Looks like adverse possession:
http://www.moeland.com/adverse.htm
And looks like 10 years in Iowa:
https://coolice.legis.iowa.gov/Cool...ory=billinfo&service=IowaCode&ga=83&input=564
I'm a bit curious about all this also. When we bought our house about 8 years ago we were under the impression we had a touch more land than we actually do. Our acreage is actually in a bit of an L shape but there is a fence that angles from one point of the "L" to the other leaving a triangle of property that I mow and "maintain" a raspberry bush on.
I never knew about this triangle until the pasture land behind my house got sold and the new owner had it surveyed. I was always under the assumption that the fence marked the property line because the guy I bought the house from told me that. The my new neighbor wanted the fence to go in right at the property line (can't blame him) but I made a bit of a stink about it. I paced it off and estimated it to be about a third of an acre and asked if he could just leave it because my wife picks raspberries from those bushes every summer. I really didn't think he would get to fired up over that little land. He did offer to sell it to me for a hefty price at which point I pretty much said "do whatever you want".
It turned out that he put the new fence in right where the old one was and we kept our raspberry bush. But looking at this "adverse possession" it seems that this land will be mine anyway within a couple years with just a bit of paper work and legal fees........interesting. May have to dig a bit deeper into this. I have no problem paying any extra property tax that would come with it, would just like the acreage to be "bigger" hence worth more.