16 



The Rothamsted Experiments. 



the cost of the manures applied shows that the mixed 

 mineral manures of Plot 2 were far too expensive in pro- 

 portion to the amount of increase they yielded for it to 

 be at all worth while to reckon the cost against the increase 

 in their case. Ammonia-salts are generally neither so 

 cheap a source of nitrogen, nor are they, when used alone, 

 so good a manure for corn crops, as Peruvian guano, which 

 contains a large proportion of phosphates as well as 

 nitrogen. Rape cake, though a recognised manure in the 

 market for wheat, acts somewhat more slowly for the 

 amount of nitrogen it contains than does guano. It will 

 be well, for the sake of comparison, to show the cost of 

 the manures at the period of the experiments, and the 

 value of the increase due to the three manures rape 

 cake, ammonia-salts, and Peruvian guano : 



Eeckoning the value of the increase against the cost of the 

 manures, there is a considerable margin in favour both of the 

 ammonia-salts and the guano, particularly the latter. The 

 evidence further indicates that these active nitrogenous 

 manures are by no means fully exhausted in the first year of 

 their application. The quantity of guano employed nearly 

 5cwt. to the acre was, however, more than it is desirable to 

 apply in ordinary practice. And it should not be inferred 

 that the practice of growing a series of corn crops by means 



