What is soil? what is the meaning of soil?
The invaluable resource for farmers and the foundation of economic development in our country is known as soil. This vital element exists across a significant portion of the Earth’s surface, resulting from a mixture of parent rocks and organic matter, allowing diverse vegetation to flourish in suitable climates. The significance of soil in human life, particularly for farmers, cannot be overstated, as it forms the basis for sustenance and livelihoods.
All living beings, including humans, rely on soil for their nourishment, obtaining food directly or indirectly from its richness. Additionally, many of our essential materials, such as cotton, silk, jute, and wool used in clothing, can be traced back to the soil as their ultimate source.
Definition of Soil
As per the definition provided by Dr. Bennett, a renowned American soil expert, “Soil is the upper layer of disorganized materials located on the Earth’s surface, resulting from a fusion of parent rocks and vegetation.”
Soil types In India
In India, soil types exhibit a diverse range owing to a combination of factors such as relief, parent material, climate, time, biodiversity, and human activities. Soil, formed from a mixture of organic matter and rock fragments on the land’s surface, comprises various components like mineral particles, decomposed organic matter, soil water, soil air, and living organisms.
India’s varied topographical features, landforms, climatic zones, and flora have contributed to the creation of distinct soil types across the nation. The interplay of parent material, relief, climate, vegetation, life forms, and time plays a crucial role in shaping the characteristics and formation of these soils.
Soil consists of four essential components: air, water, organic matter (resulting from decayed plants and animals), and inorganic or mineral matter derived from the parent material. The intricate process of soil formation, known as “pedogenesis,” occurs under specific natural conditions, with each environmental component playing a significant role in this transformative journey.
In soil science, each layer of the soil is referred to as a “horizon,” and each horizon possesses a distinctive texture and composition:
Horizon A (Topsoil): This is the uppermost layer where organic components blend with minerals, nutrients, and water, creating an essential foundation for plant growth.
Horizon B (Subsoil): This zone contains a higher concentration of minerals and less humus compared to other layers. Acting as a transition between Horizon A and Horizon C, it contains materials from both the layers above and below.
Horizon C (Weathered and Disintegrated Rock): This zone comprises loose rock materials and serves as the source for the two layers above it. It marks the initial step in soil development.
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In India, the Indian Council of Agricultural Research (ICAR) has categorized soils into eight major types, including:
1-Alluvial Soil
Alluvial soil results from the deposition of river sediments. As numerous rivers originate in the Himalayas, they carry substantial amounts of sediment that eventually settle along their banks. The composition of alluvial soil includes particles like clay, sand, and silt. This type of soil is highly fertile, enriched with essential elements such as potash, lime, and phosphoric acid, making it favorable for agricultural productivity.
Alluvial soil in India can be classified into two types:
New Alluvium (Khadar): This type of alluvial soil is also known as Khadar. It is characterized by recent sediment deposits and is commonly found in the deltas of various rivers, such as the Mahanadi, Kaveri, Godavari, and Krishna.
Old Alluvium (Bangar): Old alluvium, also known as Bangar, refers to alluvial soil formed from older sediment deposits. It is prevalent in different regions of peninsular India.
Alluvial soil supports the growth of a variety of crops, including wheat, maize, sugarcane, rice, legumes, and oilseeds. The soil typically has a light green color. In India, alluvial soil can be found in the northern plains, stretching from Punjab to West Bengal and Assam.
2-Black Soil
The black soil, commonly known as “regur” (derived from the Telugu word “reguda”), originates from volcanic rock and lava. The primary crop thriving in black soil is cotton, benefitting from the soil’s ample supply of potash, magnesium carbonate, and calcium carbonate.
This fertile type of soil is prevalent in several regions across India, including the southern states of Andhra Pradesh, Karnataka, and Tamil Nadu, as well as Gujarat, Maharashtra, and Madhya Pradesh. One of its remarkable characteristics is its excellent water retention capacity, ensuring high moisture levels in the soil. As a result, black soil is suitable for cultivating a variety of crops like cotton, wheat, millet, and tobacco.
3-Red & Yellow Soil
The “omnibus group,” commonly known as red and yellow soil, covers approximately 18.5% of the total land area in the country. This type of soil is primarily found in regions with low rainfall, particularly in the eastern and southern parts of the Deccan Plateau. Significant portions of the Piedmont region of the Western Ghats, along with areas in Chhattisgarh, Odisha, and parts of the southern central Gangetic plain, also feature this soil.
The red color of this soil is attributed to the presence of iron in crystalline and metamorphic rocks. When moist, it displays a yellowish hue. Generally, fine-grained red and yellow soils tend to be more fertile and productive compared to coarse-grained soils. However, this type of soil is typically deficient in humus, nitrogen, and phosphorus.
Farmers often utilize red and yellow soils for cultivating a range of crops, including wheat, cotton, oilseeds, millets, tobacco, and pulses. Despite its limitations, this soil type supports various agricultural activities and contributes significantly to India’s agricultural landscape.
4-Desert Soil
Desert soils, also known as arid soils, cover more than 4.42% of the country’s total land area. They exhibit colors ranging from reddish to brown. Characterized by a sandy to gravelly texture, these soils have low moisture content and limited water retention capacity. Naturally saline, some regions have such high salt content that common salt can be produced by evaporating the water.
Although desert soils possess specific levels of phosphates, they lack sufficient nitrogen. The lower soil horizons contain a high concentration of calcium, leading to the formation of pebble layers that hinder water penetration. However, when irrigation is applied, soil moisture becomes readily available, supporting healthy plant growth.
Notably, the western region of Rajasthan has a significant presence of desert soil, which is deficient in humus and organic matter. Despite the challenging conditions, these soils adapt to desert environments and are crucial in sustaining certain plant life and agricultural activities.
5-Laterite Soil
Derived from the Latin word “Latre,” meaning brick, laterite soil covers approximately 3.7% of the country’s total area. These soils are typical of regions with seasonal monsoon rainfall patterns. The combination of rainwater washing away soils rich in iron oxide and aluminum, along with lime and silica, results in the formation of laterite soil. While laterite soils are abundant in iron oxide and potash, they lack organic matter, nitrogen, phosphate, and calcium.
Though not highly fertile on their own, laterite soils respond well to the application of compost and fertilizers. States like Karnataka, Tamil Nadu, Kerala, Madhya Pradesh, and the hilly regions of Assam and Odisha are known to have significant deposits of laterite soil. Particularly, red laterite soil is highly suitable for the growth of tree crops such as cashew in Kerala, Tamil Nadu, and Andhra Pradesh.
A unique property of laterite soil is that it hardens rapidly and permanently upon exposure to air. This characteristic has led to its extensive use in southern India for making building bricks. Despite their limitations, laterite soils play a vital role in supporting specific vegetation and serve various practical applications in construction and agriculture.
6-Mountain Soil
Mountain soil is typically found in forested areas with adequate rainfall. The texture of this soil is influenced by the hilly terrain in which it is situated. On the valley sides, the soil tends to be loamy and silty, while on the upper slopes, it becomes coarse-grained. In glaciated regions of the Himalayas, this soil is characterized by acidity, lack of vegetation, and low humus content. However, the soil in the lower valleys is fertile and supports robust plant growth.
7-Alkaline Soils
Alkaline soils are known for their extreme infertility, containing high levels of sodium, potassium, and magnesium. These soils often accumulate excessive salt due to the dry climate and insufficient drainage in arid and semi-arid regions. Calcium and nitrogen are deficient in this type of soil.
To improve soil fertility measures such as increasing irrigation and drainage, adding gypsum, and cultivating salt-tolerant crops can be employed. Alkaline soils are widespread in states like Punjab, Uttar Pradesh, Bihar, Rajasthan, Haryana, and Maharashtra. Despite their limitations, certain leguminous plants can thrive in these soils.
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8-Peaty and Marshy Soils
Peat soils develop due to the accumulation of abundant organic matter in the soil, a consequence of the humid climate in the region. These soils generally exhibit low levels of phosphorus and potash. In certain districts of Kerala, peat soils can be found, while the coasts of Tamil Nadu, Bihar, Uttaranchal, and the Sundarbans in West Bengal are home to marshy soils.
Peat soils are distinctive with their black color and high acidity. They contain substantial amounts of soluble salts and boast organic matter ranging from 10 to 40 percent. These unique characteristics make them favorable environments for certain plant growth and contribute to the overall diversity of soil types in the region.
Indian Forest Soil Type
| No. | Characteristics | Forest Soil Type |
|---|---|---|
| 1 | Brown Forest Clay | – Found between 900-1800m. |
| – Rich in humus. | ||
| – Slightly acidic. |
| – Dominated by deciduous forests. | ||
|---|---|---|
| 2 | Podzol | – Found above an altitude of 1800m. |
| – Dense coniferous forests. |
| – Dense forest cover. | ||
|---|---|---|
| 3 | Alpine Grass Soil | – Found in the alpine region of the Himalayas. |
| – Contains decomposed plants. | ||
| – Either sandy soil or sandy loam. |
What is Soil Erosion?
Soil erosion refers to the process of topsoil removal from the Earth’s surface. Normally, soil formation and erosion occur simultaneously, maintaining a balance between the two. However, when this balance is disrupted, the soil is eroded at a faster rate than it is produced, leading to soil erosion.
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In arid and semi-arid regions, wind is a significant cause of soil erosion, whereas in areas with heavy rainfall, water plays a major role in soil erosion. Water erosion can occur in two main forms: sheet erosion, which happens on flat fields after heavy rains, and gully erosion, which occurs on steep slopes when runoff forms gullies, resulting in fragmented and unusable agricultural land.
Soil erosion has various adverse effects, such as carrying eroded material downstream by rivers, reducing their water-carrying capacity, and increasing the likelihood of frequent floods and damage to agricultural areas. Coastal areas are also affected, with the tidal waters of the Arabian Sea and the Bay of Bengal causing considerable damage to the soil. Severe wave erosion is observed on beaches in Gujarat, West Bengal, Odisha, Kerala, and Tamil Nadu.
Several factors contribute to soil erosion in India, including deforestation, intensive agricultural practices relying heavily on water and chemical fertilizers leading to waterlogging and salinity, and river valley projects. Approximately half of India’s total land area experiences some degree of erosion, resulting in the loss of millions of tonnes of soil and nutrients each year, negatively impacting the country’s productivity.
Soil Conservation and its Methods
Soil conservation aims to maintain soil fertility, prevent soil erosion, and restore depleted soils. Various soil conservation practices are employed to reduce erosion, such as contour bunding, contour terracing, controlled grazing, regulated forestry, cover crops, mixed farming, and crop rotation. Plantations play a vital role in reducing soil erosion and preventing deforestation is essential. Additionally, measures like storing floodwater or diverting excess rain are crucial to managing floods during the rainy season.
To address soil erosion in specific regions, various programs, and initiatives are undertaken. For example, the Chambal ravines in Madhya Pradesh undergo projects involving plugging of drains, construction of dams, leveling of drains, and planting cover crops. In areas like the Western and Eastern Ghats, as well as Northeast India, shifting of crops (slash and burn) contributes significantly to soil erosion.
Encouraging farmers to adopt terrace farming and implementing schemes to regulate shifting cultivation are essential steps to mitigate soil erosion in such regions. For instance, Northeast India has launched a beneficiary-oriented scheme to regulate shifting cultivation and promote sedentary farming practices as an alternative to Jhum cultivation.