Why aren't more Amazonian farmers using "terra preta" instead of "slash n' burn"?

Question

http://en.wikipedia.org/wiki/Terra_preta#Microorganisms_and_animals

Answer 1

Because the modern farmers in the Amazon are using industrial Green Revolution methods which are anything but sustainable. the ancient farmers simply were  lot smarter than a lot of the modern farmers and knew how to get the most out of their land for incredibly long periods-thousands of years of being able to plant on the same plot with low use of inputs vs modern farming which abuses the land, uses a lot of high use off farm inputs and the land can be used less than 100 years before it is ruined.

Answer 2

It is sad that Terra Preta is not being used more.  With the diversity of the Amazonian rainforest, we are probably losing thousands of unknown species every year.

In contrast, in areas which have not experienced rapid population growth and where sufficient land exists, slash and burn agriculture has proven more sustainable and about as productive as more modern, energy-intensive agricultural methods. When done properly over a sufficiently large area, slash and burn agriculture results in a mosaic of agricultural, secondary (i.e., abandoned), and primary (i.e., relatively undisturbed) ecosystems that mimic more closely natural disturbance regimes than does mechanized, modern agriculture. For example, slash and burn farmers typically plant or retain dozens of crop species in each field along with useful trees. In contrast, modern mechanized agriculture often results in large areas planted in a monocrop and requires the removal of almost all trees in order to use farm machinery. Because slash and burn fields typically incorporate many crop species and retain some tree species, slash and burn fields more closely mimic surrounding secondary and primary ecosystems in terms of both structure and diversity. Indeed, because farmers often incorporate useful trees into fields, slash and burn agriculture may be thought of as a form of agroforestry which because of increased diversity and physical structure has been shown to have characteristics conducive to biodiversity conservation.