The most predominant action in the first horizon of a soil profile is

The most predominant action in the first horizon of a soil profile is eluviation. Eluviation is the process by which water percolates through the soil and carries dissolved minerals and organic matter from the upper layers to the lower layers. This creates a zone of accumulation of nutrients, minerals, and organic matter in the lower layers, which is called the illuvial horizon. The first horizon of the soil profile is also known as the A horizon, which is the topsoil layer that contains the most organic matter and is the most fertile. Therefore, the process of eluviation plays a significant role in determining the fertility of the soil in the first horizon.