This study assessed the proposed application of magnesium ammonium phosphate（MAP), recovered from sewage, as a fertilizer to eelgrass（Zostera marina ）seedlings for seagrass bed restoration. Because MAP is acid-soluble at low pH, it is useful as a slow fertilizer that gradually dissolves in sediments, providing nutrients directly to eelgrass and avoiding water pollution. However, because of its high phosphorous to nitrogen ratio, combining MAP with adsorptive materials can suppress the excessive phosphorus release. To demonstrate this proposal, eelgrass was seeded in test systems using quartz sand and synthetic seawater. The effects of applying MAP with andosol to the system on eelgrass germination, shoot length, and root growth were monitored during 98 days in laboratory pot tests. MAP-applied systems exhibited higher germination ratios and marked increases in shoot length, comparable to those of control systems. Root growth was enhanced particularly in andosol-applied systems. Andosol effectively reduced phosphate leaching while promoting ammonium release, suggesting that the andosol’s content bound excess phosphorus. In conclusion, sewage-derived MAP can enhance eelgrass germination and growth. Moreover, andosol addition helps control phosphorus release, making this combination a promising approach for eelgrass bed restoration.

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