Soil Profile: Topmost Horizon is more important than all other Horizons

Soil Layers

Soil Profile: The Layers of Soil

Horizon

Soil takes a long time to form. It may take hundreds to thousands of year for one inch of soil to form. As soil forms, different layers result. A layer of soil differing from the layers above and below it is called horizon. 

6 Horizons 

Soils typically have six horizons. From the top down, they are Horizon O,A, E, B, C and R. Each horizon has certain characteristics.

O Horizon­ 

O horizon – Also called humus, this is the top-most layer of any soil with a significant amount of plant life above it. Humus is a layer of organic material (hence the ‘O’), like dead grass, fallen leaves, etc. that collects on the ground’s surface.

A Horizon­ 

The layer called topsoil

Top most horizon is more important than all other horizons because:

An A horizon is a mineral horizon. This horizon always forms at the surface and is what many people refer to as topsoil.

They are rich in organic matter, giving them a darker color.

Seeds germinate and plant roots grow in this dark ­colored layer. It is made up of humus (decomposed organic matter) mixed with mineral particles.