Composition for promoting nodulation and nitrogen fixation of leguminous plant and preparation method thereof

The invention discloses a composition for promoting nodulation and nitrogen fixation of a leguminous plant and a preparation method thereof. The composition provided by the invention comprises a fermentation extract, ammonium molybdate and ferric citrate, wherein a fermentation product is prepared by the following steps of: uniformly mixing bacillus sp. Y-25CGMCC 4092, coal, wheat bran and straw; fermenting; and collecting a product to obtain the fermentation extract. The composition further comprises boric acid and zinc sulfate. As proved by an experiment, a product (active agent) is obtained by dissolving the composition prepared with the method into water, and has the effects of simulating the growth of nodule bacteria, stimulating the increase in nodule number of the leguminous plant and enhancing the nodulation and nitrogen fixation capabilities of a single plant when used for directly treating the leguminous plant or a plant part.