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

C. Dold, J. L. Hatfield, T. J. Sauer, C. Cambardella, K. M. Wacha
Agricultural & environmental letters 2018 v.3 no.1 pp. e180007
Glycine max, Zea mays, bulk density, carbon, carbon sinks, corn, crop rotation, soil compaction, soil depth, subsoil, topsoil, Iowa
CORE IDEAS: Hydraulic sampling can affect bulk density measurements. The effect was greater for the subsoil. Correction measures had little or negative influence. 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.