Spodosols and the surface horizons of Ultisols. The mean C:N:S ratios 

 for the surface soils of the three soil orders were 112:7.1:1 for 

 Ultisols, 150:6.4:1 for Spodosols, and 166:5.9:1 for Entisols. 



The relative contribution of subsurface soil S to plant nutrition 

 was studied in a greenhouse experiment with a sorghum-sudangrass hybrid 

 ( Sorghum Sudanese (Piper) stapf 'Dekalb SX16A') in four soils with and 

 without the subsurface soil included in a simulated horizon sequence. 

 The surface soils were treated with or 20 ppm S as CaS0,*2H„0. 

 Plants were harvested each 4 weeks over a 16-week period and' analyzed 

 for S and N. Sulfur increased yields at all harvests in Myakka fine 

 sand (Aerie Haplaquod, sandy siliceous, hyperthermic). The presence of 

 soil from the spodic horizon did not improve the S status of the 

 plants; the presence of soil from the C horizon of Lakeland fine sand 

 (Typic Quartzipsamment, thermic, coated) increased S uptake slightly 

 over the check but not enough to prevent severe S deficiencies and 

 decreased dry matter yield where S was omitted. Applied S did not 

 increase yields in the surface soils of Orangeburg and Norfolk fine 

 sands (Typic Paleudults, fine-loamy, siliceous, thermic) until the 

 third harvest. The argillic horizon of the Norfolk provided adequate 

 S to maintain optimum dry matter production throughout the 16-week 

 experiment. The presence of the argillic horizon of the Orangeburg 

 improved the S status of the plants and increased S uptake but not 

 enough to prevent S deficiencies by the third harvest. In all soils, 

 S increased yields before deficiency symptoms appeared in the plants. 

 Critical S concentration in the 4-week old plants was 0.12%, and the 

 critical N:S ratio was 16. 



xm 



