Easy installation, drop the entire pack in a hole then cover with dirt
Nearly Impossible to over fertilizer to damage tree
Limits the chance of fertilizer contaminating ground water
Don't have to remember to fertilize every year.
No handling of chemical that can have advertise health effects. 
Use 1 pack per 1" caliber of tree
     
Using time-release (or controlled-release) fertilizer is like taking a vitamin tablet. If we always ate a perfect, well-balanced diet, we wouldn't need it. Unfortunately, few of us eat as we should. As a result, if we didn't supplement our diet, we would be deficient in certain vitamins and minerals.  When fertilizer is broadcast around trees, there's no way to know how much of it reaches the trees' roots. Using Nutrapro solves this problem because it's placed in the hole alongside the tree's roots.  Nutrapro has been specially formulated for trees and shrubs (16-8-8). It comes in a plastic package with micro-pores that allow the fertilizer to be released into the soil at a controlled rate (as moisture transfers thru the pores). The contents (NPK) are dissolved over time by water vapor entering the package through these micro-pores.