51 



Table 7. Selected methods used to determine sulfate and extract- 

 able sulfur in soils (from Reisenauer et al. , 1973). 







Estimated 





Correlations of measured S 



critical level 



Extractant 



with plant response 



for most crops 



water (cold) 



CaCl, 



LiCl 



Soluble Sulfates 



0.98** with S uptake (Barrow, 



1961) 

 0.94** with S uptake (Fox et al., 



1964) 

 0.73** with yield (Spencer & 



Freney, 1960) 

 0.99** with S uptake (Barrow, 



1961) 

 0.78** with S uptake (Williams & 



Steinbergs, 1959) 

 0.36* with S uptake & 0.28* with 



yield (Hoeft et al. , 1973) 

 0.86 with S uptake (Roberts & 



Koehler, 1968) 



0.89 with S uptake (Roberts & 

 Koehler, 1968) 



3.3-5.8 ppm S 

 (Bettany et 

 al. , 1974) 



KH 2 P0 4 



Ca(H 2 P0 4 ) 9 -H 2 



NH , OAc 



NaOAc (pH 4.8) 



Soluble + Adsorbed Sulfates 



0.93** with S uptake (Fox et al., 



1964) 

 0.83** with S uptake and 0.76** 



with yield (Spencer & Freney, 



1960) 

 0.95** with S uptake (Fox et al., 



1964) 

 0.37* with S uptake & 0.32* with 



yield (Hoeft et al. , 1973) 

 0.92 with S uptake (Barrow, 



1967) 

 0.69** with S uptake & 0.60** 



with yield (Spencer & Freney, 



1960) 

 0.55** with yield (Bardsley & 



Kilmer, 1963) 

 (Ensminger & Freney, 1966) 



6-10 ppm S 



6-7 ppm S 



