46 



EXPERIMENTS UPON WHEAT 



the plots receiving successive increments of nitrogen during 

 this period. It will be seen that the last 43 Ib. of nitrogen had 

 practically no effect upon the amount of grain produced and 

 but little upon the straw. 



TABLE XVII. Experiments on Wheat, Broadbalk Field. 

 Averages over 13 years (1852-1864). 



These results illustrate very clearly what is known as the 

 "law of diminishing returns," i.e., that each increment in the 

 cost of production, whether labour or manure, gives rise to a 

 smaller proportionate return, until a point is reached when the 

 value of the increased yield is more than balanced by the outlay 

 required to bring it about. This point, when the extra crop 

 ceases to pay for the manure or labour expended on it, is 

 sooner reached with low than with high prices for the crop. 

 Hence high farming (intensive cultivation and liberal expendi- 

 ture on manure) is only justified in times of high prices and 

 is no remedy for low ones. 



The diagram Fig. 5 shows a comparison between the 

 returns from these plots, (1) with corn at 24s. a quarter and 

 straw at 20s. a ton, and (2) when corn is 32s. and straw 

 at 30s. 



The straight line indicates the cost of production taking an 

 arbitrary base of 80s. per acre for the cultivation, and adding 

 30s. for each 200 Ib. of ammonium-salts. It will be seen that 

 with the lower prices the crop ceases to be profitable before the 

 third addition of manure is made ; the second addition is the 



