In my opinion, properly fertilizing a hayfield is as close to a sure bet, in terms of the return on your investment, as you can get in agriculture. It is even more important to do when, as in your situation, land is a limiting factor.
You may be interested in this thread on a website called HayTalk. If you are referring to the same product discussed there, I think it covers the subject rather well.
http://www.haytalk.com/forums/topic/16184-terra-one-thicker-pasture/
I've been told by an A&M professor that the soil pH needs to be at least 5.5 at a depth of 5 feet. I would recommend taking a soil sample at that depth. He said that a pH below 5.5 allows aluminum to impede alfalfa root growth. Therefore, alfalfa roots will stop growing wherever the pH drops...