There are many factors that contribute to the physical characteristics of the soil. The most important factors are; soil porosity, soil texture, soil structure, and bulk density.
A unit of soil is composed of organic matter, open spaces, mineral, and solid material. By volume, soils are made up of 50% solid material, and 50% pores space. The minerals primarily consist of clay, silt, and sand that make up 45% of soil. Soil also contains decaying animal and plant substances known as organic matter. The spaces in between the soul particles are important for storing water and air.
The arrangement and shape of soil in clusters is known as soil structure. Agricultural productivity is heavily affected by soil structure and composition. The main types of soil structures are; block, granular, columnar, prismatic, and platy. These soil structures are mainly formed by the clumping of many soil particles. The soil structure is not stable and can change with biological activity, weather conditions, and soil management practices.
The size of soil particles determines the texture and type of soil. Mainly only particles smaller than 2 mm are considered soil particles. Fragments larger than 2 mm are marbles or stones. The average size of soil particles ranges from 0.05 mm to 2 mm. Soil is categorized into three fractions; silt, sand, and clay.
Silt particles: The average of silt particles ranges from 0.02mm to 0.5mm. The physical appearance of clay and silt is similar. But the particles of clay are smaller than 0.2mm. Both silt and clay are not visible to the naked eye.
Sand: Sand particles are larger than silt and clay soil. The water holding capacity is sandy soul is poor and such kind of soil is not useful for agricultural practices. The sandy soil particles are further subcategories into fine sand, medium sand, and coarse sand on the basis of particle size.