Carbon farming: applying biochar to increase soil carbon

Page last updated: Tuesday, 15 March 2022 - 2:43pm

Biochar is a stable, carbon-rich form of charcoal that can be added to soil to sequester carbon and reduce net greenhouse gas emissions. It is produced by pyrolysis, a process where biomass (plant or animal waste) is heated at temperatures greater than 250°C with little or no oxygen.

The Department of Primary Industries and Regional Development provides this information to support land manager decisions about investing in carbon farming.

Summary

Biochar is a type of charcoal produced by heating organic material (plant or animal waste) to temperatures greater than 250°C in a low oxygen environment (this process is called pyrolysis). From this process, a carbon-rich, relatively stable carbon product is generated.

Converting plant material to biochar reduces carbon dioxide (CO2) released to the atmosphere. Depending on the type of source material, biocahr can remain in soils for hundreds to thousands of years.

Benefits from applying biochar

  • can increase soil fertility, water holding capacity and crop productivity
  • increases soil carbon content and provides longer-term carbon sequestration than soil organic carbon

Biochar has the potential to reduce fertiliser requirements while crop productivity is maintained, or increase crop yields at lower rates of fertiliser use due to reduced leaching. The benefits vary, depending on the type of biochar and the nature of the soil in the treated paddock and in some combinations, the impact may be detrimental. Results on heavy alkaline soils have been promising, although not consistent, and no consistent benefits have been observed on the sandy soils of Western Australia (GRDC).

Biochar can have acid or alkaline pH, and in general, the higher the pyrolysis temperature the higher the pH (What is biochar – external page). 

Opportunities in using biochar:

Applying biochar is an activity covered in the Measurement of soil carbon sequestration in agricultural systems method, and is a restricted activity (section 12:4) in the legislation. The requirements for a project to claim carbon credits from the Emissions Reduction Fund are very detailed. Applying biocahr could be one component of a farming system that results in increased carbon sequestration.

Risks from applying biochar

There are several risks:

  • All Biocars are not the same – biochar characteristics and value in the soil depends on the base material and the pyrolysis technique.
  • Biochar is expensive (production and transport) and economic returns are unlikely for commodity agriculture.
  • Obtaining sufficient quantities of biochar is difficult – there is no large-scale production.
  • Not all soil and biochar combinations will provide a positive result.
  • Some material produced as by-products of industry may contain impurities and toxins, with an unknown impact on the food web, microbial processes and nitrification.
  • Biochar absorbs and concentrates herbicides and pesticides in the root zone.

Contact information

Tom Edwards
+61 (0)8 9083 1151