Nancy, where is the split? This means everything on how to fix it. Is it in a seam or is it randomly across the cushion in the middle somewhere? If it is in a seam....easy! It will be less noticeable. Put the seam right sides together again and sew the seam back together trying to not let the stitching show. Get yourself a curved upholstery needle!! This will help in stitching upholstery that is already stapled in place. So if the split is in the middle of the fabric, you will have to carefully stitch it so the fabric does not fray. A curved needle will help with this. If you have no idea what type of needle I am referring to, check out my post:
Scroll towards the middle to end of the post and you can see the needle you will need and how to use it. I would not have been able to sew that upholstery without that needle because a straight needle gets caught without the correct angle. Good luck!
Is this real leather? Not pleather?
I wasn’t expecting real leather to have a 1 inch split in it. Real leather is worth repairing.
If you can get the leather off of the cushion, it would be best to repair this from the back.
You can go to an auto department and find repair kits that have all the equipment you need to fix the tear. Used them with my green Torino.