Section 1 Soil three phases Constitution 一、 Soil density and bulk density （一） Soil density ( or Particle density) Soil density is the density of the solid soil particles only; themeasurement does not include water weight or pore (air) space. Thedominant soil minerals- quartz, feldspars, micas, and clay minerals-average approximately 2.65 g/cm3, the “standard” value used incalculations if particle density is not measured. Individual minerals have densities from 2.0 g/cm3 for bauxite(aluminum ore) to 5.3 for hematite (iron ore) or 7.6 for galena (leadore).
（二） Soil bulk density 1. Bulk density, the density for a volume of soil as it existsnaturally, includes any air space and organic materials in thesoil volume. ρb = (mass of dry soil)/(total volume of soil) = Ms/Vt = Ms/(Vs + Vw +Va) A recently cultivated topsoil is likely to have a bulk density in the range from 0.9 to 1.2 g/cm3, while a compact subsoil may have a bulk density of 1.6 g/cm3 or even more.
Uses of soil bulk density ： ①To calculate soil porosity(p0): P0 = 1- (Bulk density/soil density) ② To calculate soil weight ③ To calculate storage of soil compositions ④ To calculate total water storage capacity and irrigation (or drainage) quota.2. Bulk density in water = (soil mass over-dry)/(precipitation volume)3. Affect the factors of soil bulk density: Texture, structure, content of organic matter, and variousnature factors and anthropogenic factors.
二 . Soil three phases constitution and pore( 一 ) 、 Soil three phases constitution and porosity
1 、 Index three phases constitutionSolid phase (%) = （ solid volume /soil body volume) ×100Liquid phase (%) = （ liquid volume /soil body volume) ×100Gas phase (%) = （ air volume /soil body volume) ×100 2 、 Soil porosity: Soil porosity is the percentage of the volume of pores to the total volume of soil. Soil porosity ＝ 1 － Solid phase (%) = Liquid phase (%) + Gas phase (%)
3 、 Void ratio The void ratio is the ratio of the volume of pores to the volume of solids. Void ratio = (volume of pores)/(volume of solids)( 二 ) 、 Calculation of three phases constitution and porosity1. Solid ratioSolid ratio = （ bulk density /density ） = ρb/ ρp2. Liquid ratio (volumetric water content)θm = (mass of water /mass of dry soil) = MW/MS θv = (volume of water/ total volume of soil) = Vw/Vt = Vw/(Vs+Vw+Va) = θm × ρb
3. Gas phase ratioPorosity(P0) =1- solid phase ratio =1- bulk density /density ） = ρb / ρpGas phase ratio = porosity- volumetric water content = P0- θv4. Actual volume ratioSolid phase ratio ＝ actual volume ratio － volumetric watercontentGas phase ratio = 1 － actual volume ratioSoil three phases ratio ＝ solid phase ratio : volumetric water content : gas phase ratio( 三 ). Suitable soil three phases ratio ：Solid phase ratio is about 50% ，volumetric water content is 25% to 30% ， Gas phase ratio is 15% to 25%.
Section 2 Soil texture 一、 Soil particle and particle fraction (soil separates) ( 一 ) Types of soil particle ： • Mineral soil particle and organic soil particle • Single particle and compound particle •Primary particle and second particle ( 二 ) Soil particle fraction (soil separates) Natural soils are comprised of soil particles of varying sizes. The soil particle-size groups, called soil particle fraction (soil separates), are sands (the coarsest), silts, and clays (the smallest).
Particle Diameter Size• Soil particle diameters range over 4 orders of magnitude – Boulders – Sand – Silt – Clay
Kachinsky classification system of soil separates Physical sandy particle: 1 mm to 0.01 mm. Physical clay particle: < 0.01 mm
二、 Soil mechanical composition and texture ( 一） Soil mechanical composition （ 二） Soil texture 1.Concept: Soil texture-The relative proportions of the various soil separates in a soil. 2. Classification of soil texture
(1) International classification ： The textural triangle is used to determine the soil texturalname after the percentages of sand (2-0.02mm), silt (0.02-0.002mm), and clay (<0.002 mm) are determined from a laboratoryanalysis. The main criterion of classification ：Clay <15% is sand and loamy groups; 15 ％－ 25 ％ is clay loam group; >25% is clay group.When soil contains silt >45% ， soil will be called “silty” ；When soil contains sand in 55%-85% ， called “sandy” ，When soil contains sand >85% ， called “ loamy sand”or “sand”.
The soil texture is divided by three main groups--sand, silt, and clay in our country. Sandy soil Loamy soil Clayed soil
三、 The fertility characteristics, utilize and improves of differentsoil textures ( 一 )The fertility characteristics of different soil 1. Sand textures• < 2 mm to > 0.02 mm• Visible without microscope• Rounded or angular in shape• Sand grains usually quartz if sand looks white or many minerals if sand looks brown,• Some sands in soil will be brown, yellow, or red because of Fe and/or Al oxide coatings.
Sand• Feels gritty• Considered non- cohesive – does not stick together in a mass unless it is very wet.
Sand• Low specific surface area• Sand has less nutrients for plants than smaller particles• Voids between sand particles promote free drainage and entry of air• Holds little water and prone to drought
2. Clay• < 0.002 mm• Flat palettes or tiny flakes• Small clay particles are colloids – If suspended in water will not settle• Large surface area – spoonful = football field
Clay• Wet clay is very sticky and is plastic or it can be molded readily into a shape or rod.• Easily formed into long ribbons• Shrink and swell
Clay• Pores spaces are very small – Movement of water and air very slow• Water holding capacity – Tremendous capacity to adsorb water- not all available for plants.• Soil strength- shrink/swell affects buildings, roads and walls.• Chemical adsorption is large
3. Loam• < 0.02 mm to > 0.002 mm• Not visible without microscope• Quartz often dominant mineral in loam since other minerals have weathered away.
Loam• Does not feel gritty• Floury feel• Wet loam does not exhibit stickiness / plasticity / malleability
Loam• Smaller size allows rapid weathering of non quartz minerals• Smaller particles – retains more water for plants and have slower drainage than sand.• Easily washed away by flowing water – highly erosive.• Holds more plant nutrients than sand.
• Silt is responsible for silting over gravel beds in rivers that are needed by fish for spawning.
Loess Cliff in China• Silt if often left as a vertical face since in this condition the landscape is less prone to water erosion than if the area was graded to a slope.
( 二） Utilize and improves of different soil textures① Foreign soil methods Soil texture can be changed only bymixing with another soil with a differenttextural class in small quantities② Deep ploughing, deep turn overetc. Adding peat or compost to a mineral soil isnot considered changing the texture – since itonly adds organic matter not sand, silt orclay!!
Section 3 Soil Structure 一、 Soil structureness（一） Concept of soil structure Soil structure- The combination or arrangement ofprimary soil particles into secondary units or peds. Thesecondary units are characterized on the basis of size,shape, and grade (degree of distinctness).( 二 ) Classes and types of soil structureTypes of structure describe the ped shape with the termsgranular, crumb, platy, blocky, subangular blocky,prismatic, and columnar. Structure classes are the ped sizes such as very fine,fine, medium, coarse (or thick), and very coarse (orvery thick).
Bad structure ： platy, blocky, subangular blocky, prismatic, and columnar Good structure: Granular二 . The genesis of granular structure( 一 ) The formation process of granular structure1. Cohesion aggregation① Condense②Cohesion of inorganic matter③ Cementation and compound of organic matter④ Complex of organic-mineral⑤ Earthworms and other small animals
2. The process of incision and modelling① Root ② Wetting and drying cycle③ Alternate freezing and thawing ④ TillageThe arrangement of soil particle
( 二） Formation process ofsoil aggregates 单个土粒 团聚体微团粒
( 四 ) Significance of granular structure in soil fertility1. There are big and small pores in granular structure
2.Balance to water and air in soil3.Coordinated to keep and apply fertilizer4. Suitable tillage5. Had good plowed layer( 五 ) Management of soil structure1. Apply organic fertilizer2. Reasonable crop rotation3. Reasonable tillage, water management and soil reclamation4. Apply soil structure modifier5. The electric current reclamation of saline-alkali soil
2. Classification of porosity (Studied by yourself)3. Aeration porosity二 . The porosity model of granular structure (Studied by yourself)三 . Equivalent pore diameter (effective aperture)Aeration pores- Greater than 0.1 mm average diameter.Size of medium sands.Capillary pores- 0.1-0.03 mm average diameter. Size of siltparticles.Storage pores-Less than 0.03 mm average diameter. Size ofclay particles.