LAW OF DIMINISHING RETURNS 



47 



most profitable, the extra 80s. for manure has produced an 

 increased return of 36s. in the crop. At the higher scale 

 of prices the crop remains profitable throughout, though the 

 third addition of manure only returns 14s. for an expenditure 



Yield. 

 Bushels or Cwt. 



Returns & Cost. 

 Shillings. 



4OO 



Mineral Manures +200 Ib. +400 Ib. ~- +600 Ib. +800 I b. Am m. Salts. 



FIG. 5. Relation between Cost of Production and Returns with varying 

 quantities of Manure. 



of 30s., and the fourth application only produces an increase of 

 crop worth 8s. 



C. Effect of the Mineral Constituents. 



The series of Plots 7, 10, 11, 12, 13, and 14 all receive 

 the same amount of nitrogen 86 Ib., in form of 400 Ib. 

 of amrnonium-salts per acre but differ in regard to their 

 mineral manuring. Plot 10 receives nothing beyond the 



