soil 1 lecture

What is soil?

A material developed through physical, chemical and biological processes, consisting of organic matter, clay, silt, sand and gravel and occurring in layers called horizons.

What are the five external factors of soil formation?

Climate, organisms, relief, parent material and time.

What is Jenny's Equation?

S = f(cl, o, r, p, t).

What does "cl" represent in Jenny's Equation?

Climate.

What does "o" represent in Jenny's Equation?

Organisms.

What does "r" represent in Jenny's Equation?

Relief.

What does "p" represent in Jenny's Equation?

Parent material.

What does "t" represent in Jenny's Equation?

Time.

Which soil-forming factor is described as the most influential?

Climate.

How does temperature affect soil formation?

Temperature influences the rates of physical, chemical and biological processes.

How does rainfall affect soil formation?

Rainfall influences the amount of water available for weathering, mineral formation and leaching.

What happens to weathering rates at low temperatures?

Weathering rates decrease.

What happens to organic matter accumulation at low temperatures?

Organic matter accumulation increases.

What happens to chemical weathering for every 10°C increase?

The rate of chemical weathering almost doubles.

How can climate extremes affect soils?

They can cause physical weathering and soil erosion.

How do microorganisms contribute to soil formation?

They influence mineral transformations, including processes such as nitrogen cycling.

How do fungi contribute to soil formation?

They extract deep-soil phosphorus and increase soil carbon levels.

How do earthworms affect soil?

They improve soil structure and incorporate organic matter through bioturbation.

How do plants affect soil formation?

They protect the surface, add organic matter, create soil pores and support microbial activity through root exudates.

What is relief?

The topography or shape of the land.

How does slope affect soil?

Slope influences drainage and erosion, with faster soil removal generally occurring on sloping land.

What happens to water and sediment in depressions?

They can accumulate.

How does aspect affect soil?

It influences temperature and moisture conditions.

How does time affect soil formation?

The amount of time influences the degree to which soil-forming processes occur.

What are the characteristics of older soils?

Older soils usually have stronger horizon development, are often redder, contain fewer primary minerals and more resistant secondary minerals.

What is a chronosequence?

A set of sites that developed over different periods of time but are otherwise similar.

What is parent material?

The material from which soil develops.

Does parent material have to be underlying bedrock?

No. It can also come from wind, water, glaciers, volcanoes or downslope movement.

What can parent material high in quartz produce?

Sandy soils.

How can parent material affect water movement?

The characteristics of the resulting soil influence the rate of downward movement of water.

What is weathering?

The breakdown of rock and minerals that contributes to soil formation.

What is mechanical weathering?

The physical breakdown of rock into smaller fragments.

What is salt wedging?

The process where salt crystals grow in rock cracks and exert pressure that widens the cracks and breaks off fragments.

Where is salt wedging particularly common?

Arid and coastal environments.

Why is salt wedging common in arid and coastal environments?

Because evaporation rates are high and salt is abundant.

How does thermal expansion cause weathering?

Heating and cooling cause minerals to expand and contract, generating stresses that can produce cracks and fragmentation.

How does water contribute to weathering?

Water erodes and transports rock fragments, causes abrasion and redistributes weathered material.

What happens when rock surface area increases?

Chemical reactivity increases.

How do joints and fractures affect weathering?

They allow weathering agents to penetrate rock and accelerate breakdown.

What is dissolution?

A chemical weathering process where soluble compounds dissolve.

What type of rock is given as an example of dissolution?

Limestone.

What is oxidation?

A chemical weathering process where mineral ions combine with oxygen; chemically, oxidation involves loss of electrons.

What is an example of oxidation in rocks?

Rust-coloured weathering of basalt.

What is hydrolysis?

A reaction between a substance and water in which water's ions can replace ions in a mineral.

What happens to feldspar during hydrolysis?

Feldspar can be transformed into fine clay particles.

What are the four major groups of soil processes?

Additions, losses, translocations and transformations.

What are additions in soil processes?

The addition of material to the soil body, such as wind- or water-transported sediments.

What are losses in soil processes?

The removal of material from the soil body, particularly through leaching and erosion.

What are translocations?

The physical movement of materials from one part of the soil profile to another.

What are transformations?

Chemical alterations of mineral or organic substances within the soil profile.

What is humification?

The breakdown of dead plant and animal material by organisms to form humus.

Which organisms contribute to humification?

Bacteria, fungi, termites and earthworms.

Why is humus important?

It contributes to nutrient cycling and helps store moisture and nutrients.

What factors affect the rate of humification?

The type of organic matter and climate, including heat and water.

What is translocation in soil?

The movement of cations and soil particles vertically or laterally through soil water.

What is eluviation?

The movement of material away from the A horizon.

What is leaching?

The rapid eluviation of ions from the A horizon.

What is illuviation?

The accumulation of material in the B horizon.

Why is translocation important?

It contributes to the zonation and development of soil horizons.

What is aggregation?

The process of bringing soil particles together into larger aggregates or peds.

What are soil aggregates also called?

Peds.

What does aggregation do to soil?

It stabilises soil and works against translocation processes.

What is cation exchange?

The storage and exchange of ions within the clay-humus colloidal complex.

Which common cations are involved in cation exchange?

Ca²⁺, Mg²⁺ and K⁺.

Why can clay and humus store plant nutrients?

Their surfaces are negatively charged and can absorb positively charged cations.

What is the medium for cation exchange?

Soil water.

What is a colluvial process?

Downslope movement of soil or sediment by gravity or shallow water.

What type of transport is colluviation?

Local transport.

What is an alluvial process?

Transport of sediment over large distances by rivers or streams.

What is an aeolian process?

Transport of sediment by wind.

What is the main difference between colluvial and alluvial transport?

Colluvial transport is generally downslope and local, whereas alluvial transport occurs through rivers and streams over larger distances.

How can human interference affect colluvial and aeolian processes?

It can accelerate them and contribute to land degradation.

What does the principle "the present is the key to the past" mean in soil science?

Current soil-forming processes can be used as models for interpreting past events.

Why can soils provide information about the past?

Many current soil properties are consequences of soil-forming processes that occurred in the past.

What are the three major types of chemical weathering in this lecture?

Dissolution, oxidation and hydrolysis.

What is the relationship between eluviation and illuviation?

Eluviation involves movement away from a horizon, while illuviation involves accumulation in another horizon, particularly the B horizon.

What is bioturbation?

The incorporation and movement of organic matter and soil material by organisms such as earthworms and other fauna.