Hydrological Cycle (Water Cycle) and The Role of Water in Crop Growth

Water, an essential resource for irrigation, is found on the surface of the earth in seas, rivers, dams, and underground reservoirs. It is vital for the physical, chemical, and biological processes necessary for the survival of plants and animals. This article discusses the processes that occur in the cycle known as the water cycle.

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The Hydrological Cycle (Water Cycle)

The hydrological cycle, also known as the water cycle or H2O cycle, refers to the continuous movement of water on, above, and below the Earth's surface. Although the overall balance of water on Earth remains relatively constant, individual water molecules move in and out of the atmosphere.

Water transitions from one reservoir to another, such as from rivers to oceans or from oceans to the atmosphere, through the physical processes of evaporation, condensation, precipitation, infiltration, runoff, and surface flow.

Water undergoes different phases during this cycle: liquid, solid (ice), and gas (vapor).

The sun drives the water cycle by heating the water in oceans and seas. As the water heats, it evaporates into the atmosphere as water vapor. Ice and snow can sublimate directly into water vapor as well.

Additionally, water evaporates from the soil and plant surfaces, a process known as transpiration. The rising air currents or wind carry the vapor into the atmosphere, where cooler temperatures cause it to condense into clouds.

As air currents move water vapor around the globe, cloud particles collide, grow, and fall as rain, snow, hail, or sleet. Some of this water accumulates in ice caps and glaciers, where it can remain frozen for thousands of years.

Most water eventually falls back into oceans or onto land as rain. On land, water flows over the ground as surface runoff, some of which enters rivers and streams, eventually flowing toward the oceans.

Runoff and groundwater are stored in freshwater lakes. Not all runoff flows into rivers; much of it soaks into the ground through infiltration. Some of this water percolates deep into aquifers, where it is stored for long periods.

Water that infiltrates near the surface can seep back into rivers and oceans as groundwater discharge. Some groundwater emerges through openings in the land as freshwater springs. Over time, the water cycle continues as the water returns to the ocean.

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The Role of Water in Crop Growth

Water plays a crucial role in the life of both animals and plants. For crops, water is essential for germination and plays several key roles in plant physiology.

These roles are made possible due to water's unique physical and chemical properties, which include:

i. Thermal properties: Regulation of temperature

ii. Solvent properties: Transportation of solutes and nutrients
iii. Biochemical reactions: Involvement in the photosynthesis process

iv. Transparency properties: Allowing sunlight to penetrate and power photosynthesis in plant cells

A physiologically active plant consists of 60–90% water. Water is needed by plants for various purposes, such as:

v. Photosynthesis: The process by which plants produce food (photosynthates) for growth and development using carbon dioxide and water, in the presence of light. The chemical equation for photosynthesis is:
6CO₂ + 6H₂O + Light energy → C₆H₁₂O₆ + 6O₂ (Carbon dioxide + Water → Glucose + Oxygen).

vi. Transport of nutrients and photosynthates: Water acts as a medium through which nutrients are absorbed from the soil and photosynthates are transported via the xylem and phloem. This is possible due to water’s solvent properties.

vii. Structural support: Water helps support the plant's structure through its various cells. It also maintains turgor pressure, which is essential for controlling the opening and closing of stomata.

viii. Transpiration: This is the evaporation of water from the surface of the plant into the atmosphere. Water released during transpiration escapes to the atmosphere. Transpiration plays a vital role in maintaining water balance within the plant system, as water is continually absorbed by the plant roots.

Water is crucial for plant and animal life, as it constitutes 60–90% of their body weight. Plants cannot survive without water. A shortage of water leads to wilting, which ultimately reduces yield. Plants require water at all stages of growth, although the amount needed may vary depending on the growth stage.

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