NOVELTY - Synergistic slow-release compound fertilizer comprises diatomite, fishmeal, cow bile powder, clam shell powder, manganese sulfate, sodium selenite, humic acid, cellulose ether, gypsum powder, stone powder, talc powder, black soil powder, silkworm excrement, sodium carboxymethylcellulose, silicate bacteria, Streptococcus faecalis, Trichoderma, and additive. The additive comprises poultry feather, sulfuric acid solution, sodium hydroxide, keratinase, copper citrate, manganese citrate, zinc citrate, medical stone powder, and sodium silicate.    USE - Synergistic slow-release compound fertilizer.    ADVANTAGE - The fertilizer is rich in nutrients, has synergistic effect, and can be easily absorbed by crops, thus, promoting crop growth. The use of diatomite and slow-release coating agent in forming double-coated fertilizer nutrients prolongs fertilizer effect and increases crop yield. The coating agent is completely degradable and harmless to soil and crops.    DETAILED DESCRIPTION - Synergistic slow-release compound fertilizer comprises 10-15 pts. wt. 1250-2000-mesh diatomite, 0.2-0.5 pt. wt. fishmeal, 0.5-1 pt. wt. cow bile powder, 2-3 pts. wt. clam shell powder, 0.2-0.5 pt. wt. manganese sulfate, 0.01-0.02 pt. wt. sodium selenite, 6-8 pts. wt. humic acid, 12-15 pts. wt. cellulose ether, 1-2 pts. wt. gypsum powder, 1-3 pts. wt. stone powder, 3-4 pts. wt. talc powder, 10-15 pts. wt. black soil powder, 2-4 pts. wt silkworm excrement, 5-8 pts. wt. sodium carboxymethylcellulose, 0.1-0.2 pt. wt. silicate bacteria, 0.1-0.2 pt. wt. Streptococcus faecalis, 0.1-0.2 pt. wt. Trichoderma, and 4-5 pts. wt. additive. The additive comprises 12-15 pts. wt. poultry feather, 30-35 pts. wt. 30-40% sulfuric acid solution, sodium hydroxide, 0.15-0.2 pt. wt. keratinase, 1-2 pts. wt. copper citrate, 1-2 pts. wt. manganese citrate, 1-2 pts. wt. zinc citrate, 20-22 pts. wt. medical stone powder, and 5-6 pts. wt. sodium silicate. The additive is prepared by washing poultry feather with water, high-temperature sterilizing, crushing, adding sulfuric acid solution, hydrolyzing for 15-18 hours, adding sodium hydroxide solution to adjust pH to 6.5-7, heating to 50-60 degrees C, adding keratinase and performing enzymolysis for 12-15 hours, adding copper citrate, manganese citrate and zinc citrate, stirring for 2-3 hours, adding sodium silicate, continuously stirring for 30-40 minutes, adding medical stone powder, uniformly stirring, drying, and grinding for 40-50 minutes. An INDEPENDENT CLAIM is included for slow-release composite fertilizer production by: (A) uniformly mixing fishmeal, cow bile powder, clam shell powder, gypsum powder, stone powder, black soil powder and silkworm excrement; adding silicate bacteria, S. faecalis and Trichoderma; uniformly mixing; and fermenting for 30-35 days; (B) mixing water with equal amount of diatomite, grinding for 20-30 minutes to prepare diatomite slurry, adding manganese sulfate and sodium selenite, uniformly stirring, and dehydrating and drying to prepare diatomite coating material; (C) mixing cellulose ether, sodium carboxymethylcellulose and deionized water, heating to 60-80 degrees C, and stirring for 40-50 minutes to obtain slow-release coating agent; and (D) uniformly mixing fermented material and diatomite coating material with the remaining raw materials, granulating, spraying slow-release coating agent on surface of granules, hot-air-drying, and cooling to room temperature.