Abstract: The sulfur-oxidizing bacteria have a characteristic of oxidating sulfur and sulfide into sulfuric acid. With the biological characteristic of sulfur-oxidizing bacteria, sulfur is oxidized into sulfuric acid which neutralizes the OH^-, so as to achieve the purpose of improved saline-alkali soil. The authors use four types of soil experiment, such as dredger fill, salina soil, farmland soil and green soil. Put certain volume of thiobacilus thiooxidans, thiobacilus thioparus and sulfur into the soil samples, then detect the pH and conductivity of the soil supernatant fluid once per 12 hours.The result shows that the thiobacilus thiooxidans and thiobacilus thioparus have significant effect to lower the pH value of soil from 7.5 to 7.2, have effect on improving the saline-sodic soil.

Key words: saline-sodic soil, sulfur-oxidizing bacteria, thiobacilus thiooxidans, thiobacilus thioparus