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Mineral Riches in the Soil

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  • Last Updated : 06 Sep, 2022
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The outermost layer of the earth is called the crust. The crust is covered with a mixture of organic and inorganic material called soil. Soil serves as a medium for the growth of plants as it is rich in minerals and useful living organisms. The mineral composition of the soil is about 45-50%, organic matter constitutes about 1-5% of it whereas the remaining space is filled with air and water. There are various types of soils based on their contents, texture, water holding capacity, aeration, etc. A few of these are as follows:

  • Sandy soil: It consists of loose particles with poor nutrient content and very little water-holding capacity. 
  • Clayey soil: Its particles remain very close together with little or no space. Aeration is poor but it has great water holding capacity.
  • Loamy soil: It has moderate aeration and water-holding capacity. It is considered the best soil for agriculture due to its rich nutrient content and the above properties.

The breakdown of various types of rocks over a period of time by natural elements leads to the formation of soil. Soil is formed by the following processes: weathering and paedogenesis. Hereunder, is a detailed explanation of minerals riches in soil.

Soil Minerals

Soil Minerals

 

Mineral is one of the part of soil composition including Humus, Living organisms, Water and air. Minerals are very essential substance found in soil. It is the largest component of the soil, making up almost 40% to 45% of the total components. Soil is rich in minerals such as iron, phosphorus, calcium, magnesium, sulphur etc. Minerals constitute the major portion of soil. Minerals are necessary for plant growth and development. The minerals present in soil are absorbed by plants through their roots. For e.g., Nitrate is an essential mineral as it helps in the synthesis of proteins. Magnesium is an important component of chlorophyll. The mineral soil is very supportive of plant growth. It also helps the soil highly rich in nutrients and make highly fertile which gives better crop result and increases economic development.

Types of Minerals in Soil

Minerals are of two types: Primary minerals and secondary minerals.

  • Primary minerals: These minerals have not undergone any alteration since their deposition. They are similar to their parent material. Often these materials are bigger in size and irregular in shape. These primary minerals are usually found in sand and silt. Primary minerals get formed at elevated temperatures on account of cooling magma during the original solidification of rock or during metamorphism. They are usually derived from igneous and metamorphic rocks in soil. In most soils feldspars, micas, and quartz are the main primary mineral constituents. Other examples of the primary minerals in soil include silica minerals and silicates, titanomagnetite, apatite, iron minerals, volcanic gases and non-crystalline inorganic constituents.
  • Secondary minerals: They are formed as a result of weathering of the primary minerals. Secondary minerals are mainly found in fine silt or clay. The particle size of these minerals is much smaller due to the weathering process. These minerals have a large surface area that helps them retain moisture. Some examples of secondary minerals in the soil are hydroxides, phyllosilicates, oxides, carbonates, phosphates, sulfates and halides. Their addition to farmland is beneficial.

Minerals present in the soil 

Common minerals present in the soil are as follows:

  1. Hematite: It is a common iron oxide compound with the formula Fe2O3 and is widely found in rocks and soils. It is red to blackish-red in color. On absorbing water it swells up to form hydrated iron oxide. Clay-sized hematite crystals occur as a secondary mineral formed by weathering processes in soil, and along with other iron oxides it is responsible for the red color of many tropical, highly weathered soils. 
  2.  Limonite: Hydrated ferric oxide is called Limonite. It is yellow to brown in color. It is an important coloring and cementing agent in soil. Limonite is a residual soil produced by the decomposition of magnesium silicate (olivine) rocks in tropical environments. During weathering process most of the original rock is leached away leaving only its iron content, which is precipitated out in the form of iron sesqui-oxides to create a soft and highly porous soil.
  3.  Goethite: Limonite when adsorbs water is called goethite. It is one of the most thermodynamically stable iron oxide. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment.
  4. Gibbsite: It is the most common aluminum compound found in soil. It is found in highly weathered soil. It is a major mineral in soils of the tropics and subtropics where it may be the dominant mineral in the clay fraction. 
  5. Carbonate Group: Magnesium hydroxide and calcium hydroxide combine with carbon dioxide to form carbonates. Carbonates buffer soil pH and are an indication of the relative abundance of bases. The most common types are calcite (CaCO3) and dolomite [CaMg(CO3)2]. Less common soil carbonates include sodium carbonate (Na2CO3) and siderite (FeCO3). 
  6. Calcite: It is generally white or colorless. It is a major constituent of sedimentary rocks and consists of calcium carbonate. Calcite is present primarily in arid and semi-arid regions, where the source was either limestone parent rock or calcareous air-borne dust, although in some climates the soil calcite is the result of coral and shells. Calcareous soils typically have a pH above 7.5.
  7. Dolomite: It is the chief source of magnesium in the soil. Dolomite, a type of limestone which provides valuable nutrients to plants and helps change the pH of the soil by raising it to match the plants’ needs. It is also known as dolomitic lime/limestone. It provides more nutrients than straight lime.
  8. Siderite: It is an important mineral found in water-logged soil. It is produced by the alteration of other iron-bearing minerals. Its chemical formula is FeCO3. This iron carbonate mineral is commonly found in sediments and soils. It has been used as iron ore and for steel production.
  9. Sulphate group: It is formed by the combination of Sulphur and Oxygen ions. It further reacts with calcium ions to form calcium sulphate.
  10. Gypsum: It is found in sedimentary rocks and desert soils. It is water-soluble and leaches easily. It is chemically calcium sulfate. It plays a  beneficial role in breaking up compact soil, especially clay soil. It is useful in changing the soil structure of excessively heavy soils.

Functions of soil nutrients

Various elements are present in the soil which perform several important functions. A few of these are listed below:

  • Element Nitrogen is an essential constituent of proteins, nucleic acids, vitamins, hormones. It is absorbed in the form of nitrates, nitrites or ammonium ions. It is required by meristematic tissues and metabolically active cells.
  • Phosphorus is absorbed in the form of phosphate ions. It is a constituent of cell membranes, certain proteins, all nucleic acids and nucleotides.
  • Potassium is required by meristematic tissues, buds, leaves and root tips. It maintains anion-cation balance in cells, is involved in protein synthesis, opening and closing of stomata, maintenance of turgidity of cells.
  • Calcium plays an important role in synthesis of middle lamella, formation of mitotic spindles etc.
  • Magnesium is an essential constituent of chlorophyll and helps in maintaining ribosome structure.
  • Sulphur is obtained as sulphate ions from the soil. It is the main constituent of several coenzymes, vitamins and ferredoxin.
  • Iron is required in large amounts compared to other micronutrients. It is obtained as ferric ions from the soil.  It is an important constituent of transport proteins, it activates catalase enzyme and is essential for the formation of chlorophyll.
  • Manganese activates many enzymes involved in photosynthesis, respiration and nitrogen metabolism. Its most important role is the splitting of water during photosynthesis.
  • Molybdenum is an important constituent of enzymes of nitrogen metabolism like nitrogenase and nitrate reductase.
  • Chlorine helps in determining solute constituent of cells and helps in maintaining its anion-cation balance. It plays important role in the water splitting reaction of photosynthesis.

Uses

  • Plants absorb essential nutrients from the soil. It forms the basis of agriculture.
  • Sandy soil is used for filtration purposes.
  • Clayey soil is used for making ceramic materials.
  • Nutrients are recycled in soil by decomposition of dead, decaying organic matter.
  • Soil provides anchorage to roots of plants. It also acts as a storehouse of water and nutrients.

FAQs on Soil Minerals

Question 1: List some common soil contaminants.

Answer:

 Arsenic, Mercury, Cadmium, Copper, Zinc

Question 2: What is earth’s body of soil known as?

Answer:

 The pedosphere is known as the earth’s body of soil.

Question 3: List the types of soil found in India.

Answer:

  • Alluvial soil  Black soil
  • Red soil 
  • Laterite soil 
  • Desert/Arid soil   
  • Mountainous soil 
  • Alkaline/Saline soil

Question 4: What is humus?

Answer:

The uppermost organic component of soil which is formed by the decomposition of leaves and other plant parts by the microorganisms present in the soil is called humus.

Question 5: What is soil profile?

Answer:

Soil has different layers as they are formed at different time intervals. These different layers or horizons of soil is called a soil profile.


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