Sampling probes affect bulk density and soil organic carbon measurements

Abstract

Soil sampling equipment can be a major source of bias in soil organic carbon (SOC) stock estimations. The objective of this study was to evaluate the impact of sampling probes on soil bulk density (BD) and SOC stocks calculated using fixed depth (FD) and equivalent soil mass (ESM) methods. Soil samples were collected to 30 cm using three probes with different diameters and divided into 0–10-, 10–20-, and 20–30-cm layers. The probe with smallest diameter measured higher BD at 0–10 cm in 42% of fields and was significantly different when averaged across fields, while no consistent differences were observed at lower depths. This study shows that sampling probes with different diameters may introduce biases in BD and SOC measurements at individual or combined soil layers when calculated using the FD approach. The ESM approach reduced the differences in mean SOC stocks calculated using different probes.