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Dryad

Soil water content determined at saturation and water holding capacity and calculated at 50% water filled pore space

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Aug 28, 2020 version files 61.19 KB

Abstract

Optimizing soil microbial activity requires an equal balance between water- and air-filled porosity, i.e. 50% water filled pore space (WFPS).  However, many soil biological investigations report water as some fraction of water-holding capacity (WHC).  This study was conducted to fill a quantitative gap between WFPS and WHC.  Soil samples (n=198) from 10 eastern U.S. states and one state in Brazil provided a wide distribution of clay (0.064-0.487 kg kg-1) and soil organic C (SOC, 5.2-52.0 g kg-1) concentrations (5-95% range).  Gravimetric soil water content (SWC) was determined at WHC and at saturation.  Both clay and SOC concentrations strongly influenced SWC; the effect of SOC was strongest and non-linear.  To achieve 50% WFPS, gravimetric SWC was 0.69+0.10 times that of WHC and 0.59+0.03 times that of saturation.  For soil biological assays, 50% WFPS could be reasonably accurately and simply achieved with calculations using gravimetric SWC at saturation multiplied by 0.59.