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



133 



13. The Amounts of Nitrogen and Organic Carbon in some Clays 

 and Marls. By Dr. N. H. J. Miller, F.C.S. (Communicated 

 by Sir John Evans, K.C.B., D.C.L., P.R.S., For.Sec.G.S. Head 

 February 25th, 1903.) 



Before discussing the results obtained from the different deposits 

 which form the subject of this note, it will be useful to consider 

 some of the changes which we know the organic matter of soils 

 is liable to undergo. The nature of these changes will depend 

 mainly on the conditions of aeration, on the climate, and on the 

 character of the mineral substances with which the vegetable matter 

 is associated ; and the chemical properties of the predominating 

 constituents of the decaying plants, which may be proteids, carbo- 

 hydrates, or resins, etc., may, according to circumstances, have 

 an important influence on the character of the products. 



Without going into the complicated questions involved in the 

 breaking-down of the different plant-constituents, or the question 

 of the production of complex organic substances from element ary 

 nitrogen, it may be stated that the general, but not invariable, 

 tendency of decaying vegetable matter is to become more nitrogenous, 

 owing to the relatively greater ease with which, under most con- 

 ditions, gaseous compounds of carbon are liberated as compared 

 with nitrogen. An example of a change of this kind is afforded by 

 some analyses made in 1865, 1881, and 1893, of the soil of the 

 continuously unmanured plot of the Rothamsted wheat-field. The 

 results (see Table I, below) show a decrease in the amount both 

 of total nitrogen and of organic carbon, the loss of carbon being- 

 relatively greater than that of nitrogen. 



Table I. — Carbon and Nitrogen in the Eotiiamsted Wheat-Soil. 

 (Broadbalk Field. First 9 inches. Plot 3.) 





Organic 

 Carbon. 



Total 

 Nitrogen. 



Carbon to 1 

 of Nitrogen. 



Nitrogen to 

 100 of 'Carbon. 



I860 



Per cent. 

 (1-100) 

 0-977 



0-888 



Per cent. 

 0-1090 

 0-1009 

 0-0940 



10-1 

 9-7 

 9-4 



9-9 

 10-3 

 10-6 



1881 



1893 





In this old, arable soil, which has had no manure at all since 

 1843, the loss of nitrogen is now hardly appreciable, while the loss 

 of carbon, although slight, is much more marked. Where there has 

 been a recent application of organic manure, the losses will naturally 



