Most farms that I've been to have an area that is used to "store" items that aren't used any more. This farm has been here for more than a hundred years, and this area has been the area where items are "stored", and over the years, where trash was burned. So there's a fair bit of metal in the dirt, along with larger items. I can't graze this area down with ruminants for fear of having them swallow bits of metal, but pigs do just fine. In fact, on my original farm, pigs dug up and restored most of the acreage, so I'll do the same here.