Unlike the morally superior but intellectually ignorant greenies, I do actually care about preserving wild spaces free from agriculture. To do that, we MUST farm as intensively as possible on the acreage in use, rather than revert to less productive methods that require additional land.
Preserve Wild Lands: Use Ammonium Nitrate!
“The BBC’s Unnatural Histories presented evidence that the Amazon rainforest, rather than being a pristine wilderness, has been shaped by man for at least 11,000 years through practices such as forest gardening and terra preta.[19]
Terra preta (black earth), which is distributed over large areas in the Amazon forest, is now widely accepted as a product of indigenous soil management. The development of this fertile soil allowed agriculture and silviculture in the previously hostile environment; meaning that large portions of the Amazon rainforest are probably the result of centuries of human management, rather than naturally occurring as has previously been supposed.[23] In the region of the Xingu tribe, remains of some of these large settlements in the middle of the Amazon forest were found in 2003 by Michael Heckenberger and colleagues of the University of Florida. Among those were evidence of roads, bridges and large plazas.[24]”
http://en.wikipedia.org/wiki/Amazon_rainforest
“Research in the late 1980s was the first to show that charcoal made from slow burns of trees and woody waste is the key ingredient of terra preta.
“With the increased level of agriculture made possible by terra preta, ancient Amazonians would have been able to live in one place for long periods of time, said geographer and anthropologist William Woods of the University of Kansas.”
“As a result you get social stratification, hierarchy, intertwined settlement systems, very large scale,” added Woods, who studies ancient Amazonian settlements.
http://news.nationalgeographic.com/news/2008/11/081119-lost-cities-amazon.html