Leaching in Soil Science

Leaching is a process that occurs in soil science and agriculture. It refers to the removal of certain substances, specifically alkali salts, from the soil through the action of water. This process is essential for maintaining healthy soil conditions and preventing soil degradation.

Explanation of the Correct Answer

The correct answer to the question is option 'A': by which alkali salts present in the soil are dissolved and drained away. This option accurately describes the process of leaching in soil science. Here is a detailed explanation of why this option is correct:

1. Alkali Salts Dissolution
Leaching involves the dissolution of alkali salts that are present in the soil. These salts are primarily composed of sodium, potassium, and other alkali metals. They may accumulate in the soil over time due to various factors such as irrigation practices, excessive use of fertilizers, and the natural mineral content of the soil.

2. Action of Water
The leaching process is facilitated by the action of water. When water is applied to the soil, it percolates through the soil layers, dissolving the alkali salts as it moves downward. This dissolution occurs due to the water's ability to solubilize the salts and carry them along with it.

3. Draining Away
As the water moves through the soil, it carries the dissolved alkali salts with it. Eventually, the water reaches a lower layer of the soil or a drainage system, where it is drained away. This draining process effectively removes the alkali salts from the soil, preventing their accumulation and potential harm to plants and soil fertility.

4. Importance in Soil Health
Leaching plays a crucial role in maintaining soil health. If alkali salts were to accumulate in the soil without being leached, they would lead to soil salinization. Excess salts can hinder plant growth, reduce crop yields, and degrade soil structure. Therefore, leaching helps to maintain a balanced soil environment that is conducive to plant growth.

5. Other Options Explained
Option 'B': by which alkali salts in soil come up with water is incorrect because leaching involves the downward movement of water, carrying the salts away from the root zone, rather than bringing them up to the surface.

Option 'C': of draining excess water of irrigation is incorrect because leaching is not primarily focused on draining excess water. While leaching does involve the movement of water, its main purpose is to remove alkali salts, rather than excess irrigation water.

Option 'D': which controls water-logging is incorrect because leaching is not specifically aimed at controlling water-logging. While leaching may indirectly alleviate water-logging issues by promoting drainage, its primary objective is the removal of alkali salts.

In conclusion, leaching in soil science is a process by which alkali salts present in the soil are dissolved and drained away through the action of water. This process is crucial for maintaining healthy soil conditions and preventing soil degradation.