If one soil is clearly dominant in a field, test that one and gear your application rate to it. If several soils are dominant, test all of them. Then gear your application rate to the one with the lowest organic-matter content. Organic matter is one of the most important soil properties that affect pesticide leaching, but not the only one. Texture and permeability are two more.
Texture refers to the relative proportion of sand, silt, and clay in the soil.
Leaching is more likely in sandy, coarse, or light-textured soils. Permeability refers to the ability of water to move through a soil. If a soil has low permeability, water from a heavy rain may pond on the surface. If a soil has high permeability, water flows through the soil more freely and may cause chemicals to leach.