THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 437 
clover-yielding capabilities of the land. On the other hand, it should be particularly 
observed that, after taking 206-8 lbs. of Nitrogen from an acre of land in the clover- 
crop of the first year, the wheat-crop of the second or succeeding year, compared with 
that of the same season in the adjoining experimental wheat-field where the crop is 
grown year after year on the same land, was about double that obtained from the plot 
which had there been unmanured for a series of consecutive years, and fully equal to that 
from a plot which had for the same period received annually a dressing of farm-yard 
manure. It should be added that, after failing to get any crop of clover at all in 1853 
and in 1854, and getting a very poor one in 1855, the land was allowed to lie fallow 
for two years; that after this, in 1858, there was obtained an over-luxuriant and laid 
crop of barley, more than twice as great as the average annual produce of eight years 
of the successive growth of the crop without manure in the same field; yet, after 
resowing with clover in the spring of 1859, and getting a small cutting in the autumn 
of the same year, the plant has again died off during the winter of 1859-60. ‘This was 
the case notwithstanding that it was a perennial variety that was last sown. 
Again, eight consecutive crops of turnips (four “ White Globe” and four “ Swedish”) 
gave an average annual yield, per acre, of about 40 lbs. of Nitrogen, without the supply 
of any in the manure. In the case of these turnips, however, the land received annually 
certain “mineral” manures. In fact, turnips grown year after year without manure of 
any kind, yielded, after a few years, only a few hundred-weights of produce per acre; 
but the percentage of Nitrogen in these diminutive unmanured turnips was very un- 
usually high. It will be observed that the average annual yield of Nitrogen per acre, 
in the turnips grown by mineral manures (containing no Nitrogen), was considerably 
more than that in the unmanured Cereal grain-crops. And, in connexion with this 
point, it is worthy of remark, that, on barley, without manure, succeeding on the land 
from which these eight mineral-manured turnip-crops had been taken, the produce 
was only about three-fourths as much as that obtained, in the same season, where 
barley was grown for the second year in succession without manure, in another field; 
and it was only about three-fifths as much as that obtained, also in the same season, 
where barley was grown as the second crop of the second course, in a series of entirely 
unmanured four-course Rotation-crops. 
It may be mentioned that, in the case of the purely Graminaceous crops, there has 
been but very little gain in the annual yield of Nitrogen per acre by the use of mineral 
or non-nitrogenous manures. But in the case of the Leguminous crops, as in that of the 
root-crops just referred to, there has been much more Nitrogen harvested over a given 
area, within a given time, when mineral manures were employed, than when no manure 
at all was used. 
It has thus far been seen, then, that the Leguminous crops yield much more Nitrogen 
over a given area than the Graminaceous ones, and, further, that the amount of Nitro« 
gen harvested in the former is increased considerably by the use of ‘ mineral” manures, 
whilst that in the latter is so in a very limited degree. It is, nevertheless, a well-known 
agricultural fact, that the growth of the Leguminous crops, which carry off such a com- 
