Before getting into the main topic, we should know, at least, the definitions of the following four terms:

• Soil
• A soil
• Soil Profile
• Soil (land-)scape

Soil

Definition

Soil is "a natural body consisting of layers (or horizons) of mineral (and/or organic constituents) of variable thickness, which differ from the parent material in their morphological, physical, chemical, and mineralogical properties and their biological characteristics." (Soil Survey Manual, page 7)

As formulated by Jenny (1941): S = f (Cl,O,R,P,T), where

S = soil; f = function; Cl = climate; O = organism (flora and fauna); R = relief; P = Parent material (lithology); and T = time (age)

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Soil Survey Manual (Online)

A soil

Definition

A soil = “pedon” is the smallest volume with a surface extent which varies from about 1 to 10 m².
For mapping soils, similar pedons are grouped into polypedons, obviously with variability (depending on scale). (Soil Taxonomy, Chapter 1)

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A Soil

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Soil Taxonomy (The soils that we classify, Chapter 1; Online)

Soil Profile (USDA Soil Survey Manual, Page 60)

Soil Profile is a vertical sequence of recognizable horizons (pedologists use to distinguish from layer, which is used in geology and sedimentalogy) resulting from the development of a soil (pedogenic processes) over time. A hypothetical profile would comprise: organic horizons (H and O) and mineral (with some organic matter) horizons (A, E, B), and C (considered by some pedologists as a layer), and R (rock) layer. (USDA Soil Survey Manual , Page 117 and/ or in Guidelines for soil description fourth edition)

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Guidelines for soil description fourth edition (full text) (Online)

Figure 1.1 depicts a soil profile: about 1m width, 2m length (not visible in the figure), and 2m depth (visible in the figure). 2m depth is recommended for tropical soils, whereas 1.5m is sufficient in arid regions. The wall, where the tape is fixed on, is facing the sun and is used to describe the profile. The two stairs in opposite side, used to get into the pit, is not visible in Figure 1.1 (see also Figure 1.2 and also from the video for more examples).

Figure 1.1: Soil Profile (Example 1)

Figure 1.2 depicts a soil profile (in Kandy- Sri Lanka), more or less with the same dimensions as mentioned above. The lines on the wall facing the sun (profile head, where people are standing) are (sub-) horizon boundaries, traced by the soil surveyor. H, O, A, B, and C are the master horizons, and may be subdivided into subhorizons, for instance Bk1, Bk2 (see in the video about BK1 and BK2, in the section on the exhibited soil monoliths, with the description next to them.

Figure 1.2: Soil Profile (Example 2)

Figure 1.3 depicts a road cut (Aveiro, Portugal), a part of which has been cleaned to describe. Road cuts like this are very useful as they clearly show the lateral variability. However, one must be cautious to collect soil samples from such cuts as they may not be chemically representative.

Figure 1.3: Soil Profile (Example 3 Once the wall is cleaned [sub-] horizons are decided on and marked by drawing lines )

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Determine (sub-) horizons in a Soil Profile (USDA Soil Survey Manual, Page 133)

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also in Pedosphere -Soil Textbook (Online, Page 89) )

Soil (land-)scape

The term Soil (land-)scape is used to imply the relationships between geology, geomorphology and soil geography-the study subjects of geopedology, as a discipline. Geopedologists model geologic-geomorpho-pedologic relationships to identify, classify and map soils (see also in USDA Soil Survey Manual, Page 9).

Figure 1.4: Soil (land-) scape

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Landscape Model

During the video, the questions were asked:

• How can we decide on the texture class of a stratified soil profile (vertical variability)?
• How to come to the texture variation in a piece of land (someone’s property), if we do not have a large scale soil map?

You will find the discussion about these questions in the section Soil Interpretation.