Concept:Leaching is the downward movement of dissolved soil nutrients caused by percolating water.Explanation:Rainwater or irrigation water soaks into the soil and dissolves soluble nutrients and minerals.As the water moves downward, it carries these dissolved substances from the upper soil layers to deeper levels.This washing effect removes essential plant nutrients from the topsoil, thereby lowering soil fertility.Therefore, the correct meaning of leaching is the washing of nutrients down from the upper layers of the soil.Answer:C. washing of nutrients down from the upper layers of the soil