Soil moisture is “the total amount of water, including the water vapor, in an unsaturated soil.” Soil moisture—sometimes also called soil water—represents the water in land surfaces that is not in rivers, lakes, or groundwater, but instead resides in the pores of the soil. It is a small proportion (only 0.15%) of the liquid freshwater on Earth, but it is an influential store of water in the hydrologic cycle.
Soil moisture modulates interactions between the land surface and the atmosphere, thereby influencing climate and weather, and is important in determining the rainfall-runoff response of catchments, especially where saturation excess runoff processes are important.
Soil moisture also influences a variety of processes related to plant growth. 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.
The roots of plants absorb water first, so their condition directly depends on its amount and aeration. Ultimately, the soil moisture effect on plants and the yield is vital.
Generally, the water holding capacity of a soil is dependent upon such parameters as; soil type, structure, depth, organic matter content, past management practices, porosity, specific surface area, mineralogical composition, salinity, pore fluid characteristics, degree of compaction, presence of contaminants, temperature and humidity. Soil moisture levels affect a range of soil and plant dynamics.
Three types of soil moisture:
Gravitational water
Gravitational water is the water that moves through the soil by the force of gravity and drains. Gravitational water moves in the larger pores of the soil and drains quickly.
Capillary water
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.
Hygroscopic water
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.
Soil moisture
