Week 4 - Soil Formation and Classification

Question 1

Name and briefly describe the first divisions of the Northcote’s factual key.

Answer 1

The first divisions of the Northcote’s factual key are organic, gradational, duplex, and uniform.
i. Organic are soils where the surface is dominated by organic matter.
ii. Gradational are soils with a gradual increase in texture with depth.
iii. Duplex are soils with a sudden increase in texture at a depth.
iiii. Uniform are soils with no change in texture with depth.

Question 2

List three (3) properties of a soil that can be identified by the presence of a red colour in that soil.

Answer 2

1. Red soil often contains a high concentration of oxidised iron (Fe3+)
2. Red soil is often well-drained. If at some stage, the soil becomes waterlogged, the Fe is reduced to Fe2+ producing grey or mottled colours.
3. Organic matter levels are low as if present, the red colours would be masked.

Question 3

List the common features of a soil profile derived from Aeolian parent material.

Answer 3

i. Buried horizons
ii. Unusual texture change with depth
iii. Located on smooth and gently undulating landscapes

Question 4

What are the known profile properties of the following soils.

Answer 4

i) Chromosol
Strong text contrast
pH > 5.5 in B horizon

ii) Vertosol
Cracking clay

Question 5

List the common profile features of a soil derived from sedentary parent material.

Answer 5

1. The horizon containing organic matter is only at the soil surface as this is where the plant residues are deposited.
2. The clay content increases with depth.

Question 6

List three (3) properties of a soil that can be identified by the presence of a yellow colour in that soil.

Question 7

Name 3 main divisions of sedentary parent materials.

Question 8

Describe one disadvantage of a parna soil.

Question 9

List two advantageous properties of a parna soil.

Question 10

What is parna?

Question 11

What will be the predominant texture of the soil?

Question 12

Describe the profile features of a soil derived from Alluvial parent material.

Question 13

Describe how soils change on a floodplain as you travel away from the river.

Explain why the changes in soil you described occur.

Question 14

Draw a labelled cross section of a natural terrace system.