Soil and Climate - Soil: Reflections on the Basis of our Existence - page 131

Sensitive soil . In some parts of Amazonia the soil is black and known as terra preta . Covering
an area as large as Great Britain, terra preta was formed by a modified version of slash and burn
agriculture used by the indigenous population and the gradual build-up of their food waste and
excrement in the soil over thousands of years. Terra preta is highly fertile thanks to its ability to
retain nutrients and water. The image shows a tract of rainforest that lacks the biochar-enriched
quality of terra preta. Such soil is quickly depleted if it is planted.
Under a microscope, biochar appears hollow and sponge-like. Adding biochar greatly
improves soils that are low in humus because it stores water in its cavities and nutrients stick
to its surfaces. The effect is greatest in tropical soils, particularly if nutrients are added to the