NOVELTY - Biogas based special liquid fertilizer, comprises (in parts weight): biogas slurry (70-90), ammonium nitrate (10-15), diammonium phosphate (2-5), potassium chloride (5-8), potassium nitrate (1-3), ferrous sulfate (1-3), magnesium chloride (0.5-0.8), zinc sulfate (0.2-0.5), boric acid (0.5-1.5), manganese sulfate (0.3-0.5), ammonium citrate (0.2-0.5), where the biogas slurry is obtained by subjecting livestock manure and crop straws to anaerobic fermentation, performing solid-liquid separation, and filtering the slurry using mixed cellulose membrane filter.    USE - As biogas based special liquid fertilizer for eggplant (claimed). The liquid fertilizer is useful for improving growth of the eggplant.    ADVANTAGE - The liquid fertilizer contains rich amount of nutrients required for growth of the eggplant, as the fertilizer is prepared using livestock manure and crop straws, hence the fertilizer effectively improves growth traits of the eggplant and improves yield of the eggplant is improved by 14% or more. The liquid fertilizer is cost-effective, as the raw materials are easily available. The liquid fertilizer is environmentally-friendly and safe, as the environmental concerns regarding transport difficulty and secondary emissions of the biogas slurry are reduced.    DETAILED DESCRIPTION - Biogas based special liquid fertilizer, comprises (in parts weight): biogas slurry (70-90), ammonium nitrate (10-15), diammonium phosphate (2-5), potassium chloride (5-8), potassium nitrate (1-3), ferrous sulfate (1-3), magnesium chloride (0.5-0.8), zinc sulfate (0.2-0.5), boric acid (0.5-1.5), manganese sulfate (0.3-0.5), ammonium citrate (0.2-0.5), where the biogas slurry is obtained by subjecting livestock manure and crop straws to anaerobic fermentation in marsh gas tank, separating the slurry by solid-liquid separation, and filtering the slurry using mixed cellulose membrane filter having pore size of 5 mu m. INDEPENDENT CLAIMS are included for the following:    (1) method for applying the above-mentioned biogas based special liquid fertilizer as foliar fertilizer on eggplant, involves (a) diluting the liquid fertilizer using clean water for 1301-1500 times and applying at seedling stage of the eggplant, (b) spraying the liquid fertilizer at four leaves stage (before transplantation) of the eggplant, and (c) spraying the fertilizer at an interval of 5-7 days during growth period of the eggplant after being transplanted to the field, including (i) diluting the fertilizer with clean water for 1101-1300 times and spraying the diluted fertilizer for at least 1-3 times during flowering period of the eggplant particularly on sunny and windless day and avoiding high temperature, strong light, dry or rainy day at a time interval of 5-7 days, and (ii) diluting the fertilizer with clean water for 800-1100 times and spraying the diluted fertilizer on fruits of the eggplants before being harvested; and    (2) method for applying the above-mentioned biogas based special liquid fertilizer in soil-less culture nutrient solution, involves (a) diluting the liquid fertilizer using clean water for 500-1000 times, (b) changing nutrient solution once every 15-20 days, and (c) performing the above-mentioned foliar application on the eggplant cultivated in the nutrient solution.