Solid-State Sensors for Real-Time Measurement of Soil CO2

Soil is a major component in the ecosystem carbon balance. The primary source of soil CO2 is derived from plants (i.e., rhizosphere respiration) and organisms (i.e., heterotrophic free-living microbes), with a combined contribution to soil carbon stores close to 2 Gt. Furthermore, belowground soil and plant respiration accounts for the annual processing of one-sixth of the total atmospheric CO2–pool.

The availability of small, solid-state sensors (i.e., Model GMM220 series, Vaisala, Inc., Helsinki, Finland) has allowed for the continuous measurement of soil CO2 in field settings.

Soil CO2 concentrations in irrigated cropping systems have yet to be quantified using continuous measurement instrumentation such as the GMM222. Seasonal fluctuation in soil CO2 is of importance in these systems, which continually undergo wetting and drying cycles. Irrigation events in semiarid climates of eastern Washington could mimic rain shower events that have been reported increased soil CO2 concentration six-fold from 1000 μmol mol−1 to nearly 6000 μmol mol−1.

A group of researchers from Washington State Univ. and USDA determined the operating parameters and season-long performance of GMM222 sensors in lab and greenhouse testing and field experiments with irrigated winter wheat.

While measuring differences in the diurnal patterns of soil CO2 concentrations are important, the researchers were most interested in checking the performance of the GMM220 series sensors under a range of environmental conditions. Therefore, lab, greenhouse, and field data were used to determine accuracy and responsiveness of the sensors.

The performance of solid-state CO2 sensors was evaluated in laboratory, greenhouse, and irrigated winter wheat. In ambient CO2 concentration, the GMM222 sensor averaged 427 ± 8.3 μL L−1 Under variable CO2 concentrations, the sensor was slightly lower than concentrations measured with an infrared gas analyzer. In greenhouse pots planted with triticale and an agricultural field of irrigated winter wheat, soil CO2 concentration exceeded the 10,000 μL L−1 limit of the GMM222. Alternatively, the GMM221 sensor, designed to measure between 0 and 20,000 μL L−1, showed soil CO2 concentrations were between 14,000 and 16,000 μL L−1

The researchers found that the GMM222 accurately measures real-time soil CO2 concentrations under field conditions that were within the sensor detection limit. However, periods of high biological soil activity require the GMM221 sensor with a higher detection limit.

Material obtained from

Performance of Solid-State Sensors for Continuous, Real-Time Measurement of Soil CO2 Concentrations
Stephen L. Young, Francis J. Pierce, Jason D. Streubel and Harold P. Collins
Agronomy Journal 2009 101: 6: 1417-1420
doi:10.2134/agronj2009.0210N

https://www.agronomy.org/publications/aj/abstracts/101/6/1417