When a tree spade is used to move trees the soil/root ball that moves along with the tree remains disconnected from the surrounding soil. Normal capillary channels that allow water to move upward from deep in the soil profile are severed by the shovels of the tree spade. Once the tree uses up the water held in the soil/root ball, no additional water can move towards the roots. Essentially, during the first few years after transplanting, a spaded tree acts just like a tree growing in a pot. And like container grown trees, you can never let the soil/root ball dry out.
To ensure transplanted trees survive, I recommend that all vegetation around the spaded trees be killed. I'd use a tractor mounted rototiller to work the soil (shallow cultivation) around each tree making sure the seam between the soil/root ball and the surrounding soil does not split open. And finally, I'd invest in a 2000 gallon water tank and trailer so I could thoroughly water each tree.
In my experience, it takes at least three years of vigilant care to get spaded trees off to a good start. After several years the soil/root ball becomes reconnected to the surrounding and the transplanted trees starts to grow at a more rapid pace.