Effect of Acid Deposition on the Chemical Properties of Soil Organic matter

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Thirteen acid soils(A_<0+1>, 0-15cm)were collected from volcanic regions of Japan(pH(H_2O)=2.81-3.93), and 9 reference soils from the regions unaffected by volcanic acids(pH=4.10-4.74). Hunic acids were extracted from those soils with 0.1M NAOH and precipitated by acidification(pH=2, HCl). After the dissolution and precipitationprocedure had been repeated 5 times, the humic acids were treated with 2% HF to reduce the ash content. and then washed with CHCl_3 to eliminate any elemental S. The resulting humic acids were freezedried and subjected to the S-analyses. The sulfur species determined in the humic acids were total S, ester sulfate-S, sulfonate-S, sulfhydryl-S, inorganic S, and C-bonded S. The C-bonded S included C-S-C. C-S-S-C, and non-ionic S-containing groups. The results obtained in this research are summarized as follows : 1)The S contents of of acid soils(0.22<plus-minus>0.10%)were clearly higher than those of reference soils(0.11<plus-minus>0.03%), and increased rapidly from ca. 0.15% to ca. 0.40% with decreasing soil PH(from 3.5 to 2.8). 2)The humic acids(AHA)from acid soils showed higher concentrations of total S(0.56<plus-minus>0.21%), total organic S(0.53<plus-minus>0.19%), and sulfonate-S(740<plus-minus>610ppm)compared with those(RUA)from reference soils(total S : 0.34<plus-minus>0.04%, total organic S : 0.33<plus-minus>0.04%, sulfonate-S : 530<plus-minus>320ppm). 3)Although the relative concentrations of sulfhydryl-S and inorganic S were low(less than 10% of total S), both components were also rich in AHA(sulfhydryl-S : 270<plus-minus> 110ppm for AHA and 90<plus-minus>70ppm for RHA, inorganic S : 370<plus-minus>190ppm for AHA and 110<plus-minus>30ppm for RRA). 4)Ester sulfate-S showed approximately constant concentrations in both samples(ABA : 1500<plus-minus> 360ppm, RHA : 1560<plus-minus>320ppm)regardless of the pH and S content of t