1. Soil Base Different climates create wet climate or dry climate soils
True soil consists of four main parts; if one of these parts is missing, the material cannot be considered soil!
Minerals
Bacteria & organic materials
Air
Moisture

2. Minerals
Minerals in soil come from rocks, and are known as parent material
Minerals become part of the soil when rock is broken down by weathering into smaller parts (sand, silt, clay)
Many of these minerals such as calcium, phosphorous & potassium are nutrients needed for plant growth

3. Bacteria & Organic Materials
When plants and animals die, they decompose with the help of bacteria in the soil
As they break down, nutrients are released
decaying organic materials form humus, which provides nutrients and moisture for plants; humus gives soil its dark colour

4. Air All living beings need air to function
Plants also need air around their roots
A high humus level (amount of decomposing animals, plants and leaves) in the soil is helpful because this creates air pockets in the soil
Air spaces are also created by worms, insects and small animals that tunnel through the soil

5. Moisture
Water dissolves nutrients in the soil and plants take them up through their roots
Water is also necessary for weathering rock and the decay of organic materials

6. How Soil is Formed
Essentially, new minerals are added at the bottom through the weathering of the parent material, while organic materials are added at the top simultaneously
The top layer of soil containing humus is called topsoil and takes a long time to form

7. Loam
A well-balanced mixture of sand, silt, clay and humus is called loam
This is the best soil for growing plants because it encourages root growth, holds moisture and allows water to pass through at a rate moderate enough to allow plants to take up nutrients

8. Leeching
This happens in areas where there is a great deal of precipitation
Continual downward movement of water through the soil dissolves the chemical nutrients in the soil and carries them away
This removes the nutrients that the plants need
In very wet climates, leeching can take water-soluble minerals so deep that plant roots cannot reach them
You can identify leeched soil by it’s poor, thin topsoil layer
Leeched soil can be developed into excellent farmland by adding fertilizer

9. Calcification
Occurs in drier climates; when the water in the topsoil evaporates, water from below is drawn up to replace it
This process is called capillary action
The water drawn to the surface evaporates, leaving behind minerals that were dissolved in it; the result is a thick topsoil layer rich in minerals (calcium is the main mineral deposited; hence the name)
However, in very dry climates, the amount of minerals deposited can be so high that the top layer formed can be poisonous to plants

10. TOPSOIL PROFILE

11. LEACHED SOIL PROFILE

12. CALCIFIED Soil profile