105 

 non-crystalline Al and Fe compounds present. Citrate-dithionite solu- 

 ble Al and Fe were not significantly correlated with soil S in the sub- 

 surface horizons. This is surprising after finding such highly 

 significant correlations with these soil properties in the surface 

 horizon. The high levels of both total and extractable S probably 

 resulted in lass than complete extraction of S either by the CaG^PO,^- 

 2H solution or by the acid after digestion. The heat digestion and 

 acid extraction of total S no doubt altered the anion exchange proper- 

 ties of the soils and could have resulted in incomplete acid extraction 

 of total S. 



Organic matter in these lower soil horizons could not possibly 

 account for the high total S levels. The thesis of Adams and Rawajfih 

 (1977) concerning the formation of sparingly soluble aluminum sulfate 

 minerals such as alunite or basaluminite in Ultisols would be a con- 

 venient proposition to explain these results. Although potential soil 



2— 3+ + 

 solution concentrations of S0 4 , Al , and K are unknown in these 



soils, data from Adams and Hajek (1978) suggested that basaluminite 



could form where S0,/A1 in the soil solution was greater than 0.25 and 



4 



0H/A1 was less than 3.0. Alunite became the dominant precipitate 

 formed when a K/Al ratio of 0.1 existed in dilute solutions of K, Al, 



and SO,. If these minerals do exist in the argillic horizons of 



4 



Ultisols, the solubilities in extractants such as the 0.01 M 



Ca(H TO ) «2H„0 used in this studv are unknown. More data under con- 

 '2422 



trolled conditions would be needed in order to establish a precise 

 relationship between measurable soil properties and total and extract- 

 able S in argillic horizons. 



