Chapter 4 Soil texture and structure
Chapter 4 Soil texture and structure
Section 1 Soil three phases Constitution Soil density and bulk density (- Soil density( or Particle density Soil density is the density of the solid soil particles only the measurement does not include water weight or pore(air) space. The dominant soil minerals-quartz, feldspars, micas, and clay minerals average approximately 2.65 g/cm, the"standard"value used in calculations if particle density is not measured Individual minerals have densities from 2.0 g/cm for bauxite (aluminum ore)to 5. 3 for hematite (iron ore)or 7. 6 for galena (lead ore
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; the measurement does not include water weight or pore (air) space. The dominant soil minerals- quartz, feldspars, micas, and clay mineralsaverage approximately 2.65 g/cm3 , the “standard” value used in calculations 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 (lead ore)
表4-1土壤中常见组分的密度(克/厘米3) 石英 260~268 赤铁矿 4.90~5.30 正长石 2.54~2.57 磁铁矿 5.03~5.18 斜长石 262~2 三水铝石 2.30~240 白云母 2.77~288 高岭石 261~268 黑云母 2.70~3.10 蒙皂石 2.53~2.74 角闪石 2.85~3.57 伊利石 260~290 辉石 3.15~3.90 纤铁矿 3.60~4.10 腐殖质 140~180 表4-2 种森林土壤表层各级土粒的密度 粒级(粒径毫米) 腐殖质(克/千克) 密度(克厘米3) 全土样 29.5 2.62 0.10~005 0 0.05~0.01 4.3 2.6 0.01~0.005 2.62 0.005~0.001 53.7 2.59 0.001 64.2 2.59
表 4－2 一种森林土壤表层各级土粒的密度 粒级（粒径毫米） 腐殖质（克/千克) 密度(克/厘米 3 ) 全土样 0.10～0.05 0.05～0.01 0.01～0.005 0.005～0.001 <0.001 29.5 0 4.3 14.8 53.7 64.2 2.62 2.66 2.66 2.62 2.59 2.59 表 4-1 土壤中常见组分的密度 (克/厘米 3 ) 石 英 正长石 斜长石 白云母 黑云母 角闪石 辉 石 纤铁矿 2.60～2.68 2.54～2.57 2.62～2.76 2.77～2.88 2.70～3.10 2.85～3.57 3.15～3.90 3.60～4.10 赤铁矿 磁铁矿 三水铝石 高岭石 蒙皂石 伊利石 腐殖质 4.90～5.30 5.03～5.18 2.30～2.40 2.61～2.68 2.53～2.74 2.60～2.90 1.40～1.80
(二) Soil bulk density 1. Bulk density, the density for a volume of soil as it exists naturally, includes any air space and organic materials in the sol volume. P=(mass of dry soil)/ (total volume of soil)=M /Vt -M/(VS+Vw+Va A recently cultivated topsoil is likely to have a bulk density in the range from 0.9 to 1.2 g/cm. while a compact subsoil may have a bulk density of 1.6 g/cm or even more
（二）Soil bulk density 1. Bulk density, the density for a volume of soil as it exists naturally, includes any air space and organic materials in the soil 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: OTo calculate soil porosity(po): Po=1- Bulk density/soil density 2 To calculate soil weight 3 To calculate storage of soil compositions 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 various nature factors and anthropogenic factors
Uses of soil bulk density： ①To calculate soil porosity(p0 ): 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 various nature factors and anthropogenic factors. P0 = 1- (Bulk density/soil density)
Soil three phases constitution and pore Soil three phases constitution and porosity 质量 体积 空气体积 空气质量=0 孔水体积 水的质量 度 土粒质量 体 积 固体体积
(一)、Soilthree phases constitution and porosity 二. Soil three phases constitution and pore
小孔隙 大孔隙
小孔隙 大孔隙
1, Index three phases constitution Solid phase(%)=(solid volume /soil body volume)X100 Liquid phase (%)=(liquid volume /soil body volume)X100 Gas phase( %)=(air volume /soil body volume)X 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(%0)+ Gas phase (%)
1、 Index three phases constitution Solid phase (%) =（solid volume /soil body volume) ×100 Liquid phase (%) =（liquid volume /soil body volume) ×100 Gas 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 ( Calculation of three phases constitution and porosity 1. Solid ratio Solid ratio =(bulk density /density)=Py pp 2. Liquid ratio (volumetric water content Am=(mass of water /mass of dry soil)=Mw/M Av=(volume of water/total volume of soil)=VwVt Vw(Vs+Vx+Va)=0n×pb
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 porosity 1. Solid ratio Solid ratio =（bulk density /density）= ρb / ρp 2. 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、Void ratio
3. Gas phase ratio Porosity(Po)=1-solid phase ratio=1-bulk density /density Gas phase ratio- porosity- volumetric water content= Po-A 4. Actual volume ratio Solid phase ratio= actual volume ratio- volumetric water content Gas phase ratio=1- actual volume ratio Soil three phases ratio solid phase ratio: volumetric water content: gas phase ratio C). 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%
3. Gas phase ratio Porosity(P0 ) =1- solid phase ratio =1- bulk density /density） = ρb / ρp Gas phase ratio = porosity- volumetric water content = P0 - θv 4. Actual volume ratio Solid phase ratio ＝ actual volume ratio－ volumetric water content Gas phase ratio = 1－ actual volume ratio Soil 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%