Physical properties of soil include colour, texture, structure, porosity, density, temperature, and air. The colours of soil vary widely from place to place and indicate some properties like organic matter, water, and redox conditions of the soil. Soil texture, structure, porosity, density, are related to the types of soil particles and their arrangement.
Properties of Soil
The soil has the following special properties:
- Texture: The texture of the soil depends upon the relative amount of these particles. Clay has the smallest sized particles. Because of its very small size, the clay is felt smooth. Silt particles are larger than clay particles. Their size range from0.002 to 0.02mm in diameter. So silt does not feel smooth. Sand particles are the largest-sized particles of soil. Their diameter is more than0.02mm
- Absorption of water: Water holding capacity in different types of soils is different. Soil absorbs water because it is porous. Sandy soil holds less water than clay soil and loamy soil. Clay soil holds more water than sandy soil. Sand absorbs less water than clay.
- Moisture: Texture decides the water holding capacity of the soil. The soil has some amount of water inside it as moisture. Water is usually present as a thin film around the soil particles. It is absorbed by the roots of the plants. The capacity of soil to hold water is important for the growth of crops.
- Colour: Soils are of different colours. They are red white and black. The red colour of the soil is due to the presence of iron oxide. The black colour soil is rich in minerals and humus. It is good for the growth of wheat and jowar.
- Soil pH: Soil can be acid, alkaline or neutral. Some plants grow in acidic soil pH below 7 like potatoes. Carrots and lettuces prefer soil with neutral pH of 7.0. The soil becomes more acidic over time as minerals are leached away.
- Percolation Rate: The process in which water passes down slowly through the sol is called the percolation of water. But water does not percolate at the same rate in all types of soils. Sandy soil allows maximum percolation of water and clay soil allows minimum percolation of water. Rainwater percolates through the soil and collects above the bedrock. This level of groundwater is called the water table. Sandy soil is quite loose, so the percolation rate of water is highest in sandy soil but lowest in clay soil because it is very compact.
- Soil contains air: Air is present in the space between the soil particles. This air provides the oxygen required for respiration by the roots of plants and other organisms. Sand particles are quite large. Sand particles cannot fit closely together, so there is a large space between sand particles. Clayey soil provides much less air to the plant root which grows in it.