522 Royal Society :— 
crop, grown in 3 out of 4 consecutive years, had giver an-average of 
120 lbs. Turnips, over 8 consecutive years, had yielded about 45 lbs: 
~ The Graminaceous crops had not, during the periods referred to, 
shown signs of diminution of produce. The yield of the Legumi- 
nous crops had fallen considerably. Turnips, again, appeared greatly 
to have exhausted the immediately available nitrogen in the soil. The 
amount of nitrogen harvested in the Leguminous and Root-crops was 
considerably increased by the use of “‘ mineral manures,” whilst that 
im the Graminaceous crops was so in a very limited degree. 
' Direct experiments further showed that pretty nearly the same 
amount of nitrogen was taken from a given area of land in wheat 
in 8 years, whether 8 crops were grown consecutively, 4 in alterna- 
tion with fallow, or 4 in alternation with beans. 
Taking the results of 6 separate courses of rotation, Boussingault 
obtained an average of between one-third and one-half more nitrogen 
in the produce than had been supplied in manure. His largest 
yields of nitrogen were in the Leguminous crops; and the cereal 
crops were larger when they next succeeded the removal of the 
highly nitrogenous Leguminous crops. In their own experiments 
ttpon an actual course of rotation, without manure, the Authors 
had obtained, over 8 years, an average annual yield of 57°7 lbs. of 
nitrogen per acre; about twice as much as was obtained in either 
wheat or barley, when these crops were, respectively, grown year after 
year on thesameland. The greatest yield of nitrogen had been in a. 
clover crop, grown once during the 8 years; and the wheat crops 
grown after this clover in the first course of 4 years, and after beans 
in the second course, were about double those obtained when wheat 
succeeded wheat. 
Thus, Cereal crops, grown year after vear on the same land, had 
given an average of about 30 lbs. of nitrogen, per acre, per annum ; 
and Leguminous crops much more. Nevertheless the Cereal crop 
was nearly doubled when preceded by a Leguminous one. It was 
also about doubled when preceded by fallow. Lastly, an entirely 
unmanured rotation had yielded nearly twice as much nitrogen as 
the continuously grown Cereals. 
Leguminous crops were, however, little benefited, indeed fre- 
quently injured, by the use of the ordinary direct nitrogenous ma- 
nures. Cereal crops, on the other hand, though their yield of ni- 
trogen was comparatively small, were very much increased by direct 
nitrogenous manures, as well as when they succeeded a highly nitro- 
i Leguminous crop, or fallow. But when nitrogenous manures 
ad been “employed for the increased growth of the Cereals, the 
nitrogen in the immediate increase of produce had amounted to-little 
more than 40 per cent. of that supplied, and that in the increase of 
the second year after the application, to little more than one-tenth 
of the remainder. Estimated in the same way, there had been in 
the case of the meadow grasses scarcely any larger proportion of 
the supplied nitrogen recovered. In the Leguminous crops the pro- 
portion so recovered appeared to be even less; whilst in the root- 
erops it was probably somewhat greater. Several possible explana- 
