Why Are Mineral-Rich Soils Essential for Healthy Plants?
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.
Alluvial soil:
This soil type is the most fertile type of soil and also the most commonly found soil type in India.
Black soil (Regur soil):
It is also known as black cotton soil, as it is great for cotton cultivation and has a black colour.
Red soil:
Red soil is red in colour due to the high iron content present in the soil.
Mountainous soil:
It is also known as forest soil and is found in the hilly and mountainous regions (especially in the Himalayas).
Desert soil:
This soil is usually deposited by wind action and is commonly found in arid and semi-arid regions like that of Rajasthan.
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:
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.
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 -
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.
Phosphorus is the element used in the creation of plasma membranes of plant cells, some Proteins, nucleic acids, and nucleotides.
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.
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.
Magnesium present in the soil is needed in the functioning of various enzymes of the body.
Sulphur is required by the plants in a minuscule quantity for the root development and nodule functions.
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.
For the synthesis of auxin, the trace element named Zinc is needed, which is again available in the soil.
An ore named Calcite is also used for the production of cement and also in agricultural soil treatment.
FAQs on Mineral Riches in the Soil: Types, Functions, and Benefits
1. What are the mineral riches in the soil?
The 'mineral riches' in the soil refer to the naturally occurring inorganic nutrients that are essential for plant growth and other life forms. These minerals originate from the breakdown of large rocks, a process called weathering. Key examples include macronutrients like Nitrogen (N), Phosphorus (P), and Potassium (K), and micronutrients such as iron, manganese, and zinc. The presence and proportion of these minerals determine the soil's fertility and the types of plants it can support.
2. How is soil formed and where do its minerals come from?
Soil is formed over thousands of years through a process called weathering, which is the breakdown of parent rocks into fine particles. The minerals in the soil are directly derived from these rocks. The key processes involved are:
- Physical Weathering: The mechanical breakdown of rocks by factors like wind, water, and temperature changes, without altering their chemical composition.
- Chemical Weathering: The decomposition of rocks through chemical reactions like oxidation and hydrolysis, which releases soluble minerals.
- Biological Weathering: The action of living organisms, such as plant roots growing into rock crevices or microbes releasing acidic compounds, which break down the rock and contribute to mineral content.
3. How do different types of soil in India, like alluvial and black soil, vary in their mineral content?
Different soil types in India have distinct mineral profiles based on their formation and parent material:
- Alluvial Soil: Found in river plains, it is rich in potash, phosphoric acid, and lime, making it highly fertile for crops like sugarcane and wheat. However, it can be deficient in nitrogen.
- Black Soil: Derived from volcanic rocks, it is rich in iron, magnesium, aluminium, and lime. Its high clay content gives it excellent moisture-retention capacity, ideal for growing cotton.
- Laterite Soil: Formed under high temperature and rainfall, it is rich in iron and aluminium oxides but poor in nitrogen, phosphorus, and potassium due to intense leaching.
4. Which layer of soil is richest in minerals and humus?
The richness of minerals and humus varies across different layers, or horizons, of the soil profile.
- The A-horizon (Topsoil) is richest in humus, which is decomposed organic matter. This layer is dark, porous, and provides essential nutrients for plant growth.
- The B-horizon (Subsoil) is where most of the leached minerals accumulate. It contains more mineral deposits like iron and aluminium compounds and clay but has significantly less organic matter than the topsoil.
5. Why are minerals in the soil essential for plants and other living organisms?
Minerals are the building blocks for life. Plants absorb these dissolved inorganic nutrients from the soil through their roots, a process central to mineral nutrition. These minerals are vital for:
- Growth and Development: Nitrogen is crucial for protein synthesis, phosphorus for energy transfer (ATP), and potassium for regulating water movement.
- Enzyme Activation: Many minerals like magnesium and manganese act as cofactors for enzymes that drive metabolic reactions.
- Structural Components: Calcium is a key component of cell walls, providing structural integrity.
6. What is the main difference between minerals and humus in the soil?
While both are crucial for soil fertility, minerals and humus have different origins and functions:
- Origin: Minerals are inorganic substances derived from the weathering of rocks. Humus is organic matter resulting from the complete decomposition of dead plants and animals by microorganisms.
- Function: Minerals provide the specific chemical elements (e.g., nitrogen, iron) that plants need for metabolic functions. Humus improves the soil's structure, increases its water-holding capacity, and provides a slow-release source of nutrients as it decomposes.
7. How can human activities like farming affect the mineral riches in the soil?
Human activities can severely deplete the mineral content of soil, leading to a loss of fertility. Key impacts include:
- Intensive Farming: Repeatedly growing the same crop in the same field removes specific minerals from the soil faster than they can be naturally replenished. This depletes the nutrient bank, making the soil less productive.
- Soil Erosion: Deforestation and improper ploughing can leave the topsoil exposed to wind and water, which carries away the nutrient-rich layers.
- Use of Chemical Fertilizers: Overuse of certain fertilizers can alter the soil's pH, which can 'lock up' essential minerals, making them unavailable to plants even if they are present in the soil.
