What to use and how to fertilize wild persimmons

My place has tons of persimmon trees about 3 to 4 inches in diameter, but they seldom bare much if any fruit. Would fertilizer help get more fruit an what should I use. I'm not much of a tree farmer so any help would be greatly appreciated.
Persimmons are male and female. Your trees may never bear fruit - although you should have some females in the bunch. I have literally hundreds on my place and not a one bears any fruit. Most are three inches or less in size. Actually starting to graft female scions onto some of my trees.
I'm with swamp cat on this one. I would be grafting different female scions on the best trees with some varied drop times. Possibly even release the best trees of competition and see what some good solid sunlight will do. On our farm it seems the volunteers produce fruit anywhere from 7-15 years. Those are not grafted, I'm sure the grafting would speed that up.

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How old are the trees? Seems they take 8-10 years. As stated, grafting to a good female scion speeds things up. They need good sunlight too. Take out any competition beside them.
I have also fertilized with triple 12 and even threw down some urea on some persimmon trees this spring. They had been slow growing. Need to check them out.