Hi
i am using local soil from my mixes and sometimes i find char deposits from burnt wood..
in my searching in the internet to see if its toxic etc i found allot of info about using charcoal as a soil conditioner and also to raise the PH and increase soil mineral concentration from running off by rain and irrigation..
i found this 

i know some people use charchoal for certail things like CP, but so far, i haven't heard anyone mentioning it for the figs.

This spring because I was too lazy to dig up the grass, I burned a fire for about 8 hours in the spot where I put my Nordland. Its been one of my most vigorous so far despite getting less light than the other spots. There are too many other factors to say it helped, but it doesn't appear to have hurt anything.

Try not to use burnt wood that used chemicals to burn it. Wood can be good in moderation. 

Hmm I would think it might help for acidic soils, but not for alkaline soils [as it would only make the soil more alkaline].

There are folks working with biochar and figs but they obviously aren't ready to share at this point and I'm not free to list their names. There is a huge amount of info online about Terra Preta and biochar.
One place to start is UC Davis at http://biochar.ucdavis.edu
Theres a couple good videos at http://www.prokashi.com and ounce you start looking there's really a lot of stuff out there.
Good luck.

Thanks. found more examples here

Biochar with NPK fertilizer compared to plain soil.

Biochar with NPK fertilizer compared to NPK fertilizer alone.

Biochar without fertilizer compared with plain soil.

Biochar only compared with NPK fertilizer only.

Marco Bernasconi of DESA, acting as a human measuring stick, inspects a cornfield that demonstrates the effect of biochar on soil fertility. In the photo above, the section without biochar is in the middle, and the sections with biochar are visible to the left and right.

Marco Bernasconi in the section with biochar. The difference is evident.

A test plot created by Kanso Technos of Japan comparing growth rates between plain soil, NPK fertilizer, and biochar plus NPK.

Here is a test plot created by Saffe, located in Hangzhou, China.