g or summer when the land is bare, that is a good time for a
green manure crop.

Green manure crops are often planted between the rows of other crops
such as corn or cotton at the last working of the crop for the benefit
of the crop which is to follow.

It is advisable to arrange for a green manure crop at least once in
three or four years.

LEGUMINOUS GREEN MANURE CROPS

_Cowpea_. (Field pea, stock pea, black pea, black-eyed pea, clay pea,
etc.) (Fig. 79.)

The cowpea is perhaps the most important leguminous plant grown for
soil improvement in the South. It will grow anywhere south of the
Ohio River and can be grown with fair success in many localities
farther north.

It is a tender annual, that is, it is killed by frost and makes its
entire growth from seed to seed in a single season. It should
therefore be planted only during the spring and summer. This crop not
only has power like the other legumes to take nitrogen from the air,
but it is also a strong feeder, that is, it can feed upon mineral
plant food in the soil that other plants are unable to make use of.
For this reason it will grow on some of the poorest soils, and is a
good plant with which to begin the improvement of very poor land. It
is a deep-rooted plant. On the farm of the Hampton Normal and
Agricultural Institute cowpea roots have been traced to the depth of
sixty-one inches.

Cowpeas will grow on almost any land that is not too wet. From one and
one-half to three bushels of seed are used per acre. These are sown
broadcast and harrowed in or are planted in drills or furrows and
cultivated a few times. Aside from its value as a green manure crop
the cowpea is useful as food for man and the farm animals. The green
pods are used as string beans or snaps. The ripened seeds are used as
a food and the vines make good fodder for the farm animals.

"Experiments at the Louisiana Experiment Station show that one acre of
cowpeas yielding 3,970.38 pounds of organic matter, turned under, gave
to the soil 64.95 pounds of nitrogen, 20.39 pounds of phosphoric acid
and 110.56 pounds of potash."--Farmer's Bulletin, 16 U.S. Dept. of
Agriculture.

"It is now grown in all the States south of the Ohio River, and in
1899 there were planted nearly 800,000 acres to the crop. Basing our
estimate on the amount of nitrogen stored in the soil by this crop, it
is fair to say that fully fifteen million pounds of this valuable
substance were collected and retained as