alot of people use an oven to bake their seedling mix as seedlings are most sensitive to pathogens and dont require hardly any soil at all.
obviously if you are talking about sterilizing cubic yards you must look at an electric soil sterilizer. im actually looking at building a small scale sterilizer with some stainless steel heating elements i found. they are exceptionally low wat density elements, so i think they could fit the bill.
the big boys use massive steam boilers to sterilize mixes. its mostly done these days for manufacturers of stuff like miracle grow bagged soil.
its my understanding that soil sterilizing as a way to control pathogens in crops is more or less restricted to green house cultivars, and is fairly even in that case rare. these days you can get hybrid plants that are very resistant to disease, and for pathogens like root knot nematodes, there are many rootstock available that are very resistant, and explosively vigorous.
i guess for the organic/heirloom crowd you might need to sterilize soil, but it has to be terribly expensive, i cant even imagine. id rather just use fresh peat lite each time than deal with that.
there are photos of massive tractor towed units that would place spikes into the ground and spray steam for several minutes. the ground would then be covered for plant out.
edit:
check this out.
http://www.soil-steaming-steam-boiler-blog.com/2010/02/university-california-steaming-automat/
lol.am i the only one that finds this stuff interesting?