In weed control, soil sterilization is that process whereby the soil is altered so that it will no longer sustain the higher forms of plant life. In most common use the term refers to the application of chemicals to the soil surface. The sterile effect obtained is not instantaneous but develops as the chemical is carried down through the soil with water or after mixing the chemical with the soil by tillage. The sterile effect obtained is not permanent as leaching, fixation, or decomposition by microbes reduce the toxic effect with time. The length of time chemicals will remain active as soil sterilants varies. Highly soluble materials will be removed much more rapidly than will relatively insoluble compounds.