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Silt Soil

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Silt is solid, dust-like sediment which is carried by wind or water or ice. Silt is composed of rock and mineral molecules that are bigger than clay but smaller than sand. Individual silt particles are so small that they are less likely to be seen with the naked eye. To be categorized as silt, a particle must be smaller than (.002 inches) across. Silt is most commonly found in soil, along with other kinds of sediment such as sand, clay and gravel. Silt sand or soil is slippery when wet, but not rocky or grainy. It is often referred to as fine silt because of being a non-plastic soil material.


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Occurrence of Silt

Let’s see the three main processes that form silt:

  1. Silt soil occurs when rock is weathered, or worn away, by water and ice. As flowing water carries tiny rock splinters, they scrape against the bottom and sides of stream beds, working away more rock.

  2. The particles mince against each other, getting smaller and smaller until they become silt-size.

  3. Glaciers can also weather away rock particles to form silt. Ultimately, wind can carry rock particles through a canyon or a landscape, thrusting the particles to grind against the canyon wall or one another.                                 

All three processes cause the formation of silt.


Soil and Its Different Types

Soil is formed by various particles such as clay, loam, humus, rock, gravel, sand and silt. Let’s discuss the types of soil in detail.

1. Sand

The widely used construction material, sand consists of particles of rock and hard minerals, like silicon dioxide. They are the biggest type of soil particles, where each particle is visible to plain sight. The large, comparatively stable sand-particle size enhances soil aeration, encourages drainage in tight soils and helps plants thrive or tilt.

When rubbed between the fingers, the larger particle sand size provides wet or dry sandy soil a grainy texture and even makes the soil crumbly and light when stuck together in your hand. The shape of sand particles is flat, rounded, elongated, angular, and subangular with a texture that is smooth, rough or polished.

2. Silt

Silt is a sediment substance with a size mediated between sand and clay. Transported by water during floods, the river silt creates a fertile deposit on the valley floor.

Being non-plastic or having low plasticity because of its fineness, silt soil allows it to be formed into balls or any desired shape when wet.

3. Clay

Finest of all the soil particles, clay measures less than 0.002 mm in size and is formed from the chemical decomposition of rocks. This fine-grained, cohesive soil glues together and creates a sticky texture when wet or dry.

Clay retains a high amount of water due to the spaces found between clay particles. Clay shrinks when getting dry but expands when in contact with water. Organic clay is extremely compressible and has very high strength when dry, which is why it is utilized in construction as mud mortar.

4. Loam

A mixture of clay, sand and silt is known to have to favour air circulation, water retention, drainage and fertility. These soils are greatly fertile, easy to work with and offer good drainage. Depending on their predominant constitution they can be either sandy or clay.


Black Silt  

Silt is granular soil whose mineral origin is quartz and feldspar. It is quite amazing to know that the fertile black river silt situated on the Nile river's banks is a symbol of rebirth, linked with the Egyptian god Anubis.


Tank Silt

One of the silt types of soil, is fine soil transported from surface runoff during rainfall from catchment areas along with crop residue and is deposited as sediment in the tank water and decomposed over a period of time. Tank silt is believed to be rich in organic matter. However, the poor physical, chemical and biological property of the soil elevates the ill effects of climatic change, which substantially affects the rain-fed cropping.


Fun Facts

  • Silty soil is generally more fertile than other types of soil, which also makes it good for growing crops. Enough clay content makes the soil too stiff for plants to flourish.

  • Silt soil encourages air circulation and water retention.

  • When there aren't abundant trees, rocks, or other materials to prevent erosion, silt can accumulate quickly.

  • The surplus of silt can also upset some ecosystems.

  • The important and national symbol of India and Vietnam – Lotus plants have their roots in silty wetlands; however, their big, showy flowers blossom above water.

  • Many species of frog lie torpid during the cold winters by embedding themselves in a layer of soft silt at the bottom of a pond or lake. Since the Water at the bottom does not freeze, and the silt renders some insulation, or warmth, for the animal.

  • In some parts of the world, agriculture has blossomed in river deltas, where silt sediments are rich, and along the sides of rivers where annual floods freshen up silt.

  • The Nile River Delta in Egypt is one classic example of a highly fertile area where farmers are harvesting crops for thousands of years utilizing river silt.

FAQ (Frequently Asked Questions)

1. What Are the Effects of Silt and Silt Sediment on the Environment?

Answer: Silt can alter landscapes. For instance, silt settles in still water. So, the accumulation of silt sediments gradually fills in places like lakes, wetlands and harbours. Floods deposited silt along flood plains and river banks. Deltas take place where rivers deposit silt since they empty into another body of water. About 60 % of the Mississippi River Delta is structured on silt.


In many parts of the world, windblown silt carpets the land. Such accumulations of silt are referred to as loess. Loess landscapes, such as the Great Plains, are generally a symbol of past glacial activity.

2. How Silt Affects Agriculture?

Answer: Agricultural and industrial discharge can obstruct ecosystems with silt and other sediments. In areas that deploy chemical fertilizers, industrial runoff can make silt toxic. Silt can also be made toxic with subjection to industrial chemicals from ships, making the silt at the bottom of harbours and ports particularly at risk. Toxic silt can poison lakes, rivers, and water streams.


"Slash and burn'' agriculture, for example, upsets the ecosystem by eliminating trees. Agricultural soil is decayed into rivers, and close by waterways are blocked with silt. Plants and animals that have adapted to live in reasonably silty soil are pushed to find a new niche for the purpose of survival. The river habitats of a few organisms in the Amazon River, like the pink Amazon River dolphin, also known as boto, are menacing. River dolphins cannot track down prey as well silt in the water.