Table 7. (Continued) 



Extractant 



Correlations of measured S 

 with plant response 



Estimated 

 critical level 

 for most crops 



Soluble + Adsorbed Sulfates + Portions of Organic S 



0.39** with yield & 0.58** with 

 S uptake (Hoeft et al., 1973) 



Ca(H 2 P0 4 ) 2 -H 2 



in 2N HOAc 

 NaHC0„ 



6-10 ppm S 



0.59** with yield (Bardsley & 

 Kilmer, 1963) 



Suggested by Kilmer & Nearpass 

 (1960) & recommended by 

 Ensminger & Freney (1966) & 

 Bardsley & Lancaster (1965) 

 in 2N 0.22 with yield and 0.42** with 

 S uptake (Hoeft et al., 1973) 



Soluble + Labile Organic S 



water (hot) 0.91 with S uptake & 0.93 with 



yield (Spencer & Freney, 1960) 



0.84** with S uptake (Fox et al.. 

 1964) 



0.90** with S uptake (Williams & 

 Steinbergs, 1959) 



NaH o P0. 

 2 4 



HOAc 



10 ppm S 



'A" values 



'L" values 



Biological Methods 



0.91 with S concentration & 0.96 

 with S uptake (Nearpass et 

 al. , 1961) 



Availability index increased 

 with successive harvests due 

 to net S mineralization 

 (Bettany et al. , 1974) 



15 ppm S 



*Significant at the 95% probability level. 

 *Significant at the 99% probability level. 



