Crucial tool for dealing with global warming lets scientists measure carbon without disturbing plants

Imaging the soil with neutrons can provide quick and detailed insight into the amount and distribution of carbon (and some other important elements) in the soil without disturbing the soil or plant roots. Credit: Berkeley Laboratory

Scientists are developing a new way to count the carbon in the ground beneath our feet – a crucial tool for managing climate change

Physicists and soil scientists from the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have teamed up to develop a new method to find the carbon stored in the soil by plants and microbes. Unlike all previous methods, this new technique makes it possible to see the carbon in the earth without digging holes or taking soil samples, such as a soil x-ray. This new method of measuring the carbon extracted from the air promises to be an important tool in combating climate change and developing more environmentally friendly forms of agriculture.

“What this instrument really does is repeat measurements over time,” said Arun Persaud, a physicist at the Berkeley lab and one of the team leaders. “With our instrument, you can get a very accurate and fast measurement of total carbon in an acre of land, without disturbing the soil or harming the organisms that live there.”

A plant transfers carbon to the soil as a natural part of its life cycle. Plants inhale carbon dioxide and exhale oxygen (which we animals then inhale). The carbon stays in the plant, used to build the molecules and cells it needs to live. Much of this carbon ends up entering the soil through the roots of the plant. Soil microbes then capture this carbon and turn it into organic matter that can persist for decades, centuries, or longer.

Plants and soil microbes play a key role in the Earth’s carbon cycle – a cycle that humans have drastically altered. The burning of fossil fuels is rapidly warming the planet. Human land use for agriculture has depleted soil organic matter, resulting in a huge soil carbon deficit that also contributes to climate change.

Extracting large amounts of carbon from the atmosphere is an essential part of virtually any plan to limit global warming to 2 degrees. Celsius or less. This need is the origin of the Carbon Negative Initiative at Berkeley Lab, which aims to develop technologies to capture, sequester and use carbon dioxide. Plants and microbes are experts at extracting carbon from the atmosphere – they’ve been doing it for billions of years. But before we can harness them to help manage atmospheric carbon, we need to accurately measure how much carbon is already locked up in the soil through plant-microbe interactions or other management strategies. Unfortunately, existing techniques for testing soil carbon content are quite destructive and error-prone on a large scale.

“We have a major limitation in understanding and quantifying how carbon enters and persists in the soil because of how we measure it,” said Eoin Brodie, a Berkeley Lab scientist. “Typically, we take a soil core from a spot in a field and bring it back to the lab. Then we burn it and measure the carbon that is released. It’s extremely laborious and expensive to do so, and you don’t even know how representative those kernels are.

Neutron test facility for fusion science

Will Larsen and Arun Persaud at the Neutron Test Facility of the Fusion and Ion Beam Science Technology Program of the Accelerator Technology and Applied Physics Division, setting up the alpha particle detector. The alpha detector measures the distribution of carbon atoms in the soil. Credit: Berkeley Laboratory

Brodie is Deputy Director of Berkeley Lab’s Division of Climate and Ecosystem Sciences and one of the leaders of the EcoSENSE program, a component of the Biological and Environmental Programs Integration Center (BioEPIC) currently in development. EcoSENSE aims to create suites of sensors to monitor the impacts of climate and weather on ecosystem functioning, and Brodie and his colleagues wanted to find a better way to measure carbon in the soil. The vast scientific expertise available at the Berkeley Lab and a timely call for proposals on underground sensor technologies from DOE’s Advanced Research Projects Agency-Energy (ARPA-E) led Brodie, Persaud and their colleagues to team up on this project. “What it really took was communication between very different programs at Berkeley Lab,” Brodie said. “We became aware of this potentially useful technology in the ATAP (Accelerator Technology & Applied Physics) division, and we joined forces.” Finally, the interdisciplinary team received a grant from ARPA-E’s ROOTS (Rhizosphere Observations Optimizing Terrestrial Sequestration) program, which made this work possible.

The new measurement method developed by the Berkeley Lab team eliminates the need to dig anything out of the ground. Instead, the as-yet-unnamed device scans the ground with a neutron beam. Then, a detector detects the weak response of carbon and other soil elements to neutrons, allowing it to map the distribution of different elements in the soil with a resolution of about five centimeters. It all happens above ground, with no holes, no pits, and no burning. “It’s like giving the ground an MRI,” said Persaud, who is a researcher at ATAP. “We get a three-dimensional picture of the soil and the distribution of carbon in it, along with other elements like iron, silicon, oxygen, and aluminum, all of which are important for understanding carbon persistence. in the ground.”

“What really excites me about this neutron imaging approach is that it allows us to efficiently and accurately image carbon distributions in soils at the scales at which carbon accounting needs to take place,” added Brody. “And we can do that repeatedly over the growing seasons, to see how that changes with different climates and land management practices. Eventually, you could use it to identify which specific land management practices more efficiently extract carbon from the atmosphere and store it in the soil.

“This new carbon sensing method is an example of thinking outside the box and bringing together researchers from diverse backgrounds, here physical sciences and earth sciences, to create new technology that addresses the challenges of climate change,” said Cameron Geddes, Director of ATAP.

Right now, the project is fresh out of the lab, and Persaud, Brodie and their colleagues are set to test it soon in real soils in an outdoor system. “We’re really excited to test this on the ground here at Berkeley Lab after the rainy season,” Persaud said.

“The next step is to make this process deployable in the field and more automated, so that it can be integrated into things like combines and tractors, so that it becomes part of the sensing capabilities that you find in farms and through forests,” Brodie added. “There really is huge, huge potential in there.”

Reference: “A fully digital associated particle imaging system for the 3D determination of isotopic distributions” by Mauricio Ayllon Unzuetaa, Bernhard Ludewigt, Brian Mak, Tanay Tak and Arun Persaud, June 14, 2021, Examination of scientific instruments.
DOI: 10.1063/5.0030499

Founded in 1931 on the belief that the greatest scientific challenges are best met by teams, Lawrence Berkeley National Laboratory and its scientists have been awarded 14 Nobel Prizes. Today, Berkeley Lab researchers are developing sustainable energy and environmental solutions, creating useful new materials, pushing the boundaries of computing, and probing the mysteries of life, matter, and the universe. Scientists around the world rely on the facilities of the laboratory for their own scientific discovery. Berkeley Lab is a multi-program national laboratory, operated by the University of California for the US Department of Energy’s Office of Science.

The DOE’s Office of Science is the largest supporter of basic physical science research in the United States and works to address some of the most pressing challenges of our time.

Teresa H. Sadler