Actually biochar – charcoal from plant waste – is not new at all. It’s incredibly ancient, and has been used for thousands of years by Amazonian natives to improve their soil and grow better crops.
In the 21st century, biochar is being rediscovered by soil scientists and organic gardeners in Australia and North America, among other places, and is the focus of research by both Australia’s leading scientific body, CSIRO, and Michigan Technological University, Houghton, Michigan.
CSIRO is looking at ways of increasing carbon levels in Australia’s thin and agriculturally poor soils, and biochar is just one of the approaches.
It is already being taken up by environmentally conscious farmers and gardeners, particularly those growing organic crops, who have to avoid inorganic fertilizers.
Biochar: Carbon from Burning Plant Waste
Waste from woody plants, such as crop stubble or tree thinnings, is heated at high temperatures without oxygen to create biochar.
This process, called pyrolysis, also produces two renewable energy sources biogas, and a usable ‘bio-oil’,
Biochar is the black carbon-rich solid left behind when the gas and oil have been removed. It is very stable, and can remain in soil for up to 5000 years.
Enriching the Soil with Non-Biodegradable Carbon
Researchers at Michigan Technological University claim biochar has almost magical properties in increasing soil fertility.
Dr Michael Moore, who led science and mechanical engineering students in the research, says the soil’s productivity was increased by 880 per cent with the addition of biochar from sawdust, tree branches, and even broken up packing palettes.
Dr Moore said the estimate of 880 per cent was based on research provided by Christoph Steiner in his dissertation, Slash and Char as Alternative to Slash and Burn, which looked specifically at improvements to soil in the Amazonian rainforest.
Australian soil scientists from CSIRO’s Land and Water Division, while acknowledging that biochar does return stable carbon to the soil, are cautious about such results.
While studies have shown that biochar can provide improvements to soil quality and enhanced crop yields, as well as better water retention, and the possibility of carbon sequestration to reduce greenhouse emissions, they warn, in a CSIRO fact sheet on biochar and agriculture, that not all biochars are the same, and they are not always beneficial.
“Some biochars may have adverse effects on plant growth, and not all soils respond to biochar additions in the same way.
“Studies that have reported positive effects with regard to crop production often involved highly degraded and nutrient-poor soils, whereas application of biochar to fertile and healthy soils does not always yield a positive change.”
Biochar and Carbon Sequestration
While the jury may still be out on the benefits to crops from biochar, there is no doubt that biochar is an effective way to lock up carbon in the soil, which would otherwise return to the atmosphere as CO2.
Because biochar is made of plant residue, much of the carbon in it initially came from CO2 in the atmosphere, which the plant used to make carbohydrates by photosynthesis.
Both the CSIRO and Michigan Technological University researchers agree that biochar prevents plant waste from releasing CO2 when it decays, and what’s more, the process of making biochar is carbon negative.
According to the CSIRO fact sheet on biochar, if biochar is produced by pyrolysis, together with biogas and bio-oil, the process leads to a net reduction of 20 percent of carbon to the atmosphere.
If this charcoal is then returned to the soil, it can sequester this carbon for hundreds, maybe thousands of years.
“Due to its high chemical stability, high carbon content and its potential to reside in the soil over decades, centuries and even millennia, biochar applications could play an important role in helping to sequester carbon from the atmosphere, and partially offset greenhouse gas emissions from burning fossil fuels,” the CSIRO researchers say.
See Also: Crude Fuel from Garden Waste
Cut Food Waste, Save Phosphorus
Sue Cartledge - I'm a science, health, nutrition and lifestyle journalist, fascinated by the way the physical world operates in all its forms, and how ...
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