Arid, saline, peaty and forest-mountain soils

Detail

Where these soils fit in the ICAR scheme

• ICAR soil classification: the Indian Council of Agricultural Research divides India's soils into 8 groups. They are alluvial, black, red and yellow, laterite, arid, saline, peaty (marshy) and forest soils.
• The first four groups cover most of the farmland. The four groups in this note are smaller and "problem" soils. Each is held back by one strong limit: too little water (arid), too much salt (saline), too much water and acid (peaty), or slope and cold (forest).
• Soil Health Card scheme (2015): each farmer gets a card that reports soil test results and advises how much fertiliser to use. The tests include pH (how acidic or alkaline the soil is) and EC (electrical conductivity, a measure of salt). These two readings matter most for the saline and peaty soils described below.

Soil	Main limit	Colour / feel	pH	Key areas
Arid (desert)	Little water and humus	Red to brown, sandy	Alkaline	Western Rajasthan
Saline / alkaline	Too much salt	White salt crust on top	Saline below 8.5; alkaline above 8.5	Rann of Kachchh, canal areas of Punjab, Haryana and western UP, coastal deltas
Peaty / marshy	Waterlogging, acidity	Black and heavy	Acidic	North Bihar, Sundarbans, Kuttanad
Forest / mountain	Slope, cold, erosion	Loamy to coarse	Acidic at high altitude	Himalaya, Western and Eastern Ghats

Arid soils

• Arid soil: the soil of hot, dry areas with little rain. It is red to brown, sandy and often saline. Class 7 NCERT calls it desert soil.
• Where: mainly western Rajasthan (the Thar Desert, west of the Aravalli range), with smaller patches in Kachchh (Gujarat) and south-west Haryana and Punjab.
• Very salty in places:

• In some spots the soil holds so much salt that people make common salt by evaporating its water.

• Why it has little humus and moisture (humus is the dark, rotted plant and animal matter that makes soil fertile):

• The climate is dry and the temperature is high.
• Water evaporates fast from the hot surface.
• Few plants grow, so little dead plant matter goes into the soil, and any that does breaks down quickly.

• Result: the soil has little humus and little moisture.

• Kankar layer:

• Kankar: hard lumps of calcium carbonate (lime) that form in the soil.
• The amount of calcium rises with depth, so kankar fills the lower horizons. (A soil horizon is one layer of a soil profile, the layers seen from the top of the soil down to the rock.)

• This hard layer stops water from soaking down (infiltration). Rainwater stays near the surface and evaporates.

• Farming with irrigation:

• Arid soil can be farmed once water is supplied, as in western Rajasthan.
• The Indira Gandhi Canal brings Sutlej–Beas water from the Harike barrage in Punjab into the Thar. It has turned large desert areas into farms growing wheat, cotton and mustard.
• There is a cost. Heavy canal irrigation over a hard kankar layer raises the water table. This brings waterlogging and salinity in parts of the canal command area. The problem is covered under soil degradation in this topic.

Saline and alkaline soils

• Saline and alkaline soils: soils with so many salts of sodium, potassium and magnesium that most crops cannot grow. They are infertile.
• Saline soil: has too many soluble salts, such as chlorides and sulphates. A white salt crust forms on the surface.
• Alkaline (sodic) soil: has too much sodium held on the clay. The soil becomes hard, sticky and airless. Its pH is above 8.5.

• Salt-affected land in the Indian subcontinent is grouped as saline, alkali/sodic and saline-alkali [3].

• Local names: usar and reh (Uttar Pradesh), kallar and thur (Punjab–Haryana belt).

• Extent: salt-affected soils cover about 6.73 million hectares in India. About 2.35 million hectares of this lies in the Indian part of the Indo-Gangetic Plains (FAO Global Symposium on Salt-affected Soils, 2021) [4].

How salt builds up in canal-irrigated land

• Over-irrigation leads to salinity:
• Too much canal water soaks down, and the water table rises close to the surface.
• Water then moves upward through tiny pores in the soil (capillary action) and carries dissolved salts with it.

• The sun evaporates the water and the salts stay behind as a white crust.

• This is seen in canal-irrigated Punjab, Haryana and western Uttar Pradesh. In the world, the same thing happens in Pakistan's Indus basin, Iraq's Tigris–Euphrates plain and the Aral Sea basin of Central Asia.

Where saline soils occur

• Arid and semi-arid areas: rain is too low to wash the salts out.
• Waterlogged and swampy tracts: poor drainage traps the salts.
• Rann of Kachchh (Gujarat): a salt marsh that the sea floods in the monsoon and that dries into a salt flat in summer.
• Coastal deltas where seawater gets in: the Sundarbans (Ganga–Brahmaputra delta, West Bengal) and the east-coast deltas of the Mahanadi, Godavari, Krishna and Kaveri. Here tides and storm surges push seawater onto the land.
• Canal command areas: Punjab, Haryana and western UP.

Reclamation (bringing the land back into use)

• Gypsum (calcium sulphate):
• Calcium from the gypsum takes the place of the sodium held on the clay.
• Water then washes the freed sodium away.

• The soil becomes crumbly again and water can pass through it.

• Drainage: surface drains and sub-surface drains (buried pipes) lower the water table and carry away salty water.

• Salt-tolerant crops: these are crops that can grow in salty soil. Examples are salt-tolerant rice and wheat varieties.
• CSSRI, Karnal (Haryana): the Central Soil Salinity Research Institute, run by ICAR.
• It found that salt-affected soils and saline water can be used to grow forest and fruit trees, forage grasses, oil-yielding crops, and aromatic and medicinal plants [3].
• The most salt-tolerant trees it lists are Prosopis juliflora, Acacia nilotica and Tamarix articulata. Fruit trees include ber (Zizyphus mauritiana), jamun (Syzygium cuminii) and guava (Psidium guajava) (FAO APANews, 2005) [3].

• When trees are planted, 3–5 kg of gypsum goes into each planting pit. This is about half the gypsum needed to reclaim the soil fully [3].

• Uttar Pradesh has the largest area of salt-affected land in India. About 4 lakh hectares of sodic land there was reclaimed and brought under cultivation in three phases (1993–2018) [4].

Peaty and marshy soils

• Peaty soil: a soil made mostly of partly rotted plant matter that piles up in wet, waterlogged places.
• How it forms:
• Heavy rain and high humidity keep the ground wet.
• Poor drainage leaves it waterlogged and short of oxygen.
• Without oxygen, dead plants decay only slowly and pile up.

• Result: the soil has very high organic matter and is black, heavy and acidic. Organic acids from the rotting plants make it acidic.

• Where:

• North Bihar, in the low-lying land between the Kosi and Gandak rivers.
• The Sundarbans (West Bengal), where the soil is also saline from tidal seawater.
• Coastal Odisha (Mahanadi delta) and coastal Tamil Nadu.

• Kuttanad, Kerala: the swampy delta near Vembanad Lake in Alappuzha and Kottayam districts.

• Kari soils of Kuttanad: very acidic, black, peaty soils.

• Kuttanad is the only system in India that grows rice below sea level. The land was made by draining delta swamps in brackish water (a mix of fresh and sea water) [2].
• Farmers build polders (low land shut off from the water by bunds) to create fields. The bunds are made of coconut by-products, sand, twigs and good-quality clay [2].
• The landscape has three parts: wetlands for paddy and fishing, garden lands for food crops, and water areas for inland fishing and shells [2]. Duck farming is also common [2].
• Kuttanad produces about 25% of Kerala's rice [2].

• FAO declared it a Globally Important Agricultural Heritage System (GIAHS) in 2013 [2]. A GIAHS is a traditional farming landscape that FAO recognises for its value to food security, biodiversity and culture. Class 7 NCERT also describes this below-sea-level farming.

• Use: these soils need drainage and liming (adding lime to reduce acidity). After that they suit rice, and coconut on the bunds.

Forest (mountain) soils

• Forest soil: soil that forms in hilly and mountain areas under forest cover, where there is enough rainfall.
• Where: the Himalaya (Jammu and Kashmir to Arunachal Pradesh), the Western Ghats, the Eastern Ghats and the hills of the north-east.
• Texture changes with the setting:

Setting	Soil character
Valley sides	Loamy and silty (fine and fertile)
Upper slopes	Coarse-grained (rocky, thin)
Snow-covered Himalayan areas	Acidic, low in humus; they suffer denudation
River terraces and alluvial fans of lower valleys	Fertile

• Denudation: the slow wearing away of the land surface by weathering, running water, ice and wind. On steep, snowy slopes it removes the topsoil before a thick soil can form.
• Why soils in high, snowy areas are acidic and poor in humus:
• Cold slows down the work of bacteria, so dead leaves rot slowly.
• Snowmelt washes the bases (calcium, magnesium) out of the soil.

• Result: a thin, acidic soil with little humus.

• Alluvial fan: a fan-shaped heap of silt and gravel that a stream drops where it leaves a steep mountain and reaches flatter land. Fans and river terraces (flat steps of old river deposits along a valley) have deep, fertile soil.

• Alpine soil (Class 7): the soil of high mountain meadows is "thin, rough and rocky".
• Crops: tea (Assam hills, Darjeeling, Nilgiris), coffee (Karnataka, Kerala, Tamil Nadu), spices (Western Ghats) and temperate fruit such as apple (Himachal Pradesh, Jammu and Kashmir). These are grown on terraced slopes, where steps cut into the hillside slow down runoff and soil erosion.

Prelims Hooks

• Kankar in arid soil = lumps of calcium carbonate in the lower horizons. Calcium increases with depth, and the layer stops water from soaking in.
• Arid soil gives very little crop until it is irrigated. Its best-known reclaimed area is western Rajasthan, through the Indira Gandhi Canal.
• Usar and reh (UP) and kallar and thur (Punjab–Haryana) are local names for saline and alkaline soils, not for arid or laterite soils.
• Gypsum (calcium sulphate) reclaims alkaline/sodic soil. Lime treats acidic peaty soil. Examiners often swap these two.
• CSSRI is in Karnal, Haryana. It is an ICAR institute and should not be confused with CAZRI, Jodhpur, which works on arid zones.
• Kari soils are acidic peaty soils of Kuttanad, Kerala. Kuttanad is India's only system of rice farming below sea level and became an FAO GIAHS in 2013 [2].
• Peaty soil = high organic matter, black, heavy, acidic. Found in north Bihar, the Sundarbans, coastal Odisha, coastal Tamil Nadu and Kuttanad.
• Forest soils are acidic and low in humus in snowy Himalayan areas, but fertile on river terraces and alluvial fans.
• India's salt-affected area is about 6.73 million ha, and UP has the largest share [4].
• Trap: saline soils are not limited to deserts. They also occur in canal-irrigated, waterlogged land and in coastal deltas.

Mains Points

• Irrigation-induced salinity (GS-III): over-irrigation in canal commands raises the water table and leaves a salt crust. This has happened in Punjab, Haryana, western UP and the Indira Gandhi Canal area. The answer is gypsum, sub-surface drainage, salt-tolerant crops and saline agroforestry (CSSRI research) [3], together with water pricing and micro-irrigation. UP reclaimed about 4 lakh ha of sodic land in 1993–2018 [4].
• Below-sea-level farming as climate adaptation (GS-I/III): Kuttanad's polder system grows about 25% of Kerala's rice in brackish delta swamps [2]. Rising seas, seawater intrusion and soil acidity now threaten it, so it offers lessons for other low deltas such as the Sundarbans.
• Mountain soils and land use (GS-I): thin, acidic and erodible Himalayan soils need terracing, forest cover and plantation crops. Deforestation and road-building on slopes speed up denudation and landslides.
• Desert soils (GS-III): irrigation turns the Thar's arid soils into farms. But the kankar layer and high evaporation mean that without drainage the gains can turn into waterlogging and salinity. Water-saving crops and sprinkler and drip irrigation keep the gains going.