Here's what I would do when I'm looking at farmland I'm interested in purchasing or leasing:
First, To get an idea of what the area will support, look at the land surrounding the parcel; it's likely that the soil and conditions for your parcel will be similar. So if they're growing hay, it's a fairly safe bet that you can grow hay; or berries, or whatever it is they're using it for. Recognize that the people who own that land have probably spent some time (years... decades...) finding out what works, and whatever it is that's what they're doing. If you're going to be doing exactly the same thing with the land that they are it's a safer bet that you'll have decent results.
Second; put your boots on and walk the ground. Are there conditions that look different on the parcel -- more or less wet, different types of soils, rocks or vegetation? Whenever there's a change in vegetation that usually is a clue that the conditions there are different in some way. A different band of soil, seasonal flooding... something causes that difference. Ask around and see what that might be. In the area that I'm in the only farmland left at decent prices is in the flood plains, and anytime you're there there's risk of floods. Check with the neighbors to see how often it floods, and how deep, and for how long. Most of the time floods don't matter to annual farming -- a flooded corn field after the corn is harvested is no big deal -- but it will affect perennial crops or things like orchards. blueberries can tolerate a bit of a flood.
Bring a shovel on that trip, and a 5 gallon bucket. Collect 1-2 cups of dirt from 3 or 4 locations that represent the entire parcel. Strip the vegetation out, and mix it all up in a bucket, and have a soil test done. It'll cost you about $60 and take a week or 10 days. They will ask you what you want to grow, and they'll give you a report that says "to grow pumpkins on this ground you need..." and give you fertilizer or amendments and amounts that they reccomend. In this area Skagit Farmers supply in conway does tests; contact your local agricultural extension or conservation district for someone near you.
For the parcel that I was asked about I'm going to guess (because of my experience with the ground in that area) that it's acidic soil with a fair bit of peat in it, and a relatively high water table. Those conditions are pretty darned good for things like cranberries or blueberries, but to grow crops like pumpkins my guess is that you'll need to add a lot of lime to bring the soil PH in line.
Your local conditions will vary, and a soil test will tell you what you need to know.
Finally, a 1-acre garden, intensively cultivated, will be quite a bit of work - more than a full-time job for one person; if you're contemplating buying more than that, you're going to need some sort of equipment to help you farm that ground. I can't say what that might be -- depends on the crops you plant -- but you may be able to horse trade a little work with the neighbors; they bale your hay in return for half, or for a per-bale fee, something like that.
These are just my thoughts on this; I'm sure that they would love to hear more thoughts from others.