SOIL HORIZONS/PROFILE

Soil

A thin layer of natural material formed by weathering and erosion, crucial for life on Earth

Climate

Most important factor in soil formation

How long does soil take to form?

400 years for 1cm

4 layers of soil

Organic Layer (O), Topsoil (A), Subsoil (B), Parent Rock (C)

O (Organic Layer)

Surface, made up of plant litter and decomposition

A (Topsoil)

First layer of soil, dark in colour, rich in organic matter and nutrients, leaching is seen here

B (Subsoil)

Lighter in colour, zone of accumulation - minerals and rainwater build up here, creating a layer of hardpan which is impermeable (waterlogging)

Waterlogging

When too much water fills the soil, causing inability for air to reach plant roots

Impermeable

DOES NOT allow liquid to pass through

C (Parent Rock)

Made up of partially weathered parent material, bedrock, undisturbed by weathering process

Leaching

Minerals, humus and nutrients are washed down through the soil horizons by rainfall

Impact of Leaching

As the nutrients are leached down, they become out of reach for plant roots causing death and waterlogging