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3 September 2006

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Measuring Soil Health by Continually Monitoring CO2

Researchers in Mexico have developed a new method for continuously measuring the carbon dioxide (CO2) emitted during respiration of microorganisms like bacteria. This accurate, low-cost, system makes it much easier to reliably determine soil fertility or contamination.

CO2 is often used as an indicator for microbiological activity in soils or sediments. Inhibition of microbial respiration indicates a contaminated soil. In agricultural science, the amount of CO2 efflux of soils is an indication of soil fertility. CO2 respiration measurements are also used to evaluate microbiological remediation processes, predicting or optimising microbial processes in contaminated soils.

Previously, continuously monitoring CO2 emission was expensive. It needed a strict flow control, repeated calibration, air filtering and continuous correction for temperature and atmospheric pressure.

The new system is an open one, with a continuous air-flow through. Evolved CO2 is absorbed and precipitated as carbonate by a Ba(OH)2 solution, causing a decrease in ionic strength and conductivity of solution. This decrease in ionic strength can be continuously detected by a conductivity meter.

The researchers connected their conductivity meter (from Orion Research Inc) to a PC running Windmill 4.3 data acquisition software. This they downloaded for free from the Windmill web site.

Windmill read the conductivity and temperature of the alkaline Ba(OH)2 solution from the meter and automatically transferred the data to Microsoft Excel software. Excel corrected the conductivity readings for temperature and calculated the CO2 concentration.

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This new laboratory method reduces costs for reliable, continuous measurements of CO2 evolution and, according to the researchers, offers the possibility for nearly all biological and chemical laboratories to adapt to this technology.

Further Reading

Afferden, M., Hansen, A.M., Kaiser, C. and Chapelain, N. (2006) 'Laboratory test system to measure microbial respiration rate', Int. J. Environment and Pollution, Vol. 26, Nos. 1/2/3, pp.220-233.

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