seed.

=Clover as a Fertilizer.=--It would probably be correct to say that no
plant has yet been introduced into American agriculture that has been
found so generally useful as clover in fertilizing land and in improving
the mechanical condition. Some who have investigated claim that there is
more nitrogen in a clover sod after the removal of a good crop of clover
than will suffice for four average farm crops, more phosphoric acid than
will suffice for two, and more potash than will suffice for six. It
begins to draw nitrogen from the air as soon as the tubercles commence
to form and continues to add thus to the enrichment of the land during
all the succeeding period of active growth. As previously stated, the
nitrogen is drawn in great part from the air; consequently, soil from
which a bountiful crop of clover has been removed will be considerably
richer in nitrogen than before it grew the same, and this will hold true
as intimated above, even though the crop should be removed and sold.
Under the same conditions it will also be true in available phosphoric
acid and potash. But the latter are gathered from the soil and subsoil
while the plants were growing. Consequently, if crops of clover are
grown in short rotation periods and if no fertilizer is given to the
land other than the clover brings to it, while it will be abundantly
supplied with nitrogen, a time will come when the supply of phosphoric
acid and potash may be so reduced that the soil will not grow even good
crops of clover. When this point is reached the soil is spoken of as
"clover sick." Happily, however, nearly all soils are so well stored
with phosphoric acid and potash that this result is not likely to follow
for many years. But lest it should, attention should be given to
fertilizing the land occasionally with farmyard manure, or with
phosphoric acid and potash applied as commercial fertilizers. Because of
this, and also for other reasons, it is usually considered more
profitable in the end to feed clover on the farm and return it to the
land in the form of manure. But clover may cease to grow on land where
once it grew well, because of other reasons, such as changes in the
mechanical condition of the soil caused by the depletion of its humus
and changes in its chemical condition, such as increased acidity. The
remedy is the removal of the cause.

The roots also put large quantities of humus in the soil. Where crops
are regularly grown in short rotati