I would afdvise asking a lot of questions before signing such a contract, and I'd want some fairly strongprotections written in if you do decide to go that route. How often would the farmer be cutting the hay? How often would he be fertilising, and with what? After 25 years of corn, your fields are going to be in pretty poor condition; if he just seeds and harvests, you're going to have nothing but dirt at the end of the contract. If he *does* plan on fertilising, would it be solid manure (best case), liquid manure (okay biologically, but won't really do much for your soil structure), or chemical fertilisers (just bad)?
Would he be planning to put on pesti/herbi/fungicides? IMO, very much not a good thing, but you may feel differently, and so may the other farmer. But if it's important to you, you'll want to haveit clearly stated in the contract what is and isn't allowed.
What will he be planting? Here, it's generally reckonned that red clover will have to be resown about every 3-4 years or so, so if someone rents a field for 4 years, and sows it to just red clover, it's pretty much going to be played out right when the contract ends. If your area is similar, you could potentially end up right back where you started from at the end of the contract: Rememer, this is the growth pattern in central Sweden, it may be(probably is) different in your region; you'll have to ask around, if you don't already know.
What kind of equipment does he use-how heavy is it? There was a dairy farmer haying the fields of our farm till we bought it last year, and he used a *really big* tractor to do so. This caused a lot of compaction on our clay-silt fields, which is going to take a number of years to fix.
Is it going to be hay, haylage or silage that he takes? This is connected to the previous question, as if he's making hay everything needs to be nice and dry, which means less compaction, while if he does haylage, he could be going over the fields when they're wetter that is good for them. We were visiting a friend earlier this week, and I happened to look out over one of her fields which she's renting out, and I saw wheel ruts that were between 6 inches and a foot deep: the person renting the field had driven over it when it was *far* too wet and left these canals in her field. Even if they plow and harrow out the ruts, they'll have left subsoil compaction.
Remember, people tend to be more...relaxed about the long-term condition of other peoples' fields than they are about their own ones, so you're going to have to make sure your land is treated the way you want it to be, and I'd strongly recommend that you get it all down in writing so there aren't any misunderstandings about that treatment. That being said, it is potentially a way to give land you don't have time to care for right now at least *some* attention-we're renting out, on an annual basis, a smaller parcel off to the east of the home farm to the dairy farmer with the big tractor: we have enough on our plates with the main land, and this way it won't overgrow while we're busy here.
Finally, if you decide you want to come to an agreement with the other farmer, perhaps you could give him the 3-4 year contract he wants for part of the 25 acres, but retain the right to take back part of it earlier, on the condition that he seeds all of it?