Soil that naturally occurs has water contained in it, which is referred to as soil water. This water which is held in water is also referred to as rhizic water. The potential of soil to hold back moisture which is available readily for plant growth and development for purposes such as irrigation and land usage is an important factor. One of the vital functions of soil is to hold and catch water at the time of periods of rainfall and store them.
On the basis of interaction of water molecules with soil, soil water can be classified into three types –
- Gravitational water
- Capillary water
- Hygroscopic water
Soil Water – Types
This is a free form of water which is held loosely in soil. This water could be easily lost by gravitational force. Majorly, these are seen in the soil’s macropores. Very little quantity of gravitational water is made available to plants as they quickly drain the water down the table in all, excluding the majority compact of soils. Hence, plants are not able to use this water as much as they move rapidly out of the soil.
It is the water that is contained in the micropores of the soil, in the soil pore spaces precisely. This water, which composes the soil solution, is loosely held around the particles of soil. This form of water is the most available water form made available to plants for utilization. It is the main water available to plants as they are trapped in the soil solution. Capillary water is retained in the soil by capillary action (force) which is less than the atmospheric pressure.
Thus, capillary water is retained in soil as the properties of surface tension (adhesion and cohesion) of the soil micropores are more strong than the gravitational attraction or gravitational force. But, since soil tends to dry out, the size of the pore increases and gravity begins to turn the capillary water into gravitational water, thus moving it down.
This form of water makes for a fine film wrapping particles of water and is typically not readily available to plants. It is found not only in pores but also on the surface of soil particles. These are tightly held in soil and cannot be eliminated except for over drying at 105 ℃.
Hygroscopic water is tightly bound to soil by adhesion properties, which causes some water only to be consumed by the roots of plants. As this form of water is seen on the particles of soil and not in pores, only some types of soils composed of several pores (such as clays) will comprise a high percentage of it.
This was a brief on types of soil water. Explore related topics on NEET at BYJU’S.