A soil with high clay and low organic matter contents is the weakest sorbent.

• A. True
• B. False
• C. Not sure
• D. Sometimes

Answer: (B)

Sorption strength in soils comes from two main components: organic matter and clay minerals. Organic matter tends to bind many pesticides very strongly because of hydrophobic interactions and specific chemical bonding, making soils high in organic matter powerful sorbents. Clay minerals also provide a large surface area and charged sites that can hold pesticides, particularly some ionic or polar ones. So even if organic matter is low, a soil with substantial clay still has meaningful sorption capacity. Calling a soil with high clay and low organic matter the weakest sorbent isn’t accurate, because the clay part still contributes to sorption. The weakest sorption would be a soil low in both organic matter and clay. In short, organic matter generally dominates sorption strength, but clay contributes as well, so that combination isn’t the weakest.