Research case study, Biochar trials

​Case study – Department of Agriculture, Fisheries and Forestry, Australia’s Farming Future
Climate Change Research Program (CCRP)

Biochar trials show positive signs for agricultural soil enrichment and reducing emissions

An ancient method of soil improvement, combined with some 21st century scientific research and development, showed potential for increasing agricultural productivity while reducing greenhouse gas emissions.

The Department of Agriculture, Fisheries and Forestry (DAFF) funded the CSIRO to carry out biochar research as part of the Climate Change Research Program, drawing on multiple partnerships with universities and state agencies.

As part of the program, preliminary trials undertaken into the use of biochars, a stable form of charcoal created by heating natural organic materials such as wood chips, crop waste or manure in a low oxygen process known as pyrolysis. The resulting product, which is rich in carbon, applied to agricultural land to replace carbon lost over time and could improve soil properties such as water-holding capacity, pH and cation exchange capacity.

The research project built on growing scientific interest and investigation into the potential uses of biochar. CSIRO have compiled a database of more than 80 biochars and their associated compositions and characteristics, forming the basis for in-depth research into how different biochars interact in different farm soil environments and their impacts on soil health, carbon sequestration and the mitigation of greenhouse gas emissions. A separate project – funded by the Grains Research and Development Corporation – is using the same database to examine how biochar might increase crop productivity.

Project leader, CSIRO’s Evelyn Krull said there is real potential for biochar to play an important role in mitigating greenhouse gas emissions and improving soil health.

“Our research was the most comprehensive on biochar to date, as it investigates biochar from sink to source,” she said.

“We looked at the production of biochars, the interaction between biochars and different soil types, the effects on productivity, the effects of climatic warming on biochar’s stability, risk factors and contamination issues, the effect of biochar on nitrous oxide emissions and the whole life-cycle of biochar and its carbon sequestration potential.”

Results from an assessment of more than 80 biochars showed that pyrolysis temperature and the type of material that it was produced from were the most important determinants of biochar properties. Wood-derived biochars tended to have the highest organic carbon concentrations, whereas manure and food waste-derived biochars had higher nitrogen and phosphorus levels.

The findings are not just confined to the laboratory, with Jos Webber, producer of Kahawa Coffee at Tintenbar on the NSW North Coast, has already seen some benefits in some plants treated with a specific biochar.

Jos established his coffee plantation eight years ago and 18 months ago commenced trials using two different types of biochar.

“We have four different treatment groups within the plantation,” said Jos. “One is untreated, another has straight compost, a third has compost with rice biochar, and a fourth has compost with poultry-litter biochar.”

After about a year, Jos began to see differences between the treatment groups. 

“The plants that were doing the best were those treated with the poultry biochar and the ones doing least well in terms of their height were those without any treatment at all.”

“There was also quite a difference in the way the two biochars reacted in the soil. The rice hull almost formed a blanket and there was very little activity in that, whereas the slightly coarser poultry litter biochar showed a lot of activity, and was incorporated into the under-layers of the soil.”

Jos believes there is great potential for locally grown coffee and hopes that the trials might provide encouragement for more growers to enter the market. 

“We have a very good climate for coffee here and the more improvements we can make to our soil the better,” he said. “There is a big demand for our product because more consumers are becoming conscious of eating and drinking Australian-made.”
However, Evelyn cautions that biochar may not work in all systems.

“We found that biochar type and soil type form a strong interaction and while we saw increases in productivity in some systems, we saw no results or decreased productivity at certain application rates in other systems,” she said.

“Generally speaking, low-nutrient and infertile soils seemed to respond more vigorously to biochar applications than nutrient-rich, clayey soils.”

As well as potential benefits to soil quality and enhanced crop yields under certain circumstances, producing biochar via pyrolysis can result in reduced greenhouse gas emissions. The organic materials converted to biochar (pyrolysed) were naturally part of the photosynthesis cycle, so took the carbon out of the cycle and locked it in biochar meant that there was a decrease of carbon dioxide (CO2) in the atmosphere.

“With the trials showing that biochars should last between 100 to 1500 years in the soil, biochar could play a key role in helping to sequester carbon and offset greenhouse gas emissions,” said Evelyn Krull.

“However, the true offset was determined by complex life-cycle analysis which was also part of the DAFF biochar project.”

The NSW Department of Primary Industries (NSW DPI) tested a range of biochars including council green waste, animal manure wastes, papermill wastes as well as residues from the sugarcane and rice industries.

NSW DPI Principal Research Scientist, Lukas Van Zwieten, said the project  tested different types of biochar in different soils under different farming systems to work out what works and why.

“Whilst we used the latest technologies to produce biochar, its origins were very old,” he said.

“There is strong evidence from ancient farming cultures, such as those in South America, that charcoal was applied for farming purposes producing 'terra preta' or 'dark earth' soil, which is far more friable and has lower bulk density and much higher carbon content. All of its nutrient properties are more amenable to growing food crops.”

“Some of the trial plots accumulated a significant amount of carbon in soil. In our best case scenario, around 40 tonnes of CO2 equivalent was stored in some of these soils after we added the biochar,” Lukas said.

“But this was dependent upon both the properties of the biochar, and the farming system it was applied to. Identification of soil constraints was important before applying amendments like biochar. Biochars have different properties and can address different soil constraints.”

Lukas said Jos Webber’s trial at Kahawa Coffee is a positive sign for the scientist working in biochar research.

“The poultry-litter biochar incorporated into the soil well, and the soil chemistry results showed we got improvements in a number of the soil functions like nutrient holding capacity and available phosphorus,” he said.

“When these soils were converted to agriculture many years ago there was a decline in soil organic carbon, and what we are doing here is simply replacing some of that carbon in the soil through applying biochar.”
Biochar was also trialled with other crops including sugar cane, macadamias, rice and avocados.

Last reviewed: 4 November 2019
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