SOLUTIONS
Biochar:
A Carbon-negative Fuel & Fertilizer
Soil profile of Amazonian Terra Preta
Terra Preta [black earth] is a 2000 year old anthropogenic soil with enhanced fertility due to high levels of soil organic matter and nutrients such as nitrogen, phosphorus, potassium, and calcium. Terra Preta soils occur in the Brazilian Amazon, Ecuador and Peru. A typical land area is about 20 hectares, and occurs in the midst of surrounding infertile soils. Cash crops such as papaya and mango grow three times faster on terra preta than elsewhere. These are Amazonian black soils, created by pre-Colombian agriculturists, that sequester twice the carbon of other soils. Why?
Charred wood [not burned wood] is stable in soils. It doesn't rapidly degrade, but becomes a fungal matrix and water filter. Water flows down into the soil, hits the char layer and flows through. As it does so, it leaves nitrogen, potassium and other essential nutrients trapped in the matrix. Fungi unlock the nutrients from the matrix and make them available to plants. For example, when sugarcane crop residue is burned in the field after harvesting, the roots do not burn, they char. As a result, that field paradoxically increases in fertility, rather than losing it.
Soil scientists are using pyrolysis to burn biomass at a high temperature [550C] in the absence of oxygen. The process produces both a charcoal termed biochar and a biofuel [oil or gas]. The first is a remarkable soil-restoration additive. The second can be burned to generate heat for the process itself; or electricity. Overall, the biochar process removes more CO2 from the atmosphere than it releases: it is carbon-negative. The growing plants have removed CO2 from the air, while the charcoal sequesters it in the soil for thousands of years. It is an affordable technology that can be applied at either village or industrial scale. Used widely, it could draw down and store billions of tons of carbon safely in soils.
Biochar remediation reduces emission from soil of another potent greenhouse gas, nitrous oxide. Adding 10 tons of biochar per hectare triples biomass yield and gives a fivefold reduction of nitrous oxide emissions. Agricultural productivity improves due to its ability to retain nutrients and moisture. In the tropics, boosting soil productivity in this way increases the number of growing seasons per year. At present, the nutrient-poor tropical soils resulting from slash-and-burn support just a few agricultural crops before they are exhausted. Biochar fertilization would grant them ‘permanent fertility’ and alleviate the pressure for more deforestation.
The biochar process allows agricultural crop residues, or many other types of biomass now classified as ‘waste’, to become potential biofuel sources. This would benefit rural economies worldwide. For example, if the U.S. adopted a cap and trade program in carbon gas emissions as the European Union has done, farmers in the Midwest could double their income by using the leaves, stalks and cobs that remain after harvest to fuel biochar pyrolysis [1].
1. Anne Casselman [2007] Scientific American Inspired by Ancient Amazonians, a Plan to Convert Trash into Environmental Treasure
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