1、第四章土壤質地和結構第一節 土壤三相組成土壤三相組成n土壤是由固、液、氣三相構成的分散系，土壤是由固、液、氣三相構成的分散系，水、氣在土壤中的協調供應，對實現土水、氣在土壤中的協調供應，對實現土壤肥力起重要作用。壤肥力起重要作用。n土壤三相的體積比大體為：固相占土壤三相的體積比大體為：固相占50%，氣相加液相占氣相加液相占50%，二者處于動態變化，二者處于動態變化之中。之中。n土壤三相之間的關系十分復雜，用公式土壤三相之間的關系十分復雜，用公式表示為：表示為：1. Dry Bulk Density b (the ratio of the mass of dried soil to its to

2、tal volume including solids and pores together) nb =Ms/Vt = Ms/(Vs + Va + Vw)2. Porosity f f = Vf/Vt =(Va +Vw)/(Vs +Va + Vw)3. Void Ratio ene =(Va +Vw)/Vs = Vf/(Vt-Vf) generally, e varoes between 0.3 and 2.04.Soil Wetness. n a.Mass Wetness w w =Mw/Ms n b. Volume Wetness , =Vw/Vt = Vw/(Vs +Vf) n c. W

3、ater volume ratio w w =Vw/Vs n d. Degree of Saturation s s = Vw/Vf = Vw/(Va + Vw) 5. Air-Filled Porosity fa =Va/Vt =Va/(Va + Vs + Vw)Additional Interrelationsn(1) Relation between porosity and void ratio: n e = f/(1-f) f = e/(1 +e) n(2) Relation between volume wetness and degree of saturation: n = s

4、f s = /fn(3) Relation between porosity and bulk density:nf = (s - b )/s = 1 -s /b b = (1- f) s n(4) Relation between mass wetness and volume wetness:n = wb /w w = w /b nhere, w is the density of water (Mw/Vw), approximately equal to 1 g/cm3.n(5) Relation between volume wetness, fractional air conten

5、t, and degree of saturation:nfa = f - = f(1-s) = f -fa Volume Mass Relations Relations Va Air MaVf Vw Water Mw MtVt Vs Solids Ms 第二節 土壤結構nSoil structure is the shape that the soil takes based on its physical and chemical properties. Each individual unit of soil structure is called a ped. Take a samp

6、le of undisturbed soil in your hand (either from the pit or from the shovel or auger). Look closely at the soil in your hand and examine its structure. Possible choices of soil structure are: 粒狀結構nGranular: Resembles cookie crumbs and is usually less than 0.5 cm in diameter. Commonly found in surfac

7、e horizons where roots have been growing. 塊狀結構nBlocky: Irregular blocks that are usually 1.5 - 5.0 cm in diameter 柱狀結構nColumnar: Vertical columns of soil that have a salt cap at the top. Found in soils of arid climates. 片狀結構nPlaty: Thin, flat plates of soil that lie horizontally. Usually found in co

8、mpacted soil. 棱柱狀結構nPrismatic: Vertical columns of soil that might be a number of cm long. Usually found in lower horizons. 無結構nSingle Grained: Soil is broken into individual particles that do not stick together. Always accompanies a loose consistence. Commonly found in sandy soils. 大塊狀結構nMassive: S

9、oil has no visible structure, is hard to break apart and appears in very large clods. 粒狀結構（Granular ）塊狀結構（Blocky）n 棱柱狀結構（Prismatic）n 柱狀結構（Columnar） Columnar Columnar 大塊狀結構（Massive）片狀結構（Platy） 無結構（Single grained） 第三節 土壤質地n土壤質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量百分比。n土壤質地根據土粒的大小即粒級劃分，分為砂粒、粉粒和粘粒，進

10、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個質地名稱。The way a soil feels is The way a soil feels is called the soil texture.called the soil texture.Soil texture depends on the amount of each size of particle in the soil.nSand, silt, and clay are names that describe the size of individual particles in the soil.

11、nSand are the largest particles and they feel gritty.nSilt are medium sized, and they feel soft, silky or floury.nClay are the smallest sized particles, and they feel sticky and they are hard to squeeze.土壤機械組成Stokes Lawn式中：為土粒沉降速度s w為土粒密度和水的密度為水的粘滯系數g為重力加速度 r為土粒半徑球體在介質中作自由落體沉降時重力（F1）是自重F2與浮力Fa之差，F1=F2-Fa=F（粘滯阻力）4/3r3g（s-w）=6r 球體作勻速沉降時 S = Vt2w-29sgr w92-sSrtg 土壤機械組成的測定及質地名稱n根據上式，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地名稱。Relative Size Comparison of Soil Particles nPlate = SiltSilt(feels floury)(0.02 - 0.002 mm, ISSS） )