NOVELTY - Method for preparing slow-release fertilizer involves using 10-14 pts. wt. iron chloride, 240-260 pts. wt. chicken manure, 110-130 pts. wt. plant ash, 10-15 pts. wt. calcium carbonate, 25-30 pts. wt. potassium nitrate, 95-105 pts. wt. carbon coal ash, 40-60 pts. wt. lees, 55-65 pts. wt. iron ore, 28-32 pts. wt. cassava starch, 6-8 pts. wt. calcium acetate, 11-15 pts. wt. biological agent comprises sulfate-reducing bacteria, iron-reducing bacteria and Bacillus subtilis in a ratio of 1:1:2 and water.    USE - The method is useful for preparing slow-release fertilizer for improving soil acidity (claimed).    ADVANTAGE - The prepared slow-release fertilizer increases the soil pH value, promotes and accumulates nitrogen in soil, activates the nutrient content of soil and improves growth of crop.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for method for preparing slow-release fertilizer, which involves (a) sintering carbon coal ash at 750-850 degrees C for 20 minutes and cooling, sintering iron ore at 500-600 degrees C for 30 minutes and cooling, mixing sintered carbon coal ash and iron ore, adding 5 mm size magnet to mixture in a ratio of 1:4, shaking mixture for 40-60 minutes and crushing to obtain 100-120 mesh size powder, (b) mixing and crushing chicken manure, plant ash and lees, placing mixture into fermentation tank and controlling mixture moisture content to 35-45%, fermenting mixture for 20-25 days, filtering fermented mixture and separating liquid and residue, (c) mixing residue with powder obtained in step (a), calcium carbonate and potassium nitrate, granulating mixture and performing magnetization at 3800-4200 mT for 10-12 seconds, (d) mixing fermented liquid obtained in step (b) and cassava starch, heating mixture liquid at 60-70 degrees C for 20-30 minutes, cooling liquid to room temperature, adding liquid to remaining raw materials except biological agent and heating at 60-70 degrees C for 30-40 minutes, cooling liquid and adding biological agent to liquid, stirring and performing magnetization at 420-460 mT for 5 minutes, and (e) coating liquid obtained in step (d) on granules obtained in step (c) using high pressure sprayer, drying granules at low temperature, weighing granules, packaging and storing in warehouse and placed away from the iron-based metallic materials.