5.1 Introduction to soil systems Flashcards
What are some important functions of soils?
- Habitat for micro-organisms and soil invertebrates
- Nutrient cycling/ decomposition
- Medium for plant growth/ agriculture
- Store of water
- Filtering materials
- Maintain water quality
- Raw materials - peat, sand, clay, gravel
What is soil?
Soil is a complex mixture of eroded rock, mineral nutrients, decaying organic matter, water, air and billions of living organisms
What are the 3 stages of soil formation?
Soil formation is a very slow process and occurs in three stages.
1. Mechanical and chemical weathering processes, resulting in the inorganic component of the soil
2. Introduction of living organisms, the biotic component
3. Decomposition and the formation of an organic component
What influences soil formation?
Influenced by environmental factors
–> that’s why in different parts of the world there is different types of soil
What are the 4 soil horizons?
“O” horizon (leaf litter layer) = uppermost layer of freshly fallen and partially decomposed leaves, twigs and animal waste
“A” horizon (top soil) = porous mixture of partially decomposed organic matter (humus) and some inorganic mineral particles
“B” horizon (subsoil) = layer where soluble mineral and organic matter tends to be deposited from the layer above, especially clay and iron salts
“C” horizon (parent material) = mainly weathered rock from which the soil forms
What is the “O” horizon? (leaf litter layer)
Uppermost layer of freshly fallen and partially decomposed leaves, twigs and animal waste
What is the “A” horizon? (top soil)
Porous mixture of partially decomposed organic matter (humus) and some inorganic mineral particles
What is the “B” horizon? (subsoil)
Layer where soluble mineral and organic matter tends to be deposited from the layer above, especially clay and iron salts
What is the “C” horizon? (parent material)
Mainly weathered rock from which the soil forms
What two soil layers are the most fertile?
The top two layer (O and A horizons) are the most fertile
What are the three minerals that make up soil texture?
Clay - very fine particles (0.002mm diameter)
Silt - fine particles (0.002 - 0.05mm)
Sand - medium sized particles (0.05 - 0.2mm)
–> The proportion of the different particles determines the soil texture
Describe the “Clay” mineral in soil?
Very fine particles (0.002mm diameter)
Describe the “Silt” mineral in soil?
Fine particles (0.002 - 0.05mm)
Describe the “Sand” mineral in soil?
Medium sized particles (0.05 - 0.2mm)
What is soil “porosity”?
A measure of the volume of spaces per volume of soil and the average space between those spaces
The fraction of soil volume that is made ip of open space
