We are killing all bacteria inside the soil by soil sterilization with aerated steam under autoclave at high temperature and pressure. Generally at 15 pounds pressure with 105 degree Celsius with three alternate day of sterilization can able to kill all bacteria from the soil. For inoculation of new bacteria in sterilized soil , required dilution (spores) of the desired microorganisms should be inserted under Laminar Flow.

thanks for your answer but its enough one time autoclave for killing bacteria or i need to keep the soil three days and then make sterilization again?

You have to sterilize the soils three alternate days, means in all five days you have to keep the soil under sterilization as after third sterilization you may remove the soil after cooling.