74 

 shaken for 30 minutes on a reciprocating, mechanical shaker. All ex- 

 tracts were filtered through Whatman no. 42 filter paper. A 5 or 10-ml 

 aliquot was used for the turbidimetric determination of sulfate S. 

 Values reported for the study of S distribution in selected Florida 

 soils were obtained by the indirect method of Hue and Adams (19 79) and 

 a 10-ml aliquot was used. All other extractable sulfate-S values were 

 determined turbidimetrically (Massoumi and Cornfield, 1963; Chaudry and 

 Cornfield, 1966) . 



Some difficulties were encountered with the turbidimetric deter- 

 mination of sulfate S in soil extracts. These difficulties, along with 

 the justification for using the Ca(H„P0, ) „• 2H extractant, and a pre- 

 liminary study of extractants are discussed in section 5.2.3. 



5.2.3 A Comparison of Two Extraction 

 Procedures for Soil Sulfur 



A suitable technique for extracting and determining sulfate S in 

 soils should be convenient to use with the laboratory facilities avail- 

 able; the procedure should be rapid and reproducible. The extractant 

 should remove a minimum of soil organic matter which could interfere 

 with sulfate determination. Extractable S must also be correlated with 

 plant uptake and/or yield. A study of the available extractants indi- 

 cated that a Ca(H P0,) -2H 9 solution (Fox et al. , 1964: Beaton et al. , 

 1968) or an NH OAc + HOAc solution (Bardsley and Lancaster, 1960, 1965) 

 would be most suitable for this investigation. However, preliminary 

 studies showed that both of these solutions alone would extract some 

 color from a few Florida soils. This color was difficult to remove 

 with the HN0-/HC10, digestion described by Beaton et al. (1968). 



