Mineral Riches in the Soil and Their Role in Plant Nutrition

All the earth’s surface, which is not covered by water, is covered with various types of soil. The soil is the uppermost layer of the earth's crust and is a mixture of organic compounds, minerals, gases, liquid and living (or dead) organisms. Soil can also be referred to as the collection of loose sediments. The mineral portion is the largest component of the soil, 45-49% of the soil is the mineral portion. While 1-5% of it consists of organic matter, and left empty space (around 50%) is filled with water and gases, their percentage in the soil can vary a lot. According to the percentage of these components and also the variation of the minerals present, the soil formed can be of many types. In India, one will be able to find these six types of soil.

1. Alluvial soil:

This soil type is the most fertile type of soil and also the most commonly found soil type in India.

2. Black soil (Regur soil):

It is also known as black cotton soil, as it is great for cotton cultivation and has a black colour. 

3. Red soil:

Red soil is red in colour due to the high iron content present in the soil.

4. Mountainous soil:

It is also known as forest soil and is found in the hilly and mountainous regions (especially in the Himalayas).

5. Desert soil:

This soil is usually deposited by wind action and is commonly found in arid and semi-arid regions like that of Rajasthan.

6. Laterite soil:

Laterite soil is formed by in-tense leaching usually caused by Tropical rainfall.

Soil Minerals

Soil minerals are the important substances found in soil that is produced as a result of the breakdown of large rocks. Examples of mineral riches in the soil are Potassium, Iron, Magnesium, Sulphur and Calcium. The mineral soil is very supportive of plant growth.

The thin layer consisting of loose material that covers the Earth’s surface is called Soil. It is composed of both organic and inorganic materials, and its formation is a lengthy process that takes up to a thousand years. Soil is formed with the help of rocks when they break into small pieces and mix with organic matter. The process is known as weathering. Thus, the soil is a mixture of various substances and particles, it is the mixture of rocks, minerals and soil.

Besides minerals, the soil consists of humus, living organisms, water and air. The organic substances formed after the decomposition of dead and decayed plants and animals is called humus. It makes the soil highly fertile. Many living organisms including microbes, worms, bacteria and fungi can be found in the soil that participates in generating the soil humus. Soil gets plenty of water through rain and underground water and also has aeration allowing living organisms to grow and function well inside the soil. Water and air in the soil are also very helpful for photosynthesis in plants.

Types of Minerals in Soil

The largest component in the soil are minerals and it makes up 40-45 per cent of the total components. The types of soil minerals are divided into two categories, which are as follows:

1. Primary Minerals in the Soil:

It is one of the types of minerals in the soil and falls into that category of soil which have not been chemically transformed since the deposition. It is similar to their parent materials and is larger with irregular shapes. These minerals are usually present in sand and silt. Examples of the primary minerals in soil include silica minerals and silicate, titanomagnetite, apatite, iron minerals, volcanic gases and non-crystalline inorganic constituents.

2. Secondary Minerals in the Soil:

It is the second category of minerals found in the soil and is formed after the weathering of primary soil minerals. It is mainly found in fine silt or clay minerals. The particle size of secondary minerals is much smaller as compared to the primary minerals since these are formed as a result of the weathering process. Having a large surface area, these minerals help in retaining moisture. Some examples of secondary minerals in the soil are hydroxides, phyllosilicates, oxides, carbonates, phosphates, sulfates and halides. These are beneficial to be added to the farmland.

Functions of the Soil Minerals

Soil plays an important role in various functions including food and other biomass production, biological habitat, gene pool, environmental interaction, physical and cultural heritage, and acts as a platform for man-made structures. The soil-forming rocks and minerals are very helpful for plant growth as it’s a great assistance to plant life. Several minerals are absorbed from the soil via the roots of the trees and plants. Most of the important minerals are magnesium and nitrate where the former helps in the production of chlorophyll allowing photosynthesis and the latter mineral is the major source of amino acids required to synthesise proteins. The absence of these essential minerals will lead to stunted plant growth.

Formation of Soil

Its formation involves the breakdown of rocks in the rock cycle. Soil being a mixture of geological and organic materials, is highly beneficial for the growth of plants. In contrast, sand is purely rocky material devoid of living organisms and therefore, sand is not great for plant growth. Mixing manures, fertilisers or compost to the sand can turn into soil. Soil has therefore two parts, rocky materials and organic matter. Soil has a life cycle of its own. 

How are Rocks Broken to Form Soil?

• Soil formation starts with the disintegration of rocks under the influence of climate.

• Sun, water and wind play important roles in weathering the rocks.

• Rainwater dissolves rock elements; temperature fluctuations may cause differential weathering i.e. expansion and contraction of rock-forming crystals.

• Also, the freezing and thawing of water in rocks widen the cracks and the lichens, generally, cyanobacteria or algae growing on the rocks release substances that help in powdering down the rocks.

• In addition, mosses help in further breaking down the rocks.

Minerals Present in the Soil

Soil forming minerals are the major components of soil and are mostly found are Sodium, Potassium and Nitrogen. Some of the other minerals of soil are as follows:

• Hematite:

It is red to blackish red in appearance and it swells up when it absorbs water forming hydrated iron oxide.

• Limonite:

It is yellow to brown and it is hydrated ferric oxide and acts as a cementing and colouring agent for soil.

• Goethite:

Goethite is formed when limonite adsorbs water. 

• Gibbsite:

It is the most common Aluminium compound present in the soil. It is present in highly weathered soil.

• Carbonate Group:

Calcium hydroxide and Magnesium hydroxide combine with carbon dioxide to form carbonates.

• Calcite:

Calcite is white or colourless and the major constituent of sedimentary rocks, consisting of calcium carbonate.

• Dolomite:

It is the chief source of magnesium found in the soil.

• Siderite:

It is an important mineral present in the water-logged soil. It is generated by the alteration of other iron-bearing minerals.

• Sulphate Group:

It is formed by the combination of oxygen and sulphur ions. It further reacts to form calcium sulphate by reacting with calcium ions.

• Gypsum:

It is found in sedimentary rocks as well as desert soils. It is water-soluble and can be leached easily.

Uses of Minerals Present in the Soil

Minerals present in the soils are important in the growth and development of different vegetation and agriculture. These minerals are also needed for many industries to function.

Some of the uses of minerals present in the soil are - 

1. The element of Nitrogen present in the soil is an essential part of different kinds of proteins, nucleic acids, vitamins, and various hormones, which are absorbed by the plants and then spread to the animal kingdom.

2. Phosphorus is the element used in the creation of plasma membranes of plant cells, some Proteins, nucleic acids, and nucleotides.

3. In plants, Potassium is a crucial element as it is needed for the process of photosynthesis. All three of these elements decide the fertility of the soil and these elements are added in the fields in the name of fertilisers.

4. Calcium is the main constituent of our teeth and bones in animals while in plants they are used in the formation of the spindle fibres.

5. Magnesium present in the soil is needed in the functioning of various enzymes of the body.

6. Sulphur is required by the plants in a minuscule quantity for the root development and nodule functions.

7. Iron is also present in the soils and one does not specify the use of iron in the animals. Certain proteins and blood all require the presence of iron in the body.

8. For the synthesis of auxin, the trace element named Zinc is needed, which is again available in the soil.

9. An ore named Calcite is also used for the production of cement and also in agricultural soil treatment.