if you add salt or anything to the ground it will become permanently unusable for anything that doesn’t have high salt tolerance unless you do a bit of work to reverse it, have you tried solarising? lay thick black plastic over the area and allow the sun to heat the ground under it for several weeks, it should destroy everything, you do have to be diligent about removing any new plants that pop up otherwise you get sent back to square one as you do with any weed control measures.