One thing you need to keep in mind-those rolls of hay represent nutrients you are removing from the field. When cattle are grazing, they return the nutrients, theoretically in an even distribution, over a period of time. When you bushhog the field, the nutrients eventually go back in the soil. when you cut hay, you are hauling off N-P-K in every roll, just like if you combined a grain crop.
The point is that after a few years of haying without adding some fertilizer, most desirable grasses are going to give way to undesirable weeds. That's when the thistles and briars will really take over.
That is a beautiful hay field. Somebody should agree to hay it for a couple of years rent free, provided they work toward getting the soil in good shape. Given the expense of fertilizer, that would not be a bad deal for the landowner and the cattleman. After a couple of years, he should expect to pay reasonable rent. I'm speaking from experience with bermudagrass in the Southeast, and what I know may not apply to your situation, but I wouldn't cut many more times without adding some fertilizer.