NOVELTY - Slow release fertilizer synergistic agent comprises 8-10 pts. wt. ammonium sulfate, 1-2 pts. wt. ammonium molybdate heptahydrate, 1-2 pts. wt. calcium cyanamide, 3-15 pts. wt. Porphyra powder, 16-19 pts. wt. kelp residue, 22-26 pts. wt. seafood scraps, 13-15 pts. wt. ammonium iodide, 2-4 pts. wt. sustained release microbial layer, 4-5 pts. wt. slow release chelated micro-element layer and 6-9 pts. wt. sustained release micro-crystalline phosphate rock coating layer and balanced amount of water.    USE - Slow release fertilizer synergistic agent used for increasing iodine content in corn (claimed) used as food for iodine deficient patients.    ADVANTAGE - The slow release increases fertilizer utilization rate, promotes corn growth and provides supplementary iodine to person every day.    DETAILED DESCRIPTION - Slow release fertilizer synergistic agent comprises 8-10 pts. wt. ammonium sulfate, 1-2 pts. wt. ammonium molybdate heptahydrate, 1-2 pts. wt. calcium cyanamide, 3-15 pts. wt. Porphyra powder, 16-19 pts. wt. kelp residue, 22-26 pts. wt. seafood scraps, 13-15 pts. wt. ammonium iodide, 2-4 pts. wt. sustained release microbial layer, 4-5 pts. wt. slow release chelated micro-element layer and 6-9 pts. wt. sustained release micro-crystalline phosphate rock coating layer and balanced amount of water, where sustained release microbial layer comprises effective micro-organism microbial inoculum, diatomite and sugar water. Sustained release chelated trace element layer is prepared by attapulgite, waste animal fur, ferrous sulfate and zinc sulfate. Sustained release micro-crystalline phosphate rock coating layer comprises rock phosphate, bone glue and water. An INDEPENDENT CLAIM is included for a method for preparing slow release fertilizer synergistic agent, which involves:    (A) mixing Porphyra powder, kelp residue and seafood waste;    (B) fermenting obtained mixture with water for 3-4 weeks;    (C) drying and crushing fermented material;    (D) spraying melted sustained release micro-crystalline phosphate rock coating layer evenly on obtained particle;    (E) grinding ammonium sulfate and ammonium iodide;    (F) stirring obtained granule with mixture of ammonium sulfate, ammonium iodide and water for 20-30 minutes to obtain core particle;    (G) spraying sustained release chelated trace element layer on core particle for 13-15 minutes;    (H) grinding and mixing ammonium molybdate heptahydrate and calcium cyanamide powder with water uniformly;    (I) spraying obtained mixture on coated core particle;    (J) spraying coated particle with mixture of micro-organism sustained release layer and remaining components; and    (K) drying coated particles at 30-40 degrees C to obtain product.