PHOSPHATIC MANURES 135 



While it is popularly supposed that basic 

 slag is not superior to superphosphate on 

 light soil under grass, it is probably not 

 maintained that there is any difference in 

 the effects of the two substances upon light 

 land under cultivation. The great majority 

 of field trials on roots have shown that there 

 is little to choose as regards effect, where 

 equal quantities of phosphoric acid are 

 supplied in the two forms of basic slag and 

 superphosphate of lime, provided the former 

 be applied a month or two before the crop is 

 sown. Certainly where equal money value 

 of these two substances has been the basis of 

 comparison, the results in the case of root 

 crops have generally been in favour of basic 

 slag. At prices hitherto current for these 

 two manures, one has been able for the same 

 expenditure to obtain about one-third more 

 phosphoric acid in the form of basic slag 

 than in superphosphate of lime. So satis- 

 factory has the former manure proved, that 

 it would not be surprising had the price risen 

 to a higher level. But old customs have 

 great tenacity, and superphosphate of lime, 

 having been used by farmers for three- 

 quarters of a century, has attained a position 

 from which the other substance has experi- 

 enced a difficulty in dislodging it. 



