NOVELTY - Arbuscular mycorrhizal fungi culturing involves preparing culturing pond and culture medium, transferring cultured arbuscular mycorrhizal fungal symbiont into the culturing pond and culturing it, performing absorption and conversion of biological fertilizer and collecting biological fertilizer. Culturing pond and culture medium preparing process involves using polyethylene film and timber piles to make the culturing pond and adding culture medium including 5-15 parts of hot plant ash, 40-60 parts of vermiculite, 20-30 parts of humus soil in the culturing pond.    USE - Method for culturing arbuscular mycorrhizal fungi, particularly Glomus intraradices, Glomus mosseae, Glomus etunicatum or Glomus caledonium used for producing biological fertilizer used in farmland (all claimed), especially for cultivation of seedlings of crops and medicinal plants.    ADVANTAGE - The method provides biological fertilizer using easily available materials in simple, eco-friendly and cost-effective manners in compare to the present technology, thus it is beneficial for modern agriculture. The obtained fertilizer can reduce use of chemical fertilizers, pesticide application rate and soil, water and atmospheric pollution, and increases yield of crops greater than 50%.    DETAILED DESCRIPTION - Arbuscular mycorrhizal fungi culturing involves preparing culturing pond and culture medium, transferring cultured arbuscular mycorrhizal fungal symbiont into the culturing pond and culturing it, performing absorption and conversion of biological fertilizer and collecting biological fertilizer. Culturing pond and culture medium preparing process involves using polyethylene film and timber piles to make the culturing pond and adding culture medium including 5-15 parts of hot plant ash, 40-60 parts of vermiculite, 20-30 parts of humus soil in the culturing pond. Transferring and culturing the cultured arbuscular mycorrhizal fungal symbiont in pond involves: transferring cultured arbuscular mycorrhizal fungal symbiont into the culturing pond; watering nutrient solution once into the culture medium every week, and pouring primary root leaching solution, amino acid nutrient solution and ammonium humate solution. The nutrient solution comprises (in mg/L): potassium nitrate (300-500), calcium nitrate (520-720), magnesium sulfate (160-360), boric acid (3-6), manganese(II) chloride tetrahydrate (1-5), zinc sulfate heptahydrate (1-5), copper(II) sulfate pentahydrate (0.05-1) and molybdic acid monohydrate (0.05-1). The primary root leaching solution is obtained by culturing RiT-DNA conserved carrot root tissues, and the amino acid nutrient solution is a mixed solution of 17 kinds of standard amino acids. The biological fertilizer absorption and conversion process is performed by: culturing host plants and arbuscular mycorrhizal fungal symbiont for 6-8 weeks in the culturing pond; dividing the culturing pond into two chambers 10-15 cm away from the host plants by 300-500-mesh nylon net; adding animal wastes, monosodium glutamate wastewater or protein hydrolyzate in one chamber of culturing pond without symbiont; and facilitating absorption and conversion of biological fertilizer of the arbuscular mycorrhizal fungi passing through the nylon net. The collection of biological fertilizer is carried out after absorption and conversion of biological fertilizer for 4-8 weeks by: removing leaves and stems of host plants; collecting roots and arbuscular mycorrhizal fungi of host plants; and mixing the collected materials together with the culture medium in the culturing pond to obtain the fertilizer comprising arbuscular mycorrhizal fungi.