QUESTION OF THE SOURCES OP THE NITROGEN OF VEGETATION. 
25 
previously obtained with the prairie subsoils containing much higher proportion of 
carbon, in showing that their nitrogen is susceptible to nitrification, provided the 
organisms, and other essential conditions, are not wanting. These new results also 
consistently show that there is more active nitrification in the leguminous than in the 
gramineous crop subsoils. This it must be supposed, is partly due to more active 
development, and greater distribution, of the organisms themselves, under the influence 
of the leguminous growth, with its excretions and residue, and partly to the greater 
actual amount of such easily changeable matters. 
The results are also confirmed by those of experiments made in the Rothamsted 
Laboratory by Mr. Wathngton, for the most part on quite distinct lines. Thus, in 
most cases, instead of determining the amount of nitrification taking place in the 
different subsoils when exposed under suitable conditions, he introduced a portion of 
the subsoil into a sterilised nitrogenous liquid, and determined whether nitrification 
took place; the result being taken to show whether or not the organisms were present 
in the subsoil. In the first experiments, the samples were taken with precautions to 
avoid any contamination by roots or other organic matter, and the conditions of the 
sterilised liquids were such as the experience of the time indicated as favourable for 
nitrification. Upon these results he says (‘Chem. Soc. Trans.,’ 1884, p. 645): “I am 
disposed to conclude that in our clay soils the nitrifying organism is not uniformly 
distributed much below 9 inches from the surface. On much slighter grounds, it may 
perhaps, be assumed, that the organism is sparsely distributed down to 18 inches, or 
possibly somewhat further. At depths from 2 feet to 8 feet, there is no trustworthy 
evidence to show that the clay contains the nitrifying organism. It is however 
probable that the organism may occur in the natural channels which penetrate the 
subsoil at a greater depth than in the solid clay.” 
Subsequently (‘Chem. Soc. Trans.,’ 1887, p. 118) he experimented wuth a greater 
variety of subsoils, taking samples from the wheat-fallow, the Trifolium repens, the 
Melilotus leucantha, and the Medicago saliva subsoils, when these were exposed for the 
collection of the samples for the various experiments, our own results relating to which 
we have given in some -detail. Further, some of the samples were now taken in ihe 
immediate neighbourhood of lucerne roots, and gypsum was added to the sterilised 
liquids. 
Among the 69 trials made in this new series of experiments, there was no failure 
to produce nitrification by samples down to 2 feet; there was only one failure out of 
11 trials down to 3 feet; but below 3 feet, the failures were more numerous. Taken 
at 6 feet about half the samples induced nitrification. The order of priority of 
nitrification diminished from the upper to the lower depths ; indicating more sparse 
occurrence, and more feeble power of development and action. 
Examination of the results shows, liowever, that quite consistently with those which 
we have described, there was notably more active nitrification with the leguminous 
than with the gramineous crop subsoils. Thus, compared with the results yielded by 
MDCCCLXXXIX.—B. 
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