However studies have also found evidence for preferential flow in sandy soils with no visible evidence of fracturing. The climate of the area usually determines the crops grown and the types of pests present. The temperature and the intensity of the sun often determine the persistence of pesticide compounds. The frequency and duration of rainstorms may influence the degree to which pesticides are transported away from site of application. The tendency for pesticides to leach or be removed in surface runoff is mainly a function of the soil composition.
Sandy soils drain rapidly and thus are susceptible to leaching problems.
Clayey soil is less porous, so water will pool at the soil surface and run off instead of infiltrating. For instance it can be difficult to distinguish transport processes from transformation processes in the field. Usually these are detections of the older, banned organochlorines, but there are also frequent detections of insecticides used for pest control in residential settings. Ag-products are infrequently detected. Most models neglect preferential flow.