Module 13

Question 1

Distinguish between soil and regolith; list the four components of soil

Answer 1

Soil is the uppermost layer of the Earth’s surface that contains both mineral and organic matter capable of supporting plants
-Inorganic matter, organic matter, soil water, and soil air

Regolith is the layer of unconsolidated rocky material covering bedrock, derived from weathered rocks

Question 2

Describe the principal soil-forming factors.

Answer 2

(1) Pedogenic processes: Soil depletions, soil additions, transformations, translocations, and mixing.
(2) Climate
(3) Soil organisms
(4) Relief (differences in elevation)
(5) Parent Material
(6) Time

Question 3

Describe the principal pedogenic soil forming processes that contribute to the formation of soils under different environmental conditions.

Answer 3

(1) Soil depletions: Occur when some aspect of the soil is lost
(2) Soil additions: Material and energy that is added to the soil
(3) Transformations: Decomposition of minerals and organic matter, development of soil aggregates
(4) Translocations: Vertical movement of materials through soil
(5) Mixing: Bioturbation, Wetting (swelling) and drying (shrinkage), cryoturbation

Question 4

Identify the physical properties of soil that influence field capacity.

Answer 4

Field capacity is the maximum amount of water soil can hold after gravitational drainage

• Soil structure and texture
• organic matter
• soil colloids

Question 5

Define the terms of a water balance: potential evapotranspiration, actual evapotranspiration, moisture surplus, moisture deficit, moisture recharge

Answer 5

potential evapotranspiration:
actual evapotranspiration:
moisture surplus:
moisture deficit:
moisture recharge

Question 6

Define the terms soil texture and soil structure.

Answer 6

Soil texture (such as loam, sandy loam or clay) refers to the proportion of sand, silt and clay sized particles that make up the mineral fraction of the soil.
Soil structure refers to the way in which soil particles naturally clump together granular, blocky, platy, and columnar

Question 7

Examine soil chemistry, including pH and cation exchange capacity (CEC), and relate these concepts to soil fertility

Answer 7

Each soil has a distinct chemical composition that is important for it’s formation and fertility
pH is the concentration of hydrogen ions (H+) present in a solution and an important indicator of soil fertility
Cation exchange capacity (CEC) is a useful indicator of soil fertility because it shows the soil’s ability to supply three important plant nutrients: calcium, magnesium and potassium.

Question 8

Describe typical soil horizons (O, A, Ae, B, C, and R)

Answer 8

O organic material
A mixture of humus and mineral grains
Ae mineral grains– quartz, feldspar (eluviated layer)
B enriched in clay or organic colloids, Fe/Al oxides (illuviated layer)
C weathered rock: parent material
R unweathered bedrock