Hydraulic Deep-Core Sampling Affects Bulk Density and Carbon Stock Measurements

Hydraulic sampling can induce artificial compaction or gaps in soil cores, which affects bulk density (BD) and carbon (C) stock estimation. We compared BD (0–120 cm) from hydraulic samples (BD) with soil pit samples (BD) within a corn (, L.)–soybean [ (L.) Merr.] rotation field in central Iowa. Although BD varied substantially compared with BD with RMSE of 0.15 g cm and with increasing soil depth, the difference was not significant and did not significantly affect C stock estimates. Correcting for sampling hole depth significantly underestimated BD and is not recommended. Calculating C stocks on a mass-based approach, thus avoiding BD effects, showed good results for the topsoil but underestimated subsoil C. This study did not account for different field conditions, which can equally affect BD. Further studies are needed to investigate the impact of hydraulic sampling induced errors.