Introduction of a guideline for measurements of greenhouse gas fluxes from soils using non‐steady‐state chambers

Abstract

Soils represent a major global source and sink of greenhouse gases (GHGs). Many studies of GHG fluxes between soil, plant and atmosphere rely on chamber measurements. Different chamber techniques have been developed over the last decades, each characterised by different requirements and limitations. In this manuscript, we focus on the non-steadystate technique which is widely used for manual measurements but also in automatic systems. Although the measurement method appears very simple, experience gained over the years shows that there are many details which have to be taken into account to obtain reliable measurement results. This manuscript aims to share lessons learnt and pass on experiences in order to assist the reader with possible questions or unexpected challenges, ranging from the planning of the design of studies and chambers to the practical handling of the chambers and the quality assurance of the gas and data analysis. This concise introduction refers to a more extensive Best Practice Guideline initiated by the Working Group Soil Gases (AG Bodengase) of the German Soil Science Society (Deutsche Bodenkundliche Gesellschaft). The intention was to collect and aggregate the expertise of different working groups in the research field. As a compendium, this Best Practice Guideline is intended to help both beginnersThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Analysis of small-scale soil CO2 fluxes in an orange orchard under irrigation and soil conservative practices

“…Several advances have been carried out into the development of CO 2 chamber techniques since long time [ 52 , 92 ]. The dimensions of the soil CO 2 flux system used in this study, in terms of diameter and height of the chamber, are quite similar in comparison to other commercial equipment, i.e., LI-8250 LI-COR Environmental (USA), WestSystems (Italy) and ADC BioScientific (UK).…”

“…The static closed volume procedure is normally used for manual gas sampling using a syringe. The dynamic open volume procedures consist in the measurement of CO 2 concentration in a gas mixture obtained from the gas coming out from the soil and a known air flux with a known CO 2 concentration, through an inverted chamber and across a known soil surface [ [50] , [51] , [52] ]. All dynamic open volume procedures are affected by possible over pressurization or depressurization into the measurement chamber, depending on the design of the instrumental apparatus and the magnitude of the air flux chosen by the operator [ 52 , 53 ].…”

“…The dynamic open volume procedures consist in the measurement of CO 2 concentration in a gas mixture obtained from the gas coming out from the soil and a known air flux with a known CO 2 concentration, through an inverted chamber and across a known soil surface [ [50] , [51] , [52] ]. All dynamic open volume procedures are affected by possible over pressurization or depressurization into the measurement chamber, depending on the design of the instrumental apparatus and the magnitude of the air flux chosen by the operator [ 52 , 53 ]. The dynamic closed volume procedures for measuring the soil CO 2 consist in determining the rate of increase of the CO 2 concentration inside an inverted chamber placed on the soil surface without using external air dilution while carrying out gas mixing, to avoid gas stratification inside the chamber.…”

“…This technique, known as the “accumulation chamber method” or “dynamic closed chamber method”, has been successfully applied in agricultural sciences to determine soil CO 2 flux and other soil gaseous species, e.g., N 2 O [ [54] , [55] , [56] ]. Several authors recognized the accumulation chamber method as the best way to measure soil CO 2 flux, being an absolute method that does not require either assumptions or corrections depending on soil characteristics [ 52 , 57 , 58 ]. However, the high costs generally associated to the use of traditional accumulation chambers make it necessary to develop low-cost devices to make the monitoring of CO 2 soil fluxes more accessible.…”

Small lateral air pressure gradients generated by a large chamber system have a strong effect on CO2 transport in soil

“…Gas fluxes between soil and atmosphere are commonly estimated by chamber measurements (Maier et al, 2022). This technique assumes diffusive gas transport, which is not always given, especially under conditions when pressure gradients might occur.…”