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and 0% with it. These differences were even larger for the third and 

 fourth harvests. 



Where the horizon sequence included the argillic horizon, yields 

 were not improved by S fertilization in any of the four harvests from 

 the Norfolk soil. Total S uptake by plants in pots without added S but 

 with the argillic horizon was almost 15 mg/pot more than by plants 

 growing in pots where washed sand replaced the argillic horizon. This 

 difference was equivalent to 2.6 ppm of available S in the subsoil dur- 

 ing the 16-week study — much less than the 15 ppm of extractable sulfate 

 S found before the experiment (Table 20) . These data indicated that 

 the surface horizon of the Norfolk soil contained adequate S for a 

 short-term crop but not enough to maintain optimum growth over a long 

 season. 



One factor not included in this study which would be of signifi- 

 cant consideration under field conditions is the depth to the argillic 

 horizon. The argillic horizon was placed only 24 cm below the surface 

 in the greenhouse pots. Data from the survey of S in Florida soils 

 showed that the mean depth of the Bl horizon in ten Florida Ultisols 

 was 69 cm (Fig. 9). The typifying pedons for the Norfolk and Orange- 

 burg series have the Bl horizons at 36 and 18 cm, respectively. The 

 depth to the 31 in five Orangeburg soils from Florida ranged from 20 

 to 56 cm with a mean depth of 35 cm (Calhoun et al. , 1974). With such 

 variation in depths to adsorbed S in the argillic horizons, predicting 

 the S fertility status of plants growing on certain Ultisols may be 

 difficult. Young seedlings and shallow-rooted plants may require S 

 fertilization whereas long-season and deep-rooted annuals and peren- 

 nials may obtain adequate S from the subsoil supplies. Anderson and 



