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1、Chapter9Soilacid-baseandredoxreactionChapter9Soilacid-baseandredoxreactionSection1Theformationofsoilacid-baseTheacid-basereactionofsoilTheacid-basereactionofsoilischangeinsoilpH.SoilpHisprobablythesinglemostimportantchemicalcharecteristicofasoil.Theknowledgeof
2、pHisneededtounderstandimportantchemicalprocessessuchasionmobility,precipitationanddissolutionequilibria,andoxidation-reductionequilibria.AknowledgeofpHisalsoneededtounderstandnutrientavailabilitytoplantsandthenegativeresponseofmanyplantspeciestosoilacidity.The
3、soilpHvalueinChinaisabout4.5-8.5.一、Soilacidity（一）Thecauseofsoilacidity1．Climaticfactor2．Biologicalfactor3．Fertilizerapplicationandirrigation1.Thesourceofhydrogenions（1）Waterdissociation（2）Carbondioxide（3）Organicacid（4）Inorganicacid(inorganicfertilizer)（5）Acidr
4、ainAcidrainAcidrainiscausedbytheburningoffossilfuels.Burningoil,gasandcoalinpowerstationsreleasesSulfuricDioxide(SO2)intotheatmosphere.Burningoilandgasolineinmotorvehiclesputsnitrogenoxides(NOX)intotheatmosphere.Thesegasesmixwithwaterdropletsintheatmospherecre
5、atingweaksolutionsofnitricandsulfuricacids.Whenprecipitationoccursthesesolutionsfallasacidrain.ExchangeableHydrogenisthemainsourceofH+atpH6andabove.BelowpH6AluminumisthemainsourceofH+duetodissociationofAlfromclayminerals.AluminumbecomesmoresolubleatlowerpH’sAl
6、3++H20---->Al(OH)+++H+Al(OH)+++H2O--->Al(OH)2++H+Al(OH)2++H20--->Al(OH)3+H+2.Aluminumactivationinsoil（二）Thetypesofsoilacidity1．ActiveacidityActiveAcidity–TheactivityofhydrogenionintheaqueousphaseofasoilexpressedasapHvalue.2．SoilpotentialacidityStrongacidityins
7、oilColloid-Al3+=Colloid+Al3+Al3++3H2OAl（OH)3+3H+(2)AcidityandweakacidityinsoilAl（OH）2++HOHAl（OH）2++H+Al（OH）2++HOHAl（OH）3++H+Or:Colloid-H+H+3.SoilexchangeableacidityExchangeableacidity-Thealuminumandhydrogenthatcanbereplacedfromanacidsoilbyanunbufferedsaltsolut
8、ionsuchasKClorNaCl.(cmol（＋）/kg）4.SoilhydrolyticacidityCH3COONa+H2OCH3COOH+NaOHH-ColloidAl+4CH3COONaNa-Colloid3Na+Al（OH）3+4CH3COOHOxide-OH+CH3COONaOxide-O-Na++CH3COOH二、Soilalkalinit
