Soil

Explanation[edit]

The soil is the topmost layer of the surface of the Earth that is filled with rocks, minerals, organic and inorganic matters, water, air and other substances that make life possible. Soil comes in different textures and is used for various purposes. One of the main purposes of the soil is to provide a medium for plants to facilitate water and nutrient supply to the roots. Soil also plays a vital role in the water cycle, as it enables the rainwater to infiltrate into the ground.

Frequently Asked Questions[edit]

How did the soil form?[edit]

Soil mainly form from both physical and chemical weathering of different types of rocks over a certain period. The rocks could be igneous rocks, metamorphic rocks, or sedimentary rocks. The other factors that contribute to the breakdown of rocks are the biological processes like plant growth and human activities. Based on the primary activities in different regions and weather, soil is diversely distributed around the world.

What are the classifications of the soil?[edit]

Soil is typically classified based on the size of the particles and texture as sand, silt, and clay. Sand particles are relatively big in size and have high porosity. Silt are quite medium in size, usually found in a water body like a river or lake. Clay is relatively small and smooth with no porosity. As any sample of soil will be diverse enough to have different textures, a texture chart is usually used to determine the type of soil.

In a more technical sense and engineering practices, we follow standardized soil classification systems adopted from the Unified Soil Classification System. For example, the Indian Standard Soil Classification System classifies the soil as follows.

Very coarse soil Boulder greater than 300 mm
Cobblestone 80 to 300 mm
Coarse soil Gravel - G Coarse 20 to 80 mm
Fine 4.75 to 20 mm
Sand - S Coarse 2 to 4.75 mm
Medium 0.425 to 2 mm
Fine 0.075 to 0.425 mm
Fine soil Silt - M 0.002 to 0.075 mm
Clay - C lesser than 0.002 mm