no good, but in certain
combinations, in some seasons, do positive harm to clover. Thus, Messrs.
Lawes and Gilbert, in a series of experiments on the growth of
red-clover, by different manures, obtained 14 tons of fresh green
produce, equal to about three and three-fourths tons of clover hay, from
the unmanured portion of the experimental field; and where sulphates of
potash, soda, and magnesia, or sulphate of potash and superphosphate of
lime were employed, 17 to 18 tons, (equal to from about four and
one-half to nearly five tons of hay), were obtained. When salts of
ammonia were added to the mineral manures, the produce of clover-hay
was, upon the whole, less than where the mineral manures were used
alone. The wheat, grown after the clover, on the unmanured plot, gave,
however, 29-1/2 bushels of corn, whilst in the adjoining field, where
wheat was grown after wheat, without manure, only 15-1/2 bushels of corn
per acre were obtained. Messrs. Lawes and Gilbert notice especially,
that in the clover-crop of the preceding year, very much larger
quantities, both of mineral matters and of nitrogen, were taken from
the land, than were removed in the unmanured wheat-crop in the same
year, in the adjoining field. Notwithstanding this, the soil from which
the clover had been taken, was in a condition to yield 14 bushels more
wheat, per acre, than that upon which wheat had been previously grown;
the yield of wheat, after clover, in these experiments, being fully
equal to that in another field, where large quantities of manure were
used.

"Taking all these circumstances into account, is there not presumptive
evidence, that, notwithstanding the removal of a large amount of
nitrogen in the clover-hay, an abundant store of available nitrogen is
left in the soil, and also that in its relations towards nitrogen in the
soil, clover differs essentially from wheat? The results of our
experience in the growth of the two crops, appear to indicate that,
whereas the growth of the wheat rapidly exhausts the land of its
available nitrogen, that of clover, on the contrary, tends somehow or
other to accumulate nitrogen within the soil itself. If this can be
shown to be the case, an intelligible explanation of the fact that
clover is so useful as a preparatory crop for wheat, will be found in
the circumstance, that, during the growth of clover, nitrogenous food,
for which wheat is particularly grateful, is either stored up or
rendered available