for Twentij Years in succession on the same Land. 331 
Lastly, with farmyard manure, whether applied to wheat or to 
barley, very much less of the supplied nitrogen was recovered 
than with any of the artificial manures. Indeed, assuming the 
dung to have provided about 200 lbs. of nitrogen per acre per 
annum, there was recovered in the increased produce of the 
wheat only about one-seventh, and in that of the barley scarcely 
one-nintli, of the nitrogen supplied by the manure. 
The general result of this new and more extended inquiry is, 
then — that with neither crop is the whole of the supplied nitrogen 
recovered in the increase of produce obtained ; that when a given 
amount of ammonia-salts was applied a much less proportion was 
recovered in wheat than in either barley or oats ; but that, even 
with wheat, more was recovered when nitrate of soda was em- 
ployed than when ammonia-salts were used. 
How is the a})parent loss to be explained ? and how is it that a 
greater loss is observed with wheat than with either barley or oats ? 
In the paper in the ' Philosophical Transactions ' i^Part II. 
1861),* already referred to, after showing the relation of the 
nitrogen in increase to that in manure in some particular cases, 
we submitted the following questions : — 
" Is the unrecovered amount of supplied Nitrogen or at any 
rate a considerable proportion of it, drained away and lost? 
" Are the nitrogenous compounds transformed within the soil, 
and their Nitrogen, in some form, evaporated ? 
" Does the missing amount for the most part remain in some 
fixed combination in the soil, onlv to be yielded up, if ever, in 
the course of a long series of years ? 
" Is ammonia itself, or Nitrogen in the free state, or in some 
other form of combination than ammonia, given off from the 
surface of the growing plant? Or, lastly, 
" When Nitrogen is supplied within the soil for the increased 
growth of the Graminaceous crop, is there simply an unfavour- 
able distribution of it, considered in relation to the distribution 
of the underground feeders of the crop ? — the Leguminous crop, 
which alternates with it, gathering from a more extended range 
of soil, and leaving a residue of assimilable Nitrogen within the 
range of collection of a next succeeding Cereal one ?" 
Briefly enumerated, the three main sources of loss of nitrogen 
here suggested are, then — drainage ; accurmilation ivithin the soil 
in a state of combination, or distribution, unfavourable for being 
taken up by the immediately succeeding crop ; or evolution in some 
form from the surface of the groioing plant. 
From some of the results reported in the same paper, and also 
* " On the Sources of the Nitrogen of Vegetation ; with special reference to the 
question whether plants assimilate free or uncombined Nitrogen." By Lawes, 
Gilbert, and Pugh. 
