X.] WHEAT YIELD WITH INCREASED NITROGEN 2^^ 



and from a series of plots, all of which receive an 

 excess of phosphoric acid, potash, etc., but varying 

 amounts of nitrogen, ranging from 43 lb. to 172 lb. 

 per acre. That the nitrogen was deficient is shown by 

 the almost negligible increase produced by the mineral 

 constituents without nitrogen ; from this point the 

 increase of yield is roughly proportional to the supply 



Table LXXXVI I.— Experiments on Wheat (Broadbalk Field, 

 Rothamsted). Averages over 13 years (1852-1864). 



of nitrogen, until it reaches an excessive amount. The 

 table also illustrates the generalisation which is familiar 

 to economists under the name of the " law of diminish- 

 ing returns " — that the first expenditure of fertiliser or 

 other factor of improvement is the most effective, each 

 succeeding application producing smaller and smaller 

 returns, until a further addition causes no increase in 

 the yield. If the cost of the fertiliser, added to a 

 prime outlay of 80s. per acre for the cultivation, 

 and the value of the returns in cash, are expressed 

 in the form of a diagram, the law is clearly expressed 



