Accumulation of Fertility. 61 



soil does not appear to have gained or lost fertility. Nitrifi- 

 cation may have gone on as usual, but the loss has been 

 made good by the amount of nitrogen stored up in the 

 stubble and underground portions of the large crops so 

 grown. When dung is applied continuously, the accumula- 

 tion of unexhausted fertility becomes very large, and the 

 removal by crops of the substance accumulated would 

 extend over a long series of years ; therefore, dung applied 

 to land in the ordinary process of agriculture will not be 

 entirely exhausted until a considerable number of years from 

 the time of its application. 



