one acre of wheat, consists of silica, of which there is an ample
supply in almost every soil. The restoration of silica, therefore, need
not trouble us in any way, especially as there is not a single instance
on record, proving that silica, even in a soluble condition, has ever
been applied to land, with the slightest advantage to corn, or
grass-crops, which are rich in silica, and which, for this reason, may
be assumed to be particularly grateful for it in a soluble state.
Silica, indeed, if at all capable of producing a beneficial effect,
ought to be useful to these crops, either by strengthening the straw, or
stems of graminaceous plants, or otherwise benefiting them; but, after
deducting the amount of silica from the total amount of mineral matters
in the wheat produced from one acre, only a trifling quantity of other
and more valuable fertilizing ash constituents of plants will be left.
On comparing the relative amounts of phosphoric acid, and potash, in an
average crop of wheat, and a good crop of clover-hay, it will be seen
that one acre of clover-hay contains as much phosphoric acid, as two and
one-half acres of wheat, and as much potash as the produce from five
acres of the same crop. Clover thus unquestionably removes from the land
very much more mineral matter than does wheat; wheat, notwithstanding,
succeeds remarkably well after clover.

"Four tons of clover-hay, or the produce of an acre, contains, as
already stated, 224 lbs. of nitrogen, or calculated as ammonia, 272 lbs.

"Assuming the grain of wheat to furnish 1.78 per cent of nitrogen, and
wheat-straw, .64 per cent, and assuming also that 1,500 lbs. of corn,
and 3,000 lbs. of straw, represent the average produce per acre, there
will be in the grain of wheat, per acre, 26.7 lbs. of nitrogen, and in
the straw, 19.2 lbs., or in both together, 46 lbs. of nitrogen; in round
numbers, equal to about 55 lbs. of ammonia, which is only about
one-fifth the quantity of nitrogen in the produce of an acre of clover.
Wheat, it is well known, is specially benefited by the application of
nitrogenous manures, and as clover carries off so large a quantity of
nitrogen, it is natural to expect the yield of wheat, after clover, to
fall short of what the land might be presumed to produce without manure,
before a crop of clover was taken from it. Experience, however, has
proved the fallacy of this presumption, for the result is exactly the
opposite, inasmuch as a better and