Granual fertilizer on a small oak tree has the potential of killing it because it releases the nutrients very fast.
I use Osmocote slow release for trees 0-2 at a tablespoon or so for the growing season. Then 2 tablespoons for 3 and 4 year old trees. It works well sprinkled on the surface or worked into the dirt around the base of the tree. I also use it when transplanting a tree from a pot to the field. Been using it for 10 years and have yet to burn a tree. Results are a very healthy tree with several growth spurts during the season where the trees are watered regularly. It is pricey and I switch to granular (triple 12), a little at a time after the tree is 6 foot tall or so.
For mature trees, I apply granular at rate as if I were fertilizing the lawn. The slow release fertilizer spikes work well for young trees 4 to 8 years old. One member here suggested 3 holes in the ground at the drip line and a handful of triple 10. I tried it with triple 12 and experienced a little burning of the leaves early this spring. I cannot provide results for this method as we have only had one good rain in my area since May 7!