1. Soils Rumi’s Seven Advices: “In modesty and humility, be like the soil

2. Soils Definition Pedogenesis-factors Classification/Taxonomy
Texture
texture triangle
Phi scale
Stoniness
Structure
Color-Munsell color pH
phosphates
Study of profiles
Sampling
Grain size distribution

3. Definition of Soil
soil - (i) The unconsolidated mineral or organic material on the immediate surface of the Earth that serves as a natural medium for the growth of land plants. (ii) The unconsolidated mineral or organic matter on the surface of the Earth that has been subjected to and shows effects of genetic and environmental factors of: climate (including water and temperature effects), and macro- and microorganisms, conditioned by relief, acting on parent material over a period of time. A product-soil differs from the material from which it is derived in many physical, chemical, biological, and morphological properties and characteristics. (Soil Science Society of America, Soil Science Glossary)
“Soil consists of the horizons near the earth’s surface that, in contrast to the underlying parent material, have been altered by the interactions of climate, relief, and living organisms over time.” (from Soil Taxonomy, USDA)
Note: Soil usually must have biological activity

4. Pedogenesis
Soils evolve naturally through a process called pedogenesis.
The five main factors the influence soil evolution and development are:
Time
Parent material
Climate
Relief and topography (geomorphology)
Flora and fauna
These factors in combination lead to the characteristics of the many individual soil types we observe in nature
Note that the first three are the same that influence geomorphology
Soils and landforms are very closely correlated
The concepts of soil associations and catenas help describe the relationships between geomorphology and soils

5. Soil Taxonomy
Soil scientists have developed taxonomies to help describe and analyze the variations and similarities among soil types
Many classifications
Mostly national, but also indigenous ones
USDA Classification
A hierarchical taxonomy with multiple levels
Order, Suborder, Great group, Subgroup, Family, series
County soil surveys focus on lower levels
FAO—Food and Agriculture Organization of the United Nations
Attempt at a world-wide classification

6. USDA Soil Taxonomy
Alfisols — moderately weathered, form under boreal or broadleaf forests, rich in iron and aluminum
Andisols — form in volcanic ash and defined as containing high proportions of glass and amorphous colloidal materials, including allophane, imogolite and ferrihydrite
Aridisols — (from the Latin aridus, for “dry”) form in an arid or semiarid climate
Entisols — do not show any "significant" soil profile development. Minimal soil horizons.
Gelisols — soils of very cold climates which are defined as containing permafrost within two meters of the soil surface
Histosols — consist primarily of organic materials
Inceptisols — form quickly through alteration of parent material
Mollisols — form in semiarid to semihumid areas, typically under a grassland cover
Oxisols — best known for their occurrence in tropical rain forest
Spodosols — typical soils of coniferous or boreal forests
Ultisols — commonly known as red clay soils
Vertisols — high content of expansive clay

7. Soil Catena

8. Soil horizons
Soil horizons develop over time as a result of the biological, chemical, and physical changes that affect soils
They are not necessarily depositional units
They are developmental units the evolve over time
There is a pretty standard sequence of major units:
A, B, C or sometimes
A, E, B, C, R
Major units can have subtypes

9. Soil horizons—Alfisols moderately weathered, form under boreal or broadleaf forests, rich in iron and aluminum

10. Soil Horizons

11. Soil Horizons

12. Basic Master Soil Horizons
Subordinate distinctions
Basic Master Soil Horizons O A E
E/B AC B BC C R
a Highly decomposed organic matter
b Buried soil horizon
c Concretions or nodules
e Intermediately decomposed organic matter
f Frozen soil
g Strong gleying
h Illuvial accumulation of organic matter
k Accumulation of carbonates
m Strong cementation
n Accumulation of sodium
o Residual accumulation of sesquioxides
p Plowing or other disturbance
q Accumulation of silica
r Weathered or soft bedrock
s Illuvial accumulation of sesquioxides
t Accumulation of clay
v Plinthite
w Color or structural B
x Frangipan character
y Accumulation of gypsum
z Accumulation of salts

13. Figure 2. Peoria loess at study site, showing 39 soil horizons.
Wang H et al. Geology 2000;28:
Figure 2. Peoria loess at study site, showing 39 soil horizons. Horizon 1 is modern Bt, and 2 to 39 are buried soil horizons, in which 36 to 39 (inset) are from a trench. Meter labels (white squares) indicate 12 m exposure above ground and 2 m exposure in trench. 14C ages obtained from corresponding soil horizons were used for 14C age-depth model.
©2000 by Geological Society of America

14. Soil Texture
Soil texture can be estimated in the field by observing its physical characteristics.
A sandy soil feels gritty and falls apart easily if formed into a ball when moist.
A loamy soil feels somewhat gritty, yet is easy to work; it has relatively even amounts of sand, silt, and clay; if formed into a ball when moist, it holds its shape, yet still breaks apart easily when squeezed.
A silty soil breaks apart easily and has a floury appearance when dry. When moist, silty soils have a slick feel and form no ribbon when pinched between fingers and thumb.
A clayey soil forms large, hard clods and cracks form on the surface. Clayey soils feel sticky and are bendable when moist. A ribbon can be formed when moist by pinching soil between fingers and thumb. A longer ribbon formed before it breaks indicates a higher amount of clay.

15. Texture: Particle size Wentworth and phi scales

16. Particle Sorting
This is about the statistical size distribution and can be studied mathematically

17. Rounding-Angularity

18. Sphericity-platyness (and rounding)

19. Sphericity

20. Field test for soil texture (simplified)

21. Soil Texture triangle

22. Soil Particle sizes Table 1. The Size of Sand, Silt and Clay Name
Particle Diameter
Clay
below millimeters
Silt
0.002 to 0.05 millimeters
Very fine sand Fine sand Medium sand Coarse sand Very coarse sand
0.05 to 0.10 millimeters 0.10 to 0.25 millimeters 0.25 to 0.5 millimeters 0.5 to 1.0 millimeters 1.0 to 2.0 millimeters
Gravel
2.0 to 75.0 millimeters
Rock
greater than 75.0 millimeters (~2")

23. Munsell Color system Hue, value, and chroma And the color name
Example:
2.5YR 5/4, reddish brown
Measure colors of mottles too