Have a fertilizer dealer do a soil test for you and see what you've got. They will help you read and understand it and ask what it would cost to get things right with commercial fertilizer applied by them. That's just for comparison.
You'll likely find very low fertility numbers. Plus, that low fertility has let weeds get a serious foothold in the fields so there was that to deal with.
You then either have to address the issue with the renter and likely add a cost for what is being removed from the ground. In reality, you're better off leaving the ground fallow and just mowing it once a year. You'll save money.
If he wants to pay more, fine, if not, it's better to just not rent it. For coaching on this you'll need a local farmer that's savvy on things like this. Maybe the fertilizer people or maybe an ag teacher at a school can help. You can look up your state and county's land rental rates online too.
You could also enter into a five year contract with someone who agrees to improve the land. Then he has skin in the game for the five years. You need a contract and common ag ones are on-line. It sounds daunting but isn't.