I believe the best product for fig trees is manure. Trees look wonderful, the fruits are bigger and keeps away nematodes. On top of that, if well composted, it does not burn.
The soil instead of accumulating salts and becoming weak, with manure it is enriched.
I am not talking about Black Cow, I am pointing at the real thing, the one you get from a place where there are barn animals. Just make certain it is well composted.
Try it: you will never go back!
Sal