Performance of Solid‐State Sensors for Continuous, Real‐Time Measurement of Soil CO 2 Concentrations

Recent advances in sensor technology provide a robust capability for continuous measurement of soil gases. The performance of solid‐state CO 2 sensors (Model GMM220 series, Vaisala, Inc., Helsinki, Finland) was evaluated in laboratory, greenhouse, and irrigated winter wheat ( Triticum aestivum L.). In ambient CO 2 concentration, the GMM222 sensor averaged 427 ± 8.3 μL L −1 . Under variable CO 2 concentrations, the sensor was slightly lower than concentrations measured with an infrared gas analyzer (IRGA). In greenhouse pots planted with triticale ( Triticale hexaploide Lart.) and an agricultural field of irrigated winter wheat, soil CO 2 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 CO 2 concentrations were between 14,000 and 16,000 μL L −1 . The GMM222 accurately measures real‐time soil CO 2 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.