NOVELTY - Purple sweet potato fertilizer comprises 100-120 pts. wt. livestock and poultry excrement, 15-20 pts. wt. potassium sulfate, 8-11 pts. wt. attapulgite, 2-4 pts. wt. water glass, 1-2 pts. wt. cellulase, 19-22 polylactic acid, 9-12 pts. wt. calcium sulfate, 2-4 pts. wt. starch ether, 4-6 pts. wt. effective microbial inoculum, 25-30 pts. wt. urea, 7-9 pts. wt. basalt powder, 8-10 pts. wt. peat, 20-24 pts. wt. diammonium hydrogen phosphate, 7-9 pts. wt. soil modifying agent and water (remaining amount).    USE - Used as purple sweet potato fertilizer.    ADVANTAGE - The fertilizer is provided with balanced nutrition, has synergistic effect and promotes absorption of plant nutrients, increases biochemical activity of soil, reduces soil compact structure, is environmentally friendly and has slow-release function.    DETAILED DESCRIPTION - Purple sweet potato fertilizer comprises 100-120 pts. wt. livestock and poultry excrement, 15-20 pts. wt. potassium sulfate, 8-11 pts. wt. attapulgite, 2-4 pts. wt. water glass, 1-2 pts. wt. cellulase, 19-22 polylactic acid, 9-12 pts. wt. calcium sulfate, 2-4 pts. wt. starch ether, 4-6 pts. wt. effective microbial inoculum, 25-30 pts. wt. urea, 7-9 pts. wt. basalt powder, 8-10 pts. wt. peat, 20-24 pts. wt. diammonium hydrogen phosphate, 7-9 pts. wt. soil modifying agent and water (remaining amount). The soil modifying agent comprises 10-20 pts. wt. long-oil alkyd resin, 1-2 pts. wt. nano-carbon powder, 4-5 pts. wt. sodium silicate, 17-19 pts. wt. methyl methacrylate, 3-4 pts. wt. selenium-enriched yeast, 2-3 pts. wt. copper sulfate, 2-3 pts. wt. zinc gluconate, 1-2 pts. wt. magnesium chloride, 2-3 pts. wt. ammonium molybdate, 1-2 pts. wt. boric acid, 4-6 pts. wt. dipentaerythritol hexaacrylate, 30-40 pts. wt. vinegar, 2-3 pts. wt. chitosan, 1-2 pts. wt. Eucalyptus oil, 3-5 pts. wt. tripropylene glycol diacrylate, 5-6 pts. wt. alum and 1-2 pts. wt. iron ore slag. Preparation of the soil modifying agent comprises mixing methyl methacrylate, dipentaerythritol hexaacrylate, tripropylene glycol diacrylate, long-oil alkyd resin, nano-carbon powder, Eucalyptus oil and iron slag, stirring uniformly, heating to 65-75 degrees C to form mixture, mixing adding remaining components and stirring completely to form vinegar solution, mixing the mixture with vinegar solution, and high speed dispersing into slurry. An INDEPENDENT CLAIM is also included for preparing the purple sweet potato fertilizer, comprising (i) mixing potassium sulfate, water glass, calcium sulfate, diammonium hydrogen phosphate, basalt powder and peat, adding specific amount of warm water, mixing uniformly, adding soil modifying agent, cellulase and starch ether, stirring continuously to obtain slurry, drying, concentrating and preparing into granule, (ii) mixing remaining components except polylactic acid and urea, maintaining moisture content to 40-45%, stirring uniformly, sealing, anaerobic fermenting at room temperature for 22-28 days, turning once for every 3-5 days, drying and preparing into granule, and (iii) mixing molten urea, polylactic acid, product obtained in the step (i), and (ii), cooling to room temperature and drying.