Carbon and terra preta

In the extreme environment of heavy rain and high temperatures of tropical rain forests, the clay and organic colloids are largely destroyed. The heavy rain washes the alumino-silicate clays from the soil leaving only sesquioxide clays of low CEC. The high temperatures and humidity allow bacteria and fungi to virtually dissolve any organic matter on the rain-forest floor overnight and much of the nutrients are volatilized or leached from the soil and lost. Carbon, however, is far more stable than soil colloids and is capable of performing many of the functions of the soil colloids of sub-tropical soils. Research into terra-preta is still young but is promising. Fallow periods “on the Amazonian Dark Earths can be as short as 6 months, whereas fallow periods on Oxisols are usually 8 to 10 years long”