I always try to apply fertilizer, even organic fertilizer, away from the trunk of my tree. I would apply the fertilizer near the drip line or slightly within the drip line. I would suggest giving it less nitrogen and more P-K. I like to give my plants some E.B. Stone Organic fertilizer, I think its something like "Bloom" and the numbers are 0-10-10. You may also want to give it dilute feeding of Fish emulsion and kelp emulsion for the minors and trace.
Cherimoyas can grow very large in a season if given too much Nitrogen. The P-K should also help to sweeten up the fruit.
Simon