Preparation method of seaweed organic fertilizer and organic fertilizer prepared by using method

The invention belongs to the fields of forestry and agricultural residues recycling and organic fertilizer production, and provides a preparation method of a seaweed organic fertilizer, a seaweed organic composite mixed fertilizer and a seaweed organic liquid fertilizer, and three fertilizers. The preparation method of the seaweed organic fertilizer comprises the following steps: (1) processing ingredients; (2) carrying out aerobic and anaerobic mixed fermentation; (3) screening and crushing an organic seaweed fertilizer; and (4) pelleting. The composite mixed fertilizer and the organic liquid fertilizer are improved on the basis of the method. Seaweed slag, a microalgae culture medium and microalgae slag in the chemical industry production are taken as raw materials; composting fermentation is carried out on the raw materials and activated sludge; waste is changed into treasures; pollution to the environment is reduced; the production cost is low; no hazardous substance is generated in fermentation preparation; water resources are saved; and no secondary pollution is generated. The seaweed contains a lot of natural active ingredients such as cytokinin and phytohormone; and the fertilizer produced from the raw materials can promote the growth of plants, enhances the ability of resisting adverse environments, and can improve the fertilizer-conserving and water-holding capacities of the soil after being used for a long period of time.