You can clear land that's been weathered/neglected, and use the bio-Slash to make biochar.
OR hardwood from furniture or pallets, just note the nails, if going for ultra clean
Even corn can be made into biochar. For example, 2000 lbs of hardwood fit in a 45 gal contort (barrel) and yields about 500-600 lbs of char, in a half to full day, 25-33% yield on avg. You want 3" max diameter, and more like 1 to 2 btw
Corn, you could fit 300 lbs in this set up and make about 70lbs a day or half day if quenching.
Now that said,
Generally speaking, even though most guys use peat and lime, which is cool, all due respect to them, I usually like to mix basic living soil something like this, for my reasons:
1 part aeration [Aluminum free if possible]
1 part aeration [2nd choice]
1 part vermicompost [home made if possible]
1 part humus-rich earth [thermophilic compost / leaf mould etc]
1 part coir fibre, rinsed [ideally for 2 years outside, salt free]
Once that base is made, if mellowing directly in the "soil", I make the following to add:
a meal recipe [neem, kelp, alfafa, shell crab, etc]
a mineral recipe. [basalt for paramagnetism, glacial rock dust for minerals, etc]
and a microbe recipe. [AACT, chia seeds and organic oats, ground into powder, applied]
The meal mix usually get applied at one cup per cubic foot at least, roughly, per year.
and the mineral mix, usually get applied at the rate of 3 or 4 cups per cubic foot, or per 7.48 US gal.
Now that said, there are tweaks... a lot of guys like 33% castings but we actually like 15%. the remainder 5% is usually used for either more aeration, or biochar, if the castings were ran finer or if the vermicompost (bacterial dom) and thermophilic compost (fungal dom) got mixed ahead of time.
Speaking of which, ahead of time is where its at so you could plan for next year at the same time.. to simplify further, I would make from scratch and then mix my all my composts to create mix A, and use 6 types of aeration to create mix B, and I would mix A and B to 50/50 if all my ratios were bang on. For example, I like to push my kelp higher in year 1 and then not reamend for 2 years. I like biochar at 10% of the mix, as one aeration, cause Aeration can also break down, over time.
My personal favs, in rough order of most fav to least:
BioChar. (permanent microlife station, breathable, porous)
Rotting WoodChunks, like Redwood (hold water and air, convert to humus and organic matter)
Rice, Cocoshell, or Buckwheat hulls. (decompaction)
Burgandy & Black Lava Rock
Leafmould
Pumice
Builder's Sand
Perlite
Vermiculite