NOVELTY - Slow-release fertilizer synergist comprises 3-4 pts. calcium formate, 2-3 pts. potassium selenite, 16-19 pts. calcium superphosphate, 13-16 pts. soybean residue powder, 33-37 pts. vermicompost, 8-12 pts. actinolite powder, 4-5 pts. potassium azide, 2-4 pts. sustained-release microbial layer, 4-5 pts. sustained-release chelation layer, 6-9 pts. sustained-release microcrystalline rock phosphate coating layer and proper amount of water.    USE - The slow-release fertilizer synergist is useful in corn for improving soil ammonium nitrogen content (claimed).    ADVANTAGE - The synergist controls the nitrate content, satisfies the nitrogen uptake from corn, reduces the loss of fertilizer nitrogen, improves the utilization of fertilizer, reduces the nitrite content in corn and improves the quality of maize.    DETAILED DESCRIPTION - Slow-release fertilizer synergist comprises 3-4 pts. calcium formate, 2-3 pts. potassium selenite, 16-19 pts. calcium superphosphate, 13-16 pts. soybean residue powder, 33-37 pts. vermicompost, 8-12 pts. actinolite powder, 4-5 pts. potassium azide, 2-4 pts. sustained-release microbial layer, 4-5 pts. sustained-release chelation layer, 6-9 pts. sustained-release microcrystalline rock phosphate coating layer and proper amount of water. The sustained-release microbial layer is prepared by inoculating 5-7 pts. effective-microorganism microbial inoculum into 120-140 pts. sugar water, stirring to obtain microbial suspension, soaking 45-55 pts. diatomaceous earth in a solution of sulfuric acid for 60 minutes, then rinsing with water to neutral, drying, baking at 400-500 degrees C for 2-3 hours, removing, cooling to room temperature, grinding into fine powder, adding microbial suspension, stirring for 20-30 minutes, filtering out fine particles, drying via blower at 30-40 degrees C. The sustained-release chelation layer is prepared by calcining 24-26 pts. attapulgite at 600-800 degrees C for 2 hours, then grinding into fine powder, hydrolyzing 16-18 pts. waste animal fur by adding 6-8 mol/l hydrochloric acid for 18-24 hours, adding the milk of lime to adjust pH to 7, filtering, adding 4-7 pts. ferrous sulfate into the filtrate, heating to 40-60 degrees C, chelating for 1-2 hours, then adding 3-5 pts. zinc sulfate and chelating at 50-80 degrees C for 1.5-3 hours, adding attapulgite powder into the resultant chelate solution, drying and crushing to obtain complex chelate powder. The sustained-release microcrystalline rock phosphate coating layer is prepared by processing 28-32 pts. rock phosphate via vibrating mill to obtain microcrystalline powder, adding 8-10 pts. cattle bone glue and proper amount of water into the rock phosphate microcrystalline powder, soaking for 8-10 hours, heating the mixture system to 70-80 degrees C and mixing uniformly. An INDEPENDENT CLAIM is also included for preparing slow-release fertilizer synergist, comprising: (i) mixing the soybean residue powder, vermicompost and actinolite powder in a composting pool, adding proper amount of water, fermenting for 25-27 days, drying the resultant fermentation product, crushing and granulating; (ii) uniformly spraying the sustained-release microcrystalline rock phosphate on the outer surface of resultant granules to obtain inner synergist layer; (iii) mixing and grinding the calcium superphosphate and potassium azide, adding proper amount of water, mixing with granules, stirring, centrifuging at 60-80 rotations/minute for 20 minutes, centrifuging again with sustained-release chelation layer at 200 rotations/minute for 8-10 minutes to obtain middle synergist layer, removing and drying the particles; (iv) grinding calcium formate and potassium selenite with proper amount of water, then uniformly spraying on outer surface of step (iii) resultant particles, then spraying sustained-release microbial layer and remaining components by mixing with water on the outer surface of particles to obtain outer synergist layer; and (v) drying the resultant granules at 40-50 degrees C using blower, then packaging and storing in a dry place.