5.1 Introduction to soil systems

Soil profile

the layers (horizons) seen in a vertical cut through soil

soil system storages

organic matter, organisms, nutrients, minerals, air and water

transfers in soil

biological mixing, leaching

leaching

minerals dissolved in water moving through soil (down)

Inputs to soil system

leaf litter, inorganic matter from parent material, precipitation, energy

parent material

the rock from which soil forms locally

outputs from soil system

uptake by plants, soil erosion

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transformations in soil

decomposition, weathering, nutrient cycling

properties of soil

mineral and nutrient content, drainage, water holding capacity, air spaces, biota, potential to hold organic matter, primary productivity

soil texture triangle

diagram to compare the composition of soil with sand, clay and loam percentages identified

physical weathering

involves the mechanical breakdown of pieces of rock into smaller pieces e.g. frost, salt, insolation and biological weathering,

chemical weathering

breaks down chemical bonds, chemically modifies the rock minerals, and produces new compounds; the most common types are oxidation, carbonation and hydrolysis. Lichens can chemically weather rock.

Pedosphere:

soil sphere

Translocation

Materials are sorted and layers are formed by water carrying particles either up or down

Horizons

Processes such as downward and upward movement of minerals leads to soil being processed into distinct horizons

Types of Horizons

* O Horizon
* A Horizon
* B Horizon
* C Horizon
* R Horizon

O horizon

Uppermost layer; has newly added organic material

A Horizon

Humus builds up - Humus Layer = "Good stuff”and forms via organic matter mixed with organic matter

B Horizon

Soluble minerals and organic matter tend to be deposited from the layer above

C Horizon

Mainly weathered rock from which soil forms

R Horizon

Parent material (bedrock)

Types of soil texture

* sandy
* silty
* clay
* loam soil

sandy soil

Gritty and fall apart easily

silty soil

Slippery and wet; hold together better than sandy soil

clay soil

Sticky and can be rolled into a ball easily

Loam soil

ideal for agriculture

Porosity

Amount of space between particles

Permeability

The ease at which gases and liquids and pass through the soil

Acidification of soil

Acid rain causing pollution, adversely affecting soil and causing damage to evergreen forestry

Fertile soil =

non renewable resource