The Biosphere 2 project was an attempt to see what the smallest self-sustaining ecosystem (that would feed humans and recycle air/water) would be. For a crew of 8 people, the area of plants, crops & wetland covered 3.14 acres.
If I recall correctly, it ran into a number of problems, and they abandoned it when oxygen levels dropped too much. So I don't think this counts as having mastered it.
https://en.wikipedia.org/wiki/Biosphere_2