Where is pesticide application less likely to contaminate groundwater?

Pesticide application is less likely to contaminate groundwater when conducted over clay soils that contain organic matter because these soils have properties that enhance their ability to retain water and reduce leaching. Clay soils have smaller particles and a high cation exchange capacity, which means they can hold onto nutrients and pesticides more effectively than other soil types. The presence of organic matter also contributes to this retention by binding with pesticides, making them less available to be washed away into groundwater.

In contrast, sandy soils tend to have larger particles and larger pore spaces, which allow for rapid drainage. This means that pesticides applied to sandy soils can easily leach down through the soil profile, increasing the risk of groundwater contamination. Areas near water bodies can have higher runoff potential, which can carry pesticides directly into surface waters and potentially affect groundwater as well. Heavy rainfall can exacerbate leaching, as the increased water movement can transport pesticides deeper into the soil, increasing the likelihood of groundwater contamination.