As the global interest in biochar continues, it is important to understand how biochar is made, how it is used and the benefits which it will bring to our soil and our environment.

How Biochar is Made

Pyrolysis is defined as “the chemical process of decomposition under the effect of heat”. If we take a waste biomass, a good example is waste wood, crop waste, forest thinnings or in fact anything that once lived or comes out of something that lived, and put it through a process of pyrolysis whereby the oxygen is limited, it will break down into gases and residual charcoal. Ideally, the produced gases are collected and can be cleanly combusted. These gases also provide the necessary energy to sustain the pyrolysis and provide renewable energy for external use.  Such examples are thermal energy and electricity generation.

With the restriction of oxygen in the pyrolysis process, we stop the biomass from turning to the ash that we would see in a normal household fireplace.

An important point to note is that biochar is not incineration ash. Nor is it reasonable to think that any biochar would be of benefit to the soil if it originated from wood treated with preservative or painted timber. Significant research would need to be done to ensure it is safe to use. Such chars may potentially be used for other industrial uses, just not as biochar to grow food.

A very large component of biochar is carbon. This is largely resistant to decomposition, thereby locking the carbon out of the atmosphere. This removal of the carbon dioxide from the atmosphere makes biochar a carbon negative product which is of benefit to the environment.

Biochar is highly porous and is capable of both ABsorption and ADsorption.

Absorption (e.g. soaking up water) is a function of the char’s porosity.

Adsorption is dependant upon the surface area . All surfaces of the char adsorb materials by electro-chemical bonds, a bit like an electric sponge.

Up close: biochar has a huge surface area and highly porous structure | Image: www.carbolea.ul.ie via Biochar Ireland

However, it must be noted that there are a number of variables involved in the production and usage of biochars:

Typically, these variables are:

  • Highest treatment temperature of the pyrolysis process
  • Original biomass type (studies on 80 different biochars have been conducted)
  • State of decay of original biomass
  • Quality of compost used as the conditioner
  • Ageing period of biochar/compost blends
  • Quantity of biochar/compost blends added to soil
  • Type of soil to which the biochar is being added

How Biochars should be used

A number of studies have been undertaken in the synergisms between compost and biochar for sustainable soil amelioration. (Fischer et al, 2012) Simply put, blending the biochar in equal parts (1:1) with a well balanced compost, allowing it to mature then adding it to the soil is beneficial as it can help capture nutrients and form humus as well as developing many other advantageous characteristics.  This process effectively charges the biochar with plant nutrients and innoculates (seeds) the biochar with a combination of living organisms. (Taylor, 2010)

It can be expected that good quality biochar used in this way, when some of it is already fine enough for compost worms and later earthworms, gains even more value following the “digestion“ process.

Typically, conditioned biochar is added to soils within the following ranges: (Taylor, 2010)

  • 2-2kg/m2
  • 2 – 2.0% by weight (incorporation to depth 10cm in soil with density 1.0)
  • 0.5 – 5% by volume (if biochar density is 0.4, 1 – 10% with density 0.2)

Many studies have demonstrated the beneficial effect of biochar on plant growth | Image supplied by author

The benefits of biochar when used as a soil amendment

Adding biochar to the soils has many benefits:-

Once in the soil , biochar keeps the compost moist and aerated, thus promoting increased biological action. (Wilson, 2014)

Biochar has been proven to increase nitrogen retention in the soil (Steiner et al, 2008) (Clough et al, 2013).

Studies have demonstrated that biochar improves compost maturity and humic content (Wilson, 2014).

Biochar compost improves plant growth. (Wilson, 2014)

There are a number of research projects being undertaken on biochar all over the world. An excellent source of information on this research is the International Biochar Initiative. Another excellent source of information is the Biochar Journal that explores and explains the many other traditional and emerging uses of chars.

Laura Jones is the owner of Mobius Biochar, a Western Australian supplier of biochars produced from oil mallees which were originally planted for soil restoration purposes.

http://www.mobiusbiochar.com.au

References

Clough et al. (2013). A Review of Biochar and Soil Nitrogen Dynamics. Agronomy, 275-293.

Fischer et al. (2012). Synergisms between Compost and Biochar for Sustainable Soil Amelioration. Management of Organic Waste, 167–198.

Steiner et al. (2008). Nitrogen Retention and Plant Uptake on a Highly Weathered Central Amazonian Ferralsol Amended with Compost and Charcoal. Journal of Plant Nutrition and Soil Science, 893-899.

Taylor, P. (2010). The Biochar Revolution. Mt. Evelyn: Global Publishing Group.

Wilson, K. (2014, October 31st). How Biochar Works in Soil. Retrieved November 4, 2014, from the Biochar Journal 2014, Arbaz Switzerland: http://www.biochar-journal.org/en/ct/32