto the upper30 to 50 cm in most tropicaland sub-tropicalsoils.(vi) At clearing of tropicalforests or woodlandsfor arablecropping(permanentorshiftingcultivation)thereis a20 to 50%reductionin organiccarbonin theseuppersoil layers.Establish-mentof pasturesimmediatelyafterdeforestation,using grasseswith a high percentageof below-groundbiomass production,canresultinmaintenanceorevenincreasein soil organic-carboncontent, though the palatabilityof the above-groundbiomassoftendecreasesgreatlyaftera few years.(vii) Organicmatterin most tropicalandsubtropicalsoils isessentialformaintenanceandimprovementof waterinfiltration424 AMBIOVOL.22 NO. 7, NOV. 1993
  10. 10. 3?:.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.4~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~1rDifference in soil organic carbon content between an anthropogenically enriched soil of the Amazon (Terra-preta-do-indio) and an adjacent nonenriched soil of the same physiographic position, clay content and clay minerology(xantic Ferralsol).andwater-holdingcapacity,for structurestability,for adequatenutrientstorageandsupply,andfor a healthysoil biological ac-tivity(mycorrhizalphosphorusrelease,biologicalnitrogenfixa-tion).Thepurposefulsequesteringof organic-carboncontentsinsuchsoils is thereforeworthwhilein its own right.(viii) Some tropical soils traditionallyenriched in organicmatter,nutrientsand cation-exchangecapacity due to ancienthumanoccupationgive indicationsthatsuchanenrichmentcanbe maintainedover severalcenturies;the supplyof phosphoruswouldseemto be a key conditioningfactor.(ix) It is often assumedthathuman-inducedglobal climaticchangewill have an overall negative effect on the amountoforganiccarboninsoils. However,if onetakesintoaccountrecentresearchdata on the so-called "fertilizationeffect" and theassociated"antitranspirationeffect"of higheratmosphericCO2levels on plant growth, above- ground and especially below-ground,thesepositiveeffectsmaymitigatethenegativeeffectsonsoil-organiccarbonlevels oreven overcomethem.(x)TheCO2fertilizationeffectanditsinfluenceonsoil organicmatterstorageimplies an automaticcurbingof any excessivelyrisingatmosphericCO2levels as causedby increasedfossil fueluse andbiomassburning.(xi) Therefore, large-scale field programmesto stimulateorganic-carbonstorage in tropical soils, especially when incombinationwithphosphorussupply(forinstancethroughlocallyavailablerockphosphates)wouldservetwopurposes:thequalityof tropical soils and their productivecapacity for a stronglygrowing populationwould improve, and at the same time thecurrentriseinatmosphericCO2levelswouldbeattenuatedtosuchanextentthatadverseeffects of human-inducedglobalclimaticchange,suchas sea-levelriseandintensificationof localclimatevariability,maybe keptdownto manageableproportions.AMBIOVOL.22 NO. 7, NOV. 1993 425
  11. 11. References and Notes1. Bouwman,A.F. (ed.). 1990.Soils andtheGreenhouseEffect.Proceedingsof theInter-nationalConferenceon Soils andthe GreenhouseEffect. JohnWiley andSons, NewYork,USA.2. FAO. 1991.Digitizedsoilmapoftheworld.WorldSoilResourcesReport67.FAO,Rome.Italy.3. FAO-Unesco.1971-1981.SoilMapoftheWorld1:5000000-Vol.I-IX.FAO,Rome,Italy.4. Ajtay,G.L., Ketner,P. and Duvigneaud,P. 1979. Terrestrialprimaryproductionandphytomass.In:SCOPEVol.13.Theglobalcarboncycle. Bolin,B.,Degens,E.T.,Kempe,S. andKetner,P. (eds). JohnWiley andSons, New York,USA, p. 129-181.5. Bohn,H.L. 1976.Estimateof organiccarbonin worldsoils 11.Soil Sci. Soc. Am.J. 40,468-470.6. Bolin, B. 1977.Changesof landbiotaandtheirimportanceforthecarboncycle. Science196, 613-615.7. Bolin, B., Degens, E.T.,Duvigneaud,P. andKempe,S. 1979.Theglobalcarboncycle.In:The global carboncycle. SCOPEVol. 13. Bolin, B., Degens, E.T., Kempe,S. andKetner,P. (eds). JohnWiley andSons, New York,USA, p. 1-56.8. Buringh, P. 1984. Organic carbon in soils of the world. In: The role of terrestrialvegetationintheglobalcarboncycle. Measurementbyremotesensing.SCOPEVol.23.Woodwell,G.M. (ed.). JohnWiley andSons, New York,USA, p. 91-109.9. Goudriaan,J.andKetner,D. 1984.A simulationstudyfortheglobalcarboncycle, inclu-ding mans impacton thebiosphere.Clim.Change6, 167-192.10. Meentemeyer,V., Box, E.O.,Volkoff, M. andGardner,J. 1981.Climaticestimationofsoil properties:pH, litteraccumulationandsoil organiccarboncontent.Ecol. Soc.Am.Bull.62, 104.11. Post,W.M.,Emanuel,W.R.,Zinke,P.J.andStangenberger,A.G. 1982.Soilcarbonpoolsandworldlife zones. Nature298, 156-159.12. Schlesinger,W.H. 1977.Carbonbalancein terrestrialdetritus.Antn.Rev.Ecol. Syst.8.51-81.13. Post,W.M.,Pastor,I.,Zinke,P.J.andStangenberger,A.G. 1985.Globalpatternof soilnitrogenstorage.Nature317. 613-616.14. Eswaran,H., VandenBerg,E.andReich,P. 1993.Organiccarboninsoils of theworld.Soil Sci. Soc. Am.J. 57, 192-194.15. Eswaran,H.,Bliss N., Lytle,D. andLammers,D. 1993.MajorSoilRegionsoftheWorld.USDA-SCS. US.Gov. Print.Office, WashingtonDC. (Inpress).16. Soil SurveyStaff. 1975.Soil taxonomy:a basicsystemof soil classificationformakinigand interpretingsoil surveys. USDAAgric. Handbook436. US. Gov. Print.Office.WashingtonDC.17. Jenkinson,D.S. andRayner,J.H. 1977.Thetumoverof soilorganicmatterinsomeof theRothamstedclassicalexperiments.Soil Sci. 125, 298-305.18. Scharpenseel,H.W.,Becker-Heidmann,P., Neue, H.U. andTsutsuki,K. 1989.Bomb-carbon,4C-datingand 3C-measurementsas tracersof organicmatterdynamicsas wellas of morphogeneticandturbationprocesses.Sci. Tot.Environi.81/82, 99-110.19. Sombroek,W.G. 1966.AmazonSoils: a Reconnaissaniceof the Soils of the BrazilianAmazonRegion.PUDOC,Wageningen,The Netherlands.20. Sombroek,W.G.1992.BiomassandcarbonstorageintheAmazonecosystems.Initerciencia17, 269-272.21. RadamBrasil (or Proyecto Radam). 1972-1978. Les!antamento de Recuirsos Naturais.Vols 1-16. Ministeriodas Minase Energia,Dep. Nac. da ProducaoMineral,Rio deJaneiro.(InPortuguese).22. Nachtergaele,F.O. 1976.Suleimiseriesbenchmarksoildescription.Techn.Bull.No.26.Soil SurveyAdm.WadMedani,Sudan.23. Whittaker,R.M.andLikens,G.E. 1975.Thebiosphereandman.In:Primaryproductionof the biosphere.Ecological Studies14. Lieth,H. andWhittaker,R.H. (eds). SpringerVerlag,Heidelberg,Berlin,New York.24. Whittaker,R.H. 1975.Communitiesand Ecosystems.MacMillan,New York,USA.25. Houghton,R.A., Boone, R.D., Fruci, J.R., Hobbie, J.E., Melillo, J.M., Palm, C.A.,Peterson,B.J., Shaver,G.R., Woodwell, G.M., Moore,B., Skole, D.L. andMyers,N.1987.The flux of carbonfromterrestrialecosystems to the atmospherein 1980duetochangesin landuse:geographicdistributionof theglobal flux. Tellus39B, 122-139.26. Brown,S. andLugo,A.E. 1992.Abovegroundbiomassestimatesfortropicalmoistfo-restsof the BrazilianAmazon.Interciencia17, 8-18.27. Schlesinger,W.H. 1982.Carbonstorageinthecalicheof aridsoils:acasestudyfromAri-zona.Soil Sci. 133, 247-255.28. Anderson,J.M. and Ingram.J.S.I. (eds). 1989. TropicalSoil Biology anidFertilits:AHandbookof Methods.CAB Intemational,Wallingford,UK.29. FAO. 1992.Estimationof Soil Propertiesand QualitiesBased oil the Soil Mapof tlheWorld.AGLS Soil ResourcesGroupWorkingPaper.Firstdraft.FAO,Rome,Italy.30. Saldarriaga,J.G.,West,D.C. andThorp,M.L. 1986.ForestsuccessionintheUpperRioNegroof ColombiaandVenezuela.Environ.Sci.Disv.Publ.2694. OakRidge,TE,USA.31. Sanford,R,L.,Saldarriaga,J.,Clark,K.E.,Uhl,C. andHerrera,R. 1985.Amazonraill-forestfires.Science227, 53-55.32. Saldariaga,J.G. 1985. Forest Succession in the UpperRio Negro of ColombiaanldVenezuela.UnpublishedPh.D.thesis, Universityof Tenessee, KnoxvilleTS.33. Feamside,P.M.1985.BrazilsAmazonforestandtheglobalcarbonproblem.Initerciencia10, 179-186.34. FAO.1992.FrameworkforCharacterizationandClassificationofTopsoilsintheWorld.AGLSSoil ResourcesGroupworkingpaper.FAO,Rome,Italy.35. Coleman,C., Oades,J.M. and Uehara,G. 1989. Dvnamicsof Soil OrganicMatterinTropicalEcosystems:Resultof a ConferenceHeldat theMauiBeachHotel,Kahuluiin,Maui,Hawaii, October7-15, 1988. Universitvof Hawaii,USA.36. Scheffer,F.andSchachtschabel,P. 1989.LehrbuchderBodenkunde.12thedition.EnkeVerlag,Stuttgart,Germany.37. Batjes,N.H.andBridges,E.M. 1992.A reviewof soil factorsandprocessesthatcontrolfluxes of heat,moistureandgreenhousegases. TechnicalPaper 23. IntemationalSoilReferenceandInformationCentre,Wageningen.38. Mulongoy, K. and Merckx, R. (eds). 1993. Soil Organic Matter Dvnamics andSustainabilitrof TropicalAgriculture.JohnWiley andSons Ltd.,Chichester,UK.39. Detwiler, R.P. and Hall, C.A.S. 1988. Tropicalforests and the global carboncycle.Science239, 42-47.40. Lal,R., Sanchez,P.A. andCummings,R.W. 1986.LandClearingandDevelopmentinthe Tropics.Balkema,Rotterdam,Boston.41. Volkoff, B. andCerri,C.C. 1988.Lhumusdes sols duBresil-Nature et relationsaveclenvironnement.CahiersORSTOM.Ser.Pedol. 24, 83-95.42. Nye, P.H. and Greenland,D.J 1960. The soil undershifting cultivation. TechnicalCommunticationNo. 51. CommonwealthBureauof Soils Harpenden,FamnhamRoyal,Bucks, England.43. Andriesse,J.P. 1989.Nutrientmanagementthroughshiftingcultivation-a comparativestudyon cycling of nutrientsintraditionalfarmingsystemsof MalaysiaandSriLanka.In:ProceedingsoftheSymposium:NutrientManagementforFood CropProductioninTropicalFarmingSystems",heldat UJnivXersita.sBrawijava,Maxlang,Indonzesia,October19-24, 1987. VanderHeide.1. (ed.). InstituteforSoil Fertility,Haren,Netherlands,p.29-62.44. Fehlherg, H.G. 1989. Shifting cultivation-some soil managementaspects for itsimprovement.In:ProceedingsoftheSvmposium:"NutrientManagementforFoodCropProduction in TropicalFarming:Ssstem.s", held at UJniversitalsBrasvsjaJ!a,Malalng,Indonesia, October 19-24, 1987. Van der Heide, J. (ed.). Institutefor Soil Fertility,Haren,Netherlands,p. 381-394.45. SerraoE.A.S., Falesi I.C.,da Vega, J.B. andTeixeiraNeto, J.F. 1979. Productivityofcultivatedpastureson low fertilitysoils of the Amazonregionof Brazil.In:PastureProductiononAcidSoilsof theTropics.Sanchez,P.A.andTergas,L.E.(eds).CIAT,Cali,Colombia, 195-225.46. Liegel, L.H. 1992.An overviewof carbonsequestrationin soils of LatinAmerica.In:OrganticCarbonSequestrationintheSoilsofPuertoRico.Beinroth,F.H.(ed.).Dept.ofAgronomyandSoils. Universityof PuertoRico, Mayaguez,PR.47. Boonman,J.G. 1993.EastAfricasgrassesandfodders:Theirecology andhusbandry.TasksforVegetationScience29. KluwerAcademicPublishers,Netherlands,Dordrecht.48. Murgueito,E. 1990.IntensiveSustainablelivestockproduction:analtemativetotropicaldeforestation.Ambio19, 397-400.49. Andrade,A. and Botero, P. 1984. Los anthrosoles(tropicPlaggepts)de Araracuara,AmazoniaColombiana.RevistaCIAF9, 25-39.50. Zech,W.,Haumeier,L.andHempfling,R. 1990.Ecologicalaspectsofsoilorganicmatterin tropicalsoils. In:HumicSubstancesin Soil and CropSciences. SelectedReadings.MacCarthy,P.,Clapp,C.E.,Malcolm,R.L.andBloom,P.R.(eds).SSSA/ASA,Madison,USA, p. 187-202.51. Tinker,P.B. andIneson,P. 1990.Soil organicmatterandbiology inrelationtoclimaticchange.In:Soils on a WarmerEarth-Developments in Soil Science20. Scharpenseel,H.W.,Schomaker,M. andAyoub,A. (eds). Elsevier,Amsterdam,Oxford,New York,Tokyo, p. 71-87.52. Sauerbeck,D.R. 1992.Thecontributionby agricultureto tracegas substancesof directandindirectrelevancetothegreenhouseeffect. In:IntergovernmentalPanelon ClimateChangeResponseStrategiesWorkingGroup.Climatechange-Proceedings of aWork-shoponAssessingTechnologiesandManagementSystemsforAgricultureandForestryin Relation to Global Climate Change. Canberra,Australia,20-23 January1992.AustralianGovemmentPub-lishingService,Canberra,Australia.53. De Wit,P.V. andNachtergaele,F.O. 1990.Explanatorynoteon thesoil mapof theRe-publicofBotswana.AG/BOT/85/01I FieldDocument30.Annex1.MinistryofAgriculture,Gaborone,Botswana.54. Soil SurveyStaff. 1982.SoilTaxonom.ABasicSystemnofSoilClassificationfor MakingandInterpretingSoil Surveys.55. Murthy,R.S., Hirekerur,L.R., Deshpande,S.B. and VenkataRao, B.V. (eds). 1982.BenchmarkSoils of India. NationalBureauof Soil Surveyand Land Use Planning,Nagpur,India.56. Goudriaan,J. 1992.Biospherestructure,carbonsequesteringpotentialandtheatmosphe-ric 14C carbonrecord.J. Exp.Bot.43, 1111-1119.57. Rozema,J. 1993.Plantresponsestoatmosphericcarbondioxideenrichment:interactionswithsome soil andatmosphericconditions.Vegetatio104/105, 173-190.58. Fajer,E.D. andBazzaz,F.A. 1992.Iscarbondioxidea good greenhousegas? GlobalEnviron.Change2, 301-310.59. Bouwman, A.F. and Sombroek,W.G. 1990. Inputsto climatic change by soil andagriculturerelatedactivities-Present statusandpossible futuretrends.In:Soils on aWarmerEarth-DevelopmentsinSoil Science20. Scharpenseel,H.W.,Schomaker,M.andAyoub,A. (eds.). Elsevier,Amsterdam,Oxford,New York,Tokyo,p. 15-30.60. Deutscher Bundestag (ed.). 1991. Protecting the Earth: A Status Report withRecommendations for A New Energy Policy. Deutscher Bundestag, ReferatOffentlichkeitsarbeit.Bonn,Germany.61. Tans,P.P.,Fung,I.Y. andTakahashi,T. 1990.Observationalconstraintson theglobalatmosphericCO, budget.Science 247, 1431-1438.62. Lenvit,S.W., Kimball,B.A., Paul,E.A. andHendry,G.R. 1992.IsotopicEstimationofInputsofCarbontoCottonSoilsunderFACE-CO,Enrichment.DOEResearchSummary.CDIAC,OakRidge,USA.63. Kem, J.S. andJohnson,M.G. 1991. Impactof conservationtillage use on soil andat-mosphericcarbonin thecontiguousUnitedStates.EPA/600/3-91/056.Env. Res. Lab.Corvallis,OR.64. Gaston,G.G.,Kolchugina,T. andVinson,T.S. 1993.Potentialcffectof no-tillmanage-mentoncarbonintheagriculturalsoilsof theformerSovietUnion.Agriculture.Ecosvst.Environ.45, 295-309.65. Acknowledgement.This article was originally presentedin the Royal Colloquium1993.Itwas preparedby W.G.Sombroek,F.O,NachtergaeleandA. Hebelof the FoodandAgriculturalOrganizationof theUnitedNations(FAO),andis reproducedherebypermissionof thatorganization.WimSombroek holds a PhDfromWageningen Universityinagriculturalsciences. From1959 to 1979 he participatedintropicalsoil and land-evaluationprojects in LatinAmerica(Brazil,Uruguay)and Africa(Nigeria,Kenya).From1979 till1991, he was Directorof the InternationalSoil Referenceand InformationCenter(ISRIC)inWageningen, and duringmost of those years he also served as Secretary-Generalofthe InternationalSociety of Soil Science (ISSS),which is ascientific associate of ICSU.He now leads the LandandWaterDevelopment Division of the Food and AgricultureOrganizationof the UnitedNations and is also theOrganizationsFocal Pointon ClimateChange matters.FreddyNachtergaele has a PhDin agronomy fromGentUniversity.Since 1989 he has been Technical Officer,SoilResources, withthe Landand WaterDevelopment Divisionof the Food and AgricultureOrganization.Before thattime,he worked mainlyas a land resources expert in several FAOfield projects in northernand eastern Africaand southeastAsia. Axel Hebel is MScgeographer from BerlinUnviersitywithspecialization in landscape ecology and regionalplanning. From1989 to 1992, he workedat the UniversityofHohenheimin Germanyand at ICRISATSahelian CenterinNigeron soil fertility.His PhDin agriculture/soilscience tobe defended in 1993. Since 1993, he has been workingintheSoil Resources Groupof the Soil Resources, Managementand Conservation Service, Landand WaterDevelopmentDivisionat FAOHeadquartersin Rome. Theiraddress: Landand WaterDevelopment Division, FAO,Viadelle TermediCaracalla,00100 Rome, Italy.426 AMBIOVOL.22 NO. 7. NOV. 1993

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