Sources of Loss of Nitrogen. 201 



in the wheat field, which is manured annually with farmyard 

 manure, retains near the surface, owing to its greatly 

 increased porosity, very much more of the rainfall than the 

 soil of the plots not so manured. Accordingly the drain 

 from the farmyard- manured plot runs much less frequently 

 than do the drains from the unmanured or the artificially- 

 manured plots. There will, obviously, be less loss of water 

 by drainage. But it is found that a given volume of the 

 drainage water from the farmyard-manured plot contains 

 from two to three or more times as much nitrogen, in the 

 form, of nitrates and nitrites, as that from the unmanured 

 plot, or from the plots with mineral without artificial nitro- 

 genous manure. Here, then, is a determined source of loss 

 of the supplied nitrogen. A considerable further loss is pro- 

 bably due to decomposition of the nitrogenous organic matter 

 within the soil and evolution as free nitrogen. 



Consequently, there is cumulative evidence to show that 

 the nitrogen supplied as farmyard manure was recovered in 

 very small proportion during the years of its application ; 

 that in after years it was recovered in constantly decreasing 

 proportion ; that there, nevertheless, remained a considerable, 

 but very slowly available, residue ; that there was a con- 

 siderable loss by drainage ; and, finally, that there is probably 

 a further loss by decomposition, and evolution into the atmo- 

 sphere. 



It is well, however, to remember that in ordinary agricul- 

 ture much less farmyard manure would be applied than in 

 these special experiments, and the losses by drainage would 

 from that cause alone be proportionately less. Much, 

 obviously, would also depend on the character of the soil and 

 the subsoil. Again, in an ordinary rotation of various crops, 

 more of the supplied nitrogen would probably be gathered up 

 before it finally passed beyond the reach of vegetation, than 

 in the case of a single cereal crop grown year after year on 

 the same land. For somewhat similar reasons a better result 

 might have been looked for with the mixed herbage, as com- 



