There is no law specific to ag land rentals in Michigan like there is in other states (e.g. Iowa) so we need to examine the situation under general contract law. Under general contract law a verbal contract is fully as binding and enforcable as a written contract. Your ability to prove what the contract entailed is the real problem with verbal contracts. That being said, the question would be first if you had an enforcable verbal contract and second whether you can prove the contract exists.

To be enforcable a contract needs 5 things.

1. Competent Parties--I assume this is covered
2. Legal subject matter. I assume this is ok as well.
3. An offer. Did you offer to rent the land for 2011 crop, or did he offer it to you?
4. Acceptance. Did you accept his offer or he yours?
5. Consideration. Each party must provide consideration. This is something of value, or something you do or promise to do in the future. In this example I would assume that his consideration would be allowing you to farm the land, and your consideration would be a promise of payment. Generally courts hold that this needs to be specific. If you told him that you would pay him $x or the same as last year, etc. this would be specific consideration. If on the other hand he said "hey you want to rent my land?" you said, "yea I would love to" then you discussed price and didn't come to a conclusion on what price to pay, a court would probably not hold that this was an enforcable contract.

To be able to prove the contract exists for a verbal contract, you pretty much need the other party to agree to the conversation or a witness, etc. This is why written contracts are much preferred, they are not subject to changing memories.