Biogas residue composite slow-release fertilizer

The invention discloses a biogas residue composite slow-release fertilizer, and aims to provide an organic slow-release fertilizer which has the advantages of complete nutrients, quick effect taking and long fertilizer effect period and is convenient to use. The biogas residue composite slow-release fertilizer comprises the following components in parts by weight: 600-900 parts of biogas residue, 10-30 parts of rice-straw ash, 100-200 parts of straw powder, 0-5 parts of nitrogen, 0-5 parts of phosphorus and 0-5 parts of potassium. The straw powder, rice-straw ash, nitrogen, phosphorus and potassium are added to the biogas fermentation residue biogas solution used as the base raw material, and the mixture is granulated to prepare the organic slow-release fertilizer. The organic slow-release fertilizer disclosed by the invention contains the basic major elements (nitrogen, phosphorus and potassium) as well as abundant organic matters, multiple minor elements and various biological active substances, has the advantage of dual functions of quick acting and slow release, and is especially suitable for producing organic and green no-pollution agricultural products.