Soils

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Soil is the mixture of rock debris and organic materials which develop on the earth’s surface. The major factors affecting the formation of soil are relief, parent material, climate, vegetation and other life-forms and time. Besides these, human activities also influence it to a large extent. Components of the soil are mineral particles, humus, water and air. The actual amount of each of these depends upon the type of soil. Some soils are deficient in one or more of these, while there are some others that have varied combinations.

It consists of three layers which are called horizons. ‘Horizon A’ is the topmost zone, where organic materials have got incorporated with the mineral matter, nutrients and water, which are necessary for the growth of plants. ‘Horizon B’ is a transition zone between the ‘horizon A’ and ‘horizon C’, and contains matter derived from below as well as from above. It has some organic matter in it, although the mineral matter is noticeably weathered. ‘Horizon C’ is composed of the loose parent material.

This layer is the first stage in the soil formation process and eventually forms the above two layers. This arrangement of layers is known as the soil profile. Underneath these three horizons is the rock which is also known as the parent rock or the bedrock.

Earlier, the soil was classified based on its fertility. The soil was either ‘Urvara,’ i.e. fertile or ‘Usara’ meaning non-fertile or sterile; but in modern-day, various characteristics are taken into consideration, and the soil type is classified based on its texture, colour, or moisture content, etc. In the year 1956, Soil survey of India, an institution was established by the Government of India to study soil and its characteristics.

Classification of Soils

The major types of soils found in India are:

Laterite Soil: The term is derived from the word ‘Later’ which means ‘brick’. Laterite soil is found in those regions of the country which receive heavy rainfall with an alternate dry and wet period – mainly, near the coasts. This kind of soil becomes soft when wet and hardens when dry. In these climatic conditions, leaching of soil takes place, which is a process in which a fertile portion of the soil gets washed away by heavy rains. They are formed from the decomposition of rocks and contain iron oxide, which gives them red or pink colour. This type of soil is ordinarily deficient in nitrogen and is weak in lime content; it is acidic soil. It is found in several parts of the country mainly Western and Eastern Ghats, Vindhyas, Malwa plateau and Satpuras. The states where this type of soil can be found are West Bengal, Andhra Pradesh, Bihar, Meghalaya, Assam, Odisha, to name a few. Laterite soil supports crops like Rice, Ragi, Sugarcane, rubber, coconut, tea, coffee and Cashew nuts.

Mountain Soils: Mountain soils are formed due to the accumulation of organic matter which is derived from the forest growth and is generally shallow in-depth and immature. This type of soil is rich in humus but has poor lime, potash and phosphorus content. It is usually sandy and has gravels. It is mainly found in the Himalayan region, Sikkim, Arunachal Pradesh, Assam, and also in Peninsular India, and the Eastern Ghats.

Characteristics of the mountain soil

Depending on the climate of the region, mountain soil can be divided into two broad groups: (1) Loamy Podzols, and (2) High Altitude Soils. The mid-altitudinal zone in the Himalaya has Podzols. This soil is acidic with low humus and is found in Assam, Darjeeling, Kashmir, Uttaranchal and Himachal Pradesh. Maize, barley, wheat and temperate fruits are grown in this soil in the Himalayan region. Plantation of crops like tropical fruits, coffee, tea or spices in the states of south India like Kerala, Tamil Nadu and Karnataka are undertaken in this type of soil. In the drier areas or deciduous forest belt, deep soil, brown in colour and rich in humus is found. It is perfect for orchard crops.

 Black Soil: This type of soil is made up of volcanic rocks and lava. Black soil is also known as ‘regur’ which is derived from a Telugu word ‘reguda’. Black soil is also known as Black Cotton Soil as cotton is an important crop which is grown in this type of soil. This soil is rich in calcium carbonate, potash, lime and magnesium carbonate but has poor phosphorus content. It is mostly found in areas such as Gujarat, Madhya Pradesh and Maharashtra. It is also found in states like Tamil Nadu, Andhra Pradesh and Karnataka. Black soil is excellent and clayey and can hold a lot of moisture. It becomes sticky in the rainy season and develops cracks when dry. Black soil is good for producing cotton, oilseeds, wheat, linseed, millets, and tobacco.

Red Soil: This type of soil is formed as a result of weathering of metamorphic and igneous rocks. The red colour of the soil comes from the high percentage of iron content. The soil’s texture varies from being sandy to clayey, but it is mainly loamy. It is rich in potash content but lacks phosphate, humus and nitrogen content. The red soil is found in regions such as Tamil Nadu, Madhya Pradesh, Jharkhand, Odisha, some parts of Karnataka and southeast Maharashtra.

Alluvial Soil: Alluvial soils are formed by the deposits of the sediments brought by rivers. Most of the rivers originate from the Himalayas and bring along a high amount of sediments with them. The soil is made up of particles like silt, sand and clay. It has an adequate amount of phosphoric acid, potash and lime. Alluvial soil is of two types – (i) old alluvium known as bangar, and (ii) new alluvium called khaddar. It is the most important type of soil found in the country as it covers about 40% of the total land. It is located in the northern plains beginning from Punjab to West Bengal and Assam. It is also found in deltas of different rivers such as Krishna, Godavari, Kaveri and Mahanadi in peninsular India. Alluvial soil is highly fertile and is light grey in colour. Crops mainly cultivated include wheat, rice, maize, sugarcane, pulses, and oilseed.

Desert Soil: The desert soil is found in regions with low rainfall in an arid and semi-arid climate. The sand in the desert areas is partly original and partly blown from Indus Valley. The soil content has 90-95% of sand and 5-10% of clay. The phosphate content in the soil is high, while the nitrogen content is low. Desert soil lacks humus and moisture, and the water content in this soil is fulfilled through irrigation only. This type of soil is found in arid and semi-arid areas. Desert soil is found mostly in areas of Rajasthan extending to Rann of Kutch, and also in some areas of Haryana and Punjab. Cacti and shrubs are the permanent vegetation which can be seen in the deserts as it is very well adapted to living without moisture for long periods. Also when it rains, the presence of phosphates and nitrates make desert soil fertile, and the desert blooms as dormant seeds wake up to life.

Saline and Alkaline Soil: There are many mineral-based and un-decomposed contents inside the earth. Due to weathering, they release certain minerals such as magnesium, sodium, sulphurous acid and calcium salts. Some of the released spices get carried by rivers and mix in sub-soils of the plains making the soils saline and alkaline. Sometimes, these water-soluble salts move upwards with a rise in the water table during evaporation and transpiration. This type of soil can be found in Uttar Pradesh and Punjab and also in some parts of Gujarat. In the coastal areas, soil salinisation occurs due to accumulation of salts from inundated seawater.

Peat Soil: The accumulation of a high amount of organic matters in the soil in humid regions results in the formation of peaty soils. These types of soils constitute about 10 to 40% of the organic matter and also a reasonable amount of soluble salts. Peaty soils are heavy, black and have high acidic content. They are low in phosphate and potash content. Peaty and marshy soils are found in a few districts of Kerala. On the other hand, marshy soils are found in coastal areas of some states such as Tamil Nadu, Bihar, Almora district of Uttaranchal and Sunderbans of West Bengal.

Problems of Soil

 

Soil plays a central role for economic and social development. It ensures food, fodder and renewable energy supplies to sustain human, animal and plant life. As such, it needs to be cared well

According to New Delhi-based National Academy of Agricultural Sciences (NAAS), the annual soil loss rate in our country is about 15.35 tonnes per ha, resulting in loss of 5.37 to 8.4 million tonnes of nutrients.

 

Soil in India suffers from a number of problems such as:

Soil erosion

It is the removal of soil by forces of nature, particularly wind & water, more rapidly than the soil forming process can replace it

It affects agricultural productivity and economy of country as whole

Water Erosion

It is the detachment and removal of soil material by water

It manifests in the form of rilling, gullying, sheetwash and rain peeling process

The rate of erosion depends on soil properties, slope and vegetation cover

Wind Erosion

The blowing wind removes the top soil layer, and wind erosion is accentuated when soil is dry, weakly aggregated and devoid of vegetation cover

The Human factors of soil erosion include:

Deforestation, that leaves the soil devoid of binding material

Overgrazing loosens the soil structure

Faulty agricultural methods such as ploughing, lack of crop rotation and practice of shifting cultivation

Deficiency in fertility

Indian soils are generally deficient in nitrogen and phosphorous, while high in potassium.

Phosphorous is low in Indo-Gangetic plains,Central and North East India.

Also, nitrogen deficiency is across the country, with the deficiency higher in central and southern India than in the Gangetic plains

Degradation of soil health has also been reported due to long-term imbalanced use of fertiliser nutrients

The ideal n-p-k use ratio is 4:2:1, but has gone from 6:2.4:1 in 1990 to 6.7:2.7:1 in 2016, according to a 2017 report by Fertilizer Association of India

The 54th report of the Parliamentary Standing Committee of Agriculture (2017-18) says that skewed subsidy policy in favour of urea and high prices of other fertilisers are behind the imbalance in the use of fertilisers in the country.

Extractive farming practices such as in-field burning of crop residues (common in north-west India), removal of crop residues are also making soil lose fertility in India.

Desertification

This is the spread of desert like conditions in arid/semi-arid regions due to man’s influence or climate change

This process can be attributed to factors such as:

Uncontrolled grazing

Reckless felling of trees

Population pressures

It has the potential to result in excessive wind erosion, decreasing productivity and increasing frequency of droughts

Waterlogging

The flat and saucer like depressions make movement of surface water sluggish leading to accumulation of rain water, thereby resulting in waterlogging

Also, seepage from unlined channels or canal systems leads to waterlogging in contiguous arable lands

Around 12 million hectares of land suffers from waterlogging in India

Allowing space for horizontal and vertical drainage could help dispose excess water, and prevent Water logging

Salinity and Alkalinity

These are the result of over irrigation in irrigated areas

When farmers indulge in over irrigation, the ground water level rises resulting in salt deposition, due to capillary action

Alkalinity implies dominance of sodium salts

Example: due to intense irrigation, the most fertile soils in Punjab & Haryana are rendered useless due to salinity/alkalinity

Hence, the need to utilise water resources judiciously

Wasteland and urban development

Soil toxicity through chemicals is increasing with urbanisation.

More municipal and industrial wastes are being dumped in the soil with heavy metals having carcinogenic effects

Studies indicate the high concentration and accumulation of heavy metals in urban soils

Industrialisation affecting Soil

Industrialisation is progressively taking away considerable areas of land from agriculture, forestry, grassland and pasture, and unused lands with wild vegetation

Example: Opencast mining is of particular focus because it disturbs the physical, chemical, and biological features of the soil and alters the socioeconomic features of a region.

Also, Mineral production generates enormous quantities of waste/overburden and tailings/slimes and hence soil from a huge land area gets degraded.

Soil Conservation

 

Soil Conservation includes all measures that help in protecting the soil from erosion and exhaustion

It has been estimated that two-thirds of our arable land needs conservation measures

Hence, the urgent need to conserve soil for sake of prosperity of Indian masses

 

The following methods are generally adopted for conserving soil:

Afforestation

Indiscriminate felling of trees should be stopped and efforts should be made to plant more trees

Efforts to increase forest cover to 33% of total land should be made; with the proportion being 20% for plains and 60% for hilly/mountainous regions

Checking overgrazing

Overgrazing of forests and grass lands should be properly checked

Separate grazing grounds should be earmarked

Changing Agricultural practices

Some of the changes suggested in this perspective are:

Crop rotation

When same crop is grown year after year, it takes away certain same nutrients away from soil, making it infertile

Hence, different crops have to be grown, as different crops take up different nutrients through out the year

Growing leguminous plants helps in fixing nitrogen to the soil

Strip cropping

When crops are cultivated in alternate strips, parallel to once another; they can be harvested at various intervals

This ensures that the land is not left fallow at any interval, thereby leaving it less prone to erosion

No-till farming

No-till farminginvolves planting seeds into the residue of the previous crop, with no tillage between harvests. 

Contour ploughing

If ploughing is done at right angles to the hill slope, following natural contours of the hill, the ridges and furrows break the flow of water down the hill

This enables plants to absorb more moisture and reduce erosion

Checking shifting cultivation

This involves persuading tribal people to switch over to settled agriculture

This can be done by making arrangements for tribal people by giving them land and agricultural equipment

Terrace farming

Terracing is the practice of creating nearly level areas in a hillside area.

The terraces form a series of steps each at a higher level than the previous

Terraces are protected from erosion by other soil barriers

Windbreaks

Windbreaks are sufficiently dense rows of trees at the windward exposure of an agricultural field subject to wind erosion.

Evergreen species provide year-round protection

Salinity Management

Use ofHumic acids may prevent excess salination, especially given excessive irrigation.

Humic acids can fix both anionsand cations and eliminate them from root zones

Planting species that can tolerate saline conditions can be used to lower water tables and thus reduce the rate of capillary and evaporative enrichment of surface salts. Salt-tolerant plants includesaltbush, a plant found in much of North America and in the Mediterranean regions of Europe

Use of Natural Fertilizers

Excessive use of chemical fertilizers can result in chemical run off and groundwater contamination

Natural fertilizer are a better alternative, as they replenish the soil with essential nutrients like nitrogen, phosphorus and potassium; while offering the added benefit of providing the soil with organic matter.

Natural fertilizers include livestock manure, mulch, municipal sludge, and legume plants such as alfalfa or clover.

Measures/Schemes for Soil Conservation in India

Watershed Development Project in Shifting Cultivation Areas (WDPSCA)

This was implemented from 1955 onwards to Protect hill slopes of Jhum areas through soil and water conservation measures on a watershed basis

NABARD Loan- Soil & Water Conservation Scheme under RIDF(2001 onwards)

The scheme envisages to promote sustainable development through conservation and management of soil and water.

Rashtriya Krishi Vigyan Yojana (RKVY)

The thrust area is to protect the loss of topsoil, improving soil fertility, enhancing crop production, land and water productivity of watershed areas comprising of wastelands, river valleys and the eco-system as a whole

Soil Health Card Schemes

The scheme aims at promoting soil test based and balanced use of fertilisers to enable farmers to realise higher yields at lower cost.

Also the objective is to aware growers about the appropriate amount of nutrients for the concerned crop depending on the quality of soil.