Yep, if in a different state, you will likely have different requirements than in my state, and you may have different requirements in your county than another county in your same state. Texas, says you need a minimum of 10 acres, but they allow the individual counties to decide, and my county sets the minimum at 20 acres.
If your land has been 'off ag' for any period of time, there 'may' be a waiting period before the exemption kicks in as well.
It was very easy to sign up for it back when I 1st did it, but I have read elsewhere that some states make it quite difficult, while I've also read that some places allow almost any kind and size of ag operation to qualify, even in people's back yards.
Are you trying to get an ag exemption for property taxes or an IRS exemption for stuff you buy?
A sales tax exemption card? They are all different but are 'connected'.
Your county extension agent should be able to point you in the right direction.