SOIL PROFILE

Definition of the soil profile

The vertical section through the soil is called as soil profile. The various layers are known as horizons.

Component of soils (volume basis)

The soil consists of four major components i.e. mineral matter (45%), organic matter (5%), soil air (20-30%) and soil water (20-30%).

1. Mineral matter

The minerals are extremely variable in size. Some are as large as the smaller rock fragments, others, such as colloids clay particles, are so small that they cannot be seen without the aid of an electron microscope.

2. Organic matter

Soil organic matter represents partially decayed and partially synthesized plant and animal residues. Such material is continually being broken down by the action of soil microorganisms.

3. Soil water

Soil water is the major component of the soil in relation to plant growth. The water is held within the soil pores. If the moisture content of soil is optimum for plant growth, plants can readily absorb water. Soil water dissolves salts and makes up the soil solution, which is important as a medium for supplying nutrients to growing plants. There is an exchange of nutrients between the soil solids and the soil solution and then between the soil solution and plant roots.

4. Soil air

A part of the soil volume that is not occupied by soil particles, known as pore space, is filled partly with soil water and partly with soil air. As the pore space is occupied by both water and air, the volume of air varies inversely with water. As the moisture content of the soil increases, the air content decreases and vice-versa.