Comparison of soda lime and infrared gas analysis techniques for in situ measurement of forest soil respiration

Soil respiration provides an indication of the activity of a forest soil. At high efflux rates the dynamic infrared gas analysis (IRGA) method generally provides a higher estimate of soil CO2 efflux than does the static soda lime absorption method. In laboratory tests, soda lime absorbed 98% of added CO2, provided sufficient moisture was present. Field comparisons in the boreal forest showed IRGA estimates of soil respiration to be fourfold greater than those for soda lime over an 8-h period, while Limited comparisons between soda lime and IRGA soil respiration estimates in a radiata pine (Pinus radiata D. Don) plantation over 24 h resulted in IRGA estimates being 40% higher (range -3 to 86%). There was no strong correlation between the two methods at either field site. Field measurements of CO2 concentration in the headspace of a chamber containing soda lime showed CO2 buildup equivalent to 20-100 min of CO2 flux from the soil. Measurements made with chambers of different volumes showed no significant difference in either soda lime or IRGA estimates of CO2 efflux. Disturbance of chambers in the field did not stimulate short-term rates of soil respiration when measured with an IRGA, nor could temporal scaling be shown to markedly overestimate CO2 efflux rates.