2013 Volume 124 Pages 25-33
Authors developed compact soil gas monitor-ing system which consisted of gas-permeable silicone rub-ber, a non-dispersive infrared CO2 gas sensor and galvanic cell O2 sensor for the purpose of evaluating changes in soil CO2 concentration in fields. In this study, 0.5-mm-thick silicone rubber sheet was used for CO2 sensing tube, which was reinforced with plastic and stainless mesh pipes. Time required to reach 95 % equilibrium of CO2 concen-tration of 0.5-mm-thick silicone rubber tube was 104 min-utes, while that of 4-mm-thick tube, which reported pre-viously, was 1175 minutes. The constructed system was buried in agricultural bare field and continuous monitor-ing of soil CO2 concentration was conducted through a year. Since an amplitude of seasonal changes in soil tem-perature in agricultural field is relatively large, e.g., > 25 °C at depth of 10 cm in this study field, temperature de-pendence of NDIR CO2 sensors was investigated. After temperature correction and calibration, monitored results agreed with the soil CO2 concentration which was mea-sured by conventional gas sampling method. Monitored data showed seasonal and daily changes in soil CO2 con-centration accompanied with changes in soil temperature. Quick response to increase in soil CO2 concentration fol-lowing each rainfall event was also observed. Simultane-ous decrease in O2 concentration suggested that microbial activity could be dominant factor of increase in soil CO2 concentration caused by rainfall.
