New technique to measure carbon in soil

Researchers at the University of Sydney’s Soil Security Laboratory have developed the soil carbon bench (SCB) - an instrument which is claimed to determine carbon levels from much larger samples, with greater accuracy and lower cost, than any existing technology.

The SCB and its results were presented last week at the International Union of Soil Sciences Global Soil Carbon Conference, held at the University of Wisconsin-Madison. The research team consists of PhD researcher Robert Pallasser, Associate Professor Budiman Minasny and Professor Alex McBratney. There were also two other University of Sydney presentations at the event.

Professor McBratney explained that Australia’s agriculture sector has the potential to participate in the carbon market, capturing and storing carbon emissions in soil. “However, there is no guarantee that the industry can benefit from the offsets in the current and future carbon economy because until now there has not been a good and efficient way of measuring soil carbon storage with statistical confidence.”

Furthermore, current methods of soil carbon analysis are labour-intensive. To ensure a representative sample with elements from all parts of the core, they have to be crushed, homogenised and carefully sampled again.

The SCB, developed by Pallasser, solves this problem by extracting and quantifying soil from cores up to a metre in length, which yields samples of 300-500 grams of soil for analysis after initial drying. The method can get an accurate representation of the variability of carbon in soil over space and depth.

“This is a great advantage over the current method that relies on ‘point analyses’ of a highly variable quality based on 0.5 gram amounts of soil at a time because current instruments are limited to these miniscule amounts,” said Associate Professor Minasny.

Pallaser explained that the SCB takes whole cores, ideally broken up and dried out. The core is inserted into the reactor, which is sealed up before a gas supply is introduced. This oxidises and transfers the products of the combustion to the analytical system.

A furnace mounted on wheels is moved to the soil material, breaking down the organic matter within the soil matrix, extracting the carbon and carrying it through to the detection system. A signal is recorded “and the amount of signal we get, or the area of the peak, is proportional to the amount of carbon in the core”, said Pallaser.

The researchers claim the technique “facilitates fast and cost-effective determination of soil carbon stocks to support mapping and modelling”, along with sequestration. Sequestration promises major environmental benefits from capturing carbon which also, by increasing the organic matter in the soil, improves productivity and resistance to land degradation.

The researchers are working on automating the instrument’s components.