78 

 In 1968, Beaton et al. listed more than 36 different methods for 

 determining total 5 in soils. Most of these methods involved acid 

 digestion or alkaline fusion of the soil to oxidize all reduced forms 

 of organic and inorganic 3 to sulfate, extraction of the residue, and 

 sulfate determination by BaSO, precipitation (gravimetric, turbidi- 

 metric, or titrimetric methods). Of the various acid treatments, 

 HC10. and a mixture of HNCL+HCIO. have been the most popular and con- 

 venient to use. These digestion procedures are not as tedious as 

 sodium carbonate-sodium peroxide fusion techniques, but they may not 

 decompose all the soil minerals in some soils. Since most of the 

 soil S in the surface horizons of Florida soils is considered to be 

 associated with soil organic matter, any technique that effectively 

 digests organic matter and removes sulfate-S should be suitable for 

 the estimation of total S in soils. The use of HC10, can be dangerous 

 without proper ventilation. The required ventilation was not avail- 

 able in the Analytical Research Laboratory where most of these analy- 

 ses were conducted; therefore, the Mg(NO_) /HNO„ digestion/oxidation 

 procedure was adopted. 



Soils which were only air dried and screened before digesting may 

 not completely react with the digesting solution. Incomplete recovery 

 of total S may result. Nine soil samples were finely ground with an 

 agate mortar and pestle and digested according to the above procedure. 

 Sulfate-S was determined turbidimetrically and compared to the results 

 of soil samples that had been screened through a 2-mm sieve. These 

 data are presented in Table 10. Grinding these samples did not seem 

 to affect the amount of S extracted after digestion. Therefore, subse- 

 quent soil samples were only air dried and screened. 



