Hippy, I pretty much covered the subject in my post above. You will wind up with a lot of ammonia and other toxic compounds (depending on soil content), not to mention about killing all the beneficial microflora and microfauna.
Air movement, whether artifical, or natural is all one need in this respect.
And works faster then you would expect!
You mean less NH4, not more.
Heat/burning oxidizes, this does not reduce.
NH4 is reduced, NO3 is oxidized N.
Excess reduced Carbon can drain O2 and reduce too much, so cooking it, boiling or baking can rapidly oxidize soil.
I'd do it about 400F for an hour, but boiling for 10-15 minutes would be best I think and less stank.
Same method is used for Worm castings to remove excess NH4, this is old old news over a decade of usage, bacteria will simply recolonize quickly thereafter, plant roots etc are loaded with bacteria.
You can do it via bacterial oxidation or thermal oxidation. End result is the same.
If you really want to promote the bacterial goodness, then a Dry start method that links oxidizing bacteria + real roots of plants would be far superior.
Because once you pull the MTS and disturb the layers of bacteria, this disrupts the bacterial zonation. This must re establish once you add it back to the tank after the mineralization process. DSM does not require this and also links the bacteria to the roots specifically from day one of the tank being flooded with water. If you plant later, you still have some disturbance, whereas there is none with DSM.
DSM also takes 4-8 weeks before flooding, so no time is really lost waiting, since you wait for the MTS a few weeks anyway. Plant roots also add much more O2 to the soil than MTS alone might. This means the bacterial zonation and colonies are more stable and higher densities.
So if you are in a rush, boiling it, or you wanna do the "natural" methods, the DSM is much better if you want to use soil for planted tanks for mineralization.