SECTION II 

 REVIEW OF LITERATURE 



1. SOURCES OF SULFUR 

 1.1 SOIL SOURCES 



All of a growing plant's S requirement can be supplied from the 

 soil. Ensniinger and Jordan (1958) reported that the amounts of S ab- 

 sorbed by crops at moderate yield levels ranged from about 9 to 

 39 kg/ha. Terman (1978) compiled values which averaged 26 kg/ha for 

 grain crops, 35 kg/ha for hay crops, cotton, and tobacco, and 48 kg/ha 

 for fruit, sugar and vegetable crops. This S is absorbed as sulfate 

 from the soil solution primarily due to mass flow of ions (Barber and 

 Olsen, 1968). The sources of this available soil sulfate may be pri- 

 mary and secondary S-containing minerals, soil organic matter, adsorbed 

 sulfate, atmospheric S, and fertilizers containing S. 

 1.1.1 Sulfur-Containing Minerals 



The original source of most soil S was probably the sulfides of 

 metals contained in plutonic rocks. As life evolved and these minerals 

 were decomposed, sulfate was taken up by living organisms and incorpor- 

 ated into organic matter. Under anaerobic conditions, S was reduced to 

 inorganic sulfides or elemental S. Sulfate was also precipitated as 

 soluble or insoluble salts of Ca, Mg , Ba, Sr, K, Fe, Cu, Zn, etc. in 

 arid climates; in humid climates, much of this sulfate was washed into 

 the sea (Tisdale and Nelson, 1975) . 



