Biochar

The Australian Government funded research to understand biochar’s ability to store carbon and reduce greenhouse gas emissions. Through the National Biochar Initiative researchers determined how biochar could be used in Australian conditions.

Key Points

  • Biochar is a stable, carbon–rich form of charcoal that is applied to soil.
  • Some biochars can increase soil fertility, water holding capacity and crop productivity.
  • Adding biochar to soil increases its carbon content and could help mitigate greenhouse gas emissions.
  • Research shows that biochars derived from grasses or crops appear to have the best balance of agricultural benefit and carbon stability.
  • Biochars derived from grass, wood, and biosolids have been shown to raise wheat germination rates by about five per cent.

Biochar is produced from heating organic materials like crop waste, grass, woodchips and manure in a high temperature, low oxygen process known as pyrolysis.

It has the potential to increase soil carbon content, which can help reduce overall greenhouse gas emissions and mitigate future climate change. Producing biochar and applying it to soils could create carbon offsets under the Carbon Farming Initiative. Biochar may also provide additional agricultural benefits such as increased soil fertility and crop productivity.

Wheat straw, and wheat straw biochar

Wheat straw (left) and wheat straw biochar (right). Photograph: Pacific Pyrolysis Pty Ltd.

About Biochar

Agricultural productivity benefits of biochar

Some studies have demonstrated that applying biochar to soils can increase agricultural productivity. In cases where agricultural productivity increased it is thought to be due to:

  • improved nutrient storage and/or availability
  • improved soil structure
  • improved water holding capacity
  • increased abundance of mycorrhizal fungi, assisting nutrient uptake by plants.

These agricultural benefits depend strongly on soil type and climate.

Biochar and greenhouse gas mitigation

Adding biochar to soil increases its carbon content and can mitigate greenhouse gas emissions. This mitigation can occur by several means:

  • long term transfer of carbon into biochar, which would otherwise decompose naturally and emit carbon dioxide and methane
  • production of syngas and bio–oil, which can be used as energy alternatives to fossil fuels
  • reduced emissions of nitrous oxide from fertiliser application.

Dr Bhupinderpal Singh (Industry and Investment NSW) showing greater growth of faba beans in biochar–treated soils (background) versus untreated soils after 3 years of initial biochar application at the Wollongbar Research Station, NSW.

Dr Bhupinderpal Singh (Industry and Investment NSW) showing greater growth of faba beans in biochar–treated soils (background) versus untreated soils (foreground) after 3 years of initial biochar application at the Wollongbar Research Station, NSW. Photograph: Annette Cowie (Industry and Investment NSW).

From source to sink: the National Biochar Initiative

Among other areas of research, the National Biochar Initiative investigated the:

  • characteristics and properties of different types of biochar
  • stability of biochar under different soil conditions
  • impact of biochar on nitrous oxide emissions from soil
  • effect of biochar application rates on wheat germination
  • production risks of using biochar.

Characteristics and properties of different types of biochar

CSIRO led a research project examining how the variable physical and chemical properties of biochar are affected by pyrolysis temperature and biomass source. Biomass sources include woodchips, manures and crop residues.

Analyses of over 80 different biochars have shown that the type of biochar used needs to suit the situation and desired outcome. The research found that grass or crop–derived biochars appear to have the best balance of agricultural benefit and carbon stability. Wood–derived biochars were more carbon rich, whereas biochars from manures and food wastes recorded higher nitrogen and phosphorus levels.

Stability of biochar under different soil conditions

Biochar stability in soil is highly variable. Therefore, the University of Sydney and Industry and Investment NSW investigated biochar stability in different soils and environments. Laboratory results suggest that the decomposition of carbon in biochar–treated soils increases with rising soil temperature and biochar production temperature, and is affected by soil properties. Future work will highlight the chemical and structural changes in biochars from interactions with different soil types and the environment.

Impact of biochar on nitrous oxide emissions from soils

Nitrous Oxide (N2O) has 310 times more global warming potential than carbon dioxide over a 100 year period1. Fertiliser, livestock waste and burning organic matter are the most common agricultural sources of N2O emissions. Soil moisture, pH level, structure, nutrient content and soil carbon content are known to interact with biochar but it isn’t known how these interactions affect nitrous oxide emissions.

Researchers from Industry and Investment NSW and the University of Western Australia explored the potential for biochar to reduce N2O emissions from soils. Early results from one WA field trial indicate that while biochar decreased soil emissions of carbon dioxide, N2O emissions remained stable or increased.

Glasshouse incubation studies of soils were conducted to identify biochar properties and other factors (e.g. fertilisation, organic carbon levels, presence of crops) that affect N2O emissions. Research also determined if biochar–caused changes to the soil environment and microorganisms affect on nitrous oxide emissions.

Field trial assessing the effect of biochar on N2O emissions

Field trial assessing the effect of biochar on N2O emissions. Photograph: Lukas van Zwieten (Industry and Investment NSW).

Effect of different biochar application rates on wheat germination

Currently, there is no information on the best biochar application rates for Australian soils. Therefore, as a starting point, research coordinated by CSIRO investigated the effect of biochar application rates on wheat germination and growth. Initial results show that grass, wood, and biosolid–based biochars raised germination by about five per cent at the optimum application rate of 10t/ha. However, germination rates were lowered for biochar derived from papermill waste.

Research has also found that some soils are better suited to certain biochars. Biomass production was greater with chicken manure biochar at 5 t/ha for South Australian soil and 10 t/ha for New South Wales soil, and wheat chaff biochar at 5 t/ha for Western Australian soil.

Impact of different rates of wheat chaff biochar (0, 10, 20, 50 and 100 tonnes per hectare) on wheat germination rates.

Impact of different rates of wheat chaff biochar (left to right: 0, 10, 20, 50 and 100 tonnes per hectare) on wheat germination rates. Photograph: Zakaria Solaiman and Dan Murphy (The University of Western Australia).

Risks of biochar

Toxicity

Biochar can contain heavy metals and toxic organic compounds, which may pose environmental or health risks. Research measured the levels of these compounds in biochars and advising on safe usage rates. Comprehensive analysis of 20 different biochars showed low levels of toxic organic compounds. These amounts are close to those found in most soils and are unlikely to pose a risk. Further analysis is planned to determine the concentration of heavy metals in biochars.

Impact of biochar on the effectiveness of agricultural chemicals

Researchers tried to work out how biochar changes the effectiveness of herbicides. Compounds like herbicides and pesticides can adsorb (stick to), or be absorbed by biochar particles, meaning soils with biochar may collect residues and need higher application rates of agricultural chemicals.

Glasshouse experiments have shown that low levels of fresh biochar in the soil deactivate herbicides rapidly leading to poor weed control. Biochar also reduced the rate of herbicide decay. These results suggest that biochar use will need to be carefully managed in agricultural situations that rely on herbicides applied to the soil.

CSIRO research has shown that biochar particles have highly variable absorption and adsorption rates for the herbicide atrazine. Biochars produced at higher temperatures (≥550°C) generally recorded higher absorption and adsorption rates than those produced at lower temperatures (≤450°C). Some biochars recorded almost complete absorption and adsorption of atrazine. These results indicate that herbicide sorption and subsequent deactivation is dependent on the type of biochar.

Partnerships

Research presented in this fact sheet is a result of partnerships between:

  • AnthroTerra Pty Ltd
  • CSIRO
  • Department of Agriculture and Food, WA
  • Industry and Investment NSW
  • National Centre for Rural Greenhouse Gas Research, University of New England
  • Pacific Pyrolysis Pty Ltd
  • South Australian No–till Farmers Association
  • University of Adelaide
  • University of New South Wales
  • University of Sydney
  • University of Western Australia.

Acknowledgement

Information contained in this fact sheet was obtained from a research progress report provided by participating research partners listed above.


References

1. IPCC 2007 Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change