Terra Preta is high in carbon, organic material and soil nutrients, formed by ancient civilizations who enriched soil with biomass-derived charcoal composted with other wastes.

It has up to 70 times more carbon than surrounding tropical soils, says Bruno Glaser, soil physics department, University of Bayreuth, Germany. This accounts for its characteristic dark color.

Modern-day Terra Preta, or biochar, “is like a sponge,” says David Laird, soil scientist at USDA-ARS National Soil Tilth Laboratory. “It has a lot of surface area and internal porosity that adsorbs water, nutrients and dissolved organic compounds. Biochar reacts with water and oxygen to form carboxylic groups [negative surface charge sites that attract positively charged cations such as potassium (K), calcium, etc.] and therefore reduce leaching of nutrients from the soil profile.

“Adding biochar to soils increases microbial activity, nutrient recycling and reduces nutrient leaching,” Laird says. “We are still not entirely sure why this happens.”