Biochar is commonly compared to or confused with basic charcoal but it is much more. You have seen the basic process of creating charcoal. A campfire or woodstove filled with sticks and logs of varied sizes burns, produces heat, and often leaves behind black, carbon-rich chunks that didn't burn to ash. The blackened chunks are raw charcoal. When charcoal is added to soil it essentially becomes biochar.
This basic principle of improving soil fertility through the use of charcoal is attributed to the natives of the Amazon basin who burned their jungles in smoldering mounds to create charcoal. Large amounts of charcoal, bone, and manure were mixed into their infertile clay soils to create extremely fertile soil that is still visible today in Brazil where sections of "Terra Preta", or "black earth", reveal this innovative, ancient practice.
Biochar, or charcoal in soil, improves the soil in many important ways. It raises the pH, improves water retention, increases microorganism activity, improves nutrient levels, and can even reduce metal contaminants in soil.
By many measures, biochar achieves the same benefits as compost (and you know I love compost), but does so with a mechanism that doesn't decompose as compost does. Biochar stays active in the soil for hundreds of years. Many low estimates say at least 300 years; the terra preta soils are over 1,000 years old and still quite viable.
When wood burns in a low-oxygen environment, water, chemicals, and gases escape leaving behind the simple carbon structure of the tree. The same holds true for any biological material that is burned in the same way. Within this carbon structure are innumerable microscopic pockets that once held cellulose and the water and gases. Think of it as resembling the structure of a sponge but on a much smaller scale. Charcoal looks solid from the outside but it contains countless air pockets and a true surface area much larger than the relative size of the chunk.
As biochar when the charcoal is added to soil, these empty pockets unleash their magic. Soil moisture finds its way into the empty, microscopic biochar chambers through capillary action and is retained very efficiently. These moist pockets then become home to billions of bacteria. These soil bacteria are critical to converting chemicals in soil into nutrients for plant uptake and form the bottom of the microorganism food chain. Compost as a soil amendment does the same things but compost continues to break down through the natural bacterial onslaught. Conversely, biochar's structure remains intact and continues to act as a home for water, air, and bacteria.
Biochar improves the texture of soil through it's own variably-sized pieces incorporating with various sizes of soil grains. It improves the fertility of the soil through the improved microorganism activity. It improves the structure of soil through the increase in pore space, aggregation, and soil stability. Biochar greatly improves overall soil tilth (for more about tilth see my article "The Dirt on Soil", Feb 24, 2011).
Lucky for gardeners, there are companies that are beginning to market biochar to consumers. Their biochar is made in a much more refined process that removes some of the impurities that remain after the simple smoldering pile method of making charcoal. This process, "pyrolysis", is quite efficient and reduces many of the air pollutants that burning wood releases into the atmosphere. Biochar companies use more than wood as their fuel. All kinds of organic waste, or biomass, are burned; these include corn stalks, manure, nutshells, leaves, and grass. Any biological matter that can be dried and burned can be turned into biochar.
My friend Lopa has been an advocate of biochar for years and has spoken around the world testifying to its amazing benefits. Only recently was I fortunate enough to learn about it and her company Soil Reef Biochar.
In the months ahead I'll be working with and writing more about biochar. I've set up test beds and plan to create my own kiln for making biochar through pyrolysis as I recycle my yard waste into beneficial soil amendments. I'm sold on the benefits of biochar and will document its effectiveness in my garden.
If you're intrigued by the idea find out more and purchase some biochar for your own garden. It's a new and innovative idea and you can be at the forefront.