The Amounts of Nitrogen and Organic Carbon in some Clays and Marls

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Abstract
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 aëration, 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, carbohydrates, 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 elementary 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 conditions, 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. An example of a change of this kind is afforded by some analyses made in 1865, 1881

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