47 

 amounts and relative proportions of proteins formed (Thompson et al., 



1970) 



The N:S ratio is relatively constant in plant protein. Dijkshoorn 

 et al. (1960) found an atomic ratio of S to N in the protein [(N:S)p] 

 of perennial ryegrass foliage ( Lolium perenne L.) of 0.027. This is 

 equivalent to a (N:S)p of 16.2:1 on a percentage basis. Dijkshoorn and 

 Van Wijk (1967) reviewed the literature on the N and S relationships in 

 plants and found that the organic N: organic S ratio [(N:S)o] in plants 

 ranged from 13.7 for grasses to 17.5 for legumes. These values were 

 similar to those for the (N:S)p ratio, since proteins constitute about 

 80% of the organic N and S present. Jones et al. (1971) found that 

 the (N:S)p in the dried tops of the legume, Stylosanthes humilis L. , 

 decreased as the S supply increased, but most researchers found this 

 ratio in legumes to be fairly constant and within the ranges defined 

 by Dijkshoorn and Van Wijk (Stewart and Whitfield, 1965; Stewart, 1969; 

 Stewart and Porter, 1969). The (N:S)o in plants of the Brassica tribe 

 is lower because of the presence of other forms of organic S. 



With adequate S fertilization, grasses tend to accumulate sulfate 

 in luxury amounts resulting in a very narrow total N: total S ratio 

 [(N:S)t]. If S is limiting, non-protein forms of N tend to accumulate, 

 and the (N:S)t ratio exceeds the (N:S)p ratio of about 14 normally 

 found in gramineous plants. Consequently, the (N:S)t ratio would 

 appear to be an effective index of the S status of many grasses 

 (Metson, 1973). Roberts and Koehler (1965) found a (N:S)t ratio of 25 

 in wheat that had not been fertilized with S and ratios of 11 to 15 

 where S was applied. Woodhouse (1969) regarded high (N:S)t ratios in 

 bermudagrass ( Cynodon dactylon L.) as one of the factors resulting in 



