Soil Formation And Types Of Soil

soil formation 

Soil forms continuously, but slowly, from the gradual breakdown of rocks through weathering. Weathering can be a physical, chemical or biological process

Physical weathering

Breakdown of rocks from the result of a mechanical action. Temperature changes, abrasion (when rocks collide with each other) or frost can all cause rocks to break down.

Chemical weathering

Breakdown of rocks through a change in their chemical makeup. This can happen when the minerals within rocks react with water, air or other chemicals.

Biological weathering

The breakdown of rocks by living things. Burrowing animals help water and air get into rock, and plant roots can grow into cracks in the rock, making it split.

The accumulation of material through the action of water, wind and gravity also contributes to soil formation. These processes can be very slow, taking many tens of thousands of years. Five main interacting factors affect the formation of soil

• Parent material:- minerals forming the basis of soil
• Living organisms:- influencing soil formation
• Climate:- affecting the rate of weathering and organic decomposition
• Topography:- grade of slope affecting drainage, erosion and deposition
• Time:- influencing soil properties.

Interactions between these factors produce an infinite variety of soils across the earth’s surface.

Parent materials

Soil minerals form the basis of soil. They are produced from rocks (parent material) through the processes of weathering and natural erosion. Water, wind, temperature change, gravity, chemical interaction, living organisms and pressure differences all help break down parent material.

The types of parent materials and the conditions under which they break down will influence the properties of the soil formed. For example, soils formed from granite are often sandy and infertile whereas basalt under moist conditions breaks down to form fertile, clay soils.

Organisms

Soil formation is influenced by organisms (such as plants), micro-organisms (such as bacteria or fungi), burrowing insects, animals and humans.

As soil forms, plants begin to grow in it. The plants mature, die and new ones take their place. Their leaves and roots are added to the soil. Animals eat plants and their wastes and eventually their bodies are added to the soil.

This begins to change the soil. Bacteria, fungi, worms and other burrowers break down plant litter and animal wastes and remains, to eventually become organic matter. This may take the form of peat, humus or charcoal.

Climate

Temperature affects the rate of weathering and organic decomposition. With a colder and drier climate, these processes can be slow but, with heat and moisture, they are relatively rapid.

Rainfall dissolves some of the soil materials and holds others in suspension. The water carries or leaches these materials down through the soil. Over time this process can change the soil, making it less fertile.

Topography

The shape, length and grade of a slope affects drainage. The aspect of a slope determines the type of vegetation and indicates the amount of rainfall received. These factors change the way soils form.

Soil materials are progressively moved within the natural landscape by the action of water, gravity and wind (for example, heavy rains erode soils from the hills to lower areas, forming deep soils). The soils left on steep hills are usually shallower. Transported soils include

• alluvial (water transported)
• Colluvial (gravity transported)
• Aeolian (wind transported) soils.
• Read more about soil erosion.

Time

Soil properties may vary depending on how long the soil has been weathered.

Minerals from rocks are further weathered to form materials such as clays and oxides of iron and aluminum.

Queensland (and Australia) is a very old weathered landscape with many ancient soils.

Soil Types

Soil is a natural resource that can be categorize into different soil types, each with distinct characteristics that provide growing benefits and limitations.

Soil can be categorize into sand, clay, silt, peat, chalk and loam types of soil based on the dominating size of the particles within a soil.

Types Of Soil

• Sandy Soil
• Clay Soil
• Silt Soil
• Peat Soil
• Chalk Soil
• Loam Soil

Sandy Soil

Sandy Soil is light, warm, dry and tends to be acidic and low in nutrients. Sandy soils are often known as light soils due to their high proportion of sand and little clay (clay weighs more than sand).

These soils have quick water drainage and are easy to work with. They are quicker to warm up in spring than clay soils but tend to dry out in summer and suffer from low nutrients that are washed away by rain.

The addition of organic matter can help give plants an additional boost of nutrients by improving the nutrient and water holding capacity of the soil.

Clay Soil

Clay Soil is a heavy soil type that benefits from high nutrients. Clay soils remain wet and cold in winter and dry out in summer.

These soils are made of over 25 percent clay, and because of the spaces found between clay particles, clay soils hold a high amount of water.

Because these soils drain slowly and take longer to warm up in summer, combined with drying out and cracking in summer, they can often test gardeners.

Silt Soil

Silt Soil is a light and moisture retentive soil type with a high fertility rating

As silt soils compromise of medium sized particles they are well drained and hold moisture well.

As the particles are fine, they can be easily compacted and are prone to washing away with rain.

By adding organic matter, the silt particles can be bound into more stable clumps.

Peat Soil

Peat soil is high in organic matter and retains a large amount of moisture.

This type of soil is very rarely found in a garden and often imported into a garden to provide an optimum soil base for planting.

Chalk Soil

Chalk soil can be either light or heavy but always highly alkaline due to the calcium carbonate (lime) within its structure.

As these soils are alkaline they will not support the growth of ericaceous plants that require acidic soils to grow.

If a chalky soil shows signs of visible white lumps then they can’t be acidified and gardeners should be resigned to only choose plants that prefer an alkaline soil.

Loam Soil

Loam soil is a mixture of sand, silt and clay that are combined to avoid the negative effects of each type.

These soils are fertile, easy to work with and provide good drainage. Depending on their predominant composition they can be either sandy or clay loam.

As the soils are a perfect balance of soil particles, they are considered to be a gardeners best friend, but still benefit from topping up with additional organic matter.