Report of Experiments on the Growth of Wheat. 459 
by virtue of tlie large accumulation within the soil from, the 
previous manuring. The results adduced show that there is no 
foundation in fact for this assumption. 
It is demonstrated that, of the nitrogen supplied in manure for 
wheat, and not removed in the immediate increase of crop, so 
much as remains in the soil is in such a state of combination, or 
distribution, as to be extremely slowly recoverable by succeeding 
crops of the same description. How far such residue would be 
more rapidly available to a succession of crops of different 
descriptions, taking different ranges within the soil, and having 
different habits, and requiring different conditions, of growth 
in other respects, is a very important question, both in a scientific 
and practical point of view. It would be impossible to consider 
adequately in this place the evidence in our possession bearing 
upon this point; but it may be remarked, in passing, that it is 
in favour of the supposition that other plants grown in alterna- 
tion with the cereals do gather up, within a given time, more of 
the nitrogen supplied for, but unused by, the latter, than a suc- 
cession of them would do ; and even barley seems capable of 
utilizing, within a given time, a much larger proportion of the 
nitrogen of manure not recovered in the immediate increase of 
the crop than wheat. 
Although the excess of the nitrogen supplied in the manure 
beyond that taken off in the increase of the crop for which it 
was applied had such little influence upon the next succeeding 
crop, analysis of the soils from several of the experimental plots 
has shown that there is an accumulation of nitrogen in some 
form. Nor can there be any doubt that, except in special cases, 
soils become richer rather than poorer in nitrogen in the course 
of cultivation ; showing a gradual accumulation of nitrogen beyond 
that annually available for the crops. In illustration, it is suffi- 
cient to refer to the fact, that the percentage of nitrogen in 
surface-soils is found to be much higher than in the subsoils on 
which they rest ; that is to say, it is the higher the more they 
are exposed to the contact of the roots, the debris of the crops, 
the manure, and the atmosphere. 
Leaving out of consideration the question whether or not there 
is an actual loss of a portion of the nitrogen supplied in the 
manure, either through the agency of the growing plant, or from 
the transformation of nitrogenous compounds within the soil, and 
evaporation in some form, or drainage beyond the reach of the 
roots, the obvious practical conclusion from the results hitherto 
adduced in this Section is, that, of the nitrogen supplied in 
manure for the growth of wheat, a large proportion remains 
unrecovered as increased yield in the immediate crop, and 
