What is meant by leaching in pesticide application?

Leaching in the context of pesticide application refers to the process through which pesticides are transported downward through the soil profile, often as a result of water movement, such as rainfall or irrigation. This movement can carry pesticides away from the root zone of plants and potentially into groundwater sources. It is significant because leaching can affect the efficiency of the pesticide application and pose environmental risks, such as contamination of water sources.

Understanding leaching is crucial for responsible pesticide use, as it highlights the importance of managing application rates and timing to minimize environmental impact. The other options focus on different aspects of pesticide behavior: air movement, surface movement on water, and degradation in soil, but leaching specifically describes the downward migration through the soil. This makes it a key consideration in both agricultural practices and environmental protection strategies.