hau Antonio, So you are preparing this area for planting fruit trees? Where on the planet are you located and what is the weather like there season by season? (I'm asking so I can give best fit information)
After you use a sub-soiler I would make a pass with good
compost then water the area with a slurry of found mushrooms (chop them up in water in a blender then dilute so you can apply).
The best time to use mycorrhizae is at the time of planting. These fungi are meant to be either touching roots or actually growing inside the roots.
It is a fair waste of inoculant to just put it in the ground, without the right roots around, they will tend to die.
Products you want will have both Endo and Ecto mycorrhizae present in large quantities.
Endo means they grow inside the root cells, Ecto means they grow on the exterior of the root and the immediately surrounding substrate(soil particles touching the root).
Redhawk