Hello everyone.
Thanks for your advice and nice comments.
Like i told you all earlier it was in my growing field for 8 years.
Before that it was in a bonsai pot nothing more than an advanced seedling. (see photo below)
Around that time i had some health issues and i had to transplant all my bonsai into my vegetable garden.
...Waiting there for better times... The only thing i deed in the meanwhile was pruning the canopes with hedge siccors (2x/year)and cutting the roots with the spade(1x/year)
Better times have come finally... and now this spring, I am going to pot up most of these old ex-bonsai trees.
This Oak is one of the examples an other example you can find here :
http://www.bonsainut.com/threads/good-size-field-grown-viburnum.22036/#post-328606
This year most of the dig up trees will be going in large pots or training crates.
Later on, as form next season 2017, I will try more drastic root pruning and nice smaller real bonsai pots.
YES this and above tree are one and the same only 8 years later.