Even though soil particles are often close together, there is always some angular space between them. All such soil voids are collectively referred to as pore space. The pore space in the soil includes a relatively consistent volume (40-60 percent of the total soil volume) that is filled with water and gases in changing amounts.
In “dry” soil, water occupies just a tiny fraction of the available area. In “wet” soil, the majority of this area is occupied by water. In reality, the soil serves as a water store for plants. The water stored in the soil may be classified into the following four groups. Rain is the primary source of water. Some of the water is collected and stored in reservoirs. This is known as runoff or runaway water. The remaining water is absorbed by the ground.
5 Types of Soil Water
(a) Gravitational water
Water that enters the soil water table as a result of gravitational force following rainfall. This type is not accessible to plants, although it is available via mechanical techniques like tube well irrigation.
(b) Hygroscopic water
Hygroscopic water is a thin coating of water that is securely retained by soil particles. The plants do not have access to this water.
Figure 1: Different types of soil water.
(c) Chemical water
The quantity of water included in the chemical compounds found in soil particles. The plants do not have access to this.
(d) Capillary water
Water exists between soil particles in small capillary pores is called Capillary water. It is the most common available form of water for absorption.
(e) Atmospheric humidity
This is water vapor present in air, which can be absorbed by hanging roots of the epiphytes due to presence of spongy velamen tissue and hygroscopic hairs.