That tree has been in a pot for decades, they will have developed feeder roots ages ago. Your fine feeder roots is what the tree uses to absorb nutrients.
Your feeder roots will be at the ends of the roots much like the tree’s foliage.
Nobody knows the condition of the soil that this tree of yours is growing in. If the only nutrients tour tree gets is on the soil surface, your rootspread will be in a 30ft radius of your tree. Remember that trees in the wild do a lot of legwork with their roots to get nutrients. Also remember my previous comment about pine roots specifically. This awesomely drawn picture might be what you’re gonna have to deal with
A pine’s roots mirror the branches and trunk. Also, a pine is less forgiving than most other trees, a deciduous tree you can dig up and hack away at roots and chop trunks and it might recover.
I’m not really the expert, I don’t have a yard to grow trees out and I don’t even have space for any big trees. But I have picked up a lot of information about field growing. B-Nut website has a ton of valuable information with people who reply rather quick (if you respect their time zone)
Do some research and make sure you know what you’re dealing with. You might even pull it off and it could be a great success. Just don’t look astonished if it fails. Be prepared for all possible outcomes