LO 1.4 - Biological factors in soil formation

Question 1

Soil Development: The main factors in soil formation.

Answer 1

• Weathering of geological materials, rock, river deposits, wind deposits.
• Mineral particles are broken down by weathering.
• Wind and water and ice can move mineral particles from one place to another.
• Soils can also move downslope by gravity.

Rock fragments alone don’t constitute soil

Question 2

Other than mineral and rock particles, what else is involved in soil formation.

Answer 2

• Organic Matter, ie Living and dead organisms and but mainly the remains of dead animals and mostly dead plant matter.

Question 3

Question

What are 5+1 factors in the development of soil?

Answer 3

1. Parent material
2. Climate
3. Biota (plants and animals)
4. Topography
5. Time

The +1 is humans.

Question 4

Question

The nature of soil is strongly affected by the it’s parent material.

What is Parent Material?

Answer 4

Parent Material of Soil.

• Soil formed from clay sediment deposited in lakes (lacustrine deposits) has small pores that prevent the free movement of water.
• Soil formed from sandy, windblown material is more porous and free-draining.
• Parent material is usually inorganic. In wet areas, where plant material accumulates at a faster rate than it decomposes, the parent material can be organic.

Question 5

How does climate effect soil formation?

Answer 5

• Higher temperatures increase rate of chemical reactions and rate of plant growth.
• High rainfall increases rate of soil formation as more water percolates through the parent material. Water passing through soil takes some elements with it. This leaching of calcium makes soil more acid.
• Soil therefore forms more quickly in warm, humid, tropical areas than in dry desert areas or in cool or frozen environments.

Question 6

Consider the role of the climate in Ireland in soil formation

Answer 6

• Big variation in annual rainfall amounts across the country; < 750 mm in east to > 3,000 mm in west.
• Higher rainfall causes soil to be more leached and therefore less fertile.
• Upland soils tend to be more leached and so less fertile because of precipitation.

Question 7

What is the name of the process behind most of Ireland’s soil development?

Answer 7

• Glacial drift – material was collected, transported and deposited by ice sheets.
• Soil erosion caused by wind commonly occurs in areas that have been overgrazed or deforested.

Question 8

The term ‘biota’ includes all living organisms.

How does it relate to soil development?

Answer 8

• Plant life on the surface of rocks plays a major role in early stages of soil formation.
• Lichens secrete acids which break down rock, releasing minerals which the lichens need.
• Dead and decaying lichens form the first layer of humus.
• As a layer of humus develops, mosses and ferns, and later grasses.
• Roots of these plants continue to break down rock.
• Larger plants such as herbaceous plants, shrubs and trees begin to grow.

Question 9

Consider

More detail in soil Biota.

Answer 9

• Living organisms influence soil by addition of organic material.
• Vegetation also stabilises soil.
• Burrowing animals materials from deeper and contribute to aeration.
• Earthworms and other invertebrates contributing to soil mixing & aeration thus enhancing soil structure.
• Earthworms ingest soil particles and organic residues, making nutrients available to plants.
• Microorganisms play a vital role in breaking down organic compounds and releasing their nutrients.
• Some bacteria and fungi have specialised roles in helping plants to take up nutrients.

Question 10

Consider this

Soil Development: Time

Answer 10

• Soils formed from alluvial deposits can be only several years old, and organic material can accumulate to form a layer of dark soil within decades.
• Most soils, however, take hundreds or thousands of years to develop.

Question 11

How fast does soil accumilate?

Answer 11

Best guestimates are around 1mm per year.

Question 12

Question

What does Topography mean?

Answer 12

• Topography refers to the shape and form of the land surface and includes slope, aspect and elevation or height.

Question 13

Question

Development of soil: Human activity

Many activities can affect the formation and development of soil.

Can you name some?

Answer 13

• Deforestation/vegetation clearance
• Grazing/overgrazing
• Cultivation
• Addition of lime, fertilisers, organic matter
• Drainage and irrigation Topography