Great question crO. I have to jump in an say CLAY is great soil. Period. You just have to learn to manage, Clay soil which is soil made of of: sand silt and clay sized particles. That is all soil is; tiny little rocks. Clay is the tiniest as well as flat which means electrostatic electromagnetic properties are heightened...Sand is the largest and has its own problems that are worse than clay. It is all about knowing your soil, knowing soil properties to be able to 'manage' the soil you already have.
The ONLY way to improve any soil type is the addition of DECOMPOSED organic matter. To the surface of a once dug, double dug, plant bed. The life in the soil, not the decomposers, need DECOMPOSED organic matter to eat for energy. Let's call it DOM, okay?
Trees are different than all other plants because they need to be planted in undisturbed soil...that is best for them to acclimate to the soil they will live with forever.
What I am disturbed about is you wanting to grow trees and then make them bare root. If you are growing in clay, you have the best soil to grow trees and be able to make them Balled and Burlapped. Clay keeps the root ball tight and smaller so nurseries can start the root ball sequestration that fills the root ball with feeder roots and prevents major stress in transplanting; to pots or left B&B in sawdust.
Bare root style nursery trees have to be very young, a whip only, dug during the first year or two during the dormant season and sold before the growing season.
Since you have clay, you should think about B&B, not bareroot. Far easier, you will have lots more time to sell and your trees will be more successful.
For clarity, you do not want to amend your soil to grow trees. Amending soil using...gravel, sand, gypsum, lime...all you'd need to do is add water and rotation and you will have concrete. DOM is the ONLY amendment to any soil any one should ever consider. Trees should be grown in undisturbed soils. All other plants I insist on making the planting bed by double digging (one time...). Not trees. Clay is perfect for growing trees as a product. Not amended one little bit.
And I have to point out that I disagree with this NO TILL fad. Bogus. Trees are different. You should consider growing your trees in buried pots of potting soil if you are set on bare root. B&B would give you an awful lot more flexibility. Those trees should be no more than a whip of 3 to 4', dug up during their dormancy only and sold before the next growing season.
This picture are my raised beds now going on 5 years all I do is clean out the trenches, throw that soil on top of the bed, rake, compress and plant. I just love this picture. The soil is unrecognizable from original...oh, I always fertilize after planting...according to specific plant needs. Balanced NPK. Always. Plants usually are getting their second shot of fertilizer when planted into the garden soil. My fertilizers have formulas in the single digits, never in double digits unless using Osmocote. Proper fertilization just enough not too much will produce a tree that is able to 'fight' disease and insect infestations.
There is always 1 to 2 weeks of acclimation for plants from artificial lighting to the light of the green house. 2 weeks minimum to acclimate to the raw sunshine. I have to cover the starts with reemay for a few nights to reduce the shock of temperature change from the 90's down to the 40's every day.
After planting DOM is dumped on the surface (AWAY from any bark) an inch or two to feed the soil organisms and smother weeds. If there are any.
Growing baby trees this would be important to do. Planting your b&b or bareroot in the garden, you would only dig down to UNDISTURBED soil to plant a tree. No disturbed soil beneath the root ball of a tree. Bark stays out of the soil, mulch. Completely.