Voice of America: In South America, the fertile soil of the Amazon River basin in Brazil is known as “black gold.” Scientists found that the secret to this rich soil was charcoal. Tribal people made it from animal bones and tree bark. They mixed the charcoal with the soil about one thousand five hundred years ago. Now, scientists in the United States have done a modern demonstration. They say charcoal fertilization offers a revolutionary way to improve soil quality for hundreds or even …