Soil Profile

Table of Contents

• Horizons of the Soil Profile
  • The O Horizon
  • The A Horizon
  • The B Horizon
  • The C Horizon
  • The R Horizon
• Summary
• Did You Know?
• What’s Next?

In the previous segment of the chapter Soil, we learnt about The importance of soil. We also had a glimpse of the soil profile and the various horizons in it. In this segment, we will understand each horizon in detail.

Horizons of the soil profile

The vertical section through which various soil layers can be seen is known as the soil profile. The soil profile consists of five different layers primarily. These are O, A, B, C, and R from top to bottom.

The O horizon

The uppermost layer of the soil profile is the O horizon. Here ‘O’ stands for ‘organic’. This horizon consists of humus. Humus is the organic matter formed from dead and decomposed animal bodies or plant parts. This makes this layer dark in appearance and rich in nutrients.

The A horizon

Beneath the O horizon is the A horizon. It is also known as the ‘topsoil’ even though it is not at the top. That is because, technically, this is the first layer of soil since the O horizon primarily consists of dead organic matter. This layer usually consists of humus and several minerals.

Hence, plant roots grow well in this layer. This is a home for many organisms like little worms and a few kinds of rodents.

The B horizon

The layer beneath the A horizon is known as the B horizon. It is also known as the ‘subsoil’. It consists of several minerals embedded in it. Iron oxide is especially present in large quantities in this horizon. The presence of iron oxide gives the B horizon a reddish-brown appearance.

Despite the presence of minerals and clay in this layer, the layer is very compact and hard. Hence, only a few large trees have their roots growing in this region.

The C horizon