Solution sulfate chemistry in three sulfur-retentive hydrandepts
1992
Wolt, J.D. | Hue, N.V. | Fox, R.L.
Highly S-retentive Hydrandepts frequently contain large quantities (> 200 mmol kg-1) of sorbed S while exhibiting low S intensities in soil solution. Solution-solid phase S relations for three representative Hydrandepts from Hawaii were investigated in terms of the nature of sorption isotherms and the role of basic Al hydroxysulfate precipitation as a mechanism for S retention. Sorption data were fit to linear, Langmuir, and multisite Langmuir isotherms using a modeling routine that performed parameter estimates and model optimization using weighted nonlinear fitting. Best-fit models indicated sorption data were adequately described by Langmuir isotherms. Total P-extractable SO4-S increased markedly at depths > 45 cm and tended to decline at depths > 120 cm. Extractable SO4-S was strongly regressed on gravimetric moisture content, a relative indicator of reactive surface for these thixotropic soils. Soil solution SO4-S concentrations were consistent with alunite or basaluminite solubility when gibbsite controlled solution Al3+.
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