Many soil properties have changed and can change as a result of management, historical land use, or even natural factors, such as drought, interacting with land use. National soil survey databases currently include soil property information for the relatively static soil properties, such as texture, and also for properties affected by management, such as soil organic matter. The databases do not, however, distinguish the values of dynamic soil properties (e.g., organic matter, bulk density, infiltration rate) according to their land use, management system, ecological state, or plant community. ?Dynamic soil properties? as defined in this Guide are soil properties that change within the human time scale. Differences that may exist in these properties can affect the performance of the soil. Furthermore, some dynamic soil properties change very little in response to management and disturbances.