Soil water is an essential component of the soil-plant-atmosphere continuum, playing a crucial role in plant growth and development. The availability of water in the soil is influenced by various factors, including soil texture, structure, and organic matter content. Based on the interaction of water molecules with soil particles, soil water can be classified into three main types: gravitational water, capillary water, and hygroscopic water.
Key Facts
- Gravitational water: This is the free form of water that occupies the larger soil pores and moves down readily under the force of gravity. It is not readily available to plants as it quickly drains out of the soil.
- Capillary water: This type of water is held in the micropores of the soil, in the soil pore spaces precisely. It is loosely held around the soil particles and is the most available form of water for plants. Capillary water is retained in the soil by capillary action and can be absorbed by plant roots[3].
- Hygroscopic water: This form of water is tightly bound to soil particles and is typically not readily available to plants. It forms a fine film around the particles of soil and is held tenaciously by surface forces. Hygroscopic water cannot be absorbed by plants unless it is heated[3].
Gravitational Water
Gravitational water is the free form of water that occupies the larger soil pores and moves down readily under the force of gravity. It is not readily available to plants as it quickly drains out of the soil. Gravitational water is typically found in the macropores of the soil, which are the larger pores that allow for rapid water movement.
Capillary Water
Capillary water is held in the micropores of the soil, in the soil pore spaces precisely. It is loosely held around the soil particles and is the most available form of water for plants. Capillary water is retained in the soil by capillary action, which is the upward movement of water in narrow spaces against the force of gravity. Capillary water can be absorbed by plant roots and is essential for plant growth and development.
Hygroscopic Water
Hygroscopic water is tightly bound to soil particles and is typically not readily available to plants. It forms a fine film around the particles of soil and is held tenaciously by surface forces. Hygroscopic water cannot be absorbed by plants unless it is heated. Hygroscopic water is typically found in the micropores of the soil, which are the smaller pores that hold water tightly.
Conclusion
The classification of soil water into gravitational water, capillary water, and hygroscopic water is based on the interaction of water molecules with soil particles. This classification is important for understanding the availability of water to plants and for managing soil water resources.
References
- http://eagri.org/eagri50/SSAC121/lec10.pdf
- https://byjus.com/neet/types-of-soil-water/
- https://agriinfo.in/classification-of-soil-water-268/
FAQs
What is soil water classification?
Soil water classification is the process of categorizing soil water into different types based on its availability to plants and its interaction with soil particles.
What are the main types of soil water?
The main types of soil water are gravitational water, capillary water, and hygroscopic water.
How is gravitational water different from capillary water?
Gravitational water is the free form of water that moves down readily under the force of gravity, while capillary water is held in the micropores of the soil by capillary action.
Which type of soil water is most readily available to plants?
Capillary water is the most readily available form of water for plants, as it is held in the soil by capillary action and can be easily absorbed by plant roots.
What is hygroscopic water?
Hygroscopic water is tightly bound to soil particles and is not readily available to plants. It forms a fine film around the particles of soil and is held tenaciously by surface forces.
How does soil texture affect soil water classification?
Soil texture, which refers to the relative proportions of sand, silt, and clay in the soil, influences the amount and type of water that the soil can hold. Sandy soils have larger pores and less capillary water than clay soils, which have smaller pores and more capillary water.
How does soil structure affect soil water classification?
Soil structure, which refers to the arrangement of soil particles, also affects soil water classification. Soils with good structure, such as those with a crumbly or granular structure, have more pore space and can hold more water than soils with poor structure, such as those with a compacted or platy structure.
How does organic matter content affect soil water classification?
Organic matter content influences soil water classification by increasing the soil’s water-holding capacity. Organic matter can hold up to 20 times its weight in water, making it an important factor in soil water retention.