Abstract: In order to develop new,safe and highly efficient phosphate-solubilizing microbial fertilizer,several strains were isolated and screened from farmland. The strain X-P18 with the strongest phosphate-solubilizing ability was selected by validating phosphate-solubilizing effect,and was identified as Bacilus velezensis by 16S rDNA. Meanwhile,the phosphate-solubilizing mechanism of the strain was preliminarily explored by optimizing the liquid fermentation conditions and measuring the contents of low-molecular-weight organic acids in the fermentation. The phosphate-solubilizing bacterium was applied to the potted Chinese cabbage,and growth indicators of the Chinese cabbage were analyzed. The results showed that the solubilized phosphorus content in the inorganic phosphorus liquid medium by X-P18 reached 495.4 mg/L,and it characterized with secreting acetic acid and other low-molecular-weight organic acids. The X-P18 strain demonstrated the best phosphate-solubilizing ability and its effective phosphorus content reached 582.4 mg/L,which was 17.6% higher than before the optimization,when inoculation quantity was 1%,the initial pH was 8.0,the carbon source was mannose,the nitrogen source was（NH₄）₂SO₄ and the culture temperature was 30℃. The growth promoting effect on Chinese cabbage was the most obvious,the fresh weight increased by 65.5%,and the total phosphorus content of leaves increased by 46.9%,when X-P18 was added in the amount of 2×10⁹ CFU/pot.

Key words: phosphate-solubilizing bacterium, Bacilus velezensis, Chinese cabbage, growth promotion