Evaluation of a Portable Chamber System for Soil CO2Efflux Measurement and the Potential Errors Caused by Internal Compensation and Water Vapor Dilution

Abstract

A portable, easy-to-install chamber system for rapid measurement of soil CO2efflux is needed for the immediate analysis of CO2flushes after events such as tillage and grassland renovation. We conducted field measurements and simple simulations to validate the effectiveness of a portable chamber system with an infrared CO2gas analyzer (IRGA) and a temperature/humidity sensor (the SIR system). We confirmed that a measurement period of 60-180s after the closure of the chamber was sufficient for the calculation of soil CO2efflux. We compared the SIR system with a closed static chamber system and an automated open/closed chamber system. The efflux data obtained with the SIR system were linearly related to the data obtained with the other systems, and the relationships between the soil temperature and efflux were similar in the three systems. These results show that the SIR system provided soil CO2efflux values with a reasonable accuracy relative to the other systems. We also examined how the calculated efflux values were affected by the internal compensation of the IRGA for environmental parameters and water vapor dilution in the chamber. The potential error caused by the default internal compensation of the IRGA was within 3.1% under general environmental conditions. The effect of water vapor dilution was large (>20%) for small CO2effluxes. The combined effects of the default internal compensation and water vapor dilution were larger for small CO2effluxes than for large CO2effluxes, and the effects became larger under low air pressure conditions. We recommend that accurate environmental compensation and water vapor correction be applied for analysis of small CO2effluxes when there is a rapid increase in water vapor, especially under low air pressure conditions. © 2011, The Society of Agricultural Meteorology of Japan. All rights reserved.