第四章土壤質(zhì)地和結構

第四章土壤質(zhì)地和結構第一節(jié)土壤三相組成土壤是由固、液、氣三相構成的分散系，水、氣在土壤中的協(xié)調(diào)供應，對實現(xiàn)土壤肥力起重要作用。土壤三相的體積比大體為：固相占50%，氣相加液相占50%，二者處于動態(tài)變化之中。土壤三相之間的關系十分復雜，用公式表示為：1.DryBulkDensity

ρb(theratioofthemassofdriedsoiltoitstotalvolumeincludingsolidsandporestogether)ρb=Ms/Vt=Ms/(Vs+Va+Vw)2.Porosityff=Vf/Vt=(Va+Vw)/(Vs+Va+Vw)3.VoidRatioee=(Va+Vw)/Vs=Vf/(Vt-Vf)generally,evaroesbetween0.3and2.04.SoilWetness.a.MassWetnessww=Mw/Msb.VolumeWetnessθ,θ=Vw/Vt=Vw/(Vs+Vf)

c.Watervolumeratioυw

υw=Vw/Vsd.DegreeofSaturationss=Vw/Vf=Vw/(Va+Vw)5.Air-FilledPorosity

fa

=Va/Vt=Va/(Va+Vs+Vw)AdditionalInterrelations

(1)Relationbetweenporosityandvoidratio:e=f/(1-f)f=e/(1+e)(2)Relationbetweenvolumewetnessanddegreeofsaturation:

θ=sfs=θ/f(3)Relationbetweenporosityandbulkdensity:f=(ρs-ρb)/ρs=1-ρs/ρbρb=(1-f)ρs

(4)Relationbetweenmasswetnessandvolumewetness:θ=wρb/ρww=θρw/ρb

here,ρwisthedensityofwater(Mw/Vw),approximatelyequalto1g/cm3.(5)Relationbetweenvolumewetness,fractionalaircontent,anddegreeofsaturation:fa=f-θ=f(1-s)θ=f-fa

VolumeMassRelationsRelations

Va

Air

MaVf

Vw

Water

Mw

MtVt

Vs

Solids

Ms

第二節(jié)土壤結構Soilstructureistheshapethatthesoiltakesbasedonitsphysicalandchemicalproperties.Eachindividualunitofsoilstructureiscalledaped.Takeasampleofundisturbedsoilinyourhand(eitherfromthepitorfromtheshovelorauger).Lookcloselyatthesoilinyourhandandexamineitsstructure.Possiblechoicesofsoilstructureare:粒狀結構Granular:Resemblescookiecrumbsandisusuallylessthan0.5cmindiameter.Commonlyfoundinsurfacehorizonswhererootshavebeengrowing.塊狀結構Blocky:

Irregularblocksthatareusually1.5-5.0cmindiameter

柱狀結構Columnar:

Verticalcolumnsofsoilthathaveasalt"cap"atthetop.Foundinsoilsofaridclimates.片狀結構Platy:Thin,flatplatesofsoilthatliehorizontally.Usuallyfoundincompactedsoil.

棱柱狀結構Prismatic:

Verticalcolumnsofsoilthatmightbeanumberofcmlong.Usuallyfoundinlowerhorizons.

無結構SingleGrained:Soilisbrokenintoindividualparticlesthatdonotsticktogether.Alwaysaccompaniesalooseconsistence.Commonlyfoundinsandysoils.

大塊狀結構Massive:

Soilhasnovisiblestructure,ishardtobreakapartandappearsinverylargeclods.粒狀結構（Granular）塊狀結構（Blocky）

棱柱狀結構（Prismatic）

柱狀結構（Columnar）

Columnar

Columnar

大塊狀結構（Massive）片狀結構（Platy）

無結構（Singlegrained）

第三節(jié)土壤質(zhì)地土壤質(zhì)地指人對于土壤粗細程度的感覺，有時也用機械組成表示，即指土壤中各粒級的土粒所占的質(zhì)量百分比。土壤質(zhì)地根據(jù)土粒的大小即粒級劃分，分為砂粒、粉粒和粘粒，進一步分為砂土組、壤土組、粘土組，及砂土、砂壤、輕壤、中壤、重壤、粘土6個質(zhì)地名稱。Thewayasoil"feels"iscalledthesoiltexture.Soiltexturedependsontheamountofeachsizeofparticleinthesoil.Sand,silt,andclayarenamesthatdescribethesizeofindividualparticlesinthesoil.Sandarethelargestparticlesandtheyfeel"gritty."Siltaremediumsized,andtheyfeelsoft,silkyor"floury."Clayarethesmallestsizedparticles,andtheyfeel"sticky"andtheyarehardtosqueeze.土壤機械組成——StokesLaw式中：υ為土粒沉降速度ρsρw為土粒密度和水的密度η為水的粘滯系數(shù)g為重力加速度r為土粒半徑球體在介質(zhì)中作自由落體沉降時重力（F1）是自重F2與浮力Fa之差，F(xiàn)1=F2-Fa=F（粘滯阻力）4/3πr3g（ρs-ρw）=6πrηυ

球體作勻速沉降時S=Vt土壤機械組成的測定及質(zhì)地名稱根據(jù)上式，測定已知直徑的土壤顆粒沉降于某一定點的深度，計算出所需時間，用吸管法或比重計法，測定出該粒級土粒的重量及百分含量，由下面的三角圖給出質(zhì)地名稱。RelativeSizeComparisonofSoilParticles

Plate=Silt

(feelsfloury)(0.02-0.