Measuring soil respiration in the field: an automated closed chamber system compared with portable IRGA and alkali absorption methods

Abstract

With the objective of testing whether a series of automated chambers linked to IRGA equipment gave improved estimates of soil respiration, measurements using the automated system were compared with those obtained from (a) an alkali absorption method and (b) a hand-held commercially available instrument (EGM-1). Comparisons were made on occasions between autumn 1996 and spring 1999 across treatment plots which had a variety of harvest residue materials incorporated into them distributed across 5 sites. Spot readings made using the EGM-1 showed a wide range and greater variability compared to those made with the automated IRGA system. This was attributed to the reproducible location and larger area of the latter chamber. The range in values of estimated total daily CO₂ flux made using KOH absorption and the automated IRGA method similar (0.1–4.0 g C m^{− 2} day^{− 1}), but, although highly correlated, the slope of the regression line was significantly different from unity. Below 0.9 g C m^{− 2} day^{− 1} the KOH method over-estimated the CO₂ flux, but above this value under-estimated it, relative to the automated IRGA system, with the coefficient of variance being consistently smaller for the KOH method. This was ascribed to inefficient absorption of CO₂ at high efflux rates and the presence of an artificially high concentration gradient at low efflux rates for the KOH method. The results indicated that the automated IRGA system offered a robust estimate of both instantaneous and time-integrated CO₂ efflux rates, and therefore has potential application in measurements of organic matter decomposition in agricultural soils.

Acknowledgments

The authors would like to thank their colleagues at ADAS for assistance with making measurements and management of the experiments concerned, and to PP Systems Ltd. for useful discussions. The financial support of the UK Ministry of Agriculture Fisheries and Food is also gratefully acknowledged.