The idea of Biochar comes from the Amazonian rain forests of Brazil, where a civilization thrived for 2,000 years, from about 500 B.C. until Spanish and Portuguese explorers introduced devastating European diseases in the mid-1500s. Using only their hands, sticks and stone axes, Amazonian tribes grew cassava, corn and numerous tree fruits in soil made rich with compost, mulch and smoldered plant matter.
Amazingly, these “dark earths” persist today as a testament to an ancient soil-building method you can use in your garden. Scientists disagree on whether the soils were created on purpose, in order to grow more food, or if they were an accidental byproduct of the biochar and compost generated in day-to-day village life along the banks of the Earth’s biggest river. However they came to be, there is no doubt that Amazonian dark earths (often called terra preta ) hold plant nutrients, including nitrogen, phosphorous, calcium and magnesium, much more efficiently than unimproved soil. Even after 500 years of tropical temperatures and rainfall that averages 2000 mm a year, the dark earths remain remarkably fertile.
Commercial manufacturing of Biochar:
Pyrolysis systems use kilns and retorts and other specialized equipment to contain the baking biomass while excluding oxygen. The reaction vessel is vented, to allow pyrolysis gases to escape. Pyrolysis gases are often called “syngas”. The process becomes self-sustaining as the syngas produced is combusted, and heat is released.
There are two types of pyrolysis systems in use today: fast pyrolysis and slow pyrolysis. Fast pyrolysis tends to produce more oils and liquids while slow pyrolysis produces more syngas.
Finding Free Biochar:
Biochar’s soil building talents may change the way you clean your woodstove. In addition to gathering ashes (and keeping them in a dry metal can until you’re ready to use them as a phosphorus-rich soil amendment, applied in light dustings), make a habit of gathering the charred remains of logs. Take them to your garden, give them a good smack with the back of a shovel and you have biochar.
If you live close to a campground, you may have access to an unlimited supply of garden-worthy biochar from the remains of partially burned campfires. The aftermath of veld fires is another source of biochar.
Charcoal briquettes used in grilling are not a good choice. Those designed to light fast often include paraffin or other hydrocarbon solvents that have no place in an organic garden. Plain charred weeds, wood or cow pies are better materials for using this promising soil-building technique based on ancient gardening wisdom.
Using Biochar in the garden:
If you want to raise rich, lush flowers and vegetables in your garden, adding charcoal to the soil is a simple and effective method. There are many reasons to add charcoal to your garden, including raising the soil’s pH, improving air circulation and increasing the soil’s ability to retain water and nutrients. Once added, the benefits of charcoal continue for years.
Biochar alone added to poor soil has little benefit to plants, but when used in combination with compost and organic fertilizers, it can dramatically change the fertility of your soil.
There are other reasons to use biochar apart from improving soil texture, such as the need for more soil organic material (SOM) and improving microbial activity, but soil texture is pretty important in the grand scheme of the world underneath your feet. Soil texture is determined by the amount of sand, silt in clay in a given soil profile. Think of sand as the big boy of the bunch and clay as the tiniest with silt holding down the middle range for particle size.
The soil texture triangle is a great way to understand what kind of soil you’re dealing with. The center of the triangle is generally the sweet spot for most growing situations. When you get closer to the pointy parts of the soil texture triangle, the different soil separates each have different strengths and weaknesses when it comes to different soil properties or behaviors.
Adding Biochar to your garden beds:
Till the garden area to a depth of 20cm. Discard any rocks, roots or other debris you encounter. If your garden is wet, wait until it dries out to the point that the soil is not sticky before tilling.
You need about 500gr of charcoal for every square 60cm of garden area. Spread the charcoal evenly over your garden, and then till it completely into the soil. You can do it all at once or work in sections. Get the charcoal into the soil to a depth of 15 to 20cm for best results, though even adding a small amount to the top 5cm of soil can provide substantial benefits to your plants.
Water and fertilize your garden thoroughly. Now that your soil contains charcoal, it will retain both the water and the fertilizer much better than it did previously, and these will be available to your new plants. Once the ground has dried out enough to work, your garden is ready for planting.
There are proponents of Biochar and there are sceptics. For further reading: http://www.biochar-international.org/ http://permaculturenews.org/2010/11/18/beware-the-biochar-initiative/