Carbon Dioxide in Arable Soil Profiles: A Comparison of Automated and Manual Measuring Systems

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Carbon dioxide (CO2) concentrations in arable soil profiles are influenced by autotrophic and heterotrophic respiration as well as soil physical properties that regulate gas transport. Although different methods have been used to assess dynamics of soil CO2 concentrations, our understanding of the comparability of results obtained using different methods is limited. We therefore aimed to compare the dynamics in soil CO2 concentrations obtained from an automated system (GMP343 sensors) to those from a manually operated measurement system (i.e., soil gas sampled using stainless steel needles and rods). In a winter wheat field in Denmark, soil CO2 concentrations were measured from 29 November 2011 to 14 June 2012 at upslope and footslope positions of a short catena (25 m). Carbon dioxide was measured at 20- and 40-cm soil depths (i.e., within and below the nominal plow layer) using the two measurement systems. Within the measurement range for the GMP343 sensors (0–20,000 ppm), mean results from the two systems were similar within the plow layer at the upslope (P = 0.060) and footslope (P = 0.139) position, and also below the plow layer at the upslope position (P = 0.795). However, results from the two systems deviated for the soil from the footslope position below the plow layer (P = 0.001). These results were partly attributed to larger variation in soil parameters below than within the nominal plow layer. The data suggested that generally the application of either system may be adequate; however, differences may occur in response to soil spatial variability. A better coverage of spatial variability is more easily addressed using manually operated systems, whereas temporal variability can be covered using the automated system. Depending on the aim of the study, the two systems may be used in combination to enhance both spatial and temporal data coverage.