A faster, simpler way to measure soil carbon

Measuring soil organic carbon quickly and efficiently is essential in the fight against climate change. An article in a scientific journal shows that LaserAgTM is the right tool for the job. Based on laser technology, plasma physics and artificial intelligence, this instrument invented by Logiag determines carbon faster and more ecologically than traditional methods.

The staple food of plants, carbon dioxide (CO2), is also one of the most important greenhouse gases. Using solar energy, plants extract the carbon present in CO2 and transform it into stems, leaves and roots. This carbon is then transferred to the soil, where it helps to improve underground life, retain water and… fight climate change.

The carbon present beneath our feet, or soil organic carbon (SOC), is therefore an asset to be preserved. Quantifying it is also important for assessing reductions in atmospheric CO2, among other things. But current chemical methods for measuring SOC are slow, costly and wasteful.

LaserAgTM breaks the mould: based on laser technology, plasma physics and artificial intelligence, this instrument invented by Logiag analyzes SOC faster, more ecologically and at a lower cost than other methods. The publication of an article on LaserAgTM in Scientific Reports – a publication belonging to the Nature portfolio – demonstrates that this tool represents a real breakthrough in laser technology and soil analysis.

The author of the Scientific Reports article, Carla Pereira de Morais, talks about her research into LaserAg analyses of soil organic carbon.

Dry combustion: accurate, but expensive

Currently, dry combustion is the most common method for determining carbon concentration in soil. This method uses a gas to burns the soil sample entirely then quantifies some of the elements resulting from this combustion, including carbon.

While dry combustion gives highly accurate results, it cannot meet the growing demand for SOC analysis. Firstly, it is too slow: it takes between 5 and 10 minutes to analyze a single sample, whereas 40 samples are needed to properly analyze barely 100 hectares! What’s more, this method is expensive, particularly because of the gases it requires for combustion.

The power of LIBS

In the 1980s, another technology appeared in laboratories: laser-induced breakdown spectroscopy (LIBS). LaserAgTM was the first commercially available instrument that uses this technology to analyze SOC.

Despite the challenges inherent in LIBS, this technology is well worth the effort. Compared to dry combustion, it enables the simultaneous analysis of several elements, four times faster and at lower cost, with minimal sample handling and a total absence of by-products.

Like dry combustion, LaserAgTM first requires dried, crushed and homogenized soil samples. Then LaserAgTM adds another step: the LaserAg press applies a pressure of 1.6 t per cm2 to the samples. This hardens, homogenizes and densifies their surface, improving laser performance.

The samples are then placed in the LaserAg Quantum machine, 14 at a time. One after the other, they receive a succession of 200 laser beams, 12 times. In less than a minute, the operation transforms all these impact points into plasma, i.e. a gas of around 10,000 ⁰C! At this heat, all these sample bits are disintegrated: they no longer contain molecules, but only atoms such as calcium, magnesium, iron… and carbon.

Quantum physics to the rescue

Subsequently, measuring the concentration of carbon and other atoms relies on quantum physics. This physics tells us that the electrons in the atoms absorb the energy of the laser, exciting them. It also tells us that, once the laser is switched off, the electrons return to their normal state, re-emitting the energy received. Finally, quantum physics tells us that the energy coming from the electrons (transmitted in wavelengths) makes it possible to identify both the atom to which they belong and their intensity.

In practical terms, the LaserAg Quantum machine’s spectrometer converts these wavelengths into a spectrum, i.e. a series of peaks, each peak corresponding to a specific atom. But the job is far from over.

The challenge lies in the spectra themselves, which do not always reflect true atomic concentrations. “This is due to the texture and composition of the soil, which considerably influence the measured signals,” explains Carla Pereira de Morais, lead author of the article in Scientific Reports and Team Leader, R&D at Logiag. “For example, even when they contain the same amount of carbon, soils with different textures can show carbon peaks of different intensities.”.

To ensure reliable results, LaserAg therefore uses two additional strategies: calibration and artificial intelligence.

Calibration or comparing LIBS with dry combustion

Calibration involves using dry combustion, then the LaserAg Quantum machine to analyze around 1,000 soil samples with different textures and carbon concentrations. “This process enables us to determine which real carbon value is associated with which spectrum,” explains Carla Pereira de Morais, who completed a PhD on LIBS technology.

The next step is artificial intelligence. This is used to train a mathematical model to link the calibration results, i.e. the spectrum of a given sample with its carbon concentration. Over time, the model can interpret the spectrum of new samples and determine by itself which carbon concentration to associate with it.

Once the model is well trained, it still needs to be validated! Basically, the LaserAgTM team uses the Quantum machine to analyze samples for which they already know the carbon concentration – and checks the results! Today, 90% of LaserAgTM results are at least 70% similar to those of dry combustion. “This excellent result has enabled us to publish in Scientific Reports,” enthuses Ms. Pereira de Morais.

An evolving model

Four LaserAg Quantum machines are already operating around the world, including one in the Longueuil laboratories of Eurofins EnvironeX and two in Africa. The results they produce continue to improve the LaserAgTM algorithm. Indeed, LaserAgTM includes a tool that detects out-of-range results, i.e. those with a carbon concentration below 0.75% or above 10%. “Samples with such concentrations are sent for dry combustion, and the results of this second analysis are correlated with the initial spectrum, and then reintroduced into the algorithm, further enhancing LaserAg Quantum’s reliability and accuracy,” explains the researcher. Last but not least, LaserAgTM offers many other advantages, such as a mobile application and software associated with the machine, making it easier to take samples in the field and trace them throughout the analysis chain. Add to this LIBS technology, artificial intelligence and quantum physics, and you have everything you need to revolutionize soil analysis.

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