Honestly, I, myself couldn't get it figured out for years. So, before last years crop, I contact 4 farmers that had a good reputation in the area and asked them to bid cash rents on the ground. I figured I let local demand set the cash rent.
I had discussions with each of them beforehand what fertilization requirements I had and how it'd work. Then I selected 2 and gave 2 farms to each of them.
What that seemed to do, without it being my initial goal, was create an ongoing competition of "do it right" each and every year according to the lease because there's someone else who'd be glad to take that ground that I'm already working with. I didn't select the highest bidder, I selected 2 that through conversation, had the same goals as I did of improving/taking care of the ground and what their role would be, and what mine would be.
I'm in the 2nd year of this process.
Where the first years fertilization application didn't meet what the crop removed, extra was being put on this year to make up for the delta. It took some discussions, but I think we all have the understanding that I'm not the bank in this process.
All the farms but 1 were limed this year, all but 1 were grid sampled. It's been a process but with commodity prices high, now is the time to get a good agreement/management practice put in place imo.
20a is a little more difficult as it won't be a huge draw for a lot of farmers, but it's still ground someone would want to have.
Figure out what your goals are and go from there.
Good luck.