If you really want to kill all the beneficial organisms in soil you can get formadehyde from some chemists, but why would you want to? Chemical sterilisation will kill good and bad bugs but not weed seeds, you need heat for this. I use a lot of garden soil and loam for my own compost making and have never felt the need to sterilise it.

I think its for organic gardening and or for potting BB?
I dont know about non commercial chemicals available? but for a non chemical potting mix place soil in an oven roasting bag and add some water, tie the bag, make 1 hole and place bag on roasting pan. Pre heat the oven to between 170-180 degrees. when the soil has reached 170 (test with meat thermometer through the hole you mad then leave at this heat for 30 mins. You could use the microwave 2lbs x 2.5mins but I havent done this and I only did it once or twice in the oven the smell put me off!

I have never sterilized the soil in my garden but this is what I found for you using the sun:

Garden soil is a bit more difficult to sterilize, but it can be done using a process called solarization. This is a method of using heat from the sun to kill disease organisms that cause plant problems like verticillium wilt, root rot, damping off and others. In order for your garden to have the full benefit of solarization, the soil needs to reach a temperature of 114 degrees F (46 degrees C) for at least four to six weeks. Here’s how to solarize your soil:

Rototill the soil in the area you want to solarize.
Water the area so that the top foot is moist.
Cover the area with clear plastic, held down with bricks or tacks.
Leave in place for at least a month. In cooler areas, leave in place for two months.
Check the soil every two weeks to make sure it is still moist.
Remove plastic and plant the garden!
A few notes about sterilizing garden soil: For the most part, beneficial organisms will survive the solarization. You can add humic acid or compost to the soil to put back in the good stuff after you’ve solarized. It is not a bad idea to test the compost for weed seeds by watering a little and seeing if it grows. You can water with compost tea to add beneficials back as well.

Solarization goes most quickly in the south, during sunny, dry days. For almost every location, it works best in the summer. If you solarize in the summer, try to leave the soil covered with black plastic during the winter, or plant a thick green mulch crop to build up fertility, and keep weed seeds out until you plant the following spring. (Always remove the plastic before planting!)

Farmers use steam on fields and greenhouses again no chemicals?
I dont know if this is what you had in mind but I hope it helps?

Armillatox. I use it as a soil sterilant for roses in the winter.

That sounds of use to me Jonathan? as I have one patio rose that really suffers from black spot. Can you tell me how you do it and the quantity?

Drc no organic gardener would 'sterilise' their soil with anything!

When people in the USA talk about sterilizing the soil, they usually mean that they want to kill the soil to where it won't grow weeds or anything for the next 10 years or more. Usually they are planning to use the area as a parking lot, but some misguided souls just want to have a "low maintenance yard"!!

I think you will find some do MG by heat and or steam!