440 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON 
in the Rotation experiment was in the case of a clover-crop, grown once during the 
twelve years, and which constituted the Leguminous crop of the first course. After both 
this clover-crop (in which was removed such a large amount of Nitrogen) and beans which 
replaced it in the second and third courses (but which gave a very small yield of Nitrogen), 
the wheat-crop was about double as much as the average where wheat has been grown 
succeeding wheat, and it was about equal to the average per crop when wheat was 
grown after fallow, or after beans, in the experiments already referred to. 
It has been seen, then:—that even Cereal crops grown, year after year, on the same 
land, gave an average of about 244 1bs. of Nitrogen per acre, per annum; that, under 
similar circumstances, Leguminous crops gave much more; that, nevertheless, the pro- 
duce of the Cereal crop was nearly doubled when it was preceded by the more highly 
nitrogenized Leguminous crop; that the produce of the Cereal crop was also nearly 
doubled when it was preceded by fallow; and lastly, that in an actual rotation of crops, 
though entirely without manure, there was also an average annual yield of Nitrogen 
nearly twice as great as that obtained in the continuously grown Cereal. 
It has been incidentally mentioned, too, that the highly nitrogenous Leguminous crops 
are comparatively little benefited by the direct application of nitrogenous manures (am- 
monia-salts). It has also further been stated, on the other hand, that, notwithstanding 
the comparatively small amount of Nitrogen harvested in a Cereal crop, and that both 
the crop and its Nitrogen are very much increased when succeeding upon the growth 
and removal of a highly nitrogenous Leguminous crop, yet the application of nitroge- 
nous manures is also one of the surest means of increasing the produce, and the yield of. 
Nitrogen, of a Cereal crop. 
D.—Relation of the increased yield of Nitrogen in the produce, to the amount 
supplied, when nitrogenous manures are employed. 
Not only do we harvest in our crops (particularly the Leguminous ones) a large 
amount of Nitrogen, the source of which, it will afterwards be seen, is by no means fully 
explained, but, when we increase their growth (particularly that of the Cereals) by the 
direct application of nitrogenous manures, it is found that, over a series of years, a con- 
siderable proportion of the so-supplied Nitrogen is not recovered in the increase of crop. 
Thus, when a certain amount of ammonia-salts (in addition to a complex mineral 
manure) was applied, year after year, for the growth of wheat, the result, taken over a 
period of six years, was, that the increased yield of Nitrogen in the crop was only equal 
to about 43 per cent. of the Nitrogen which had been supplied in the manure. When 
double the amount of ammonia-salts was employed, by which the crop was still further 
increased, the proportion of the supplied Nitrogen which was recovered as increase was 
almost identically the same; but with more still, the proportion was less. 
Again, when the smaller amount of ammonia-salts was applied annually, for six years, 
to barley, the increased yield of Nitrogen corresponded to only about 42 per cent. of the 
