Charcoal, Sawdust and Organic Compost Mimic ‘Dark Earth' Soils in Amazonia.

Residues of vegetable and animal origin, as well as charcoal residue from cooking fires, that were incorporated into the soil under native Indian villages were the major ingredients that formed Dark Earth soils. Dark Earth soils has been considered a model for soil management of the weathered, infertile soils of the Amazon. The objectives of this study were to (1) investigate the effect of charcoal, sawdust and organic compost on the chemical, physical and biological properties of a representative, low fertility, Amazonian soil in an attempt to reproduce the fertility of Dark Earth soils; (2) study the potential of charcoal to increase the uptake efficiency of phosphate fertilizer and decrease the nitrogen and potassium loss by leaching; and (3) study the potential of charcoal, sawdust and organic compost to increase corn and bean biomass/grain production. Both sawdust and biochar increased corn biomass, with the effect of charcoal (273% increase) being greater than that of sawdust (108% increase). The biomass production increased from the first to the second crop. For the first crop, 120 t ha^-1 of charcoal and 80 t ha^-1 of sawdust produced 1,700 kg ha^-1 of corn biomass and 534 kg ha^-1 of grain production. Eighty t ha^-1 of charcoal and 120 t ha^-1 of sawdust with the second crop produced 11,500 kg ha^-1 of corn biomass and 1,130 kg ha^-1 of grain. Associated with better growth was an increase in the P and N content of the corn crop; while Al uptake by the crop appeared unaffected.