Those trees look super healthy, did you add anything to the dirt before planting?
No I don't use any ammendments when planting on most plants. On the stuff that is super vigorous and hungry I will add composted yard waste or cow manure. Things like watermelons, banana, papaya get some. Any hardwood fruit tree (avocado, annonas, stone fruits, citrus, mango, etc) gets no ammendments. Only top dressed with lots of mulch and then later fertilized from the top and watered in.
The soil is very sandy/rocky and low in organic matter. Which provides plenty of drainage and minerals without causing root rot.