NOVELTY - A carbon-based biogas fertilizer comprises the raw materials (parts by weight (pbw)): biological black carbon (20-45), biogas liquid (20-50), biogas residue (30-60), organic matters (10-15), beneficial microbial inoculums (0.01-1), and forming aids (1-5).    USE - As a carbon-based biogas fertilizer (claimed) for application in agricultural production.    ADVANTAGE - The carbon-based biogas fertilizer is effective for a long time of being applied for one time; has a high utilization rate; saves fertilization cost and energy consumption; is good for large-scale popularization and stable production; can efficiently manage saline-alkali soil, change the volume weight of soil, and ensure the safeties of foods by being applied in the soil with a heavy metal pollution; provides improved soil, so that the productions of grains, fruits and vegetables are greatly increased, low and medium-yield farmlands are changed to be medium and high-yield farmlands; and increases the utilization rate of soil. The production technique for the fertilizer is simple, economic and environment friendly.    DETAILED DESCRIPTION - A carbon-based biogas fertilizer comprises the raw materials (parts by weight (pbw)): biological black carbon (20-45), biogas liquid (20-50), biogas residue (30-60), organic matters (10-15), beneficial microbial inoculums (0.01-1), and forming aids (1-5), where the carbon-based biogas fertilizer is prepared by transporting the biogas liquid and biogas residue to the fertilizer workshops of a factory by a biogas liquid special vehicle, mixing each raw material according to the matching ratio, entering in a granulator to granulate, causing the diameters of the fertilizer grains to be 3.5-6.5 mm, weighing and packaging after the granulation is finished, or preparing to be powder-shaped according to the requirement of a user, then weighing and packaging. The organic matters comprise cow dung, pig effluent and rotten straw. The beneficial microbial inoculums comprise azotobacter, phosphobacteria, silicate bacteria and bacillus. The forming aids comprise bentonite, fulvate powder and tapioca.