354 
MESSRS. J. B. LAWES AND J. H. GILBERT ON THE RESULTS OF 
from the nitrogen in those crops the amount obtained during the same period in the 
produce without manure, the so reckoned increased amount taken off, due to the action 
of the ammonia-salts, would be little more than one-fourth of that supplied. Again, 
during the last seven years of the 20, little more than half instead of three-fourths as 
much nitrogen was removed in the total produce of plot 5 as was supplied in the 
ammonia-salts during that period ; or if as before we deduct the amount taken 
up without manure, less than 20 per cent, of that supplied would appear to have been 
recovered. 
We have then, according to the mode of reckoning, from one-fourth to three-fourths 
of the supplied nitrogen unrecovered in the crops during the 13 years ; and, as already 
intimated, there was almost identically the same amount of nitrogen taken up during the 
next seven years from plot 6, where the application of the ammonia-salts was stopped 
and mineral manures were applied instead, as on plot 5, where the application of the 
ammonia-salts was continued. Still, the total amount of nitrogen taken off in the 
produce of plot 6, over 20 years, was scarcely as much as had been supplied during 
the first 13 years, and if the yield without manure be deducted, more than 
GO per cent, of that supplied during the 13 years remained unrecovered as increase 
in the 20 years. 
Determinations of nitrogen, made by the soda-lime method, in the soils and subsoils 
of the unmanured plot 3, and of the continuously ammonia-manured plot 5, after the 
20 years, did indicate some accumulation of nitrogen, so determinable, in the soil and 
subsoils of the ammonia-plot, down to the depths examined, namely, 54 inches, but far 
from sufficient to account for the otherwise unrecovered amount of supplied nitrogen ; 
and, judging from somewhat parallel cases, it would be concluded that at any rate 
some would be retained by the soil and subsoil in an only slowly available condition, 
but that a considerable proportion of the supplied ammonia would be oxidated, and 
pass away in the drainage, as nitrites and nitrates, beyond the reach of the roots. 
It would thus appear probable that after the 13 years’ application of ammonia-salts 
to plot G, some at any rate of the supplied nitrogen remained within the soil, and that 
some of this was available to the growing plants during the succeeding seven years. 
But that as much was taken up as where the ammonia-salts were still annually 
applied would seem to require some further explanation. 
In reference to this point we have the significant fact, as will be fully illustrated 
further on, that the surface soil of plot G showed at the end of the 20 years—that is, 
after the mineral manures had been applied for seven years—a notably lower per¬ 
centage of nitrogen than the corresponding layer of plot 5 ; thus pointing to a source 
of nitrogen to the plants similar to that which is supposed to have contributed to the 
high nitrogenous yield of plot 7, where the mineral manures alone, including potass, 
had been applied throughout the 20 years. It remains to consider whether, not only 
the conditions of manuring, but the characters of the vegetation, were also consistent 
with, in great measure, a similar source of nitrogen in the two cases. 
