From that wiki page: > After about three to five years, the plot's productivity decreases > due to depletion of nutrients along with weed and pest invasion,

From that wiki page: > After about three to five years, the plot's productivity decreases > due to depletion of nutrients along with weed and pest invasion, > causing the farmers to abandon the field and move over to a new area. It sounds like the Native Americans weren't farming the land to exhaustion then moving on and repeating the process elsewhere. They were just burning an area and letting it return "naturally" (yes I know that sounds weird). I imagine that it was also not performed on quite the same scale as it is in recent times in, say, the Amazon.