Soonami, if you are using a very poor quality soil and switch to a better mix of coarse you will see an improvement. The point is that a good soil is reflected by its ability to contain water and hold fertilizer. The reason that there is no one soil mix that is best is because people are growing trees in different climates. Those in the NW US are going to have a very different thoughts about high organic contents then those in the midwest. You could use the same soil in both places but you would need to shield plants in the northwest or risk root rot. Soil is relative.
All I'm saying is that soil isn't underrated. How many threads are there regarding soil mixes? They far out number those regarding the importance of how and when to feed trees.
OK, my mood to debate has passed
Soil is important!!! Just know what your tree's needs are.