Question

Which horizon is considered the topsoil, and which is considered the subsoil?

Short answer

O and A horizon composed of topsoil whereas B horizon composed of subsoil.

Step-by-step solution

Step-1 Introduction

Soil has many horizons and the horizons are classified according to many factors and the composition of matter present in it such as; composition of organic matter, mineral content, and water holding capacity. There are four different layers of soil horizon classified as O, A, B, and C horizons respectively.

Step-2 Explanation

The soil surface containing freshly decomposing organic matters or humus is called the O horizon. The A horizon consists of both mixtures of organic as well as inorganic products. Topsoil or the top-most layer of soil mainly ranges from two to three inches deep and can vary also. So, the top layer of soil is composed of the O horizon and some parts of the A horizon.

The layer below the topsoil is called subsoil which is classified as the B horizon that accumulates mainly minerals and clay soil. Calcium carbonate depositions are also present in the B horizon.