4c - 4f - Soil formation & Profile

Why is soil so important (6 reasons)

• Non-renewable natural resource (takes very long to form)

• Needed for plant growth

• Acts as a habitat for many species

• 95% of the world’s food comes from soil, hence it also creates many jobs

• Soil helps purify water

Explain the 2 steps of formation of soil

1. Weathering and erosion – The parent rock is broken into small particles by weathering. These particles are then moved by water, wind, or ice through erosion, helping to form different soil types. The parent rock gives the soil properties such as color, minerals, acidity, and permeability.

2. Addition of humus – Humus is dead, decayed organic matter from plants and animals. It is dark in color and makes the soil more fertile. The amount of humus depends on the climate* and the type and number of plants and animals in the area.

• Warm + moist climate → faster decomposition → more humus is produced.

• Cold or dry climate → slower decomposition → less humus is produced.

4 main components of soil

• Mineral particles (from weathered rock)

• Water

• Air

• Organic matter (living and decaying/humus)

What is a horizon

a layer of soil consisting of the same material

What is a soil profile

a vertical cross-section showing the different layers of soil/horizons

4 factors that affect what type of soil is formed

• texture

• depth

• colour

• organic content

Horizons of a typical soil profile

• O Horizon – organic matter (litter/dead layer of plant residues in relatively undecomposed form)

• A Horizon – topsoil/surface soil (most fertile, high humus content - dark colour)

• B Horizon – subsoil (contains most minerals; iron, clay, aluminum - orange colour)

• C Horizon – substratum (partly weathered parent rock)

What’s found below horizon C

R Horizon (Bedrock) = the solid, unweathered parent rock.

What are 5 common features of Maltese Soils

1. Young and immature (still greatly resemble parent rock; only started to form a few thousand of years ago)

2. High percentage of calcium carbonate (used in cement)

3. Alkaline (due to high percentage of lime). Hence, acid needs to be added to achieve an optimal neutral condition

4. Little humus. Hence, nutrients constantly need to be added through fertilizers

5. Very small chance of forming horizons due to it not being very deep and often disturbed by man

What are the 3 main types of Maltese soil

1. Terra Rosa

2. Xerorendzina Soil

3. Carbonate Raw Soil

Name the following properties of terra rossa soil

• Its parent rock

• Percentage of calcium carbonate

• Structure

• Colour

• What locations it is found

• Parent rock = Upper and Lower Coralline Limestone

• Low percentage of calcium carbonate

• Shallow and stony

• Red colour (due to the presence of iron oxide in it)

• Found in the northern and southwestern parts of Malta

Name the following properties of Xerorendzina Soil

• Its parent rock

• Age

• Percentage of calcium carbonate & colour

• Humus content

• What locations it is found

• Parent rock = greensands & globigerina (soft limestone)

• Very young soil

• High calcium carbonate, so it has an ash-grey colour

• Highly rich in stone and chalk content

• Very low humus content

• Central parts of Malta & Valleys

Name the following properties of Carbonate Raw Soil

• Its parent rock

• Age

• Percentage of calcium carbonate & colour

• Porous? Permeable?

• What locations it is found

• Parent rock = blue clay

• Very young

• High percentage calcium carbonate, hence has a whitish colour

• Porous and impermeable; holds a lot of water and is heavy and difficult to work with in wet weather. The advantage of this is that it is a moist soil, helping it resist the heat of the sun

• Found close to cliffs and north east Malta

• + lime + fertilisers = suitable for agricultural purposes