The movement of herbicide down through the soil is called?

• A. Runoff
• B. Absorption
• C. Leaching
• D. Evaporation

Answer: (C)

Leaching is the downward movement of dissolved substances through the soil with percolating water. When a herbicide is applied, if it dissolves in soil water and isn’t strongly bound to soil particles, rainfall or irrigation can push that solution down the soil profile, potentially past the root zone and toward groundwater. This process is influenced by how soluble the herbicide is, how well it adsorbs to soil particles (clay and organic matter), soil texture (sandy soils tend to leach more than heavy, organic-rich soils), and how quickly the chemical degrades. In contrast, runoff involves water flowing across the surface, carrying contaminants with it, while evaporation removes water from the surface, and absorption generally refers to uptake by roots rather than downward transport through the soil. So the downward, water-driven movement of the herbicide through the soil is leaching.