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Title: Short-term C mineralization (aka the flush of CO2) as an indicator of soil biological health

item Franzluebbers, Alan

Submitted to: CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2018
Publication Date: 9/10/2018
Citation: Franzluebbers, A.J. 2018. Short-term C mineralization (aka the flush of CO2) as an indicator of soil biological health. CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources. 13(17).

Interpretive Summary: Healthy soils are needed so that agriculture can continue to work for us by producing abundant food, feed, and fiber in the face of climate change and rising input costs. A key question these days is ‘how should we measure the health of soil?’ Chemical, physical, and biological dimensions of soil health are important to consider. A seminal biological indicator is the breath of soil itself. Like us, soil is living and therefore breathes – the more it breathes, the more it needs to be fed – the more it is fed, the more work it can do. This review was prepared by a scientist at the USDA-ARS in Raleigh NC to describe a test that creates a snapshot of how much a soil breathes for a short period following rewetting. Short-term C mineralization provides strong indications of (a) how well soil offers crops nitrogen from organic matter, a process called mineralization, (b) how soil becomes aggregated and able to filter and cycle water effectively in the environment, (c) providing readily utilizable substrates to support a diversity of soil microrganisms, and (d) the potential of soil to sequester C from the atmosphere, as well as store plant nutrients in slowly-accessible forms of soil organic matter. As an example, soil that has been fed a robust diet of crop diversity and kept intact with conservation tillage works hard to provide sufficient nitrogen to crops. In contrast, not knowing how much nitrogen is really available often leads to over-application of fertilizer and potential environmental degradation. This review summarizes some of the key findings from analysis of short-term C mineralization, also known as the flush of CO2, soil CO2 burst, or soil-test biological activity.

Technical Abstract: Soil biological activity is a key component of soil health assessments, as it (a) indicates soil nutrient cycling capacity from various organic matter sources to inorganic availability, (b) relates to soil structural conditions, (c) informs about the potential to harbor biodiversity in soil, and (d) often parallels changes in soil organic C and N storage in surface soils. The flush of CO2 following rewetting of dried soil represents a burst of microbial activity that can be considered an artifact, but has very strong relationship with longer term C mineralization and basal soil respiration across a diversity of soils. This review demonstrates also the strong association of the flush of CO2 with soil microbial biomass C and net N mineralization. Weaker associations occur with total and particulate organic C and N. The flush of CO2 has been evaluated for assessing both short- and long-term impacts of crop and forage management. It also has strong temporal and spatial variations that can be related to availability of organic substrates and landscape-specific environmental conditions. Variations in methodology have recently appeared in the literature and standardization is needed if results are to be compared. The flush of CO2 should be considered a rapid, robust, and reliable method to indicate soil biological activity, and as such should be a major component of any soil health assessment.