374 INVESTIGATION BY CULTURE EXPERIMENTS 



yield for the succeeding years is greater than the average of all, 

 excluding, of course, the yields eliminated. 



The data recorded will be especially useful for working out as- 

 signed problems, and it has been brought together from several 

 different publications, and the complete records are made possible 

 only through the kindness of Director Hall of Rothamsted, who 

 has furnished the author with some unpublished data. 



The last column in Table 62 shows in greater detail about the 

 same fact as is well illustrated in the data from the twin plots, 

 17 and 18, in Table 60; namely, that commercial nitrogen must be 

 utilized by the crop for which it is applied, or it will be largely lost 

 in drainage water. 



While plot 16 received 172 pounds of nitrogen in 800 pounds of 

 ammonium salts per annum for 13 years (1852 to 1864), and pro- 

 duced 39.5 bushels of wheat per acre as an average for those years, 

 there is apparently but little residual effect except for one year 

 after the application was discontinued, the average yields of the 

 19 years without fertilizers being 14.6 bushels of wheat and 1400 

 pounds of straw per acre. 



The following statement will be of some interest in this connec- 

 tion: 



TABLE 63. WHEAT YIELDS ON BROADBALK FIELD, ROTHAMSTED 

 Thirteen Years' Average, 1852-1864 



While the second addition of nitrogen produced almost as large 

 an increase as the first, the third addition gave but little increase of 

 grain, and the fourth still less, although the yield of straw was very 

 appreciably increased, even by the fourth increment of nitrogen. 



For convenience a general summary of some of the more impor- 



