Different Types Of Water In Soil

What is Soil Water?

Soil water is the water which is available in the soil and which can be taken up by plants for their growth and survival. The water stored in the soil serves as the major medium through which nutrients reach the plant's roots to be absorbed for conducting physiological activity.

Soil water availability and movement have a big impact on its structure, fertility, and health. So, the soil water relations, concerning the absorption and retention of soil water become important for the balance of soil moisture and are determinants for good agricultural productivity. Understanding soil-water dynamics helped in effective irrigation management and soil conservation.

Types of Soil Water

Various types of soil water are listed below.

Gravitational Water

• Gravitational water is free water in the soil moving down the soil profile due to the force of gravity.

• Most of it is found in the macropores and drains freely soon after rainfall or irrigation.

• It will eventually seep through and recharge groundwater and deep soil moisture.

• It influences the aeration and drainage of the soil and causes the leaching of salts and other solutes from the soil.

Capillary Water

• Capillary water is water which is held by capillary forces in the pores of soil and, therefore forms a continuous film around the soil particles.

• This water is held against gravity and is available to plants.

• It is the chief source of the water supply to plant roots since it is held in the root zone and can be easily assimilated by plants.

• It supports plant hydration and nutrient uptake.

Hygroscopic Water

• Hygroscopic water is a thin film of water molecules adhering tightly to soil particles because of forces of adhesion.

• Not available to plants, since the particles hold the water too strongly.

• Hygroscopic water affects the amount of moisture in the soil and also about dryness or the availability of water to plants.

Bound Water

• Bound water refers to water that is chemically attached to the soil particles or organic matter.

• It is distinguished from free water and capillary water by the strength of attachment to the constituents in the soil.

• The bound water has effects on the texture, structure and compaction of the soil.

• It is very important in binding together the matrix of the soil and hence controlling the physical properties of the soil.

Free Water

• This is the unbound, mobile, and flows freely under gravity in soil.

• It tends to accumulate in soils during the time of heavy precipitation or irrigation periods.

• Free water contributes to soil saturation and thereafter affects soil drainage and aeration.

• Free water, therefore, needs to be managed properly to prevent waterlogging and to enable the healthy growth of plants.

Comparison of Different Types of Soil Water

The difference between different types of soil water is:

Soil Water Availability

Soil texture is the proportion of sand, silt, and clay particles in soil. It influences the water retention and drainage of the soil. For instance, sandy soils drain quickly and have reduced water-holding capacity while clayey soils retain more water but may never drain well.

Fine soil structure promotes water infiltration and retention. If the soils are well aggregated with ample pore space, they can accommodate more water. Organic matter improves the water-holding capacity of the soil due to improved soil porosity hence enhancing the aggregation. This acts like a sponge in soaking and holding water that plants can tap into during dry periods.

Different Types of Water in Soil NEET MCQs (With Answers & Explanations)

The key concepts to be covered under this topic for different exams are:

• Types of Soil Water

• Comparison of different Soil Water

Practice Questions for NEET

Q1. Edaphic factor refers to:

1. Water

2. Soil

3. Relative humidity

4. Altitude

Correct answer: 2) Soil

Explanation:

Edaphic factors refer to the soil-related components that influence the living organisms within an ecosystem. These factors include soil texture, pH, nutrient content, moisture, temperature, and the presence of microorganisms. Edaphic factors play a significant role in determining plant growth, species distribution, and overall ecosystem productivity. They interact with other environmental factors like climate and can be altered by human activities such as agriculture or urbanization.

Hence, the answer is the option 2) Soil.

Q2. Which of the following water increases the water table but is not available to the plants?

1. Hygroscopic water

2. Gravitational water

3. Capillary water

4. None of these

Correct answer: 2) Gravitational water

Explanation:

Gravitational water forms the groundwater under the influence of gravity. It increases/maintains the water table but goes beyond the reach of the roots of the plants.

Although gravity causes water to flow through the soil it tends to percolate too deeply for plants to reach, even though it may raise the water table. Generally speaking, plants depend on capillary water—the water stored in the tiny soil pores that are accessible to their roots—for absorption. The root zone rapidly loses gravitational water rendering it inaccessible to plants.

Hence, the correct answer is option 2) Gravitational water.

Q3. Which of the following represents the water capacity of soil that is available to the plants?

1. Field capacity

2. Storage capacity

3. Echard

4. All of these

Correct answer: 2) Storage capacity

Explanation:

Storage capacity is the amount of capillary water present in the unit weight of the soil. The capillary water is available to the plants. Capillary water is held in the soil by capillary forces, filling the micropores between soil particles. It is the primary source of water available to plants for their metabolic processes. The storage capacity varies depending on soil texture, with finer soils like clay holding more capillary water than coarse soils like sand. However, excessive water retention in the soil can lead to waterlogging, which restricts oxygen availability to plant roots. The amount of capillary water is also influenced by the soil's field capacity, which is the point where the soil retains the maximum water after gravitational drainage. Efficient management of capillary water is essential for optimal plant growth and crop yield.

Hence, the correct answer is option 2) Storage capacity.

Also Read:

• MCQs on Different Types of Water in Soil

• Diffusion

• Passive Transport

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