DryStoneGarden

Science Daily has a vein of articles about biochar, the concept of adding charcoal to soil to improve it’s fertility. I had previously read about biochar in a National Geographic article, Our Good Earth, with the term “terra preta” (black earth). Basically, the concept comes from patches of human-made dark fertile soil in the Amazon, where fertile soil is supposedly impossible to create. Hundreds of years ago, people added tons of charcoal to the soil, in some places up to six feet deep, and the soil is still fertile today, in the same conditions where modern agriculture can’t keep the soil fertile for five years.

Soil scientists are now making their own terra preta and studying it. Apparently, the charcoal binds with nutrients to keep them from washing away and it creates air pockets for beneficial microbes; the soil becomes loose and friable and full of all the stuff that plants like. And because charcoal doesn’t decompose like compost, it’s a permanent soil amendment, or better than a soil amendment, really, a soil catalyst. It changes the structure of the soil, and the soil then amends itself.

It doesn’t seem like a particularly new concept–I learned about slash-and-burn agriculture in fourth or fifth grade, and I think it’s been practiced all over the world for thousands of years–but apparently it’s a question of scale and technique. Slash-and-burn leaves the charcoal/ash on, or near, the surface; it creates good soil for a few years but then the top layer washes away and leaves the soil ruined. Biochar adds larger quantities–descriptions of six-foot deep terra preta make it sound like ancient Amazonians trucked the stuff in from Pennsylvania–and it mixes the charcoal deeper into the soil. Biochar is like french-intensive, when everyone else has just been top-dressing.

So, we’ll see what happens. Soil fertility is a huge deal in the world; it’s one of the many natural resources we’re wasting at a dangerous rate. Also, some people think that we could use the technique to sequester carbon in the soil. Today’s article said it worked great, another said the biochar’s bacterial growth spike released carbon out of the soil that counterbalanced the carbon put into the soil, leaving almost no net gain. My own thought is that someone should be able to someday figure out a way to capture carbon released from coal-burning plants and use that to make a product for agricultural soil. I’m always attracted to the idea of using bi-products, and carbon is one of the major bi-products of our time. It would be great if it could be used for something other than warming our climate. I can picture them selling charcoal briquets at the garden centers.

Global Warming has a long post about biochar for the home garden. BioEnergy Lists and Biochar FAQ also have information and links.

ryan 12/21

Tags: biochar, global warming, soil

This entry was posted on Sunday, December 21st, 2008 at 9:54 am and is filed under sustainability. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.