Moisture In Soil

Soil

Soil is one of the most important naturally occurring resources. It is the natural habitat of plants and many microorganisms. It nourishes plants with water and essential nutrients hence enabling their growth. Soil is the most important raw material for agriculture. Agriculture provides food, clothing and shelter to all entities either directly or indirectly. Hence soil is an inseparable part of our living.

Soil consists of different layers such as:

  • Gravel

  • Sand

  • Clay

  • Water

  • Humus

What Is Soil Moisture?

Water in soil is referred to as soil moisture. Water absorption in soil is determined by various factors. It plays a major role in soil formation. As a result of precipitation, water arrives at the surface. The particle size distribution of soil determines its porous nature and causes downward movement of water vertically which is known as infiltration. This penetration continues deep in the layers of soil until it reaches saturation.

Water, on reaching this barrier, cannot seep vertically further, hence moves sideways. Formation of puddles as a result of saturation is called surface ponding which can be long-lasting. Water that is available to plants is called Root zone moisture while surface soil moisture is the water available in the immediate upper region of soil.

Moisture content in the soil can be measured using a device known as Tensiometer. They are water-filled tubes which are sealed with a porous ceramic tip towards the bottom and a gauge at the top which is devoid of air molecules. They are penetrated into the soil till the root level. Water passes between the tip of the device and the ambient soil until it reaches an equilibrium and hence tension is recorded on the gauge. Readings thus obtained gives a measure of soil moisture in that region.

Types of Soil Moisture

The different types of water present in the soil include:

Gravitational Water

The water that reaches the water table of the soil due to the gravitational force is referred to as gravitational water. This is not available to the plants.

Hygroscopic Water

This water is also not available to the plants. It is a thin film of water tightly held by the soil particles.

Chemically Combined Water

The chemical compounds present in the soil particles contain water. This is known as chemically combined water. This is also not available to the plants.

Capillary Water

This water is available to the plants for absorption. This water exists between soil particles in small capillaries.

Atmospheric Humidity

The hanging roots of the epiphytes absorb the moisture in the air due to the presence of hygroscopic hairs and spongy velamen tissues.

Importance Of Soil Moisture Content

  • Soil water carries food nutrients for the growth of plants

  • Soil moisture content determines the yield of the crop in a region

  • Crucial in maintaining soil’s temperature

  • Soil moisture acts as nutrients

  • Important for soil formation

  • Moist soil is ideal for the growth of many plants that demand a huge supply of water (Ex: Rice)

  • Soil moisture catalyses biological activities of microbes in the soil.

  • Water is a primary need for photosynthesis in plants.

Measuring Soil Moisture

The soil moisture can be measured by various tools mentioned below:

Tensiometers

These measure the tension of soil moisture. They are water-filled tubes, with a porous ceramic tip at the bottom. These are sealed and have a vacuum gauge at the top. They are inserted in the soil to the depth of the plant root zone. The readings obtained in the tensiometers indicate the availability of water in the soil.

Electrical Resistance Blocks

These consist of two electrodes connected to lead wires extending to the soil surface. The electrodes are embedded in the blocks of porous material. It is used to measure soil water tension.

Time Domain Reflectometry (TDR)

TDR is used to determine the soil moisture content. Steel rods are placed in the soil and electrical signals are sent through them. The returned signals are measured to determine soil water content.

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