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 (BDhs) with soil pit samples (BDpit) within a corn (Zea mays, L.)-soybean [Glycine max (L.) Merr.] rotation field in central Iowa. Although BDhs varied substantially compared with BDpit with RMSE of 0.15 g cm(-3) 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 BDhs 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 BDhs. Further studies are needed to investigate the impact of hydraulic sampling induced errors.