Acidity is more important with some types of pesticides than others and is less important overall than organic matter and texture. Other geologic and environmental factors also affect pesticide leaching to groundwater. Depth from the soil surface to groundwater is very important. The closer the water is to the surface, the less chance there is for a pesticide to be filtered and degraded in the soil. Weather plays an important role in many ways.
Pesticides break down faster in warm, moist soil than in cooler or drier soil.
The timing and amount of rainfall or irrigation influence how much water percolates through the soil. If heavy rainfall or irrigation occurs soon after a pesticide application, the percolating water can carry the pesticide deep into the soil where it breaks down more slowly. Also, the type of tillage practiced can affect soil temperature, moisture, and water infiltration, all of which have an impact on pesticide degradation and leaching. The following is an explanation of how we made these calculations, which are presented in Table 1. For example, a soil with an organic matter content of more than 2 percent would have a rating of 10, the highest.