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This article in SSSAJ

  1. Vol. 24 No. 4, p. 265-268
     
    Received: Nov 21, 1959
    Published: July, 1960


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doi:10.2136/sssaj1960.03615995002400040015x

Determination of Reserve Sulfur and Soluble Sulfates in Soils1

  1. C. E. Bardsley and
  2. J. D. Lancaster2

Abstract

Abstract

Organic and reduced inorganic sulfur (reserve sulfur) are converted to sulfates by ignition of a soil-sodium bicarbonate mixture at 500° C. Converted and soluble sulfates (soil sulfur) are then extracted with a solution that is 2N to HAc and 0.1N to NaH2PO4·H2O and determined turbidimetrically as BaSO4 after acidifying a portion of the filtrate with 1:1 HCl. Acceptable recovery of sulfur has been obtained from elemental sulfur, plant material, methionine, cystine, and cysteine.

Soluble sulfates are extracted from a separate sample with 0.5N NH4OAc + 0.25N HAc. Activated charcoal is added to decolorize the extract. A portion of the filtrate is acidified with 1:1 HCl containing a “seed” solution of sulfate, and sulfur is determined turbidimetrically as BaSO4. Reserve sulfur is the difference between soil sulfur and soluble sulfates.

The multiple correlation of reserve and sulfate-sulfur with total nitrogen in soils was highly significant (R = 0.971). Reserve sulfur was highly correlated with yield of sulfur from three harvests of white clover grown in the greenhouse (R = 0.790). The relation of reserve sulfur and sulfates to the sulfur status of soils is discussed.

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