Vol. 59.] NITROGEN AND CARBON IN CLAYS AND MARLS. 



137 



shown by Hilgard to be favourable to the accumulation of 

 carbon. 



As already hinted, the study of ordinary soils and subsoils is 

 complicated by the presence of organic residues of two widely 

 separated periods. A few feet below the surface the organic matter 

 must, however, be mainly that which was deposited along with the 

 soil. In the following table are some average results which were 

 obtained with soil-samples from nine of the Rothamsted grass-plots 

 (which have been under grass for at least 300 years, and probably 

 much longer), and also the averages obtained with all the plots of 

 the wheat-field (excluding the surface-soil of the two dunged plots). 



Table V. — Organic Carbon and Total Nitrogen in Rothamsted Soils. 



Depths 



Cm 



hon. 



Nitrogen. 



Carbon to 

 nitrogen. 



Nitrogen to 

 100 carbon. 









1 J 





| 







of 

 9 inches. 



Park- 

 .7 



sou. 



1876. 



Wheat- 

 soil. 

 1893. 



Park- 

 soil. 

 1876. 



Wheat- \ 

 soil. 

 1893. 



Park- 

 soil. 

 1876. 



Wheat- 

 soil. 

 1893. 



Park- 

 soil. 

 1876. 



Wheat- 

 soil. 

 1893. 





Per cent. 



Per cent. 



Per cent. 



Per cent. 











1st ... 



3-292 



1076 



0-247 



0-1149 



13-3 



9-4 



7-5 



10-7 



2nd... 



0-845 



0-640 



0*081 



0-0784 



10-4 



8-2 



9-6 



12-2 



3rd... 



0-432 



0-492 



0-050 



0-0666 



8-6 



7-4 



11-6 



135 



4th... 



0-310 



0-339 



0043 



00511 



72 



6-6 



13-9 



15-1 



5th... 



0-251 



0279 



0040 



00472 



6-3 



5-9 



15-9 



169 



6th... 



0-215 



0-256 



0-036 



0-0430 



60 



5-9 



16-7 



16-8 



7th ... 





0-248 





00420 





5-9 





16-9 



8th... 



... 



0-215 





0-0396 1 





5-4 





18-4 



9th... 



... 



0-189 





0-0391 i 



... 



4-8 



... ! 



20-7 



10th ... 



! 

 1 



0-188 





0-0375 i 





5-0 



! 



19-9 



It is of interest to note, that while the surface-soil of the grass- 

 plots contains much more organic matter than that of the wheat-field, 

 the subsoil contains rather less. The composition of the organic 

 matter of the subsoil, as indicated by the relation of nitrogen to 

 carbon, is almost the same in the two fields. In view of the com- 

 paratively slight changes in the amount of total nitrogen below 

 4 feet, the diminution in the percentage of carbon is greater 

 than would be expected ; it may, to some extent, be due to recent 

 root-residues, which would diminish in quantity with the distance 

 from the surface. It seems safe to conclude that the original organic 

 matter of these soils had a high relation of nitrogen to carbon, and 

 that the conditions under which the soils were formed were favourable 

 to the elimination of carbon. 



Q. J. G. 8. No. 234. x 



