I don't think that's an easy assumption to make. Cost of living, average income, and average plot size are very different in rural areas. I don't know Idaho so I can't speak to land value there, but I can say farmable land in rural Alabama goes for between $1k and $6k per acre depending on the land. If you really want to farm it for anything more than a homestead, 40+ acres is a minimum IMO. On the high end that works out to $480/year, but with an average income in the area closer to $25k/year that number isn't insignificant when its a tax just for the right to continue to own land I already bought. Add to that the extreme challenge of even breaking even in farming today, I'd be impressed if anyone farming 40 acres in rural Alabama could reliably turn $25k in profit each year.
Related to that while we're at it, what is the government's justification for taxing the value of land I own outright? Are we classifying land and property ownership as a privilege rather than a right? And in a rural area where land isn't changing hands as frequently and farmland can often sit for sale for months or years, how does the government accurately assess value? In my own experience land value in rural areas is only really adjusted when new structures are built or a specific parcel changes hands, but maybe that is handled differently elsewhere.