土壤质地和结构

1、第四章土壤质地和结构第一节 土壤三相组成土壤三相组成n土壤是由固、液、气三相构成的分散系，土壤是由固、液、气三相构成的分散系，水、气在土壤中的协调供应，对实现土水、气在土壤中的协调供应，对实现土壤肥力起重要作用。壤肥力起重要作用。n土壤三相的体积比大体为：固相占土壤三相的体积比大体为：固相占50%，气相加液相占气相加液相占50%，二者处于动态变化，二者处于动态变化之中。之中。n土壤三相之间的关系十分复杂，用公式土壤三相之间的关系十分复杂，用公式表示为：表示为：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 第二节 土壤结构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: 粒状结构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. 块状结构nBlocky: Irregular blocks that are usually 1.5 - 5.0 cm in diameter 柱状结构nColumnar: Vertical columns of soil that have a salt cap at the top. Found in soils of arid climates. 片状结构nPlaty: Thin, flat plates of soil that lie horizontally. Usually found in co

8、mpacted soil. 棱柱状结构nPrismatic: Vertical columns of soil that might be a number of cm long. Usually found in lower horizons. 无结构nSingle Grained: Soil is broken into individual particles that do not stick together. Always accompanies a loose consistence. Commonly found in sandy soils. 大块状结构nMassive: S

9、oil has no visible structure, is hard to break apart and appears in very large clods. 粒状结构（Granular ）块状结构（Blocky）n 棱柱状结构（Prismatic）n 柱状结构（Columnar） Columnar Columnar 大块状结构（Massive）片状结构（Platy） 无结构（Single grained） 第三节 土壤质地n土壤质地指人对于土壤粗细程度的感觉，有时也用机械组成表示，即指土壤中各粒级的土粒所占的质量百分比。n土壤质地根据土粒的大小即粒级划分，分为砂粒、粉粒和粘粒，进

10、一步分为砂土组、壤土组、粘土组，及砂土、砂壤、轻壤、中壤、重壤、粘土6个质地名称。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.土壤机械组成Stokes Lawn式中：为土粒沉降速度s w为土粒密度和水的密度为水的粘滞系数g为重力加速度 r为土粒半径球体在介质中作自由落体沉降时重力（F1）是自重F2与浮力Fa之差，F1=F2-Fa=F（粘滞阻力）4/3r3g（s-w）=6r 球体作匀速沉降时 S = Vt2w-29sgr w92-sSrtg 土壤机械组成的测定及质地名称n根据上式，测定已知直径的土壤颗粒沉降于某一定点的深度，计算出所需时间，用吸管法或比重计法，测定出该粒级土粒的重量及百分含量，由下面的三角图给出质地名称。Relative Size Comparison of Soil Particles nPlate = SiltSilt(feels floury)(0.02 - 0.002 mm, ISSS） )