Performance of Continuous CO2 Measurements in Soils: A Preliminary Assessment.

Sensors for the continuous measurement of CO₂ concentrations in soil are available but are not validated for real time, in situ measurement of CO₂ in actively growing cropping systems. This study evaluated the Vaisala GM222 CO₂ sensor over a range of soil conditions in the greenhouse and in the field. The CO₂ sensors had a range of 0 – 10,000 µmol mol^-1 were connected to an 8 channel data logger along with thermistors to measure soil temperature, Campbell Scientific CS615 soil moisture sensors, and a Figaro galvanic cell O₂ sensor as needed for each evaluation.  Data from the sensors were obtained every minute and transmitted via a wireless Ethernet connection to a server and data automatically stored in a data base.  In the greenhouse, sensors were installed in eight 30 cm diameter pots containing Walla Walla silt loam (coarse-silty, mixed, superactive, mesic Typic Haploxerolls) soil and seeded with Triticale (Triticale hexaploide Lart.) at a rate equivalent to115 kg ha^-1. Sensors were subjected to various environmental changes of heat, light, and moisture. In one field experiment, 8 sensor arrays were installed in bare Warden silt loam (coarse-silty, mixed, superactive, mesic Xeric Haplocambids) soil in a grid arrangement to assess the variability among sensors.  Finally, sensor arrays were installed in a bioenergy experiment under various crops and irrigation regimes. This paper will summarize the performance of CO₂ sensors under a range of soil and crop conditions.