•    Due to weathering of rocks different kinds of sand particles are formed like sand, clay etc., their ratio in soil depends on the kind of rock from which these particles are formed. 
•    soil contain various biotic and abiotic factors. Former includes bacteria, plant roots, earthworms, nematodes etc. Later includes water, air, minerals etc. 
•    Classification of soil is based on proportion of soil particles of various sizes. 
    (a) Sandy Soil: Soil contains greater proportion of big size particles. 
    (b) Clayey Soil: Proportion of fine particles is relatively higher 
    (c) Loamy Soil: Amount of large and fine particles is almost same. 
•   On the basis of size, soil particles are broadly classified into following categories:
    (i) Gravel or Stones → 2 mm
    (ii) Sand 0.05 to 2 mm
    (iii) Silt and clay below 0.05 mm

•   Properties of different soil depends on sizes of soil particles it have. In sandy soil, particles size is quite large so they can not fit closely together and have large spaces between them. These spaces are filled with air. Thus, soil is well  aerated having less             water holding capacity. Hence sandy soil is light, well aerated and dry. 
•    In clayey soil, soil particles are much smaller, tightly packed and having little air space. Thus, clayey soil, have little air, more water holding capacity and great amount of humus. 
•    Loamy is best soil for growing plants. Loamy soil contains equal mixture of sand, silt and clay soil particles. Size of silt particles is between sand and clay. Loamy soil have great water holding capacity, large amount of humus and is well aerated so, it is              regarded as best soil for growth of plants.

Soil types

Sandy Soil

The first type of soil is sand. It consists of small particles of weathered rock. Sandy soils are one of the poorest types of soil for growing plants because it has very low nutrients and poor water holding capacity, which makes it hard for the plant’s roots to absorb water. This type of soil is very good for the drainage system. Sandy soil is usually formed by the breakdown or fragmentation of rocks like granite, limestone and quartz.

Silt Soil

Silt, which is known to have much smaller particles compared to sandy soil and is made up of rock and other mineral particles, which are smaller than sand and larger than clay. It is the smooth and fine quality of the soil that holds water better than sand.  Silt is easily transported by moving currents and it is mainly found near the river, lakes and other water bodies. The silt soil is more fertile compared to the other three types of soil. Therefore, it is also used in agricultural practices to improve soil fertility.

Clay Soil

Clay is the smallest particle among the other two types of soil. The particles in this soil are tightly packed together with each other with very little or no airspace. This soil has very good water storage qualities and makes it hard for moisture and air to penetrate into it. It is very sticky to the touch when wet but smooth when dried.  Clay is the densest and heaviest type of soil which does not drain well or provide space for plant roots to flourish.

Loamy Soil

Loam is the fourth type of soil. It is a combination of sand, silt and clay such that the beneficial properties of each are included. For instance, it has the ability to retain moisture and nutrients; hence, it is more suitable for farming. This soil is also referred to as agricultural soil as it includes an equilibrium of all three types of soil materials, being sandy, clay, and silt, and it also happens to have humus.  Apart from these, it also has higher calcium and pH levels because of its inorganic origins.