Saying soil is important is an understatement. From serving as the medium where most of our food is grown, to sequestering carbon and reducing atmospheric CO2 concentrations, to being the home for enormous quantities of biodiversity—including antibiotic-producing bacteria—soil is key to life on Earth.
However, current agriculture and land use practices degrade soil, and there are many unknowns about what factors make a healthy, resilient soil, mainly due to limited methods for assessment. Researchers at UConn are working to fix this.
"What's measured can be managed," says Assistant Research Professor in the Department of Plant Science and Landscape Architecture Huijie Gan. Gan and her co-authors are working on a cost-effective way to efficiently assess soil health at scale. Their findings are published in Soil Biology and Biochemistry.
"If you don't know quantitatively what is missing, it is difficult to say how are you going to change anything," says Gan.
Gan explains this project grew out of the larger project by the USDA's Natural Resource Conservation Service (NRCS), to find university collaborators to help quantify different aspects of soil functions and to see how soils function under different management practices. The goal of this project is to find a way to easily measure if certain soil improvements or conservation practices are successful or not, and why. This is increasingly important, especially for the development of climate-resilient agriculture practices that can help ensure food production in the face of climate change.
"We want to quantify a soil's ability to support food production, but also other important ecosystem functions like regulating water infiltration and storage, reducing greenhouse gas emissions, and ability to store carbon," says Gan. "Soils contain a lot of organic matter. Microbes are consistently breaking down complex forms of organic matter into simpler biologically active forms, releasing mineral nutrients for plant uptake and some CO2 in the process. We want enough of this kind of active carbon in the soil to support microbial activity and ecosystem functions, but we also want more stable soil carbon that is not easily released to the atmosphere."
Gan explains that soil organic matter also functions like a sponge that absorbs water and affects how water moves through the soil. The resulting water dynamics affect the microbial decomposition of the organic matter, and these many soil processes are often intertwined which is why the concept of soil health emphasizes the need to look at soil with a holistic view.
However, soil health assessment is not easy, Gan explains. There is a debate in the soil science community regarding how soil health assessment should be done. A common approach is to quantify a select set of soil physical, chemical, and biological properties that are indicative of important soil functions and then assign soil health scores based on the range of measurement results from soils in the same region.
One widely used soil health indicator is called CO2 burst or short-term carbon mineralization, which is in the minimal data set recommended by USDA-NRCS and the Soil Health Institute. The standard protocol requires air drying the soil and then adding a predetermined amount of water. The water kickstarts microbial activity, which releases a burst of CO2. The amount of CO2 released during the incubation period is indicative of many things, such as total microbial biomass, the active organic matter pool, and plant nutrient availability.
"There are a few specialized commercial or governmental soil testing laboratories that will do this kind of soil health assessment," says Gan. Most use the conventional alkali trap method, which uses small containers with an alkali solution to absorb CO2 from microbial respiration or rely on gas analyzers to measure changes in CO2 concentrations inside incubation jars over time.
With an interest in simplifying the process, Gan had concerns about how to scale up the measurements. While troubleshooting, she says a colleague suggested simple CO2 monitors frequently used in greenhouses or other enclosed spaces. Having relied on standard protocols for measuring CO2 in the laboratory using chemicals, calculations, and precision equipment, Gan had never considered another method.