What is Biochar
Biochar is Charcoal. We use the name biochar specifically for charcoal which is used to improve soil rather than cook on the BBQ. Previously charcoal used for soil amendments was usually called horticultural charcoal. Biochar has "green" implications of renewable energy, carbon sequestration and sustainability.
The term BIOCHAR comes from Peter Read and refers to charcoal used to improve soil.
How is biochar made?
All charcoal is made by heating biomass in low oxygen conditions. This process is called pyrolysis. This causes the biomass, whether it is wood, sawdust, corn husk, leaves or any other biological material such as dried manure or tall grass, to decompose into volatile gasses, leaving primarily carbon behind. It's just a fancy way of saying that charcoal is produced.
Charcoal can be made very easily by allowing wood to partly burn then covering it so that the access to air is greatly limited. The covering can be as simple as throwing a few shovel of sand on the fire and letting it smoulder till it goes out.
There are several by-products of charcoal manufacture. Water is produced as is carbon monoxide, some carbon dioxide, hydrogen and methane among other product. This is the combustible syngas component and has been the subject of much research.
Syngas has a heat density of about half that of natural gas. In order to improve the quality of the gas, it is further processed to remove most of the carbon dioxide.
A second product of the biochar manufacture is creosote. Creosote is also made from coal but the composition is quite different and much more toxic. Coal based creosote is used as a wood preservative. Wood based creosote is not as toxic and has been used as fuel and has been used as a food preservation. It is the smoky flavouring and preservative part of real smoked meats. It is not a very good wood preservative.
Both syngas and creosote can be used to help fuel the charcoal production. Charcoal production produces more energy than it requires to drive the process. Alternatively the syngas and creosote can be captured and used as separate fuels.
Some very interesting projects have been done using syngas generators mounted on motor vehicles. As the wood or whatever fuel is being treated, the gas is produced and helps move the vehicle. Here is a link to wood gas powered automobiles.
By modifying the process variables such as temperature and amount of air allowed in the amount of gas vs. the amount of charcoal can be favoured, depending on the desired end product.
Wood pieces are used to make BBQ charcoal. Pressed briquettes are made from many fuels and compressed with a binder to hold the charcoal dust together.
Why is biochar interesting.
Charcoal is a very stable product and can stay in the soil for several thousand years. Charcoal is one of the things archaeologist find when digging in very old sites.
Biochar is made from fresh material as opposed to fossil fuels. It releases more energy than is required to make the charcoal. The energy can be used to fuel more biochar production or used for other purposes.
The net result is carbon is taken out of the atmosphere while still releasing some energy for use.
Biochar is a method of safely taking Carbon Dioxide, a greenhouse gas, out of the atmosphere and storing it as stable carbon. This is known as carbon sequestration.
Plants fix carbon dioxide into plant products, in the presence of light. The process is one part of photosynthesis.
There is currently quite a lot of projects and research going on to determine what the effect is and what other factors are involved. The next few years will tell us if biochar really lives up to its promise of carbon sequestration and net removal of carbon dioxide.
Wait, it gets better. Biochar is actually good for the soil
When the Portuguese and other explorers and conquerors came to South America and the in the Amazon basin, they noticed that some of the black earth was very fertile and remained so while other soils rapidly got exhausted.
These soils are referred to as anthropogenic, which means they owe their existence to human intervention. The Terra Preta as it is known has obvious signs of human interaction associated with it. Artefacts and pottery are found in it.
It is not clear if the original inhabitants knew enough to add lots of charcoal to their soil, along with manure and bones or if it just happened because of how they lived, but the net result was a spectacularly successful and stable soil. Terra Preta was most certainly produced over many years and maintained by generation after generation.
Charcoal has a couple nice qualities. It can hold water because it is very porous, and it has a high Cation Holding Capacity. A fancy term used to mean it can bind to positive ions such as potassium, phosphorus and nitrogen. These are the macro nutrients which are indispensable to most plants. There are also many micronutrients which are also attracted to the biochar. This means that the nutrients are not leached out during rains but rather are kept in the soil and made available to the plants.
Nice as biochar is, it is not by itself rich in nutrients. That's why nutrients have to be added. Manure, ashes and compost are natural sources of fertility (good cations) and these were found in the terra preta along with the charcoal. These fertile elements come from the usual sources, manure, bones etc. What biochar is good at, is hanging on to the nutrients.
Adding Charcoal to your soil does not mean you magically have Terra Preta, since charcoal is only one component. It is however one of the steps in its making.
Slash and Char VS. Slash and Burn
Slash and burn is the practice of cutting down vegetation and burning it. This clears the soil and gives a few seasons of good crops until the fertility of the soil and that added by the ashes is used up or washed away by the rain. Farmers then have to move on to a new patch of ground and start over, while leaving sadly depleted, eroded and bare ground which is difficult to rehabilitate
Slash and burn is only sustainable if the population is very small and there is sufficient time for the land to recover. Unfortunately this is no longer the case. Large patches of land are being laid to waste faster than they can recover. This is a cause of desertification.
It is speculated that the original inhabitants used a slash and char method which ensured that biochar was produced and added to the soil along with fertilizing additives such as manure. This produced the Terra Preta. This method helped keep the soil texture in good condition, helped the soil hang on to nutrients and as long as some form of fertilizer was added, in the form of manure, bones, ashes or compost, the farmer could stay in place and grow crops in a sustainable way.
Because of the inevitable ash content of biochar, it has the advantage of reducing the acidity of the soil which is usually helpful. Many soils are more acidic than is ideal for agriculture.
But wait, there's more.
Biochar assists in one more thing. It helps encourage the various microorganisms that make up the soil ecology. These in turn interact with the plant life to make it more resistant to disease and to absorb nutrients better. The large surface area and multiple pores of biochar create a favourable environment for the growth of the various bacteria, moulds, micro-organisms etc. that exist in a healthy productive soil.
Improving the population of beneficial organisms is one of the reasons for using compost to inoculate the biochar. It takes some time before the biochar is colonized and it is useful to inoculate the biochar with compost / manure and good soil, before it is added as a soil improver. Some people claim that colonization can take several years to complete.
Experiments abound where a soil is amended with biochar then fertilized. The control soil is also fertilized. After crops are planted the biochar plot often shows spectacular results compared with the fertilized plot with no biochar.
BUT... The other side of the medal.
There is no doubt that biochar can improve soil increasing the productivity and stability.
I don't think there is any doubt that it is a better solution than just incinerating organic waste, or slash and burn agriculture.
Where it becomes iffy is in all the (sometimes bordering on fanatical) claims that it will magically solve the greenhouse gas emissions and fix our energy problems. Research is lively but has not been ongoing for very long and not all the results are in.
Ecology is complicated and we have to look at the big picture to understand if biochar is as effective as we would all like it to be.
Terra Preta is brought as a shining example but we have to keep in mind that although charcoal is a part of Terra Preta, it is NOT the only part. These soils have evolved over long periods. The charcoal gradually mixed in by human activity and other forces such as armies of earthworms. The terra preta was gradually colonized by the right microorganisms. Bones, ashes, manure and compost patiently added.
On the left links column there are a couple of interesting articles of opponents of Biochar. Worth a read. It's at the bottom of the column.
Making charcoal/biochar. My experiments
email me: Christine