Agri Quiz: Soil Science: Soil Profile

Correct Answer: A vertical section of soil showing horizons
A soil profile is defined as a vertical section of the soil that exposes its different layers or horizons. It serves as a record of soil-forming processes.

Correct Answer: O horizon
The O horizon, consisting of organic matter, is the uppermost layer in undisturbed soils like forests. It is generally absent in regularly cultivated (arable) land.

Correct Answer: Maximum leaching (eluviation)
The A horizon, particularly the A2 or E horizon, is characterized as the zone where maximum leaching or washing out (eluviation) of materials like clay, iron, and aluminum oxides occurs. This process often results in a lighter color compared to horizons below.

Correct Answer: B horizon
The B horizon is the zone of illuviation, characterized by the accumulation ('washing in') of materials like silicate clays, iron (Fe), and aluminum (Al) oxides leached from the overlying A and E horizons. It often develops blocky or prismatic structures.

Correct Answer: Solum
The 'Solum' is considered the 'true soil' and encompasses the most weathered and biologically active layers. It specifically refers to the combination of the A and B horizons (or A + E + B).

Correct Answer: A + B + C horizons
Regolith refers to all the unconsolidated material overlying the solid bedrock. In terms of soil horizons, it includes the A, B, and C horizons combined (or A + E + B + C).

Correct Answer: Unconsolidated parent material
The C horizon is found below the Solum (A and B horizons) and consists of the unconsolidated parent material from which the soil is formed. It is less affected by soil-forming processes compared to the horizons above it.

Correct Answer: Pedon
A 'Pedon' is considered the smallest volume or unit of soil that exhibits all the characteristic layers (horizons) and properties of a specific soil type found in an area. It is typically hexagonal and ranges from 1-10 m² in area.

Correct Answer: Silicate clay iron and aluminium
The main feature distinguishing the E horizon (eluviation layer) is the loss (leaching) of silicate clay, iron (Fe), and aluminium (Al). This loss typically results in a lighter color compared to the A horizon above and B horizon below.

Correct Answer: A horizon
The A horizon is generally considered the top most mineral horizon in a soil profile, located beneath the O horizon (if present). It is rich in humus mixed with mineral particles.

Correct Answer: Blocky and Prismatic
The B2 horizon, being a zone of accumulation, often leads to the development of specific soil structures. Blocky and Prismatic structures are noted as importantly developing in this horizon.

Correct Answer: It is more like A than B
In transitional horizons, the first letter indicates the dominant horizon characteristics. Therefore, an AB horizon has properties of both A and B, but it is more similar to the A horizon than the B horizon.

Correct Answer: Bedrock
The R horizon denotes the layer of hard, consolidated bedrock found beneath the C horizon. It represents the base material upon which the soil profile has developed.

Correct Answer: C horizon
The C horizon, consisting largely of weathered parent material, is considered to be 'outside the zone of major biological activities' compared to the A and B horizons above it. It is less influenced by roots and soil organisms.