Farmers need to be aware of the limitations of the National List when it applies to farm inputs. Producers may only use substances listed for crop use on crops. For example, phosphoric acid is permitted in livestock sanitation, but not as a fertilizer. A material listed for a specific use is restricted to that use, i.e. soap is listed for insect control but not disease control. Some materials have specific restrictions, for instance – copper must be used in a manner that minimizes accumulation in the soil.