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Superdirt Made Lost Amazon Cities Possible?

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Author Topic: Superdirt Made Lost Amazon Cities Possible?  (Read 172 times)
Bianca
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« on: November 22, 2008, 06:12:23 pm »










                                                  Organic matter and nutrients


      Charcoal's porosity brings a better retention of organic matter, of water and of dissolved organic

         nutrients, as well as of pollutants such as pesticides and aromatic poly-cyclic hydrocarbons.







Organic matter



The high absorption potential of organic molecules (and of water) is due to the porous structure
of charcoal.

The Terra preta soils, containing these great quantities of charcoal, are equally characterized by a
high concentration of organic matter (on average three times more than in the surrounding poor soils, up to 150 g/kg.

Organic matter can be found at 1 to 2 metre deep.

Gerhard Bechtold proposes to call "Terra Preta" the soils that show, at 50 cm depth, a minimum proportion of organic matter superior to 2.0 or 2.5%. The accumulation of organic matter in moist tropical soils is a paradox, because of optimum conditions for degradation.  It is remarkable that these anthrosols regenerate in spite of these tropical conditions' prevalence and the fast mineralisation rates. It has been demonstrated that the stability of organic matter is mainly due to the biomass being only partially consumed.






Nutrients



Terra preta soils also show higher quantities of nutrients, and a better retention of these nutrients,
than the surrounding infertile soils. The proportion of P reaches 200-400 mg/kg. The quantity of N is also higher in anthrosol, but that nutrient is immobilized because of the high proportion of C over N in the soil.

The anthrosol's availability of P, Ca, Mn, and Zn is clearly higher than the neighbouring Ferrasol. The absorption of P, K, Ca, Zn, and Cu by the plants increases when the quantity of available charcoal increases. The production of biomass for two crops (rice and Vigna unguiculata (L.) Walp.) increased
by 38-45% without fertilization (P < 0.05), compared to crops on fertilized Ferrasol.

Amending with pieces of charcoal approximately 20 mm in diameter, instead of ground charcoal, did not change the results of experience except for manganese (Mn), for which absorption considerably increased.

Nutrient drainage is minimal in this anthrosol, despite their abundant availability, resulting in high fertility. When inorganic nutrients are applied to the soil, however, the nutrients' drainage in anthrosol exceeds that in fertilized Ferralsol.

As potential sources of nutrients, only C (via photosynthesis) and N (from biological fixation) can be produced in situ. All the other elements (P, K, Ca, Mg, a.s.o.) must be present in the soil. In Amazonia the approvisionning in nutrients from composting in situ is excluded for natural soils heavily washed-out (Ferralsols, Acrisols, Lixisols, Arenosols, Uxisols, ...) that do not contain these elements in high concentration. In the case of Terra preta, the only possible nutrient sources are primary and secondary.



The following components have been found:



Human and animal excrements (rich in P and N);

Kitchen refuse, such as animal bones and tortoise shells (rich in P and Ca);

Ash residue from incomplete combustion (rich in Ca, Mg, K, P and charcoal);

Biomass of terrestrial plants (e.g. compost); and

Biomass of aquatic plants (e.g. algae).



Saturation in pH and in base is more important than in the surrounding soils (Sombroek, 1966; Smith, 1980; Kern and Kämpf, 1989; Sombroek et al., 1993; Glaser et al., 2000; Lehmann et al., 2003;
Liang et al., 2006).
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