

DETERMINATIONS OF NITROGEN IN THE SOILS OP 

 SOME OP THE EXPERIMENTAL PIELDS AT ROTHAM- 

 STBD, AND THE BEARING OP THE RESULTS ON THE 

 QUESTION OP THE SOURCES OP THE NITROGEN OP 

 OUR CROPS. 



By Sir John Bennet Lawes, Bart., LL.D., P.R.S., P.C.S., and Joseph 

 Henry Gilbert, Ph.D., P.R.S., P.C.S., P.L.S. 



Introduction. 



It is just about a century since the question of the sources of the 

 nitrogen of vegetation became a subject of experimental inquiry, and 

 also of conflicting opinion. It is nearly half a century since Bous- 

 singault was led by a study of the chemistry of agricultural produc- 

 tion to see the importance of determining the sources of the nitrogen 

 periodically available to vegetation over a given area of land. Some- 

 what later the Rothamsted experiments, now in their fortieth year, 

 were commenced, and in their progress many facts have been elicited 

 bearing upon the same subject. Still, almost from the date of Bous- 

 singault's first investigations, the question has been one of contro- 

 versy, and at the present time very conflicting views are entertained 

 respecting it. 



Por ourselves, we have pointed out how entirely inadequate is the 

 amount of combined nitrogen coming down in the measureable 

 aqueous deposits from the atmosphere to supply the nitrogen of the 

 vegetation of a given area. Other possible supplies of combined 

 nitrogen from the atmosphere have also been considered, and pro- 

 nounced inadequate. Again, the question whether or not plants 

 assimilate the free or uncombined nitrogen of the atmosphere has 

 been the subject of laborious experimental inquiry, and also of critical 

 discussion, at Rothamsted. Finally, the question whether the stores 

 of the soil itself are an important source of the nitrogen of our crops 

 has frequently been considered. 



It may at the outset be frankly admitted that so long as the facts 

 of production alone are studied, without knowledge of, or reference 

 to, the changes in the stock of the nitrogen in the soil, it would seem 

 essential to assume that a large proportion of the nitrogen of crops 



