Milpas (p. 220)
"A milpa is a field...in which farmers plant a dozen crops at once, including maize, avocados, squash and beans, melon, tomatoes, chilis, sweet potato, jicama, amaranth, and mucuna.  In nature, wild beans and squash often grow in the same field as teosinte [an ancestor of corn?], the beans using the tall teosinte as a ladder to climb toward the sun; below ground, the beans' nitrogen-fixing roots provide nutrients needed by teosinte.  The milpa is an elaboration of this natural situation, unlike ordinary farms, which involve single-crop expanses...

Milpa crops are nutritionally and environmentally complementary.  Maize lacks digestible niacin, the amino acids lysine and tryptophan necessary to make proteins and diets with too much maize can lead to protein deficiency and pelagra, a disease caused by lack of niacin.  Beans have both lysine and tryptophan, but not the amino acids cysteine and methioninne, which are provided by maize...The milpa...is one of the most successful human inventions ever created.
 
In Europe and Asia farmers try to avoid stressing the soil by rotating crops; they may plant wheat one year, legumes the next, and let the field lie fallow in the year following.  Then farmers use artificial fertilizer, which at best is expensive, and at worst may inflict long-term damage on the soil... [But] the milpa has a long record of success.  There are places in Mesoamerica that have been continuously cultivated for four thousand years and are still productive.  The milpa is the only system that permits that kind of long-term use.
 
Terra Preta do Indio (p. 344)
"In the 1990s researchers began studying unusual regions [in the Amazon] of terra preta do Indio--rich, fertile "Indian dark earth" that anthropologists believe was made by human beings.  Throughout Amazonia, farmers prize terra preta for its great productivity; some have worked it for years with minimal fertiization...More surprising still, the ceramics in the farm's terra preta indicate that the soil has retained its nutrients for as much as a millenium...Because terra preta is subject to the same punishing conditions as the surrounding bad soils, its existence is very surprising...If you read the textbooks, it shouldn't be there...Most big terra preta sites are on low bluffs at the edge of the flood-plain. 

Typically, they cover five to fifteen acres, but some encompass seven hundred or more.  The layer of black soil is generally one to two feet deep but can reach more than six feet...Another clue to its human origin is the broken ceramics with which it is usually mixed. They practiced agriculture here for centuries, but instead of destroying the soil, they improved it, and is something we don't know how to do today in tropical soils...The key to terra preta's long-term fertility...is charcoal: terra preta contains up to sixty-four times more of it than surrounding red earth.  Organic matter sticks to charcoal, rather than being washed away..

.Over time, it partly oidizes, which keeps providing sites for nutrients to bind to...Because charcoal contains few nutrients ...high nutrient inputs...waste such as turtle, fish, and animal bones are necessary.  Special soil microorganisms are also likely to play a role in its persistent fertility...Instead of completely burning organic matter to ash, ancient farmers burned it incompletely to make charcoal, then stirred the charcoal into the soil.  In addition to its benefits to the soil, slash and char releases much less carbon into the air than slash and burn, which has large potential implications for climate change...Nobody in Europe or Asia...ever understood the properties of charcoal in soil."