Extraction and Determination of Sulfur in Organic Horizons of Forest Soils

Abstract

Abstract Little information exists on the accuracy, precision, and make‐up of extractable S in surface organic horizons of forest soils. Eight extractants (H 2 O, 0.01 M CaCl 2 , 0.01 M KCl, 0.01 M LiCl, 0.003 M NH 4 OAc, 0.003 and 0.01 M NH 4 Cl, and 500 mg P L −1 as Ca(H 2 PO 4 ) 2 ·H 2 O) were evaluated for the extraction and determination of SO 4 ‐S and total extractable S in surface organic horizons of five forest soils. The analyses for SO 4 ‐S and total extractable S were performed by ion chromatography (IC) and inductively coupled plasma atomic emission spectrometry (ICP‐AES), respectively. Each of the weak salt extractants removed similar amounts of SO 4 ‐S and total extractable S. Water was the least desirable extractant because it removed more organic S than the salt extractants, was the most variable for IC analysis, and produced inconsistent results. The 0.01 M NH 4 Cl extractant, however, was found to be the most consistent extractant. The precision ranged from 3.7 to 8.9% for the IC analyses excluding the aspen ( Populus tremuloides Michx.) sample and from 1.9 to 8.4% for the ICP‐AES analyses. Poor precision in the SO 4 ‐S determination of the aspen organic horizon was due to the elution of an unidentified peak adjacent to the S peak. Quantitative recoveries from 102 to 108% and from 97 to 108% were obtained in the 0.01 M NH 4 Cl extract by the IC and ICP‐AES methods, respectively. The effect of varying solution to soil ratios was also determined for 0.01 M NH 4 Cl. The 10:1 solution to soil ratio was the most consistent. Ratios <10:1 had significantly lower concentrations of extractable S and SO 4 ‐S for three soils and caused logistical problems in the laboratory (i.e., slower filtering, more sample required) because of the low solutin‐to‐soil ratio. Storage of airdried material at room temperature (20 ± 4 °C) for 1.5 yr resultd in increased total extractable S and SO 4 ‐S concentrations.