52 The Rothamsted Wheat Experiments. 



artificial manures have been used. It is indeed an ascertained 

 fact that, to accumulate nitrogen in the soil, it must be in 

 combination with carbon, though very little is yet known in 

 regard to the various compounds of carbon existing in the 

 soil. But, respecting the subject now under discussion, the 

 evidence as to the underground fertility of plots 2, 3, and 7, as 

 brought out in the analyses of their soils to various depths, 

 is both interesting and instructive. It is estimated that, 

 within 27in. from the surface, the nitrogen on plot 2 (farm- 

 yard manure) will amount to more than 80001b. per acre, and 

 that it would exceed the amount on plot 7 (mixed minerals 

 and ammonia-salts) to the same depths by more than 17001b., 

 and that on plot 3 (permanently unmanured) by more than 

 22001b. By far the largest amount of this difference is found 

 in the first 9in. of depth ; to that depth the dunged land con- 

 tained nearly double the amount of nitrogen which is found 

 on the unmanured plot, and more than one and a half times 

 as much as is found on the plot receiving minerals and 

 ammonia-salts ; and it is estimated that plot 3, after the 

 removal of forty unmanured crops of wheat in succession, 

 still contains about 24001b. of nitrogen per acre in the first 

 9iu. from the surface ; this, in fact, represents the residue of 

 the natural fertility, or, to use a term imported into the 

 Agricultural Holdings Act, the inherent capability of the soil. 

 The relation between the carbon and nitrogen in these 

 three soils, which differ so greatly in their total amounts of 

 nitrogen, indicates that they do not differ much in their 

 character. On the unmanured land there is not quite ten of 

 carbon to one of nitrogen ; on plot 7, receiving minerals and 

 ammonia-salts, it is ten and a half to one ; on the dunged 

 land it is not quite twelve to one. Yet the unmanured plot 

 has received neither carbon nor nitrogen in manure ; plot 7 

 has received a very large amount of nitrogen, but no carbon ; 

 whilst the dunged plot has received a very large amount of 

 both carbon and nitrogen. The relation of carbon to nitrogen 

 in the farmyard manure is about twenty to one a proportion 



