Too Close or Too Far? Chamber Placement Biases Soil CO2 Emission Estimates in Row Crop Agricultural Fields

Accurate quantification of soil CO2 emissions is essential for representative estimates of field-scale carbon fluxes. Chambers are widely used for this purpose, but their small measurement footprint can introduce placement-driven bias in row-crop agricultural fields. We quantified soil CO2 fluxes in two adjacent maize fields (75 cm row spacing) on contrasting clay and loam soils and identified a single chamber location that best represents the between-row mean flux. Automated chambers measured CO2 fluxes at hourly intervals throughout the season at 20 and 37.5 cm from the maize stem base. During the reproductive growth stage, a portable survey chamber was used to quantify fluxes at two additional distances (10 and 30 cm) to capture the full cross-row gradient. In both soils, CO2 fluxes declined sharply with increasing distance from the crop row, consistent with strong root-zone influence. In the clay field, fluxes near the row (20 cm) were, on average, 50% higher than those at the inter-row position (37.5 cm), whereas the corresponding difference in the loam field was 21%. Spatial patterns were consistent with root biomass distribution and soil microclimatic variation, particularly volumetric water content. The mean CO2 emission across the full row spacing involving measurements from four distances identified 20 cm as the optimal single-point location, with the smallest deviation from the mean flux in both soils. These results demonstrate that chamber placement strongly influences soil CO2 flux and support 20 cm from the stem base as a robust, texture-independent location when a single between-row measurement position is required.