5.1 Introduction to soil systems Flashcards
soil storages
organic matter, organisms, nutrients, minerals, air, water
soil transfers
- Biological mixing: Organisms like earthworms move soil particles and organic matter.
- Leaching: Water-soluble substances move downward through the soil profile.
soil profile order
O, A, E, B, C
O horizon
Organic: the topmost layer, consisting of organic matter like leaf litter and decomposing organisms.
A horizon
Also known as topsoil, rich in organic matter and minerals.
E horizon
eluvial or leached horizon
- leaching removes material from the horizon
B horizon
Subsoil, where materials leached from upper layers accumulate.
C horizon
Partially weathered parent material.
soil profile definition
a vertical section through a soil, from the surface down to the parent material, revealing the soil layers or horizons.
inputs of soil
inputs: organic (i.e. leaf litter) and parent material (inorganic matter), precipitation, energy
outputs of soil
- uptake by plants
- soil erosion
- energy
transformations of soil
- decomposition
- weathering
- nutrient cycling
soil structure
the shape and arrangement of individual soil particles
soil texture
the proportion of differently sized material - usually sand, silt, and clay - present in a soil
sand particle size
less than 0.2mm in diameter
silt particle size
less than 0.02mm
clay particle size
less than 0.002mm
clay characteristics
- Small particles (<0.002mm)
- Poor drainage
- Small air spaces
- High water-holding capacity
- High nutrient content
sand characteristics
- Large particles (0.05-2mm)
- High drainage
- Large air spaces
- Low water-holding capacity
- Low nutrient content
field capacity
the max amount of water that a soil can hold
loam soil
- best soil for cultivation
- Balanced drainage
- Good water-holding capacity
- Adequate air spaces
- Moderate to high nutrient content
- size: mix of sand, slit and clay
soil functions for humans
- medium for plant growth (most food for humans is grown in soil)
- soils contain an important store of relatively accessible freshwater (approx. 0.005% of global freshwater)
- soils filter materials added to the soil thereby maintaining water quality
- some recycling of nutrients takes place in soil → breakdown of dead organic matter
- provide raw materials in the form of peat, clays, sands, gravels, and minerals
is fertile soil renewable or non-renewable?
non renewable because it takes so long to develop and because of the current rate of resource use compared to the length of time required for resources to be replaced
soil forming processes involve
- gains and losses of material to and from the profile
- movement of water between the horizons
- chemical transformations within each horizon
what kind of systems are soils
open system in a steady state equilibrium
contrast in soils of tropical vs cold climates
tropical (Borneo):
- extremely deep due to the warm, wet year-round climate
cold (Iceland):
- thin or non-existent due to the lack of chemical weathering
physical conditions in soil that restrict root growth
- absence of cracks
- shortage of oxygen due to waterlogging
- dryness
- temperatures that are too high or too low
advantages of triangular graphs
- a large number of data can be shown on one graph
- groupings are easily recognizable
- dominant characteristics can be shown
- classifications can be drawn up
primary productivity of different soils
- sandy soil: low primary productivity due to poor water holding capacity and low nutrient status
- clay soil: quite low primary productivity due to poor aeration and poor water infiltration
- loam soil: high primary productivity due to medium infiltration rate, water holding capacity, nutrient status, aeration, and ease of working
primary productivity of soil depends on :
- mineral content
- drainage
- water holding capacity
- air spaces
- biota
- potential to hold organic matter
Soil is an example of …
non-renewable natural capital
ratio air, water, etc .
system definition
an assemblage of parts, working together, forming a functional whole
a soil horizon
distinct layer within the soil profile
chemical conditions in soil that restrict root growth
- high aluminium concentration, usually associated with low pH
- low nutrient supply
- chemicals toxic to plants (phytotoxic chemicals) in anaerobic soil (eg. saliniy associated with insecticides)
disadvantages of triangular graphs
- difficult to interpret
- easily get confused
humus defintion
not in syllabus, for own understanding
dark, organic material that forms in soil when plant and animal matter decays
parent material definition
not in syllabus, for own understanding
a weathered rock or deposit from and within which a soil has formed
