<；P>；PROBLEM TO BE SOLVED: To provide a method for supplying iron content, supplying soluble iron content easily ingestible by aquatic plants such as marine alga and seaweed, into water for a long period, widely usable by using materials available in large quantity at a low cost, and applicable to a wide water area such as a lake and a sea area. <；P>；SOLUTION: The method for supplying iron content includes installing, into water, a mixture made by mixing dredged soil containing steel slag and fulvic acid, preferably dredged soil having a fulvic acid content of not less than 0.002 mass%. iron content (bivalent iron content) eluting from steel slag, and fulvic acid contained in the dredged soil are bound together to produce a fulvic acid iron content, and the fulvic acid iron content is supplied into water for a long period. <；P>；COPYRIGHT: (C)2011,JPO&INPIT
