第四章土壤質(zhì)地和結(jié)構(gòu)第一節(jié)土壤三相組成土壤是由固、液、氣三相構(gòu)成的分散系，水、氣在土壤中的協(xié)調(diào)供應(yīng)，對(duì)實(shí)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(dòng)態(tài)變化之中。土壤三相之間的關(guān)系十分復(fù)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(jié)構(gòu)Soilstructureistheshapethatthesoiltakesbasedonitsphysicalandchemicalproperties.Eachindividualunitofsoilstructureiscalledaped.Takeasampleofundisturbedsoilinyourhand(eitherfromthepitorfromtheshovelorauger).Lookcloselyatthesoilinyourhandandexamineitsstructure.Possiblechoicesofsoilstructureare:粒狀結(jié)構(gòu)Granular:Resemblescookiecrumbsandisusuallylessthan0.5cmindiameter.Commonlyfoundinsurfacehorizonswhererootshavebeengrowing.塊狀結(jié)構(gòu)Blocky:

Irregularblocksthatareusually1.5-5.0cmindiameter

柱狀結(jié)構(gòu)Columnar:

Verticalcolumnsofsoilthathaveasalt"cap"atthetop.Foundinsoilsofaridclimates.片狀結(jié)構(gòu)Platy:Thin,flatplatesofsoilthatliehorizontally.Usuallyfoundincompactedsoil.

棱柱狀結(jié)構(gòu)Prismatic:

Verticalcolumnsofsoilthatmightbeanumberofcmlong.Usuallyfoundinlowerhorizons.

無(wú)結(jié)構(gòu)SingleGrained:Soilisbrokenintoindividualparticlesthatdonotsticktogether.Alwaysaccompaniesalooseconsistence.Commonlyfoundinsandysoils.

大塊狀結(jié)構(gòu)Massive:

Soilhasnovisiblestructure,ishardtobreakapartandappearsinverylargeclods.粒狀結(jié)構(gòu)（Granular）塊狀結(jié)構(gòu)（Blocky）

棱柱狀結(jié)構(gòu)（Prismatic）

柱狀結(jié)構(gòu)（Columnar）

Columnar

Columnar

大塊狀結(jié)構(gòu)（Massive）片狀結(jié)構(gòu)（Platy）

無(wú)結(jié)構(gòu)（Singlegrained）

第三節(jié)土壤質(zhì)地土壤質(zhì)地指人對(duì)于土壤粗細(xì)程度的感覺(jué)，有時(shí)也用機(jī)械組成表示，即指土壤中各粒級(jí)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(jí)劃分，分為砂粒、粉粒和粘粒，進(jìn)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(gè)質(zhì)地名稱(chēng)。Thewayasoil"feels"iscalledthesoiltexture.Soiltexturedependsontheamountofeachsizeofparticleinthesoil.Sand,silt,andclayarenamesthatdescribethesizeofindividualparticlesinthesoil.Sandarethelargestparticlesandtheyfeel"gritty."Siltaremediumsized,andtheyfeelsoft,silkyor"floury."Clayarethesmallestsizedparticles,andtheyfeel"sticky"andtheyarehardtosqueeze.土壤機(jī)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(shí)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(shí)S=Vt土壤機(jī)械組成的測(cè)定及質(zhì)地名稱(chēng)根據(jù)上式，測(cè)定已知直徑的土壤顆粒沉降于某一定點(diǎn)的深度，計(jì)算出所需時(shí)間，用吸管法或比重計(jì)法，測(cè)定出該粒級(jí)土粒的重量及百分含量，由下面的三角圖給出質(zhì)地名稱(chēng)。RelativeSizeComparisonofSoilParticles

Plate=Silt

(feelsfloury)(0.02-0.