That kind of negotiation can take years

For 20 years we've been trying to buy an extra 5 acres from our nice neighbour. They are always happy to chat about it, and in principal it's been agreed, but we don't have it, and we've now accepted we never will.
It's possible, as you say, that it's left for the wildlife, and the owner might get a grant for that.
I thought initially you were going to say you wanted it as a veggie garden, which is of course very appropriate to railways, which always used to have the stationmaster's veggie patch next to the station. The owner might agree to that, but I see it being a much greater problem for pigs.
You, would need to know what planning rules cover that type of business before you even approached him. There's no reason that you shouldn't introduce yourselves to him without mentioning the land at all at first. I wouldn't suggest knocking on his door, just speak when you bump into him
