39 

 total amounts of plant nutrients (N, P-0 , and K 0) applied per ha have 

 only increased from 720 to 775 kg/ha (7.6% increase) (Statistical 

 Reporting Service, 1965-1979; Hargett, 1976). These data are surpris- 

 ing when considering the increased yields and intensive management of 

 modern crop production, but point out the trend toward less fertilizer 

 S applied to Florida farmlands. 



Most fertilizer-applied S is in the soluble, sulfate form in 

 ordinary superphosphate, gypsum, potassium sulfate, sulfate of potash- 

 magnesia, etc. All of these soluble sulfates as well as thiosulfates 

 and polysulfides are about equally effective and immediately available 

 to growing plants (Beaton et al. , 1974). Finely-ground, elemental S 

 is rapidly oxidized in most arable soils (Burns, 1967). Rhue and 

 Kamprath (1973) showed that finely-ground elemental S was completely 

 oxidized during the winter months in a North Carolina soil. Prilled S 

 (325-mesh) offered some resistance to oxidation and remained in the 

 surface soil longer. Beaton et al. (1974) recommended that 25% of the 

 total S should be in a soluble sulfate form if the soil is extremely 

 low in S and if the elemental form cannot be applied 4 to 6 weeks 

 prior to planting a crop. 



2. PLANT SULFUR NUTRITION 

 2.1 THE ROLE OF SULFUR IN PLANT NUTRITION 



Sulfur is considered a secondary nutrient along with Ca and Mg, 

 but it is needed by many plants in about the same quantity as P 

 (Tisdale, 1977). The Technical Affairs Committee of the Canadian 

 Fertilizer Institute recommended in 1978 that S should be ". . . 

 classified in governmental regulations and by the fertilizer industry 



