a result of the planting of
the cowpea alone. This at fifteen cents per pound (the market price of
nitrogen) would be worth something more than $2,000,000 for nitrogen
alone."--Year Book of the Department of Agriculture, 1902.

_The Clovers._--These are the most extensively grown plants for green
manure purposes in the United States. They are deep-rooted, and are
able to use mineral food that is too tough for other plants. They
furnish large crops of hay or green forage and a good aftermath and
sod to turn under as green manure, or the entire crop may be plowed
under.

_Red Clover_ is the most widely planted (Fig. 80). It is a perennial
plant and grows from the most northern States to the northern border
of the Gulf States. It grows best on the loams and heavier soils well
supplied with water, but not wet. It is sown broadcast at the rate of
from ten to twenty pounds of seed per acre. In the North it is
generally sown in the spring on fields of winter grain. In the South,
September and October are recommended as the proper sowing times. It
is the custom to let it grow two years, cutting it for hay and seed,
and then to turn the aftermath and sod under.

_Mammoth Red Clover_, also called sapling clover and pea-vine clover,
closely resembles the red clover, but is ranker in growth and matures
two or three weeks later. It is better adapted to wet land than the
red clover.

_Crimson Clover_, also called German clover and Italian clover, is a
valuable green manure crop in the central and southern States east of
the Mississippi. It is a hardy annual in that section and is generally
sown from the last of July to the middle of October, either by itself
or with cultivated crops at their last working. Fifteen and twenty
pounds of seed are used to the acre. It makes a good growth during the
fall and early winter and is in blossom and ready to cut or plow under
in April or May. It grows at a season when the cowpea will not live.
Crimson clover will grow on soils too light for other clovers.

The _Soy Bean_, also called soja bean and Japanese pea, is another
leguminous crop used for green manuring (Fig. 81). It was introduced
into this country from Japan and in some localities is quite
extensively planted. It grows more upright than the cowpea and
produces a large amount of stem and foliage which may be used for
fodder or turned under for green manure The seeds are used for food
for man and beast. The soy bean is planted and c