I won't use the word study, as it is only observational.  But when it is wet in the spring, I use a disc very sparingly, and If I do parts of a field with a disc, all summer I can see the drastic difference, and the line is not gradual, it is exactly where the disc ended.  But that may be a here thing too.  Best tool here is a plow, the only uncompactor I have.  Do a perfect job of plowing, and no other tool is required.