I think you will probably be under the lower limit with 4 acres. I think it’s a number of hectares, and 4 acres is less than 2 hectares. But I’m talking England and Wales, and I may be slightly out of date, so do check.
You will also have to hold the entitlements, which are bought and sold as commodities. You must be able to control the land, be actively farming it, hold entitlements for it, and claim it.