In South America, the rich soil of the Amazon River basin in Brazil is known as "black gold". Scientists found that the secret of this rich soil was charcoal . Local people made it from animal bones and tree branches. They mixed the charcoal with the soil about 1.500 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 thousands of years. Mingxin Guo and his team at Delavare State University heated tree leaves, corn stalks , small pieces of wood and poultry waste into "biochar" . They reported their findings at a recent meeting of the American Chemical Society in New Orleans. Biochar could be good news for farmers with poor soil and hungry populations to feed. Professor Guo says it could even help against global warming. Intensive  farming and overuse of chemical fertilizer give out carbon dioxide into the atmosphere. Biochar does the opposite, he says. It traps carbon in the ground. The researchers planted winter wheat in containers of soil in a greenhouse -- some with biochar, some without. Professor Guo says the wheat grows much better in the pots with biochar. The soil was added two percent charcoal to. But he says even a one percent treatment will increase productivity. The results demonstrated that biochar can increase organic matter in soil. Loss of nutrients in soil is an increasing problem worldwide as farmers try to grow more food for growing populations. Next, the team will carry out a five-year study of biochar with spinach , green peppers and tomatoes. Mingxin Guo says he learns about the "black gold" in Brazil from a magazine story. He explains that it was discovered in the jungle, in the area where waters flow to the Amazon, in the 1960's. But it was not until recent years that scientists began to bring public attention to it. Biochar has the following advantages EXCEPT that   _  .
it can improve the condition of the soil it can be used as a kind of energy it can help against global warming it can increase productivity of the corn