103 

 Only one soil, a Red Bay from Santa Rosa County, had more than 7 ppm 

 extractable sulfate S in the surface horizon. This soil contained more 

 than twice as much extractable S as any other Ultisol studied. In 

 general, the mean values for the Al and A2 horizons were similar to S 

 levels in the Spodosol Al and A2 horizons (Figs. 7 and 9). A remark- 

 able increase in both total and extractable 3 occurred in all argillic 

 (B2) horizons. Sulfate S accounted for only 8% of the total S in the 

 surface horizon of the Ultisols and less than 7% of the total S in the 

 entire profile of the Spodosols. However, more than 40% of the total 

 S in the argillic horizons of the Ultisols was extracted as sulfate S. 



Total S was also significantly correlated with organic C and 

 total N in the surface horizon (r = 0.85 and 0.90, respectively) 

 (Table 17). Extractable S was significantly correlated with citrate- 

 dithionite soluble Al (r = 0.89) and Fe (r = 0.88), gibbsite in the 

 clay fraction (r = 0.89), the percent clay in the horizon (r = 0.75), 

 as well as organic C (r = 0.50). 



No single soil property was highly correlated with either total or 

 extractable S in the subsurface horizons of Ultisols (Table 17). The 

 highest correlation with total and extractable S was with crystalline 

 gibbsite [A1(0H) ] (r = 0.67 and 0.79, respectively). Only three 

 series, Dothan, Blanton, and Red Bay from Santa Rosa County had gibb- 

 site in the argillic horizons. With a higher clay content in these 

 horizons and crystalline gibbsite in equilibrium with amorphous Al 

 hydroxides and oxyhydroxides , larger sulfate adsorption was not sur- 

 prising. 



Extensive mineralogical studies would have to be made of individ- 

 ual soils in order to relate sulfate adsorption to the crystalline and 



