第四章土壤质地和结构素材.ppt

第四章 土壤质地和结构 第一节 土壤三相组成 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，对实现土壤肥力起重要作用。 土壤三相的体积比大体为：固相占50%，气相加液相占50%，二者处于动态变化之中。 土壤三相之间的关系十分复杂，用公式表示为： Additional Interrelations (1) Relation between porosity and void ratio: e = f/(1-f) f = e/(1 +e) (2) Relation between volume wetness and degree of saturation: θ = sf s = θ/f (3) Relation between porosity and bulk density: f = (ρs - ρb )/ρs = 1 -ρs /ρb ρb = (1- f) ρs (4) Relation between mass wetness and volume wetness: θ = wρb /ρw w = θρw /ρb here, ρw is the density of water (Mw/Vw), approximately equal to 1 g/cm3. (5) Relation between volume wetness, fractional air content, and degree of saturation: fa = f -θ = f(1-s) θ = f -fa 第二节 土壤结构 Soil 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 sample 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 Granular: Resembles cookie crumbs and is usually less than 0.5 cm in diameter. Commonly found in surface horizons where roots have been growing. 块状结构 Blocky: Irregular blocks that are usually 1.5 - 5.0 cm in diameter 柱状结构 Columnar: Vertical columns of soil that have a salt cap at the top. Found in soils of arid climates. 片状结构 Platy: Thin, flat plates of soil that lie horizontally. Usually found in compacted soil. 棱柱状结构 Prismatic: Vertical columns of soil that might be a number of cm long. Usually found in lower horizons. 无结构 Single 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 Massive: Soil 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） 棱柱状结构（Prismatic） 柱状结构（Columna