This is a tree question... a little background first. We are in Middle River, MD & I recently (within the last 2 weeks), ripped up our existing yard which was overgrown with weeds. I hard raked the soil, fertilized it and installed sod.
I have been watering it twice a day and the sod is taking off great. However, smack dab in the middle of the yard is a 15-20 year old magnolia tree.
The majority of the leaves are beginning to turn yellow and fall off. They are all over the yard. I am thinking of pruning the tree a little, but I do not want to waste my time if the tree is dying or dead and needs to be removed.
Sounds like you damaged the root of the tree when you "ripped up our existing yard --and hard raked the soil". A magnolia trees roots are in the first foot or so of soil. and if they are damaged you will get dieback of the foliage to compensate for the amount of root damage. Pruning will not help. Pruning will take the ends of the branches off and this is where the new growth is. Check and see if you are getting new growth on the ends of the branches. This would mean that the tree is still alive and over time will recover.
Another "normal" characteristic of magnolia trees is they do drop leaves in the spring as new growth comes on.
The leaves fall off along the branches as the new growth comes on. Looking underneath, or inside a magnolia tree, you see lots of branches that are bare except for at the ends. Its just the natural process of the tree's growth. So, if your tree is losing a tremendous amount of leaves, especially in the spring, that is normal. They have to fall off to make room for new leaves.
I think you maybe are getting a double dose of leaf fall from the soil/root damage and the time of the year of leaf drop for magnolia. Time will tell but I would do nothing right now and wait to see if the tree can recover on is own.