A lot of people seem to be posting on the assumption that this farm is going to be a free-for-all, that allows griefers to make farmers grow doomed to fail crops and ruin the land. It wont be.
They'll educate the virtual farmers in the possible options via blogs and videos, and then there will be a vote on which option to pick. Yeah, virtual farmers will have a say, and there's likely to be some left-field options picked out from community discussion, but ultimately all possible decisions are engineered by someone who actually knows what they're doing. The people behind this aren't academics and game designers looking to test out a theory; this farm is the source of the owner and employees livelihood, even as part of a charity. The risks are very high, naturally they're going to be taking steps to reduce them wherever possible.
That said, I'm still not sure it will work. I've never played Farmville, but I'm pretty sure that you don't have to wait 6 months to see a result from your decision on what crop to plant.
The beauty of gaming is that it it's a way of putting in short term effort for definite results and fast gratification; we can see and feel our progress in ways that most of us probably don't get to experience often in our real lives. Running a real farm isn't going to give people that kind of satisfaction. The outcome takes too long, and as part of a team of hundreds or maybe thousands of players, it won't really feel like it's your individual actions that get results anyway.
It seems like they've decided that Farmville is successful because people like farming; when in reality Farmville is successful because people like playing games, and Farmville is part of a newer, more widely accessible source of being able to do that.