Sterilizing Soil with Steam: sterilize potting soil and should be done for at least 30 minutes or until the temperature reaches 180 F. (82 C.).
Sterilizing Soil with an Oven: You can also use the oven to sterilize soil. For the oven, put some soil (about 4 inches deep) in an oven-safe container, like a glass or metal baking pan, covered with foil at 180-200 F. (82-93 C.) for at least 30 minutes
Sterilizing Soil with a Microwave: you can place two pounds of moist soil in a polypropylene bag. Put this in the microwave with the top left open for ventilation. Heat the soil for 2 to 2 1/2 minutes on full power (650 watt oven).
For quick sterilization of soil is intermittent sterilization for 3 consequent days is prescribed for soil sterilization.
Sterilization by autoclaving can alter soil properties and this could be a problem if you want to compare your results with an "unsteralized group".
The sterilization of soil with gamma radiation (about 60 kGy, the dose depends on the biological activity of the material) is the best way to sterilize soil for your purposes