Soil Science
Chapter 4. Soil architecture and physical properties (*: important concept)
Zueng-Sang Chen (陳尊賢)
Tel: 2369-8349, soilchen@ccms.ntu.edu.tw; http://Lab.ac.ntu.edu.tw/soilsc/
Printed on Sep. 15, 2004
4.1 Soil color
 Munsell color chart (Hue, value, and chroma, eg. 7.5YR 4/6, plae 22 after p112)
 Three major factor influences the soil color
 *Interpreting of soil color on: pedogenic degree, time, horizon, and hydration.
4.2 Soil texture
 Soil particle classification by IUSS and USDA (Fig 4.1, p123)
4.3 Soil texture classes*
 Soil texture classes: 12 classes (Fig 4.6, p129, Table 4.2, p128)
 Determined by feeling (Box 4.2, p130)
 Determined by pipette method and hydrometer (Fig 4.8, p131)
 Stokes’ Law V=Kd2 (Box 4.3, p132)
4.4 Soil structure of mineral soils
 *7 types of soil structure (Fig 4-10, p134): granular, crumb, plate, angular, subangular, columnar, prismatic.
4.5 Soil density
 *Particle density (Pd): 2.75 Mg/m3
 *Bulk density (Bd): 0.9-1.3 Mg/m3 depend on soil groups (Fig 4.12, p137, Fig 4.14, p138)
 Soil management and human activity influence on the soil bulk density
4.6 Pore space of mineral soils
 *Porosity (p%) = (1-(Bd/Pd)) x 100%
 Macropore and micropore classes and their function (Table 4.5, p149)
 Packing pore, interped pore, and biopore (Fig 4.25, p150); pore distribution of soil pedon (Fig 4.26,
p151)
4.7 Formation of soil aggregate
 Hierarchical organization of soil aggregates (Fig 4.28, p154)
 **Flocculation by calcium ions, dispersion by sodium ion
4.8 Tillage and structural management of soil
 *Conventional tillage system (Fig 4.35, p162) and conservation tillage system (Fig 4.36, p163)
 Soil crusting
 Soil conditioners: gypsum, organic polymers, and various humic substances. (p164)
4.9 Soil properties related to engineering uses
 *Soil consistency (loose, soft, hard in dry condition, and loose, friable, and firm in moist to wet
condition, Table 4.9, p166)
 expanding soils in Vertisols: swelling and shrinkage, crack, and wedge-shape soil structure (Fig 4.43, p
170)
 *Atterberg limit (shrinkage, plastic, and liquid limit) and COLE value (Fig 4.44, p171)
Discussion:
1. The meaning of soil color on soil formation and soil characteristics.
2. What’s difference on the bulk density of Andisols, Histosols, and Vertisols? (p138)
3. Compare the differences on the advantages and disadvantages between sandy loam soil and clay loam
soil.
4. What was the changes in pore size distribution and porosity for soil surface 20 cm depth caused by the
forest timber harvesting or mechanical tillage on rural soils?
5. How to improve your soil structure in your home garden?
6. Please explain the plastic and stick characteristics of clayey soil.
7. Compare the sand% and silt % in two soil texture classes, sandy clay loam and silty clay loam.