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Reduction of Organic Sulfur in Soils with Tin and Phosphoric Acid
Author(s) -
Pirela H. J.,
Tabatabai M. A.
Publication year - 1988
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1988.03615995005200040011x
Subject(s) - soil water , chemistry , reagent , phosphoric acid , distillation , environmental chemistry , organic chemistry , soil science , environmental science
The chemical nature of organic S in soils is not well understood. In this study, a Sn‐H 3 PO 4 reagent was used for reduction of organic S in soils to H 2 S for subsequent determination as methylene blue. The reduction of soil organic S was compared with that of model S compounds, and with the fractions reduced with HI and with Raney Ni. Results showed that, in general, most of the reduction of organic S in 13 Iowa and 7 Chilean surface soils occurred after distillation for 1 to 3 h, but some soils continued to release H 2 S for up to 10 h of distillation with this reagent. Expressed as a percentage of total organic S in Iowa surface soils, the amounts of Sn‐H 3 PO 4 ‐reducible S ranged from 15 to 64% (avg = 35%) and from 42 to 91% (avg = 60%) for 1 and 10 h of distillation, respectively. The corresponding percentages of the Chilean surface soils were from 8 to 73% (avg = 25%) and from 29 to 100% (avg = 55%). The Sn‐H 3 PO 4 ‐reducible S values were significantly correlated with organic S [ r = 0.71*** ( P < 0.001) and 0.88*** for 1 and 10 h of distillation, respectively]. The amounts of organic S potentially reducible ( S r ) with this reagent ranged from 35 to 86% (avg = 61%) of organic S in Iowa surface soils. The corresponding values for the Chilean soils ranged from 33 to 100% (avg = 66%). The times required to distill 50% of S r ranged from 0.3 to 1.7 h (avg = 0.8 h) for the Iowa soils, and from 0.4 to 9.2 h (avg = 3 h) for the Chilean soils. Studies with five Iowa soil profiles showed that the percentages of organic S reduced with Sn and H 3 PO 4 in 1 and 10 h of distillation varied with depth of sampling and that these values were similar, lower, or greater than those obtained with the HI‐reducing mixture.