THE SOUECES OF THE JNTTKOGEN OF VEGETATION, ETC. 441 



Nitrogen supplied in the manure ; and when the double amount of the manure was 

 employed for barley, over the same series of years, only about 43 per cent, of the sup- 

 plied Nitrogen were recovered as increased yield. 



To the statement of these facts it should be added that the Nitrogen (equal in amount 

 to, say 60 per cent, of that supplied in the manure) which is not obtained as increased 

 yield in the immediate crop does not appear to exist in the soil availably for an imme- 

 diately succeeding crop. Thus, when by the use of nitrogenous manures an increased 

 yield of Nitrogen has been obtained in the first succeeding wheat-crop, equal in amount 

 to about 40 per cent, of the Nitrogen supplied in the manure, the increased yield obtained 

 in the second crop, without any further supply, is equal to little more than one-tenth of 

 the remainder. 



In connexion with this subject it may be mentioned that, so far as our experiments with 

 meadow-grasses at present show, it does not appear that the increased yield of Nitrogen 

 in the crop on the use of nitrogenous manures bears a much higher proportion to the 

 amount supplied in their case than in that of either wheat or barley. In the case of 

 the Leguminous corn-crops, the proportion of the increased yield to the amount supplied 

 appears to be even less than in that of the Cereal grains. Root-crops, on the other hand, 

 would seem to gather up an increase of Nitrogen bearing a larger proportion to the 

 quantity directly supplied in the manure. 



On the assumption that the relation of the immediately increased yield of Nitrogen 

 to the amount supplied in manure represents really or approximately the proportion of 

 the directly supplied Nitrogen which is actually recovered iu the immediate crop, the 

 following questions seem to suggest themselves : — 



Is the unrecovered amount of supplied Nitrogen, or at any rate a considerable pro- 

 portion of it, drained away and lost 1 



Are the nitrogenous compounds transformed within the soil, and their Nitrogen, in 

 some form, evaporated] 



Does the missing amount for the most part remain in some fixed combination in the 

 soil, only to be yielded up, if ever, in the course of a long series of years 1 



Is ammonia itself, or Nitrogen in the free state, or in some other form of combination 

 than ammonia, given off from the surface of the growing plant % Or, lastly, 



When Nitrogen is supplied within the soil for the increased growth of the Grami- 

 naceous crop, is there simply an unfavourable distribution of it, considered in relation 

 to the distribution of the underground feeders of the crop 1 — the Leguminous crop, 

 which alternates with it, gathering from a more extended range of soil, and leaving a 

 residue of assimilable Nitrogen within the range of collection of a next succeeding 

 Cereal one 1 



But other and wider questions than those just enumerated present themselves on a 

 careful review, as a whole, of the Nitrogen-statistics of field-produce to which attention 

 has briefly been directed. For the moment, all may be asked in one — namely, What 



3p2 



