Chapter5SoilAcidityandAlkalinity第五章土壤酸碱度Thedegreeofacidityoralkalinityisamaster（显著的，主要的）variable（易变的）thataffectsnearlyallsoilproperties—chemical,biological,andphysical.CommonlyexpressedassoilpH,thisvariablelargelycontrolsplantnutrientavailabilityandmicrobialreactioninsoils.有1000克土样，分别含H+，Mg2+，Ca2+，Na+，K+和Al3+离子8，5，16，1，1和4cmol，土样中有机质含量为2%（有机质平均CEC约为350cmol/kg），粘粒含量是25%，求:(1)土壤的CEC(2)土壤盐基饱和度(3)若土样仅为一种粘粒矿物组成,试推断是何种矿物?•C.E.C.=8+5+16+1+1+4=35cmol(+)/kg•BSP=(5+16+1+1)×100/35=65.71%•Hu=2%,CEC=2×350/100=7cmol(+)/kg——有机质•粘粒矿物CEC=35-7=28cmol(+)/kg•若为单一矿物，则：CEC=28·100/25=112cmol(+)/kg——蒙脱石一土壤酸度的存在形式和相互关系(Formsandtheirrelationshipofsoilacidities)1活性酸度：土壤溶液中游离的H+活度Activeacidity—theactivityofhydrogenionintheaqueousphaseofasoil.2潜性酸度：土壤胶体上吸附的交换性H+，Al3+所显示的酸度Potentialacidity—theactivitydisplayedbyexchangeableH+andAl3+thatwereabsorbedonsoilcolloid.第一节土壤酸度Section1Soilacidity3总酸度(Totalacidity)：活性酸与潜性酸的总和活性酸与潜性酸的关系：(1)处于相互转化的动态平衡(2)潜性酸远大于活性酸(3)土壤酸度的根本来源(起源)—活性酸H+Al3+≒H+,Al3+二土壤酸度产生的原因(一)活性酸1土壤生物活动产生H+(1)生物呼吸放出CO2+H2O—H2CO3—H++HCO3-(2)有机质分解产生有机酸(3)土壤中的的铵盐和硫化物在特殊微生物(如:硝化细菌,硫化细菌)的作用下转化成酸(HNO3,H2SO4)2大气，土壤空气中的CO23吸附态H+，Al3+通过解离和水解变成活性酸4土壤中H2O的解离(二)潜性酸1吸附态，结合态以及官能团上H+的解离和交换2吸附态Al3+(1)吸附态Al3+的产生—氢铝转化过程(土壤胶体上吸附态H+减少而Al3+增加的现象)只有Al3+粘土，没有H+粘土Al+Ca2+Ca+Al3+Oncethealuminumenterthesoilsolutionitreactswithwatertoformhydroxyaluminumcompoundsandfreehydrogenions.Al3++H2OAl(OH)≒2++H+Al(OH)2++H2OAl(OH)≒2++H+Al(OH)2++H2OAl(OH)≒3+H+(2)吸附态Al3+产生酸的机制思考:1红壤用酸不断淋洗,最后得到什么胶体?2南方强酸性土与弱酸性土通过Al3+产生酸度的机理是否相同?为什么?Themainsourcesofnetacidinputsareasfollows:•ThedissolutionofCO2inthesoilwatertoformcarbonicacidwhichdissociatesaccordingtoCO2+H2OH2CO3H++HCO3-H++CO32-•Theaccumulationandhumificationofsoilorganicmatter,producinghumicresidueswithahighdensityofcarboxylandphenolicgroups(羧基和酚基)thatdissociateH+ions.•InputsofH2SO4,HNO3and(NH4)2SO4fromtheatmosphereor‘acidrain’.•Insoilsformedonmarinemuds(海相沉积),orcoal-bearingsedimentaryrocks（碳基沉积岩）,theoxidationofironpyrites（黄铁矿）FeS2givesrisetoacidsulphate（硫酸盐）soils.•NitrificationofNH4+ions,producingH+ions,andNO3-whichissusceptible(易受影响的)toleaching.RemovalofCa2+andMg2+PlantandanimalresiduesATMOSPHERESOILAtmosphericinputsOfacidityWetanddrydepositionH+insolutionBiomassactivity-acidproductionMineralizationandnitrificationH+NO3RespirationH2CO3ProductionoforganicacidsAcidattackofsoilminerals-acidconsumptionH+H+SolutionAl3+,Ca2+,Mg2+,K+,H+e.g.Al(OH)3+3H+Al3++3H2OCaCO3+2H+Ca2++H2O+CO2Rootactivity-acidproductionCationandanionuptakeH+orOH-releaseRespirationH2CO3Exudatione.g.CitricacidLeachingCationexchange-acidstorageExchangeableCa2+Mg2+K+Al3+H+H+,Al3+Ca2+,Mg2+K+Solution+-+-ClayHumus-----LeachingIntogroundwaterAl3+Ca2+Mg2+K+H+Theprocessofsoilacidification叁土壤酸度的表示方法(Indicativemethodsofsoilacidity)(一)活性酸度—pH值：是土壤酸度的强度指标(Intensityindex)Activeacidity—duetotheH+an...
