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Terra Preta or dark soil is a unique form of soil which has been created through human activity. This anthropogenic soil has some unique properties; in addition to being incredibly fertile and retaining that fertility for hundreds of years, Terra Preta is also a form of carbon sequestration. Both of these traits have led to widespread interest in Terra Preta around the world, with some people even proposing that it could be used to create a carbon negative fuel, using an energy generation technique called gasification.
Before delving into all of the claims for Terra Preta, it may help to understand what, exactly, it is. Dark soils were noticed in the Amazonian basin by many early explorers, and as early as the mid-1800s, people were wondering where these soils came from. They were notably richer than neighboring soils, and they clearly had distinct properties which were identifiable even in this age of science. Investigation revealed that Terra Preta was heavily laced with bio-char, or charcoal, and some people theorized that it came from volcanoes.
In fact, closer analysis of the components of Terra Preta indicates that it was made by people, possibly the same pre-Columbian civilization which shaped large swaths of the rainforest. In addition to bio-char, Terra Preta also contains plant remains, manure, shards of pottery, and the remnants of fish. In a sense, Terra Preta is glorified compost, but it is extremely mineral rich and very deep in many parts of the Amazon.
To make Terra Preta, people used a technique called slash and char, in which sections of the forest were cleared and burned in partially smothered, low intensity fires to generate charcoal. This charcoal, in turn, locked in carbon instead of releasing it into the atmosphere, which explains why people are excited about the possibility of using Terra Preta as a carbon sequestration tool. In addition, the blended contents of Terra Preta make it very rich, encouraging beneficial bacteria and fungi to grow.
In theory, Terra Preta could be produced anywhere, and it could end up being a valuable tool for amending severely damaged soils. Widespread use of harsh chemical fertilizers around the world could be replaced by Terra Preta, which would also help to repair soils damaged by these chemicals. In addition, Terra Preta could be burned in gasification engines, potentially sequestering carbon while it creates energy. Gasification is an old technique for generating energy by burning biomass in controlled conditions which turns it into a form of gas; this gas can and has powered an assortment of vehicles.
While I was writing the previous posts, it occurred to me that this activated carbon is a likely solution to non-point source pollution (agricultural run-off.)
In addition to trapping the nutrients which keeps them from polluting the water, the action of trapping reduces or eliminates the need for new fertilizer.
This is a major issue in my area, as we have two 1400 acre lakes which are the two most polluted in the state, and they now support blue-green algae to the point that the lakes aren't usable for recreation except very early in the spring, and people living near the lakes (within 1 mile) are suffering from poisoning during August and September.
While the methods you suggest produce good soil, it must be repeated annually (why the Native Americans used a fish per corn hill.)
In a rain forest, none of the nutrients from such would be in the soil for very long, and there would be fish, but not manure (no draft animals in the Americas.) Remember, we're talking feet of rain, not inches, with added flooding every season.
The suggestion is not to burn the soil, but to add partially burnt cellulose to the soil (along with broken pottery shards, the hardest objects locally available.)
Terra Preta, often called Amazon Dark Earth or ADE is special for a couple reasons.
Rain forest soils are extremely poor in nutrient value--which is counter intuitive because of the lush vegetation, but the soil itself is poor, all the nutrients are in the vegetation.
This is largely because nutrients which ARE in the soil rapidly dissolve and/or are washed away in the extremely heavy rainfall.
The benefit of the char in ADE is that it is high in activated carbon, a form of carbon which has acres of surface area in the volume of a sugar cube. Activated carbon has the property of attaching to most organic compounds. This traps the nutrients and prevents them from
being carried away, while still permitting the plant roots to access them. This vastly reduces the need for new nutrients, as they are trapped every time dying vegetation releases them--effectively acting as a form of permanent fertilizer due to the cycle of trap an release.
There are farms in areas with ADE which claim to have been farmed for more than 40 years with no added fertilizer, and no soil depletion.
Typically, ADE contains around 20% char by weight.
Commercially produced activated carbon will do the same job, and is increasingly found in horticultural soil mixes.
Because the carbon traps nutrients, it could potentially greatly reduce the amount of non-point source pollution (farm run-off.) As well as potentially vastly reducing or eliminating the need for added fertilizer (provided that the unused plant mater is mulched and not hauled off the land.)
It also provides an answer to something of an historical mystery.
When Columbus first landed on the NE edge of S.America, he found it heavily populated with large cities.
Returning some five years later, he found only scattered tribes...the people having been nearly wiped out by disease.
Until the discovery of ADE, it was a bit of a mystery as to how the Amazon rain forest could possibly support that many people.
There are extremely few remains of any of these cities, such remains being mostly limited to the large squarish raised areas in the jungle which are about 1 meter above the areas close to them. These raised areas appear to have been man-made, and the soil consists largely of ADE.
The reason that there are no artifacts from these people, lies in the nature of the Amazon--there are no rocks. The only materials available to make things are organic, and no organic item left alone in a rain forest will last more than a few months.
Charcoal burning is one of those skills winch is deceptive...it's a specialized skill to get a good efficiency. If you aren't knowledgeable, you get around 30-40% charcoal and the rest is ash.
A civilization which uses charcoal doesn't need a lot of makers, but they tend to be away from inhabited areas (both to be close to the trees, and so the smoke doesn't irritate the neighbors.)
My theory is that slash and char evolved out of slash and burn (probably fires started by lightening.
When the Spanish sailors went ashore, they undoubtedly did what sailors have always done, which is probably how the diseases got established.
Diseases in general tend to take the youngest and oldest disproportionately. This would leave mostly young adults, who might know that the fields needed fire, but probably not that it was the char that made the system work.
The charcoal burners would have come in over time with their loads, and sicken and die--there wouldn't be many of them to begin with.
Now you have a very small population (estimates range below 10%) consisting of people who only 'sort of' know how their civilization works. Any records they had would have been oral or on organic materials, the oral stuff would mostly be lost, and the organics would be mush within weeks or months.
So, knowing that they need to burn the trees to farm, they would revert to slash and burn, which would suffice to support the reduced population.
The civilization would vanish, almost like it never existed. Leaving only raised agricultural plots and modified soil-and a bunch of young adults in a "Lord of the Flies" situation.
When the Spanish returned, the entire region would be different (5 years is long enough for a jungle to overgrow nearly anything, and their buildings would be mostly rotted it that time.)
Graham:it's the burning that forms the terra preta. actually one can create a similarly fecund soil without burning, by repeated mixing in fish(ideally not edible species)
But: the stench is horrendous and the method does not sequester carbon. Horse manure can also create a very fertile soil but the weed growth is a serious problem for years. The burning super accelerates the formation with few nasty side effects.
I've created super soil by various methods and realized, for instance a third crop of eggplant(a warm weather crop in November; ditto for tomatoes and peppers.
This was in coastal Virginia and night-time temperatures were low enough to create frost which by all accounts should have killed my plants. And yes
:after one year my sandy soil turned black and resembled the soil that was created in Europe by the demise of the prehistoric black Forrest that covered the continent from Russia to the shores of the North Sea at the west, the Baltic sea at the North and the Mediterranean at the south.
Great so we create the perfect soil and then you recommend burning it. Doh!