HE THIRD CUTTING]

As explained on page 32 the leguminous crops have the power of drawing
nitrogen from the air and, by means of their root-tubercles, of storing
it in the soil. Hence by growing these crops on poor land the expensive
nitrogen is quickly restored to the soil, and only the two cheaper plant
foods need be bought. How important it is then to grow these leguminous
plants! Every farmer should so rotate his planting that at least once
every two or three years a crop of legumes may add to the fruitfulness
of his fields.

Moreover these crops help land in another way. They send a multitude of
roots deep into the ground. These roots loosen and pulverize the soil,
and their decay, at the end of the growing season, leaves much humus in
the soil. Land will rarely become worn out if legumes are regularly and
wisely grown.

From the fact that they do well in so many different sections and in so
many different climates, the following are the most useful legumes:
alfalfa, clovers, cowpeas, vetches, and soy beans.

=Alfalfa.= Alfalfa is primarily a hay crop. It thrives in the Far West,
in the Middle West, in the North, and in the South. In fact, it will do
well wherever the soil is rich, moist, deep, and underlaid by an open
subsoil. The vast areas given to this valuable crop are yearly
increasing in every section of the United States. Alfalfa, however,
unlike the cowpea, does not take to poor land. For its cultivation,
therefore, good fertile land that is moist but not water-soaked should
be selected.

Good farmers are partial to alfalfa for three reasons. First, it yields
a heavy crop of forage or hay. Second, being a legume, it improves the
soil. Third, one seeding lasts a long time. This length of life may,
however, be destroyed by pasturing or abusing the alfalfa.

[Illustration: FIG. 231. SHEEP FATTENING ON ALFALFA STUBBLE]

Alfalfa is different from most plants in this respect: the soil in which
it grows must have certain kinds of bacteria in it. These cause the
growth of tubercles on the roots. These bacteria, however, are not
always present in land that has not been planted in alfalfa. Hence if
this plant is to be grown successfully these helpful bacteria must
sometimes be supplied artificially.

There are two very easy ways of supplying the germs. First, fine soil
from an alfalfa field may be scattered broadcast over the fields to be
seeded. Second, a small mass of alfalfa tubercle germs may be put int