The color scheme of carbon content: A simpler approach to gauging soil health

Carbon is an important component of all living things. It’s fundamental to energy capture in photosynthesis for plants. It’s in the sugars, fats, and proteins we use for food. 

Carbon is also in our atmosphere as carbon dioxide. Humans breathe in oxygen and breathe out carbon dioxide (CO2). However, human activity has increased the amount of CO2 in the atmosphere. Rising CO2 is linked with climate change. Thus, reducing atmospheric CO2 has been a goal of scientists for decades.

samples of soils of different colors

The ground we walk on is a massive carbon sink

Soil is the largest terrestrial carbon reservoir, more than the atmosphere and all the earth’s vegetation combined. Carbon cycles through soil in a continuous loop. Carbon provides energy for microorganisms and nutrients for plants while increasing water holding capability and soil stability. The amount of soil organic matter is a good gauge of ecosystem health.

Soil acts as a carbon sponge. As concerns about climate change grow, there is growing interest in how to increase soil carbon storage and quantify it.

For being such a key player in the global carbon cycle, accurate assessments of soil carbon across different areas is limited. Soil organic matter is highly variable. It is affected by factors including climate, land use, and local flora and fauna. The very nature of carbon cycling keeps the numbers dancing as plant and animal matter decays and land use rapidly changes. It is difficult to measure or predict carbon concentrations in the soil, especially across different landscapes. Researchers must collect, dry, and analyze a wide variety of soils—an expensive and arduous chore.

An easier, less costly way to measure soil carbon is needed

Last year, Garrett Liles and a team of soil scientists from the University of California, Davis proposed a simpler approach for tracking carbon using a basic but telling attribute: soil color. This research was published last October in the Soil Science Society of America Journal.

“Color is the central interface between humans and soils,” Liles says. “As organic matter increases, soils get darker. Civilizations realized this with early agricultural success occurring on dark, fertile, carbon-rich soils. Darkness as an indicator for soil organic matter became a central component of how we classify soils.”

With this in mind, Liles thought assessing carbon in soils might be easier using quantified measurements of color. “A soil’s color tells you a lot about what going on,” Liles says. “For carbon, darkness does all the work.”

This research surveyed over 1900 forest soil samples in northern California. The researchers developed models to accurately predict carbon concentrations across a broad range of soil types driven by color alone. Soils represent a diverse color palette and refuse to be summarized simply in all cases. For example, increasing red pigments, as soils develop, interfere with the basic darkness-carbon relationship. The researchers were able to account for this in their model.

One goal of this work was to bring more attention to the importance of soils in the carbon cycle. Soils have an ability to act as an agent in emerging conservation markets, including cap and trade offset assessments.

“If a rancher could easily quantify their soil carbon resource, additional revenues by selling carbon offset credits, could be generated to support conservation practices.” Liles says. Using quantified color measurements and predictive models should help simplify this process. “This way you can collect many samples and analyze them efficiently with a simple reproducible measurement,” he adds. “This is one way to address variability and produce accurate assessments.”

Climate change, land use, and intensive management practices create challenges for maintaining healthy soils and resilient ecosystem function. Retaining and increasing organic matter content is a central approach to maintain soil quality all over the world. The ability to  monitor soil carbon with a simple low cost approach is an important tool to better understand soils as a resource, support informed management decisions and strategies, and tap into the future carbon economy.

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