Gray, I grow most of our own food, and could do 100% if we had to. For the sake of variety and convenience, I don’t do 100% at the moment.
I have 20+ acres. I supplement that with hunting, foraging, guerrilla gardening, and trading. A few things are store bought and again, they are a convenience rather than necessity. Hubby likes his Brown Cow yogurt and Fuji apples! I love grapes! The 20 acres is not a fully closed system, basically because the land was incredibly infertile when I moved here. In order to quickly get food to feed our farm, I brought in outside resources (green waste, lava sand, manure, epson salt, lime, boron, soil microbes, etc). To maintain fertility, I still do some of that although the farm now produces much of its own resources. Some resources it cannot self-produce enough of, such as calcium. I still bring in coral sand and bones. I also bring in ocean water. But since these are gathered from within my own district, one could say that they are not imported. Thus the reason I questioned if you meant 1 acre or a 1000. People have different ideas of what “closed system” includes. Just about everything for my farm comes from within a 10 mile radius (it’s 10 miles to the ocean).
I also bring in food waste to feed to my chickens and pigs, who in turn produce manure for my food production. I could indeed skip that, but to what benefit? Just to brag that I have a closed system? The food is not only free, but I get paid money to pick it up from the local businesses. So it generates farm income. Using this waste stream reduces the need for me to work harder to produce all my own livestock feed.
So while I have a good working system, it’s not completely closed. Yes, I could close it. But I prefer to just limit what I go out and buy to bring to the farm.
One other thought...........by closed system, just how closed would the purist demand it to be? Would bringing in gasoline to run garden equipment mean that the system isn’t closed? Would one need to revert to horse drawn, homemade equipment? Just something to think about,