Grade 9 Soil Formation

Soil Formation

Soil is made up of 4 main parts
1. Minerals:
- Come from broken rock which is called parent mineral and provides
nutrients to plants
2. Bacteria and Organic Material
- Partially decomposed plant and animal materials
- Form humus that provides nutrients
3. Air
- Need air around roots of plants
- Air holes are created by worms, insects, and small animals
4. Moisture
- Water dissolves nutrients so they can be taken up by plants
- Helps break down rock and decay organic material

Soil profile
O - Organic Material:
- Dying material (plants and animals) or things in process of breaking down
A horizon - Topsoil:
- Rich in organic materials and take hundreds of years to produce
- Thin layer
B horizon - sub-soil:
- Mainly inorganic material with some organic material
C horizon - parent material:
- Broken pieces of rock and/or solid rock

Leaching:
- Where there is a lot of precipitation
- Precipitation leads to water moving downwards through soil
- Water dissolves nutrients and carries downwards

Calcification:
- Drier climates
- Water drawn to the surface by capillary action
- Water evaporates
- Nutrients that dissolved in soil water are carried back to the surface and
deposited there as water evaporates
- Can lead to rich topsoil, full of nutrients
- So much can be deposited the soil becomes poisonous to plants