440 MB. J. B. i..\wi;s. DB. GILBERT, a.Mj DB. PUGfB OS 



in die Rotation experiment was in Hip cage of a clover-crop, grown once faring the 

 twelve vears, and which constituted the Leguminous crop of the Brat coui te. After both 



this clover-crop (in wliieli was removed such a large amount of Nitrog< n ) and beam whi< h 

 replaced it in the second and third courses (hut which gave a verj -mull j ield of Nitrogen), 

 the wheat-crop was about double as nincli as the average where wheat lias 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 24^ lbs. 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 crop-. 

 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 



