Under which conditions are pesticides more likely to leach through soil?

Pesticides are more likely to leach through sandy soil that is low in organic matter due to the characteristics of the soil itself. Sandy soil has larger particles and fewer surface areas compared to clay or loamy soil, which means it tends to have larger pore spaces. This allows water and any dissolved substances, including pesticides, to move more rapidly and easily through the soil profile.

When organic matter is low, the soil has reduced ability to retain moisture and nutrients. Organic matter typically enhances soil structure and improves its water-holding capacity. In the absence of sufficient organic matter, any absorbed pesticide molecules are prone to being washed away quickly with the movement of water, especially during rain or irrigation events. Thus, sandy soil with low organic matter presents a scenario where leaching is highly likely because it cannot effectively hold onto the pesticide.

In contrast, clay soils and organic-rich soils tend to retain more water and nutrients and can mitigate the leaching process to a significant extent.