Separation of Coarse Organic Particles from Bulk Surface Soil Samples by Electrostatic Attraction

Different separation procedures are suggested for studying the stability and functionality of soil organic matter (OM). Density fractionation procedures using high‐molarity, water‐based salt solutions to separate organic particles may cause losses or transfers of C between particle and soluble OM fractions during separation, which may be a result of solution processes. The objective of this study was to separate coarse organic particles (>0.315 mm) from air‐dried surface soil samples to avoid such solution processes as far as possible. Air‐dried surface soil samples (<2 mm) from nine adjacent arable and forest sites were sieved into five soil particle size fractions (2–1.25, 1.25–0.8, 0.8–0.5, 0.5–0.4, and 0.4–0.315 mm). Coarse organic particles were separated from each of these fractions using electrostatic attraction by a charged glass surface. The sum of the total dry matter content of the electrostatically separated coarse organic particles ranged from 0.05 to 140 g kg −1 Scanning electron microscopy images and organic C (OC) analyses indicated, however, that the coarse organic particle fractions were also composed of 20 to 76% mineral particles (i.e., 200–760 g mineral kg −1 fraction). The repeatability of the electrostatic attraction procedure falls within a range similar to that of accepted density fractionation methods using high‐molarity salt solutions. Based on the similarity in repeatability, we suggest that the electrostatic attraction procedure will successfully remove coarse organic particles (>0.315 mm) from air‐dried surface soil samples. Because aqueous solutions are not used, the electrostatic attraction procedure to separate coarse organic particles avoids C losses and transfers associated with solution‐dependent techniques. Therefore, this method can be used as a pretreatment for subsequent density‐ or solubility‐based soil OM fractionation procedures.