"Read" the soil to know how to fertilize

Most roots grow and "feed" in the top 12-18 inches of the Earth. If the soil below that layer is much paler than what's above, the Earth is telling you that nutrients leach very readily from the root zone.

Below where a backhoe has just cut away a bank and left the tree roots sheared or hanging, two blue lines mark the top layer.

In such a place, be sure to fertilize a little bit at a time, frequently, or use only slow release organic fertilizer. Anything else would be mostly wasted as it dissolves and flows down out of the roots' reach.