Soil Carbon: The promise in biochar

ENVIRONMENT SOIL CARBON

Promise in biochar

Words by: Karen Trebilcock

NZ Landcare Trust hopes to hold field days throughout New Zealand soon on incorporating biochar into NZ pastoral

systems.

Biochar is any material from renewable sources high in carbon which has been heated at high temperatures without oxygen so the carbon is mostly in a stable state when it is buried.

It can be made from wood from production forests, orchards or the building industry or from straw and even animal manure.

Massey University research director Jim Jones says it is an alternative way to reduce waste from many industries including horticulture and farming and about five million tonnes of biomass produced every year in NZ could be made into biochar.

If left to rot, the organic matter is broken down and released into the atmosphere as carbon dioxide and other greenhouse gasses.

“And although biochar is not covered by the government’s Emissions Trading Scheme, if carbon prices rose high enough and it was included, then the cost of making biochar could be mostly covered.”

As well as reducing greenhouse gas emissions, biochar is also good for the soil as it is porous.

“It retains moisture and nutrients in the soil and stops them leaching into waterways and also contains small amounts of nitrogen, phosphorus and potassium as well, depending on the source.”

Massey University has built its own

biomass kiln and found reducing gas emissions during the process was vital or any benefit was lost.

No one yet knows what effect biochar could have on NZ’s soil carbon levels.

“Our soil carbon levels are about 100 tonnes of carbon per hectare and we suspect adding biochar will increase these levels but we don’t know. We need longterm studies to find out.

“For carbon to be considered sequestered it has to be stable in the ground for more than 100 years.

“The IPCC (Intergovernmental Panel on Climate Change) has established if biochar is made at 600C or more then after 100 years about 89% of it will still be there because it has been turned into a stable form.

“If the biochar is made at between 350 and 450C then only about 65% will be sequestered.”

Massey University trials has shown about half of the carbon of the biomass could be captured after the carbon used to make it such as from transporting the biomass was subtracted.

“The cost of production depends on the scale but it is about $400/t to make.

“We need it to be included as a recognised carbon sink then it looks a lot more economically possible.”

‘It retains moisture and nutrients in the soil and stops them leaching into waterways and also contains small amounts of nitrogen, phosphorus and potassium as well, depending on the source.’

Massey University research director Jim Jones.