| The availability of trace elements in soils has become a focus in the fields of agricultural and environmental sciences. Fertilization is an important way for trace elements to enter the soils. Clarifying and revealing the relationship between fertilization and the availability of trace elements in soils can provide scientific reference for agricultural practice. In this paper, the contents, fractions, distribution characteristics and changes of trace elements in soils under long-term fertilization were studied, the factors affecting the availability of trace elements in soils were analyzed, and the mechanism of the changes was explored. The main conclusions were as follows:(1)The soil pH value and Ca CO3 content were decreased after long-term crop planting and fertilization, while the content of soil organic matter was increased. The largest decrease of soil pH value was observed at 0-15 cm depth in the continuous alfalfa cropping system, which was decreased by 0.44 pH units compared with the fallow soil in 2015. In the crop-legume rotation cropping system, soil Ca CO3 content was reduced by 48% compared with that in 2002 at 0-15 cm depth. Soil organic matter accumulated significantly in the alfalfa continuous cropping system, and it was increased by 134.9% at 0-15 cm depth compared with the fallow soil. Fertilization increased the available P content in soils, compared with the no-fertilizer control, the application of N and P fertilizers and manure resulted in 34.3 times and 11.69 times increase in the crop-legume rotation cropping system at 0-15 cm and 15-30 cm depths, respectively. The ratio of humic acid and fulvic acid in soils was more than 1 under continuous fertilization. The application of manure increased soil total reducing substance, the crop-legume rotation cropping system had a 107.14% increase under the application of N and P fertilizers and manure at 0-15 cm depth compared with the no-fertilizer control.(2)Soil available Cu and Fe contents were increased by crop planting and fertilization for many years. Fertilization could improve the available Mn content. The alfalfa, wheat continuouscroppingsystemandtheapplicationofmanurecouldsignificantlyimprovetheavailablezncontent.thelargestincreasesoftheavailablecu,mncontentsat0-15cmdepthinsoilswererespectivelyinthewheatcontinuouscroppingsystemundertheapplicationofmanure(0.69mgkg-1),thecrop-legumerotationcroppingsystemundertheapplicationofnandpfertilizersandmanure(58.91%)in2015comparedwiththatin2002.thealfalfacontinuouscroppingsystemmadesoilavailableznandfecontentsincreaseby1.95timesand2.05timesthanthatin2002at0-15 cmdepth.(3)themainfractionoftraceelementsinsoilswasmineral-bound,oxide-boundmnalsohadthelargerproportion.comparedto2015and2002,thechangesoftheproportionsofcu,zn,fefracionswerenotobvious,whilethechangeofmnfractionswaslarger,theproportionsofmineral-bound,exchangeablemnincreased,andtheproportionsofcarbonate-,oxide-,organicmatter-boundmndecreased.(4)theactivationofznandcuinsoilswasverysmallthroughlong-termcropplantingandfertilization,butthecontentsofexchangeablemnandfewereincreased.exchangeablemnwasincreasedsignificantlyinthealfalfacontinuouscroppingsystemat0-15cmdepthin2015,whichwas8.03 timeslargerthanthatinthefallowsoil.theapplicationofnandpfertilizersandmanureincreasedconsiderablyexchangeablefemorethantheno-fertilizercontrolinthecrop-legumerotationcroppingsystemat0-15 cmdepth,andtheincreasewas84.36%.thecontentsofcuandznfractionswereincreasedwiththeincreaseofcropplantingandfertilizationyears,butthemineral-boundcuwasincreasedonlywhenthechemicalfertilizerwasapplied.thecarbonate-,oxide-,organicmatter-boundcuwereincreasedconsiderablyinthewheatcontinuouscroppingsystemundertheapplicationofmanureat0-15 cmdepth,whichwereincreasedby2.01mgkg-1,1.7mgkg-1,3.54mgkg-1comparedwiththatin2002,respectively.thealfalfacontinuouscroppingsystemincreasedsoiloxide-boundznat0-15 cmdepth,theincreasewas94.26%comparedwiththatin2002.cropplantingonlyreducedcarbonate-boundmncontent.carbonate-boundmncontentreducedmorethanthatin2002inthealfalfacroppingsystemat0-15cmand15-30 cmdepths,whichweredecreasedby59.95mgkg-1and35.65mgkg-1respectively.thewheatcontinuouscroppingsystemincreasedorganicmatter-boundmnsignificantlyat15-30cmdepth;theincreasewas2.63 timescomparedwiththefallowsoil.thedifferentfractionsoffeinsoilswereincreasedinthewheatcontinuouscroppingsystem.carbonate-boundfewereincreasedby114.52%and183.69%,organicmatter-boundfewereincreasedby1.08timesand3.3timesrespectivelyat0-15cmand15-30cmdepthscomparedwiththatin2002 undernofertilizer.fertilizationalmostdecreasedthecontentsofdifferentmnandfefractions.thecrop-legumerotationcroppingsystemsignificantlyincreasedorganicmatter-boundmn,andtheincreasewas8.2timescomparedwiththeno-fertilizercontrol.(5)soilphvaluehadsignificantnegativecorrelationwiththeavailablecu,mn,zn,feunderlong-termcropplantingandfertilization,theavailablep,humicacid,fulvicacidwereopposite.soilorganicmatter,totalreducingsubstancesignificantlynegativelyrelatedwiththeavailablecu,andtheavailablemn,znandfewereonthecontrary.soilmoisturepositivelyrelatedwiththeavailablecuandzn,butithadnegativecorrelationwiththeavailablemnandfe.thehighestdirectpathcoefficientswithdtpa-cu,mn,znandfeinsoilsweresoilmoisture(0.781),humicacid(0.652),organicmatter(0.895)andorganicmatter(0.83),respectively.thehighernegativedirectpathcoefficientswithdtpa-cu,mnandfeweretotalreducingsubstance(-0.509),fulvicacid(-0.595),caco3(-0.501).(6)exchangeablecu,mnandfepositivelycorrelatedwiththeavailablecu,mnandfe,andthedirectpathcoefficientswerethehighest,whichwere0.829,0.445and0.122,respectively,thereforeexchangeablefractionwasthedirectandmajorsourceoftheavailablecu,mnandfeinsoils.carbonate-boundcuhadthepositivecorrelationwiththeavailablecu,andtheindirectpathcoefficientbetweencarbonate-boundcuandexchangeablecuwaslargest(0.479),whichindicatedthatitcouldincreasethecontentoftheavailablecuinsoilsbythetransformationtoexchangeablecu.thedirectpathcoefficientbetweenmineral-boundcuandexchangeablecuwas0.571;itshowedthatmineral-boundcucouldberegardedastherepositoryoftheavailablecuinsoils.thecorrelationcoefficients,directpathcoefficientsbetweencarbonate-bound,organicmatter-boundandtheavailablemn,znandfewerepositive,whichindicatedthatthesetwofractionswerethesourceoftheavailablemn,znandfeinsoils.oxide-boundznwassignificantlypositivelycorrelatedwiththeavailablezn,anditwasalsoanavailablesourceofzincinsoils.(7)thelong-termapplicationofmicroelementfertilizercouldincreasethesoilorganicmatter,totalreducingsubstance,theincreaseswerethelargestundertheapplicationofcufertilizerinsurfacesoilsin2015,whichwere25%and24.74%respectively.theapplicationofmicroelementfertilizermadesoilavailablep,caco3,humicacidandfulvicacidcontentsalmostdecrease.thecontentsofcaco3at0-15cmand15-30 cmdepthsweredecreasedsignificantly,andthedecreaseswere32.35%and41.25%respectivelycomparedwiththecontrol.theapplicationofznfertilizerresultedintheavailablepthelargestdecreaseinthesufacesoil,thedecreasewas55%.theratioofhumicacidandfulvicacidwaslessthan1 aftertheapplicationofmicroelementfertilizer.humicacidcontentwasreducedmostundertheapplicationofmnfertilizerinthesurfacesoil,andthedeclinewas77.87%.thebiggestincreaseoffulvicacidcontentwasfoundat15-30 cmdepthundertheapplicationofznfertilizer,theincreasewas2.27 timescomparedwiththecontrol.thecontentsoftotalcu,znandtheavailablecu,zninsoilswereincreasedsignificantlyafterlong-termapplicationofmicroelementfertilizer;thephenomenonofsurfaceaccumulationwasobvious.thecontentsoftotalcu,znwereincreasedby131.82%and108.71%,theavailablecu,znwereincreasedby6.03timesand6.97timesinthesurfacesoilcomparewiththecontrolin2015.thechangesofsoiltotalmn,theavailablemnwerenotobvious.comparedto2015and2001,theincreaseoftotalmnwaslessthan12%.comparedwiththecontrol,theavailablemnat30-45 cmdepthwasincreasedmost,theincreasewas26.54%in2015,andtheincreasesofothersoildepthswerelessthan6%.theproportionofexchangeablecu,zninthetotalcu,znhadasignificantincreaseaftertheapplicationofmicroelementfertilizer,whilethechangeoftheproportionofdifferentmnfractionsintotalmnwasnotobvious.thecontentsofcu,mn,znfractionswereincreasedwiththeincreaseoffertilizationage,especiallyinthesurfacesoil,butthemineral-boundmnwasopposite.theoxide-,carbonate-boundcuhadalargerincreaseinthesurfacesoil,whichwere23.46timesand16.35 timeshigherthanthatinthecontrolsoils.soilpropertieshadnoobviouscorrelationwiththeavailablecu,mn,zn,whilehadsomeinfluencesonthefractionsoftraceelement:humicacidwassignificantlynegativelycorrelatedwithothercufractionsinadditiontoexchangeablecuandorganicmatter-boundmn;fulvicacidhadasignificantpositivecorrelationwithoxide-boundzn.therewasasignificantpositivecorrelationbetweentheavailablecuandcarbonate-,oxide-andorganicmatter-boundcu,thelargestloadofthesecondprincipalcomponentwasexchangeablecu,thusthesefourfractionswerethesourceofsoilavailablecu.theavailablemnwassignificantlypositivelycorrelatedwithexchangeablemn;theloadsofoxide-andtheorganicmatter-boundmnwerelargerinthefirstprincipalcomponent,whichindicatedthatthesethreefractionswerecloselyrelatedtotheavailablemninsoils.theavailableznhadsignificantpositivecorrelationwithexchangeable,oxide-andorganicmatter-boundzn;itshowedthatthesethreeznfractionshadgreatercontributiontotheavailablezn.(8)theinteractionsbetweenapplyingmicroelementfertilizerandsoilavailabletraceelementswereasfollows:znrestrainedcu,butcudidnotrestrainzn.mnwasbeneficialtocu,whilecurestrainedmn.znrestrainedmn,butmndidnotrestrainzn.mnfertilizerwasconducivetotheincreaseoftheavailablefeinsoils. 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