Iron supply agents for plant growth

An iron supply agent for plant growth that provides iron, a trace

• element essential for the growth of marine and terrestrial plants, comprising sodium ferrous citrate solution prepared by combining sodium bicarbonate with iron citrate,
• wherein citric acid, water and iron are stir-mixed with aqueous citric acid solutions containing from 10 g to weight of citric acid dissolution limit of the water temperature of citric acid (100% purity equivalent) per 100 ml of water and iron (equivalent to 100% purity) at a ratio of 5˜60 mass parts when the citric acid content is 100 mass parts to obtain iron citrate, wherein sodium bicarbonate (equivalent to 100% purity) is combined at a ratio of 80˜120 mass parts per 100 ml of water when the citric acid content is 100 mass parts, thereby producing an aqueous solution of sodium iron citrate, thereby producing an aqueous solution of sodium iron citrate, and
• a chelating agent mixed with said aqueous solution of sodium iron citrate, characterized in that said chelating agent is lignin sulfonic acid derived from lignin waste.