Technical Abstract: Recent advances in sensor technology provide a robust capability for continuous measurement of soil gases. The performance of solid-state CO2 sensors (Model GMM220 series, Vaisala, Finland) was evaluated in laboratory, greenhouse, and irrigated wheat (Triticum aestivum L.). 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 tricale (Triticale hexaploide Lart.) and an agricultural field of irrigated wheat, soil CO2 concentration exceeded the 10,000 µL L-1 limit of the GMM222. Alternatively, the GMM221 sensor, designed to measure between 0-20,000 µL L-1, showed soil CO2 concentrations were between 14,000 and 16,000 µL L-1. 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.