This is a lengthy process. It is formed by a process of physical or chemical weathering of rocks. Microorganisms then help breakdown the organic matter in the soil. The decaying of plants and animals helps with this process. Earthworms recycle nutrients, thereby making the soil richer.
Types of Soil
Clay, sandy and loamy are the three classifications given to soil. Most soils are a blend of all three types, but loams are a mixture of clay, sand and silt and are considered the most fertile. The texture and appearance of soil depends on the content of each of these soil types. Sandy is mainly granular and is composed of rock particles and minerals. Clay has fine-grained minerals and high water content. Silt is a granular material derived from rock.
Composition of Soil
Soil holds 0.01% of the earth's water. Soil is a composition of 49% Oxygen, 33% Silicone, 7% Aluminium, 4% Iron, and 2% Carbon. Air and water make up 50% of the soil and minerals and organic matter make up the rest.
Layers of Soil
The topmost layer is called topsoil. It contains high amounts of humus and microorganisms. Most biological activity occurs in this layer, and it is from this layer that plants derive their nutrients. Not much humus remains present in the layer below the topsoil. The process of leaching brings down the minerals from the upper layers to the layers below. The bottom-most layer consists of withered rock.
Life in the Soil
ike the atmosphere, soil also has layers and these are called horizons. There are 4 main horizons, called Horizon O, Horizon A, Horizon B and Horizon C. H-O is the very top thin 4cm depth of topsoil, H-A is next and is part topsoil and composed of roots and beneficial micro-organisms that assist with the decay of organic matter and all other life forms like worms and insects. H-B is a tough, impenetrable layer that plant roots will not break into or through. H-C contains the 'parent' material from which all other layers are formed – rocks and old soil formations.
1 sqm of soil can hold up to 1 billion life forms, including spiders, insects, worms, centipedes, mites, fungi and bacteria.
There are more microorganisms in one handful of soil than there are people on earth.
1.4 million earthworms can be found in just 0.4 of a hectare.
Archaeologists have determined that the demise of many sophisticated civilisations such as the Mayans of Central America and the Harappan of India resulted directly from the mismanagement of their soils.
US agriculture currently produces about 500 million tons of crop residue each year. Mostly this is recycled, and contributes to the maintenance of soil organic matter. If plans to use these crop residues for bioenergy production are introduced, it could deprive agricultural ecosystems of important inputs for future soil productivity that are essential for maintaining existing soil balances.
Arsenic from smelter emissions and other pesticide residues bind strongly to soil and will likely remain near the surface for hundreds of years giving populations a long term source of exposure.