What is the necessary condition for leaching to occur?

Leaching is the process through which soluble substances are washed out from the soil, primarily due to the movement of water. For leaching to occur effectively, there must be an excess of water that percolates through the soil. This excess water helps dissolve nutrients and other soluble materials, facilitating their transport downward through the soil layers.

When water is abundant, it can carry away these substances as it moves, resulting in the leaching process. In contrast, limited rainfall would not provide sufficient water to dissolve and transport substances, while heavy tillage might mix materials but does not create the necessary conditions for leaching. Additionally, the presence of impermeable layers can inhibit water movement, preventing leaching from occurring altogether. Thus, the requirement of excess water percolating through the soil is crucial for initiating and sustaining the leaching process.