PRINCIPLES OF MANURING 109 



the necessary element present in least amount 

 (in this case nitrogen and phosphoric acid 

 respectively) that determines the yield. 



Similar results appear from the barley 

 experiments, which have been continued 

 since 1852. Whereas 3$ cwts. of super- 

 phosphate added only 4'8 bushels to the crop 

 when used alone, it was responsible for an 

 increase of 13'4 bushels when used as an 

 addition to ammoniacal manure. Similarly 

 with regard to 200 Ib. per acre of ammonium^ 

 salts, which, when used alone, increased 

 the crop by 11*2 bushels, whereas when added 

 to superphosphate they were accountable for 

 19-8 bushels. 



Not only does the Law of Minimum in- 

 dicate that an intelligent farmer should take 

 steps to discover which is the weakest link 

 in the chain of nutritive substances in his 

 land, but it also shows that weakness in any 

 one link cannot be compensated for by 

 strengthening other links. If, for example,, 

 the natural supplies of nitrogen in the land 

 are deficient, no improvement in the crop 

 can take place by the use of additional 

 supplies of phosphoric acid or potash. 



The Law of Minimum is usually considered 

 in relation to manures, but it is equally 

 applicable to any other essential ^condition 



