Abstract:

A soil respiration monitoring equipment was designed to overcome the inconvenience of conventional open chambers which required gas sampling in an infrared gas analyzer to measure CO₂ concentration, and a correction calculation method was proposed for unstable CO₂ concentration. A compact and lightweight low-cost non-dispersive infrared sensor module was installed in a suitable position inside the chamber as an alternative to the infrared gas analyzer through computational fluid dynamics simulation analysis. Under the controlled gas flow rate of 3, 4, 5 L·min^-1, the CO₂ concentration field inside the chamber at soil respiration rates of 0.5, 2, 5, 10 μmol·m^-2·s^-1 was obtained according to the simulation software. The center point of the bottom surface of the chamber was used as the origin to establish Cartesian coordinate system. Combined with the analysis of sensor module dimensions, it was found that for the chamber described in this research, the average error in measuring CO₂ volume fraction to calculate soil respiration rate did not exceed 15% in the spherical area determined by the point (-0.046 5, 0.071 7, 0.209 0) (unit: m) as the center and the diameter of 0.05 m. After the deployment of sensors, the performance of the equipment was compared with the LI-8100 automated soil CO₂ flux system and the self-made closed chamber in field, and the mean error was 10.8%, which was consistent with the results of the simulation analysis.

Key words: soil respiration, open chamber, simulation analysis