Soil properties that affect pesticide movement include texture, permeability, and organic matter content. Soil texture is determined by the relative proportions of sand, silt, and clay. Texture affects movement of water through soil, and therefore also movement of dissolved chemicals such as pesticides. The coarser the soil, the faster the movement of percolating wafer and the less opportunity for adsorption of dissolved chemicals. Soils with more clay and organic matter tend to hold water and dissolved chemicals longer. These soils also have far more surface area on which pesticides can be adsorbed. The coarser textured the soil, the greater the chance of the pesticide reaching groundwater.
Soil permeability is a measure of how fast water can move downward through a particular soil. Water moves quickly through soils with high permeability. Dissolved chemicals may also move with the percolating water.
| Soil Properties | ||
|---|---|---|
| Texture (affects movement of water particles) | Permeability (measures speed of water's downward movement) | Organic Content(measures volume of water and soil's ability to adsorb pesticides) |
| coarse (sand) | high permeability (fast flow) | low organic content = faster water flow & little adsorption of pesticides |
| smooth (clay, silt) | low permeability (slow now) | high organic content = higher water retention & greater adsorption of pesticides |
Soil organic matter influences how much water a soil can hold and how well it is able to adsorb pesticides. Increasing the soil's organic content through practices such as applying manure or plowing under cover crops increases the soil's ability to hold both water and dissolved pesticides in the root zone where they will be available to plants and to eventual degradation.