The Nitrogen of the Soil. 41 



Rothamsted, from soil, seed, rain, &c., only about two-thirds 

 are removed in the crop, whilst one-third goes into the drains 

 and is lost. The experiments under discussion provide an 

 explanation of the fact that on some soils more especially 

 the newly cultivated soils of the United States and of Canada 

 a large increase in the wheat crop frequently follows the 

 application of mineral manures. Soils rich in organic matter 

 may yield an increased amount of nitric acid by the applica- 

 tion of phosphates and potash, but in all cases the source of 

 the nitrogen is the soil ; and the loss by the unmanured soil 

 of perhaps from SOOlb. to lOOOlb. of nitrogen per acre during 

 the forty years of these experiments is a fact of the greatest 

 importance. 



CONTINUOUS GROWTH OF WHEAT UPON THE 

 SAME LAND WITH AMMONIA-SALTS ALONE. 



Leaving the mineral-manured plot, the next subject to study 

 is the produce of plots 10a and 106 (ammonia-salts without 

 minerals), and plots 17 and 18 (ammonia-salts in alternation 

 with minerals). Recent legislative enactments, giving the 

 cultivator of the soil a claim for the manure ingredients 

 possessing a pecuniary value, which he has applied and left 

 in the land, add greatly to the interest of this and allied 

 investigations. The difference between the plots lOa and 106 

 is that lOo. received one dressing of minerals followed by 

 thirty-nine dressings of salts of ammonia, whereas 106 

 received three dressings of minerals in the course of the 

 first seven years, since when both plots have been treated 

 exactly alike. Table VI. indicates (1) the produce of each 

 plot in each of the first eight years ; (2) the average produce 

 over succeeding periods of eight years each ; (3) the average 

 produce over thirty-two years. To be precise, it should be 

 stated that 106 received minerals alone in 1844 and 1850, 

 was unmanured in 1846, received minerals with ammonia- 



