46 



EXPERIMENTS UPON WHEAT 



91 bushels more than Plot 5 with no nitrogen, another 43 lb, 

 of nitrogen on Plot 7 produce a further increase of 8 "9 bushels^ 

 whereas the next addition of 43 lb. of nitrogen only produces 

 an increase of 4*2 bushels. 



During the first 13 years of the experiment one of the plots 

 received a still further addition of nitrogen, making 172 lb. in 

 all. The Table (XVII.) shows the yield of grain and straw of 

 the plots receiving successive increments of nitrogen during 

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

 practically no effect upon the amount of grain produced and 

 but little upon the straw. 



Table XVII. — Experiments on Wheat, Broadbalh Field. 

 Averages over lo 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 croj) 

 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. 



