QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
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of plants of a higher order. Several of the more important of the investigations in 
the lines here indicated seem to have been instigated by the assumption that com¬ 
pensation must be found for the losses of combined nitrogen which the soil sustains 
by the removal of crops, and also for the losses which result from the liberation of 
nitrogen from its combinations under various circumstances. 
At the meeting of the American Association for the Advancement of Science, held 
at Montreal in 1882, we gave a paper entitled —‘^Determinations of Nitrogen in the 
soils of some of'the Experimental Fields at Rothamsted, and the hearing of the results 
on the question of the Sources of the Nitrogen of our crops and again, at the 
Meeting of the British Association, held at Montreal, in 1884, we gave further results 
on the subject, in a paper—“ On some points in the Composition of Soils; luith I'csults 
illustrating the Sou7'ces of the FeiRlity of Manitoba Prawie Soils.” * 
It is the object of the present paper to summarise some of our own more recently 
published results bearing on various aspects of the subject, to put on record additional 
results, to give a preliminary notice of new lines of enquiry, and to discuss the 
evidence so adduced with reference to the results and conclusions of others which have 
recently been put forward, as above alluded to. 
PART I. 
Results relating to other Sources than Free Nitrogen. 
1. Summary of previously published Rothamsted Results chiefly relating to nitric acid 
in soils and subsoils. 
Before directing attention to the new results it will be desirable, with the view of 
bringing out their significance the more clearly, to give a brief resume of our previous 
results and conclusions bearing on the subject. 
In the last mentioned paper, after reviewing previously existing evidence as to the 
sources of the nitrogen of crops, we concluded, as we had done before, that, excepting 
the small amount of combined nitrogen annually coming down in rain, and the minor 
aqueous deposits 'from the atmosphere, the source of the nitrogen of vegetation was, 
substantially, the stores within the soil and subsoil, whether derived from previous 
accumulations or from recent supplies by manure. 
Results of determinations of the nitrogen as nitric acid, in soils of known history 
as to manuring and cropping, and to a considerable depth, in some cases to 108 inches, 
were given, which showed that the amount of nitrogen in the soil in that form was 
much less after the growth of a crop than under corresponding conditions without a 
crop. In the case of gramineous crops, the evidence pointed to the conclusion that 
most, if not the whole, of their nitrogen was taken up as nitric acid from the soil and 
* Afterwai’cls revised and published in the ‘ Transactions of the Chemical Society ’ for June, 1885. 
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