08. Other sources of biochar in the soil

These trials involve adding biochar to soils but it is possible that soils already contain some native (natural) biochar, or biochar that has been added directly or indirectly from human activities. In order to work out the effect of the added biochar, control plots are used, and the soil tested for its properties pre-addition of biochar.

Black carbon (biochar & soot) is present for example tests found in soils 0.2% (median) and sediment 0.5% (median). Some studies predict charcoal is more significant in the global carbon cycle, with charcoal accounting for between 1 and 20% of organic carbon in soil.

This black carbon may be the result of:
Airborne deposition: from pollution
Terrestrial deposition: often moved by water from processes including charcoal making
Fires: natural or deliberate.

Aftermath of a fire at Harmony Farm near Beng Melia, Cambodia early 2010.

Informal discussions with many farmers from Siem Reap have shown that it is actually common for farmers to add charcoal to the soil, which is a biochar-like substance. These are usually smaller pieces left from charcoal making or using the burned rice husk waste from making palm sugar for example.

Pigs laying in rice husk biochar residue from palm sugar refining, Don Keau Commune, Siem Reap.

Biochar has been found to be commonly used by garden centres (See pics of biochar being used in garden centre), and as a potting compost for growing seedlings at some medium sized commercial farms.

Rice husk biochar used in potting plants at a garden centre in Siem Reap town. May 2010

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